How Suitable Are Highly Productive, North-Temperate Reservoirs for Hybrid Striped Bass Growth?

Highly productive tributary reservoirs can become in part hostile environments for fish during summer, owing to high epilimnetic temperatures (> 30°C) and low hypolimnetic dissolved oxygen (DO) levels (< 1 mg/L) that can reduce access to quality habitat for growth and survival. As part of a large research effort designed to explore the suitability of Ohio reservoirs for expansion of a hybrid striped bass (Morone saxatilis x M. chrysops) stocking program, we conducted laboratory experiments to quantify how temperature and DO influence hybrid striped bass consumption and growth and then combined these results with field data to assess habitat quality in two Ohio reservoirs that varied in depth and prey fish (i.e., gizzard shad Dorosoma cepedianum) production.  Experiments were conducted in a 3x3x2 factorial design (n=4 replicates/treatment) at three temperatures (20°, 22°, 29°C) and three DO levels (3.0, 5.0, and 7.5 mg/L), using two sizes of juvenile hybrid striped bass (40 g and 80 g). Our results show that, if DO was > 5.0 mg/L, consumption increased with temperature, whereas growth increased up to 22°C but remained unchanged at higher temperatures.  Consumption and growth declined for both size classes of fish at 3.0 mg/L of DO regardless of temperature. Using these data in combination with spatially-explicit field observations of DO, temperature, and prey fish biomass in a bioenergetics model, we show that habitat suitability for hybrid striped bass can vary both within and among Ohio reservoirs by providing a moderate to completely unsuitable conditions.  We ultimately discuss the implications of these findings for fisheries management in these systems.