Temporal Trends in Largemouth Bass Mortality, with Fishery Implications

Abstract

We reviewed estimates of annual exploitation (u) and total mortality (Z) for populations of largemouth bass Micropterus salmoides and used a simulation model to explore how temporal changes in u have influenced those populations. The review produced 32 estimates of u and 30 of Z spanning 51 years. Fishing mortality was roughly parabolic through time, with a mean of 0.35 for 1976–1989 and a mean of 0.18 for 1990–2003. Thus, average fishing mortality rates have declined by about one-half since about 1990. Total mortality declined with the decline in u, suggesting that changes in u caused lower overall total mortality rates. The evidence further suggests that the decline in u was caused by the voluntary release of fish by anglers rather than by changes in overall fishing effort. The simulation model showed that the decline in exploitation increased adult largemouth bass abundance but reduced the ability of size and bag regulations to improve population metrics owing to low rates of directed harvest. Discard mortality (i.e., the mortality of fish caught and released) would not negate the benefits of lower exploitation unless the mortality of fish caught and released was 0.3 or higher. Changes in angler behavior have substantially reduced fishing mortality for largemouth bass fisheries, which should be considered when developing management plans for this species and others with high rates of voluntary release.