Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews, Fife, United Kingdom.
PLoS One. 2013 Nov 27;8(11):e80727. doi: 10.1371/journal.pone.0080727. eCollection 2013.
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 satellite tags deployed on harbour seal pups from the Orkney population (n = 24) 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.
苏格兰北海岸奥克尼群岛的港湾海豹数量在 2001 年至 2010 年间减少了 65%。造成这种下降的原因尚不清楚，但肯定会影响到该种群的人口统计参数。在这里，卫星遥测数据被用于检验以下假设，即幼崽死亡率的增加可能是奥克尼种群数量下降的主要驱动因素。利用部署在奥克尼种群（n=24）和苏格兰西海岸另一种群（n=24）幼海豹身上的卫星标签的运行时间来估计幼崽死亡率和标签失效参数，在该西海岸种群中，海豹数量稳定。两个种群的生存概率都由一个通用伽马分布最佳表示，彼此之间没有差异，这表明幼崽死亡率的增加不太可能是奥克尼种群数量下降的主要原因。从两个种群中估计的 6 个月存活率为 0.390（95%置信区间 0.297-0.648），标签失效由正态分布表示，估计平均值为 270（95%置信区间 198-288），标准差为 21（95%置信区间 1-66）天。这些结果表明，成年海豹的存活率是导致数量下降的最可能的直接原因。它们还展示了一种从遥测数据中获得特定年龄死亡率的新方法。
