Shortjaw cisco COSEWIC assessment and status report: chapter 2

Executive Summary

Shortjaw Cisco

Coregonus zenithicus

Introduction

The shortjaw cisco (Coregonus zenithicus) is a widespread species in the salmonid subfamily, Coregoninae. Originally described from Lake Superior at Duluth, Minnesota by Jordan and Evermann in 1909, it was subsequently discovered in most of the Laurentian Great Lakes and many smaller lakes in central North America. Large specimens generally approach 300 g in mass, and exceptionally large fish can reach 1.0 kg. The biology is best known in the Great Lakes (including Lake Nipigon) where the species was once a major component of vigorous food fisheries, occupying intermediate depths of 20-180 m.

Distribution

While best known from the Great Lakes, shortjaw ciscoes have a widespread distribution throughout central Canada. The species was last verified in Lake Erie prior to 1970, in Lake Michigan in 1975, Lake Huron in 1982, and was never reported from Lake Ontario. It still persists in Lake Superior where it has significantly declined in relative abundance. Other than the Great Lakes, shortjaw ciscoes have been reported from at least 22 lakes in Canada extending from Ontario to the Northwest Territories.

Protection

Shortjaw ciscoes were listed as Threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). No specific protection has been provided for the shortjaw cisco in Canada, except for general protection afforded through the Fisheries Act.

Patterns of Phenotypic and Genetic Variability

Shortjaw ciscoes exhibit morphological variability across their geographic range and two basic groups of shortjaw ciscoes exist across Canada. The most common morph is found in large lakes such as Lake Superior, Lake Nipigon, and Great Slave Lake and is characterized by more and longer gillrakers than a morph that seems more typical of small lakes such as Basswood Lake (Ontario), George Lake (Manitoba), and Barrow Lake (Alberta).

Population Sizes and Trends

Shortjaw ciscoes have been an important part of the food fishery in the Great Lakes since at least the mid-1800s. Landing records, on the whole, were not recorded by species, but were lumped into a general category, “chubs”, for all the deepwater cisco species that excluded the shallow-water lake herring. Shortjaw ciscoes seem to have been relatively uncommon in Georgian Bay waters of Lake Huron, but reached levels of 17 - 19% of chub catches from Lake Huron proper in the 1950s.  Only individual specimens were taken in the 1970s, and a lone individual was taken in Lake Huron in 1982.

In Lake Michigan, the species (including fish identified as C. alpenae) made up about 21% of the chub catch in the 1930s, dropping to 6% in the 1950s, 2% by the early 1960s, and disappeared from the lake in the 1970s.

Other than the few specimens reported from the original paper on Lake Erie shortjaw ciscoes (described as longjaw ciscoes, C. alpenae), no subsequent specimens were ever collected.

The species still persists in Lake Superior, but has declined in relative abundance from nearly 90% of the chub catch in the 1920s to about 25% of the catch in the late 1950s, to 6-11% in Michigan waters in the 1970s. Two small collections made in Michigan waters in 1997 revealed abundances of 5% and 11%, in the same range as the 1970s. The abundance of the species in Lake Superior has not been adequately studied, however, and, other than its definite presence in the lake and a drastic decline since the 1920s, little can be said about recent trends.

Extensive, long-term data on the species in Lake Nipigon are lacking, although periodic population assessments have been made since the 1970s. Shortjaw ciscoes comprised 31% of the total catch of ciscoes in 1973 and more recent assessments (1997) from graded-mesh research nets have provided values of 3.4%

Population trends in other lakes that the species inhabits are generally unknown, but different sampling methods in the 1960s selectively caught more shortjaw ciscoes; however, the species has probably been stable over the past few decades. The species undoubtedly forms a portion of food-fishery captures in some of the larger lakes, such as Great Slave Lake, that have either assessment programs or fishery statistical offices, but, in the past, identification of such catches to individual species was apparently not done. Recent efforts to collect specimens from Great Slave Lake have varied in their success at finding any shortjaw ciscoes.

