Influence of fishing practices on lake trout bycatch in the Canadian lake-whitefish commercial fishery in Lake Huron

Rehabilitation of lake trout (Salvelinus namaycush) populations is a priority for fisheries management in the upper Laurentian Great Lakes. In Lake Huron, lake trout are frequently caught as bycatch in the commercial fishery for lake whitefish (Coregonus clupeaformis). Given the frequency of lake trout capture and the importance of limiting mortality for achieving rehabilitation goals, understanding factors that affect lake trout bycatch is valuable. We used catch and effort data from commercial logbooks and onboard observer reports to assess potential effects of factors in the operation of the lake whitefish fishery on lake trout bycatch and to develop standardized indices of lake trout abundance. Factors considered in our analysis were season, mesh size, region, and license holder, which were recorded in both datasets, and set type and depth, which were only recorded in the observer dataset. In general, we found that environmental factors affected whether lake trout bycatch occurred, but that if bycatch occurred, factors related to the fishing gear affected its magnitude. Although we observed seasonal interactions with depth and mesh size, the probability of bycatch was lowest in shallow waters, and the magnitude of bycatch was lowest in shallow waters, alternative set types, and larger mesh sizes. Standardized indices of lake trout abundance from both datasets gave comparable estimates of relative trends; an increase in abundance up to 2004-2005 followed by a decline. Our findings show utility for the use of the observer dataset from the lake whitefish fishery as part of lake trout management in Lake Huron.