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

Scope and Method of Study. Gizzard shad Dorosoma cepedianum, the primary prey in many lakes and reservoirs of the southern U.S., often comprise a majority of the prey biomass in the systems in which they are found. However, they rapidly grow to a size that surpasses the preferred prey sizes of most piscivores. Lakes and reservoirs may, therefore, be prey limited if age-0 gizzard shad abundances are low. Previous studies have not considered the effect of the prey supply of age-0 gizzard shad on the entire piscivore community in a reservoir or the effect of age-0 gizzard shad availability on the growth and condition of piscivores in reservoirs. This study used bioenergetics modeling and Monte Carlo simulations to quantify the abundance of age-0 gizzard shad necessary to sustain seven sport fish, common to the southern U.S., at diverse growth rates, population sizes, mortality rates, and proportions of gizzard shad diets.;Findings and Conclusions. The potential for gizzard shad prey resource limitation in reservoirs of the southern U.S. is high according to the performed simulations. Annual necessary gizzard shad abundance (accounting for non-predation mortality and reproductive surplus required for prey sustainability) estimates ranged from < 10/ha/piscivore population to > 128,000/ha/piscivore population. Monte Carlo simulations indicated insufficient gizzard shad abundance, required to support piscivores, at the 50th percentile of published age-0 gizzard shad abundances ≥ 69% of the time. The findings of this study support the hypothesis that systems must have high prey resource availability if they are to support diverse sport fish communities with high-condition and abundance.