Incorporating Mortality from Catch and Release into Yield-per-Recruit Analyses of Minimum-Size Limits

Abstract

We evaluated the effect on yield per recruit of mortality from catch and release of fish smaller than a legal minimum length. Catch-and-release mortality reduces the potential effectiveness of minimum size limits for increasing yield per recruit by an amount that depends on the fishing mortality coefficient, the minimum size limit, and the probability that undersized fish survive if released. For a given probability of survival, catch-and-release mortality has its greatest influence when fishing mortality and the minimum size limit are large, because these factors determine the number of undersized fish that are caught and released. As the survival probability declines, minimum size limits become less effective for increasing yield per recruit because greater numbers of undersized fish die and cannot contribute to future catches. With low survival probabilities, minimum size limits may actually reduce yield per recruit. We calculated yield per recruit for red snapper (Lutjanus campechanus) in the Gulf of Mexico for minimum size limit ranging from 254 to 635 mm total length, survival probabilities ranging from 0.20 to 1.00, and several natural (M) and fishing mortality coefficients. A recently implemented 330-mm minimum size limit is predicted to increase yield per recruit as long as the survival probability exceeds 50% if M = 0.25; the survival probability must exceed 60% if M = 0.35.