Quantification of Abundance and Mortality of Maumee River Larval Walleye

Quantifying the contribution of specific fish stocks in large ecosystems is crucial to whole-system fishery management.  The Maumee River supports an important spawning sub-stock of Lake Erie’s walleye (Sander vitreus) population; consequently, our objective was to quantify Maumee River larval walleye production, export, and mortality.  Larval fish are inherently variable across space and time making accurate quantification difficult.  To account for spatial and temporal variability larval samples were collected three times a week at three locations in the River; upstream, downstream, and in a power plant intake canal. Multiple larval tows were spatially distributed at each location by depth and transect.  A Bayesian hierarchical model was used to account for spatial and temporal variability which propagates through as uncertainty in the final estimates.  Larval fish export from the Maumee River varied substantially between years, from 97 million in 2010 to 43 million in 2011. Total in-river mortality in 2011 was 78% of the 199 million fish produced. Power plant mortality in 2010 and 2011 was small relative to export contributing little to total in-river mortality, 4.4% and 2.6% respectively.  The high variability of annual contribution to the lake population and in-river mortality is likely driven by environmental factors.