Movement behaviours of stocked and wild lake trout Salvelinus namaycush determined using acoustic telemetry.

Abstract

Hatchery practices are a critical tool of fisheries management to supplement diminished fish populations and restore extirpated species. However, stocking programs that successfully restore self-sustaining populations are rare. Unintentional artificial selection and domestication of hatchery-reared fish are potential limitations to the success of stocked individuals by selecting for behaviours that are poorly suited for natural conditions. Here, we compared seasonal movement behaviours between an established population of hatchery origin (stocked) and naturally produced (wild) lake trout (Salvelinus namaycush) in Lake Champlain at a range of sizes, including immature and mature fish. Fifty-six stocked and 34 wild lake trout were implanted with acoustic transmitters, including 45 transmitters with temperature and pressure (depth) sensors, to evaluate three-dimensional movement. Movement behaviours were assessed based on the number of distinct lake regions used, proportional time spent among lake regions, average daily distance travelled and depth distribution. Overall, horizontal and vertical movements were similar between stocked and wild lake trout across sizes, although individuals tended to occupy shallower depths at larger sizes. Seasonal differences in movement behaviours were observed and in some cases were dependent on origin. For all lake trout, average daily movement was greatest during fall and least during summer. Depth occupied, however, had an opposite trend, with the deepest average depths during summer and shallowest during fall and winter. The proportion of time spent among lake regions and variability in depth occupied also varied seasonally but only for wild fish, and included less time spent in individual regions and greater depth variability during fall compared to other seasons. While origin had insignificant effects in most models we evaluated, model predictions consistently suggested stocked lake trout had slightly smaller movements than wild fish. These results suggest that hatchery practices may have long-term, unintended effects on fish behaviour yet overall differences are likely subtle.