Predation Rates of American White Pelicans on Hatchery Rainbow Trout in Idaho Reservoirs

In southern Idaho, growth of two American White Pelican Pelicanus erythorhynchos nesting colonies generated concerns about pelican predation impacts to angler catch of hatchery Rainbow Trout Oncorhynchus mykiss (hereafter catchables). To evaluate this question, pelican predation rate on catchables was compared to angler catch of catchables over three years at southern Idaho waters. We PIT-tagged and anchor-tagged 5,863 catchables and stocked them in the spring. We also directly fed 1,073 PIT-tagged fish to pelicans across all study waters. After the juvenile pelicans fledged in the fall, we recovered 523 PIT tags from the nearest pelican nesting colonies. The difference in recovery rates of stocked and fed tags allowed us to estimate PIT-tag recovery efficiency, which enabled us to estimate total pelican predation. Subsequent estimates of pelican predation averaged 17% and ranged from 0-48%. Angler exploitation averaged a similar rate of 19% and ranged from 0% to 82%. In general, there were inverse relationships between nesting colony distance and tag recovery efficiency, and between pelican predation and angler catch of hatchery catchables. Our findings suggest that where pelican predation is concentrated in Idaho, pelicans are exploiting as many catchables as anglers, and they are in competition for this resource.