COSEWIC Assessment and Status Report on the Brook Floater Alasmidonta varicosa in Canada - 2009

Table of Contents

Brook Floater Alasmidonta varicosa

List of Figures

List of Tables

List of Appendices


Brook Floater Alasmidonta varicosa

Photo of the Brook Floater Alasmidonta varicose.

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Special Concern 2009

COSEWIC -- Committee on the Status of Endangered Wildlife in Canada

COSEWICstatus reports are working documents used in assigning the status of wildlife species suspected of being at risk. This report may be cited as follows:

COSEWIC. 2009. COSEWICassessment and status report on the Brook Floater Alasmidonta varicosa in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 79 pp.

Production note:

COSEWICwould like to acknowledge Katherine A. Bredin and André L. Martel for writing the status report on the Brook Floater Alasmidonta varicosa in Canada, prepared under contract with Environment Canada, overseen and edited by Janice Smith and Dr. Dwayne Lepitzki, COSEWICMolluscs Specialist Subcommittee Co-chairs.

For additional copies contact:

COSEWICSecretariat
c/o Canadian Wildlife Service
Environment Canada
Ottawa, ON
K1A 0H3
Tel.: 819-953-3215
Fax: 819-994-3684
COSEWIC E-mail
COSEWIC Website

Également disponible en français sous le titre Ếvaluation et Rapport de situation du COSEPACsur l’alasmidonte renflée Alasmidonta varicosa au Canada.

Cover photo: Brook Floater - Provided by the author.

© Her Majesty the Queen in Right of Canada, 2009.
Catalogue No. CW69-14/580-2009E-PDF
ISBN978-1-100-12944-0

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COSEWIC Assessment Summary -- April 2009

Common name: Brook Floater
Scientific name: Alasmidonta varicosa
Status: Special Concern
Reason for designation: A medium-sized freshwater mussel that is confined to 15 widely scattered watersheds in Nova Scotia and New Brunswick. This mussel was never abundant, usually representing only 1-5% of the total freshwater mussel fauna present. The habitat is subject to impacts (shoreline development, poor agricultural practices, and other water quality issues) with potential cumulative degradation on larger stretches of rivers. Populations appear to have been lost from two historic locations, although new populations have been formed recently. Because this mussel has disappeared from approximately half of its USA locations, the Canadian population now represents an important global stronghold for the species.
Occurrence: New Brunswick, Nova Scotia
Status history: Designated Special Concern in April 2009. Assessment based on a new status report.

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COSEWIC Executive Summary

Brook Floater - Alasmidonta varicosa

Species information

The Brook Floater, Alasmidonta varicosa (Lamarck, 1819), is a medium-sized freshwater mussel (50-65 mm long) with a kidney-shaped shell that is swollen in cross section. The shell is relatively thin, with a small patch of tiny ridges on the posterior edge that run perpendicular to the growth lines, creating a corrugated appearance. It is yellowish, greenish or brownish to black in colour, often with broad dark rays running from the top to the bottom. The Brook Floater has a cantaloupe-coloured foot that can be seen when the valves are still gaping as live individuals are removed from the water.

Distribution

The Brook Floater is distributed in eastern North America from northeastern Georgia through the eastern USA to central Nova Scotia and the southern half of New Brunswick, with a small discontinuity in northern New Hampshire and southern Maine. The species has disappeared from about half of the known locations in the USA. In Canada, the Brook Floater occurs in a relatively small number of rivers, including the St. Croix, Magaguadavic, Petitcodiac, Southwest Miramichi, Shediac, Scoudouc, Bouctouche and Kouchibouguacis watersheds in New Brunswick, and the Annapolis, LaHave, Gays, Wallace, East St. Marys and Salmon Rivers in Nova Scotia.

Habitat

The Brook Floater is usually considered to be a habitat specialist that requires running water environments such as shallow rivers or streams with moderate to high water flows. In New Brunswick it has only been found in rivers. In Nova Scotia, although primarily occurring in rivers, this species is occasionally found in small sandy-bottomed lakes with no evident water flow. It usually prefers sand or fine gravel substrates but is occasionally found in pockets of sand within cobble and rocky bottom areas. Although Brook Floater habitat in the USA is highly fragmented by dams and impoundments, this is not generally the case in Canada.

Biology

The male releases sperm into the water, which are drawn into the female’s mantle cavity during filter-feeding. Fertilization occurs in the female’s egg-filled marsupial pouches in the gills, where the glochidia (larvae) develop. Spawning occurs in summer, with brooding of the glochidia through fall and winter and release in spring. The glochidia are parasitic on fishes, attaching to their gills or fins. Potential host fishes in Canadian waters include Ninespine Stickleback, Yellow Perch, Golden Shiner and Blacknose Dace. After a period of development on the host fish, the juveniles drop off and burrow into the river bottom where they grow into adults. Like other mussels, this species feeds on bacteria, algae and other organic particles filtered from the water.

Population sizes and trends

The Brook Floater is never very abundant in rivers where it occurs, usually representing only 1-5% of the total freshwater mussel fauna present. In some Nova Scotia and New Brunswick rivers they are scarce, occurring at few sites within the river system with population estimates ranging from <100–<1000 individuals. Brook Floater abundance is higher in other rivers, ranging from 1000-10,000 individuals or possibly more. Although populations are disappearing throughout the USA, this does not seem to be the case in Canada, where only a few historically known populations were not re-confirmed during recent surveys. Recent discoveries of additional populations in the Maritimes likely reflect increases in survey effort rather than an increase in abundance and range.

Limiting factors and threats

Brook Floaters are threatened by aquatic habitat degradation in the form of silt, nutrient and sewage loads, due to poor agricultural and land management practices along a number of Maritime rivers where intensive agriculture and forestry are the principal forms of land use. Increased residential and cottage development, with associated damage to riparian and aquatic habitats, is also a potential threat to the typically small and disjunct populations of Brook Floaters.

Special significance of the species

About 8% of the Brook Floater’s global range occurs in Canada. With increased surveys in recent years, nine new populations have been discovered in the Maritimes at a time when populations are being lost in the USA. With declines south of the border, the Canadian population represents an important global stronghold for the species in a region with comparatively less habitat disturbance.

Existing protection or other status designations

Brook Floater habitat is protected by provincial and federal legislation. The federal Fisheries Act prohibits the release of substances deleterious to fish, and activities that disrupt or destroy fish habitat. Forestry companies are required to leave unharvested zones along waterways, including rivers, streams and lakes, which help reduce siltation and inhibit summer water temperature increases. Under the Nova Scotia Environment Act, all wastewater discharges, construction of dams, and watercourse flow alterations are subject to review and approval. The Clean Water Act in New Brunswick protects surface waters from the effects of building construction, vegetation clearing, forestry activities, and the installation of dams or obstructions to water flow, by requiring an approved permit for such activities within 30 metres of a watercourse. Both provincial governments and the Canadian federal government require Environmental Impact Assessment Reviews for major developments, including those near waterways.

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions (2009)

Wildlife Species
A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)
A wildlife species that no longer exists..

Extirpated (XT)
A wildlife species no longer existing in the wild in Canada, but occurring elsewhere..

Endangered (E)
A wildlife species facing imminent extirpation or extinction..

Threatened (T)
A wildlife species likely to become endangered if limiting factors are not reversed..

Special Concern (SC)*
A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats..

Not at Risk (NAR)**
A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances..

Data Deficient (D)***
A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species risk of extinction.

* Formerly described as "Vulnerable" from 1990 to 1999, or "Rare" prior to 1990.
** Formerly described as "Not In Any Category", or "No Designation Required."
*** Formerly described as "Indeterminate" from 1994 to 1999 or "ISIBD" (insufficient scientific information on which to base a designation) prior to 1994. Definition of the (DD) category revised in 2006.

The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.

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Species Information

Name and classification

Scientific name: Alasmidonta varicosa(Lamarck, 1819)
English common name: Brook Floater
French common name: Alasmidonte renflée (Martel et al. 2007)

The current authority for the taxonomy and scientific nomenclature for freshwater mussels in North America is Turgeon et al.(1998). Placement of the genus in the subfamily Unioninae, rather than Anodontinae as suggested by Clarke (1981a,b), follows the most recent work by Graf and Cummings (2007).

Phylum: Mollusca
Class: Bivalvia
Order: Unionoida
Superfamily: Unionoidea
Family: Unionidae
Subfamily: Unioninae
Genus: Alasmidonta
Species: Alasmidonta varicosa

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Morphological description

The Brook Floater is a small to medium-sized freshwater mussel with a subovate or subtrapezoidal, kidney-shaped shell (Athearn and Clarke 1962; Clarke 1981a,b; Strayer and Jirka 1997). Maximum dimensions of the shell are 70 mm long, 40 mm high and 30 mm wide (Clarke 1981a,b). Most adult individuals found in Atlantic Canada have shell lengths of 50-65 mm (Martel et al.2008). The shell is relatively thin, reaching a thickness of 1 to 2 mm at the centre in adult individuals.

When the valves are closed, the shell appears laterally inflated and wide or swollen in cross section. The posterior half of the shell displays a broad ridge, which runs diagonally from the umbo region to the ventro-posterior corner of the shell (Figure 1). A careful examination of the dorso-posterior slope region, above the ridge, reveals a corrugated posterior slope (Athearn and Clarke 1962) with very small, well-defined wrinkles, or ridges, running perpendicular to the growth lines or shell edge. These tiny ridges are particularly clear in juveniles or young adults. The ventral margin is nearly straight, with a slight but definite concave or indented curvature, giving the impression of a very slightly bent shell, especially in older individuals. The umbo is small and low, rising slightly above the dorsal shell margin, and usually shows distinct signs of erosion in older individuals. The periostracum ranges from yellowish, greenish or brownish to almost black, especially in older individuals. In young or fresh adult shells the periostracum usually displays distinct broad greenish or tan-coloured rays that run from the umbo region to the ventro-posterior corner of the shell on either side of the swollen posterior shell ridge. The nacre is usually bluish-white but may have a distinct olive or pinkish tint. The pseudocardinal teeth are weak and flat, numbering two in the left and one in the right valve. There are no lateral teeth. The anterior adductor muscle scar is shallow yet well defined. In contrast, the posterior adductor muscle scar is less visible and difficult to locate.

Figure 1. Shell morphology of the Brook Floater, Alasmidonta varicosa.

Two images showing the shell of the Brook Floater. One shows the outside of the right valve, and the other shows the inside of the left valve. Features of the shell are named.

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In brief, the shell of the Brook Floater can be distinguished from other unionids by its (i) relatively small adult size, (ii) subovate or kidney shape, (iii) inflated posterior ridge, (iv) corrugated posterior slope, and (v) characteristic hinge teeth. The internal anatomy of the Brook Floater is typical of unionids. When live individuals are removed from the water, and while their valves are still gaping, they may display a cantaloupe or peach-coloured foot.

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Genetic description

There have been no studies examining the population genetic structure of the Brook Floater. As Kneeland and Rhymer (2007) have now developed molecular genetic markers for the glochidia of all species of unionids found in the state of Maine (including the Brook Floater) by using DNA extracted from positively identified adults, such studies will be possible in the future. Studies on other unionid species along the North Atlantic Slope (e.g., Kat and Davis 1984, Kelly and Rhymer 2005; King et al. 1999) and other coastal drainages (Bouza et al. 2007) have described these unionid populations as distinct biogeographic "islands" of diversity (Sepkoski and Rex 1974), with each population being on its own evolutionary trajectory. This significant biogeographic structure observed for other unionids in coastal zones suggests that natural population fragmentation exists to the point where populations are unlikely to quickly recolonize watersheds if resident populations are lost. Thus, until molecular data show otherwise, it is prudent to assume that Brook Floater populations in Nova Scotia and New Brunswick are similarly fragmented.

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Designatable units

In the absence of genetic information on differentiation among Canadian populations and because all populations are within COSEWIC’s Maritimes Freshwater Biogeographic Zone, a single designatable unit applies at this time.

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Distribution

Global range

The global range of the Brook Floater is restricted to northeastern North America; it extends from northeastern Georgia through the eastern US to the southern half of New Brunswick and central Nova Scotia (Figure 2). An area of discontinuity in northern New Hampshire and southern Maine divides the range into northern and southern nodes. The present distribution has been influenced by glaciation, and particularly the location of, and subsequent dispersal from, glacial refugia. While many parts of the southern node of distribution were not glaciated, more northerly areas of this southern node were likely repopulated with mussels from two refugia, the Middle Atlantic Coastal Plain Refugium and the Northeastern Coastal Plain Refugium (Nedeau et al. 2000). The northern node of the Brook Floater range, in Northern Maine and the Maritimes, was completely glaciated, and was probably repopulated from two Northeastern Coastal Plain Refugia, one near Georges Bank and a second off the Scotian Shelf (Nedeau et al. 2000).

Figure 2. Global range of the Brook Floater, Alasmidonta varicosa, in eastern North America (based on information from jurisdictions).

Map showing the global range of the Brook Floater in eastern North America.

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The Brook Floater was historically much more widespread across numerous Atlantic drainages from Nova Scotia to Georgia, but its present distribution has become spotty and fragmented due to human development and the subsequent habitat loss or deterioration. Significant declines and loss of occurrences have been noted in southern and central areas of its range, including North Carolina, Virginia, Pennsylvania, Maryland, New York, Massachusetts and New Hampshire, where approximately 60-80 extirpations of about 150 known historical sites have been recorded (NatureServe 2007; Table 1). This decline in occurrences has resulted in a significant reduction in the global area of occupancy over the last century (NatureServe 2007).

Table 1. Comparison of historical and present abundance and distribution of the Brook Floater in USA states of occurrence, showing the widespread incidence of recently extirpated populations throughout the species' range in the USA.
US StateHistorical abundance/ distributionCurrent abundance/ distribution (post-2000)Additional commentsSource
GeorgiaChattooga River, upper reachesUpper Chattooga River, from Tugaloo L.
to GA-SC border
Still widely distributed and abundant in upper reaches of river (survey by J. Alderman, 2005)Wisniewski pers. comm. 2007
South CarolinaFormerly more widespread in several riversNow extant only in: 1) Savannah River basin, 2) Steven’s Creek basin and Flat Creek, and
3) portions of Lynches River
Extant populations are small and isolated in these three watershedsSouth Carolina Department of Natural Resources 2007
North CarolinaFormerly more widespreadNow extant only in 11 isolated rivers and streams North Carolina Nongame and Endangered Wildlife Program 2007
VirginiaShenandoah River system: About 15 known historic Brook Floater populationsAll 15 populations now presumed extirpated; no live Brook Floater observed since before 1990.
3 extant populations: 2 in the James River and 1 in Broad Run, a small tributary of the Potomac River.
Recent surveys conducted in 2000 and 2004Hobson pers. comm. 2007; Chazal 2005; DNH Biotics database, quoted in Chazal 2005.
DelawarePrior to 1981, known from Red Clay Creek in the Christina watershedThis population now considered extirpatedDesignated extirpated in DelawareKalalsz pers. comm. 2007
Rhode IslandFormerly known from Rhode Island c. 1900.Not documented for about 100 yearsConsidered extirpated in Rhode IslandWicklow 2004
New York

At least 20 known locations in the Susquehanna, Delaware and Hudson River watersheds 1

Neversink River population "formerly healthy".

Live Brook Floater recorded at 1 of 10 surveyed sites; valves at 2 other sites. 1

Population declined by about 38,000 individuals during mid-1990s.

10 of 20 known locations surveyed in 1990-1.
Range contraction within Susquehanna River Basin from 1965 -1997.2

Jirka 1991,1

Strayer and Fetterman 1999.2

Strayer and Jirka 1997

New Jersey, Connecticut, New YorkKnown populations in Housatonic and Passaic River basinsThese populations have apparently disappeared Cordeiro and Bowers-Altman 2007; New York Natural Heritage Program 2007
PennsylvaniaOccurred in 19 counties in Pennsylvania prior to 1980Now found in just 12 counties in the state Pennsylvania Natural Heritage Program 2007
MarylandAt least 17 populations/ or historical occurrences14 of 17 known to be extirpated. 4 known extant populations, all with very low abundance (i.e. no more than 1-3 live individuals found)Intensive surveys in 2006-7 assessed known status of all recent & historical localities, except 2 upper Potomac River localities with no recent survey data.McCann pers. comm. 2008
Massachusetts17 known sites prior to 1980Only 4 known sites with extant populationsSubstantial reduction in rangeGabriel pers. comm. 2007; Massachusetts Division of Fisheries and Wildlife 2007
New HampshireAt least 31 historic known occurrencesPresently 14-20 occurrences, though only 2-3 considered fair or better in terms of viability.Reduction in abundance of known populationsTash pers. comm. 2007
MainePopulations were larger and healthier than in other areas of US rangeLocal extirpations from Dennys and Presumpscot RiversStill quite healthy despite evidence of some recent extirpationsNedeau et al.2000

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Canadian range

In Canada, the Brook Floater is known only from New Brunswick and Nova Scotia, where approximately 8% of the species' current global range occurs (as calculated from Figure 2, using GIS). The first record of the Brook Floater in the Maritimes was from the LaHave River in Nova Scotia in 1921 (Academy of Natural Sciences 2007). It was first recorded in New Brunswick by H.D. Athearn in the Renous River in 1948, although he did not publish this record until thirteen years later (Athearn 1961). The species was subsequently found in the Petitcodiac River in 1952 (Athearn 1952) and in the Aroostook River in 1960, where it was recorded as Alasmidonta marginata, of which it was then considered to be a subspecies (Sabine 2006). Early records in Nova Scotia from the Wallace River, the St. Marys River near Sherbrooke, the Annapolis River at Lawrencetown, and the Stewiacke River east of Stewiacke, are cited in Athearn and Clarke (1962).

