© 2005 International Council for the Exploration of the Sea
Bathymetric shift in the distribution of Atlantic surfclams: response to warmer ocean temperature
National Marine Fisheries Service, Northeast Fisheries Science Center 166 Water Street, Woods Hole, MA 02543, USA
*tel: +1 508 495 2000. e-mail: james.weinberg{at}noaa.gov.
Standard research vessel surveys during the 1980s and early 1990s demonstrated that Atlantic surfclams (Spisula solidissima solidissima) were common in the southern portion of their range (37–38°N) along the east coast of North America in the Delmarva region. Based on data from these surveys, the probability of capturing surfclams in shallow water (i.e. 20 m) tows of the Delmarva region was 75–85% in 1994 and 1997. In 1999 and 2002, this probability declined to 40–55%. The probability of capturing surfclams in survey tows from deeper waters (40–50 m) also declined, but this change was relatively small compared with that in shallower water. These changes were not the result of commercial clam fishing. Unusually warm water, which induces thermal stress in S. s. solidissima, was prevalent within the period from 1999 to 2002 over the Delmarva continental shelf during fall when annual bottom temperature was peaking. The combined effects of poor physiological condition and thermal stress likely resulted in mortality of Atlantic surfclams in shallow water habitats in the Delmarva region. This resulted in a shift in the bathymetric distribution of the population to deeper water. Between 1982 and 1997, most of the surfclams in the Delmarva region occurred at depths between 25 and 35 m, whereas in 1999 and 2002, most of the Delmarva population occurred at 35–40 m.
Keywords: Atlantic surfclams, bivalve, climate change, distribution, ocean temperature, spisula, thermal stress
Received 29 June 2004; accepted 27 April 2005.