Pup mortality in a rapidly declining harbour seal (Phoca vitulina) population
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The harbour seal population in Orkney, off the north coast of Scotland, has reduced by 65% between 2001 and 2010. The cause(s) of this decline are unknown but must affect the demographic parameters of the population. Here, satellite telemetry data were used to test the hypothesis that increased pup mortality could be a primary driver of the decline in Orkney. Pup mortality and tag failure parameters were estimated from the duration of operation of atellite tags deployed on harbour seal pups from the Orkney population (n = 4) and from another population on the west coast of Scotland (n = 24) where abundance was stable. Survival probabilities from both populations were best represented by a common gamma distribution and were not different from one another, suggesting that increased pup mortality is unlikely to be the primary agent in the Orkney population decline. The estimated probability of surviving to 6 months was 0.390 (95% CI 0.297 – 0.648) and tag failure was represented by a Gaussian distribution, with estimated mean 270 (95% CI = 198 – 288) and s.d. 21 (95% CI = 1 – 66) days. These results suggest that adult survival is the most likely proximate cause of the decline. They also demonstrate a novel technique for attaining age-specific mortality rates from telemetry data.
Hanson , N N , Thompson , D , Duck , C D , Moss , S & Lonergan , M 2013 , ' Pup mortality in a rapidly declining harbour seal ( Phoca vitulina ) population ' PLoS One , vol 8 , no. 11 , e80727 . DOI: 10.1371/journal.pone.0080727
© 2013 Hanson et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
DescriptionThis research was funded by the Scottish Government (www.scotland.gov.uk), Scottish Natural Heritage (www.snh.gov.uk) and the Natural Environment Research Council (www.nerc.ac.uk). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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