Modeling the Lake-Wide Sustainability of Lake Trout Stocks in Lake Superior

Following the recovery of lake trout stocks in Lake Superior due to stocking, sea lamprey control, and harvest regulations, agencies developed statistical catch-at-age (SCAA) models to determine if accepted total annual mortality rates were sustainable.  The developed SCAA models assumed that immigration and emigration rates among stocks were equal and thus could be ignored.  Lake Superior is divided into individual management units, each of which has been treated as a separate stock.  Recent studies of lake trout movement have shown that immigration and emigration among stocks are not equal (Kapucinski et. al 2005).  In our study, SCAA models are used to develop a simulation model that includes movement rates to determine future sustainability of lake trout stocks assuming movement.  Preliminary simulations focused on the Apostle Islands region revealed the sustainability of this management unit to be altered by movement of fish into and out of the area.  Allowing for immigration and emigration of fish in the zone meant higher sustainability of the population.  Simulations will be completed for other management zones in the lake to determine lake-wide sustainability and what implications this has for current management practices.