Lake Whitefish (Coregonus clupeaformis) Stocks of the Ontario Waters of Lake Huron

Abstract

Historical and contemporary data on lake whitefish (Coregonus clupeaformis) from the Ontario waters of Lake Huron were examined for evidence of stocks with the objective of defining population boundaries. We delineated the spatial distribution of five stocks from tag–recapture data and the general location of six additional stocks on the basis of population parameters such as growth rate, age structure, and abundance trends.Samples of fish collected (summer and fall) from 5 of the 11 potential stocks were evaluated on the basis of 11 morphometric and 7 meristic characters. We also examined osseometric features such as shape of scales and otoliths, and electrophoretic characteristics at 32 loci associated with 12 enzyme systems.The summer and fall samples for each group were generally not significantly different. For the phenotypes examined electrophoretically, each stock was in Hardy–Weinberg equilibrium; 12 of the 32 loci considered were polymorphic and 4 of the 10 possible genetic distances differed significantly from zero.The Inner Basin stock was distinctly different from all other stocks. The Blind River stock was also found to be different by osseometrics, but not by morphometrics or electrophoresis. Osseometrics separated the stocks by basin of origin. Two stocks, Outer Basin and Burnt Island, appeared to be the most similar and could be separated from each other only on the basis of growth rate and tagging data. These two stocks are adjacent to each other in the main basin of Lake Huron, along the south shore of Manitoulin Island.Whitefish stocks of Lake Huron represent groups of fish that differ phenotypically and genotypically in varying degrees, are spatially separated, and behave as cohesive units. We conclude that they should be regarded as functional units for management purposes.Key words: lake whitefish, Coregonus clupeaformis, Lake Huron, stocks, tag–recapture data, population structure, morphometrics, meristics, osseometrics, scale and otolith shape, starch gel electrophoresis, biochemical genetic variation