PARENT SESSION
Poster Session 39: Late Breaking and Newsworthy Posters
Friday, August 12, 8:30 AM - 10:30 AM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Regional shift from larval supply- to disease-dominated dynamics in New England lobsters: A challenge to forecasting recruitment.

Wahle, Richard^*,1, Gibson, Mark², ¹ Bigelow Laboratory for Ocean Sciences, W. Boothbay Harbor, ME, USA² Rhode Island Department of Fish & Wildlife, Jamestown, RI, USA

ABSTRACT- Understanding the relative importance of pre- and post-settlement processes to the dynamics of marine open populations at multiple scales remains a central challenge in marine ecology. A practical application of this knowledge is in forecasting recruitment trends in fisheries, a goal that has been particularly elusive for many lobster and crab fisheries. In a case study with the American lobster (Homarus americanus), we describe the first demonstration for any clawed lobster the predictive relationship between a post-larval settlement index and the resultant abundance of so called pre-recruits, older lobsters about to enter the fishery. As part of a New England-wide effort to assess the predictive link between the settlement index - collected by divers - and subsequent pre-recruits - collected by trawls - we focus on a region of southern New England with a sufficient time series to evaluate such predictive relationships, and where shell disease is suspected to have caused significant mortality in recent years. In coastal Rhode Island pre-recruit lobster abundance peaked in 1993, and then began to falter somewhat before dropping precipitously after 1997, a trend coincident with the onset and spread of shell disease in southern New England. Importantly, though, not all of the decline in pre-recruits during the late 1990's can be attributed to shell disease. Prior to 1997 fully 88% of the variation in pre-recruits is explained by variable settlement alone. But once shell disease became prevalent it was necessary to include an additional disease severity term in a modified form of a standard Ricker stock-recruitment model to explain the further decline in pre-recruits. It is noteworthy that despite declining catches settlement has remained strong suggesting that a substantial portion of southern New England's lobster fishery is dependent on egg and larval production in offshore populations still unaffected by disease. The appropriate management response to this recent crisis will benefit from a better understanding of the source-sink linkages among regions.

Key words: Homarus americanus, stock-recruitment, forecasting, larvae