2013 Final Annual Report
The primary objectives of this project in 2013 were to (1) evaluate management initiatives implemented to reduce predation on juvenile salmonids (Oncorhynchus spp.) by Caspian terns (Hydroprogne caspia) 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) collect, compile, and analyze data needed to assist in completion of the NEPA analysis required for management of (a) double-crested cormorants (Phalacrocorax auritus) nesting on East Sand Island and (b) Caspian terns nesting at colonies in the Columbia Plateau region; (3) investigate the numbers of other piscivorous colonial waterbirds (i.e., Brandt’s cormorants P. penicillatus, California brown pelicans Pelecanus occidentalis californicus, American white pelicans P. erythrorhynchos, and gulls Larus spp.) that use the Columbia River to nest or roost and assess their potential impacts on smolt survival; and (4) assist resource managers as technical advisors in the development of plans for long-term management of avian predation on juvenile salmonids from the Columbia River basin, as warranted.
The Caspian tern colony on East Sand Island, the largest for the species in the world, consisted of about 7,400 breeding pairs in 2013. This is an increase from the estimate of 6,400 pairs in 2012, and the first increase since the initiation of habitat reduction on East Sand Island in 2008, when the colony numbered about 10,000 breeding pairs. In addition to the increase in colony size, Caspian terns at this colony were more resilient to disturbances by bald eagles and associated gull depredation on tern eggs and chicks compared to during 2010-2012. The Caspian tern colony on East Sand Island produced about 1,480 fledglings in 2013 (average of 0.20 young raised/breeding pair), a significant increase from 2010-2012 (average of 0 - 0.06 young raised/breeding pair), but lower than in other years during 2001-2009. The average proportion of juvenile salmonids in the diet of Caspian terns during the 2013 nesting season was 32%, similar to 2009-2012. The estimated total smolt consumption by Caspian terns nesting at East Sand Island in 2013 was 4.6 million (95% c.i. = 3.9 - 5.3 million), similar to 2012. Recoveries of smolt passive integrated transponder (PIT) tags on the Caspian tern colony at East Sand Island indicated that tern predation rates on salmonid smolts that were interrogated passing Bonneville Dam on the Columbia River or Sullivan Dam on the Willamette River were similar in 2013 and 2012. Also similar to previous years, tern predation rates were significantly higher on steelhead populations (8.6 – 12.5%, depending on the population) compared with salmon populations (0.6 – 1.4%, depending on the population). Despite the increase in the size of the tern colony in 2013 compared to 2012, predation rates on ESA-listed steelhead and salmon populations have trended lower since tern habitat reductions were initiated in 2008.
Caspian tern management actions in the Columbia River estuary continued in 2013. The U.S. Army Corps of Engineers, Portland District (Corps) maintained 1.58 acres of suitable nesting habitat for Caspian terns on East Sand Island, the same area of habitat as in 2012, and 32% of the area of nesting habitat provided during 2001-2007. The restriction in available tern nesting habitat on East Sand Island to 1.58 acres caused Caspian terns to nest at an average density of 1.17 nests/m2, an increase from 1.06 nests/m2 in 2012, and the highest tern nesting density so far observed in the Columbia River estuary. In addition, several hundred pairs of Caspian terns attempted to nest in three discrete satellite colonies on the upper beach of East Sand Island, adjacent to the 1.58-acre area of designated tern nesting habitat; however, no young were successfully raised in these satellite colonies. Passive deterrence measures (stakes, ropes, and flagging) installed by the Corps to dissuade Caspian terns from nesting on areas of the upper beach near the main colony along with tidal inundations of some nest sites were effective in limiting the formation and size of satellite colonies.
