Movement Patterns of Late-Stage Ovigerous Female Lobsters (Homarus Americanus Milne Edwards) at Jeddore, Nova Scotia

Abstract

A total of 217 late-stage ovigerous female lobsters, Homarus americanus, were carapace tagged from May 15 to June 20,1988, and another 14 tagged with ultrasonic transmitters from June 14 to August 12, 1988, in the Jeddore area of the eastern shore of Nova Scotia. Between May 25 and August 7,1988,47 of the carapace tagged lobsters were recaptured. Temperature and salinity were monitored in both Jeddore Harbour and Clam Bay throughout the study.

There was little evidence of migration of carapace or sonic tagged lobsters into die harbour from Clam Bay, although homing was observed for at least one sonic tagged lobster translocated into Clam Bay. A computer model of egg development in a variety of annual temperature regimes suggests that there is no physiological advantage for ovigerous females to either locate in the harbour year-round or to migrate seasonally into the harbour. Late-stage ovigerous females demonstrated 'resident* behaviour in areas with suitable lobster habitat (moving rarely, and only short distances), and 'transient* behaviour on featureless sand or gravel bottoms (where greater distances were covered, and at faster speeds). There appeared to be specific sites where hatching occurred. The activity of ovigerous females increased with egg development. This increase in movement did not appear to be temperature-related. Movement was not correlated with diel or tidal rhythms. It is suggested that most movement probably occurs due to changes in motivation of the animal based on food and shelter requirements and both intra- and interspecific interactions. Hatching was observed between July 19 and August 23,1988, requiring 4-7 days. Two sonic tagged females molted in the harbour 4-5 weeks after hatching.

The results of this and other recent studies in the Jeddore area suggest that hypotheses that 1) there exists a "longitudinal recruitment cell" on the Atlantic coast of Nova Scotia, and 2) that protected bays are important areas for larval development, may not be true. The harbour does not appear to be an important brood area. The predicted hatching dates of ovigerous female lobsters in both Clam Bay and Jeddore Harbour appear to leave sufficient time for subsequent larval development. The ovigerous females in the harbour contribute less than 20% of the egg production for the area as a whole. It is suggested that lobsters in Jeddore Harbour may be a largely resident population. In the late fall some lobsters probably migrate out of the harbour, returning in the spring or going to another nearshore area. Many, however, probably remain in the harbour over winter.