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Corps Chooses Not to Further Reduce
Estuary Habitat for Salmon-Eating Terns

by Staff
Columbia Basin Bulletin, April 4, 2014

(STEVE RINGMAN / THE SEATTLE TIMES) Caspian terns fill the skies on East Sand Island, a home to which they were lured by federal agencies. Now the government says it's moving time again. A U.S. Army Corps of Engineers "environmental assessment" released March 25 concludes that further reducing Caspian tern nesting space on the lower Columbia River estuary's East Sand Island "would likely impact juvenile salmonids in the Columbia River Basin more in 2014" than continuing the status quo.

The Corps document weighed whether or not to maintain the Caspian tern nesting space allowed over the past three years, or reduce it further in hope that more of the fish-eating birds would be inclined to move to areas outside the estuary.

The Caspian tern breeding colony observed each year on East Sand Island during the past decade or more is considered to be the largest of its kind in the world. It consisted of about 6,400 breeding pairs in 2012, continuing what has been a downward trend in colony size from the peak of about 10,000 pairs in 2008.

Caspian terns nested on an average of five acres from 2001 to 2004 on East Sand Island. But that acreage has since been gradually reduced to about1.5 acres as new habitat, approximately seven to eight acres, has been created at other sites to make up for the loss.

The "Caspian Tern Plan" created as a predation management tool identified an ultimate target colony size as 3,125 to 4,375 nesting pairs over an acreage of 1.5 to 2.0 acres (with a final goal of 2,500 to 3,125 nesting pairs).

But greater than expected nesting density, which resulted in higher than desired numbers of East Sand nesting pairs last year, led to consideration of reducing the nesting area to less than 1.5 acres.

But now is not the time to ratchet down East Sand nesting space, according to the Corps' EA released last week.

The National Environmental Policy Act assessment was prompted by the desire to, in the long term, shift the largest share of terns that nest each spring on East Sand to other areas, mostly in central Oregon and northern California, where the birds would likely include fewer salmon and steelhead in their daily diet.

The terns' annual spring-summer colonization of the lower Columbia estuary blossomed in the 1980s and 1990s, in large part because of the human-caused deterioration of nesting sites elsewhere up and down the West Coast and because of the creation of new islands in the river through the deposition of dredge materials from the maintenance of navigation channels.

The new islands, Rice and East Sand, in particular, represented desirable tern habitat in an area where juvenile salmon and steelhead from across the Columbia, Willamette and Snake river basins are funneled as they migrate toward the Pacific Ocean. Many of those young fish are from depleted stocks that are listed under the Endangered Species Act.

According to the Corps EA, Caspian first nested on East Sand Island in the Columbia River estuary in 1984 following deposition of fresh dredged material at the eastern tip of the island in 1983. By 1985, vegetation covered the East Sand Island nesting site making it unsuitable for nesting, and the newly established tern colony had by 1986 shifted to Rice Island, a dredged material disposal site 16 miles upriver.

The Caspian terns were shifted to East Sand in 1999 and 2000, with the Corps leading an effort to make unhospitable Rice Island tern habitat and enhance nesting grounds at East Sand. Rice Island is upstream of Astoria, Ore., and East Sand is downstream, between the Oregon city and the Columbia's mouth at the Pacific Ocean.

The theory was that relocating the birds to East Sand would reduce their consumption of ESA-listed salmon because their feeding area would include more marine prey species than could be found around near Rice Island. The Corps relocation effort included the deployment of decoys and playing of pre-recorded callbacks.

The relocation was successful, both in shifting nesting activity, and decreasing salmon consumption.

A next step in the effort to reduce predation on salmon involved creating favorable tern habitat -- islands --at inland sites to attract terns while at the same time scaling down the available nesting space at East Sand in order to encourage nesting elsewhere.

But, "drought conditions in the interior in 2014 are creating undesirable nesting conditions for Caspian terns resulting from 'landbridging' of islands where nesting colonies are located, which allows for access and nest predation by a variety of mammals, and by poor foraging conditions created by low water," the EA says.

"Failed nesting in the interior would likely result in these terns relocating to the mid-Columbia region and/or back to the estuary. The diets of these relocated terns would likely consist of a greater percentage of juvenile salmonids than terns in the vicinity of East Sand Island because of the increased scarcity of marine forage fish with distance upriver.

"For these reasons, it is desired to adopt the No Action alternative of maintaining the colony at 1.58 acres in 2014 in an effort to "keep" more terns in the lower estuary where juvenile salmonids represent less of a percentage of the diet than farther upriver.

The documents assess environmental impacts in 2014 from reducing the Caspian tern nesting area on East Sand Island from 1.58 to 1.08 acres, and from retaining the nesting habitat area at 1.58 acres. Potential impacts of Caspian tern predation on endangered juvenile salmon and steelhead protected under the ESA were primary concerns in making this decision.

"The actions taken per the Caspian Tern Plan and Corps' ROD did not result in the anticipated reduction of consumption of juvenile salmonids by Caspian terns," the EA says. "The amount of nesting habitat available to Caspian terns on East Sand Island has been reduced since 2006 from about 6.5 acres to the current 1.58 acres.

"Year 2013 marked the third year that Caspian tern habitat was managed between 1.58 to two acres. This reduction was expected to result in 3,125 to 4,375 nesting pairs as identified in the ROD (for 1.5 to two acres).

"Despite incremental reductions in the amount of nesting habitat, numbers of nesting pairs and amount of predation on juvenile salmonids have remained fairly constant," the EA says. "In 2013, at 1.58 acres of nesting habitat on East Sand Island, the number of nesting pairs was near 7,111 and predation on juvenile salmonids was near 4.7 million (Roby et. al. 2013)."

The failure to achieve colony reduction goals prompted consideration of an additional East Sand habitat reduction.

The final Environmental Assessment and Finding of No Significant Impact for implementation of the No Action Alternative are available on the Portland District website at

For more information about the Caspian Tern Management Plan, visit

Corps Chooses Not to Further Reduce Estuary Habitat for Salmon-Eating Terns
Columbia Basin Bulletin, April 4, 2014

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