Abstract
Small groups of harbour seals are scattered along the entire Norwegian coastline and in some fjords. Some of these groups are separated by long distances from larger populations, and these groups may run a risk of extinction due to demographic and environmental stochasticity. Here we studied the viability of small groups of harbour seals assuming no migration between the smaller, isolated groups and larger populations. We applied a stochastic population model and population parameters recorded for harbour seals at the Norwegian coast. The model was divided into twenty-one different age categories (0–20 years of age), each with potential different survival and reproduction probabilities. Survival and reproduction were modelled at the level of the individual. The Minimum Viable Population (MVP) was defined as the minimum population size that ensures ≥95 % probability that the population will survive for a period of 100 years. For a hypothetical population that was stable using a deterministic population model, the MVP was about 50 seals. In a population with annual growth of 1 % the MVP was estimated at 30 seals. If hunting mortality of one seal per year was added to the latter population and the hunting mortality was random among all age groups of males and females, the MVP increased to about 120 seals.
