Perch Recruitment Research
John M. Dettmers, John Janssen (UW-Milwaukee), D. Jude (U of Michigan), D. Mason (NOAA-GLERL), and A. S. McNaught (Central Michigan U)
We explore possible factors that limit yellow perch recruitment in Lake Michigan. Although yellow perch recruitment has been poor for over a decade, the mechanisms driving poor recruitment are not clear. Hence, we investigate three hypotheses that may influence yellow perch recruitment success: (1) limiting zooplankton resources, (2) alewife predation on larval yellow perch, and (3) offshore transport of larvae that may either benefit or reduce recruitment. By conducting simultaneous lakewide sampling for zooplankton and larval yellow perch, we can understand the role played by food availability in determining early growth and survival of yellow perch. We also are comparing the spatial and temporal overlap between alewife and larval yellow perch with hydroacoustics, neuston nets, and trawling to quantify the impact predation by alewife may have on larval yellow perch abundance. Finally, we are exploring the role played by upwelling/downwelling events in transporting larvae from nearshore environments to offshore habitats that may be more or less favorable for larval fish growth. We evaluate the extent to which upwelling events structure larval nearshore larval fish catches by sampling on either side of the lake during upwelling and by sampling from nearshore to offshore for both zooplankton and larval yellow perch. By comparing results of these three focus areas, we can begin to explain why yellow perch recruitment has been poor in Lake Michigan during the recent past.