Evaluation of a 15.0-Inch Minimum Length Limit on Largemouth Bass and Spotted Bass Catches at Table Rock Lake, Missouri

Abstract

The largemouth bass Micropterus salmoides and spotted bass Micropterus punctulatus fisheries in two areas of 43,000-acre Table Rock Lake, Missouri, were studied from 1973 through 1983 to evaluate the effects of a 15.0-in minimum length limit initiated in 1976. The length limit was expected to improve catch rates for bass anglers and increase the harvest rates of black bass (Micropterus spp.) 15.0 in and longer. Changes in the bass populations and fisheries were monitored annually in the James River Arm with night electrofishing during April and May and with roving creel surveys on the James River and Long Creek arms. Indirect evidence indicated that the size limit increased annual survival rates of protected-size largemouth bass and spotted bass. Year-class strength was highly variable for both species, but particularly for largemouth bass, which experienced weak year classes among the first four classes protected by the size limit. Growth rates of both species declined during the study, apparently in response to decreased availability of food and, in some years, to higher abundance of largemouth bass. In the James River Arm, yearly angler effort for black bass doubled to almost 60 h/acre after the size limit was established. Average annual catch rates for bass (species combined) by bass anglers increased from 0.30 to 0.61 bass/h. Estimated annual harvest of bass declined from 8.2 to 3.1 bass/acre, but estimated annual catch of bass (kept or released) tripled to 32 bass/acre. The percentage of bass anglers who kept one or more bass declined from 41 to 18%. No improvements in angling success were detected in the Long Creek Arm, probably because of a more severe and extended period of weak year classes than in the James River Arm. Weak year classes of largemouth bass and the longer period over which natural mortality operated as fish grew to the 15.0-in harvestable size may have masked some of the advantages of protecting largemouth bass in this study. However, the length limit increased opportunities for anglers to catch them and should prove to be a successful regulation for largemouth bass under more typical conditions of year-class strength and food availability. Spotted bass at Table Rock Lake grow more slowly than largemouth bass, do not live as long, and might be better managed with a lower minimum length limit.