Depth Selection and Vertical Migration in Siscowet Lake Trout Revealed By Pop-up Satellite Tags

Prior studies have demonstrated that differences observed in morphometry and lipid levels between wild lean and siscowet lake trout persist when the morphotypes are reared from eggs to adults under identical environmental conditions (hatchery).  This suggests a genetic or epigenetic basis for these differences.  Wild leans and siscowets also separate on the basis of bathymetry; siscowets inhabiting deep water (>80 m) and leans being more shallow inhabitants (<80 m).  The basis for selecting different depths has never been addressed in these lake trout forms.  We used pop-up satellite tags (PSATs) to test whether leans and siscowets reared from eggs to adults under identical environmental conditions, would demonstrate the same bathymetric preferences as wild morphotypes.  We also tagged wild leans and siscowets for comparison.  The initial PSAT results suggest that hatchery-reared siscowets select deep habitats when released to Lake Superior.  Further, we observed that both wild and hatchery siscowets exhibited periods of vertical migrations from the bottom to the surface that at times exhibited diurnal frequencies under periods of low light.  Episodes of vertical migrations were dispersed between periods in which the fish remained deep.  The results suggest a genetic or epigenetic basis for depth selection by siscowet lake trout.