GEOGRAPHICAL TRENDS IN WEIGHT AND CONDITION INDEX OF SURFCLAMS (SPISULA SOLIDISSIMA) IN THE MID-ATLANTIC BIGHT

A survey of surfclam (Spisula solidissima) stocks was conducted in an area from northern New Jersey to southern Virginia during June and July 2004 to evaluate the progress of mortality, apparently related to warming of the Mid-Atlantic Bight. One component of the survey was the measurement of condition index at 146 locations from the Delmarva Peninsula to northern New Jersey. The program followed a pilot study in 2002 that suggested that surfclam mortality off Delmarva was likely caused by warmer temperatures that decreased feeding and subsequently led to starvation. Condition index was highest inshore, with the exception of a few of the most inshore stations, and lowest at the offshore edge of the clam's range. An estimate of meat weight for a standard 120-mm clam, from site-specific length weight regressions, revealed that the animals near the center of the inshore offshore distribution had a greater weight per length than those living at the edges of the clam's range, probably a result of the influence of temperature on feeding and growth. Low condition in the extreme inshore locations suggests that warmer temperatures continue to affect surfclam nutrition negatively and indicates the continued susceptibility of clams along the southern and inshore range boundary to warming in the Mid-Atlantic Bight. Low condition offshore may be the result of a delay in gametogenesis or inadequate nutrition resulting from low temperatures reducing feeding rate and food supply.