The Corps has constructed nine islands as alternative Caspian tern nesting colony sites since early 2008, 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 2013, and one is no longer being monitored for Caspian tern nesting activity. Of the six islands that were monitored for Caspian tern nesting activity, five supported nesting Caspian terns. A combined total of over 1,100 breeding pairs of Caspian terns nested at these five alternative colony sites in 2013, a 50% increase from 2012. Estimated productivity was low among the five sites, however, ranging from an average of 0 to 0.37 young raised/breeding pair, depending on the site. In 2013, mammalian and avian nest predators, displacement by other colonial waterbird species (i.e., California gulls L. californicus, American white pelicans), drought, adverse weather condition, and likely low forage fish availability (due to drought), limited Caspian tern colony formation, colony size, and nesting success at one or more of the alternative colony sites. A substantial number of Caspian terns that were banded at the colony on East Sand Island in the Columbia River estuary, however, did use the alternative colony sites created by the Corps; 57 terns banded in the Columbia River estuary were seen at the alternative colony sites in interior Oregon and 110 were seen at the alternative colony sites in the Upper Klamath Basin during the 2013 nesting season. Based on estimated movement rates (5.3%) calculated from Caspian terns banded as adults, 684 Caspian terns (including both banded and unbanded terns) were estimated to have moved from East Sand Island to alternative colony sites in 2013.
To further reduce the impacts of predation by Caspian terns nesting at East Sand Island on salmonid stocks from the Columbia River basin, more terns will need to be relocated to colonies outside the basin; the management objective is to reduce the size of the East Sand Island tern colony to 3,125 - 4,375 breeding pairs, less than 45% of its pre-management size (ca. 10,000 breeding pairs), while attracting the displaced Caspian terns to alternative colony sites.
The double-crested cormorant colony on East Sand Island consisted of about 14,900 breeding pairs in 2013. This is the largest double-crested cormorant colony ever recorded on East Sand Island, and is about 15% larger than it was during 2011-2012. This one colony likely includes more than 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, an estimated 1,550 pairs of Brandt’s cormorants nested in the cormorant colony on East Sand Island in 2013. 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.
Juvenile salmonids represented about 11% (by biomass) of the double-crested cormorant diet in 2013, compared to about 20% in 2012. Our estimate of total smolt consumption by double-crested cormorants nesting on East Sand Island in 2013 is 16.3 million smolts (95% c.i. = 11.4 – 21.1 million), not significantly different from the number of smolts consumed by cormorants from this colony in 2012. The majority of these consumed smolts (about 11.4 million or 70%) were sub-yearling Chinook salmon (O. tshawytscha) smolts consumed predominantly in the latter portion of the cormorants breeding season (June – August), as was the case in 2012. Estimated consumption of spring migrating smolts (coho [O. kisutch], yearling Chinook, and sockeye [O. nerka] salmon along with steelhead [O. mykiss]), however, was 4.8 million smolts (95% c.i. = 3.8 – 5.8 million), significantly less than consumption of spring migrants in 2012 (8.1 million smolts [95% c.i. = 6.2 – 9.9 million smolts]). This approximately 41% reduction in consumption of spring migrants occurred despite a 21% increase in peak cormorant colony size, suggesting a pronounced decline in proportion of spring migrants in the diet of double-crested cormorants during the 2013 nesting season.
As in other recent years, estimates of total smolt consumption by double-crested cormorants nesting on East Sand Island in 2013 were significantly higher than that of Caspian terns nesting on East Sand Island. During 2004 – 2013, estimates of total annual smolt consumption by the East Sand Island double-crested cormorant colony have varied widely, from a low of 2.4 million smolts to a high of 20.5 million smolts (mean = 12.3 million). This large inter-annual variability in smolt consumption (coefficient of variation {CV} = 49%) has occurred over a period of relatively stable colony size (10,950 – 14,900 breeding pairs; CV = 9%) and has closely tracked the proportion of the cormorant diet that was salmonid smolts (2 – 20% of biomass consumed; CV = 47%); the proportion of smolts in the cormorant diet is an important input parameter in the bioenergetics calculations.
