Data from: Age specific survival rates of Steller sea lions at rookeries with divergent population trends in the Russian Far East

After a dramatic population decline, Steller sea lions have begun to recover throughout most of their range. However, Steller sea lions in the Western Aleutians and Commander Islands are continuing to decline. Comparing survival rates between regions with different population trends may provide insights into the factors driving the dynamics, but published data on vital rates have been extremely scarce, especially in regions where the populations are still declining. Fortunately, an unprecedented dataset of marked Steller sea lions at rookeries in the Russian Far East is available, allowing us to determine age and sex specific survival in sea lions up to 22 years old. We focused on survival rates in three areas in the Russian range with differing population trends: the Commander Islands (Medny Island rookery), Eastern Kamchatka (Kozlov Cape rookery) and the Kuril Islands (four rookeries). Survival rates differed between these three regions, though not necessarily as predicted by population trends. Pup survival was higher where the populations were declining (Medny Island) or not recovering (Kozlov Cape) than in all Kuril Island rookeries. The lowest adult (> 3 years old) female survival was found on Medny Island and this may be responsible for the continued population decline there. However, the highest adult survival was found at Kozlov Cape, not in the Kuril Islands where the population is increasing, so we suggest that differences in birth rates might be an important driver of these divergent population trends. High pup survival on the Commander Islands and Kamchatka Coast may be a consequence of less frequent (e.g. biennial) reproduction there, which may permit females that skip birth years to invest more in their offspring, leading to higher pup survival, but this hypothesis awaits measurement of birth rates in these areas.

在经历剧烈的种群数量下降后，北海狮（Steller sea lion）在其绝大多数分布范围内已开始恢复。然而，西阿留申群岛（Western Aleutians）与指挥官群岛（Commander Islands）的北海狮种群仍在持续下降。
对比不同种群动态区域间的存活率，或可揭示驱动种群动态变化的核心因素，但已发表的生命率相关数据极为匮乏，尤其是在种群仍处于下降态势的区域。
所幸的是，我们获取了俄罗斯远东地区繁殖地内标记北海狮的空前数据集，借此可明确22龄以内北海狮按年龄与性别划分的存活率。本研究聚焦俄罗斯分布范围内三个种群动态各异区域的存活率：指挥官群岛（Commander Islands）的梅德尼岛（Medny Island）繁殖地、堪察加半岛（Kamchatka）东部的科兹洛夫角（Kozlov Cape）繁殖地以及千岛群岛（Kuril Islands）的四个繁殖地。
这三个区域的存活率存在显著差异，但其差异未必与种群动态的预测趋势相符。种群处于下降态势（梅德尼岛）或未恢复（科兹洛夫角）的区域，其幼崽存活率均高于所有千岛群岛的繁殖地。梅德尼岛的成年（3龄以上）雌性北海狮存活率最低，这或为该区域种群持续下降的关键诱因。
但科兹洛夫角的成年个体存活率最高，而非种群数量正增长的千岛群岛，据此我们推测，出生率差异或许是导致这些种群动态分化的重要驱动因素。
指挥官群岛与堪察加海岸的幼崽存活率较高，或源于当地繁殖频次较低（例如每两年繁殖一次）：这使得跳过繁殖年的雌性个体可将更多资源投入到后代抚育中，进而提升幼崽存活率，但该假说仍有待上述区域出生率实测数据的验证。