Reproductive Timing of Lake Trout Morphotypes in Northern Lake Superior

At least four self-sustaining lake trout morphotypes are still present in Lake Superior.  Lean and siscowet lake trout have been shown to reproduce at the same time of the year (fall) in southern Lake Superior. However, historical accounts from commercial fishermen and more recent reports indicate that lake trout morphotypes reproduce at other times of the year in different parts of Lake Superior, particularly in the north.  To further investigate this, lean, siscowet, redfin and humper lake trout were sampled in the spring, summer and fall at sites surrounding Isle Royale National Park.  Lean, redfin and humper lake trout had developing gonads in the spring, mature ovaries and testes in the summer, and were spent by October.  In contrast, populations of siscowet lake trout were observed with fully mature (postvitellogenic) ovaries in June as well as August.  It appears that in the vicinity of Isle Royale, lean, redfin and humper lake trout reproduce once/year in the late summer or early fall. In contrast, siscowet lake trout appear to spawn twice; in the spring and in late summer/early fall.  It is unclear whether the siscowet lake trout that reproduce at different times represent stocks that are genetically distinct.