Local egg production and larval losses to advection contribute to interannual and long-term variability of American lobster (Homarus americanus) settlement intensity

Abstract

American lobster (Homarus americanus) egg production and settlement intensity were examined over a 19-year period (1995–2013) in the Gulf of St. Lawrence at the Magdalen Islands (MI), where the population is spatially isolated during the benthic phase. Settlement and hatch dates by year were back-calculated from observed young-of-the-year size structure and juvenile and larval growth models. Drift of locally released larvae, from stage I to the end of stage III, was simulated using an ocean circulation model. Settlement intensity was related positively to egg production and negatively to drift distance. There was a strong positive trend in settlement intensity explained largely by increasing egg production, as well as by declining larval duration and drift distance. In the last years of the study, settlement intensity may have been limited by nursery saturation. The results suggest that demographic connectivity through larval drift is highly dynamic in time and that it declined during our study period. The demographic dependence of the MI lobster population on other populations in the Gulf of St. Lawrence is probably low.