Clarke provided a synopsis of the distribution of the Brook Floater in the Maritimes from historical records and preliminary surveys (mostly unpublished) that he conducted in the 1950s and the 1960s (Clarke 1981a). There have been many additional freshwater mussel surveys in the region since Clarke’s synopsis, especially in the last 10 years (1997-2007), which are detailed in POPULATION SIZES AND TRENDS. Data compiled from these recent surveys, and some historical surveys, were used to map the current distribution of the Brook Floater in Nova Scotia (Figure 3) and New Brunswick (Figure 4). A list of data sources used to produce the maps is included in Appendix 1.

Figure 3. Current distribution (1980-2007) and historical records (1940-1980) for the Brook Floater, Alasmidonta varicosa, in Nova Scotia based on records from data sources listed in Appendix 1.

Map showing current distribution (from 1980 to 2007) and historical records (from 1940 to 1980) for the Brook Floater in Nova Scotia.

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Figure 4. Current distribution (1980-2007), historical records (1940-1980), and a record of a partial valve found in a midden (2001), for the Brook Floater, Alasmidonta varicosa, in New Brunswick based on records from data sources listed Appendix 1.

Map showing the current distribution of a partial valve found in a midden for the Brook Floater in New Brunswick.

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Populations of the Brook Floater in Nova Scotia are disjunct, occurring in separate watersheds with little chance of population mixing. Some New Brunswick populations occur closer together, although the species occupies nine separate watersheds. Maps of historical records are unlikely to indicate overall distribution at the time, because so few freshwater mussel surveys had been conducted prior to 1980. It is thus difficult to assess temporal changes in the distribution of the Brook Floater within the Maritimes. With greatly increased survey efforts, six new populations have been recorded from New Brunswick since 2001, i.e., in the Magaguadavic (2001), Scoudouc (2004), Shediac (2002), Bouctouche (2002), Kouchibouguacis (2001) and Southwest Miramichi (2006) Rivers. Increased survey effort in Nova Scotia from 1998 to 2007 led to the discovery of four new sites i.e., Mattatall Lake (2000), Gays River (2002), Salmon River (2006) and Borden’s Lake in the Salmon River system (2002), and range extensions within watersheds with earlier records (e.g., Annapolis and St. Marys Rivers).

Historical populations not re-discovered

Brook Floaters were not confirmed alive in three rivers where they historically occurred: the Stewiacke (NS) and Aroostook and Renous Rivers (NB) (Figures 3 and Figure 4).

Stewiacke River

Despite a cumulative total of five person-hours of recent NS DNR surveys at five sites on the Stewiacke River, including the historical location, the species was not found.

Aroostook River

The only Brook Floater record from the Saint John River system and its tributaries was H. B. Herrington’s record from the Aroostook River in 1960, recorded as a subspecies of the Elktoe, Alasmidonta marginata. Unfortunately the specimen is missing and its identity cannot be confirmed (Martel pers. obs.). Canadian Museum of Nature data indicate that Herrington also collected the Triangle Floater, Alasmidonta undulata, at the same site on the same day, so it seems unlikely that the A. marginata was a misidentified A. undulata. Brook Floaters have not yet been confirmed in the Aroostook River or other areas of the Saint John River watershed despite extensive surveys of the US portion of the Aroostook (PEARL 2008), and recent surveys of the Saint John River and tributaries in Canada (see Figure 5).

Renous River

Brook Floater records from the Renous River were not re-confirmed during surveys near the town of Renous in 2006, or at the confluence of the Renous and the Southwest Miramichi Rivers in 2002. Brook Floaters could be present in the upper reaches of the Renous River and its branches, but these relatively inaccessible areas have never been surveyed.

In addition, Brook Floaters have not been collected live from the Wallace River (NS) since 1975. The species was recorded from this river by Athearn and Clarke (in 1962), David H. Stansbery (in 1967) and D.S. Davis (in 1975) (OSU online database 2007; Davis 2007), but surveys undertaken by NS DNR in 1999-2001 failed to confirm its occurrence in the Wallace River. Surveys for this report in 2006 resulted in single, relatively fresh valves but no live individuals from each of three locations. This suggests that a small extant population of Brook Floaters remains somewhere in the Wallace River.

Figure 5. Map of the distribution of Brook Floaters, Alasmidonta varicosa, in New Brunswick showing a subset of mussel sampling sites that likely involved water search effort sufficient to detect Brook Floaters (if not very rare at the site), historical records, and location of record for partial valve found in a muskrat midden. For data sources see Appendix 1.

Map showing the distribution of the Brook Floater in New Brunswick. The map also shows a subset of mussel sampling sites that likely involved water search effort sufficient to detect Brook Floaters (if not very rare at the site), historical records, and the location of a partial valve found in a muskrat midden.

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Potential sites for further investigation

With the discovery of the Brook Floater in the Magaguadavic River, and confirmation of populations in the St. Croix and Petitcodiac Rivers, systematic surveys of additional New Brunswick rivers with potential Brook Floater habitat that flow into the Bay of Fundy, such as the Digdeguash, Lepreau, New and Big Salmon Rivers (see Figure 4) are warranted. The recent discovery of a substantial population of Brook Floaters in a section of the Southwest Miramichi River suggests that suitable unsurveyed habitat may exist in other similar tributaries in the Miramichi watershed. Two Brook Floater valves were found in the Little Southwest Miramichi in October 2008 (Collins pers. comm. 2008), too late to be included elsewhere in this report but indicating the need for further survey of this tributary. The collection of a partial Brook Floater valve from a muskrat midden in the Northwest Miramichi River in 2001 (Sabine 2006) suggests that surveys in areas of suitable habitat are also warranted in this river. In Nova Scotia, additional surveys would be worthwhile close to known populations, for example in upstream tributaries of the Annapolis River and in other sandy rivers of the Annapolis valley such as the Cornwallis River (see Figure 3).

Extent of occurrence

The extent of occurrence (EO) was calculated in GIS using a minimum convex polygon, except for the St. Croix River section along the Canada-US border, where the polygon was clipped to the Canadian boundary (i.e., internal angles greater than 180° were included). The EO within Canada is 76,856 km². This value includes portions of the Bay of Fundy and the Northumberland Strait. Historical sites in New Brunswick where the species has not been found since 1960 were not included in the calculation.

Area of occupancy

In Canada the presently known total area of occupancy (AO) is estimated to be 3.02 km²(Table 2), with 0.99 km² in Nova Scotia and 2.04 km² in New Brunswick. Length of occupied river reach (Table 2) was calculated by determining the river length between the furthest upstream and furthest downstream Brook Floater record for the river. This tends to overestimate AO; with microhabitat preference for sandy patches with moderate flow, Brook Floaters are highly patchy in distribution within river reaches and would not be expected to occur throughout the entire reach of river included in Table 2. Without detailed habitat maps for each river, though, removal of portions of the reach from the length calculation could not be justified. For example, the entire reach of the St. Marys River (NS) between the extreme upstream and downstream record locations was included in the length calculation since records for Brook Floater occurred sporadically throughout the reach of the river, although it is unlikely that the entire river reach is occupied. Entire river reaches for the Petitcodiac main stem, North River and Little River (NB) between all extreme upstream and downstream record locations were also included in the calculation. It is similarly unlikely that these entire sections of reach were continuously occupied by Brook Floaters.

Table 2. Area of occupancy (AO)for all known current subpopulations of Brook Floaters in New Brunswick and Nova Scotia, calculated by multiplying the length of the occupied reach x the mean width of the occupied reach. These 24 subpopulations were condensed into 15 populations, one population per river system. Historical populations (i.e., those not confirmed extant within the last 30 years) were not included in the calculation.
RIVER or LAKELength of Occupied Reach (km)Mean Width of Occupied Reach (m)Area of Occupancy (km²)
Total NS  0.9855
Total Canada  3.0215
St. Croix R., NB11.015.00.1650
Magaguadavic R., NB1.015.00.0150
Petitcodiac R. (main stem), NB23.030.00.6900
North River R. (Petitcodiac), NB5.512.00.0660
Little River R. (Petitcodiac), NB7.012.00.0840
Northwest Miramichi R., NB1.010.00.0100
Southwest Miramichi R., NB28.020.00.5600
Kouchibouguacis R., NB28.08.00.2240
Bouctouche R., NB9.06.00.0540
Luke Brook (Bouctouche), NB3.04.00.0120
South Branch Bouctouche R., NB5.05.00.0250
Shediac R., NB7.08.70.0610
Weisner Brook (Shediac), NB8.56.80.0580
Scoudouc R.2.06.00.0120
Total NB  2.0360
Annapolis R., NS18.012.00.2160
Gays R., NS3.09.00.0270
Wallace R., NS5.012.00.0600
Mattatall Lake, NS1.015.00.0150
LaHave R., NS6.012.00.0720
St. Marys R., NS30.015.00.4500
Lochaber Lake (St. Marys), NS8.012.00.0960
Eden Lake (St. Marys), NS3.012.00.0360
Salmon R., NS1.09.00.0090
Borden’s Lake (Salmon), NS0.59.00.0045

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The index of area of occupancy (IAO) was calculated using the IUCN grid method of applying a 2 km x 2 km grid over the species’ occurrences within the EO. This method calculated an IAOfor Brook Floaters in New Brunswick of 450.7 km² (not a multiple of four due to clipping at the international border) and in Nova Scotia of 256 km², with a total IAO for Canada of 707 km². The species would have to be found in an additional 323 2 km x 2 km grid squares (a 65% increase in current IAO) before it would exceed the threshold for Threatened (< 2,000 km²).

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Habitat

Habitat requirements

Important factors relating to Brook Floater habitat requirements include water flow, water quality, substrate, and tolerance to habitat disturbance.

The vast majority of Brook Floater populations occur in running water habitats with a range of flow conditions, from small creeks and streams to large rivers (Athearn and Clarke 1962; Nedeau et al.2000). They are usually reported from moderate to high current speeds and intermediate water depths (Strayer and Ralley 1993; Sabine 2006) and are absent from high-velocity, high-gradient streams and scour-prone areas of flow chan­nels (Nedeau et al. 2000; Wicklow 2004). Most habitat descriptions report that the Brook Floater is a riverine species that does not occur in slow water (Nedeau et al. 2000) or in water bodies with static flow such as ponds or lakes (Pennsylvania Natural Heritage Program 2007). However, in North Carolina, Brook Floaters occur in areas of relatively slow current (North Carolina Nongame and Endangered Wildlife Program 2007), and they occasionally inhabit small sandy-bottomed ponds in Massachusetts (Massachusetts Division of Fisheries and 2007). In Nova Scotia, some Brook Floaters also locally occur in small and medium-sized lakes with no evident water flow (Davis 2007; Nova Scotia Department of Natural Resources 2005; Hall pers. comm. 2007; Pulsifer pers. comm. 2007).

Accounts of substrate preference usually indicate that Brook Floaters require stable substrates ranging from sand to gravel (Hanson and Locke 2001; Athearn and Clarke 1962; Strayer and Jirka 1997), and prefer microhabitats of sandy bars or shoals, or pockets of sand downstream from rocks or logs (Clarke 1981a; Beaudet et al. 2002; Sabine 2006). Variations on this typical substrate preference are occasionally reported for local populations. Brook Floaters in North Carolina were observed in sandy or silty substrate in cracks between boulders (North Carolina Nongame and Endangered Wildlife Program 2007) and they have also been reported from cobble and rocky substrates (Clarke 1981a; Caissie 2005; Connecticut Department of Environmental Protection 2007; Davis 2007).

Strayer and Ralley (1993) examined the microhabitat characteristics of an assemblage of stream-dwelling unionids, including Brook Floaters, in the Neversink River in New York State. The strongest predictor of Brook Floater occurrence was the presence of fine to medium sand in the river sediments. The second most important variable was the number of sediment cores that could be extracted per quadrat, which Strayer and Ralley (1993) used as a measure of the extent of patches of fine sediment available for unionids to burrow in. This quantitative work by Strayer and Ralley in the Neversink River confirms the observations of a number of authors (see above) that this mussel is typically found in microhabitats containing sand.

Strayer (1993) examined six ecological variables that affect freshwater mussel distribution on a macrohabitat scale (1-10 km) in the Susquehanna, Delaware and Hudson River drainages. The main predictor of Brook Floater occurrence was lower calcium content of the water; Brook Floaters prefer softer water. As it seemed unlikely that a high calcium concentration per se would be deleterious to Alasmidonta spp., Strayer postulated that factors correlated with higher calcium concentration, such as nutrients like phosphate and nitrite that contribute to eutrophication, may be inhibiting the occurrence of Alasmidonta spp.The other five ecological variables-stream size, stream gradient, hydrologic variability, physiographic province, and the presence or absence of a tide-did not statistically influence the distribution of Brook Floaters in these watersheds. A preference for nutrient-poor water was evident in the Bouctouche River in New Brunswick, as Brook Floaters only occurred in the upper reaches of the river where agriculture was less prevalent (Caissie 2005). They prefer clean, well-oxygenated waters with low siltation loads (Sabine 2006; New York Natural Heritage Program 2007; North Carolina Nongame and Endangered Wildlife Program 2007; South Carolina Department of Natural Resources 2007) and occur in association with rooted aquatic vegetation (Nedeau et al. 2000). As a species primarily found in running water, the Brook Floater may also be more sensitive to eutrophication than mussel species more typically found in slow-water habitats (Nedeau et al. 2000).

Davis (2007) reported that Brook Floaters prefer waters with a pH greater than 5.4, indicating that acidity may be an important factor. For example, the tea-coloured tannin-laden waters of the Cocagne River in New Brunswick are devoid of Brook Floaters and have few unionids present overall, while immediately to the south, the clear, spring fed Shediac River has larger numbers of freshwater mussels, including many Brook Floaters, even though the substrates and flow characteristics of the two rivers are similar (Caissie and Audet 2006; Bredin personal observation). However, there are differences in physical, chemical, and biological characteristics of the two systems (Hebda pers. comm. 2009).

Like most species of freshwater mussels, Brook Floaters are vulnerable to habitat disturbance due to biological characteristics that either render them unable to escape from disturbance or enhance or prolong their exposure to habitat degradation and to their complex life cycle and reliance on a fish host to complete their life cycle. These biological characteristics and the implications for risk to effects of habitat degradation include: 1) their longevity (prolonged exposure), 2) delayed maturity (prolonged exposure), 3) sedentary lifestyle (unable to avoid disturbance or habitat degradation), and 4) a juvenile stage that grows and feeds entirely within the substrate (unable to avoid disturbance, enhanced exposure) (see Biology).

Due to the Brook Floater’s fairly specific habitat requirements, potential habitat and, thus, the location of present populations are quite discontinuous throughout the species range in Canada (Figure 3 and Figure 4). Fragmentation of river habitat by dams and impoundments prevents host fish migration, resulting in diminished recruitment rates and reduced gene flow (Strayer et al. 2004; Wicklow 2004). Although Brook Floater habitat is highly fragmented in the US by dams and impoundments (Watters 1996), these structures are not major causes of habitat fragmentation in Canada.

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Habitat trends

Habitat availability

Throughout the Brook Floater’s range in Canada, there is substantially more apparently suitable habitat than is actually occupied by the species. Many rivers appear to have the required combination of flow speed and substrate to possibly harbour the species. Freshwater mussel surveys in many Maritime rivers with potential Brook Floater habitat have not produced records for the species (Figure 5 and Figure 6), and a number of rivers with the potential for Brook Floater occurrence have not yet been thoroughly surveyed.

Habitat quantity

In contrast to USportions of its range where dam construction and urbanization have reduced available habitat, there has been no substantial loss of Brook Floater habitat in Canada in the last 10-20 years despite construction of causeways on two rivers that support significant populations. The causeway built across the Petitcodiac River (NB) in 1968 contributed to the extirpation of the Dwarf Wedgemussel (Alasmidonta heterodon), by limiting upstream fish passage (Hanson and Locke 2000; Locke et al. 2003). Because the causeway is approximately 20 kmbelow the former head of tide at Salisbury, it has not reduced habitat available to the Brook Floater and has had little impact on the non-anadromous fishes most likely to be its hosts (Wicklow and Richards 1995; Bogan 2002; and see Biology). A causeway was built at Granville Ferry near the mouth of the Annapolis River (NS) in 1960 (Wells 1999), 45 km below the head of tide, with tidal power turbines installed in the causeway in the early 1980s (Wells 1999). However, Brook Floaters occupy the middle and upper reaches of the Annapolis, well upstream of areas impacted by siltation, changes in channel flow, and impediments to fish passage.

