ABSTRACT: The duration of maternal foraging trips has been regarded as an indicator of foraging conditions in many marine mammals, including northern fur seals Callorhinus ursinus (NFS). However, previous work has focused on individual variation, was conducted during limited portions of the lactation period, and/or reached conclusions based on relatively small sample sizes. Here, we build upon the substantial foundations of this previous work to establish maternal foraging trip duration (MFTD) as an index of foraging success at the rookery level. We found that a 1 d increase in rookery-averaged MFTD corresponded to a 6.52% reduction in the average mass of female pups. Furthermore, rookery-averaged MFTD increased by 0.34 d per 1°C increase in average ocean bottom temperature. The magnitude of variation observed in both MFTD and pup mass is likely too small to help explain the general decline in population size seen over recent decades. However, the correlation between rookery-averaged MFTD and pup mass highlights the potential power of the MFTD index to detect bottom-up effects on pup growth, a likely indicator of survival. Furthermore, when compared with concurrently conducted studies on prey distribution, availability, and quality, the relationship between MFTD and bottom temperature suggests a northward shift in distribution of NFS preferred prey, walleye pollock Gadus chalcogrammus, that is associated with an increase in trip duration across the study period. Thus, rookery-averaged MFTD is a promising metric for tracking broad environmental changes, such as northerly shifts in the Eastern Bering Sea cold pool.

中文翻译：

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产妇觅食旅行持续时间作为北部海狗觅食和生殖成功的人口水平指标

摘要：母体觅食旅行的持续时间已被视为许多海洋哺乳动物，包括北部海狗海豹Callorhinus ursinus觅食状况的指标（NFS）。但是，先前的工作集中在个体差异上，是在哺乳期的有限时间内进行的，和/或基于相对较小的样本量得出的结论。在这里，我们以先前工作的坚实基础为基础，建立产妇觅食旅行持续时间（MFTD），作为在鸡群一级觅食成功的指标。我们发现，家禽平均MFTD的增加1 d对应于雌性幼仔的平均质量减少6.52％。此外，平均海底温度每升高1°C，洋行平均MFTD就会增加0.34 d。MFTD和幼犬质量中观察到的变化幅度可能太小，无法解释近几十年来总体规模的下降。然而，羊群平均MFTD与幼犬质量之间的相关性凸显了MFTD指数检测自下而上对幼犬生长的影响的潜在能力，这可能是生存的指标。此外，与同时进行的猎物分布，可获得性和质量的研究相比，MFTD与底部温度之间的关系表明，NFS首选猎物壁角狭鳕的分布向北移动。Gadus chalcogrammus，与整个研究期间的出行时间增加有关。因此，平均车队平均MFTD是跟踪广泛的环境变化（例如东白令海冷池向北移动）的有前途的指标。