Abstract
The harbour seals (Phoca vitulina) in Svalbard are the northernmost population of this species. The population size is thought to be less than 1,000 individuals; these animals reside principally within a national park on Prins Karls Forland on the west coast of Spitsbergen, Svalbard, at about 78°20′N. The material presented in this study was collected from 367 live-captured animals, aged based on growth layers read from stained, decalcified incisor sections (except for pups of the year). Standard length (F1,246=45.70, P<0.0001) and body mass (F1,258=25.28; P<0.0001) were both significantly influenced by sex when age was taken into account. Adult males are both longer [152.9±4.8 (SE) vs 140.1±2.0 cm, standard length] and heavier (104.0±5.0 vs 83.2±2.7 kg, body mass) than adult females in this population. Age at sexual maturity was assessed based on analyses of sex hormones. Testosterone levels in males showed an abrupt increase at 6 years of age, while estradiol levels in females increased from age 4. The reproductive rate of adult females was 0.93. The longevity of Svalbard harbour seals was short compared to harbour-seal populations from other areas. However, these seals are not exposed to terrestrial predation; there is no known mortality due to fisheries or hunting and their pollution burdens are low. Extreme seasonality and perhaps other harsh environmental conditions at the northern edge of this species’ distribution may exert long-term low levels of stress that result in short life span, or there are currently unknown acute sources of mortality in this population. To our knowledge, this is the first study of population parameters on a pinniped species using cross-sectional, non-terminal sampling.
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Acknowledgements
This study was funded by University Studies on Svalbard (UNIS), the Norwegian Polar Institute and the Norwegian Research Council (the “Arctic Light and Heat”—Research Programme). We thank Magnus Andersen, Signe May Andersen, Christian Jørgensen, Bjørn Krafft, Hans Lund and Sonja Reder for their help with the fieldwork, Dr. Ward Testa and Dr. Bruce Mate for interesting discussions regarding potential sources of mortality, and Dr. Jon Aars and Dr. Peter Corkeron for valuable advice regarding revision of the manuscript.
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Lydersen, C., Kovacs, K.M. Growth and population parameters of the world’s northernmost harbour seals Phoca vitulina residing in Svalbard, Norway. Polar Biol 28, 156–163 (2005). https://doi.org/10.1007/s00300-004-0656-7
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DOI: https://doi.org/10.1007/s00300-004-0656-7