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ICES Journal of Marine Science: Journal du Conseil 2006 63(6):1136-1144; doi:10.1016/j.icesjms.2006.04.001
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© 2006 International Council for the Exploration of the Sea

Growth and population parameters of ringed seals (Pusa hispida) from Svalbard, Norway, 2002–2004

Bjørn A. Kraffta, Kit M. Kovacsa,*, Anne Kirstine Frieb, Tore Haugb and Christian Lydersena

a Norwegian Polar Institute 9296 Tromsø, Norway
b Institute of Marine Research 9294 Tromsø, Norway

*Correspondence to K. M. Kovacs: tel: +47 777 50526; fax: +47 777 50501. e-mail: kovacs{at}npolar.no.

Samples were collected in Svalbard, Norway, during April and May 2002–2004 from 272 ringed seals (Pusa hispida; 62.5% males, 37.5% females) to study growth and population parameters. The age of the animals ranged from 1 to 32 years. Asymptotic values for standard length and body mass were 127.7 ± 1.6 (s.e.) cm and 69.0 ± 2.7 kg for males (maxima: 144 cm and 92 kg) and 127.6 ± 2.3 cm and 68.9 ± 2.5 kg for females (maxima: 141 cm and 91 kg). All animals were sexually mature at an age ≥6 years and the ovulation rate was 0.86. Mean Age at Maturity (MAM) was 4.2 ± 0.2 years for males and 3.5 ± 0.3 years for females, values significantly lower than calculated for ringed seals from the same area 20 years ago. This change in MAM suggests that either the prey base for ringed seals in the area has increased or alternatively that the density of ringed seals has declined, such that more resources are available per capita. If the climate of the Arctic changes in the manner predicted by a host of climate-change scenarios, it is likely to have a strong impact on ringed seal populations in future, although there are no data to suggest that dramatic changes have taken place yet in fish and invertebrate populations in the Svalbard area. Although cause-and-effect cannot be firmly established, there is a possibility that the substantial increase in the number of polar bears (Ursus maritimus) over the past 20 years, since hunting the species in Svalbard ceased in 1973, may have played a role in the observed change in the ringed seal population.

Keywords: demography, ecosystem monitoring, growth curves, Phoca spp., predation pressure, Pusa hispida

Received 5 September 2005; accepted 1 April 2006.


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