Modeling the Impact of Climate Change on Larval Connectivity and Recruitment of the American Lobster off of Southern New England
Funding Agency: NOAA – Saltonstall-Kennedy Program
Investigators:
James Churchill (Woods Hole Oceanographic Institution)
Richard A. Wahle (University of Maine)
G. Cowles and Kevin Stokesbury (SMAST, U. Mass Dartmouth)
Robert Glenn and Tracy Pugh (Mass. Division of Marine Fisheries, New Bedford, MA)
Lobster Management Area-2 (LMA-2), comprised of inshore waters off of Rhode Island and the southern Massachusetts, had until the beginning of the current century been one of the most valuable commercial fisheries of southern New England. In the late 1990s, the American lobster fishery in LMA-2 employed approximately 700 lobstermen and produced annual harvests with a value of greater than $28,000,000. However, commercial landings from LMA-2 have been at historically low levels since 2003, resulting in a > 50% decline in the number of lobstermen active in the LMA-2 fishery. The falloff in lobster landings has been coupled with documented declines in lobster abundance and postlarval settlement in LMA-2 and with significant warming of coastal waters off of southern New England. Since 2000, temperatures recorded in eastern LMA-2 (at Woods Hole and Cleveland Ledge, MA) have shown a dramatic increase in the number of days with water temperature > 20 oC. This is significant as there is a growing body of evidence indicating that 20 oC marks a temperature stress threshold for American lobsters. A rise in water temperature above 20 oC has been linked with depression of immunocompetence in lobsters and with an increased incidence of disease. Furthermore, rising water temperatures in LMA-2 is likely responsible for an offshore shift in the distribution of egg-bearing female lobsters off of southern New England. Female lobsters in LMA-2 have historically migrated into shallow water during spring to release eggs. Recent data from commercial hauls and fisheries-independent surveys indicate that female lobsters are now found primarily in deeper, colder waters during the critical period of egg release, a behavior consistent with laboratory studies indicating that summer-acclimated lobsters prefer water with temperature between 12 and 18 °C, and actively avoid water warmer than approximately 19 °C.
LMA-2 thus stands out as an area where rising ocean temperatures may have significantly impacted lobster behavior and early-stage recruitment, and have precipitated a sharp decline in the overall lobster population. Management of the lobster resource in LMA-2, and other areas that may experience a similar change in environment, will clearly benefit by a better understanding of how early-stage lobster recruitment is impacted by warming ocean waters. Towards this end, our team will employ data analysis and biophysical modeling to diagnose the impact of rising ocean temperatures, and the geographic shift in lobster egg release, on postlarval lobster settlement and early-stage survival in LMA-2. This work will have two overarching objectives: 1) Determine the impact of the shifting egg-bearing female population on lobster recruitment off southern Massachusetts and Rhode Island, and 2) Determine how the survival of recently settled juveniles is impacted by increasing near-shore water temperatures.
To meet Objective 1, we will employ a coupled biophysical modeling system comprised of a high-resolution regional hydrodynamic model (SEMASS-FVCOM) of the coastal ocean off of Massachusetts and New York and an Individual-Based Model (IBM) of lobster larval transport.
To meet Objective 2, we will use the temperatures derived from SEMASS-FVCOM to characterize the near-bottom thermal stress experienced by newly-settled juveniles in the coastal zone of LMA-2.
Throughout the course of the project we will reach out to the lobsterman community and to lobster managers, apprising them of our findings and seeking their feedback. We expect our findings to useful in managing the LMA-2 lobster resource. For example, they will be of value to the Atlantic States Marine Fisheries Commission Lobster Management Board in formulating target reference points for rebuilding the southeastern New England lobster stock. All of our findings and the IBM code will be posted on the project website. The code will be will be made as user-friendly as possible so that it can be employed by researchers and/or managers with interest in examining the impacts of environment change on lobsters (or similar species) in other regions.
Image (above): Figure 6. Observations of ovigerous females bearing late-stage eggs from a commercial at-sea sampling in the Massachusetts portion of LMA-2 from: 1992 – 1995, 2006 – 2008, and 2009 – 2010.