Predation of Sea Scallops (Placopecten magellanicus) by Lobsters (Homarus americanus) and Rock Crabs (Cancer irroratus) in Underwater Cage Enclosures

Abstract

Predation studies in underwater cage enclosures on natural substrates were conducted in 1979 and 1980 to assess the propensity of adult American lobsters, Homarus americanus, and rock crabs, Cancer irroratus, to prey upon sea scallops, Placopecten magellanicus. In 1979, the initial prey by both predator species was large, embedded horse mussels (Modiolus modiolus). In the enclosure containing lobsters, this was followed by lobster cannibalism and, finally, when lobster density was reduced, predation on large sea scallops (80–110 mm shell height). No cannibalism or predation on large scallops occurred in the rock crab enclosure. In 1980, small scallops (40–55 mm shell height) were presented to lobsters and rock crabs; predation occurred regardless of predator density. Large sea scallops and unembedded horse mussels were consumed when crustacean densities approached natural levels. These studies demonstrate that small sea scallops and embedded horse mussels can be readily consumed by lobsters and rock crabs under field conditions, but that natural predation of large scallops by either rock crabs or lobsters is of lesser magnitude.Key words: sea scallops, crabs, lobsters, predation, prey selectivity