Harp seals as indicators of the Barents Sea ecosystem

Abstract

Abstract In 1960–1994, harp seal ( Pagophilus groenlandica ) population ecology was studied in the White Sea. In the 1980s, substantial changes were revealed in the population ecology, affecting the distribution, migrations, age composition and breeding of the seals. In 1982–1989, unusual harp seal invasions were observed in the estuaries of the rivers flowing into the White Sea (Severnaja Dvina, Koida), movements of seals to the Murmansk coast in summer, and the presence of harp seals in summer and autumn in the White Sea. A sharp reduction in the abundance of younger animals on moulting grounds was also noted, which may indicate high mortality of animals during their first year of life. This trend also characterized the age composition of breeding females on breeding grounds. In the 1980s, harp seal females attained sexual maturity later than normal, and the rates of follicle maturation in ovaries slowed down. Pup weight also decreased. The changes in the ecology of the White Sea harp seal population occurred at a time of profound changes in the Barents Sea ecosystem in the 1980s under the influence of human economic activities. A sharp reduction in fish stocks, particularly polar cod ( Boreogadus saida ) and capelin ( Mallotus villosus ), resulted in deterioration of feeding conditions and subsequent changes in the population ecology. The results of the investigations point out the potential of using harp seals as specific indicators of the state of the ecosystem.