Habitat

In Lakes Superior, Michigan, and Huron, the shortjaw cisco generally inhabits waters 55 to 144 m in depth, although they have been recorded from as deep as 183 m and occasionally in more shallow water. Seasonal differences were noted in Lake Superior with movement into shallower water during spawning, and the fish inhabited 110-114 m in spring, 55-71 m in summer, and 73-90 m in winter. In Lake Nipigon, shortjaw ciscoes inhabit depths of 10-60 m, although the occasional individual has been captured deeper than 60 m. Habitat preferences in smaller lakes are poorly known.

General Biology

Spawning occurs in either the fall or spring in the Great Lakes. Shortjaw ciscoes in Lakes Michigan, Huron, and Erie spawned solely in the fall. However, Lake Superior fish have been found spawning in either the spring or the fall. Fecundity of shortjaw ciscoes is likely similar to that of other deepwater species such as the bloater, ranging from 3,230 eggs for a fish 241 mm total length (TL) to 18,768 for a fish 305 mm TL (Emery and Brown 1978).

As in most fish species, shortjaw ciscoes grow quickly in their first year of life.  While the sexes have been found to have similar growth in length, females grew faster in weight than the males. Maturity occurs in about the fifth year.  Coregonines are opportunistic, particulate feeders that generally ingest prey one item at a time. Availability is important, and seasonal prey such as insects show up in the diets of fish in small lakes. Because shortjaw ciscoes may live in the deeper parts of lakes, terrestrial input is limited, and limnetic crustacea (copepods and cladocerans) and benthic organisms (Mysis and Diporeia) dominate their diets.

Limiting Factors

No single factor is known to be responsible for the decline of the shortjaw cisco in the Great Lakes. In Lake Erie, profound ecological changes have occurred that have shifted the lake to a more mesotrophic condition. While the physical conditions of Lakes Michigan and Huron have not changed much (with the notable exception of Saginaw Bay), the biological community has become considerably altered. The food fisheries had a negative impact earlier in the 1900s, especially on the larger individuals, at first, then on smaller individuals as mesh sizes were reduced to maintain catch levels. However, competition and predation from rainbow smelt and alewives have certainly had more of an impact during the last 30 years--years in which the food fisheries for chubs have been much less extensive than historically. Sea lamprey predation continues to take a toll on Great Lakes species, and affects smaller species such as chubs in addition to larger species such as lake trout, burbot, and lake whitefish. Abiotic factors such as weather and thermal changes in the lakes have also been suspected to play a role in population destabilization.

Factors limiting populations in smaller lakes are essentially unknown. Rainbow smelt have been introduced into many cisco lakes, including Lake Nipigon, Ontario, and have had a noticeable effect on the ecological makeup of those systems.

Special Significance of the Species

The shortjaw cisco, along with the lake herring, appear to be the ancestral colonizing species for most of the post-glacial distribution region of the Mississippi Refugium. Within the Great Lakes, the shortjaw cisco represented one lineage in the most spectacular radiation of sympatric forms in northern lakes. It is a unique form with a distribution that is intimately tied with post-glacial hydrology, and is thus of great scientific interest. Food fisheries in the Great Lakes, especially, included the species as part of a highly desirable and commercialized smoked chub market, but it was not considered more desirable than other cisco species of its same size and condition.

Evaluation

The absence of Coregonus zenithicus from Lakes Michigan (since 1975), Huron (since 1982), and Erie (since 1957) supports a conclusion that the species has been extirpated in these lakes. The great and gradual decline of the species in Lake Superior throughout this century, coupled with its extirpation in the lower Great Lakes, should be viewed with alarm. And the introduction of smelt into at least some of the remaining habitat of the shortjaw cisco in Canada could ultimately be detrimental to the species. The species is vulnerable to excessive food harvest, habitat degradation, and introduced exotic species throughout its range. Presently, the U.S. Fish and Wildlife Service is considering the shortjaw cisco for designation as a candidate for potential listing as Threatened or Endangered.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) determines the national status of wild species, subspecies, varieties, and nationally significant populations that are considered to be at risk in Canada. Designations are made on all native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fish, lepidopterans, molluscs, vascular plants, lichens, and mosses.

COSEWIC Membership

COSEWIC comprises representatives from each provincial and territorial government wildlife agency, four federal agencies (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biosystematic Partnership), three nonjurisdictional members and the co-chairs of the species specialist groups. The committee meets to consider status reports on candidate species.

Definitions

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 (DD)***
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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