Recruitment Dynamics in an American Lobster (Homarus americanus) Population

Abstract

We examined relationships between successive life history stages of an American lobster (Homarus americanus) population for evidence of density-dependent control. Analysis of a time series of larval production estimates for the Northumberland Strait region of the southern Gulf of St. Lawrence during 1949–63 (D. J. Scarratt. 1964. J. Fish. Res. Board Can. 21: 661–680; D. J. Scarratt. 1973. J. Fish. Res. Board Can. 30: 1819–1824) provided no indication of density-dependent regulation during the pelagic larval phase. However, an asymptotic relationship between the final (fourth) larval stage and stock size 5–7 yr later was demonstrated, indicating the possibility of density-dependent regulation between larval settlement and subsequent recruitment to the fishery. A second analysis supported these results based on trends in population size over several generations. A recruitment mechanism of this type is highly stabilizing and can explain the apparent capacity of lobster populations to sustain high levels of fishing mortality. The postulated recruitment mechanism for Northumberland Strait lobsters may reflect competition for critical resources. We propose that shelter is an important limiting resource and that shelter competition experiments be undertaken in the field and laboratory to test this hypothesis. Finally, we demonstrate the use of a multistage recruitment model which accounts for the general form of observed interstage relationships. The asymptotic relationship between stage IV production and subsequent stock results in a stable population which is resilient to exploitation.