POTENTIAL REGULATION OF AGE-0 GIZZARD SHAD BY HYBRID STRIPED BASS IN OHIO RESERVOIRS

Piscivores can control prey populations in north temperate lakes, lead ing to increased zooplankton and reduced phytoplankton. In reservoirs with gizzard shad Dorosoma cepedianum, an omnivorous planktivore, this cascade occurs with lower probability because while this fish is shor ter than 60 mm in total length (TL) it readily consumes zooplankton bu t also switches to phytoplankton and detritus. Prospects for gizzard s had control probably hinge on piscivore consumption of age-0 individua ls. Hence, we quantified capture efficiency of hybrids of striped bass Morone saxatilis X white bass M. chrysops (small: 190-250 mm, TL; lar ge: 310-360 mm, TL) 500-L aquarium. Small hybrid striped bass selected 40-mm gizzard shad but preferred neither 60-mm nor 80-mm prey. Large hybrid striped bass demonstrated no selection for 40-120-mm gizzard sh ad. We incorporated these data into a bioenergetics model to evaluate whether hybrid striped bass could sufficiently reduce abundance of age -0 gizzard shad in Ohio reservoirs to permit increased zooplankton, th ereby improving the potential for resident sport fish recruitment in r eservoirs. Hybrid striped bass potentially increased larval sport fish occurrence only when they were stocked at high densities (greater tha n or equal to 350 fish/ha or greater than or equal to 22 kg/ha) couple d with age-0 gizzard shad suffering low natural mortality and occurrin g at an intermediate peak density of 25 fish/m(3) or less. We believe gizzard shad are largely immune to control by hybrid striped bass in O hio reservoirs. Hence, managers must consider combining watershed mana gement with predator stocking to regulate gizzard shad.