Age-0 gizzard shad prey supply and predator demand: Analysis of the trophic support capacity of southern U.S. reservoirs

Gizzard shad Dorosoma cepedianum often comprise a majority of the prey biomass in reservoir systems.  However, they rapidly grow to a size surpassing the preferred prey sizes of most piscivores.  Therefore, even reservoirs with high gizzard shad abundance may be prey limited if age-0 abundance is low.  Previous studies have not considered the effect of the prey supply of age-0 gizzard shad on the abundance, growth, or condition of the entire piscivore community in reservoirs.  We used bioenergetics modeling and Monte Carlo simulations to quantify the abundance of age-0 gizzard shad necessary to sustain seven piscivore species at low, medium, and high (based on published values for each species) growth rates, population sizes, mortality rates, and proportions of gizzard shad in piscivore diets.  Annual necessary gizzard shad abundance (accounting for non-predation mortality and reproductive surplus required for prey sustainability and scaled to August 15^th) ranged from < 10·ha^-1·piscivore population^-1 to > 37,000∙ha^-1∙piscivore population^-1.  Monte Carlo simulations indicated that the 50^th percentile of published age-0 gizzard shad abundances was insufficient to support piscivore communities ≥ 69% of the time.  Our results suggest that systems must have high prey resource availability to support diverse sport fish communities with high-condition and abundance.