Forage Fish Temporal and Spatial Dynamics In Ohio Reservoirs 1999–2010

Recognizing the significant connection between sportfish abundance and reservoir productivity as mediated by forage fish, mobile hydroacoustic surveys to determine forage fish density and biomass were conducted in up to 16 reservoirs annually in Ohio during 1999–2010 (n = 159 surveys).  Some reservoirs were sampled each year, providing an intensive temporal understanding of trends in forage fish, whereas others sampled less frequently helped build an intensive spatial dataset, providing a state-wide perspective of forage fish trends.  Here, we illustrate some of these temporal and spatial trends while also demonstrating the tight coupling between Ohio reservoir productivity (Secchi transparency = 0.90 +/- 0.14 m [mean +/- standard error], total phosphorus concentration = 63.5 +/- 13.8 micrograms/L, chlorophyll concentration = 43 +/- 7 micrograms/L) and forage fish abundance (density = 70,754 +/- 8,393 fish/ha, mean biomass = 221 +/- 21 kg/ha).  Although simple trends could be found in our dataset (e.g., forage fish density increased as a function of total phosphorus concentration), more complex patterns, such as a decrease in variance of forage fish abundance in reservoirs with Secchi transparency > 1.0 m, were also found.  Both simple trends and more complex patterns indicate that multiple trophic levels control forage fish abundance even in Ohio’s most productive reservoirs.  Understanding how various trophic levels and abiotic factors both in the reservoir and in the watershed affect forage fish abundance, and in turn sportfish abundance, remains the focus of this program.