CHINOOK SALMON EPIZOOTICS IN LAKE-MICHIGAN - POSSIBLE CONTRIBUTING FACTORS AND MANAGEMENT IMPLICATIONS

Stability of the Lake Michigan fishery for chinook salmon Oncorhynchus tshawytscha at high levels became questionable after stocks declined dramatically following spring epizootics in which bacterial kidney dis ease (BKD) was a major factor, initially stocked in 1967. favorable su rvival and growth of chinook salmon through the 1970s led to increases in abundance and in popularity with anglers. Returns of chinook salmo n improved annually until the late-1980s, when, with little warning, s pring epizootics reduced the abundance of adult salmon by 50% or more. Reduced abundance of alewives (Alosa pseudoharengus), coupled with an increase in chinook salmon density and heavy parasite infection rates were hypothesized to have reduced chinook salmon growth and fitness a nd to have increased their susceptibility to BKD. Evidence of slower g rowth exists and low food availability may be the stressor that trigge red the epizootics. Chinook salmon were a major component of the econo mic development, and subsequent hardship of the sportfishing industry on Lake Michigan. Sustaining the chinook salmon fishery at previous le vels may require managing for high abundance of alewives, which may be inconsistent with overall fish community management goals, The future sustainability and role of chinook salmon needs to be reevaluated in the context of the entire Lake Michigan fish community.