River Otters - High Mountain Lakes [ds813]

In California, River Otters (Lontra canadensis) are most commonly associated with food-rich lowland aquatic habitats where they forage primarily on fish and crustaceans. Their distribution in high-elevation montane regions of the state, areas in which fish and crayfish were absent historically, is largely unknown. We compiled occurrence records of River Otters in California from elevations >1100 m, and evaluated them using evidentiary standards. Based on 126 records, we report the widespread presence of River Otters in the Klamath, southern Cascades, and Sierra Nevada mountain ranges, including at elevations exceeding 3000 m. Sixty-three percent of the records met our definition as ''verified'', and the remaining 37% were considered ''unverified''. The distribution of observations through time and habitats in which observations were made were similar between verified and unverified records. River Otter records spanned the period from 1900 to 2017, with 50% occurring between 1991 and 2010. Ninety-three percent of the water bodies with records of River Otters contained nonnative prey (fish and crayfish). Those lacking nonnative prey all supported native prey, including amphibians and reptiles. Based on records that contained River Otter foraging observations, nonnative fishes and crayfish were represented in 89% of the total accounts, and native frogs and invertebrates were represented in 22%. It remains unclear whether River Otters occurred in California's high-elevation water bodies prior to the introduction of fish and crayfish, and additional research is needed to understand the possible influence of nonnative prey in allowing River Otters to expand their distribution in these habitats.在加利福尼亚州，北美水獭（River Otter, Lontra canadensis）通常与食物富足的低地水生栖息地相关联，其主要觅食对象为鱼类与甲壳类动物。该州历史上本无鱼类与螯虾分布的高海拔山地区域中，北美水獭的分布状况仍未得到充分探明。我们收集了加利福尼亚州海拔高于1100米区域的北美水獭出现记录，并依据证据标准对其开展评估。基于126条记录，我们证实北美水獭广泛分布于克拉马斯山脉、南喀斯喀特山脉以及内华达山脉，甚至涵盖海拔超过3000米的区域。其中63%的记录符合我们设定的"已验证"判定标准，剩余37%则被归为"未验证"记录。已验证记录与未验证记录在观测时间分布以及观测所涉及的生境类型上均表现出相似特征。北美水獭的记录时间跨度为1900年至2017年，其中50%的记录集中于1991年至2010年期间。存有北美水獭观测记录的水体中，93%包含外来猎物（鱼类与螯虾）；未发现外来猎物的水体则均有本土猎物栖息，包括两栖类与爬行类动物。基于包含北美水獭觅食行为观测的记录，89%的记录条目涉及外来鱼类与螯虾，22%的记录条目涉及本土蛙类与无脊椎动物。目前仍无法确定在鱼类与螯虾被引入之前，北美水獭是否曾栖息于加利福尼亚州的高海拔水体中；此外，还需开展进一步研究以明确外来猎物在推动北美水獭拓展此类生境分布范围过程中可能产生的影响。