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Examining indirect effects of lake trout recovery
Citation:
Sierszen, M. AND M. Vinson. Examining indirect effects of lake trout recovery. IAGLR Conference, Burlington, VT, May 25 - 29, 2015.
Impact/Purpose:
not applicable
Description:
With the recovery of lake trout populations in Lake Superior, there are indications of decreased forage fish abundance and density-dependence in lake trout. In Lake Superior, lean lake trout historically occupied depths < 60 m, and siscowet lake trout occupied depths > 60 m. Siscowets have been known for their high lipid content (in excess of 65% in filets) which affords buoyancy that assists in diel vertical migration, an important adaptation to life in profundal habitats. However, in recent years several lines of evidence suggest that lipid concentrations in Great Lakes lake trout have declined. To explore changes in lipids and their energetic consequences, we compared lipid content and swimming costs among siscowet lake trout collected in 1953-1963, 2005, and 2011, and trends in lean and siscowet depth occurrences. We found ca. 40% declines in filet lipid content of similarly-sized siscowet between 1953 and 2011, a concomitant doubling of swimming costs, and a trend for siscowet to occur in shallower waters over the past decades. Mechanisms behind these trends would be clarified through further investigations in Lake Superior and other recovering systems.