PROGRAM DESCRIPTION
Background

Published research suggests that avian predation can, under some conditions, be a substantial source of mortality for juvenile salmonids. Mace (1983) estimated that 10.4-31.7% of hatchery-released chinook smolts in the Big Qualicum River on Vancouver Island succumbed to avian predation within just 2 km of the hatchery. A subsequent study on the same river estimated that predation by merganser broods alone accounted for 24-65% of smolt production (Wood 1987). Feltham (1995) estimated that mergansers removed 3-16% of smolt production on two Scottish rivers. In a 3-year study on the Penobscot River in Maine, predation by double-crested cormorants on hatchery-reared Atlantic salmon accounted for 7.5% to 9.2% of the run (Krohn and Blackwell 1996; Blackwell 1995). Perhaps most impressive is the estimate by Kennedy and Greer (1988) that 51-66% of smolts from a wild run in an Irish river were lost to cormorant predation.

Aggregations of piscivorous birds have been observed on the Columbia River near dams (Ruggerone 1986; Steuber et al. 1993; Jones et al. 1996), at hatchery (Schaeffer 1991; Schaeffer 1992) and barge release points (K. Collis, CRITFC, pers. obs.), and in the estuary (Bevan et al. 1994) near the large waterbird breeding colonies at Rice and East Sand islands. Predation by birds on radio-tagged chinook salmon smolts has been documented in the tailraces below The Dalles and John Day dams and in the Columbia River estuary (C. Schreck, OSU, pers. comm.). In 1995, 11.3% (11/97) of radio-tagged yearlings and 4.1% (4/71) of subyearlings fell prey to gulls below The Dalles Dam (J. Snelling, OSU, pers. comm.). In 1996 and 1997, between 10% and 30% of radio-tagged chinook yearlings migrating through the Columbia River estuary were consumed by terns or cormorants nesting in that area (C. Schreck, OSU, pers. comm.). The bioenergetics approach of estimating prey consumption yielded estimates of 5.4-14.2 million juvenile salmonids consumed by the Rice Island Caspian tern colony in both 1997 and 1998 (Roby et al. 2003). This is equivalent to 5-15% of the estimated number of out-migrating smolts to reach the estuary in those two years.

Caspian terns (Sterna caspia) are one of the more important predators of juvenile salmonids in the Columbia River Basin. Caspian terns are the largest tern species in the world and strictly piscivorous. Until the 2000 breeding season, Rice Island, a dredged material disposal island in the Columbia River estuary, was home to the largest Caspian tern colony in North America (ca. 8,000 nesting pairs; Roby et al. 2002), and perhaps the world (Cuthbert and Wires 1999). Numbers of breeding adults in the Columbia River estuary have increased by about an order of magnitude since the colony was first established in 1986 (G. Dorsey, USACE, pers. comm., Roby et al. 2002). In addition, there is another smaller Caspian tern colony above Bonneville Dam on Crescent Island, and terns nesting at this colony are mostly reliant on juvenile salmonids as a food source (Collis et al. 2002a; Antolos et al. in press).  In 2004, terns nesting on East Sand Island and Crescent Island consumed an estimated 3.5 and 0.5 million smolts, respectively.

Double-crested cormorants (Phalacrocorax auritus) are a common piscivore in the lower Columbia River. A large cormorant colony has become established on a rock jetty at the west end of East Sand Island in the Columbia River estuary. Just 15 years ago there were less than 100 pairs of double-crested cormorants nesting on East Sand Island, and cormorant nesting pairs throughout the estuary numbered in the hundreds. Now East Sand Island supports the largest double-crested cormorant colony in North America (Carter et al. 1995; Anderson 2002; L. Wires, pers. comm.). East Sand Island, plus nearby pilings and channel markers, supported a total population of roughly 13,000 breeding pairs in 2004 (Collis et al. 2005). This is consistent with continent-wide growth in double-crested cormorant populations and increasing frequency of conflicts with salmonid fisheries (Nettleship and Duffy 1995).  We estimate that cormorants nesting in the Columbia River estuary consumed between 2.5 and 10.3 million juvenile salmonids in 2004, and now may exceed the predation rate by Caspian terns nesting in the estuary (Collis et al. 2005).

Large breeding colonies of glaucous-winged/western gulls (Larus glaucescens x L. occidentalis) are located on three islands in the Columbia River estuary. These colonies have either grown substantially or become established in the last 15 years. In 1998, approximately 17,000 gulls were counted on aerial photography of colonies in the Columbia River estuary (Collis et al. 2002a), and consumed an estimated 0.4-3.9 million juvenile salmonids during that year (Collis et al. 1999). Given the numbers, population trajectories, species diversity, diets, and wide distribution of piscivorous waterbirds on the lower Columbia River, total losses of juvenile salmonids to avian predators now comprises a significant proportion of several runs.