Habitat quality

The quality of habitat available to Brook Floaters in Canada has changed recently in many rivers due to increased impacts of industrial, agricultural and recreational activities. These negative trends have been countered at some locations by habitat improvement activities undertaken by government and non-government habitat protection and stewardship organizations. The net 10-year trend in New Brunswick appears to be primarily one of stable habitat quality at many Brook Floater sites, but with continuing decreases at others (Table 3). A similar 10-year pattern is observed in Nova Scotia, with the notable exception of the Annapolis River where habitat stewardship activities led by the Clean Annapolis River Project have resulted in a general improvement in water quality in the last ten years (Table 4). Recent trends in rivers in the US portions of the Brook Floater’s range have been complex, with some improvements in habitat quality resulting from active habitat protection activities generally outpaced by effects of urbanization, intensified agriculture and industrial activity, leading to an overall reduction ­in habitat quality.

Table 3. Factors influencing habitat quality in New Brunswick river systems that support Brook Floater populations, and assessments of trends in habitat quality

St. Croix River
NB River SystemDetailsReference
Present occupied areaBetween St Croix, NB (opposite Vanceboro, ME) and Upper Little Ridge, below Grand Falls Dam (opposite Kelleyland, ME)Sochasky pers. comm. 2007
Dams on river3 of 9 dams on river are in areas occupied by Brook Floater: 1) Vanceboro/St. Croix; 2) Canoose Flowage; 3) Grand FallsAdams pers. comm. 2007
Purpose of damsManaged for power production and effluent dilution at Woodland pulp mill, downriver from sites occupied by Brook FloaterAdams pers. comm. 2007
Water level changes1) Vanceboro/St. Croix: 2.3m drawdown (maximum: 4.3m); 2) Canoose flowage: great flow variation, headpond empties and fills completely;
3) Grand Falls: drawdown 0.3 – 0.5m, minimal variation in downstream flow
Adams pers. comm. 2007
Primary land useForestry 
Industrial dischargesNone in this section of riverSochasky pers. comm. 2007
Agricultural pollutionNone in this section of riverSochasky pers. comm. 2007
DevelopmentNot substantially increasing 
Riparian integrityGood 
Water quality monitoring?Yes: repeatedly over past 20 years by St. Croix International Waterway Commission and partners 
Water quality 10 years agoExcellentNB DOE 2007c
Present water qualityExcellentNB DOE 2007c
Ten-year trend in habitat qualityStable, no recent declineSochasky pers. comm. 2007
Habitat improvement measures?No mitigation of drawdown impacts 
CommentsDecline in Brook Floater habitat occurred 60-100 years ago when dams were constructed, generally stable since then 

 

Magaguadavic River
NB River SystemDetailsReference
Present occupied areaUppermost 7 km of river 
Dams on river1) 1 at head of the river at outlet of Magaguadavic Lake, 2) 2 on Northwest Branch Magaguadavic, an upstream tributary, 3) 1 near river mouth at St. George, NBHoyt pers. comm. 2007
Purpose of damsPower generation 
Water level changes0.3-0.5m downstream from first dam; lowest water levels in summerHoyt pers. comm. 2007
Primary land useForestry, recreation (boating, camps and cottages)NB DOE 2007a
Industrial dischargesDownstream from present Brook Floater locations only (fish hatcheries, yarn factory, inactive mine) 
Agricultural pollutionNot significant 
DevelopmentNot increasing substantially 
Riparian integrityGood 
Water quality monitoring?Yes: Eastern Charlotte Waterways (ECW) 1997 – 1999; 2007Craig pers. comm. 2007
Water quality 10 years agoExcellentNB DOE 2007a
Present water qualityExcellent upstream from and in vicinity of Brook Floater locationsNB DOE 2007a CCME 1999
Ten-year trend in habitat qualityNo change in upper section of river 
Habitat improvement measures?None 
CommentsHabitat declines occurred > 10 years ago when dams built. Flow regime unaltered for 20 years, though flow variations may limit area of suitable habitat. 

 

Petitcodiac River (including Little River, North River)
NB River SystemDetailsReference
Present occupied areaRural sections: 1) in main stem of Petitcodiac between Boundary Creek and town of Petitcodiac, 2) lower sections of Little and North Rivers close to where they join the Petitcodiac 
Dams on riverNone on main stem or tributaries near areas occupied by Brook Floater 
Purpose of damsN/A 
Water level changesN/A 
Primary land useForestry and agricultureNB DOE 2007b
Industrial dischargesNot significant in areas with Brook Floater 
Agricultural pollutionYes: nutrient loading, agricultural chemicalsPavey 2006
DevelopmentNo substantial increase in Brook Floater areas, some degradation in downstream urban areasPavey 2006
Riparian integrityModerate; some removal of natural vegetation 
Water quality monitoring?Yes: by Petitcodiac Watershed Alliance (PWA ) since 1999Richard 2007
Water quality 10 years agoIn Brook Floater areas: fair to good in main stem of Petitcodiac, good in regions of Little River, marginal to fair in North RiverNB DOE 2007b
Present water qualitySimilar to abovePavey 2006
Ten-year trend in habitat qualityApparent continued decline in North River. No clear trend in Petitcodiac and Little River 
Habitat improvement measures?Minor scattered PWA projects to improve stream habitat qualityNB DOE 2007b
CommentsDecline in quality primarily occurred > 10 years ago with increased intensity of agriculture; recent severe degradation in urban areas further downstream 

 

Southwest Miramichi River
NB River SystemDetailsReference
Present occupied areaMiddle reaches in vicinity of Doaktown 
Dams on riverNone in areas with Brook Floater 
Purpose of damsN/A 
Water level changesN/A 
Primary land useForestry 
Industrial dischargesSewage treatment by local communities has improvedCollins pers. comm. 2007
Agricultural pollutionNegligible 
DevelopmentResidential development is low density 
Riparian integrityGood 
Water quality monitoring?Yes: by Miramichi River EAC since 1993, at 30 stations in the watershedCollins pers. comm. 2007
Water quality 10 years agoExcellentCollins pers. comm. 2007
Present water qualityExcellentCollins pers. comm. 2007
Ten-year trend in habitat qualityNo trendCollins pers. comm. 2007
Habitat improvement measures?NBDNR : Watercourse Buffer Zone Guidelines in Forest Management Manual; Guidelines for Construction of Forestry Roads and WatercoursesNB DNR2004a
NB DNR 2004b
CommentsOverall water quality remains excellent 

 

Kouchibouguacis and Bouctouche Rivers
NB River SystemDetailsReference
Present occupied areaMiddle reaches of both rivers 
Dams on riverNone 
Purpose of damsN/A 
Water level changesN/A 
Primary land useForestry, agriculture, residential 
Industrial dischargesNone in areas with Brook Floater 
Agricultural pollutionMinor 
DevelopmentIncrease in small road construction and residential development along the riversRichard pers. comm. 2007; Plourde pers. comm. 2008
Riparian integrityIncrease in clearing and degradation of riparian zone, often to water’s edge
Water quality monitoring?No long-term monitoring 
Water quality 10 years agoGood 
Present water qualityIncreased siltation, especially after rain events 
Ten-year trend in habitat qualityDecrease 
Habitat improvement measures?Minor measures by local watershed groups. Required 60m setback for dwellings not always adhered to; buffer zone violations common on private woodlots along middle reaches of river; lack of enforcement capacity.Plourde pers. comm. 2008
CommentsSandy substrates make these river beds prone to erosion and ensuing siltationPlourde pers. comm. 2008

 

Shediac and Scoudouc Rivers
NB River SystemDetailsReference
Present occupied areaMiddle reaches of Shediac, two sites on ScoudoucCaissie and Audet 2006
Dams on riverNone 
Purpose of damsN/A 
Water level changesN/A 
Primary land useAgriculture, forestry, recreation, residentialSBWA 2007c
Industrial dischargesRaw sewage depositionSBWA 2007c
Agricultural pollutionSome pollution due to fecal coliforms, nutrientsSBWA 2007c
DevelopmentIncreasing residential developmentSBWA 2006
Riparian integrityDecreasing due to cattle and ATV crossings, denuded riparian zones from increased development, and poor road construction, agricultural and forestry practicesSBWA 2006
Water quality monitoring?Yes: provisional water classification assessment 2000-2003; annual water quality monitoring initiated at 15 sites in 2007NB DELG 2002; SBWA2007a; SBWA 2007c
Water quality 10 years agoGood 
Present water qualityResidents report increased bank erosion and sedimentation, anglers report markedly reduced fish densitiesSBWA 2006; Audet pers. comm. 2007
Ten-year trend in habitat qualityDecrease 
Habitat improvement measures?SBWA stream restoration projectsSBWA 2007a
CommentsSBWA and residents report decline, though little empirical evidence available 

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Table 4. Factors influencing habitat quality in Nova Scotia river systems that support Brook Floater populations, and assessments of trends in habitat quality

Annapolis River
NS River SystemDetailsReference
Present occupied areaApproximately 15 km in middle reaches, from Lawrencetown to Wilmot 
Dams on riverSeveral power dams upstream from area of Brook Floater occurrences 
Purpose of damsPower generation 
Water level changesMinimal in areas occupied by Brook Floater 
Primary land useAgriculture 
Industrial dischargesFew in areas occupied by Brook Floater 
Agricultural pollutionExtensive pollution from nutrients, fecal coliform bacteria, agricultural chemicalsSharpe 2007; MacMaster 2008
DevelopmentIncrease in rural housing development, increase in urbanization near Greenwood, stable level of farming over past 15 years 
Riparian integrityFairly good, though high rainfall events cause sudden increases in sediment, nutrient and coliform loadsSharpe 2007; MacMaster 2008
Water quality monitoring?Yes: by Clean Annapolis River Project (CARP): for the past 15 years 
Water quality 10 years agoFair 
Present water qualityFair to good, as sewage treatment capacity and land management practices increaseSharpe pers. comm. 2007
Ten-year trend in habitat qualityOverall general improvement in water quality; but local and temporal declinesSharpe 2007; MacMaster 2008
Habitat improvement measures?Many CARP habitat improvement projects with local communities, farms, and domestic householdsSharpe 2007
CommentsWater quality is variable in the watershed; and high nutrient and coliform levels at stations close to farms with poor land management practices may offset gradual improvements in water qualitySharpe 2007; MacMaster 2008

 

Stewiacke River
NS River SystemDetailsReference
Present occupied areaHistorical record upstream from Stewiacke 
Dams on riverNone in areas occupied by Brook Floater 
Purpose of damsN/A 
Water level changesN/A 
Primary land useAgriculture, forestry 
Industrial dischargesTreated effluent from local mines 
Agricultural pollutionAgricultural chemicals, fecal coliforms 
DevelopmentIncreased sod farming along main branch of Stewiacke River, between Middle and Upper Stewiacke, where historical records for Brook Floater occurredArchibald pers. comm. 2007
Riparian integrityWatercourse buffers not required for agricultural activities in NS; cattle access river at many locations; sod cultivated and cropped close to river bank, with increased siltation during heavy rains.Archibald pers. comm. 2007; Warren and Neil 1988
Water quality monitoring?No 
Water quality 10 years agoFair 
Present water qualityFair 
Ten-year trend in habitat qualityApparent decrease 
Habitat improvement measures?Unknown 
CommentsForestry unchanged in past ten years; good compliance with Special Management Zone buffer requirements of the NS Forests ActArchibald pers. comm. 2007, Nova Scotia Forests Act 1994-1995

 

Gays River
NS River SystemDetailsReference
Present occupied areaOne site near Stewiacke RiverBredin pers. obs.
Dams on riverNone 
Purpose of damsN/A 
Water level changesN/A 
Primary land useAgriculture, forestry 
Industrial dischargesResumption of lead-zinc mining in 2007, 5 km upstream of town of Gays River, effluent from mine polishing pond released into Anand Brook, a tributary of Gays RiverMelanson pers. comm. 2008
Agricultural pollutionSome pollution from nutrients, fecal coliforms 
DevelopmentTypes and level of agriculture and forestry same or declining over past ten yearsArchibald pers. comm. 2007
Riparian integrityFair, cattle have access to river at many locationsBredin pers. obs.
Water quality monitoring?No 
Water quality 10 years agoGood 
Present water qualityGood 
Ten-year trend in habitat qualityLittle evident change (no monitoring) 
Habitat improvement measures?Toxic effluent release prohibited by provincial and federal regulationsMelanson pers. comm. 2008, NS Environment Act 1989, Metal Mine Effluent Regulations (Fisheries Act)
CommentsNo concerns to date with toxic effluent releasesMelanson pers. comm. 2008

 

Wallace River and Mattatal Lake
NS River SystemDetailsReference
Present occupied areaMiddle reaches of Wallace River, scattered sites along Mattatal Lake shorelineNSDNR, Hall pers. comm. 2007
Dams on riverNone 
Purpose of damsN/A 
Water level changesN/A 
Primary land useAgriculture, forestry 
Industrial dischargesNone 
Agricultural pollutionSmall amounts upstream on Wallace RiverBredin pers. obs.
DevelopmentIncrease in development of residential and vacation properties along the Wallace River and Mattatal LakeRushton pers comm. 2008; Hall pers. comm. 2007
Riparian integrityMaintained by low density development set back from water, although impact of cottage development on habitat in Mattatal Lake is uncertainBredin pers. obs.; Hall pers. comm. 2007
Water quality monitoring?No 
Water quality 10 years agoGood 
Present water qualityGood 
Ten-year trend in habitat qualityNo evident change (no monitoring) 
Habitat improvement measures?None known 
CommentsFew forestry buffer zone violations; cattle access Wallace River at many locationsHall pers. comm. 2007; Bredin pers. obs.

 

LaHave River
NS River SystemDetailsReference
Present occupied areaLower-middle reaches upstream from Bridgewater 
Dams on river1 dam located 15 kmupstream from Brook Floater locations 
Purpose of damsPower generation 
Water level changesNo water level changes ("run of river" dam); although ineffective fish ladder may impede upstream fish passageTaylor pers. comm. 2008; DeMonde pers. comm. 2007
Primary land useForestry, agriculture 
Industrial dischargesNone 
Agricultural pollutionEffluents from cattle, poultry and horse farms. Christmas tree growing operations in the upstream drainage employ aerial application of fertilizerMacCullouch pers. comm. 2007
DevelopmentRecent increase in residential and suburban development, forestry unchangedRodenhizer pers. comm. 2008
Riparian integrityClearing of riparian vegetation associated with development, cattle access river at several locationsRodenhizer pers. comm. 2008
Water quality monitoring?Yes: recently initiated by Bluenose Coastal Action Foundation, no long-term dataRodenhizer pers. comm. 2008
Water quality 10 years agoGood 
Present water qualityFair 
Ten-year trend in habitat qualityApparent decrease 
Habitat improvement measures?Yes: Lunenburg-Queens Federation of Agriculture works with local farmers to mitigate threats to river habitatsRodenhizer pers. comm. 2008
CommentsNew wastewater treatment plant opened in 2006 in Cookville, close to 2002 Brook Floater location; effects on Brook Floater habitat unknown. Recent declines in Atlantic Salmon (Salmo salar) numbers and higher summer water temperatures.Rodenhizer pers. comm. 2008; DeMonde pers. comm. 2007

 

St. Marys River system (including Lochaber and Eden Lakes)
NS River SystemDetailsReference
Present occupied areaPortions of East River St. Marys, Lochaber and Eden Lakes 
Dams on riverNone 
Purpose of damsN/A 
Water level changesN/A 
Primary land useAgriculture, forestry, residential (cottages) 
Industrial dischargesNone in areas occupied by Brook Floater 
Agricultural pollutionSome pesticide runoff from corn and blueberry cropsGunn pers. comm. 2007
DevelopmentIncrease in residential development, intensification of agriculture with conversion to corn and blueberry cropsGunn pers. comm. 2007
Riparian integrityClearing of riparian vegetation, leading to siltation from storm events, higher peaks in water flow, widening of the river channel; some infractions of Special Management Zone buffer requirementsGunn pers. comm. 2007
Water quality monitoring?No systematic long-term monitoring 
Water quality 10 years agoVery good 
Present water qualityGood 
Ten-year trend in habitat qualityApparent decreaseGunn pers. comm. 2007
Habitat improvement measures?Special Management Zone buffers prescribed by NS Wildlife Habitat and Watercourses Protection Regulations 
Comments  

 

Salmon River (including Borden’s Lake)
NS River SystemDetailsReference
Present occupied areaUpstream reaches of Salmon River, and Borden’s Lake east of St. Marys River 
Dams on riverNone 
Purpose of damsN/A 
Water level changesN/A 
Primary land useForestry, agriculture 
Industrial dischargesNone 
Agricultural pollutionNot significantPulsifer pers. comm. 2007
DevelopmentNot substantially increasingPulsifer pers. comm. 2007
Riparian integrityGood 
Water quality monitoring?No systematic long-term monitoring 
Water quality 10 years agoVery good 
Present water qualityVery good 
Ten-year trend in habitat qualityNo apparent trend 
Habitat improvement measures?Special Management Zone buffers prescribed by NS Wildlife Habitat and Watercourses Protection Regulations 
Comments  

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Habitat protection/ownership

New Brunswick

Very little Brook Floater habitat in New Brunswick is legally protected. Although two New Brunswick Protected Natural Areas do provide some protection for the St. Croix River watershed, insufficient area is included to protect all locations in the river.

