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Ecology and salmon related articles

Ongoing Research Tracks Movements, Steelhead Predation
by Caspian Terns in Mid-Columbia Basin

by Staff
Columbia Basin Bulletin, January 3, 2014

(Bird Research Northwest) Not a single Caspian tern chick has survived due to disturbances caused by eagles. Even as plans are being made to reduce the impact of Caspian terns on salmon and steelhead in the Columbia River plateau region, the predatory birds are continuing to be what researchers call "the single most significant (per capita) avian predator" on juvenile steelhead migrating from the Snake River basin and the upper Columbia.

And the hungry birds that nest each spring and early summer at five plateau colony sites are ranging far and wide to do it.

Data collected during the 2013 research season indicates that a total of 23 Caspian terns nesting at Goose Island were marked with GPS tags and tracked during foraging trips over several days. Goose Island is a 5-acre island located near the southern end of Potholes Reservoir, near the city of Moses Lake in southeastern Washington.

That's not new, since previous research has shown that terns fly more than 30 kilometers from the Goose Island nesting colony to forage on the Columbia River, and recoveries of PIT tags on the island indicated the birds pose a significant threat the survival of salmonids, especially Upper Columbia River steelhead.

Nearly half of the GPS-tagged terns made foraging trips to the mid-Columbia River, including Wanapum Reservoir, Priest Rapids Reservoir, and Hanford Reach.

"Surprisingly, four GPS-tagged terns made foraging trips to the lower Snake River, including one tern that exhibited the greatest foraging range ever documented in a breeding Caspian tern: 93 km straight-line distance from the colony," according to a study abstract prepared for early December's Anadromous Fish Evaluation Program annual review, a three-day session hosted by the U.S. Army Corps of Engineers' Walla Walla District.

The ongoing research is being conducted by a team of researchers from Oregon State University and Real Time Research, Inc., which include Dan Roby, Ken Collis, Allen Evans, Don Lyons, Pete Loschl, Yasuko Suzuki, Kirsten Bixler, Brad Cramer, Mike Hawbecker, Jessica Adkins, and Tim Lawes.

A variety of research topics, related largely to finding ways to improve fish survival through the Columbia-Snake river hydro system, are funded through the Corps' Columbia River Fish Mitigation Program, are on the agenda for the annual AFEP review.

Both the upper Columbia and Snake River steelhead stocks are listed for protections under the Endangered Species Act, as are Upper Columbia spring chinook salmon and Snake River spring/summer and fall chinook and Snake River sockeye salmon.

The Corps has developed an Inland Avian Predation Management Plan and associated draft environmental assessment for managing birds that prey on ESA-listed fish species in the Columbia and Snake rivers.

This effort by the Corps and the Bureau of Reclamation is part of the overall attempt to comply with the Federal Columbia River Power System 2008 biological opinion from the NOAA Fisheries, as updated by the 2010 Supplemental BiOp. The BiOp outlines actions NMFS feels necessary to improve survivals of listed fish.

The Inland Avian Predation Management Plan focuses on colony-based habitat management actions on federal lands. Previous research has determined that the greatest benefit could be achieved by managing Caspian tern colonies with demonstrated high rates of predation on ESA-listed fish species, the Corps says.

The draft plan proposes management actions at Goose Island (Potholes Reservoir in Grant County, Wash.) and Crescent Island (within McNary Reservoir on the Columbia River in Walla Walla County, Wash.) to dissuade Caspian terns from nesting at these locations.

Public comments on the draft EA and Corps draft Finding of No Significant Impact were accepted Dec. 2. The Corps is now at work preparing final documents.

Goose and Crescent islands annually hold the plateau region's largest Caspian tern colonies. The colonies are small, 340 and 395 nesting pairs respectively, this past year as compared to the lower Columbia estuary's East Sand Island, which held an estimated 7,400 pairs in 2013.

"Predation rate estimates based on PIT tag recoveries on Caspian tern colonies indicated that impacts were again highest on upper Columbia River steelhead smolts (14.9 percent depredated by Goose Island terns) and Snake River steelhead smolts (2.8 percent by Crescent Island terns)," according to preliminary data collected at the plateau islands. That data was presented at the AFEP conference in Walla Walla, Wash.

Predation rates on UCR spring chinook were much less than on UCR steelhead for Caspian terns from both Goose Island and Crescent Island colonies, the researchers say.

"Predation rates at the small Caspian tern colony in the Blalock Islands were an order of magnitude less than those of terns nesting at Goose and Crescent islands, but steelhead were still highly susceptible to terns from this colony. The predation rate of terns nesting at the Blalock Islands on steelhead smolts could be of concern to managers if the colony were to increase in size as a result of ongoing and/or prospective management actions elsewhere," the researchers say. Blalock Islands are located in the Columbia River reservoir created by John Day Dam.

Researchers in 2013 observed a small number of banded terns that originally nested on East Sand Island in the Columbia River estuary, where management actions have been implemented, at the Goose Island and Crescent Island. That management work at East Sand has resulted in a reduction of the available habitat there in hopes a large share of the terns move to specially prepared habitats in southern and central Oregon and northern California that are well away from the Columbia salmon migration corridor.

Prior to 2011, when tern management intensified at East Sand Island, movement to the Columbia Plateau region by banded Caspian terns that previously nested on East Sand Island had not been documented. The 2013 preliminary estimates are that 57 East Sand birds shifted to Goose Island and 56 went to Crescent. There was movement back and forth across the plateau too, with 92 terns moving from Goose to Crescent and 23 moving from Crescent to Goose.

"Relocation of Caspian terns from East Sand Island to Columbia Plateau colonies could offset benefits to salmonids of tern management in the estuary because per capita impacts on smolt survival are higher for terns nesting in the Columbia Plateau region relative to those nesting in the estuary, where their diet is dominated by marine forage fishes," according to the study abstract prepared for the AFEP review.

If a plateau re-location management strategy is employed, it appears they have options, the researchers say.

"Band re-sighting data indicate high connectivity among tern nesting sites in the Columbia Plateau region and colonies elsewhere in western North America, from Mexico to Alaska, both inland and along the coast. This suggests that terns displaced from these two Columbia Plateau colonies may re-nest at existing or newly-created colony sites outside the Columbia River basin."

The Corps stresses that preliminary 2103 study results presented at the conference are for the benefit of the scientific and technical community.

Related Pages:
Army Corps of Engineers Looks to Save Salmon from Caspian Terns by Annette Cary, Tri-City Herald, 3/15/12

Ongoing Research Tracks Movements, Steelhead Predation by Caspian Terns in Mid-Columbia Basin
Columbia Basin Bulletin, January 3, 2014

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