Distribution, abundance and biology of ringed seals (<i>Phoca hispida</i>): an overview

Abstract

The ringed seal (Phoca hispida) has a circumpolar Arctic distribution. Because of its great importance to northern communities and its role as the primary food of polar bears (Ursus maritimus) the ringed seal has been studied extensively in Canada, Alaska, Russia, Svalbard and Greenland as well as in the Baltic Sea and Karelian lakes. No clear-cut boundaries are known to separate ringed seal stocks in marine waters. Adult seals are thought to be relatively sedentary, but sub-adults sometimes disperse over long distances. Stable ice with good snow cover is considered the most productive habitat although production in pack ice has been little studied. Populations appear to be structured so that immature animals and young adults are consigned to sub-optimal habitat during the spring pupping and breeding season. Annual production in ringed seal populations, defined as the pup percentage in the total population after the late winter pupping season, is probably in the order of 18-24%. Most ~stimates of maximum sustainable yield are in the order of 7%.The world population of ringed seals is at least a few million. Methods of abundance estimation have included aerial surveys, dog searches and remote sensing of lairs and breathing holes, acoustic monitoring, correlation analysis by reference to sizes of polar bear populations, and inference from estimated energy requirements of bear populations. Aerial strip survey has been the method of choice for estimating seal densities over large areas. Adjustment factors to account for seals not hauled out at the time of the survey, for seals that dove ahead of the aircraft, and for seals on the ice within the surveyed strip but not detected by the observers, are required for estimates of absolute abundance.Male and female ringed seals are sexually mature by 5-7 years of age (earlier at Svalbard). Pupping usually occurs in March or early April and is followed by 5-7 weeks of lactation. Breeding takes place in mid to late May, and implantation is delayed for about 3 months. In at least some parts of their range, ringed seals feed mainly on schooling gadids from late autumn through early spring and on benthic crustaceans and polar cod (Boreogadus saida) from late spring through summer. Little feeding is done during the moult, which takes place in late spring and early summer. Pelagic crustaceans offshore and mysids inshore become important prey in late summer and early autumn in some areas. Ringed seals have several natural predators, the most important of which is the polar bear in most arctic regions. Arctic foxes (Alopex lagopus) kill a large percentage of pups in some areas.From a conservation perspective, the ringed seal appears to be secure. Levels of exploitation of arctic populations have usually been considered sustainable, except in the Okhotsk Sea. Large fluctuations in production of ringed seals in the Beaufort Sea and Amundsen Gulf are thought to be driven by natural variability in environmental conditions. While concern has been expressed about the potential imp...

Cadmium toxicity to ringed seals (Phoca hispida): an epidemiological study of possible cadmium-induced nephropathy and osteodystrophy in ringed seals (Phoca hispida) from Qaanaaq in Northwest Greenland

“…Hence no effects on the calcium metabolism could be detected as functions of age, pregnancy or endocrinological changes. Female ringed seals do not go into a postmenopausale period as women and that could explain the maintained calcium homeostasis (Smith 1987, Reeves 1998). …”

Probabilistic biokinetic modelling of radiocaesium uptake in Arctic seal species: verification of modelled data with empirical observations

“…The ringed seal (Phoca hispida) is the smallest of the seal species, with an adult mean length of about 130 cm and mean adult body mass between 50 and 90 kg (Lydersen and Gjertz, 1987). The most abundant and widely distributed seal species in the northern hemisphere (Reeves, 1998), ringed seals are also the most abundant seal on the Svalbard archipelago, with an estimated population size of more than a hundred thousand (Lydersen, 1998). These seals occur in the archipelago all year round, but are most numerous during winter to early summer when there is ice in the fjords and bays.…”

Movements and diving of adult ringed seals ( Phoca hispida ) in Svalbard

“…They associate closely with land-fast ice and drifting pack ice for large parts of the year, and may be found in waters of all depths (Reeves 1998).…”

“…Ringed seals are believed to feed intensively from late summer to early spring to replenish their fat losses in connection with breeding and moulting (Ryg et al 1990;Lydersen 1998;Reeves 1998). Prey type varies according to region and season, but pelagic schooling ®sh dominate the diet from late autumn to spring, while in late summer and early autumn pelagic crustaceans dominate (Reeves 1998).…”

“…Ringed seals (Phoca hispida) are found throughout most of the Arctic Ocean and bordering seas (Frost and Lowry 1981;Reeves 1998). They associate closely with land-fast ice and drifting pack ice for large parts of the year, and may be found in waters of all depths (Reeves 1998).…”