St. Croix River

About 50% of the land in the St. Croix River watershed is privately owned (CCNB 2007) and 80% is forested (NB DOE2007c). Approximately 30,000 ha of the watershed is protected by two New Brunswick Protected Natural Areas (PNAs) under the New Brunswick Protected Natural Areas Act (2003), which prohibits industrial, commercial, and agricultural uses, but permits recreational uses with minimal environmental impact. The Canoose Flowage PNA protects an upstream tributary that joins the St. Croix River at an area of Brook Floater occurrence. The Spednic Lake PNA is immediately upstream from Brook Floater occurrences on the main stem of the St. Croix. Most St. Croix River Brook Floater locations fall outside these areas.

Magaguadavic River

About 65% of the land in the Magaguadavic watershed is provincial crown-owned and almost 85% is forested, 14% is water or wetland, and 1.5% is used for agriculture (NB DOE 2007a). None of the watershed is legally protected.

Petitcodiac watershed

More than 95% of the land within 5 km of the main stem of the Petitcodiac River is privately owned, primarily for residential and agricultural uses. Most land immediately adjacent to Little River is also private, but the upper reaches of the Little River watershed are largely provincial crown land. About 75% of Little River watershed is forested, and 25% is agricultural (NB DOE 2007b). About 70% of land along North River is privately owned and used for agriculture (NB DOE 2007b). None of the watershed is legally protected.

Southwest Miramichi River

In the section on the Southwest Miramichi where Brook Floaters are known to occur, almost all the land in a 2-km strip adjacent to the river is privately owned and is low density residential. The remainder of the watershed is about half provincial crown land and half privately owned by forest companies, and is used primarily for forestry (Conservation Council of New Brunswick [CCNB] 2007). None of the watershed is legally protected.

Kouchibouguacis River

Almost 90% of the Kouchibouguacis watershed is provincial crown land, about 20% of which is leased to forest companies (i.e., provincial crown forestry leases). Though the lower 6 km of the Kouchibouguacis River estuary is within Kouchibouguac National Park, the entire freshwater reach of the river where Brook Floaters occur is outside of the National Park.

Bouctouche River

Almost 90% the lands immediately adjacent to the lower half of the Bouctouche River are privately owned and used for forestry, agriculture and housing, but in the upper reaches of the watershed about 30-40% of the area is owned by the provincial crown (CCNB2007). None of the watershed is legally protected.

Shediac and Scoudouc Rivers

In the Shediac and Scoudouc watersheds, about 80% of the lands are privately owned and about 20% are provincial crown land, some of which is leased to forestry companies. Forestry comprises about 85% of land use, and agriculture about 10% (SBWA 2007c). Neither of these watersheds is legally protected.

Nova Scotia

No areas in Nova Scotia that are immediately adjacent to riverine habitat occupied by Brook Floaters are legally protected. Designated Wilderness Areas do protect small areas in the uppermost reaches of two watersheds beyond the reaches in which Brook Floaters occur, and the Salmon River has the greatest proportion of provincial crown land and designated Wilderness Area.

Annapolis River

The majority of the land bordering the Annapolis River is privately owned and used for varying forms of agriculture. About one third of the area of upstream portions of the Nictaux River watershed, a main tributary of the Annapolis, is provincial crown land. Approximately 6 km of south bank Annapolis River frontage is federally owned as Canadian Forces Base Greenwood, and is immediately upstream from known Brook Floater occurrences.

Stewiacke watershed

All lands along the Gays River and most of the Stewiacke watershed are privately owned, though there is a small parcel of provincial crown land in the upper Stewiacke watershed representing approximately 5-10% of the total area of the watershed.

Wallace River and Mattatal Lake

All lands along the Wallace River and around Mattatall Lake are privately owned except for Wentworth Provincial Park, approximately 3 km² in the upper Wallace River watershed, and a few small areas of provincial crown land representing about 5% of the watershed area.

LaHave River

Land ownership along most of the LaHave River is private, but 40 km above known Brook Floater occurrences in the uppermost reaches of the LaHave watershed is the provincially owned Cloud Lake Wilderness Area and some smaller areas of provincial crown land. Nova Scotia Wilderness areas are set aside under the Wilderness Areas Protection Act (1998) and are protected from resource extraction (e.g., forestry, minerals), and invasive recreational use (e.g., camping, fires and vehicles are prohibited).

St. Marys River

Although most lands immediately adjacent to East River St. Marys, Eden Lake, Lochaber Lake and the main stem of the St. Marys River are privately owned, about 50% of the upper watershed is provincial crown land.

Salmon River

Approximately 20% of lands immediately adjacent to the Salmon River and about 50% of the upper Salmon River watershed are provincial crown land. The uppermost reaches of the Salmon River watershed are protected by Ogden Round Lake Wilderness Area.

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Biology

Life cycle and reproduction

As there is little information specific to the Brook Floater, relevant information on the general life cycle of unionids is provided as background.

In the Brook Floater, sexes are separate (gonochoristic) (Hoeh et al. 1995; Parmalee and Bogan 1998) but not sexually dimorphic as in some species. Reproduction in female freshwater mussels typically involves the transfer of mature ovocytes (eggs that have almost completed the meiotic division) from the ovary to two specialized brooding pouches (marsupial) located among the numerous gill lamellae (Mackie 1984; McMahon and Bogan 2001). These pouches contain compartments where the eggs are held and eventually develop into specialized larvae called glochidia. Male mussels release sperm into the water via the excurrent siphon. As the females filter-feed, the sperm are drawn through the inhalant siphon into their mantle cavities and then into the egg-filled marsupia where fertilization occurs (Parmalee and Bogan 1998). Success of fertilization may be reduced where mussels occur in extremely low densities, e.g., 0.01-0.1 individuals/(Neves 1997), which may be the case with rare species like the Brook Floater.

Once fertilized, Brook Floater eggs undergo normal molluscan spiral cleavage and develop into glochidia (Mackie 1984). Females are bradytictic, i.e., they are long-term brooders that retain their glochidia from early fall until release the following spring (Mackie 1984; Clarke 1981a,b; Nedeau et al. 2000). Each marsupium contains millions of glochidia, evidence of the high fecundity necessary for freshwater mussel reproductive success (Bauer 1987, 1994; Jansen and Hanson 1991; McMahon and Bogan 2001).

The reproductive cycle of gravid female freshwater mussels is linked to its host fish (Kat 1984; McMahon and Bogan 2001). The female is stimulated to release glochidia when a host fish is near, in response to factors such as shadows cast, touching of the female’s tissues, or the release of chemicals by the host (McMahon and Bogan 2001). Glochidia are equipped with specialized hooks on their valves to clamp onto the gills or fins of their host; glochidia typically measure 300-380+ µm in length once they are encapsulated in the host’s tissues (Mackie 1984). Encapsulated glochidia metamorphose into small juveniles with a tiny foot, adductor muscles and gill buds (Kat 1984; Zardus and Martel 2002). The juveniles then drop off the host and settle to the bottom, beginning their benthic existence. This life cycle enables the dispersal of larvae over potentially significant distances, even upstream of the reproducing adults. It is generally assumed that the relative survival of the juvenile stage is extremely low, whereas that for adults it is high (McMahon and Bogan 2001).

There are no detailed studies on the reproductive period of the Brook Floater in Canada but gravid individuals have been observed from August to May in coastal rivers of the eastern US (Clarke 1981b). Nedeau et al. (2000) reported the period of glochidial release for a bradytictic species like the Brook Floater is from April to June, or possibly later in the summer. Assuming that the distinct dark bands on the surface of the shell are annual rings, examination of preserved specimens from the Petitcodiac River, NB, suggested that most individuals were 7 to 14 years old (Martel personal observation). This means an estimated average generation time of 10 years (Martel pers. comm. 2009).

In Canada, the only information on specific hosts is from a study of the Kouchibouguacis River, NB, where a single Brook Floater glochidium was found attached to a Ninespine Stickleback (Pungitius pungitius) (Beaudet 2006). In rivers of the eastern US, fishes that have been reported as hosts for the Brook Floater include Longnose Dace (Rhinichthys cataractae), Blacknose Dace (Rhinichthys atratulus), Golden Shiner (Notemigonus crysoleucas), Pumpkinseed Sunfish (Lepomis gibbosus), Slimy Sculpin (Cottus cognatus), Yellow Perch (Perca flavescens), and Margined Madtom (Noturus insignis) (Wicklow and Richards1995; Bogan 2002). Several of these species occur in New Brunswick and/or Nova Scotia and may be potential hosts for the Brook Floater. Yellow Perch are relatively ubiquitous throughout the region, except for the Bay of Chaleur drainage (Scott and Crossman 1973) where no Brook Floaters have been found. Ninespine Stickleback are broadly distributed throughout the region (CRI 2008) and are likely in all watersheds with Brook Floaters. Golden Shiners, present throughout most of the region, are absent from the Bouctouche and Shediac Rivers in NB (CRI 2008), both of which support significant populations of Brook Floaters. Blacknose Dace occur throughout NB but have a patchy distribution in NS that only partly overlaps the range of the Brook Floater (CRI 2008; Gilhen and Hebda 2002).

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Predation

Predation on freshwater mussels can be significant. Several vertebrates including the Common Muskrat (Ondatra zibethicus) (Oesch 1984; Hanson et al. 1989; McMahon and Bogan 2001), the North American River Otter (Lontra canadensis), the Raccoon (Procyon lotor), the American Mink (Neovison vison), and turtles (Oesch 1984; McMahon and Bogan 2001) eat mussels.

Muskrats are widespread across the range of the Brook Floater, and may be a significant source of mortality (see Limiting Factors and Threats). Muskrat middens containing numerous Brook Floater shells occur in the Petitcodiac (Hanson and Locke 2001), Southwest Miramichi and Annapolis (Bredin pers. obs.) and Kouchibouguacis Rivers (Beaudet pers. comm. 2007). Predation of rare and endangered mussels by muskrats can be significant (Neves and Odum 1989).

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Physiology

There are no data on physiology of the Brook Floater. This species has relatively specific physical habitat requirements (i.e., clean, well-oxygenated water in rivers with moderate current speeds, and sand or fine gravel substrates, see Habitat requirements), in comparison with co-occurring, more tolerant mussels (e.g., Elliptio complanata). Brook Floaters may be more physiologically adaptable than is commonly thought, however, as they have also been reported from sandy-bottomed ponds and lakes (Nova Scotia Department of Natural Resources 2005; Massachusetts Division of Fisheries and Wildlife 2007), and in silty sand in cracks between boulders (North Carolina Nongame and Endangered Wildlife Program 2007).

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Dispersal / migration

Adults are largely sedentary. Depending on the species and type of substrate, adult mussels move slowly along a lake or river bed, usually travelling centimetres to metres in a day. More rapid dispersal over longer distances is accomplished via the movement of host fishes to which the glochidia are attached. Mussel larvae may be dispersed several hundred metres to many kilometres both upstream and downstream within a watershed. Thus gene flow occurs through host fish movements.

Seawater at the mouths of occupied rivers in Nova Scotia and New Brunswick prevents dispersal among adjacent watersheds if the glochidia are attached to an obligate freshwater host fish species, such as a dace or shiner. The Ninespine Stickleback (a potential host) is capable of traversing fresh, salt and brackish water habitats (Scott and Crossman 1973) and may facilitate dispersal across watersheds, especially if adjacent occupied rivers drain into a protected estuarine environment. The Ninespine Stickleback moves from estuaries into creeks and streams in summer to spawn. Yellow Perch are also tolerant of brackish water, at least for short periods of time, and will move from brackish into fresh waters in spring to spawn. Whether fishes such as these could disperse Brook Floaters among watersheds depends on the salinity tolerance of the glochidia, which has not been studied.

As noted in Genetic description, populations of most Atlantic Slope species of unionids are considered to be naturally fragmented to the point where populations would be unlikely to quickly recolonize following a local extirpation. Rescue effect from populations in the US is extremely unlikely because US populations are rapidly declining.

The Canadian population of Brook Floaters (Figure 5 and Figure 6) is fragmented. Populations are not continuous within a watershed; rather, occurrences tend to be clustered within a small reach or tributary. Furthermore, populations are widely scattered and seldom found in adjacent watersheds. Although most of the total area of occupancy is in small habitat patches, the size of habitat patch required to support a viable population is unknown.

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Interspecific interactions

In addition to interspecific interactions with predators and host fishes (see above), several types of parasites may also affect freshwater mussels. Parasites infecting Brook Floaters may include trematodes, such as digenean worms, and freshwater mites. In Catatonk Creek, New York, Fischthal (1954) reported that one in seven Brook Floaters was infected by the cercaria (larval stage) of a trematode, Cercaria fischthal (Family: Gorgoderidae). Freshwater mites (family: Uniocolidae) are commonly found in freshwater mussels of the subfamily Unioninae. Mites have been observed on the gills of live freshwater mussels from British Columbia to New Brunswick (Martel pers. obs.). The mites feed on internal tissues, and heavy infestation may lead to the shedding of parts of the gills, abortion of developing glochidia, or even death (see review by McMahon and Bogan 2001). Because Canadian research is lacking, specific impacts of parasitism on Brook Floaters in the Maritimes remain unknown.

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Adaptability

Brook Floaters are adapted to running water environments and usually cannot survive in an impounded, lake-like reservoir although they have occasionally been found in ponds and small and medium-sized lakes (see Habitat requirements). The construction of a dam or impoundment changes the hydrology, sedimentation, physical-chemical limnology and biology of a river (Baxter 1977), and can eliminate or severely impact populations of freshwater mussels within the impounded section and for considerable distances downstream (Vaughn and Taylor 1999). In addition, management of impounded rivers often involves rapid water level reductions above and below dams, which strand and expose freshwater mussels and cause mortality from desiccation and increased predation (Parmalee and Bogan 1998; Nedeau et al.2000). Residential and urban development near rivers, intensive agriculture and forestry, and road construction may damage the riparian zone and have been directly linked to catastrophic declines in freshwater mussels and their host fishes (Morris and Corkum 1996; Poole and Downing 2004). Brook Floaters have been unable to adapt to these types of changes along rivers in the US, and have suffered sharp population declines (see Global range).

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Population Sizes and Trends

Search effort

New Brunswick

Historical surveys

Historical surveys for freshwater mussels in NB were conducted by Athearn in the 1940s and 1950s, by Herrington in the 1950s, and by Clarke in the 1950s and 1960s (Athearn 1961; Athearn and Clarke 1962; Clarke 1981a). These surveys usually involved some water search using viewing buckets, but there is little information on associated survey effort. The surveys found Brook Floaters in the Renous River (1948, in Athearn 1961), the Aroostook River (Herrington 1960, recorded as A. marginata, Sabine 2006) and the Petitcodiac River (Athearn 1952; see Canadian range). Clarke’s province-wide surveys found Brook Floaters in the Petitcodiac River system but not in new watersheds in NB. Clarke surveyed numerous accessible sites throughout the Maritimes but seldom investigated less accessible middle and upper reaches of watersheds where Brook Floaters are often found (Clarke 1981a). The small number of confirmed historical records reflects in part the typically low densities and patchy distribution of Brook Floaters, in comparison to other freshwater mussels in the Maritimes.

Recent surveys

Greatly increased survey efforts in the last 15 years, including surveys for this report, resulted in the discovery of new populations of Brook Floaters in seven rivers in NB, i.e., the St. Croix (1994), Magaguadavic (2001), Southwest Miramichi (2006), Kouchibouguacis (2001), Bouctouche (2002), Shediac (2002) and Scoudouc (2004) Rivers (Table 5, Figure 5).

Table 5. Summary of mussel sampling effort in New Brunswick rivers with recent records of Brook Floaters, showing the number of sites surveyed, number of sites with Brook Floaters, number of Brook Floaters found per site, total number of Brook Floaters found and person-hours of search effort per water body

Bay of Fundy drainage
New Brunswick RiverNo. of sites surveyedNo. of sites with Brook FloaterNumbers of live individuals found (or abundance) at each siteTotal no. live Brook Floater foundPerson-hours on river or length searchedSampling methods and effort in person-hours (p-h) or length searchedYear and source of surveys
St. Croix1453,2,1,13,32219semi-quantitative timed search: buckets and snorkelling, midden and shoreline inspection1994: Nedeau et al. 2000; MDIFW 2007
St. Croix900013semi-quantitative timed search with buckets, midden and shoreline inspection2001: Bredin and d’Entremont 2002
St. Croix30006semi-quantitative timed search with buckets, midden and shoreline inspection2006: Bredin, this report
Magaguadavic1115153semi-quantitative timed search with buckets, midden and shoreline inspection2001: Sabine 2006
Magaguadavic351338semi-quantitative timed search with buckets, midden and shoreline inspection2006: Bredin, this report
Petitcodiac16614rare at 9 sites2 scarce at 4 sites common at 1 site> 30029.3 km129.3 km1 of river searched visually with buckets; inspection of middens, shorelines, and sand or gravel bars; excavation of large sand or gravel deposits with 6 mm mesh push net1997-2000: Hanson and Locke 2001
Aroostook≥11 > 1?no information1960: Herrington, CMN data
Aroostook2000~3presence/absence visual search, midden and shoreline inspection primary focus on Lampsilis cariosa2001: McAlpine pers. comm. 2007; NB DNR data
Aroostook20004semi-quantitative timed search with buckets, midden and shoreline inspection2006: Bredin, this report

1 During Petitcodiac River system surveys, effort was measured in distance surveyed rather than time searched.

2 Petitcodiac unionid abundance data were categorized as A = abundant (> 1/ sq. m); C = common (<1 but > 0.1 per sq. m); S = scarce (10 to 100 per site); R = rare (< 10 per site) (Hanson pers. comm. 2007).

