PDF(Pubmed)
Abstract：
The lack of recovery of Chinook salmon (Oncorhynchus tshawytscha) in the Pacific Northwest has been blamed in part on predation by pinnipeds, particularly the harbor seal (Phoca vitulina). Previous work at a limited number of locations has shown that male seal diet contains more salmon than that of female seals and that sex ratios at haul-out sites differ spatiotemporally. This intrapopulation variation in predation may result in greater effects on salmon than suggested by models assuming equal spatial distribution and diet proportion. To address the generality of these patterns, we examined the sex ratios and diet of male and female harbor seals from 13 haul-out sites in the inland waters of Washington State and the province of British Columbia during 2012-2018. DNA metabarcoding was conducted to determine prey species proportions of individual scat samples. The sex of harbor seals was then determined from each scat matrix sample with the use of quantitative polymerase chain reaction (qPCR). We analyzed 2405 harbor seal scat samples using generalized linear mixed models (GLMMs) to examine the factors influencing harbor seal sex ratio at haul-out sites and permutational multivariate analysis of variance (PERMANOVA) to examine the influence of sex and haul-out site on harbor seal diet composition. We found that the overall sex ratio was 1:1.02 (female:male) with notable spatiotemporal variation. Salmoniformes were about 2.6 times more abundant in the diet of males than in the diet of females, and Chinook salmon comprised ca. three times more of the average male harbor seal\'s diet than the average female\'s diet. Based on site-specific sex ratios and diet data, we identified three haul-out sites where Chinook salmon appear to be under high predation pressure by male harbor seals: Cowichan Bay, Cutts Area, and Fraser River. Our study indicates that combining sex-specific pinniped diet data with the sex ratio of haul-out sites can help identify priority sites of conservation concern.
摘要：
西北太平洋的奇努克鲑鱼（Oncorhynchustshawytscha）缺乏恢复，部分原因是被大头鱼捕食，尤其是海豹港(Phocavitulina)。先前在有限数量的地点进行的工作表明，雄性海豹饮食中的鲑鱼含量要比雌性海豹多，并且在运输地点的性别比例在时空上有所不同。与假设空间分布和饮食比例相等的模型所建议的相比，这种种群内捕食的变化可能会对鲑鱼产生更大的影响。为了解决这些模式的普遍性，我们研究了2012-2018年华盛顿州和不列颠哥伦比亚省内陆水域13个运放地点的雄性和雌性海豹的性别比例和饮食.进行DNA元编码以确定单个scat样品的猎物物种比例。然后使用定量聚合酶链反应（qPCR）从每个scat基质样品中确定海豹的性别。我们使用广义线性混合模型（GLMMs）分析了2405个港口海豹样本，以检查影响运输地点港口海豹性别比的因素，并使用置换多变量方差分析（PERMANOVA）检查性别和运输地点对港口海豹饮食组成的影响。我们发现总体性别比为1：1.02（女性：男性），具有明显的时空变化。在男性的饮食中，沙门氏菌的含量是女性饮食中的2.6倍，奇努克鲑鱼约为。平均雄性海豹的饮食比平均雌性海豹的饮食多三倍。根据特定地点的性别比例和饮食数据，我们确定了三个运输地点，在这些地点中，奇努克鲑鱼似乎受到雄性海豹的高度捕食压力：Cowichan湾，卡茨区,弗雷泽河我们的研究表明，将特定性别的固定饮食数据与运输地点的性别比例相结合，可以帮助确定优先保护地点。
