Abstract

Keystone predators can impact many prey species, including those that are endangered. A requisite to assess the impact predators have on different prey populations is to identify the species being consumed in different types of communities, while accounting for possible seasonal variation in consumption. Here we used analysis of North American river otter (Lontra canadensis) scat to assess the impact river otters have on their prey populations, particularly endangered salmonids and migrating birds. We analyzed the prey composition of 1,411 river otter scats collected from 10 sites in Humboldt County, California, between 2011 and 2012. Analysis of prey items in scat placed study sites into four distinct clusters based on diet. Fish, mostly from the families Gasterosteidae, Cottidae, and Pholidae, formed the primary prey component, and crustaceans, birds, amphibians, and insects, also were important components of river otter diet. Salmonids constituted < 5% of overall diet, but river otters consumed the largest percentage of salmon during salmon spawning season at the inland cluster where salmonids spawn. Scat marking intensity varied between clusters and seasons, with the most scats collected in the autumn and the fewest in the winter/spring, except at the inland cluster where the pattern of marking activity was reversed. River otters may be responding to seasonal migrations of endangered and threatened salmonids. Diet surveys of this type are useful for monitoring resource use by top predators in aquatic ecosystems.

中文翻译：

---

不同季节和水生群落的河獭（Lontra canadensis）饮食和活动的变化

摘要

基石捕食者可以影响许多猎物物种，包括那些濒临灭绝的物种。评估捕食者对不同猎物种群的影响的一个必要条件是确定不同类型群落中被消费的物种，同时考虑消费的可能季节性变化。在这里，我们使用了北美河獭（Lontra canadensis）的分析) 评估水獭对其猎物种群的影响，特别是濒临灭绝的鲑鱼和候鸟。我们分析了 2011 年至 2012 年间从加利福尼亚州洪堡县 10 个地点收集的 1,411 只河獭粪便的猎物组成。对粪便中猎物的分析将研究地点根据饮食分为四个不同的集群。鱼类，主要来自 Gasterosteidae、Cottidae 和 Pholidae，是主要的猎物成分，甲壳类、鸟类、两栖动物和昆虫也是水獭饮食的重要组成部分。鲑鱼占总饮食的 <5%，但在内陆鲑鱼产卵的鲑鱼产卵季节，河獭消耗了最大比例的鲑鱼。Scat 标记强度因集群和季节而异，除标记活动模式相反的内陆集群外，秋季收集的粪便最多，冬季/春季收集的粪便最少。水獭可能对濒危和受威胁鲑鱼的季节性迁徙做出反应。这种类型的饮食调查可用于监测水生生态系统中顶级捕食者的资源使用情况。