3 One site on the Magaguadavic River was abandoned due to presence of silt.

Gulf of St. Lawrence drainage
New Brunswick RiverNo. of sites surveyedNo. of sites with Brook FloaterNumbers of live individuals found (or abundance) at each siteTotal no. live Brook Floater foundPerson-hours on river or length searchedSampling methods and effort in person-hours (p-h) or length searchedYear and source of surveys
Miramichi: NW Miramichi111 valvepartial valveN/Amidden inspection2001: Sabine 2006
Miramichi: NW Miramichi31 06semi-quantitative timed search with buckets, midden and shoreline inspection2006: Bredin, this report
Miramichi: Southwest Miramichi & Cains1465,10,4,9,2,104040.75semi-quantitative timed search with buckets, midden and shoreline inspection2002: Bredin 2002, 2006, 2007: Bredin, this report
Miramichi: Renous?1≥1≥1?presence/absence water search, no time data available1948: Athearn 1961
Miramichi: Renous30009semi-quantitative timed search with buckets, midden and shoreline inspectionBredin 2002, 2006: Bredin, this report
Kouchibouguacis15103,1,1,4,1,2,30,2, 41,18660semi-quantitative timed search with buckets and snorkelling, midden and shoreline inspection2001: Beaudet et al. 2002
Bouctouche1873,1,12,2,2,27,35072semi-quantitative timed search with buckets, midden and shoreline inspection2004: Caissie 2005
Bouctouche41448semi-quantitative timed search with buckets, midden and shoreline inspection2002: Bredin 2002
Shediac224, 1 valve44semi-quantitative timed search with buckets, midden and shoreline inspection2002: Bredin 2002
Shediac8630,14,4,2,27,2610332semi-quantitative timed search with buckets, midden and shoreline inspection2005: Caissie and Audet 2006
Scoudouc3218,1191219 p-hof semi-quantitative timed search with buckets, midden and shoreline inspection2005: Caissie and Audet 2006

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St. Croix River

Brook Floaters were first reported from two sites on the St. Croix River in 1994 during surveys for the Maine Freshwater Mussel Atlas Project (Nedeau et al. 2000). Surveys at nine additional sites in 2001 (Bredin and d’Entremont 2002) and at three sites close to the previously known US locations in 2006 failed to detect additional Brook Floaters. However, Maine Department of Inland Fish and Wildlife (MDIFW) surveys detected three new locations for the species during 2.75 person-hours of snorkelling in the St. Croix River in 2006 (MDIFW unpublished data 2007, Swartz pers. comm. 2007) with 13 live individuals recorded from one site.

Magaguadavic River

Brook Floaters were first recorded from the Magaguadavic River in 2001 when 15 live individuals were detected with 3 person-hours (p-h) of search effort (Sabine 2006). Although four additional downstream sites were surveyed for 2 p-h each in 2006, they were found at just one site, 200 m downstream from the 2001 location (Figure 4). At both sites on the Magaguadavic, Brook Floaters were found partially buried in pockets of coarse sand behind mid-stream boulders. Additional surveys are required in less-accessible sites upstream from known locations in order to fully delineate the extent of the species in this river.

Petitcodiac River

Prompted by conservation concern for the Dwarf Wedgemussel, Hanson and Locke (2001) surveyed 66 sites over a total distance of 29.3 km in the Petitcodiac watershed from 1997 to 2000. They found locally abundant beds (e.g., > 20 individuals; one bed > 300 individuals) of Brook Floaters in sand or gravel bars, and small groups (5-20 individuals) in pockets of coarse sand behind boulders, in both the main Petitcodiac River and in the Little River. Brook Floaters were found in smaller numbers at two sites on the North River. Individuals less than 15 mm long were found at sites on Little River and the main Petitcodiac River, confirming recent recruitment.

Saint John River System - Aroostook River

The only Brook Floater record from the Saint John River system was Herrington’s record from the Aroostook River in 1960, recorded as Alasmidonta marginata, of which A. varicosa was considered a subspecies at the time (Sabine 2006). Unfortunately the specimen is missing and its identity cannot be confirmed (Martel pers. obs.). During surveys of the Saint John River system for the Yellow Lampmussel (Lampsilis cariosa) in 2001, 3 p-h of surveys at two sites on the Aroostook River failed to locate any Brook Floaters, as did four person-hours of survey at two nearby locations in 2006 (Table 5). Extensive MDIFWsurveys in the Aroostook, most of which is in Maine, also failed to detect Brook Floaters anywhere in the watershed, including the middle reaches where the species would most likely be found (PEARL 2008). Recent surveys of the Saint John River system, including surveys of suitable habitat in tributaries such as the Canaan, Kennebecasis, Salmon and Eel Rivers (Bredin 2002; Bredin and d’Entremont 2002; Bredin and Brunelle 2004; Sabine 2006) have produced no additional Brook Floater records in the watershed.

Miramichi River system - Southwest Miramichi

Brook Floaters were anecdotally reported from the Southwest Miramichi River by Susi von Oettingen of the US Fish and Wildlife Service, while on a kayak trip in 2002. Over 14 p-h of surveys conducted for this report in 2006 and 2007 confirmed Brook Floaters at six of seven sites near Doaktown. They were not detected during surveys in 2002 at five locations 20-50 kmfurther downstream from Doaktown where the River is wider, deeper and faster, or in the Cains River, a tributary of the Southwest Miramichi (Bredin 2002).

Miramichi River system - Northwest Miramichi

Sabine (2006) reported a partial Brook Floater valve from a midden on the shore of the Northwest Miramichi in 2001. The report writers were unable to confirm the presence of Brook Floaters during 6 p-h of surveys at three nearby locations on the Northwest Miramichi in 2006. Surveys conducted in 2008 by the Miramichi River Environmental Assessment Committee (MREAC) across the Miramichi watershed and close to this location also failed to detect Brook Floaters (Collins pers. comm. 2008). Access to this vast and remote section of the watershed is very limited, and widespread surveys for Brook Floaters would be logistically difficult, costly and time-consuming.

Miramichi River system - Renous River

Nine p-h of surveys at the historical site at the town of Renous, at a site 5 km further upstream, and at the confluence with the Southwest Miramichi River failed to confirm the species (Bredin 2002). No other live mussels were visible in the Renous River at the town of Renous, suggesting some habitat degradation since Athearn’s day (Bredin pers. obs.). Brook Floaters may be present in the upper reaches of the Renous River and its branches, but these have not been surveyed.

Kouchibouguacis River

Beaudet et al. (2002) surveyed freshwater mussels at 15 sites in the Kouchibouguacis River and 10 sites in the adjacent Kouchibouguac River using a 4 p-h timed search method (after Metcalfe-Smith et al.2000), for a total of 100 p-h and a sampled surface area of approximately 21,000 on these two river systems (Beaudet et al.2002). A total of 86 live Brook Floaters were found at 11 of 15 survey sites in the Kouchibouguacis River, but none were recorded from the Kouchibouguac River (Beaudet et al. 2002). Brook Floaters were very rare at nine of the eleven sites on the Kouchibouguacis (1-4 live individuals) but more abundant at two sites, though still a small proportion of the total mussel fauna present (30 of 459, or 6.5%, of all live mussels recorded at one site and 41 of 289, or 14%, of mussels at the second site (Beaudet et al. 2002). Juveniles with shell lengths less than 30 mmwere observed at a number of sites (Beaudet pers. comm. 2007).

Shediac, Scoudouc and Bouctouche Rivers

During timed search surveys of 2 p-h/site of the Richibucto, Coal Branch, Bouctouche, Shediac and Cocagne Rivers, Brook Floaters were recorded from one site on the Bouctouche River and two on the Shediac River (Bredin 2002). Caissie (2005) and Caissie and Audet (2006) conducted intensive timed search surveys (4 p-h/site) of 55 sites on six river systems flowing into the Northumberland Strait including the Chockpish, Bouctouche, Little Bouctouche, Cocagne, Shediac and Scoudouc Rivers and some of their tributaries (Figure 4, Figure 5). Brook Floaters were found on three rivers, the Bouctouche, Shediac, and Scoudouc Rivers, at 15 sites, though only seven sites had more than four live Brook Floaters present. Juveniles (less than 30 mm in length) were present at six sites on the Shediac and at one site on the Bouctouche River (Caissie 2005; Caissie and Audet 2006).

Nova Scotia

Historical surveys

Historical surveys for freshwater mussels in NS were also conducted by Athearn (1940s and 1950s) and Clarke (1950s and 1960s) (Athearn 1961; Athearn and Clarke 1962; Clarke 1981a). In the 1970s, Nova Scotia Museum staff surveyed several rivers to confirm interesting records following an evaluation of their Mollusca collection (Davis pers. comm. 2008). Although there is little accompanying data on survey effort, these historical surveys found Brook Floaters in the Annapolis River at Lawrencetown (Athearn 1953, see Davis 2007), the Stewiacke River upstream from the town of Stewiacke (Athearn 1951, see Athearn and Clarke 1962), the Wallace River near South Middleboro (Clarke 1960, see Athearn and Clarke 1962), the LaHave River (B. Long 1921, ANSP 2007) and the St. Marys River near Sherbrooke (Athearn 1946, see Athearn and Clarke 1962) (see also Canadian range).

Recent surveys

Nova Scotia DNR staff initiated a three-year program of provincial surveys in 1999 to obtain a broad scale freshwater mussel distribution in the province and to update information from Clarke’s surveys. Surveys were conducted by regional biologists and summer staff at more than 500 sites in northern and eastern NS, with a lower level of survey effort in southern NS. Surveys were generally carried out by wading with viewing buckets. The surveys (Table 6, Figure 6) were designed to include many locations of differing habitat types and were not intensive (usually 30 to 60 minutes in duration). The majority of sampling locations were sites with convenient water access, and where depths and flow rate posed no danger to surveyors (Pulsifer pers. comm. 2007).

Table 6. Summary of mussel sampling effort in Nova Scotia waters with records of Brook Floaters, showing the number of sites surveyed, number of sites with Brook Floaters, the number of Brook Floaters found per site, total numbers of Brook Floaters found and person-hours of search effort per water body.

Number of live Brook Floaters found was not recorded for all sites on the St. Marys River and Lochaber Lake. Due to data duplication within datasets it was not possible to discern exactly how many sites were surveyed on the St. Marys River and Lochaber Lake or the total number of person-hours of survey

Bay of Fundy drainage
Nova Scotia River or LakeNo. of sites surveyedNo. of sites with Brook FloaterNumbers of live individuals found at each siteTotal no. live Brook Floater foundPerson-hours on riverSampling methods and effortYear and source of surveys
Annapolis774,12,5,1,2,2,43011semi-quantitative timed search with buckets, midden and shoreline inspection, some excavation in loose substrate2006 Bredin, this report
Stewiacke111-21-2≥0.5presence/absence survey with water search, data is available on encounter rate per time searched1951: Athearn (historical)
Stewiacke50005semi-quantitative timed search with buckets, midden and shoreline inspection1999-2001: NSDNR
Gays21225semi-quantitative timed search with buckets, midden and shoreline inspection, some excavation2002: Bredin 2002

 

Gulf of St. Lawrence drainage
Nova Scotia River or LakeNo. of sites surveyedNo. of sites with Brook FloaterNumbers of live individuals found at each siteTotal no. live Brook Floater foundPerson-hours on riverSampling methods and effortYear and source of surveys
Wallace1112≥12?presence/absence survey, time and water search information unavailable1967: OSU online database 2007
Wallace11≥1≥1?presence/absence survey with water search, time data unavailable1975: NSM data, Davis 2007
Wallace50004semi-quantitative timed search with buckets, midden and shoreline inspection1999-2001: NS DNR data
Wallace43(1,1,1) valves(3)valves3.25semi-quantitative timed search with buckets, midden and shoreline inspection2006: Bredin, this report
Mattattal Lake11~20-30~20-304Canoe-based visual survey, water and shoreline inspection, general estimate of # of individuals present/area2001: NS DNR data, Hall pers. comm. 2007

 

Scotian Shelf Drainage
Nova Scotia River or LakeNo. of sites surveyedNo. of sites with Brook FloaterNumbers of live individuals found at each siteTotal no. live Brook Floater foundPerson-hours on riverSampling methods and effortYear and source of surveys
LaHave721,8919semi-quantitative timed search with buckets, snorkelling, midden and shoreline inspection, some excavation2002: Bredin 2002
St. Marys~95N/A≥5~9presence/absence search of specified duration with buckets, midden and shoreline inspection1999-2001: NSDNR, NSM, Davis 2007
Lochaber L.(St. Marys)~53N/A≥3~4presence/absence search of specified duration with buckets, midden and shoreline inspection1999-2001: NSDNR, NSM
Eden L. (St. Marys)3111~1.5presence/absence search of specified duration with buckets, midden and shoreline inspection1999-2001: NSDNR, NSM data
Salmon River3111> 2Nine 1 m² quadrat surveys, 3 habitats: 3 plots/habitat type2006: NS DNR, Pulsifer pers. comm. 2007
Borden’s Lake11≥1≥11presence/absence search of specified duration with buckets, midden and shoreline inspection2001: NS DNR

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Figure 6. Map of the distribution of Brook Floaters, Alasmidonta varicosa, in Nova Scotia showing mussel sampling sites and a historical record.

Map showing the distribution of Brook Floaters in Nova Scotia, with mussel sampling sites and a historical record.

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Annapolis River

Athearn’s single 1953 Brook Floater record in the Nova Scotia Museum (Davis 2007) from Lawrencetown prompted 11 p-h of surveys at seven sites in 2006 for this report. Brook Floaters were present throughout the entire section of river surveyed but were most abundant near Middleton where the river was moderately deep (~1 m), clear, and sandy, with occasional boulders.

Stewiacke and Gays Rivers

Five p-h of surveys by NSDNRpersonnel from 1999 to 2001 at five locations on the Stewiacke River, including the historical site, did not reconfirm Brook Floaters there. However, Bredin (2002) discovered two Brook Floaters at one site in the Gays River, a tributary of the Stewiacke, on a substrate of coarse sand, with clear water, moderate depths (0.5-1.0 m) and gentle current.

Wallace River

David H. Stansbery collected 12 live Brook Floaters from the Wallace in 1967, indicating that there must have been a modest population present at that time (OSU 2007). The species was again collected near South Middleboro in 1975 (Davis 2007). Four p-h of surveys by NS DNR at five sites in 1999, 2001 and 2002, including those near South Middleboro, failed to confirm Brook Floaters. One fresh Brook Floater valve was collected from each of three sites during 3.25 p-h of surveys in 2006 for this report, although no live individuals were seen.

Mattatall Lake

In a separate watershed, 5 km northeast of the Wallace River, a dispersed patch of Brook Floaters was found at a density of 1 mussel / 3-5 over a section of the shallow sandy-gravel, wind-exposed shoreline of Mattatall Lake (Hall pers. comm. 2007). They were not found in other areas of the lake, although half of the total shoreline was searched and much of the rest was unsuitable habitat with emergent vegetation (Hall pers. comm. 2007).

Other NSNorthumberland Strait Rivers

Almost 17 p-h of surveys by NSDNR at 26 sites in adjacent rivers also draining into Northumberland Strait, including the Tidnish, Shinimicas, Dewar, French, Waughs, River Philip and River John, did not find any additional Brook Floaters.

LaHave River

The first Brook Floater record for the Maritimes was from the LaHave River in 1921 (Clarke 1981b; ANSP 2007). There were few additional surveys on this river (see data in Davis 2007) until 2002 when 19 p-h of survey detected Brook Floaters at two of seven sites, both with very diverse habitats, dense concentrations of unionids, and the greatest amount of search effort (3.5 and 4 p-h) (Bredin 2002).

St. Marys River system

The Brook Floater was discovered further upstream from the 1946 record (near Sherbrooke) in East River St. Marys (Davis 2007). Nova Scotia DNRsurveys produced additional Brook Floater records scattered throughout the St. Marys watershed, including three lentic sites from Lochaber Lake and one from Eden Lake-the headwaters of East River St. Marys.

