PROGRAM DESCRIPTION

Background, Rationale, and Significance

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, the Caspian tern 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 consumed 2 - 9 million and 0.4 - 4 million juvenile salmonids, respectively, in 1998. 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 tern diets 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 estuary.  

A management plan implemented in 2000 sought to relocate the Rice Island tern colony 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 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, compared to 90% of prey items at Rice Island. The relocation of nearly all the nesting terns from Rice Island to East Sand Island resulted in a sharp drop in consumption of juvenile salmonids. Total smolt consumption by Caspian terns nesting in the Columbia River estuary in 2000 was estimated at 8.2 million (95% confidence interval = 6.7 - 9.7 million). This represents a reduction of about 5.6 million (41%) compared to the 1999 smolt consumption estimate.  

During 2001-2005, all Caspian terns nesting in the Columbia River estuary used restored habitat on East Sand Island. The size of the East Sand Island colony has remained at about 9,000 pairs over the last five years. Tern nesting success at the East Sand Island colony during 2001-2004 was high (average of 1.1 young raised per nesting pair), apparently a reflection of high forage fish availability. In 2005, a year of poor ocean conditions due to late onset of coastal upwelling, Caspian tern nesting success on East Sand Island was relatively poor, only 0.37 young raised per nesting pair. The proportion of juvenile salmonids in the diet (23%) and the estimated consumption of juvenile salmonids (3.6 million smolts, 95% c.i. = 3.0 - 4.2 million) by the East Sand Island tern colony in 2005 was still much less (> 70% less) than when all terns were nesting on Rice Island.

Further management of Caspian terns to reduce losses of juvenile salmonids in the estuary is imminent; the Final Environmental Impact Statement (Final EIS) for Caspian tern management in the Columbia River estuary identified the redistribution of approximately two-thirds of the East Sand Island tern colony to alternative colony sites in Washington, Oregon, and California as the preferred alternative (USFWS 2005). This management is intended to further reduce smolt losses to terns in the estuary by 60-70%. Management options to reduce or limit smolt losses to the expanding double-crested cormorant colony are under consideration, but any management of double-crested cormorants will require additional research and NEPA analysis. Relocation of a portion of the cormorants nesting on East Sand Island to alternative colony sites outside the estuary is one option. Pilot studies designed to test the feasibility of employing habitat enhancement and social attraction (i.e., decoys, audio playback systems) to relocate nesting cormorants have shown some promise; cormorants have been induced to nest at several sites on East Sand Island where they had not previously nested, and at a site 23 km up-river from East Sand Island where cormorants had not attempted to nest in several years. 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 birds.

In 2006, we will monitor and evaluate management initiatives implemented to reduce Caspian tern predation on juvenile salmonids in the Columbia River estuary. We will also monitor population size and diet composition of unmanaged piscivorous waterbird populations in the Columbia River estuary (i.e., double-crested cormorants), populations that could potentially contribute to significant smolt mortality. We will use a bioenergetics modeling approach to quantify the numbers of juvenile salmonids consumed by managed and unmanaged colonies of fish-eating waterbirds in the Columbia River estuary, 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 vulnerability of various salmonid species and stocks (especially steelhead) to avian predation in the Columbia River estuary. Finally, we will continue to provide technical assistance to regional fish and wildlife management agencies in developing short- and long-term management plans to reduce avian predation on juvenile salmonids in the Columbia River estuary.

Funding

Previously (1999-2003) funding for this research program (as described above) came entirely from the Bonneville Power Administration.  In 2004 and 2005, funding for this research came from three different funding agencies: the Bonneville Power Administration, the U.S. Army Corps of Engineers - Portland District, and the U.S. Army Corps of Engineers - Walla Walla District.  Most of the funding for work conducted on the Columbia River above The Dalles Dam came from the U.S. Army Corps of Engineers - Walla Walla District; this funding will continue in 2006. The research objectives and tasks associated with that work are not provided here. In 2004 and 2005, work conducted in the Columbia River estuary was funded primarily by the U.S. Army Corps of Engineers - Portland District, with substantial additional funding from the Bonneville Power Administration.  In 2006, very limited funding is available from the Portland District - USACE ($24,000), so the vast majority of  support for RM&E on avian predation in the Columbia River estuary will come from BPA. The attached statement of work describes the research objectives and tasks for work conducted on the lower Columbia River in 2006, with emphasis on the Columbia River estuary.