Northwest Fisheries Science Center

Display All Information

Document Type: Contract Report
Center: NWFSC
Document ID: 4687
Title: Measuring estuary avian predation impacts on juvenile salmon by electronic recovery of passive integrated transponder (PIT) tags from bird colonies on East Sand Island, 2012
Author/Editor: J. E. Zamon, Tiffanie A. Cross, Benjamin P. Sandford, Allen F. Evans, Bradley Cramer
Publication Year: 2013
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Portland, Oregon
Pages: 52
Date: June 2013

A factor limiting recovery of Columbia River Basin salmon is avian predation. We present results from a project which recovered PIT tag codes from seabird colonies located on East Sand Island, OR in the Columbia River estuary. Code recoveries were used by NOAA Fisheries and collaborators with Bird Research Northwest to derive estimates of estuary predation by Caspian terns (Hydroprogne caspia), double-crested cormorants (Phalacrocorax auritus), and Brandt’s cormorants (P. penicillatus) on juvenile salmon.

On the Caspian tern colony, we recovered 15,298 unique tag codes in 2012. Codes were found from all 13 ESU/DPS groups listed by the Endangered Species Act. On the double-crested cormorant colony, we recovered 13,829 unique tag codes, also representing all 13 listed ESU/DPS groups. Detection efficiencies on the Caspian tern colony ranged from 42% to 90%; those on the double-crested cormorant colony ranged from 56% to 81%, comparable to prior years’ measurements. BRNW used tag code recoveries to measure off-colony tag deposition rates for double-crested cormorants. They reported an estimated 44% of tags being deposited on the colony, implying up to 56% of tags consumed are deposited off the colony.

Estimates of estuary predation rates for tag groups with geographical origins entirely above Bonneville Dam (Columbia River) or Sullivan Dam (Willamette River) showed Caspian terns have the greatest impact on steelhead (7.4%-10.0%), with a lesser impact on other groups (0.7%-2.2%). Double-crested cormorants had the greatest impact on upper Columbia River ESU steelhead (7.2%), with impacts of  0.6%-5.4% on other ESU/DPS groups. Upper Willamette spring Chinook salmon experienced the least avian predation impact (<1%). Brandt’s cormorants appeared to have minimal impact on any of the population groups we examined (<1%).

Fifty-two sources contributed to PIT-tagged tagged Lower Columbia River ESU Chinook salmon during migration year 2012. Three hatcheries accounted for 66.3% of tagged fish released into the Columbia River. We estimated overall predation rates on tagged fish from this ESU to be 0.91% for Caspian terns, 2.9% for double-crested cormorants, and 0.15% for Brandt’s cormorants. Due to the complexity of the life history types included in this ESU, and the lack of a comprehensive, representative tagging program for the ESU, generalizing these predation rates to the entire Lower Columbia River ESU should be done with extreme caution.

Comparisons of barge-transported vs. in-river migrant Snake River ESU fall Chinook salmon were made in two ways. First, annual predation estimates were calculated. Second, paired daily comparisons were made on days when at least 100 fish were detected entering the estuary from both transported and naturally-migrating fish. Caspian terns and double-crested cormorants had higher impacts on barge-transported fish (0.7% and 3.3%, respectively) than on in-river migrants (0.5% and 1.3%, respectively); Brandt’s cormorants had low impacts on in-river migrants (0.1%) and barged fish (<0.1%). Paired comparisons showed tern and double-crested cormorant predation were higher on transported fish (0.5% and 2.7%, respectively) than on migrants (0.3% and 1.0%, respectively), although the difference was only statistically significant for cormorants. For Brandt’s cormorants, transported vs. migrant rates were identical (0.2%). The implication is barging is not necessarily an effective tool for decreasing estuary avian predation on Snake River ESU fall Chinook salmon. How

Theme: Recovery, Rebuilding and Sustainability of Marine and Anadromous Species
Foci: Investigate ecological and socio-economic effects of alternative management strategies or governance structures.