Movement and activity of the American lobster (Homarus americanus) and implications for the species' ecology and demography

Abstract

The overarching goal of this thesis was to enhance our understanding of the implications of benthic movements by American lobster Homarus americanus to the species’ ecology and demography. The first chapter discusses the use of an ultrasonic telemetry system to track juvenile lobsters in nature for the first time. Juveniles were highly active and mobile, and they behaved as “central place foragers”, which kept them on productive but patchy nursery grounds despite the extensive movements they displayed. Juveniles did not display an increase in time spent outside of shelter or average daily home range with increasing body size, as was predicted in the literature. The second chapter discusses the use of two complimentary ultrasonic systems to simultaneously track juvenile, adolescent and adult lobster for the first time. This study confirmed some of the observations made in Chapter 1, such as lobsters being very active, displaying diurnal activity rhythms (more active at night than during the day), and behaving as central place foragers, as well as juveniles not demonstrating an increase in activity with increasing body size. It did, however, reveal ontogenetic changes in behavior over the expanded size range, with daily home range increasing gradually with increasing body size, and study length displacements being markedly greater for adolescents/adults than for juveniles. The third chapter re-analyzed data from an extensive mark-recapture study conducted in the southern Gulf of St. Lawrence between 1980-1996 to estimate, for the first time, the relative contribution of benthic movements and larval dispersal to demographic connectivity in lobster. Estimates of pelagic and benthic movements were comparable, when accounting for the fact that adults can disperse over the course of several years while larvae disperse over a single season only. This novel finding, along with the fact that benthic movements are not constrained by currents the way pelagic dispersal is, and that lobsters move relatively little in our study area compared to other parts of the species’ range, suggest strongly that more consideration should be given to the contribution of benthic movements to connectivity and stock structure in the management of the American lobster.