2014 Final Annual Report
The primary objectives of this study in 2014 were to (1) evaluate management initiatives implemented to reduce predation on juvenile salmonids by Caspian terns nesting on East Sand Island in the Columbia River estuary, including the monitoring of alternative Caspian tern nesting islands built by the Corps outside the Columbia River basin; (2) evaluate management implemented to reduce predation on juvenile salmonids by Caspian terns nesting on Goose Island in Potholes Reservoir by (a) collecting PIT-tags from piscivorous waterbird colonies to estimate smolt predation rates and (b) monitoring Caspian tern dispersal patterns associated with activities to dissuade nesting on the Goose Island colony; (3) monitor and evaluate colony size and juvenile salmon consumption by double-crested cormorants (Phalacrocorax auritus) nesting on East Sand Island and other sites in the lower Columbia River estuary; and (4) provide technical assistance to resource managers on the topic of avian predation on ESA-listed juvenile salmonids, as warranted.
The management plan entitled, Caspian Tern Management to Reduce Predation of Juvenile Salmonids in the Columbia River Estuary was first implemented in 2008 and continued in 2014. As part of this plan, the U.S. Army Corps of Engineers – Portland District (Corps) maintained 1.55 acres of suitable nesting habitat for Caspian terns on East Sand Island in 2014, slightly less than the area of nesting habitat provided during 2012-2013 (1.58 acres), and a 69% reduction in area of tern nesting habitat on East Sand Island compared to what was provided during 2001-2007, prior to implementation of the management plan. In 2014, Caspian terns nested on the East Sand Island colony at an average density of 1.06 nests/m2, a decrease from the average nesting density recorded in 2013 (1.17 nests/m2), but still a higher nesting density compared to pre-management (average of 0.55 nests/m2). Passive nest deterrence measures (stakes, ropes, and flagging) installed by the Corps to dissuade Caspian terns from nesting on the upper beach near the main tern colony and elsewhere on East Sand Island were successful in preventing Caspian terns from forming satellite colonies anywhere on East Sand Island in 2014.
The Caspian tern colony on East Sand Island, the largest for the species in the world, consisted of about 6,270 breeding pairs in 2014. This is a decrease from the estimate of 7,400 pairs in 2013 and the smallest Caspian tern colony size recorded at East Sand Island since the initiation of reductions in tern nesting habitat on the island in 2008, as part of the Caspian Tern Management Plan. This represents a decline of about 41% in the size of the Caspian tern colony on East Sand Island from its peak in 2008 (ca. 10,670 breeding pairs). As was the case in 2013, Caspian terns at this colony were relatively resilient to disturbances by bald eagles (Haliaeetus leucocephalus) and associated gull (Larus spp.) depredation of tern eggs and chicks, limiting factors that caused the Caspian tern colony to fail or nearly fail during 2010-2012. The Caspian tern colony on East Sand Island produced roughly 1,700 fledglings in 2014 (average of about 0.28 young raised/breeding pair), an increase compared to 2010-2012 when productivity averaged 0 – 0.06 young raised/breeding pair, but still lower than the average during the previous decade (2000-2009).
The average proportion of juvenile salmonids in the diet of Caspian terns nesting on East Sand Island during the 2014 nesting season was 33%, similar to the average observed over the previous eight nesting seasons. The estimated total smolt consumption by Caspian terns nesting at East Sand Island in 2014 was 4.5 million (95% c.i. = 3.9 - 5.1 million), not significantly different from total annual smolt consumption during 2011, 2012, and 2013, but significantly less than pre-management. Predation rates on specific populations of salmonids (ESUs/DPSs) by Caspian terns in 2014 were similar to those observed during 2011-2013, but were generally lower than those observed during the period 2007-2010. Reductions in tern predation rates following the implementation of management coincided with comparable reductions in tern colony size, suggesting that Caspian tern management initiatives to reduce tern nesting habitat on East Sand Island are resulting in lower predation rates on particular ESUs/DPSs of salmonids in the Columbia River estuary. Similar to previous years, Caspian tern predation rates were significantly higher on populations of steelhead (O. mykiss) smolts (8.6 – 11.4%, depending on DPS) compared with populations of salmon (0.9 – 1.6%, depending on ESU).
