Retention Probability Varies with Cull Ring Size in Traps Fished for Blue Crab

Abstract

AbstractThe blue crab Callinectes sapidus is a commercially important crustacean species fished along the Atlantic and Gulf of Mexico coastlines. Cull rings on traps are required to allow for egress of sublegal blue crabs in commercial and recreational fisheries in this region. We undertook a study to estimate contact selectivity (retention probability) of traps with different cull‐ring sizes fished for male crabs. We estimated retention probability using logistic models and catch data from 38.1‐mm square mesh traps, each affixed with one size of cull rings (58.7, 60.3, or 61.9 mm internal diameter), and fished along with control traps (no cull rings). Each experimental trap type displayed relatively steep retention around its l50, the carapace width at which 50% of individuals are selected. The l50 for traps with 58.7‐mm cull rings was less than the minimum legal crab size in North Carolina (127 mm carapace width) while the l50 for traps with 60.3‐mm or 61.9‐mm cull rings was greater than the minimum legal size. Mean catch rates of legal male crabs were not statistically different among the three experimental trap types; however, catch rates of sublegal males were significantly lower in traps with the two larger cull ring sizes. We conclude that traps with 61.9‐mm cull rings are most appropriate for the North Carolina trap fishery because they maintain catch rates of legal males but show the greatest reduction in catch rates of sublegal males. The use of larger cull‐ring sizes would reduce rates of fishing mortality resulting from excessive trap confinement, injury during commercial culling, or intentional harvest by fishers who do not cull their catch.Received April 29, 2015; accepted October 22, 2015