Walleye (Sander vitreus) movement ecology in Lake Winnipeg, Canada

Abstract

Identifying differences in movement behaviour and the variance in behavioural strategies that may exist across a single species occupying a heterogeneous landscape can provide valuable ecological and evolutionary insights; taking movement heterogeneity into account in management and conservation efforts may ultimately improve the sustainability of species with significant economic and ecological value, such as walleye (Sander vitreus). Lake Winnipeg (Manitoba, Canada) supports the second largest commercial fishery for walleye in North America. The lake is divided into two relatively separate basins connected by an intermediate channel, which differ dramatically in both abiotic and biotic features. Despite this, little is known about whether (or how) walleye move or use variable habitats throughout the lake. Historical mark-recapture models from tagged walleye revealed low but measurable rates (0.3-1.2%) of movement annually between the north and south basins of Lake Winnipeg. Contemporary estimates using acoustic telemetry data detected a greater but comparably low rate of transition between the basins annually for walleye (7-8.5%). Both historical and current models revealed that movement was more likely to occur in a south to north direction. Additionally, annual survival across both basins of the lake was higher historically (54%) then it is currently (37%). To further investigate contemporary patterns of inter-basin movement, I assessed female walleye tagged across the south. I uncovered repeatable patterns of individual fish movement, where migratory walleye consistently travelled into the north basin for a period of time, and resident walleye remained within the south basin. I found that migrants significantly increased home (95%) and core (50%) ranges during the summer and fall associated with a northern shift in latitudinal distribution. Finally, putative repeat spawning in the year following tagging appeared to be greater for migrants (65%) compared to residents (40%). This thesis describes the first formal description of walleye movement in Lake Winnipeg, and suggests connections between movement patterns (i.e., migrants and residents) to potential differences in life history (i.e., differential probability of repeat spawning). Direct movement results presented here should prove useful to fisheries management and policy for both commercial and recreational activities across the separately managed basins of Lake Winnipeg.