2017年，一只怀孕的雌性河狸鼠在加利福尼亚州默塞德县古斯汀附近的一处私人湿地中被捕获。加州鱼类和野生动物部门表示，河狸鼠此前已被宣布于1978年从该州根除，此后直至重新被发现，均未有报告称发现该物种。2017年夏季，官员在草原生态区又捕获了19只河狸鼠。一项2025年发表于《进化应用》的研究发现，加州目前的河狸鼠种群在基因上与俄勒冈州中部的入侵性河狸鼠最为相似。
In 2017, a pregnant female nutria was captured in a private wetland near Gustine in Merced County, California. The California Department of Fish and Wildlife says nutria had been declared eradicated from the state by 1978, with no reported detections between then and their rediscovery. During the summer of 2017, officials captured 19 additional nutria in the Grasslands Ecological Area.A 2025 study published in Evolutionary Applications found that California’s current nutria population was genetically most similar to invasive nutria in central Oregon.
研究结果表明，该物种近期被引入后迅速扩散，尽管基因证据无法确定动物抵达加州的确切路径。该入侵威胁着中央谷地的湿地和农田，河狸鼠可能破坏植被、侵蚀溪岸和堤坝，并导致水土流失。为调查这些动物的来源，研究人员分析了2020年至2022年间采集的267只加州河狸鼠的6809个基因标记。他们将结果与俄勒冈州、华盛顿州、路易斯安那州、得克萨斯州、马里兰州和弗吉尼亚州种群的基因数据进行了比较。
The findings suggest a recent introduction followed by rapid spread, although the genetic evidence cannot establish the precise route by which the animals reached California. The invasion threatens wetlands and agricultural land in the Central Valley, where nutria can damage vegetation, undermine streambanks and levees, and contribute to soil erosion. To investigate the animals’ origins, researchers analyzed 6,809 genetic markers from 267 California nutria sampled between 2020 and 2022. They compared the results with genetic data from populations in Oregon, Washington, Louisiana, Texas, Maryland, and Virginia.
该研究还检查了历史博物馆标本，以评估当前种群是否可能源自加州早期的河狸鼠种群。DNA结果加州河狸鼠形成了一个独特的基因簇，但其最近的亲缘关系来自俄勒冈州中部，而北俄勒冈州的河狸鼠在基因上与华盛顿州相关联。科学家还检查了母系遗传的DNA，发现所有加州河狸鼠共享同一标记，该标记也出现在俄勒冈州和华盛顿州的河狸鼠中。
The study also examined historical museum specimens to assess whether the current population might descend from earlier nutria populations in California.DNA resultsThe California nutria formed a distinct genetic cluster, but their closest relatives came from central Oregon, while nutria from northern Oregon were genetically linked to Washington. Scientists also examined maternally inherited DNA and found that all California nutria shared the same marker, which also appeared in nutria from Oregon and Washington.
历史标本提供了一种将当前种群与早期几十年的河狸鼠进行比较的方式。研究人员对加州毛皮农场动物的皮毛、头骨和骨骼进行了测序，大多数标本可追溯至1930年至1960年。
Historical specimens provided a way to compare the current population with nutria from earlier decades. Researchers sequenced pelts, skulls, and bones from California fur farm animals, with most specimens dating from 1930 to 1960.
较老的标本拥有母系DNA标记的四种变体，表明其遗传多样性高于当前种群中发现的单一变体。其中一种历史变体与现代加利福尼亚州水獭鼠的标记相匹配。然而，这种基因重叠并不能确定当前种群源自在该州未被发现存活下来的动物。由于历史种群和当前种群共享一个母系标记，仅凭这一证据无法判断早期种群是否持续存在，还是水獭鼠被再次引入。作者认为，考虑到加利福尼亚州有利的气候和该动物的繁殖潜力，近期引入后迅速扩散的可能性较大。
The older specimens had four variants of the maternal DNA marker, indicating greater diversity than the single variant found in the current population. One of the historical variants matched the marker found in modern California nutria. However, this genetic overlap does not establish that the present population descended from animals that survived undetected in the state. Because the historical and current populations shared a maternal marker, the evidence alone cannot determine whether the earlier population persisted or whether nutria were introduced again. The authors considered a recent introduction followed by rapid splikely, given California’s favorable climate and the animals’ reproductive potential.
官方对此持何看法？在2026年4月7日的新闻稿中，加利福尼亚州鱼类和野生动物部表示，基因发现表明，目前的入侵是由一次故意的再次引入造成的，这些动物很可能是从俄勒冈州中部运来的。根据《加利福尼亚州鱼类和野生动物法典》第2118条和《加利福尼亚州法规》第14编第671条，运输水獭鼠属于违法行为。基因分析支持近期引入的假设，但无法确定是谁运输了这些动物，也无法确定其释放背后的具体情况。
What do officials think about it? In an April 7, 2026, news release, the California Department of Fish and Wildlife said the genetic findings suggest that the current invasion resulted from an intentional reintroduction, with the animals likely transported from central Oregon. Transporting nutria is prohibited under California Fish and Game Code Section 2118 and Title 14, Section 671, of the California Code of Regulations. The genetic analysis supports the hypothesis of a recent introduction, but it does not identify who transported the animals or establish the circumstances behind their release.
该部门报告称，自2017年以来，加利福尼亚州水獭鼠根除计划已清除7,841只水獭鼠。官方估计，根除工作每年耗资约500万美元。搜寻团队在从圣巴勃罗湾到金斯县的数十万英亩湿地和河岸栖息地中开展搜索，利用直接观察、运动探测相机和粪便探测犬来定位动物以便设捕。
Since 2017, California’s Nutria Eradication Program has removed 7,841 nutria, the department reported. Officials estimated that eradication efforts cost the state about $5 million annually. Teams search hundreds of thousands of acres of wetland and riparian habitat from San Pablo Bay to Kings County, using direct observation, motion-detection cameras, and fecal-detection dogs to locate animals for trapping.
该研究还为根除工作提供了指导。由于研究人员在入侵范围内发现的遗传分化很小，他们主张管理者可将中央谷地视为单一根除单元进行处理。
The study also offers guidance for eradication efforts. Because researchers found little genetic differentiation across the invaded range, they argued that managers could treat the Central Valley as a single eradication unit.
河流距离在解释基因流动方面似乎比直线距离更重要，这表明水道有助于水獭鼠在景观中移动。进入受影响区域也构成挑战，因为入侵范围的大部分属于私人所有，且一些湿地在狩猎季和筑巢季无法设置捕兽夹。
River distance appeared to matter more than straight-line distance in explaining gene flow, suggesting that waterways help nutria move through the landscape. Access to affected areas also poses a challenge because much of the invaded range is privately owned, and some wetlands cannot be trapped during hunting and nesting seasons.
为了追溯种群的起源，研究人员克里斯滕·阿伦斯联系了加利福尼亚州各地的博物馆和大学，以获取历史标本。一份不同寻常的贡献来自比尤特县衡量局，该局提供了一只水獭鼠制成的标本。阿伦斯还报告称，研究团队已建立一个全球遗传参考数据库，以帮助其他科学家比较水獭鼠种群并调查入侵路径。该项目获得了加利福尼亚州水资源部与美国农业部动植物卫生检验局合作提供的资助。
To trace the population’s origins, researcher Kristen Ahrens contacted museums and universities across California to obtain historical specimens. One unusual contribution came from the Butte County Weights and Measures Department, which provided a taxidermied nutria. Ahrens also reported that the research team had developed a global genetic reference database to help other scientists compare nutria populations and investigate invasion routes. The project received funding from the California Department of Water Resources in cooperation with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service.