Survivorship of a declining population of southern elephant seals, Mirounga leonina, in relation to age, sex and cohort
Survivorship of a declining population of southern elephant seals, Mirounga leonina, in relation to age, sex and cohort
复制标题
南象海豹 (Mirounga leonina) 种群数量下降时的存活率与年龄、性别和队列的关系
作者：
Pierre A. Pistorius;M. Bester;SP Kirkman
摘要这项研究量化了幼年和成年象海豹的年龄和性别存活率，并测试了马里恩岛南部象海豹种群年龄特定存活率的年际差异。从1983年开始，马里恩岛的幼崽每年都被标记，一致的重新捕获计划产生了数据，并使用软件包Mark进行分析，以获得生存和捕获概率的最大似然估计。平均1年生存率为0.5 8和0.6 2，前3 年的平均存活率分别为0.69和0.74。4~9年，男性和女性的平均存活率分别为0.66和0.75。10-13岁象海豹的存活估计也给出了，尽管这些估计是基于非常小的样本量。比较了早期(主要是1983-1987年的队列)和较晚的(主要是1988-1992年的队列)的年龄特定生存估计的平均值，观察到第四和第五年的男性存活以及第四年的女性存活显著减少。相对较低的成体存活率被认为是马里恩岛种群数量下降的直接原因，而能量需求相对较高的象海豹存活率下降所导致的食物限制是导致马里恩岛种群数量下降的最终原因。虽然没有与人口下降挂钩，但1987、1990和1993年被确定为死亡率高的年份。
Abstract This study quantified both the age- and sex-specific survival rates of juveniles and adults, and tested for interannual differences in age-specific survival rates of the southern elephant seal population at Marion Island. Pups were tagged on an annual basis from 1983 onwards at Marion Island, and a consistent recapture program yielded data that was analysed using the software package MARK to obtain maximum-likelihood estimates of survival and capture probability. On average, 1st-year survival was 0.58 and 0.62, and survival rate averaged over the first 3 years of life, 0.69 and 0.74 for males and females, respectively. From years 4 to 9, the average survival rate was 0.66 and 0.75 for males and females, respectively. Survival estimates for elephant seals in their 10th–13th year are also presented, although these are based on very small sample sizes. Averages of age-specific survival estimates from the earlier (mostly 1983–1987 cohorts) and later (mostly 1988–1992 cohorts) periods were compared and considerable reductions were observed in 4th- and 5th-year male survival, and 4th-year female survival. The comparatively low adult survival is suggested as the proximate cause, and food limitation as deduced from the decline in survival of elephant seals with comparatively high energetic demands as the ultimate cause behind the population decline at Marion Island. Although not tied in with the decline of the population, 1987, 1990 and 1993 were identified as high-mortality years.