SUMMARY

Piscivorous colonial waterbirds (i.e. Caspian terns, double-crested cormorants [Phalacrocorax auritus], several species of gulls [Larus spp.], American white pelicans [Pelecanus erythrorhynchos]) are collectively having a significant impact on survival of juvenile salmonids in the lower Columbia River. Prior to management, Caspian terns nesting at the breeding 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 that reached the estuary during those two migration years. Additionally, double-crested cormorants and glaucous-winged/western gulls (L. glaucescens X L. occidentalis) 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 Caspian terns nesting at these colonies consisted primarily of juvenile salmonids. Due to growing concern over the impact of Caspian tern predation on recovery of ESA-listed salmonids in the Columbia Basin, 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 higher than at the Rice Island colony. Juvenile salmonids comprised 47% of the prey items of Caspian terns nesting at East Sand Island in 2000, compared to 90% of prey items for terns nesting at Rice Island in that year. Additional management of the Caspian tern colony on East Sand Island was intended to further reduce losses of juvenile salmonids in the estuary by reducing the size of the East Sand Island colony; the Records of Decision (RODs) for the management plan entitled, "Caspian Tern Management to Reduce Predation of Juvenile Salmonids in the Columbia River Estuary" were signed in November 2006, and stipulated that approximately two-thirds of the East Sand Island tern colony would be redistributed to alternative colony sites in Oregon and California (USFWS 2005, 2006). This management was intended to reduce smolt losses to Caspian terns in the estuary by more than 50%. The U.S. Army Corps of Engineers has constructed nine islands specifically for Caspian tern nesting in southern Oregon and northeastern California (the SONEC region; i.e. at Fern Ridge Reservoir, Crump Lake, Summer Lake Wildlife Area [3 separate islands], Tule Lake National Wildlife Refuge [NWR], Lower Klamath NWR [2 separate islands], and Malheur NWR). More recently, five additional tern islands were constructed in the southern portion of San Francisco Bay at Don Edwards NWR. Concurrently, the Corps has been 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.

During 2001–2017, Caspian terns nesting in the Columbia River estuary have nested almost entirely on habitat prepared for them on East Sand Island. Concomitant with the relocation of nesting Caspian terns from Rice Island to East Sand Island and the managed reduction in the amount of suitable nesting habitat provided for terns on East Sand Island starting in 2008, there has been a reduction in the number of Caspian terns nesting in the Columbia River estuary. Associated with this reduction, there has been a decline in consumption of ESA-listed salmonids by Caspian terns nesting in the Columbia River estuary, the stated goal of the management plan.

In 2018, we will assist with the continued implementation of the Caspian Tern Management Plan for the Columbia River Estuary and monitor the effects of adaptive management under the Plan in reducing Caspian tern (Hydroprogne caspia) predation on ESA-listed juvenile salmonids (Oncorhynchus spp.) from the Columbia River basin. To accomplish this goal, we will (1) create 1 acre of suitable Caspian tern nesting habitat at the location of the current colony site on the east end of East Sand Island (designated colony area), (2) restrict Caspian tern nesting on East Sand Island to just the designated colony area using passive and active tern nest dissuasion techniques, (3) monitor seasonal colony attendance, measure colony size and nesting density, estimate nesting success, and identify factors limiting colony size and nesting success at the Caspian tern breeding colony on East Sand Island, (4) evaluate movement rates of Caspian terns to the East Sand Island colony by resighting marked terns previously color-banded at other colony sites, (5) assess the population status and trends for the Pacific Flyway population of Caspian terns using empirically derived vital rates and demographic modeling, and (6) evaluate tern diet composition and use a bioenergetics modeling approach to estimate the numbers of juvenile salmonids and other prey types consumed by Caspian terns nesting on the designated colony area at East Sand Island in 2018. Finally, we will continue to provide technical assistance to BPA and other regional fish and wildlife management agencies in developing and implementing management initiatives for Caspian terns to reduce their impacts on fish species of conservation concern in the Columbia River basin.