A Review of the Research on the Benthos of Lake Winnipeg

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Flannagan, J.F.
Cobb, D.G.
Flannagan, P.M.
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Department of Fisheries and Oceans, Winnipeg, MB
Lake Winnipeg, a remnant of Glacial Lake Agassiz, is the eleventh largest (by area) freshwater lake in the world and the seventh largest in North America. Bordered on the north and east by the Precambrian Shield, and on the south and west by the Central Plains, the lake is the focal point of rivers draining its 953,250 km2 watershed. It is extremely shallow relative to its area and does not stratify thermally during the open water season. This, together with the high nutrient load entering from the watershed, especially the south and western parts, have resulted in the lake being highly productive and supporting a very large commercial fishery. Compared to other Canadian Great Lakes, with the possible exception of Lake Erie, the offshore benthos of Lake Winnipeg are relatively well known. This knowledge results from three main sources: 1) a survey of the benthos of several large Manitoban lakes related to their capacity to support fish, carried out by Ferris Neave and Alexander Bajkov in the late 1920's and early 1930's (Bajkov 1930; Neave 1932, 1933, 1934); 2) . a "baseline survey" of the physical, chemical and biological condition in the lake carried out by staff of the Freshwater Institute (FWI) in 1969, when it was thought that some major changes in the lake's drainage basin may have been influencing the lake (benthos papers include: Flannagan 1979; Flannagan and Cobb 1981, 1984, 1991, 1994; Chang et al. 1992, 1993, 1994); and 3) the continuing program on the lake carried out by biologists from the Fisheries Branch of the Manitoba Provincial government (many manuscript reports including Rybicki 1963, 1966; Stone and Cober 1965; Crowe 1969, 1972a, b, 1973a, b; Slack 1973; Kristofferson et al. 1975). These latter publications are unrefereed internal Departmental reports not generally available to the scientific community, thus reference will only be made to them when it is considered that the information they contain is not available elsewhere. Ekman grabs of various sizes, and mesh sieves of 0.2-1.27 mm opening were used in all surveys, except for some Provincial government studies, where Ponar and Peterson grabs were used (Table 1). Comparisons using the latter two grabs or widely different mesh sizes must be carefully made, since the use of different grabs (Flannagan 1970) or different mesh sizes (Reish 1959) can affect species counts and abundance estimates. This report attempts to collate the existing knowledge of the species composition, distribution, life history, production and changes in the benthos of Lake Winnipeg. As a result, it will be possible to better understand changes to the lake ecosystem. Potential threats to the presentlake biota include: 1) direct introduction of undesirable species (e.g. zebra mussels) via inter-basin transfer of boats; 2) diversion of water originating in the Mississippi/Missouri watershed into the Lake Winnipeg watershed (e.g. Garrison Dam and diversion in the north-central United States) perhaps providing the necessary water routes required for the introduction of exotic species (Flannagan and Flannagan 1982); and 3) predictions of climate warming, and its effect on water temperature and water supply.
Benthos, Lake Winnipeg, Oligochaeta, Hirudinea, Crustacea, Ephemeroptera, Plecoptera, Trichoptera, Chironomidae, Mollusca
Flannagan, J.F., D.G. Cobb, and P.M. Flannagan. 1994. A review of the research on the benthos of Lake Winnipeg. Can. Manuscr. Rep. Fish. Aquat. Sci. 2261: iv + 17 p.