The magnitude of predation on juvenile salmonids by Caspian terns nesting on Rice Island led to management action in 1999. A pilot study was conducted to determine whether the Rice Island tern colony could be relocated 26 km (16 miles) closer to the ocean on East Sand Island (river mile 5), where it was hoped terns would consume fewer salmonids. Habitat restoration, social attraction (decoys and audio playback systems), and selective predator removal were used to encourage terns to nest on East Sand Island. About 1,400 pairs of Caspian terns nested at the new colony site on East Sand Island in 1999.  In 2000, about 8,500 pairs of Caspian terns nested on East Sand Island, or 94% of all terns nesting in the estuary.  In 2001-2004, all Caspian terns nesting in the Columbia River estuary used East Sand Island, an average of 9,200 breeding pairs nesting at this one site.

Our results also indicate that relocating the tern colony to East Sand Island enhanced the productivity of Caspian terns nesting in the Columbia River estuary. Nesting success of Caspian terns on East Sand Island (0.57-1.39 young raised per breeding pair on average during 1999-2003) was consistently higher than for terns nesting on Rice Island, both prior to tern management (1997-1998: 0.06-0.45 young raised per breeding pair) and post-management (1999-2000: 0.15-0.55 young raised per breeding pair). The productivity measured at Rice Island was considerably lower than at other well-studied Caspian tern colonies in North America (range of 0.6-1.6 young raised per breeding pair; Cuthbert and Wires 1999).  

Terns nesting on East Sand Island foraged more in marine and brackish water habitats than did the terns nesting on Rice Island. The diet of East Sand Island terns averaged between 24% and 47% salmonids during the years 1999-2003, compared to the diet of Rice Island terns, which consisted of 77% and 90% salmonids in 1999 and 2000, respectively. The relocation of all nesting terns from Rice Island to East Sand Island resulted in a sharp drop in consumption of juvenile salmonids by terns nesting in the Columbia River estuary. Total consumption of juvenile salmonids in 2000, when most terns nested on East Sand Island, was estimated at 8.2 million (95% c.i. = 6.7-9.7 million), a reduction of about 4.2 million (34%) compared to 1998.  Total smolt consumption by terns nesting on East Sand Island in 2001-2004, when all terns nesting in the estuary used East Sand Island, was approximately 5.8, 6.5, 4.2, and 3.5 million, respectively. This represents 53%, 48%, 66%, and 72% reductions in estimated smolt consumption compared to 1998.  Caspian terns nesting on East Sand Island in 2004 still consumed an estimated 2.9 - 4.0 million smolts, with some ESA-listed stocks still suffering significant losses to tern predation (Ryan et al. 2001a; Ryan et al. 2001b; Ryan et al., unpubl. data).  To achieve further reductions in consumption of juvenile salmonids by Caspian terns in the estuary it will likely be necessary to reduce the size of the East Sand Island tern colony by relocating a portion of the colony to alternative sites outside the estuary.

Despite the higher nesting success of Caspian terns nesting on East Sand Island and reductions in tern predation on juvenile salmonids, several bird conservation groups sued the federal government (USACE, USFWS) to stop management of Caspian terns in the Columbia River estuary. The suit was successful, and in August 2001 a federal district judge in Seattle awarded the plaintiffs a permanent injunction against management of any fish-eating birds in the Columbia River estuary to benefit salmonids. Had the injunction stood, all Caspian terns nesting at East Sand Island would likely have returned to the former colony site on Rice Island within a few years.

In 2005, the U.S. Fish and Wildlife Service will begin implementing the preferred alternative of the Final EIS to further reduce Caspian tern predation on ESA-listed juvenile salmonids in the Columbia River estuary (USFWS 2005).  The preferred alternative recommends that the East Sand Island tern colony be reduced to 2,500-3,125 nesting pairs by limiting suitable nesting habitat on East Sand Island to 1-1.5 acres.  Terns displaced by this management action on East Sand Island are expected to relocate to smaller tern colonies in Coastal Washington (i.e., Dungeness Spit), Coastal and Interior Oregon (i.e., Crump Lake, Summer Lake, and Fern Ridge Reservoir), and Coastal California (i.e., San Francisco Bay) by 2010.  Increasing the amount of suitable habitat at these locations, while reducing habitat on East Sand Island, should advance relocation efforts.  This proposed research described here will gather information to help (1) assess the efficacy of the preferred tern management alternative outlined in the Final EIS, (2) assess the impacts of unmanaged bird populations, and (3) assist resource managers in developing management initiatives that will further reduce the impacts of piscivorous waterbirds on juvenile salmonids, if warranted by the results.  

Rationale and Significance

Caspian terns nesting on East Sand Island continue to consume millions of juvenile salmonids in the Columbia River estuary annually, despite the reduction in smolt consumption associated with relocation of the tern colony from Rice Island to East Sand Island (Roby et al. 2002, CBR 2003).  Based on smolt PIT tags recovered from the East Sand Island tern colony in 2000 and 2001 (Ryan et al. 2001a, 2001b), some ESA-listed salmonid stocks from the Columbia River basin, especially steelhead, continue to suffer significant losses to tern predation. Approximately two-thirds of Caspian terns in the Pacific coast population of North America are now nesting at East Sand Island, by far the largest known colony of its kind in the world (Cuthbert and Wires 1999, Wires and Cuthbert 2000). Risks to both Columbia Basin salmonids and the tern population may be further reduced if plans outlined in the Final EIS are successful over the course of the next several years.  This research will evaluate the efficacy of the preferred alternative outlined in the Final EIS as it is implemented.

