Juvenile Pacific salmon Oncorhynchus spp. experience high mortality at marine entry, yet our quantitative understanding of predation during this critical period is limited. We evaluated spatial, temporal, and size‐based patterns of predation on hatchery‐ and wild‐born juvenile Chum Salmon O. keta by two abundant predators in Southeast Alaska estuaries: the Pacific Staghorn Sculpin Leptocottus armatus and Dolly Varden Salvelinus malma. For the predators we sampled, Chum Salmon comprised 4.5% of the diet by weight for Pacific Staghorn Sculpin (n = 937) and 19.6% of the diet by weight for Dolly Varden (n = 448), with 88% of the individual Chum Salmon consumed originating from hatcheries. Variation in occurrence of Chum Salmon in diets was driven by date, site, and local Chum Salmon density. The quantity of Chum Salmon consumed by Pacific Staghorn Sculpin varied with predator length, Chum Salmon density, and the proportion of hatchery fish present; however, date was the only important predictor for Dolly Varden. The mean length of Chum Salmon in the diets of both predators was significantly shorter than that of concurrent hatchery releases or seine catches, suggesting size‐selective predation on smaller individuals. This pattern indicates that hatchery strategies of releasing larger individuals may reduce the initial vulnerability of hatchery salmon to estuarine predators.

中文翻译：

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阿拉斯加东南部近岸鱼类进入海洋时孵化场和野生生幼鲑的鲑鱼时空变化和大小选择捕食

少年太平洋鲑鱼Oncorhynchus spp。在进入海洋时会经历很高的死亡率，但是我们在此关键时期对捕食的定量理解是有限的。我们评估了阿拉斯加东南部河口的两个捕食者：太平洋Staghorn Sculpin Leptocottus armatus和Dolly Varden Salvelinus malma在孵化场和野生幼体Chum Salmon O.keta上的捕食时空分布。对于我们采样的捕食者，Chuck Salmon占太平洋Staghorn Sculpin饮食的4.5％（n  = 937）和Dolly Varden饮食饮食的19.6％（n  =  448），其中88％的鲑鱼消费来自孵化场。日粮中鲑鱼鲑鱼发生率的变化受日期，部位和当地鲑鱼鲑鱼密度的影响。Pacific Staghorn Sculpin食用的鲑鱼数量随着捕食者的长度，鲑鱼密度和孵化场鱼类的比例而变化。但是，日期是多莉·瓦尔登（Dolly Varden）唯一重要的预测指标。两种捕食者饮食中Chum Salmon的平均长度明显短于同时孵化场释放或围网捕捞的长度，这表明较小个体的捕食规模选择。这种模式表明，释放较大个体的孵化场策略可能会降低孵化场鲑鱼对河口捕食者的最初脆弱性。