Smallmouth bass populations have expanded far beyond their native range and these predatory fish present a pervasive threat to native aquatic species throughout North America. In the western United States, smallmouth bass are now present in river and reservoir habitats where Pacific salmon are found and are considered a potential threat to salmon recovery in many locations. We conducted a study to determine if smallmouth bass are expanding their range in the mainstem Willamette River, Oregon, and developed a model to assess habitat overlap between smallmouth bass and juvenile Chinook salmon. Sampling during 2011–2022 revealed that the distribution of smallmouth bass had expanded throughout that timeframe to encompass the entire mainstem Willamette River, including important rearing habitats for juvenile Chinook salmon. The model predicted that smallmouth bass and juvenile Chinook salmon habitat overlap was substantial, highlighting the need for additional research to evaluate for potential negative impacts to salmon recovery in the basin. The model was also used to evaluate the efficacy of using flow management to reduce interactions between these two species, but the scenarios we examined suggested that this was not a viable option. These results highlight the need for continued research to assess interactions between smallmouth bass and juvenile salmon, and other native species of concern, in the Willamette River Basin. The development of the model is useful for resource managers to understand interactions between these species to prioritize locations for sampling in the future.

中文翻译：

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俄勒冈州威拉米特河小口黑鲈分布的扩大和与幼年奇努克鲑鱼的栖息地重叠

小口黑鲈的数量已经远远超出了它们的原生范围，这些掠食性鱼类对整个北美洲的原生水生物种构成了普遍的威胁。在美国西部，小口黑鲈现在出现在发现太平洋鲑鱼的河流和水库栖息地，并被认为对许多地方的鲑鱼恢复构成潜在威胁。我们进行了一项研究，以确定小口黑鲈是否正在扩大其在俄勒冈州威拉米特河干流的活动范围，并开发了一个模型来评估小口黑鲈和幼年奇努克鲑鱼之间的栖息地重叠。2011 年至 2022 年期间的采样显示，在此期间小口黑鲈的分布范围已扩大到整个威拉米特河主干流，包括幼年奇努克鲑鱼的重要饲养栖息地。该模型预测，小口黑鲈和幼年奇努克鲑鱼的栖息地重叠程度很大，突出表明需要进行额外的研究来评估对该流域鲑鱼恢复的潜在负面影响。该模型还用于评估使用流量管理来减少这两个物种之间相互作用的有效性，但我们检查的场景表明这不是一个可行的选择。这些结果强调需要继续研究以评估威拉米特河流域小口黑鲈和幼鲑以及其他值得关注的本地物种之间的相互作用。该模型的开发有助于资源管理者了解这些物种之间的相互作用，从而确定未来采样地点的优先顺序。