Lake Winnipeg, the tenth largest freshwater lake in the world, is the home of the second largest walleye fishery in North America. The North Basin of the lake is larger in surface area and volume, deeper (mean depth = 13 m) and less turbid than the South Basin (mean depth = 9 m), and differs in prey fish community composition. One of the most important differences especially relevant to this study is the presence of the invasive rainbow smelt (Osmerus mordax) in the North Basin, and its absence in the South Basin.
The objective of this study was to determine if there is a difference in the growth (length-at-age) of normal walleye, dwarf walleye and sauger in the South Basin versus the North Basin of Lake Winnipeg. The influence of different diet regimes on growth variation in the two basins was studied concurrently.
Normal walleye, dwarf walleye and sauger were caught from both basins of Lake Winnipeg, in all four seasons, using gill-nets of varying mesh sizes. Growth was determined by aging sagittae otoliths and examining the age-length relationship. The gut contents of fish were inspected concurrently to assess any differences in diet.
Results/Conclusions
An analysis of covariance revealed that the length-at-age of normal walleye was significantly greater than that of sauger which was significantly greater than that of dwarf walleye. More importantly, there was a significantly greater length-at-age found for the North Basin versus the South Basin for both species of fish. There was a distinct difference in the diet of the normal walleye, dwarf walleye and sauger from each basin with a higher species composition in the South Basin versus the North Basin, which consisted mostly of the invasive rainbow smelt. This may potentially result in the differential growth observed and may be an important finding for the management of this multi-million dollar fishery.