Northern brook lamprey (Ichthyomyzon fossor) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Search effort

Given the difficulty in collecting and identifying ammocoetes, sampling is usually limited to post-transformation individuals in the fall, or sampling in early spring before post-spawning mortality.  Most of the distribution information in this report is based on incidental catch data obtained through assessment of sea lamprey by Department of Fisheries and Oceans and United States Fish and Wildlife Service (USFWS) staff. Sea lamprey control surveys target larval sea lamprey, and are biased toward streams with known sea lamprey populations. Backpack electrofishing surveys constitute the majority of this effort. A smaller proportion of the data are derived from surveys conducted by boat in deeper water using the granular formulation of the lampricide “Bayluscide”. Other collections were made during TFM stream treatments.

Stewart and Watkinson (2004) imply that the search effort in Manitoba has not been thorough, as they suggest that this species may have a larger distribution than available data indicate.

In the spring of 2000 and 2001, assessment staff at the SLCC conducted electrofishing surveys explicitly to identify undocumented locations of adult and transformed northern brook lamprey. These efforts identified two previously unknown locations in the Lake Nipissing drainage (Wolsely River and Bear Creek), and confirmed other existing populations in the Great Lakes region (SLCC, unpublished data).

Abundance

Scott and Crossman (1973) stated that this species is not known to be abundant anywhere in its range. However, over 5700 Ichthyomyzon lamprey ammocoetes were incidentally caught through larval sea lamprey assessment in Canadian tributaries to the Great Lakes between 2000 and 2004. In the previous five year period (1995-1999), over 8000 Ichthyomyzon ammocoetes were collected in a similar collecting effort (SLCC, unpublished data). This identification is only to genus, but due to the rarity of collection of adult silver lamprey in assessment traps, one can assume that a high percentage of these ammocoetes are likely northern brook lamprey, suggesting that this species is much more abundant than previously thought.

In a survey of streams in the Lower Peninsula of Michigan, northern brook lamprey were the most common species of lamprey, occurring in 31 streams in the drainage areas east of Lake Michigan and west of Lake Huron and Lake Erie (Morman 1979).

Abundance data are not available for the Manitoba and Quebec populations.

Fluctuations and trends

It is difficult to examine trends in the distribution and abundance of northern brook lamprey because of the difficulty in identifying ammocoetes and collecting ammocoetes and adults, and limited targeted sampling of native lampreys. However, some trends can be derived from the literature, and from the limited data available.

In the Great Lakes basin, Schuldt and Goold (1980) compared the occurrence of Ichthyomyzon ammocoete (likely both northern brook lamprey and silver lamprey) data for Lake Superior between two time periods (1953-1972, 1973-1977).  They found that their presence in Canadian streams had dropped from 41 to 17 streams. This reduction is likely due to the effects of lampricide treatments. Recent data (1990-2004) indicate that 20 Canadian tributaries to Lake Superior currently have Ichthyomyzon ammocoetes, indicating a stabilization of these populations (Table 2). This is likely the result of most of these populations not being exposed to lampricide treatments.

In the Lake Superior basin, adult northern brook lamprey have not been recently (i.e. in the last 15 years, or approximately three generations) recorded in three of the nine streams where they were historically (1960-1989) present, including Chippewa River, Neebing-McIntyre River, and Black Sturgeon River (Figure 2). In the Lake Huron basin, they have been recently documented in most streams where they were historically present (except Bannockburn River, Bayfield River, St. Mary’s River, Thessalon River, Koshkawong River and North River) and in several streams where they were not found before (Figure 2). One other stream where northern brook lamprey have historically been found, but have not been documented between 1990 and 2004, is Big Otter Creek (Lake Erie).

Currently, 13 of 28 streams where adult northern brook lamprey have been collected in the Canadian Great Lakes basin are not inhabited by sea lamprey and have not been exposed to lampricide. Densities are much higher in these streams than in the treated streams (SLCC, unpublished data). Populations in untreated sections of treated streams (e.g. those above barriers) and in untreated streams tend to be stable (SLCC, unpublished data). As mentioned previously, several new streams have been found to harbour northern brook lamprey in recent years (including Wabuno Creek, tributary to the Thames River, and Bear Creek and Wolsely River, tributary to Lake Nipissing). These new records are likely a result of a lack of earlier directed survey efforts, rather than novel populations. Similarly, streams that have not received intensive survey efforts which are indicated on the map as not recently having northern brook lampreys present may be due to this lack of effort.

In other areas of Ontario, they have been recently found where they were historically present in the St. Clair and Ottawa rivers, and recently found in parts of the Lake Nipissing basin (Figure 2).

In Quebec, there are too few records to examine trends in northern brook lamprey. Vladykov (1952) reported a high abundance of ammocoetes in the Yamaska River; however, Renaud et al. (1995) reported that the northern brook lamprey was no longer found in similar areas of the stream.  This stream was not treated with lampricide, and the decline is attributed to pollution.  Renaud et al. (1995) indicated that one other Quebec river, the Saint-François River, documented by Vladykov (1952) as having northern brook lamprey still had them as of 1990. In addition to the Yamaska River, the northern brook lamprey was only collected prior to 1960 in Lac Saint Louis (1941), Rivière Nicolet Sud-Ouest (1951), and the St. Lawrence River at Lachine (1950) (Figure 2). It was collected only in Rivière Hinchinbrooke and Rivière Trout in 1976 (D. Banville, pers. comm.). Finally, it has been collected only since 1990 at Rivière Châteauguay (1990, 1992), Rivière Richelieu (1990), Rivière des Prairies (1998), Rivière Gatineau (1999) and Rivière aux Outardes-Est (2002) (Figure 2). The current distribution of northern brook lamprey, in the St. Lawrence basin is likely accurate as a result of recentextensive fishing effort within the Réseau de suivi ichtyologique du Saint-Laurent (La Violette and Richard, 1996; La Violette et al. 2003; Société de la faune et des parcs du Québec, unpublished data).

In Manitoba, the northern brook lamprey was first reported in a small portion of the Winnipeg River system in 1979 (Jyrkkanen and Wright 1979). Too few specimens have been caught to infer trends, but the most recent record caught in 2003 indicates that this population is still extant (Stewart and Watkinson 2004). Stewart and Watkinson (2004) feel that this species may be more widespread in Manitoba.

Rescue effect

The non-migratory nature of northern brook lamprey suggests that potential rescue effects between streams are minimal. Within streams, dispersal of larval lampreys occurs through downstream drift (Purvis 1970, Potter 1980b). Schuldt and Goold (1980) documented streams which, after lampricide treatments of the lower section, have re-populated with brook lampreys from upper reaches of the stream.

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