Salmon River

In 2002, Brook Floaters were recorded from Borden’s Lake in the eastern sector of the Salmon River system, and in 2006 one individual was discovered in the upstream reaches of the River (Pulsifer pers. comm. 2007). Survey coverage across this region of NS is considerable (NSDNRdata), though survey effort per river was not intensive, in contrast to the surveys conducted in some Northumberland Strait rivers of NB, where a minimum of 4 p-h was spent per site (see Search effort). Without more comprehensive surveys (many sites per river) it is impossible to determine whether Brook Floaters are more continuously distributed throughout the Salmon River watershed or whether they are as patchy as current records suggest.

Abundance

Virtually all of the recent surveys for freshwater mussels in Maritime rivers that support Brook Floaters have employed semi-quantitative sampling techniques (see Table 5 and Table 6). In most cases, surveys consisted of timed-searches using viewing buckets and a search effort of <1 to 4 p-h/site; a few surveys also involved snorkelling. Most surveyors also searched the shoreline and muskrat middens for shells, and a few included the casual (i.e., unsystematic) excavation of sand or gravel deposits to locate buried individuals. Hanson and Locke (2001) devised a unique sampling technique for their surveys of the Petitcodiac River (described below) that was also semi-quantitative. With the exception of the Kouchibouguacis and Shediac River surveys, the actual area searched at a given site was not recorded. Quantitative surveys were conducted in a small area of the Salmon River as part of a field biology course (Pulsifer pers. comm. 2007).

Although timed searches are generally considered to be the best sampling method for detecting rare species of mussels, they were not designed for estimating population density or size. To quote Strayer and Smith (2003), "Although timed searches often are used as a rough measure of population density, they offer no information about the actual size or density of a mussel population, and they are burdened with large and unknown errors." Data from timed-search surveys are, however, the only data available for estimating the sizes of Brook Floater populations in the Maritimes. Sources of error associated with such data and their influence on population estimates are considered at the end of this section.

Catch Per Unit Effort (CPUE), that is, the number of Brook Floaters detected during a specified period of search time at a site, can be used as a proxy for abundance-although it will clearly be an underestimate. If the area of the river or lake searched is also known, then an approximate value for density can be calculated. The Kouchibouguacis and Shediac Rivers are the only systems for which both parameters were measured. In these rivers, surveyors recorded four GPS waypoints at the corners of each survey site. The area of each site was calculated from the four waypoints using GIS, and then multiplied by the number of sites surveyed to determine the total area searched per river. The total number of live Brook Floaters found in each river (from Table 5), divided by the total area searched, yielded an approximate mean density of individuals in the surveyed areas of the river. Assuming that Brook Floaters would be continuously distributed at the same density throughout the occupied reach in each river, population estimates were determined by extrapolating the mean density to the total AO (from Table 2). As shown in Table 7, sizes of the Brook Floater populations in the Shediac and Kouchibouguacis Rivers were thus estimated to be 6100 and 980 individuals, respectively.

Table 7. Estimates of population size for Brook Floater populations in the Shediac and Kouchibouguacis Rivers, NB, using mean "density" estimates based on CPUEextrapolated to the total AO in each river (see text for details). Shediac River surveys in 2002 (see Table 5) were not included in this calculation as search area was not recorded.
RiverTotal area searched within the reach of river where Brook Floaters were presentTotal number of Brook Floaters found in searched area of river"Density" of Brook Floaters in searched area of riverEstimated total area occupied (AO) by Brook Floaters in riverEstimate of population size, i.e., total # individuals (rounded values)
Shediac2009 m²
103
0.0513/m²119000 m²
6100
Kouchibouguacis18821 m²
82
0.0044/m²224000 m²
980

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Hanson and Locke (2001) surveyed 66 sites in the Petitcodiac River watershed, measuring effort in terms of distance surveyed rather than p-h of search time. The number of mussels of each species found at each site was categorized as abundant (> 1/), common (<1 but > 0.1/), scarce (10-100 individuals/site) or rare ( <10 individuals/site). Brook Floaters were found at 14 sites. The abundance of Brook Floaters at sites where they were scarce or rare was calculated as a range by multiplying the low and high values for each category the number of sites in that category. Abundance at the one site where it was common was calculated as a range by multiplying the low and high densities for that category the area of river searched. A total population estimate of 730-7300 Brook Floaters was calculated (Table 8). As this estimate applies only to the 66 sites surveyed, it represents a minimum population estimate for the Petitcodiac River watershed. In considering the accuracy of this estimate, it should be noted that Hanson and Locke (2001) were very familiar with the watershed and almost certainly sampled most of the running water areas where Brook Floaters would be most likely to occur. They also employed several search techniques at each site, including visual searches, digging through sand and gravel around rocks and boulders and sieving all large deposits of sand or gravel through a 6 mm push net to locate buried individuals. It is therefore likely that the population estimate for Brook Floaters based on the 66 surveyed sites is a realistic estimate for the entire watershed. Hanson (pers. comm. 2007), who has extensive field experience with mussel populations and habitats in the Petitcodiac River, speculated that there are in the order of 10,000 Brook Floaters in the Petitcodiac system, suggesting that the higher estimate of 7300 individuals may be more accurate than the lower estimate of 730.

Table 8. Estimates of total numbers of Brook Floaters at 14 sites where they occurred in different categories of abundance in the Petitcodiac River system, NB, and estimate of population size for the entire system, based on data from Hanson and Locke (2001). 1 Data provided by Hanson (pers. comm.2007).
Abundance category and number of Brook Floater sites falling into each categoryDefinition of abundance categoryRange of abundance/siteRange of abundance at all sites in each category
Estimate of total population size  730 to 7300
Rare: 9 sites< 10/site1-9
9-81
Scarce: 4 sites10 to 100/site40-400
40-400
Common: 1 site< 1 but > 0.1/m²1sampled area = 6800 m²
680 to 6800
Abundant: 0 sites> 1/m²0
0

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CPUE was known for all of the remaining waterbodies in NB and NSwhere Brook Floaters were found (except for Mattatall Lake and the St. Marys and Salmon Rivers, which are dealt with below), but search area was not recorded for any of the surveys. Thus, it was not possible to calculate an approximate estimate of mean "density" for these systems as was done for the Kouchibouguac and Shediac Rivers, and estimates of population size could not be obtained. However, assuming that the Kouchibouguacis and Shediac Rivers are representative of Maritime rivers inhabited by Brook Floaters, then data from these rivers could be used to derive a constant, which in turn could be used along with information on AO and CPUE to calculate an estimate of population size for each of the other waterbodies (Table 9). Calculation of the constant and an illustration of its application using data from the St. Croix River are presented in Appendix 2.

Table 9. Estimates of population size for Brook Floaters in the rivers and lakes in New Brunswick and Nova Scotia where it occurs, and the parameters used to calculate these estimates (see text for details). Frequency of occurrence was considered in calculating estimates for Mattatall Lake and the St. Marys and Salmon Rivers only, but is presented for the other systems for comparison.
Water bodyFrequency of occurrence of Brook Floaters
(% of surveyed sites)
CPUE for Brook Floaters (number/p-h; number/ in one case)Estimated AO in river, from Table 2 (km²)Population estimates for Brook Floaters (number of individuals: rounded values)
Canadian Total  23,000-34,000
St. Croix R., NB19.2%0.580.165950
Magaguadavic R., NB33.3%1.90.015290
Petitcodiac R., NB21.2%N/A0.840730 to 7300
Southwest Miramichi R., NB43%0.980.5605600
Kouchibouguacis R., NB73.3%1.650.224980
Bouctouche R., NB33.3%0.680.091630
Shediac R., NB80%3.220.1196100
Scoudouc R., NB66.6%1.580.012190
Annapolis R., NS100%2.730.2166020
Gays R., NS50%0.400.027110
Wallace R., NS50%0.380.060233
Mattatall Lake, NS100%1 individ/ 3-50.01550-200
LaHave R., NS28.6%0.470.072350
St. Marys R., NS53%N/A0.5821000-5000
Salmon R., NS50%N/A0.014100-500

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CPUE was unknown for Mattatall Lake and the St. Marys and Salmon Rivers in NS. For these waterbodies, population "guesstimates" were arrived at based on factors such as total number of Brook Floaters found, number of sites occupied, relative abundance (% of the freshwater mussel community), AO, and amount of available habitat (Table 9). According to Hall (pers. comm. 2007), there were on the order of 100 Brook Floaters in Mattatall Lake; thus, population size was estimated to be 50-200 individuals. In the St. Marys River, Brook Floaters were found at about half of all sites surveyed and represented less than 3% of the freshwater mussel community, but because of the large area of river that may potentially be occupied, the population size was estimated to be 1000-5000 animals. Four sites were surveyed on the Salmon River and one Brook Floater was found at each of two sites, including a site in Borden’s Lake. The population in this system was assumed to be quite small, on the order of 100-500 animals.

To determine the accuracy of the overall population estimate of 23,000-34,000 Brook Floaters in Canada (Table 9), sources of error associated with the sampling techniques used and assumptions made during the calculation of population estimates for each system must be considered. The sources of error and the anticipated magnitude and direction of their effects on estimates of population size are as follows:

  1. Population sizes may have been overestimated because the assumption was made that Brook Floaters would be continuously distributed throughout the occupied reach in each river, when in fact they are patchily distributed in suitable habitats of sand or sandy gravel in areas of moderate flow.
  2. Population sizes may have been underestimated because all surveys except those on the Petitcodiac River relied primarily on visual searches for mussels occurring at the surface of the substrate, when in fact recent studies have shown that as much as 30-80% of mussels may be buried. Schwalb and Pusch (2007) found that the proportion of a mussel population that is buried varies with discharge volume of the river, day length, water temperature, and possibly reproductive cycle and may be as high as 75%. McAlpine (pers. comm. 2007) found that about 30% of Yellow Lampmussels in the Saint John River were buried in the substrate. During quadrat surveys with excavation in the upper Grand River in Ontario, 17.8% of animals of four species were found at the surface and just 16.7% of Elktoes, Alasmidonta marginata, a species closely related to the Brook Floater, were at the surface (Morris pers. comm. 2008).
  3. Population sizes may have been underestimated because timed searches, which were used for most surveys, do not locate all mussels present at a site; rather, they locate only those found during the amount of search time allocated. A direct comparison between 4.5 p-htimed searches and quantitative surveys with excavation at four sites on the Sydenham River in southwestern Ontario showed that only 1-4% of the mussels present were detected during the timed searches (Metcalfe-Smith pers. comm. 2008). It is unlikely that the figure would be this low for Maritime rivers with Brook Floaters because areas of suitable habitat are much more patchily distributed than in the Sydenham and the depth of the overlying loose substrate is generally much thinner (Bredin pers. obs.), such that mussels cannot dig as deeply and would be more easily seen. However, the magnitude of this error would still be significant, especially because timed searches conducted in Maritime rivers were typically of short duration (range = <1-4 p-h; mean = 2 p-h; n = 29 surveys).
  4. Population sizes may have been underestimated because the occupied reach in some rivers, notably the Annapolis, Salmon, and Miramichi River systems, may be greater than is presently known and Brook Floaters may yet be found in rivers that have not been surveyed to date.

Considering the above sources of error, it is possible that the total population estimate of 23,000-34,000 Brook Floaters in Canada may be as much as an order of magnitude too low. According to NatureServe (2007), the size of the global population of Brook Floaters is about 10,000-100,000 individuals; however, this estimate is likely out of date and erroneous.

Fluctuations and trends

Recent discoveries (since 2000) of Brook Floater populations in the Salmon River and Mattatall Lake in NS, and in the Magaguadavic, Southwest Miramichi, Kouchibouguacis, Bouctouche, Shediac, and Scoudouc Rivers in NB almost certainly reflect a significant increase in survey effort rather than an increase in abundance or a range extension. There are only a few populations of Brook Floaters in Canada that have been known for long enough to provide information on trends.

New Brunswick

Brook Floaters were first collected from the Renous River in 1948, but were not reconfirmed through more recent surveys at the original and nearby locations, suggesting a decline. Additional surveys are required to determine if the species is present in the upper reaches of the Renous River. No trend information is available for the long known and recently surveyed population in the Petitcodiac River. The first record for the Petitcodiac was in 1949, and there are other early records from 1951 and 1966, but there is no mention of abundance to compare with Hanson and Locke’s (2001) more recent thorough surveys.

Nova Scotia

There are no data on the initial abundance of the LaHave River population that was discovered in 1921. Therefore, when Brook Floaters were confirmed extant in the LaHave in 2002 after 80 years of habitation and development along the river, trend information was unfortunately nonexistent. On the St. Marys River, Brook Floaters were recorded as "occasional" (3-9 specimens per half-hour) in 1946 at Sherbrooke (Athearn and Clarke 1962). More recent collections showed them to be scattered in the East River St. Marys watershed, but there is no information on population trends at the Sherbrooke site. Athearn and Clarke (1962) also reported Brook Floaters as "occasional" in the Annapolis River at Lawrencetown. Surveys in 2006, however, found just two live Brook Floaters in three quarters of an hour at Lawrencetown. A decline in abundance in the Annapolis River, as shown anecdotally by these two reports, would not be unexpected given the increase in agriculture and development that has taken place in the last 45 years, but no conclusion can be drawn from this meagre information. In the Stewiacke River, Athearn and Clarke (1962) recorded Brook Floaters as "rare" (1-2 per half-hour). Although still extant in the upper reaches of the Stewiacke watershed, in Gays River, Brook Floaters appear to have declined in the main stem of the Stewiacke as they were not detected during NSDNRsurveys at locations close to sites where they were previously found.

In the Wallace River, Athearn and Clarke (1962) recorded Brook Floaters as "occasional" at South Middleboro. This is a greater encounter rate than indicated by two recent survey projects (NS DNR 1999-2002; surveys for this report in 2006). Stansbery’s collection of 12 live Brook Floaters from the Wallace River in 1967 (OSU 2007) suggests that the population present at the time must have been fairly large. Few recent surveys throughout the species’ range in the Maritimes recorded more than 12 live Brook Floaters present at a single site-let alone in sufficient numbers to prompt the collection of this many individuals (see Table 5 and Table 6). Brook Floaters were collected live from the Wallace River in 1975 at South Middleboro with no accompanying abundance information (Davis 2007). The species was not confirmed extant during NSDNR surveys at the same and other nearby locations. The Wallace River population, though likely still extant, as evidenced by the fresh valves collected from three sites in 2006, has apparently declined to the point where no live individuals could be found despite thorough searches of very accessible and easily inspected sites (Bredin pers. obs.).

Rescue effect

Brook Floater populations throughout the US are not as healthy as those in Canada (see references in Table 1 and NatureServe 2007 for information on US population declines). Between 40 and 50% of historically known populations in the US are now extirpated (see Global range) and the species is ranked as SX (extirpated), SH (possibly extirpated), S1 (critically imperiled) or S2 (imperiled) in 14 of the 17 states where it occurs (see EXISTING PROTECTION OR OTHER STATUS DESIGNATIONS). The healthiest populations in the US are in Maine (species ranked S3 or vulnerable), which adjoins New Brunswick. Canada shares one population of Brook Floaters with the US, i.e., the small population in the St. Croix River that forms part of the Canada-US (NB-Maine) border. Canadian populations represent the global stronghold for this species and any rescue effect would likely be from Canada to the US rather than vice versa.

A potential host fish for the Brook Floater is the Ninespine Stickleback (see BIOLOGY), which spawns in fresh water but may move to brackish and salt water at other stages of its life cycle (Scott and Crossman 1973). Dispersal of Brook Floaters between rivers may be prevented by intolerance of the glochidia to salt water as host fishes such as the Ninespine Stickleback move seawards. This intolerance would impede the re-establishment of an extirpated population with individuals from a nearby river. However, if the glochidia are well encysted within the host’s tissues they may be able to survive a period of salt water immersion-thus enabling the host to move Brook Floaters among adjacent rivers that merge along the coast of NB and NS. As there is no information available on the genetic structure of Brook Floater populations throughout the species range, it is not known if a population extirpated from a Maritime river could be successfully re-introduced from a population in an adjacent watershed (see Genetic description).

Limiting Factors and Threats

The primary threats to Brook Floaters are described below. Threats are listed in approximate order of decreasing potential impact on the species; however, this distinction is not clear-cut. Some threats are localized and imminent in limited parts of the range (e.g., impoundment drawdowns), while others are more widespread and less catastrophic (e.g., effects of agricultural run-off and enhanced nutrient input into rivers). The environmental conditions in each river and lake where Brook Floaters occur in Canada are described in Habitat trends. A summary of habitat quality and trend, proportion of the estimated total population, and primary imminent threats to each population, including one historic, are shown in Table 10.

