Simulation modelling of the effects of oil spills on population dynamics of northern fur seals

Models of population dynamics and migration were developed and combined with an oil spill simulation model to determine the effects of potential oil spills on the Pribilof Island fur seal (Callorhinus ursinus) population. In the population dynamics model, mortality of pups on land and juveniles up to 2 years of age is density-dependent, while that of older seals is age- and sex-specific and constant at all population sizes. Movement patterns of seals within the Bering Sea are functions of date, sexual status and age, conforming to probability distributions based on field observations of their movements and timing.

Two simulations of hypothetical 10 000-barrel oil spills were performed. One occurs near Unimak Pass during the peak migration of pregnant females to the Pribilof rookeries, oiling 3% of the total female population. The other occurs near St. Paul Island during the pupping season, and oils 2–4% of the female population. By comparison, about 16% of females die from natural causes each year. Depending on the assumed oil-induced mortality rate in the range 25–100%, ‘effective’ recovery of the popylation from these spills (i.e. the number of years before the oil-affected population numbers were within 1% of the non-affected population numbers) took 0–25 years.


Reed, M, D.P. French, J. Calambokidis, and J. Cubbage. 1989. Simulation modelling of the effects of oil spills on population dynamics of northern fur seals. Ecological Modelling 49:49-71.