North American River Otter (Lontra canadensis) predation on salmon is of concern in the Lake Ozette watershed due to potential impacts on ESA listed Lake Ozette Sockeye Salmon (Oncorhynchus nerka). To better understand the impact of River Otters on Lake Ozette Sockeye Salmon, we examined prey remains recovered from 291 scat samples collected around Lake Ozette and near a fish counting weir in the Ozette River between 1998 and 2003. We found evidence that prey taxon differs by habitat type with significantly greater occurrence of fish and amphibians recovered from scat collected in the lake habitat, while a significantly higher occurrence of invertebrates was identified in scat from the river habitat. We also found a significantly greater frequency of adult salmon prey remains in scat collected in the river habitat than in the lake habitat. It is likely the fish counting weir increased adult salmon vulnerability to River Otter predation in Ozette River. Genetic analysis revealed that 79.4% of the adult salmon consumed by River Otters were Lake Ozette Sockeye Salmon. The frequency of occurrence of adult Sockeye Salmon in scat samples peaked in July with 25% of scat collected having adult Sockeye Salmon remains, well after the late May to the middle of June peak in upriver migration. Predation of Sockeye Salmon at all life stages has been listed as a key factor in limiting the ability of Sockeye Salmon to recover in the Lake Ozette watershed. Efforts are currently underway to address many of the factors limiting recovery of Lake Ozette Sockeye Salmon. The high occurrence of adult salmon remains near the fish counting weir, and results of past studies, suggests that predator mitigation at the weir through acoustic harassment devices or other methods could benefit the recovery of Lake Ozette Sockeye Salmon.
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Vol. 97 • No. 1