Introduction of non-native piscivores has been implicated in the decline of native Chinook Salmon Oncorhynchus tshawytscha via predation during juvenile life stages. However, isolating effects of predation on Chinook Salmon survival is complicated by changes in physical habitat that are often concomitant with non-native piscivore establishment. We performed two field experiments with enclosures deployed in tidal freshwater habitat to quantify effects of non-native Largemouth Bass Micropterus salmoides density and habitat type on the survival and movement behavior of juvenile Chinook Salmon. In experiment one, bass densities were doubled and quadrupled across treatment levels with a baseline value of field-observed densities. In experiment two, three habitat types (dock, submerged aquatic vegetation (SAV), and open water) were tested while bass density was held at the medium (doubled) value. Juvenile Chinook Salmon implanted with passive integrated transponders were released into the enclosures to assess their survival and movement through the treatments over multiple trials. Mark-recapture models indicated that the survival of juvenile Chinook Salmon was reduced in the medium bass density, but not the high-density treatment, when compared to the lowest density value suggesting relationships may be non-linear. The SAV treatment had a well-supported negative effect on juvenile Chinook Salmon survival relative to a dock or open water. Residence time was positively related to bass density. Relationships with a habitat were not consistently different. These results suggest that restoration strategies targeting non-native SAV control could reduce predation on juvenile Chinook Salmon by Largemouth Bass. However, piscivore density manipulation may only be effective over a narrow range of densities.

在幼年期的捕食过程中，非本地食肉动物的引入与当地奇努克鲑鱼Oncorhynchus tshawytscha的减少有关。但是，捕食对奇努克鲑鱼生存的孤立影响由于物理栖息地的变化而变得复杂，而这些变化通常伴随着非本地食肉动物的建立。我们进行了两次现场试验与部署在潮汐淡水栖息地的外壳量化非本地大口黑鲈的影响加州鲈密度和栖息地类型对奇努克鲑鱼生存和移动行为的影响。在实验一中，低音密度在整个治疗水平上都翻了一番并翻了两番，而场观察到的密度则为基线值。在实验二中，测试了三种栖息地类型（船坞，水下水生植物（SAV）和开阔水域），而低音密度保持在中等（两倍）值。植入被动集成应答器的奇努克鲑鱼被释放到围场中，以通过多次试验评估它们的存活和运动。Mark-recapture模型表明，与最低密度值相比，中等鲈鱼密度的幼鱼Chinook Salmon的存活率降低了，但高密度处理却没有降低，表明关系可能是非线性的。相对于码头或开阔水域，SAV处理对青少年奇努克鲑鱼的存活具有充分支持的负面影响。停留时间与低音密度呈正相关。与栖息地的关系并没有始终如一的不同。这些结果表明，针对非本地SAV控制的恢复策略可以减少大嘴鲈鱼对奇努克鲑鱼的捕食。但是，食肉动物的密度操纵可能仅在狭窄的密度范围内有效。