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, 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 2001–2007, all Caspian terns nesting in the Columbia River estuary used restored habitat on East Sand Island. The size of the East Sand Island tern colony has remained at about 9,000 pairs over the last six years. During 2001-2006, estimated consumption of juvenile salmonids by Caspian terns nesting on East Sand Island averaged 4.8 million smolts (sd = 1.26 million, n = 6 years), a reduction by about 65% 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 imminent; the recently signed Record of Decision (ROD) for Caspian tern management in the Columbia River estuary stipulated the redistribution of approximately half 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 about 50%. 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 on two islands > 20 km up-river of East Sand Island where they had not recently nested. 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 2008 and 2009, 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 lower Columbia River, 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 lower Columbia River, 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 lower Columbia River. 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 lower Columbia River.

FUNDING

As was the case in 2004-2007, work conducted in the Columbia River estuary in CY 08 and CY 09 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 for the two year study ($960,000) will provide for the basic monitoring of the Caspian tern and double-crested cormorant colonies on East Sand Island to include data collection on colony size, productivity, diet composition, smolt consumption, and factors limiting the size and productivity of the estuary tern and cormorant colonies.  Funding from the U.S. Army Corps of Engineers – Portland District in CY 08 and CY 09 will cover complementary yet different 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., San Francisco Bay area and interior Oregon) and double-crested cormorant colonies both inside and outside the Columbia River estuary. Joint funding from BPA and the USACE 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 proceed with cormorant management in the Columbia River estuary, if warranted by the results.

Beginning in 2004, the U.S. Army Corps of Engineers – Walla Walla District has been funding research, monitoring, and evaluation of avian predation on the Columbia Plateau; funding that will continue in CY 08 and CY 09. Collectively, this proposal (to BPA) along with the two projects funded by the USACE will provide a comprehensive look at avian predation throughout the Columbia River basin. Unless noted otherwise in the Statement of Work below, there is no overlap in funding of research proposed here with that proposed to the USACE in 2008 and 2009.