Effect of the T/B North Cape Oil Spill on the Surf Clam (Spisula Solidissima) in the Coastal Waters of Southern Rhode Island1

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ABSTRACT On 19 January 1996, the T/B North Cape grounded on the south shore of Rhode Island and spilled approximately 828,000 gallons of home heating oil. Storm waves mixed the oil into the water column, and currents transported the plume of contaminated water over an area of about 400 km2. Immediate post-spill observation of animals stranded on the beach within the impact area estimated 330,000 surf clams (Spisula solidissima), along with hundreds of thousands of crustaceans including lobsters and crabs. Field studies of the impact of the oil spill on the surf clam resource within the impact area and an adjacent control, unimpacted area were conducted over a 2-year period. Mortality of surf clams within the impact area was high. Using the density estimates of the adjacent control area, it is believed that most of the surf clams killed in the impact area were stranded ashore. More interesting, however, has been the recovery of the surf clam resource in the impact area, as compared to the control area. Densities of young of the year surf clams in the impact area, as observed in the winter/spring of 1997, about 1 year after the spill were very high, greater than 400/km2 at one station. Control area mean densities of the same year class were less than 2/m2 at all stations. A second field sampling conducted about 2 years after the spill indicated surf clam densities were reduced to maximum of 100/m2 within the impact area, and between 0–1/m2 in the control area. It is believed that the success of the post-spill set of surf clams in the impact area, as compared to the control area, is due to the loss of predators associated with the spill. Thus, with respect to the surf clams, this fishery resource has not only recovered, but has been enhanced by the spill.