Field Observations of Social Behavior, Shelter Use, and Foraging in the Lobster, Homarus americanus.

Abstract

Over a three-year period (1978-1981) behavioral observations of the lobster, Homarus americanus, were made by snorkeling in a shallow cove. Three hundred and thirty-four (334) animals were individually marked and this was the only time they were disturbed. In summer, the resident population numbered about 30 animals. The size composition, activity patterns, and habitat use of this population are described in a companion paper (Karnofsky et al., 1989). Shelters are of prime importance in the life of the lobster. Lobsters spent most of their time in shelters, leaving only at night. They dug shelters under eelgrass, rocks, and boulders; shelter locations appeared clustered. Some animals changed shelters frequently whereas others occupied the same shelters for up to 10 weeks. Premolt behavior was characterized by multiple shelter use. Cohabitation in the same shelter occurred only during periods of pair formation: when a mature female shared a male's shelter prior to and following her molt. We report the only field evidence for such courtship cohabitation. Food foraging behavior was rare (0.35 instances/observation hour); most foraging involved live prey. Similarly, intraspecific interactions were surprisingly infrequent (0.2 instances/observation hour) and most, by far, did not involve physical contact. Although puncture wounds suggested intraspecific aggression, actual observations of escalating fights were rare. Premolt residents were involved in 65% of the interactions observed. In 70% of the interactions the larger animal won. However, smaller males and females could successfully defend their shelters against larger females. We report results from three homing experiments. The results suggest that much of the time that resident lobsters spend outside shelters is used to remain familiar with their constantly changing physical and social environment.