SUMMARY

Piscivorous colonial waterbirds (i.e., terns, cormorants, gulls, pelicans) are having a significant impact on survival of juvenile salmonids in the lower Columbia River. Prior to management, Caspian terns at the nesting colony on Rice Island, an artificial dredged material disposal island in the Columbia River estuary, consumed an estimated 5.4 - 14.2 million juvenile salmonids in both 1997 and 1998. This represents about 5 - 15 % of all salmonid smolts reaching the estuary during those two migration years. Additionally, double-crested cormorants and glaucous-winged/western gulls nesting in the Columbia River estuary in 1998 consumed 8.0 – 22.0 million and 0.4 – 4.0 million juvenile salmonids, respectively. Research on two smaller Caspian tern colonies located further up-river (i.e., Three Mile Canyon Island, Rkm 411, and Crescent Island, Rkm 509) indicated that diets of terns nesting at these colonies consisted primarily of juvenile salmonids.  Due to growing concern regarding the impacts of avian predators on recovery of ESA-listed salmonids, regional fish and wildlife managers in 1999 called for immediate management action to reduce losses of juvenile salmonids to Caspian terns in the Columbia River estuary.  

A management plan implemented in 2000 sought to relocate the Rice Island Caspian tern colony, the largest of its kind in the world, to a restored colony site on East Sand Island, 21 km closer to the ocean, where it was hoped terns would consume significantly fewer juvenile salmonids. Over 94% of the terns shifted to nesting on East Sand Island in 2000, where nesting success was nearly four times higher than at the Rice Island colony. Juvenile salmonids comprised 47% of the prey items of terns nesting at East Sand Island in 2000, compared to 90% of prey items for terns nesting at Rice Island.

During 2001–2011, all Caspian terns nesting in the Columbia River estuary used restored and maintained habitat on East Sand Island. The size of the East Sand Island tern colony has remained at about 7-10,000 breeding pairs over the last 11 years. During 2001-2011, estimated consumption of juvenile salmonids by Caspian terns nesting on East Sand Island averaged 5.3 million smolts, a reduction by more than 50% of the annual consumption of smolts compared to when all terns were nesting on Rice Island.

Further management of Caspian terns to reduce losses of juvenile salmonids in the estuary is in progress; the Records of Decision (RODs) for Caspian tern management in the Columbia River estuary, signed in November 2006, stipulated the redistribution of approximately two-thirds of the East Sand Island tern colony to alternative colony sites in Oregon and California (USFWS 2006). This management is intended to further reduce smolt losses to terns in the estuary by more than 50%. The U.S. Army Corps of Engineers has constructed eight artificial islands, five in interior Oregon and three in interior northeastern California, as alternative nesting habitat for Caspian terns currently nesting on East Sand Island near the mouth of the Columbia River. The Corps has plans to construct at least one more tern nesting island in the next year. Concurrently, the Corps is reducing the area of suitable nesting habitat for Caspian terns on East Sand Island, and hazing terns that attempt to establish new nesting colonies elsewhere in the Columbia River estuary.

Management options to reduce or limit smolt losses to the expanding double-crested cormorant colony on East Sand Island, which was estimated to have consumed 22.6 million juvenile salmonids (95% c.i. = 16.4 million to 28.8 million) in 2011, are under consideration. But any management of the East Sand Island cormorant colony, which numbered about 13,000 breeding pairs in 2011, will require NEPA analysis and likely the preparation of an Environmental Impact Statement. Relocation of a portion of the cormorants currently nesting on East Sand Island to alternative colony sites outside the estuary is one option. Restoration, enhancement, or establishment of tern and cormorant colony sites outside the Columbia River estuary would likely benefit Columbia Basin salmonids without negatively affecting protected populations of fish-eating migratory birds.

In 2012, we will monitor Caspian tern predation on juvenile salmonids in the Columbia River estuary, as well as monitor and evaluate the managed reduction of tern nesting habitat on East Sand Island, which is designed to reduce the size of the Caspian tern colony. Together with funding from the U.S. Army Corps of Engineers – Portland District, we will also monitor population size, diet composition, and smolt consumption of cormorants nesting in the Columbia River estuary. We will use a bioenergetics modeling approach to quantify the numbers of juvenile salmonids consumed by terns and cormorants nesting on East Sand Island, and to convert those numbers into predation rates on particular stocks of Columbia Basin salmonids.  In addition, we will evaluate the factors that influence the susceptibility of various salmonid species, run-types, and rearing types (i.e., hatchery-reared vs. wild) to avian predation in the lower Columbia River. Finally, we will continue to provide technical assistance to BPA and other regional fish and wildlife management agencies in developing short- and long-term management plans to reduce avian predation on juvenile salmonids in the lower Columbia River.

FUNDING

As was the case in 2004-2011, work on avian predation conducted in the Columbia River estuary in CY 12 will be jointly funded by the Bonneville Power Administration and the U.S. Army Corps of Engineers – Portland District.  Funding from the Bonneville Power Administration ($535,341 in CY 12) will provide for the basic monitoring of the Caspian tern colony on East Sand Island, to include collecting data on colony size, productivity, diet composition, smolt consumption, and factors limiting the size and productivity of the estuary tern colony.  A small proportion of the funding from BPA will be used to support RM&E of other colonies of avian predators, including the double-crested cormorant colony, the Brandt’s cormorant colony, and the gull colonies on East Sand Island. Funding from the U.S. Army Corps of Engineers – Portland District in CY 12 will support research and monitoring of Caspian tern colonies at alternative colony sites identified in the Caspian Tern Management Plan for the Columbia River estuary (i.e., sites in interior Oregon and the Upper Klamath Basin, California). In addition, USACE – Portland District will support research initiatives on double-crested cormorants nesting in and outside the Columbia River estuary, studies that are designed to provide data necessary for completion of an EIS for management of double-crested cormorants in the Columbia River estuary. Joint funding from BPA and the USACE-Portland District is needed to collect all the necessary information to evaluate the efficacy of the Caspian Tern Management Plan and to complete the NEPA analysis required to develop and implement a cormorant management plan in the Columbia River estuary.

Beginning in 2004, the U.S. Army Corps of Engineers – Walla Walla District funded research, monitoring, and evaluation of avian predation on the Columbia Plateau; funding from the Walla Walla District for limited field work and monitoring in the Columbia Plateau region will continue in CY 2012, but at a much reduced level as a means of providing basic monitoring while fish and wildlife resource managers devise a management plan. Collectively, this proposal to BPA, along with the two projects funded by the USACE, will support a comprehensive investigation of avian predation on salmonid smolts throughout the Columbia River basin. Unless noted otherwise in this Statement of Work, there is no overlap in funding of research proposed here with that proposed to the USACE in 2012.