Using Pop-up Satellite Tags to Uncover Bathymetric and Environmental Habitat Selection in Lake Trout Morphotypes in Lake Superior

In Lake Superior there are several ecotypes of lake trout (Salvelinus namaycush) including leans and siscowets that are separated on the basis of morphometry, lipid levels and bathymetry.  While leans are thought to be shallow inhabitants and sicowets deep, detailed bathymetry is unknown. We used pop-up satellite tags (PSATs) to characterize the bathymetric behavior of wild leans and siscowets throughout the year.  Since the PSATs recorded light and temperature, we could also compare depth selection behavior with photoperiod and water temperature.  We found that leans selected depths that were generally <60m throughout the year.  In contrast, siscowets were frequently found at depths >100m.  However, siscowets also exhibited periods in which they underwent extensive vertical migrations from the bottom to the surface and at times these migrations appeared to occur at night.  In the spring we also observed siscowets that remained at the surface for up to a month regardless of light levels. Leans were found in water up to 15^oC, while siscowets did not inhabit water above 11^oC.  The bathymetric behavior of siscowets is complex with periods of great and shallow depths, punctuated with periods of extensive vertical migrations.  We hypothesize that these are opportunistic behaviors related to feeding.