Since 2008, the Corps has constructed nine islands as alternative colony sites for Caspian terns displaced from East Sand Island, six in interior Oregon and three in the Upper Klamath Basin region of northeastern California. Two of these islands were not available for tern nesting in 2014, and one is no longer being monitored for Caspian tern nesting activity. The other six Corps-constructed islands were monitored for Caspian tern nesting activity in 2014, and nesting attempts by Caspian terns were recorded at five of these islands. A combined total of 786 breeding pairs of Caspian terns attempted to nest at Corps-constructed tern islands in 2014, a 27% increase from the average number of breeding pairs that nested on Corp-constructed tern islands in 2008-2013 (618 breeding pairs). Estimated average productivity among the five Corps-constructed islands, however, was somewhat higher in 2014 (0.27 young raised/breeding pair) compared to 2013 (0.18 young raised/breeding pair). The increase in average nesting success by Caspian terns at the Corps-constructed islands from 2013 to 2014 was in large part due to increased predator control efforts at these sites. Regardless, nest predation by mammalian and avian predators, displacement by other colonial waterbird species (i.e., California gulls [L. californicus] and American white pelicans [Pelecanus erythrorhynchos]), drought, adverse weather conditions, and apparent low availability of preferred forage fish (due to drought) continued to limit Caspian tern colony formation, colony size, and nesting success at the Corps-constructed islands. Nevertheless, a substantial number of Caspian terns that were banded at the colony on East Sand Island in the Columbia River estuary used the Corps-constructed islands as alternative colony sites; a total of 84 Caspian terns banded in the Columbia River estuary were resighted at one or more of the Corps-constructed islands in interior Oregon and northeastern California during the 2014 nesting season. Based on the estimated movement rate of Caspian terns from East Sand Island to the Corps-constructed islands (3.1%; calculated using Program MARK on mark-resighting data of banded adult Caspian terns), about 461 Caspian terns (3.1% of breeding individuals at the East Sand Island colony in 2013, including both banded and unbanded birds) moved from East Sand Island to the Corps-constructed islands in 2014. This high number of Caspian terns moving from East Sand Island to the Corps-constructed islands in a single year (461 individuals) demonstrates the connectivity of the East Sand Island colony with the colonies that have formed on the Corps-constructed islands in interior Oregon and northeastern California.
To further reduce the impacts of predation by Caspian terns nesting at East Sand Island on survival of salmonid smolts in the Columbia River estuary, more Caspian terns (1,895-3,145 breeding pairs) will need to be relocated to colonies outside the basin based on the size of the colony in 2014 (6,270 breeding pairs) relative to the target colony size for Caspian terns nesting on East Sand Island identified in the management plan (3,125 - 4,375 breeding pairs). This will likely require a further reduction in area of suitable Caspian tern nesting habitat on East Sand Island by at least one third, or down to about 1 acre of nesting habitat.
In 2014, efforts to monitor of the double-crested cormorant colony on East Sand Island in the Columbia River estuary were reduced from previous years, awaiting the completion and release of the Double-crested Cormorant Management Plan to Reduce Predation of Juvenile Salmonids in the Columbia River Estuary, with management actions scheduled for implementation as early as the spring of 2015. Objectives for monitoring the double-crested cormorant colony on East Sand Island in 2014 were to (1) estimate colony size and (2) estimate stock-specific predation rates on juvenile salmonids. The double-crested cormorant colony on East Sand Island consisted of about 13,600 breeding pairs in 2014, about 26% more than the average number of double-crested cormorants that nested on East Sand Island in 1997-2013 (ca. 10,775 breeding pairs). This one colony includes at least 40% of the breeding population of double-crested cormorants in western North America, and is the largest known breeding colony of the species anywhere. In addition to double-crested cormorants, ca. 1,630 pairs of Brandt’s cormorants (P. penicillatus) nested in the cormorant colony on East Sand Island in 2014. Brandt’s cormorants first nested in this mixed-species colony in 2006, and numbers increased each year through 2012, when 1,680 breeding pairs were counted.
