Natural Dynamics of Population Structure and Habitat Use of the Lobster, Homarus americanus, in a Shallow Cove

We report the results of a nonmanipulative field study of the lobster, Homarus americanus, using long-term behavioral observations of marked individuals. We observed a freely mobile population in an open shallow cove habitat (50 m x 150 m) in Buzzards Bay, Massachusetts. Lobsters larger than 50 mm carapace length (CL) living in or entering the study site were marked individually (334 during the 19-month study). Without further manipulation, the animals were observed as long as they remained in the study site. Of the marked animals, 48% were transient, i.e., seen only once. The population was made up largely of subadults with a sex ratio of M:F = 1.8. The summer and fall resident population consisted of about 30 animals. Maximum residency was over 13 months. Half of the resident population, mostly small animals (50-59 mm CL), apparently overwintered in the site. A distinct peak in molting occurred both years in the spring at a water temperature of about 15°C. Injured animals were seen frequently (26% of the population) including a high proportion of mature resident males missing claws. Most other injured animals were transient (60%). These results suggest that the shallow cove is used as a refuge for injured mature males. Activity was strictly nocturnal with a peak 1-3 h after sunset and declining through the night. Activity levels were equal for both sexes. Overall activity was correlated with seasonal variations in water temperature (0-24°C). At times, activity was correlated more with molting (premolt activity peak) than with temperature. Behavioral interactions in this population are described in a companion paper (Karnofsky et al., 1989).