Population Assessment and Minimum Length Limit Evaluations for White Bass in Four Alabama Reservoirs

Abstract

White bass Morone chrysops were collected by electrofishing from tributaries of four Alabama reservoirs during spring spawning migrations to document longevity, growth, relative weight, and survival. We also conducted simulation modeling to explore the potential effects of minimum length limits of 229, 254, and 305 mm in two reservoirs with disparate growth rates and relative weights. The oldest fish collected was age 7 (N = 1), and 98% of all fish collected (N = 1,113) were age 5 or younger. In all populations, fish grew rapidly and reached 305 mm in about 2 years, but lengths at age and relative weights varied among reservoirs. Based on catch curve regressions, annual mortality ranged from 42% to 57%. In the faster-growing population with higher relative weights, minimum length limits of 254 and 305 mm could increase yield relative to that with a 229-mm minimum length limit if conditional natural mortality were 30% or less and exploitation exceeded 30%. At higher rates of conditional natural mortality (40% and 50%), predicted yields were similar among minimum length limits. In the slower-growing population, minimum length limits greater than 229 mm would provide similar or reduced yield at progressively higher levels of conditional natural mortality. The number of fish that could be harvested at minimum lengths greater than 229 mm would be severely reduced in the slower-growing population. Minimum length limits should only be considered for fast-growing white bass populations in Alabama where exploitation is high. In reservoirs with erratic recruitment, protection of older, abundant year-classes by means of high minimum length limits will not sustain a fishery longer than 3–4 years owing to the short life expectancy of this species.