Territorial Behavior of the American Lobster Homarus americanus

Abstract

Territorial behavior of the American lobster Homarus americanus was studied by observing shelter occupancy at a site on the northeast coast of Newfoundland year-round. Lobsters left their shelters only at night; nocturnal activity began at dusk, peaked around 2–3 hours after darkness, and dropped to a very low level before dawn. Nocturnal activity was virtually nil during winter, increased with increasing temperature during July, peaked during August, and declined during autumn as temperature dropped. Although lobsters commonly returned to the same shelter after nocturnal wandering, in July-August half the shelters occupied during one of two consecutive daily checks were empty the other day. Within the 0.19 km2 study site, individual lobsters observed 1–2 months occupied an average two shelters; those observed for 11–12 months occupied an average five shelters. During these same observation periods, the same lobster was in the same shelter for 77% and 48% of the sightings, respectively. Occupancy rate was about 70% for shelters observed up to 8 months, and about 50% for those observed over longer periods. Shelters were occupied by only one lobster at a time, but each accommodated an average 2.4 different lobsters over 1–4 months, and 10.7 lobsters over 25–30 months. Of the lobsters sighted in the study area at least five times, 39% returned to a particular shelter after absences ranging to more than 7 months. Received May 23, 1983 Accepted March 19, 1984