Canadian Journal of Fisheries and Aquatic Sciences, Ahead of Print.
Drift-feeding fish are typically considered size-selective predators. Yet, few studies have explicitly tested which aspect of prey “size” best explains size selection by drift-foraging fish. Here, we develop a Bayesian discrete choice model to evaluate how attributes of both prey and predator simultaneously influence size-selective foraging. We apply the model to a large dataset of paired invertebrate drift (n = 784) and rainbow trout (Oncorhynchus mykiss) diets (n = 1028). We characterized prey “size” using six metrics (length, width, area, hemispherical area, volume, mass) and used pseudo-R2 to determine which metric best explained observed prey selection across seven taxa. We found that rainbow trout are positively size-selective, they are selecting prey based upon differences in prey width, and size-selectivity increases with fish length. Rainbow trout demonstrated strong selection for the adult and pupae stages of aquatic insects relative to their larval stages. Our study provides strong empirical evidence for size-selective foraging in rainbow trout and demonstrates prey selection is based primarily upon width, not length or area as has been widely reported.

中文翻译：

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随着猎物变厚：虹鳟鱼根据宽度而不是长度选择猎物

加拿大渔业和水产科学杂志，提前印刷。
漂流鱼通常被认为是大小选择性的捕食者。然而，很少有研究明确测试猎物“大小”的哪个方面最能解释漂流觅食鱼的大小选择。在这里，我们开发了一个贝叶斯离散选择模型来评估猎物和捕食者的属性如何同时影响尺寸选择性觅食。我们将该模型应用于配对无脊椎动物漂移 (n = 784) 和虹鳟鱼 (Oncorhynchus mykiss) 饮食 (n = 1028) 的大型数据集。我们使用六个指标（长度、宽度、面积、半球面积、体积、质量）来表征猎物“大小”，并使用伪 R2 来确定哪个指标最能解释七个分类群中观察到的猎物选择。我们发现虹鳟鱼具有积极的尺寸选择性，它们根据猎物宽度的差异来选择猎物，并且尺寸选择性随着鱼的长度而增加。相对于幼虫阶段，虹鳟鱼对水生昆虫的成虫和蛹阶段表现出强烈的选择。我们的研究为虹鳟的大小选择性觅食提供了强有力的经验证据，并表明猎物的选择主要基于宽度，而不是广泛报道的长度或面积。