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Trade-offs between foraging efficiency and pup feeding rate of lactating northern fur seals in a declining population

机译：在人口减少的情况下，北部哺乳期的觅食效率与幼崽摄食率之间的取舍

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Foraging strategies and their resulting efficiency (energy gain to cost ratio) affect animals' survival and reproductive success and can be linked to population dynamics. However, they have rarely been studied quantitatively in free-ranging animals. We investigated foraging strategies and efficiencies of wild northern fur seals Callorhinus ursinus during their breeding season to understand potential links to the observed population decline in the Bering Sea. We equipped 20 lactating females with biologgers to determine at-sea foraging behaviours. We measured energy expenditure while foraging using the doubly-labelled water method, and energy gained using (1) the types and energy densities of prey consumed, and (2) the number of prey capture attempts (from acceleration data). Our results show that seals employed 2 foraging strategies: one group (40%) fed mostly in oceanic waters on small, high energy-density prey, while the other (60%) stayed over the shallow continental shelf feeding mostly on larger, lower quality fish. Females foraging in oceanic waters captured 3 times more prey, and had double the foraging efficiencies of females that foraged on-shelf in neritic waters. However, neritic seals made comparatively shorter trips, and likely fed their pups similar to 20 to 25% more frequently. The presence of these strategies which either favor foraging efficiency (energy) or frequency of nursing (time) might be maintained in the population because they have similar net fitness outcomes. However, neither strategy appears to simultaneously maximize time and energy allocated to nursing, with potential impacts on the survival of pups during their first year at sea.
机译：觅食策略及其产生的效率（能量获取成本比）会影响动物的生存和繁殖成功，并可与种群动态联系起来。但是，很少在自由放养的动物中对它们进行定量研究。我们调查了野生北海狗海豹Callorhinus ursinus在繁殖季节的觅食策略和效率，以了解与观察到的白令海人口下降的潜在联系。我们为20名哺乳期雌性动物配备了生物记录仪，以确定海上觅食行为。我们使用双标签水法测量了觅食时的能量消耗，并使用（1）消耗的猎物的类型和能量密度以及（2）捕获猎物的次数（来自加速度数据）获得了能量。我们的研究结果表明，海豹采用两种觅食策略：一组（40％）主要在海域中以高能量密度的小型猎物为食，而另一组（60％）则在浅大陆架上为食，主要以较大，质量较低的食性为食鱼。在海洋水域中觅食的雌性捕获的猎物多出3倍，并且在野性水域中现成觅食的雌性的觅食效率提高了一倍。但是，海豹幼崽旅行的时间相对较短，它们喂食幼崽的频率可能会提高20％至25％。这些有利于觅食效率（能量）或护理频率（时间）的策略可能在人群中得以维持，因为它们具有相似的净适应性结果。但是，这两种策略都无法同时最大化分配给护理的时间和精力，这可能会对幼仔在海上的第一年的生存产生潜在影响。

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