Table 10. Summary of habitat quality and trend and primary imminent threats for Brook Floater populations in New Brunswick and Nova Scotia. Proportion of total population calculated using population maxima. See text and other tables for details.
Water bodyPopulation estimatesProportion of total populationHabitat quality trendPrimary imminent threats
Canadian Total23,000 to 34,000100.0%8 current decline (~60.8% of total population) 
St. Croix R., NB9502.8%stable, decline > 10 yrs agowater drawdown
Magaguadavic R., NB2900.9%decline > 10 yrs agopossibly water drawdown
Petitcodiac R., NB730 to 730021.5%decline1habitat degradation from poor agricultural practices1
Southwest Miramichi R., NB560016.5%no trend, excellent qualitynone
Kouchibouguacis R., NB9802.9%declinehabitat degradation from widespread damage to riparian
Bouctouche R., NB6301.9%declinehabitat degradation from widespread damage to riparian
Shediac R., NB610017.9%declinehabitat degradation from widespread damage to riparian
Scoudouc R., NB1900.6%declinehabitat degradation from widespread damage to riparian
Annapolis R., NS602017.7%variable, some increasepoor agricultural & land management practices, some mitigation
Stewiacke R., NS0 (historic)0.0%fair quality, declinepoor agricultural & land management practices
Gays R., NS1100.3%good quality, no monitoringnone
Wallace R., NS25 (0 live)0.0%good quality, no monitoringresidential development
Mattatall Lake, NS50 to 2000.6%good quality, no monitoringresidential development
LaHave R., NS3501.0%fair quality, declineresidential development
St. Marys R., NS1000 to 500014.7%good quality, declinepoor agricultural & land management practices, residential devt.
Salmon R., NS100 to 5001.5%very good, no trendnone

1 North River habitat quality has declined, and this subpopulation is more threatened than the Little River and Main Petitcodiac River subpopulations whose habitat quality shows no recent trend; the decline in the Petiticodiac quality occurred over 10 years ago

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Agricultural and land management practices

A number of Maritime rivers with Brook Floaters are impacted by agricultural activities that degrade freshwater mussel habitat (see Bogan 1993; Richter et al. 1997; Brim-Box and Mossa 1999; Poole and Downing 2004; Brainwood et al. 2006). Habitat degradation due to poor agricultural practices is the principal threat to Brook Floaters in the Petitcodiac River System, especially in the North River tributary, where poorly controlled agricultural practices have had very deleterious effects on the river (Hanson and Locke 2001) and cattle are allowed direct river access (Pavey 2006). Brook Floaters are less threatened in areas of the Little River and the main Petitcodiac, where agricultural practices are better (Hanson and Locke 2001). Throughout the watershed, cattle have sporadic access to the shoreline and, during high rainfall events, there are increases in sedimentation, nutrient runoff and E. coli counts (Pavey 2006). The impact of these threats on freshwater mussels is well known (see Richter et al. 1997). In the Shediac, Scoudouc, Bouctouche and Kouchibouguacis Rivers, Brook Floaters are also threatened by habitat degradation (i.e., bank erosion and denuded riparian zones) that result from increased agricultural development and poor agricultural practices, including cattle with uncontrolled river access (Richard pers comm. 2007; SBWA 2006; SBWA2007a,b; Plourde pers. comm. 2008).

Brook Floaters are also threatened by habitat degradation due to poor agricultural and land management practices in the Annapolis, Stewiacke and St. Marys Rivers in NS. In the Annapolis River, storm events and periods of high rainfall cause sudden increases in sediment and E. coli counts, and nutrient loads have been recorded at levels sufficient to cause significant eutrophication (Sharpe 2007). The river becomes progressively browner and more opaque with silt as it flows south from Middleton toward Lawrencetown, which is the exact stretch of river occupied by Brook Floaters (Bredin pers. obs.). The threats in the Annapolis are imminent and some harm to habitats is likely, but threats are being mitigated by continuing water quality education and stewardship programs (Sharpe pers. comm. 2007).

Intensification of agriculture along the St. Marys River, with a conversion of fields to corn and blueberry crops (Gunn pers. comm. 2007), and along the Stewiacke, with increased sod farming (Archibald pers. comm. 2007), threaten water quality due to increased pesticide, fertilizer, and sediment loads and reduced riparian vegetation. Threats on these two rivers seem less imminent and more diffuse within these larger watersheds, so that harm to populations is less likely.

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Residential development

Increased residential development is a potential threat along the St. Marys, Wallace and LaHave Rivers and especially around the three lakes where the species occurs in NS - Lochaber, Eden and Mattatall Lakes (Gunn pers. comm. 2007; Hall pers. comm. 2007; Pulsifer pers. comm. 2007; Rodenhizer pers. comm. 2008). The threat is imminent, but the likelihood of actual harm is uncertain and depends on a number of factors, including construction and land-clearing practices at various sites and the degree to which natural shoreline habitat is destroyed. Degradation and clearing of riverside vegetation associated with suburban development has been shown to reduce the size of populations of freshwater mussels and inhibit recruitment (Brainwood et al. 2006).

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Combined threats and fragile habitat

In the Shediac, Scoudouc, Bouctouche and Kouchibouguacis Rivers, Brook Floaters face habitat degradation as a result of widespread damage to the riparian zone from a combination of imminent threats, including: 1) cattle, tractor and ATV crossings, 2) increased residential and agricultural development, 3) poor forestry practices, 4) injurious small road construction practices (e.g., poorly installed and maintained culverts), as well as 5) sewage discharge from increasing residential development (Richard pers comm. 2007; SBWA2006; SBWA2007a,b; Plourde pers. comm. 2008). Although the threats are currently localized at a number of sites along these rivers, their effects are cumulative over time and may eventually degrade large sections of the rivers. The sandy soils and fine substrates that create good Brook Floater habitat in these areas also make the riparian zone and river bed more prone to damage. These threats are being mitigated to some degree by regional watershed associations who are working with local land owners and land users to conserve, protect and improve freshwater habitat in the four watersheds (Richard pers comm. 2007; SBWA 2006; SBWA2007a,b; Plourde pers. comm. 2008).

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Water level fluctuations

Abrupt drawdown of water levels in impoundments and riverine stretches upstream from dams results in very low water levels that can strand Brook Floaters above the water line, causing either direct mortality through desiccation or increased predation (Vaughn and Taylor 1999). Other studies on the effects of drawdown on mussels include: Samad and Stanley (1986), Tetzloff (2001), Tucker et al.(1997), Howells et al. (2000), and Burlakova and Karatayev (2008). More gradual fluctuations may also expose mussels and may cause secondary impacts due to changes in stream flow, water depth, and water temperature. Cycles of flooding and low water in rivers can cause mortality of mussels due to riverbed scouring, and can displace both juveniles and adults to unfavourable downstream habitat. The effects of these stressors on Brook Floaters depend in part on whether individuals are located in microhabitats within the river that provide protection from low water levels. Freshwater fishes, including species that are potential host fish, are similarly negatively affected by fluctuations in hydrological regimes (Travnichek and Maceina 1994).

River drawdown is the primary threat faced by Brook Floaters in the St. Croix River, because the mussels occur in areas of the river that are directly influenced by the operation of dams at Vanceboro/St. Croix, Grand Falls, and Canoose Flowage (Adams pers. comm. 2007). Very low water levels (Table 3) may result from these drawdowns, especially in years of low rainfall. This threat is imminent given increasing fluctuations in summer temperatures and rainfall. Extreme water level fluctuations due to operations of the power dam at the outlet of Magaguadavic Lake (Hoyt pers. comm. 2007), especially in hot dry years, is likely a threat to populations in the Magaguadavic River.

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Introduced fishes

Two introduced species of freshwater fish, Chain Pickerel (Esox niger) and Smallmouth Bass (Micropterus dolomieu), are now present and spreading throughout a number of lakes and rivers in the Maritimes (LeBlanc pers. comm. 2004; Goodwin 2007). These fishes prey on a wide variety of smaller fishes and may therefore exert increased predation pressure on the host(s) of the Brook Floater, which is/are likely to be small species (see BIOLOGY). In a small lake, it usually takes only a few years to eliminate most of the cyprinids once Chain Pickerel are present (LeBlanc pers. comm. 2004), and small lakes typically have few cyprinids left shortly after Smallmouth Bass have been introduced (Martel pers. obs.). Smallmouth Bass have become the third most preferred sportfish for NS anglers, and illegal introductions continue despite efforts at control (LeBlanc pers. comm. 2004). Smallmouth Bass are now known to be present in Mattatall Lake (LeBlanc pers. comm. 2004) and pose an imminent threat to small fishes in that lake.

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Mining effluents

Effluent from a new lead-zinc mine upstream from Brook Floater occurrences in the Gays River watershed is a potential threat to this mussel and its host fish. Effluent is released from a mining company’s polishing pond into Anand Brook, a tributary of Gays River. An array of federal and provincial legislation governing mining operations, frequent and broad-based effluent testing, and regular reporting make it unlikely, however, that a toxic spill will occur in the Gays River system. The effluent is sampled weekly, and tested for pH, suspended solids, and several chemicals toxic to freshwater aquatic life including arsenic, nickel, lead, zinc, and cyanide. The mining company is required to meet Fisheries Act substance release guidelines, to provide monthly effluent samples from ore processing for acute lethality testing using Daphnia spp. and Rainbow Trout (Oncorhynchus mykiss) and to report quarterly to Environment Canada (Melanson pers. comm. 2008). Although the threat of a spill is not imminent, if one should occur, adult mussels and especially juveniles would likely be significantly harmed. Juveniles represent a sensitive life stage particularly susceptible to toxic effluents (Layzer and Madison 1995; Newton et al. 2003; Wicklow 2004).

The mining company has also proposed a future diversion of a small section of the Gays River to obtain access to ore under the riverbed (Elderkin pers. comm. 2008). This threat is not imminent as the diversion will be subject to an Environmental Impact Assessment and may not be approved.

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Muskrat predation

When a large muskrat population co-occurs with a remnant population of a rare mussel, this predator can pose a threat to the mussel’s survival. Hanson and Locke (2001) discovered a muskrat midden containing more than 90 Brook Floater shells adjacent to the largest single concentration of Brook Floaters in the Petitcodiac watershed. Seventeen complete shells were collected from a muskrat midden in the Southwest Miramichi, and shells were also numerous in middens on the Annapolis and Kouchibouguacis Rivers (Bredin pers. obs.; Beaudet et al.2002). These observations support the view that muskrats may pose a threat if predation occurs where a rare mussel species happens to be locally abundant (Hanson and Locke 2001).

Tyrrell and Hornbach (1998) noted that muskrats preferred mussels with shell-lengths in the 20-80 mm range and seemed to select species that were more easily opened due to thinner shells or lighter valve musculature. Most Brook Floater shells fall within this size range and are relatively thin, though they possess substantial hinge musculature. In a study of mussel size-selection by muskrats on the Petitcodiac River, Zahner-Meike and Hanson (2001) found that the preferred size range was 60-110 mm for Margaritifera margaritifera and 60 to 120 mm for Pyganodon cataracta. Because Brook Floaters seldom grow longer than 50-65 mm (Morphological description) muskrats may prefer these larger species when they are present in greater abundance than Brook Floaters, which is often the case.

Muskrat predation probably posed little threat to healthy Brook Floater populations in the past, but may now be a more serious threat where populations have already been reduced to low numbers in isolated locations due to human-caused environmental degradation (Neves and Odum 1989).

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Special Significance of the Species

The Brook Floater was once widespread throughout its North American range but has recently undergone a significant range contraction, with the sweeping decline and loss of many populations throughout the US (see Global range). Populations in Canada appear to be faring better. Although Canadian populations account for only about 8% of the current global range, they may represent the last global stronghold for the species.

Increased survey efforts in the last 15 years have resulted in the discovery of seven new populations of Brook Floaters in NB and two new populations in NS. That so many new populations should be discovered in Canada while many occurrences in the US are declining and disappearing adds even more weight to the global significance of the Canadian population. Brook Floater populations in the Kouchibouguacis and Miramichi Rivers represent the northern limit of the species’ range.

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Existing Protection or Other Status Designations

The Brook Floater is considered globally vulnerable (G3) and is listed as nationally vulnerable (N3) in the US and nationally imperiled (N2) in Canada (NatureServe 2007). This species is not currently listed under Canada’s Species at Risk Act or the Endangered Species Act of the US. The IUCN Red List Category for the Brook Floater is Data Deficient. The Brook Floater was assessed in 2004 under the National General Status Assessment Process and was assigned a national rank of 3 (Sensitive) in Canada and NS and 2 (May be at Risk) in NB (CESCC 2006). The Brook Floater is ranked as critically imperilled (S1) in 11 of the 17 states in which it occurs and possibly extirpated (SH) or extirpated (SX) in two other states (Table 11). Several states have also designated the species as Endangered, Threatened or of Special Concern. The American Fisheries Society designated the species as Threatened in North America (Williams et al. 1993), but is currently in the process of revising its 15-year-old assessment of the conservation status of freshwater mussels in the US, Canada, and Mexico.

Table 11. Status designations for the Brook Floater by jurisdiction and designation process.
JurisdictionProcessDesignationReference
Range-wideGlobal RankingG3 - VulnerableNature Serve 2007
CanadaNational general statusSensitiveCESCC 2006
CanadaNational RankingN2 - ImperiledNature Serve 2007
New BrunswickProvincial general statusMay be at RiskCESCC 2006
New BrunswickSub-National RankingS1S2Nature Serve 2007
Nova ScotiaProvincial general statusSensitiveCESCC 2006
Nova ScotiaSub-National RankingS1S2Nature Serve 2007
USANational RankingN3 - VulnerableNature Serve 2007
ConnecticutSub-National RankingS1Nature Serve 2007
DelawareSub-National RankingSXNature Serve 2007
Dist of ColumbiaSub-National RankingSNRNature Serve 2007
GeorgiaState designationSpecial ConcernState web-site 2007
GeorgiaSub-National RankingS2Nature Serve 2007
MaineSub-National RankingS3Nature Serve 2007
MarylandSub-National RankingS1Nature Serve 2007
MassachusettsState designationEndangeredState web-site 2007
MassachusettsSub-National RankingS1Nature Serve 2007
New HampshireState designationThreatened (proposed)Tash pers. comm. 2007
New HampshireSub-National RankingS1Nature Serve 2007
New JerseySub-National RankingS1Nature Serve 2007
New YorkState designationThreatenedState web-site 2007
New YorkSub-National RankingS1Nature Serve 2007
North CarolinaSub-National RankingS1Nature Serve 2007
PennsylvaniaState DesignationSpecial ConcernState web-site 2007
PennsylvaniaSub-National RankingS1Nature Serve 2007
Rhode IslandSub-National RankingSHNature Serve 2007
South CarolinaState designationEndangeredState web-site 2007
South CarolinaSub-National RankingSNRNature Serve 2007
VermontState designationThreatenedState web-site 2007
VermontSub-National RankingS1Nature Serve 2007
VirginiaSub-National RankingS1Nature Serve 2007
West VirginiaSub-National RankingS1Nature Serve 2007

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Freshwater mussels are protected as shellfish under Canada’s federal Fisheries Act, and collection of live mussels is governed by the Act and by both federal (e.g., Maritime Provinces Fishery Regulations) and provincial regulations made pursuant to the Act. The Fisheries Act also provides for broad protection of aquatic habitat by prohibiting the release of substances deleterious to fish and activities that disrupt or destroy fish habitat. In NS, Brook Floaters obtain some measure of habitat protection from the following Acts and Regulations: 1) Nova Scotia Wildlife Habitat and Watercourses Protection Regulations (1989) under Section 40 of the Forests Act, designed to protect water quality; 2) Activities Designation Regulations under Section 66 of the Environment Act, intended to protect surface water from human influences; and 3) Environmental Assessment Regulations pursuant to the Environment Act, which requires developments to undergo environmental assessment if they may cause significant environmental impacts, including those to freshwater habitat.

Aquatic freshwater mussel habitat is protected in NB, pursuant to the following legislation and regulations: 1) the Watercourse and Wetland Alteration Regulation permit program under the Clean Water Act, designed to protect surface water resources from the effects of activities such as building construction, uncontrolled landscaping and forestry activities, and the installation of dams and water obstructions; 2) the Clean Environment Act, which requires major projects to undergo environmental assessment; and 3) the Crown Lands and Forests Act designed to govern forestry activities on provincial crown land through standards, criteria, and procedures in the Forest Management Manual, which mandates areas of undisturbed vegetation (watercourse buffer zones) adjacent to all natural watercourses.

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Technical Summary

Alasmidonta varicosa

Brook Floater - Alasmidonte renflée
Range of Occurrence in Canada: New Brunswick and Nova Scotia

Demographic Information

Generation time (average age of parents in the population): 10 years (estimated)
[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last [10 or 5 years, or 3 or 2 generations]. Trend data are unavailable for most populations. Anecdotal information on populations in the Renous (NB) Wallace, Stewiacke and Annapolis Rivers (NS) suggests possible declines in these systems: Unknown
[Projected or suspected] percent [reduction or increase] in total number of mature individuals over the next [10 or 5 years, or 3 or 2 generations]: Unknown
[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over any [10 or 5 years, or 3 or 2 generations] period, over a time period including both the past and the future: Unknown
Are the causes of the decline clearly reversible? N/A
Are the causes of the decline understood? N/A
Have the causes of the decline ceased? N/A
Projected trend in number of populations: No declines expected
Are there extreme fluctuations in number of mature individuals? No
Are there extreme fluctuations in number of populations? No

Extent and Area Information

Estimated extent of occurrence: 76,856 km²
Observed trend in extent of occurrence: Apparently stable
Are there extreme fluctuations in extent of occurrence? No

Estimated area of occupancy: AO = 3.02 km² - AO calculated as length X width of occupied reach in each system summed over all occupied systems: IAO = 707 km² - IAO calculated using the IUCN grid method of applying a 2 km X 2 km grid over each occurrence and summing over all occurrences

Observed trend in area of occupancy: Apparently stable
Are there extreme fluctuations in area of occupancy? No
Is the total population severely fragmented? Unknown - Because the size of the minimum viable population is unknown, IUCN guidelines on what constitutes severe fragmentation can not be applied.
Number of current locations: 15
Trend in number of locations: Possible decline - Populations in the Renous and Stewiake Rivers may have been lost. No Brook Floaters were found at or near the historic Renous River location in surveys conducted in 2002 and 2006.
Are there extreme fluctuations in number of locations? No
Trend in area and/or quality of habitat: Decline in quality at some locations. Area and extent of habitat apparently stable - Decline in quality of habitat in the North, Kouchibouguacis, Bouctouche, Shediac, Scoudouc, Stewiacke, LaHave and St. Marys Rivers. Declines in habitat occurred > 10 years ago in the St. Croix, Magaguadavic and Petitcodiac Rivers. Habitat quality has recently improved in the Annapolis River following earlier decline.

