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East Sand Cormorant Colony Increasing; Estuary’s Single Most Significant Source Of Smolt Mortality
Posted on Friday, January 03, 2014 (PST)

Salmon-chomping double-crested cormorants that have been nesting in greater numbers each spring and summer at the lower Columbia River estuary’s East Sand Island showed that they could be pushed by human dissuasion from one spot to another, but only a small fraction left the area altogether, according to preliminary results produced during 2013 monitoring.

 

The research data comes from one of several ongoing studies guided by, and funded through, the U.S. Army Corps of Engineers to determine the effect estuary and inland bird populations are having on Columbia and Snake River salmon and steelhead stocks, many of which include naturally produced fish that are protected under the Endangered Species Act.

 

Preliminary analysis of data collected in 2013 in a variety of avian predation studies was presented during the Corps’ Anadromous Fish Evaluation Program Annual Review held in early December in Walla Walla, Wash.

 

The avian predation studies also aim to evaluate potential strategies for reducing impacts on juvenile salmon swimming down through from the Columbia-Snake-Willamette river basin. The Corps is amidst the process of completing an environmental impact statement regarding potential options for reducing East Sand-based cormorant predation.

 

In 2010 and 2011 respectively, the colony consumed approximately 19.2 million and 20.5 million hatchery and ESA-listed juvenile salmonids per year, as the fish migrated toward the Pacific Ocean, according to the Corps.

 

That is the single most significant source of mortality affecting juvenile salmonids in the estuary, researchers say.

 

Researchers estimate that losses of smolts to predation by Caspian terns and double-crested cormorants nesting on East Sand Island in the Columbia River estuary were about 24 million fish in those years.

 

This represents about 15-20 percent of all smolts that survived to the estuary.

 

The cormorant colony size has grown each over the 1990s and 2000s at East Sand to become the largest on the West Coast and likely in the world.

 

In 2012, as in 2011, smolt consumption by cormorants nesting on East Sand Island exceeded smolt consumption by Caspian terns nesting on East Sand Island by a factor of about 4, according to a team made up of Oregon State University-based researchers as well as NOAA Fisheries scientists. The team is led by Dan Roby of the U.S. Geological Survey-Oregon Cooperative Fish and Wildlife Research Unit at OSU and Ken Collis of Real Time Research.

 

A tern management plan is already well under way, with nesting habitat reduced to 1.58 acres, a 68 percent reduction from the East Sand colony area that existed in 2001-2007.

 

That attempt is to persuade terns to relocate away from the estuary’s salmon freeway. The Corps has since 2008 guided the construction of nine islands, six in interior Oregon and three in the upper Klamath River basin region of northern California, as alternative nesting sites. The Corps, and Bureau of Reclamation, operate dams in the Federal Columbia River Power System. The

 

Corps is also responsible for maintaining a Columbia River navigation channel that allows upstream passage of cargo chips. Dredged materials from channel maintenance has in the past been relocated in-river and has resulted in the creation or expansion of islands such as East Sand.

 

Seven of those sites were available in 2013 and five were used by terns, according to preliminary results presented at the AFEP gathering by OSU’s Yasuko Suzuki on Caspian tern management in the Columbia River estuary.

 

Productivity at the inland islands was relatively low due to a variety of factors, according to the abstract for Suzuki’s presentation. Limits included mammalian and avian predation on the tern nests and drought and other adverse weather conditions.

 

“A substantial number of Caspian terns from the colony on East Sand Island in the Columbia River estuary, however, did use the alternative nesting sites created by the Corp; 57 terns originally banded in the Columbia River estuary were seen at the alternative sites in interior Oregon and 110 were seen at the alternative sites in the Upper Klamath Basin during the 2013 nesting season,” according to the preliminary analysis described in the abstract, “Implementation of the Caspian Tern Management Plan: Status of Tern Colonies in the Columbia River Estuary and at Corps-constructed Colony Sites.”

 

The East Sand cormorant colony experienced a year of change in 2013, some human caused and others not so easy to explain, according to “Ecological Developments at the Double-Crested Cormorant Colony on East Sand Island: Status, Dispersal, Management Pilot Studies, and Implications for Salmonid Restoration,” a review of 2013 preliminary data presented at the AFEP conference by Roby.

 

“The double-crested cormorant colony on East Sand Island consisted of about 14,900 breeding pairs in 2013,” according to the study abstract prepared for the AFEP review. Results presented at the conference are preliminary. Analysis of data is for the most part fine-tuned over the winter and finalized ahead of the next research season.

 

“This is the largest colony ever recorded on East Sand Island, and is about 15 percent larger than it was in 2011-2012. This one colony likely includes more than 40 percent of the breeding population of double-crested cormorants in western North America, and is the largest known breeding colony of the species anywhere.

 

“Juvenile salmonids represented about 10 percent of the double-crested cormorant diet (by biomass) in 2013, compared to 20 percent in 2012. Estimates of total smolt consumption (based on bioenergetics calculations) and stock-specific predation rates (based on PIT tag recoveries) by double-crested cormorants from the East Sand Island colony are not yet available for 2013,” the abstract says.

 

Estimated commorant consumption of smolts in 2012 was about 18.9 million, and population-specific predation rates for salmonid populations originating above Bonneville Dam ranged from 0.6 percent to 7.2 percent of fish that survived to the estuary, depending on the salmonid population.

 

This past summer the Corps expanded on a pilot study that was initiated in 2011 to test possible strategies for limiting the size of the cormorant colony. Fences were built to bisect the colony, visually separating a 4-acre plot from the other 75 percent of the former colony nesting area. Hazing was then employed to prevent cormorants from nesting outside of the four-acre area. That effort was successful, according to preliminary results.

 

A sampling of cormorants were satellite tagged so that post-hazing movements could be monitored. About 96 percent of the tagged birds dispersed from the island, but 96 percent of them returned and attempted to nest.

 

But some of the dispersed birds were later located at colonies and roost sites elsewhere in the estuary, on the lower Columbia River below Bonneville Dam (which is located at river mile 146) and up the Willamette River, on the outer Washington coast including Willapa Bay and Grays Harbor, outer Vancouver Island in British Columbia and in Puget Sound.

 

“No cormorants satellite-tagged on East Sand Island early in the 2013 nesting season were detected along the coast of Oregon during the nesting season,” according to the preliminary data.

 

The AFEP studies evaluate passage success up and down the Columbia-Snake river hydro system, survival, and fish condition for surface bypass technologies at the dams, transportation of fish down through the system, conventional bypass systems, spill as a passage alternative, the effect on fish of total dissolved gas stirred up by hydro operations such as spill, adult migration/passage, in-river passage and turbine passage. Most are developed as integral components of larger studies and evaluation features of the Corps’ Columbia River Fish Mitigation program related to new passage technologies, while others evaluate the pros and cons of existing hydro project features.

 

The research is largely funded by the Corps through congressional appropriations. Those appropriations are repaid to the U.S. Treasury by the Bonneville Power Administration, which markets power generated in the hydro system and is obligated by federal law to mitigate for system impacts on fish and wildlife.

 

“In these drafts and preliminary research documents, opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the U.S. Army,” according to the Corps.

 

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