Despite a smaller colony in 2014, recoveries of smolt PIT tags on the East Sand Island cormorant colony in 2014 indicated that ESU/DPS-specific predation rates were up substantially compared with 2013 and were some of the highest recorded since the colony was first scanned for PIT tags in 1999. Predation rates on salmon ESUs were especially high relative to previous years, with an estimated 8.5% (95% c.i. = 6.1 - 13.2%) and 6.1% (95% c.i. = 3.9 - 10.1%) of Snake River spring/summer Chinook (O. tshawytscha) and Upper Columbia River spring Chinook, respectively, consumed by cormorants in 2014. Predation on steelhead DPSs ranged from 6.4% (95% c.i. = 3.7 - 10.7%) on Middle Columbia River steelhead to 10.4% (95% c.i. = 7.3 - 16.3%) on Upper Columbia River steelhead. As demonstrated by smolt PIT tag data collected in 2014 and previous years, inter-annual variation in the impact of cormorant predation on survival of salmonid smolts in the Columbia River estuary was poorly explained by differences in colony size alone. Factors that have been linked to high inter-annual variation in cormorant predation (smolt consumption and predation rates) include river discharge into the estuary and ocean conditions (i.e., the North Pacific Gyre Oscillation) as they influence the abundance and availability of alternative prey (marine and estuarine forage fishes).
Native piscivorous colonial waterbirds that nest in the Columbia Plateau region include Caspian terns, double-crested cormorants, American white pelicans, California gulls, and ring-billed gulls (L. delawarensis). Of these, Caspian terns have been identified as having the greatest impact on ESA-listed juvenile salmonids in the Columbia Plateau region. The impacts of Caspian tern predation in the Columbia Plateau region on survival of ESA-listed steelhead populations from the Upper Columbia River and Snake River have been especially high. In January 2014, the U.S Army Corps of Engineers – Walla Walla District completed the Inland Avian Predation Management Plan (IAPMP). The goal of the IAPMP is to reduce Caspian tern predation rates on ESA-listed Columbia Basin salmonids to less than 2% (per colony and per ESA-listed population) by redistributing Caspian terns from the two largest nesting sites in the Columbia Plateau region (i.e., colonies on Goose Island in Potholes Reservoir and on Crescent Island in the mid-Columbia River) to sites outside the Columbia River Basin. In 2014, the Corps and the Bureau of Reclamation (BOR) implemented Phase I of the IAPMP by reducing nesting habitat on Goose Island and actively discouraging Caspian terns from nesting there.
In 2014, as part of a separately study funded by the U.S. Army Corps of Engineers – Walla Walla District and the U.S. Bureau of Reclamation (see separate report; BRNW 2014b), we monitored Caspian tern nesting activity throughout the Columbia Plateau region to help evaluate the effectiveness of the nest dissuasion actions implemented at Goose Island in dispersing Caspian terns to alternative colony sites outside the basin. These nest dissuasion actions were successful in preventing all but three breeding pairs of Caspian terns from nesting on Goose Island proper in 2014 (340 breeding pairs nested there the previous year). The three breeding pairs that nested on Goose Island each laid a single egg that was collected under permit soon after it was laid. Formation of a Caspian tern breeding colony on Goose Island was prevented in 2014 without causing any apparent disruption of breeding California and ring-billed gulls on the island. Surveys throughout the Columbia Plateau region in 2014 indicated that Caspian terns attempted to nest at four additional sites where they had previously nested and two new sites not previously used by nesting Caspian terns. The four previously used Caspian tern colony sites that were also active in 2014 were: Crescent Island on the mid-Columbia River (474 breeding pairs); Twinning Island in Banks Lake (67 breeding pairs); the Blalock Islands on the mid-Columbia River (45 breeding pairs); and Harper Island in Sprague Lake (8 breeding pairs). The new Caspian tern breeding sites were on a small rocky islet adjacent to Goose Island in Potholes Reservoir (dubbed “Northwest Rocks”; 156 breeding pairs) and amongst a small colony of gulls on a small island in Lenore Lake (2 breeding pairs). Of these seven sites, only the colonies at Crescent Island, the Blalock Islands, and Northwest Rocks succeeded in raising any young.
