Estimating Double-Crested Cormorant Consumption on Leech Lake, Minnesota

Double-crested cormorants, historically common to Leech Lake, resumed colonizing in 1998.  The colony expanded rapidly and peaked in 2004 near an estimated 10,000 birds.  Concurrent declines in percid populations and their fishery prompted aggressive management actions in 2005; including annual lethal cormorant control measures and aggressive walleye fry stocking.  A complementary diet study and modeling evaluation were initiated to assess the potential effects of cormorant consumption on the fish community and its fishery.  This current work expands on previous studies to incorporate observed variability among annual consumption patterns into total consumption estimates.  Our objectives were to estimate the total fish and species-specific consumption by cormorants in the system and compare simulated culling scenarios.  Preliminary data suggested that current control efforts have reduced cormorant use and thereby cormorant predation on fish populations by approximately 55-65%.  If the timing of the culling is weighted toward the beginning of the control season, total annual consumption could be reduced by an additional 15-20% beyond current control measures with no change to the cormorant management target.  Continued work will monitor cormorant population and diet trends and how their consumption relates to the fishery.