Population model for sea otters in western Prince William sound. Restoration project 93043-3. Sea otter demographics. Exxon Valdez oil spill restoration project final report

A large portion of the western Prince William Sound (PWS) sea otter population was killed by the Exxon Valdez oil spill in March 1989, but little is known about the dynamics of the population before the spill in March 1989, or the rate at which the population can be expected to recover. We estimated age-specific reproductive and survival rates for the western PWS population before the spill based on examinations or reproductive tracts and the age structure of carcasses collected in 1989. We developed a new technique for estimating survival rates that uses age-structure and age-at-death data, and does not require the assumption of a stable age structure. Because of the lack of data for estimating juvenile survival rates, were considered a series of 4 potential scenarios. The population was projected to decrease slightly during the first year under all of the scenarios and then begin increasing, achieving maximum rates of increase ranging from 10% to 14% per year and recovering to its estimated 1985 population size in 10 to 23 years. Projected population sizes during the first few years after the spill are in broad agreement with estimates based on boat surveys in 1990, 1991, and 1993.