Evaluation of a 254-mm Minimum Length Limit on Crappies in Delaware Reservoir, Ohio

Abstract

A 254-mm minimum length limit on black crappies Pomoxis nigromaculatus and white crappies P. annularus was evaluated during a 6-year trial (1991–1996) at Delaware Reservoir, Ohio. The primary objective of the length limit was to increase the size of crappies harvested without substantially reducing yield. Mean length at harvest increased up to 66 mm following implementation of the length limit. However, a 78% average decrease in total annual harvest was too great to compensate for the larger size at harvest and to compensate for annual yield (kg) reductions of 38–76% while the regulation was in effect. Annual catch-and-release rates of crappies at Delaware Reservoir increased from 35–43% to 84–97% and became the greatest in Ohio. Likewise, Delaware Reservoir had greater angler catch per effort and mean size at harvest compared with unregulated crappie fisheries in Ohio. Both crappie species maintained preregulation growth rates despite modest density increases of sublegal fish, whereas relative weight decreased for larger black crappies (23–25-cm classes) and white crappies (25–26-cm classes). Growth may have been too slow and conditional natural mortality was probably too great for the regulation to sustain near preregulation yield or for conspicuous improvements in age and size structure. Delaware Reservoir also was predominated by black crappies, which may recruit to the fishery later than white crappies of the same age. In addition, recruitment to harvestable sizes was lower than expected at Delaware Reservoir after the 254-mm length limit was imposed, and the impact of catch-and-release fishing was suspect. After the 6-year trial and evaluation, the 254-mm length limit was reduced to 229 mm to allow anglers consumptive use of crappies that may have become unavailable rather than more abundant under the 254-mm length limit.