Longitudinal Trends in Walleye and Sauger Population Dynamics in the Upper Ohio River

The sauger Sander canadensis and walleye S. vitreum populations in the upper Ohio River provide popular recreational fisheries, but management has proven to be difficult as a result of the tremendous variation inherent in these populations.  While, the upper Ohio River sauger and walleye populations exhibit the annual variations in reproductive success, growth, and mortality that are characteristic of most Sander spp. populations, these populations also exhibit tremendous spatial variation (upstream vs. downstream) in these rate functions.  The purpose of this study was to explore variations in the dynamic rate functions of walleye and sauger among the upper Ohio River pool populations.  Shoreline electrofishing surveys were conducted in the dam tailwaters to derive estimates of abundance, mortality, and growth for the sauger and walleye populations in nine upper Ohio River pools.  Population assessments were conducted in four pools every year (intensive pools) and at least twice in the other five pools (extensive pools) during November 2005-2010.  Sauger were much more abundant in all pools than walleye, accounting for 95% of the total catch during these surveys.  Reproductive success (indexed as age-0 CPH) of both species varied among years (good vs. bad years) and also showed distinct longitudinal trends among pools.  Sauger reproductive success was lowest in the upstream pools and increased in a downstream direction.  Conversely, walleye reproductive success was highest in the upstream pools and decreased in a downstream direction.  Total annual mortality of sauger and walleye in the intensive pools was estimated for the 2005, 2006, and 2007 cohorts via catch curve analysis from age-0 through age-3.  In general, total annual mortality of sauger and walleye in all pools was high (46-85%) and did not vary among pools.  First-year growth (indexed as age-0 mean length) of sauger and walleye was highly variable in the upstream pools and was much more consistent in the downstream pools.  The physical, hydrological, and chemical characteristics of the Ohio River change substantially over the 724 km reach in which this study was conducted, and the subsequent changes in the dynamics of the sauger and walleye populations that reside in these waters presents a challenge to the effective management of these populations.