Estimates of pup production, age at first parturition and natural mortality for hooded seals in the west ice

Abstract

An analysis of the population of hooded seals breeding in the West Ice near Jan Mayen was carried out on the basis of catch statistics for 1946-1978 and age samples comprising a total of 5 094 four years old and older breeding females. A deterministic population model for females without density dependent control was constructed and applied to estimate pup production, age at first parturition and natural mortality. The method was based on minimizing devations between the age structure of the hypothetic population generated by the model and the age composition in samples. The mean age at first parturition was estimated to 4.9 years. Production was estimated to 95 000 pups in 1956 (samples collected in 1961-1965) and 54 000 pups in 1978 (samples 1972-1978). Combining these figures in the model, instantaneous natural mortality was estimated to 0.12. By projection, pup production in 1979 was estimated to 50 000 pups from a population of 100 000 females. These figures are, however, very sensitive to the estimate of natural mortality.