During 2004 - 2013, the type of salmonid consumed in the largest numbers by double-crested cormorants nesting at East Sand Island was sub-yearling Chinook salmon (ca. 7.8 million smolts/year), followed by coho salmon, steelhead, and yearling Chinook salmon (ca. 2.4, 1.1, and 1.0 million smolts/year, respectively). Recoveries of smolt PIT tags on the East Sand Island cormorant colony in 2013 indicated that population- or ESU-specific predation rates ranged from 0.7% to 2.9% for populations originating upstream of Bonneville Dam on the Columbia River or upstream of Sullivan Dam on the Willamette River. Despite the increase in the size of the cormorant colony in 2013, the ESU-specific predation rates measured in 2013 were some of the lowest recorded since 2007. Similar to consumption estimates (number of fish consumed based on bioenergetics calculations), cormorant predation rates on particular populations or ESUs of salmonids based on smolt PIT tag recoveries have been highly variable among salmonid populations and among years. As demonstrated by the data collected in 2013, variability in the impacts on salmonids from cormorant predation cannot be explained by differences in colony size alone. Factors driving the large inter-annual variation in impacts of cormorant predation (smolt consumption and predation rates) are poorly understood, but may include environmental conditions in the estuary, the abundance and arrival timing of marine forage fish in the estuary, differences in cormorant nesting chronology and success, and/or other biotic and abiotic factors that influence cormorant feeding behavior.
In 2013, the USACE expanded a pilot study initiated in 2011 to test possible strategies for limiting the size of the East Sand Island cormorant colony. Prior to the nesting season, two 8-foot-high privacy fences were built to bisect the colony. These fences visually separated 4.0 acres (25%) of the ca. 16 acres of available cormorant nesting area at the west end of East Sand Island. We used human disturbance to haze cormorants during the nest initiation period, and were successful in dissuaded them from using areas outside the 4.0-acre designated area in 2013. Some double-crested cormorants were satellite-tagged (n = 83) to follow their post-hazing movements to prospective new nesting sites. About 96% of these tagged cormorants (80/83) dispersed from the East Sand Island colony after tagging, and of these about 96% eventually returned to East Sand Island (73/76) and attempted to nest there. Tagged cormorants dispersing from East Sand Island during the nesting season were detected at colonies and roost sites (1) elsewhere in the Columbia River estuary (n = 76), (2) on the lower Columbia River below Bonneville Dam (n = 27), (3) on the outer Washington coast (including Willapa Bay and Grays Harbor; n = 21), and (4) in Puget Sound (n = 1). No double-crested cormorants satellite-tagged on East Sand Island early in the 2013 nesting season were detected along the coast of Oregon during the nesting season.
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 the single most significant avian predator (per capita) in the Columbia Plateau region on salmonid smolts, particularly ESA-listed steelhead populations from the Upper Columbia River and Snake River. Total numbers of Caspian terns nesting in the Columbia Plateau region declined from ca. 870 breeding pairs during 2005-2012 to ca. 775 breeding pairs in 2013, distributed among five breeding colonies. In 2013, the two largest Caspian tern colonies in the Columbia Plateau region were at Crescent Island (395 breeding pairs) on the mid-Columbia River and at Goose Island (340 breeding pairs) on Potholes Reservoir, WA. The size of both of these Caspian tern colonies declined from 2012 to 2013, but nesting success at both colonies increased in 2013. A small number of Caspian terns (about 26 breeding pairs) established nests at the Blalock Islands in the mid-Columbia River, but nesting success was quite limited. We observed a small number of banded Caspian terns that were originally banded as adults on East Sand Island in the Columbia River estuary, where management actions have been implemented, at the Goose Island (n = 1) and Crescent Island (n = 4) colonies in 2013. Prior to 2011, when tern management intensified at East Sand Island, movement to the Columbia Plateau region by banded adult Caspian terns that previously nested on East Sand Island had not been documented.
