Lake whitefish (Coregonus clupeaformis) in Lake Simcoe COSEWIC assessment and status report: chapter 3

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Species Information

Name and classification

Description

Lake whitefish are elongate in form, the greatest body depth occurring at the front of the dorsal fin (Figure 1). The mouth is inferior, being distinctly overhung by the snout. Overall colour is silvery and fins are usually clear or lightly pigmented in Great Lakes populations; the fins of more northerly populations are often darker and are usually black tipped. Scales are large and cycloid, numbering 70-97 in the lateral line. Breeding males develop nuptial tubercles on at least 3 rows of scales above the lateral line and on 6 rows below (Scott and Crossman 1973). Lake Simcoe lake whitefish were found to have significant phenotypic and genetic differences compared to lake whitefish specimens from Lakes Huron, Ontario, Opeongo and Lavieille (Ihssen et al. 1981).

Figure 1.  Lakewhitefish (Coregonus clupeaformis). Illustration from Scott and Crossman (1973 [1998 reprint]) with permission of the authors. The specimen used for this sketch was a female collected from the Koksoak River, Quebec, July 1957.

Taxonomy

The lake whitefish has one of the broadest distributions (all of Canada excepting the Arctic archipelago) of any Canadian freshwater fish. At the species level there would be no consideration of risk; however, the species presents a confused taxonomic picture (see Scott and Crossman 1973) and assorted forms and morphs are variously suggested. Taxonomic relationships in coregonines have been difficult to resolve due to morphological plasticity, character convergence, and the effects of Pleistocene glaciations (Reist et al. 1998).

Electrophoresis has been used to study biochemical variation among allopatric and sympatric whitefish populations. Enzyme differences between lake whitefish in the Yukon and western Canada were demonstrated by Lindsey et al. (1970) and Franzin and Clayton (1977), indicating that these races were descended from fish that had survived glaciations in Beringian, and Mississippi-Missouri refugia. Foote et al. (1992) demonstrated the presence of a third Nahanni glacial refuge race in British Columbia and the Northwest Territories. Lindsey et al. (1970) had also postulated an Atlantic refugium based on present day distribution and morphological differentiation of fishes in the area of the Laurentian Great Lakes and the St. Lawrence River drainage. Bernatchez and Dodson (1990; 1991) examining mtDNA variation concluded that there were five glacial refuge races in North America. An Acadian race in lakes of New Brunswick, Nova Scotia, Maine and the Gaspé Peninsula descended from fish surviving glaciation in a Northeastern Banks refugium. The Atlantic race occurring in Maine and southern Quebec survived in an Atlantic glacial refugium. Although two Beringian races occur in the extreme northwest of the species range, the largest part of the current distribution including all of Ontario was colonized from a Mississippian refugium (Bernatchez and Dodson 1991). Allozyme evidence presented by Bodaly et al. (1992) is consistent with the conclusions of Bernatchez and Dodson (1991) based on mtDNA results, and they postulated the existence of at least four genetically and geographically definable races of lake whitefish: a Bering glacial refuge race in central and southern Yukon, a Mississippi-Missouri race occupying most of the central range, a Nahanni race in British Columbia and the southwest sector of the Northwest Territories, and an Acadian race occupying the Gaspé peninsula and the Maritimes.  Bernatchez and Dodson (1994) suggested that the Atlantic race sould be included as a fifth race based on their earlier (Bernatchez and Dodson 1991) and subsequent work.

There is evidence to suggest that sympatric forms have diverged in morphological and life history traits such as gill raker counts, feeding traits, growth, age at maturity, and differences in place and timing of spawning, and that most are reproductively isolated (Kennedy 1943; Fenderson 1964; Bodaly 1979; Kirkpatrick and Selander 1979; Bruce 1984; Fortin and Gendron 1990; Bodaly et al. 1991). Bodaly et al. (1992) found no evidence of reproductive isolation where geographic races overlap, but they did find that historic, geographic, and environmental barriers have limited the mixing of alleles between races and sympatric pairs. This is not surprising since the study was designed to examine differences between, not within races; they postulated that geographic races have diverged, genetically, to a greater extent than sympatric populations, and that the amount of genetic divergence, as measured by allozyme frequencies is a poor predictor of reproductive isolation within races. Bernatchez and Dodson (1990) on the other hand, postulated that mtDNA data may indicate differences in forms within races, at least in sympatric forms in Maine, and Como Lake in Ontario.

The Lake Simcoe whitefish have been separated from nearby stocks in Georgian Bay for some 7000 to 10000 years by geographic and man-made barriers (Prest 1976; Bailey and Smith 1981). Ihssen et al. (1981) examined morphological, ecological, and electrophoretic variation among five allopatric populations of lake whitefish in Ontario (lakes Huron, Ontario, Simcoe, Opeongo and Lavielle) and found that the populations differed in terms of diet, growth rate, movement patterns, fecundity, egg size, larval size, morphological characters (number of gill rakers, number of pyloric ceca, size) and allele frequency differences. Some of the differences, especially those related to life history and ecological parameters may be explained by differences in environmental and ecological factors in the habitats of the five lakes, for example, water temperature, availability of food, nature of substrates, etc., whereas others may reflect local adaptation resulting in genetic differentiation. Allele frequency differences were found at 6 of 32 loci examined, and standard genetic distances between the populations correspond roughly to the order in which they are thought to have become isolated following the retreat of the glaciers (Ihssen et al. 1981).

Ihssen et al. (1981) caution that electrophoretic differences among stocks may not necessarily reflect recent local adaptation, but on the other hand speciation can occur with little electrophoretic differentiation as shown in sympatric stocks of lake whitefish in the Allegash Basin (Kirkpatrick and Selander 1979). Wilson et al. (1977) and Clayton (1981) argue that organismal and biochemical evolution are not coupled and that biological differentiation may involve only regulatory genes rather than the structural genes that have been studied with electrophoretic techniques. MtDNA analysis was not available at the time of these earlier studies and the argument here is similar to the differences discussed by Bodaly et al. (1992) regarding the differences in their electrophoretic results and the mtDNA results of Bernatchez and Dodson (1990, 1991, 1994).

Designatable units

The inference drawn from Ihssen et al. (1981) is that Lake Simcoe whitefish have been geographically isolated from nearby stocks for an adequate period of time for local adaptation to occur, and that genetic divergence has probably taken place as a result of adaptation to local conditions. Recognizing the perceived importance of genetic diversity and the evidence of local adaptation and uniqueness as presented by Ihssen et al. (1981), COSEWIC, in 1987, accepted the eligibility of the Lake Simcoe population of lake whitefish as a distinct stock and assigned a status of Threatened to the population (Evans et al. 1988).

Although there is little or no new information related specifically to distinctness of this population, the work of Bodaly et al. (1992) and Bernatchez and Dodson (1990, 1991, 1994) suggests that there may be a relationship between electrophoretic and mtDNA analysis and their respective usefulness in predicting genetic divergence and reproductive isolation. However, the inferences of Ihssen et al. (1981) may not be valid in that regard since theyare probably not justified by their genetic data. Although significant differences were observed among the set of five populations examined, these differences were driven by the distinctiveness of the Opeongo population versus all others. Examination of the genetic distance estimates (Table 11 of Ihssen et al. 1981) shows that the Lake Simcoe population lies between but is not significantly different from either the Lake Huron or Lake Ontario populations. Thus, without further work to clarify the distinctness of this population the information at hand is not an adequate basis for identifying this population as a Designatable Unit under the current COSEWIC guidelines [Committee on the Status of Endangered Wildlife in Canada (COSEWIC) 2004].