Factors Affecting Largemouth Bass Size Structure at Wheeler and Guntersville Reservoirs, Alabama

Largemouth bass Micropterus salmoides fisheries place a high value on quality size structure. Guntersville and Wheeler Reservoirs, Alabama are popular largemouth bass fishing destinations that experienced declines in catch rates of fish greater than 500mm total length in the late 1990s early 2000s. Although size structure has since recovered to historical norms at Guntersville, continued low catch rates of large fish at Wheeler has raised questions regarding factors affecting largemouth bass size structure at these reservoirs. We compared growth, recruitment, and mortality (including largemouth bass virus prevalence) estimates between the two reservoirs to assess factors affecting size structure. Fish reached a larger size at age early in life (ages 1-4) but achieved a smaller asymptotic length at Wheeler, and these differences were statistically significant for males. Despite differences in growth, simulations suggested the differences were not enough to explain the differences in size structure. Catch curve estimates suggested that differences in total mortality are likely responsible for differences in size structure between reservoirs. Growth-specific catch curves indicated possible positive associations between mortality and early growth rates, which may relate to macrophyte densities at these lakes. Our results could have implications for management of bass stocks and habitat at these reservoirs.