Estimates of Caspian tern predation rates on salmonids based on smolt PIT tag recoveries on tern colonies in the Columbia Plateau region indicated that impacts were greatest on the upper Columbia River steelhead population (14.9% depredated by terns from the Goose Island colony) and on the Snake River steelhead population (2.8% depredated by terns from the Crescent Island colony). Predation rates by Goose Island terns on upper Columbia River yearling Chinook were also notable (2.1%), but significantly lower than predation rates on steelhead. Predation rates by Caspian terns nesting at the small colony in the Blalock Islands were an order of magnitude less than those of terns nesting at Goose and Crescent islands, but steelhead were still highly susceptible to predation by terns from this colony.
A total of 23 adult Caspian terns nesting at Goose Island were marked with GPS tags and tracked during foraging trips over several days. Nearly half of the GPS-tagged terns (n = 11) made foraging trips to the mid-Columbia River, including Wanapum Reservoir, Priest Rapids Reservoir, and Hanford Reach. Of note, four GPS-tagged terns made foraging trips to the lower Snake River, including one tern that exhibited the greatest foraging range ever documented in a breeding Caspian tern: 93 km straight-line distance from the colony.
Management of the Caspian tern colonies at Goose and Crescent islands to reduce their impacts on ESA-listed salmonids is currently under consideration by regional managers. Band re-sighting data indicate high connectivity among Caspian tern colonies in the Columbia Plateau region and colonies elsewhere in western North America from Mexico to Alaska, both inland and along the coast. This suggests that Caspian terns displaced from these two Columbia Plateau colonies may re-nest at existing or newly-created colony sites outside the Columbia River basin.
Total numbers of double-crested cormorants nesting in the Columbia Plateau region decreased slightly in 2013, from about 1,570 breeding pairs during 2012 to about 1,400 breeding pairs at four colonies in 2013; the largest colonies were in the North Potholes Reserve (ca. 800 nesting pairs) and on Foundation Island in the mid-Columbia River (ca. 390 nesting pairs). Numbers of American white pelicans nesting on Badger Island in the mid-Columbia River, a colony that experienced rapid growth during 2004-2011, appear to have stabilized at about 2,100 adults. The numbers of California gulls nesting on Miller Rocks, a colony located just downstream of John Day Dam on the Columbia River, were similar to those observed in recent years (ca. 4,800 adults). Following the abandonment of the large California gull colony on Three Mile Canyon Island (ca. 6,200 adults were counted on-colony in 2009), there was a commensurate increase in the number of California gulls nesting on islands in the Blalock Islands complex during 2012-2013; in 2013 ca. 8,100 nesting gulls (mostly California gulls) were counted on two islands in the Blalock Islands, whereas in 2009 no gulls nested there.
Currently there are no plans to manage colonies of cormorants, gulls, or white pelicans in the Columbia Plateau region based on previous research investigating their relative impacts on survival of juvenile salmonids. Recently-collected smolt PIT tag data, however, casts new light on the impacts of certain gull colonies on smolt survival, in particular the California gull colonies on Miller Rocks and Crescent Island. Deposition rates of smolt PIT tags on nesting colonies (percentage of smolt PIT tags that were consumed by gulls and subsequently deposited by the gull on-colony and used to estimate predation rates) by California gulls were significantly lower than those of Caspian terns and double-crested cormorants. Average on-colony PIT tag deposition rates by California gulls was just 17% (95% c.i. = 14% - 19%) in 2012 and 2013. Incorporation of on-colony deposition rates into predation rate models increased the estimates of colony-wide predation rates on juvenile salmonids by a factor of about 6 for California gulls, compared to previously published estimates. After adjusting for on-colony deposition rates, colony-wide predation rates on juvenile salmonids varied significantly by salmonid ESU and gull colony (range: < 0.1% to 8.5%); the California gull colonies on Miller Rocks and Crescent Island had a much greater impact on smolt survival compared to the California gull or ring-billed gull colonies on Island 20 (on the mid-Columbia River near Richland, WA) and the Blalock Islands. These results suggest that smolt predation rates by gulls nesting at some colonies in the Columbia Plateau region are comparable to, if not higher than, those of Caspian terns and double-crested cormorants nesting at colonies in the Columbia Plateau region.
-Bird Research Northwest
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