Number of mature individuals in each population

Population - N Mature Individuals

New Brunswick
St. Croix R.: 950
Magaguadavic R.: 290
Petitcodiac R.: 730-7300
Southwest Miramichi R.: 5600
Kouchibouguacis R.: 980
Bouctouche R.: 630
Shediac R.: 6100
Scoudouc R.: 190

Nova Scotia
Annapolis R.: 6020
Gays R. (Stewiacke tributary): 110
Wallace R.: 233
Mattatall Lake: 50-200
LaHave R.: 350
St. Marys R.: 1000-5000
Salmon R.: 100-500

Total: 23,000-34,000 (minimum) - Because of uncertainties in population estimates due to sources of error associated with sampling methods and assumptions applied to calculations, the size of the Canadian population may be up to an order of magnitude larger.

Number of populations (locations): 15

Quantitative Analysis

None available

Threats (actual or imminent, to populations or habitats)

Some threats are localized and imminent in limited parts of the range while others are more widespread and less catastrophic.

In the Shediac, Scoudouc, Bouctouche and Kouchibouguacis Rivers, Brook Floaters face habitat degradation as a result of widespread damage to the riparian zone from a combination of imminent threats, including: 1) cattle, tractor and ATV crossings, 2) increased residential and agricultural development, 3) poor forestry practices, 4) injurious small road construction practices (e.g., poorly installed and maintained culverts), as well as 5) sewage discharge from increased residential development.

In the North River (Petitcodiac watershed) Brook Floaters face imminent threat of habitat degradation due to poor agricultural practices.

In the Annapolis, Stewiacke and St. Marys Rivers, Brook Floaters face imminent threat of habitat degradation due to poor agricultural and land management practices. Threats are being mitigated to some degree on the Annapolis River.

In the LaHave and St. Marys Rivers and in Lochaber, Eden and Mattatall Lakes, Brook Floaters face imminent threat from increased residential development.

Rescue Effect (immigration from an outside source)

Status of outside population(s)
USA: N3; IUCN: Data Deficient

US sub-national (NatureServe) and legislated state ranks for Brook Floater: Connecticut (S1), Delaware (SX), DC (SNR), Georgia (S2) and state species of Special Concern, Maine (S3), Maryland (S1), Massachusetts (S1) and state Endangered, New Hampshire (S1) and proposed state listing as Threatened, New Jersey (S1), New York (S1) and state Threatened, North Carolina (S1), Pennsylvania (S2) and state Species of Special Concern, Rhode Island (SH), South Carolina (SNR) and state Endangered, Vermont (S1) and state Threatened, Virginia (S1), and West Virginia (S1).
Is immigration known? No
Would immigrants be adapted to survive in Canada? Likely
Is there sufficient habitat for immigrants in Canada? Yes
Is rescue from outside populations likely? No

Current Status

COSEWIC: Special Concern

Status and Reasons for Designation

Status: Special Concern
Alpha-numeric code: not applicable
Reasons for Designation: A medium-sized freshwater mussel that is confined to 15 widely scattered watersheds in Nova Scotia and New Brunswick. This mussel was never abundant, usually representing only 1-5% of the total freshwater mussel fauna present. The habitat is subject to impacts (shoreline development, poor agricultural practices, and other water quality issues) with potential cumulative degradation on larger stretches of rivers. Populations appear to have been lost from two historic locations, although new populations have been found recently. Because this mussel has disappeared from approximately half of its USA locations, the Canadian population now represents an important global stronghold for the species.

Applicability of Criteria

Criterion A (Declining Total Population): Not applicable. Although there has likely been a decline in the total number of mature individuals in a few rivers, overall sampling intensity has been insufficient to accurately quantify a population trend for the species.
Criterion B (Small Distribution, and Decline or Fluctuation): Not applicable. The current IAO (707 km²) meets the threshold for Threatened (<2,000 km²), although the number of locations (15) does exceed the Threatened threshold. However, the species is naturally fragmented and impacted by habitat degradation.
Criterion C (Small Total Population Size and Decline): Not applicable. The lowest estimate of the total number of mature individuals (23,000) exceeds the threshold of <10,000 for Threatened.
Criterion D (Very Small Population or Restricted Distribution): Not applicable because the lowest estimate of the total number of mature individuals (23,000) exceeds the threshold of <1000 for Threatened and IAO (707 km²) exceeds the threshold of <20 km²
Criterion E (Quantitative Analysis): Not applicable; no data available.

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Acknowledgements and Authorities Contacted

Acknowledgements

Funding for the preparation for this report was provided by Environment Canada. Thanks to Anne Varner and Charlane Bishop for assistance with field work. The following individuals and organizations generously provided Brook Floater occurrence and abundance data used in the preparation of this report: Atlantic Canada Conservation Data Centre, Dr. A. Bogan, J.M Gagnon, R. Hall, Dr. J.M. Hanson, A. Hebda, D. McAlpine, M. Pulsifer, D.L. Sabine and B.I. Swartz. Thanks to the many individuals who provided habitat and land use information concerning the watersheds and rivers discussed in this report, and to the biologists and scientists who provided information on the status of Brook Floater in various jurisdictions in the US; these many individuals are cited as personal communication in the Information Sources section of the report. Jean Sealy provided invaluable assistance with literature research. Thank you to Jenny Wu for preparing the maps and for providing the GIS-based calculations. The report writers are grateful to Richard Elliot for assistance with derivation of formulae for abundance and for editing, Jacqueline Madill for her assistance with production of the figures and editing, and Kathryn Klein for helpful editorial comments on earlier versions of the manuscript.

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Authorities contacted

Audet, D., Executive Director, Shediac Bay Watershed Association, Shediac, New Brunswick.

Beaudet, A. Biologist, Kouchibouguac National Park, 186 route 117, NB Ste. Anne de Kent, New Brunswick.

Collins, H., Coordinator, Miramichi River Environmental Assessment Committee (MREAC), Miramichi, New Brunswick.

Craig, N. Manager, Water Science Section, New Brunswick Department of the Environment, Fredericton, New Brunswick.

Davis, D.S. Curator Emeritus and former Senior Curator, Nova Scotia Museum, Halifax, Nova Scotia.

Elderkin, M. Biologist, Species at Risk, Nova Scotia Department of Natural Resources, Kentville, Nova Scotia.

Gunn I.H. Certified Forestry Technician, Nova Scotia Dept. of Natural Resources, Stillwater, Nova Scotia.

Hall, R. Former Wildlife Biologist, Nova Scotia Department of National Resources, Truro, Nova Scotia.

Hanson, J.M. Ecosystems Research, Oceans & Science Branch, Gulf Fisheries Centre, Moncton, NB.

Hebda, A. Curator of Zoology. Summer Street, Nova Scotia Museum, Halifax, NS

Hoyt, M. Plant Engineer, Lake Utopia Paper, Utopia, New Brunswick.

McAlpine, D. Research Curator, Head, Zoology Section; Chair, Department of Natural Science, New Brunswick Museum, Saint John, New Brunswick.

Morris, T.J. Species at Risk Research Biologist, Fisheries and Oceans Canada, Great Lakes Laboratory for Fisheries and Aquatic Sciences, 867 Lakeshore Rd., Burlington ON L7R 4A6 Canada.

Plourde, M-A. Director, Friends of the Kouchibouguacis, St. Louis de Kent, New Brunswick.

Pulsifer, M. Wildlife Biologist, Nova Scotia Department of National Resources, Antigonish, Nova Scotia.

Rodenhizer, W. Project Coordinator: LaHave River Water Quality Monitoring Program. Bluenose Coastal Action Foundation (Email), Mahone Bay, Nova Scotia.

Sabine, D.L. Wildlife Biologist, Big Game & Furbearer Program, Fish & Wildlife Branch, New Brunswick Department of Natural Resources, P.O. Box 6000 Fredericton, New Brunswick.

Sharpe, A. Science Coordinator, Clean Annapolis River Project, Annapolis Royal, Nova Scotia.

Sochasky, L. Executive Director, St. Croix International Waterway Commission, St. Stephen, New Brunswick.

Swartz, B.I. Wildlife Biologist, Wildlife Resource Assessment Section, Maine Department of Inland Fisheries and Wildlife, Bangor, Maine, USA.

Zanatta, D. Ph.D. candidate. Royal Ontario Museum, University of Toronto. Toronto, ON.

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Biographical Summary of Report Writers

Katherine A. Bredin was a Zoologist / Marine Biologist with the Atlantic Canada Conservation Data Centre (AC CCD) from 1998-2005. She has a B.Sc. in Microbiology from the University of Manitoba, an M.Sc. in Biopsychology from Memorial University of Newfoundland and a L.L.B in Marine Environmental Law from Dalhousie University. She has 20 years’ experience as a biologist with Bird Studies Canada, the Atlantic Canada Conservation Data Centre, the Canadian Wildlife Service, Memorial University and the University of Manitoba. While at the AC CDC, Kate assessed the status and distribution of freshwater mussels in the three Maritime provinces, working cooperatively with scientists and biologists from provincial and federal government departments. As AC CDC Zoologist she conducted five years of extensive freshwater mussel surveys in New Brunswick and Nova Scotia, with additional survey funding from the New Brunswick Wildlife Trust Fund, Nova Scotia Department of Natural Resources, Environment Canada and Mountain Equipment Co-op. As Zoologist at the AC CDC from 1998 to 2005, Kate helped compiled region-wide mussel data from a number of agencies and organizations into the AC CDC freshwater mussel database. She has authored four reports on the status and distribution of freshwater mussels in Atlantic Canada.

André Martel (co-author) is a Research Scientist in the Life Sciences Section (Malacology) at Canadian Museum of Nature (CMN), in Gatineau, Quebec. Martel's career in malacological research began in 1982 with an MSc (Université du Québec à Chicoutimi) on the life history of marine molluscs in the Gulf of St Lawrence. He obtained his PhD in 1990 at the University of Alberta (reproduction, larval biology and dispersal mechanisms in marine bivalves and gastropods), with his field research conducted at the Bamfield Marine Station, in BC. After his PhD he accepted a position as Curator of Malacology (1991) at the CMN, followed by a position of Research Scientist in Malacology (1992) at the same institution. His current research program focuses on the life history, identification and taxonomy of both freshwater and marine mussels. He has published over 35 publications and reports on Canadian molluscs (marine and freshwater). He recently shared a position as Assistant Director at the Bamfield Marine Station in BC and taught field courses at the Huntsman Marine Sciences Centre in New Brunswick and the Queen's University Biological Station in Ontario. He regularly gives activities, workshops and talks to schools and nature groups.

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Collections examined

The following collections were examined or consulted for Brook Floater:

Canadian Museum of Nature. 1740 Pink Road, Aylmer, Quebec. Curator: Dr. André Martel

New Brunswick Museum, 277 Douglas Avenue, Saint John, New Brunswick, Research Curator, Head, Zoology Section: Dr. Donald McAlpine

Nova Scotia Museum of Natural History, 1747 Summer Street., Halifax, Nova Scotia, Curator of Zoology, Andrew Hebda

H.D. Athearn Museum of Fluviatile Mollusks, at North Carolina State Museum of Natural Sciences, Raleigh, North Carolina Curator of Aquatic Invertebrates: Dr. A. Bogan

Academy of Natural Sciences (ANSP). 2007.

OSU (Ohio State University) online database. 2007.

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Appendix 1. List of datasets used in the compilation and mapping of freshwater mussel sampling sites and Alasmidonta varicosa sites of occurrence in New Brunswick and Nova Scotia

Academy of Natural Sciences (ANSP). 2007.

Atlantic Canada Conservation Data Centre. Freshwater mussel database. September 2007. Data received from K. A. Bredin and S. Gerrriets.

Beaudet, A., E. Tremblay and A. Martel. 2002. Data compiled from: Inventaire des moules d'eau douce dans les rivières Kouchibouguac, Kouchibouguacis et Black du Parc National Kouchibouguac, Nouveau-Brunswick. Parcs Canada Rapport de surveillance et de données relatives aux écosystèmes. Rapport 006. 71 pp.

Caissie, C. 2005. Freshwater Mussel Inventories of the Chockpish, Bouctouche, Little Bouctouche and Cocagne watersheds, New Brunswick in 2003 and 2004. Data compiled from report prepared for the New Brunswick Wildlife Trust Fund. February 2005.

Caissie, C., and D. Audet. 2006. Freshwater Mussel Inventory in the Shediac and Scoudouc Rivers, New Brunswick. Data compiled from report prepared for the New Brunswick Wildlife Trust Fund. March 2006. 47 pp.

Canadian Museum of Nature. Freshwater mussel data for New Brunswick and Nova Scotia. November 2007. Data received from A. Martel and J.M. Gagnon.

Hanson, J.M. and A. Locke. 2001. Data compiled for: Survey of Freshwater Mussels in the Petitcodiac River Drainage, New Brunswick. Canadian Field Naturalist 115(2): 329-340. Data received from J.M. Hanson.

Maine Department of Inland Fish and Wildlife. Unpublished freshwater mussel survey data for the St. Croix River. Data received from B. I. Swartz.

New Brunswick Museum Freshwater mussel data for New Brunswick and Nova Scotia. November 2007. Data received from D. A. McAlpine.

Nova Scotia Department of Natural Resources Freshwater Mussel Database. November 2005. Data received from M. Pulsifer.

Nova Scotia Museum Freshwater Mussel data for New Brunswick and Nova Scotia. November 2007. Data received from A. Hebda.

OSU (Ohio State University) online database. 2007.

Power, T. and D. Gouthro. 2002. Data compiled from: A survey of freshwater mussels (order Unionoida) with the Fortress of Louisbourg National Historic Site and Greater Ecosystem, Cape Breton, Nova Scotia. Report prepared for Cape Breton Highlands National Park, Survey of Species at Risk, Biodiversity Research Associates. 63 pp.

Sabine, D.L. Freshwater Mussel surveys data for the Salmon, Magaguadavic and Northwest Miramichi Rivers. Data received from D. L. Sabine.

New Brunswick Department of Natural Resources. Freshwater mussel surveys data. Data received from D. L. Sabine.

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Appendix 2. Calculation of Brook Floater population size estimates for Maritime rivers having no information available on search effort

Background

The size of a mussel population in a river may be estimated using the following equation:

N (total abundance) = AO(Area of Occupancy) Density (# mussels found/area searched)

For the Kouchibouguacis and Shediac Ribers, Catch Per Unit Effort (CPUE/area searched) was used as a proxy for density, such that:

N = AO(CPUE/area searched)

Where the area searched is not known, as is the case for the St. Croix, Magaguadavic, Southwest Miramichi, Bouctouche and Scoudouc River in NB and the Annapolis, Gays, Wallace and LaHave Rivers in NS, a constant (K R) derived from the Kouchibouguac and Shediac Rivers was applied to the available data for AOand CPUE in order to permit the calculation of N for the former rivers, as follows:

N E = (AOE x CPUEE) x K R

Where E refers to the river requiring an estimate of population size and R refers to the reference rivers.

Calculation of the constant, K R

N R = the total population estimate (number of individuals) for the two rivers, or 980 (Kouchibouguac) + 6100 (Shediac) = 7080

CPUER = the total number of individuals found in the two rivers (194) divided by the total number of person-hours of searching in the rivers (96) = 2.021

AO R = the total occupied area within the two rivers combined, or 0.224 km² + 0.119 km² = 0.343 km²
Solving for K R: K R = N R / AO R CPUE R= 10213.5

Applying the constant, K R, to the estimation of population size for Brook Floaters in the St. Croix River, NB

N St. Croix = (AO St. Croix) x CPUE St. Croix) x K R

Thus, N St. Croix = (0.1651 x 0.582) x 10213.5 = 948 Brook Floaters in the St. Croix River

1estimate of AO from Table 2; 2 CPUE calculated from data in Table 5.

The calculated estimate of 948 Brook Floaters for the St. Croix River compares favourably with the report writers’ initial "guesstimate" of 500-2000 individuals based on their knowledge of the river and its mussel populations.