Diets of double-crested cormorants in the Columbia River estuary, especially those nesting on Rice Island or nearby channel markers, include a significant proportion of juvenile salmonids (Collis et al. 2001; Collis et al. 2002a). The cormorant breeding population in the estuary is also large, grew rapidly in the 1990's (Collis et al. 2002a), and continues to grow (Collis et al. 2005). The double-crested cormorant colony on East Sand Island now numbers over 12,500 breeding pairs, the largest known colony of this species anywhere in North America (Collis et al. 2005). Cormorants are large birds, with concomitant high food requirements. Finally, shifts in the nesting distribution of Caspian terns in the estuary may affect diet composition and smolt consumption rates of cormorants through compensation, contributing further to smolt losses to double-crested cormorants in the estuary. These factors taken together suggest that the magnitude of predation by double-crested cormorants on juvenile salmonids in the Columbia River estuary may be sufficient to warrant management, now or in the future. An understanding of the dynamics of double-crested cormorant predation on juvenile salmonids will help resource managers develop and implement effective management initiatives to reduce predation, if warranted.

Previous estimates of population trends and diet composition at some colonies of piscivorous waterbirds in the lower Columbia River (above Bonneville Dam) suggest that predation on juvenile salmonids may be increasing and could potentially reach levels that are of concern to fisheries managers (Roby et al. 1998; Collis et al. 1999; CBR 2003: Collis et al. 2002a). For example, the proportion of juvenile salmonids in the diets of Caspian terns nesting at Crescent Island have rivaled that of the former colony of Caspian terns on Rice Island CBR 2003; Collis et al. 2002a). Increasing numbers of cormorants and American white pelicans have been observed on the Columbia River in recent years (S. Bickford, pers. comm.), particularly near dams. Bird wires installed to protect juvenile salmonids from plunge-diving avian predators (i.e., gulls and terns) are less effective in preventing predation by birds that forage from the surface (i.e., cormorants and pelicans). On-average, proportions of juvenile salmonids in diets of piscivorous waterbirds nesting at most up-river colonies (i.e., gulls, pelicans) are low (Collis et al. 2002a). Some individual predators may, however, have specialized in foraging on juvenile salmonids at particular sites where smolts are vulnerable, such as at dam tailraces and hatchery outflows. Studies are needed to determine the extent and dynamics of total losses of juvenile salmonids to avian predators on the lower Columbia River above Bonneville Dam. These bird populations may pose an increasing threat to salmon survival in the future because (1) the geographic range, abundance, and size of their colonies have been increasing throughout Washington and Oregon in recent years, and (2) current and future management of piscivorous waterbirds in the Columbia River estuary (e.g., Final EIS), and western Washington in general, may result in large numbers of these birds relocating to colonies further up-river.

Answers to these questions have profound short- and long-term implications for the management of salmon and birds. Management plans outlined in the Final EIS seek to shift the majority of the Caspian terns nesting in the estuary to newly restored and existing colony sites along the Pacific Coast and inland as a way to further reduce their impacts on Columbia Basin salmonids. Some of these birds may relocate to colonies in inland Washington and Oregon, including sites along the mid-Columbia River.  This study will help determine to what extent bird predation is a problem on the lower Columbia River, which colonies pose the greatest risk to salmonid survival, and how management in the estuary affects the distribution of breeding piscivorous waterbirds further up-river. These data will be important in assuring that smolt survival gains associated with bird management in the estuary are not offset by increased bird predation on juvenile salmonids at up-river locations.  Perhaps more importantly, data collected as part of this study will help guide managers in developing management initiatives on the lower Columbia River that are science-based, defensible, cost-effective, and have a high probability of success.

Funding

Previously (1999-2003) funding for this research program (as described above) came entirely from the Bonneville Power Administration.  Beginning in 2004 and continuing this contract year (2005), funding for this research will come 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.  In general, most of the funding for work conducted on the Columbia River above The Dalles Dam will come from the U.S. Army Corps of Engineers - Walla Walla District.  The research objectives and tasks associated with that work are not provided here.  As was the case in 2004, work conducted in the Columbia River estuary will be jointly funded by the Bonneville Power Administration and the U.S. Army Corps of Engineers - Portland District in FY05.  The attached statement of work describes the research objectives and tasks for work conducted in the Columbia River estuary in 2005, completion of which depends on joint funding from BPA ($220,000 in CY 05)  and the USACE ($310,638 in CY 05).  If less than $310,638 becomes available from USACE for this project by the beginning of the field season (March 2005), then the attached SOW and budget will require revision. We have indicated below the proposed source of support for each subtask or, if the support is split between the two funding agencies, the proportion of total support by each agency.