Trapping interactions of crabs and American lobster in laboratory tanks

Abstract

The relationship between trap catches of decapods and their abundance is not well established. Because it is difficult to manipulate density in the field, laboratory tanks were used to examine 10 hypotheses about the intra- and interspecific interactions of rock crab (Cancer irroratus), green crab (Carcinus maenas), and American lobster (Homarus americanus). The proportion of rock crabs captured did not differ among high, medium, and low densities, but the proportion captured was reduced at high densities for both green crabs and lobsters. Additional experiments demonstrated that large green and rock crabs in the tanks reduced the catch of small green and rock crabs and that the presence of lobsters reduced the catch of both crab species considerably. However, small rock crabs did not reduce the catch of large rock crabs, and neither green nor rock crabs reduced the catch of each other. Reductions in the catch of a target species caused by interactions in the field can perhaps be lessened by removing the catch from the trap at intervals of less than 24 h. Then the catches would be summed over 24 h for an index of abundance.