Recoveries of smolt PIT tags on the colony at Northwest Rocks indicated that Caspian terns nesting there consumed 2.9% (95% c.i. = 1.9 - 5.1%) and 0.3% (95% c.i. = 0.1 - 0.7%) of Upper Columbia River steelhead and yearling Chinook salmon, respectively. Estimated predation rates by Caspian terns nesting at Northwest Rocks in 2014 were the lowest recorded for Caspian terns nesting at Potholes Reservoir to date, and significantly lower than pre-management estimates during 2007-2013. These results indicate that efforts to dissuade Caspian terns from nesting on Goose Island in Potholes Reservoir were successful at reducing smolt consumption by Caspian terns in the Columbia Plateau region in 2014. The reduction in Caspian tern predation rate on steelhead smolts, however, was not below the 2% threshold target established by the IAPMP.
In conjunction with the efforts to dissuade Caspian terns from nesting on Goose Island in 2014, we evaluated the individual responses of 28 Caspian terns that were captured on Goose Island prior to egg-laying and fitted with solar-powered satellite telemetry tags. We observed three types of initial response by tagged Caspian terns to elimination of tern nesting habitat on Goose Island: (1) stay in the area and compete for reduced available nesting habitat (i.e. Northwest Rocks), (2) move to one of several nearby colonies (70 – 125 km away) and attempt to nest there, returning to the Goose Island area if nesting fails, and (3) nomadic wandering throughout the region, without a sustained association with any colony. Tern foraging activity was reduced in areas of the mid-Columbia River where terns have previously had substantial impacts on Upper Columbia River steelhead (i.e. the Wanapum and Priest Rapids pools). Displaced terns did not leave the larger Columbia Plateau region at an appreciable rate during the primary smolt outmigration period, however. Consequently, some predation may have been shifted to other locations and/or other Columbia Basin salmonid populations. Additional IAPMP actions to be implemented in 2015, including an expansion of nest dissuasion from Goose Island to the nearby adjacent islets, initiation of nest dissuasion at Crescent Island, and enhancement of nesting habitat for Caspian terns in San Francisco Bay, appear poised to address several of the factors limiting the displacement of terns from the Columbia Plateau. Marginal nesting habitat at Banks Lake, Sprague Lake, or in the Blalock Islands in the Columbia River (John Day Pool) may be a continued draw for displaced Caspian terns, however. The inability of tagged terns to nest successfully anywhere away from the rocky islet adjacent to Goose Island in 2014 suggests that the long-term goal of reducing tern predation on Columbia Basin salmonids by encouraging fidelity to nest sites outside the Columbia Basin will likely require a sustained, multi-year effort.
The largest Caspian tern breeding colony in the Columbia Plateau region during 2014 was on Crescent Island in the mid-Columbia River. A total of about 474 breeding pairs of Caspian terns attempted to nest on Crescent Island in 2014, a 21% increase in colony size compared to 2013. Resighting of banded Caspian terns on the Crescent Island tern colony suggested that much of the increase in colony size at Crescent Island was related to management actions at Goose Island to reduce colony size there, causing some Caspian terns to immigrate to the Crescent Island colony, about 100 km away. Despite increases in colony size at both Crescent Island and other Caspian tern colonies in the Columbia Plateau region in 2014, the overall size of the Caspian tern breeding population in the region did not increase, and apparently declined slightly in 2014 (758 breeding pairs) compared to 2013 (773 breeding pairs).
Predation rates on steelhead populations by Caspian terns nesting on Crescent Island were higher in 2014 compared to previous years (2007-2013). In 2014, predation rates on Upper Columbia River steelhead (3.4%; 95% c.i. = 2.5 - 4.9%) and Snake River steelhead (4.7%; 95% c.i. = 3.7 - 6.9%) and were the first and second highest predation rates recorded since 2007, respectively. Impacts on survival of salmonid smolts, both steelhead and salmon, from Caspian terns nesting on Twinning Island and the Blalock Islands in 2014 were lower than for Caspian terns nesting on Crescent Island, due in part to the much larger size of the Crescent Island tern colony (474 pairs), compared with the Caspian tern colonies on Twinning Island (66 pairs) or the Blalock Islands (45 pairs). Over-all (all Caspian tern colonies combined) predation rate estimates indicate that actions to dissuade Caspian terns from nesting in Potholes Reservoir in 2014 resulted in lower impacts on upper Columbia River ESUs/DPSs compared to previous years, suggesting that management actions in 2014 benefited fish survival, particular survival of Upper Columbia River steelhead.
-Bird Research Northwest
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