An Evaluation of the Value of Harvest Restrictions in Managing Crappie Fisheries

Abstract

We used an equilibrium yield model to simulate the effect of reducing exploitation on yield and average weight of white crappies Pomoxis annularis, based on empirical growth data and various levels of conditional natural mortality. Modeling indicated that reducing exploitation would likely increase yield as fish growth increased and natural mortality decreased; however, reducing exploitation would not substantially affect yield when conditional natural mortality exceeded 30–40%, regardless of growth. For instance, a 250-mm minimum length limit provided higher yield than a 200-mm minimum length limit only if growth was above average and conditional natural mortality was less than 30–40%. Average weight of crappies harvested increased with growth and length at recruitment to the fishery but decreased with exploitation and conditional natural mortality. Our results suggest that a length limit could improve both yield and average weight for crappie fisheries only if growth is rapid and natural mortality is low. If natural mortality is not low, a length limit could improve average weight of fish harvested without substantially reducing yield.