Recruitment of Largemouth Bass in Alabama Reservoirs: Relations to Trophic State and Larval Shad Occurrence

Abstract

Factors affecting recruitment of largemouth bass have frequently been evaluated, but few studies have assessed recruitment potential among a range for reservoirs of varying trophic states. We examined densities of larval threadfin shad Dorosoma petenense and gizzard shad D. cepedianum from Mar to Jul from nine Alabama impoundments. Using shoreline rotenone sampling and daily otolith rings, we estimated density, age, and growth of age-0 largemouth bass Micropterus salmoides in late Jun–Jul. Density and growth of larval gizzard shad, larval threadfin shad, and age-0 largemouth bass increased with chlorophyll a across impoundments. Duration of occurrence for larval gizzard shad and threadfin shad was positively related to chlorophyll a. Eutrophic reservoirs contained larval shad that were 40% or less of mean age-0 largemouth bass total length (i.e., the size at which they would probably be vulnerable to predation) in late Jun–Jul, whereas larval shad were generally not collected in late Jun or Jul in oligo–mesotrophic impoundments. Thus, piscivory on age-0 shad by age-0 largemouth bass was more likely to occur in eutrophic than in oligo–mesotrophic reservoirs. Eutrophic impoundments have high chlorophyll-a values and high larval threadfin shad and gizzard shad densities, and they may provide for greater recruitment of largemouth bass than oligo–mesotrophic impoundments.