Calculations were made of herring gull and common tern population recovery from potential oilspill damage in the U.S. mid-Atlantic Outer Continental Shelf (OCS) oil leasing area. Population recovery was examined using a density-dependent age-specific life history table for each species. Both a deterministic and a stochastic approach were used in the calculations. In the deterministic approach, it was assumed that an oilspill contact to a seabird colony had occurred. Using the density-dependent model, population recovery was calculated for several different mortality scenarios. Assuming that all age classes suffer 95% mortality from an oilspill contact, a worst case scenario, it was estimated that the herring gull and common tern populations could recover to their pre-spill levels in approximately 45 years and more than 100 years, respectively. In the stochastic approach, the probabilities of oilspill contacts to these seabird colonies were calculated using an oilspill trajectory analysis model. Oilspill contacts to these colonies were simulated during the expected 30 year active life of the lease area. For each lease lifetime, the number of oilspill contacts to a seabird colony was sampled from a Poisson distribution and assigned randomly on a seasonal basis. This analysis indicated that the oilspill risks from the development of proposed lease tracts in the mid-Atlantic region pose minimal risk (3–5%) of severe population reduction for both herring gulls and common terns. If the oilspill risks from tanker transportation of crude oil imports are included along with the proposed lease tracts, then the risks of severe population reduction are increased to approximately 10% for herring gulls and 18% for common terns.
