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Using PIT Tags to Estimate Pelican Predation of Smolts in the Umatilla River

Jerimiah Bonifer, Gene Shippentower, Aaron Quaempts, Zoe Johnson, and Craig Contor

Confederated Tribes of the Umatilla Indian Reservation, 4611 Timine Way, Pendleton, OR 97801

The predation rates of salmon and steelhead smolts by American white pelicans in the Umatilla Basin were unknown. Pelicans began appearing during the spring in the Umatilla Basin soon after Badger Island was created on the Columbia River from dredge tailings in 1993. Badger Island pelican colony population growth expanded to over 6,000 birds. Weekly pelican counts on the lower 129 km of the Umatilla River documented an average of 259 birds per day (April -June, 2023) with a maximum count of. Each pelican consumes 1.8 to 2.3 kg of fish per day.  Based on feeding rates and average bird counts (259), pelicans could potentially eat more than 45,000 kg of smolts from Umatilla River each spring. A Unites States Fish and Wildlife permit to effectively examine pelican stomach contents was not approved.

PIT tags provide an alternative method for estimating smolt predation rates by local pelicans. We fed 478 PIT tagged fish to pelicans to determine the deposition rate of PIT tags onto the colony islands by pelicans feeding in the Umatilla River. Thirty percent (146 or 30.5%) of the 478 fed PIT tags were detected on the colony islands by Real Time Research.  Fifteen PIT tags from our naturally produced salmon and steelhead smolts were also detected on Badger Island.  Expanded estimates of pelican predation of naturally produced steelhead smolts from Meacham Creek and the upper Umatilla River were 4.6% and 0.89% respectively.  Predation rates of naturally produced spring Chinook smolts were similar (Meacham 4.9%, Umatilla 0.34%).  Additional evaluations in 2024 and 2025 will provide information about the variability of pelican abundance, distribution, and predation of smolts within and between years.