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NW Fishletter #386, Oct. 2, 2018

[6] Funding Losses Threaten Caspian Tern Predation Control

A Bonneville Power Administration-supported project to lure Caspian terns away from the Columbia River estuary to reduce predation on salmon and steelhead smolts has been largely successful, but may stall if its funding continues to fall, the project's lead researcher told the Northwest Power and Conservation Council on Sept. 11.

The program's goal of leaving East Sand Island with a third as many nesting pairs may not be reached without funding to conduct the environmental analysis needed to continue to shrink their nesting area, said Peter Roby, a professor of wildlife ecology at Oregon State University and the project leader for the U.S. Geological Survey.

Since 1997, scientists have been working to reduce the number of nesting pairs on the island from about 9,400 to about 3,125 by reducing the area where terns will nest from six acres to one acre, he said. They came close to their goal in 2017, with about 3,500 nesting pairs, but those numbers jumped back to 5,000 pairs in 2018 when the terns unexpectedly nested at higher densities.

To maintain a lower population, he said, it's "going to take further reduction in their nesting habitat. But none is planned," he said. "It's going to remain at one acre."

The project--one of three in the Columbia River Basin to control birds that prey on salmon and steelhead--has had multiple funding sources, including support from Bonneville every year since it began, Roby said. For the last six years, BPA has awarded OSU $535,341 each year to implement the tern project on East Sand Island.

But, Roby said in an email to NW Fishletter, the U.S. Army Corps of Engineers is no longer providing any funds for the project, and "we have been notified by BPA that we can expect a major reduction in the grant amount for 2019, likely about half of what we were funded in recent years," the email said.

In his presentation, Roby said that Caspian terns and double-crested cormorants nesting on East Sand Island have consumed up to 25 million smolts each year--or about 15 percent of the Columbia River Basin smolts that survived into the estuary. He said the Columbia River estuary's East Sand Island once boasted the world's largest Caspian tern breeding colony. Their nesting period overlaps with much of the smolt out-migration period.

Over the last several years, scientists have reduced the area suitable for nesting on the island using a variety of methods, including erecting rope fencing and stakes with flagging. "The terns do not like to nest in and amongst this material," he said. Other parts of the island were also fenced and staked to ensure that the terns did not move to a new site nearby, he said.

Photo Courtesy of Dr. Madeline Kalbach

At the same time, with Corps funding, they created and monitored 14 alternative nesting sites on eight different islands on their migration route outside the Columbia basin, and used social attractants--including decoys--to lure them to these new sites. The alternative islands are mostly in Oregon, and are as far away as the Tule Lake National Wildlife Reserve in Northern California.

Roby said seven of those sites on seven different islands are now being used by nesting Caspian terns, many of them originally from the colony on East Sand Island. But without continued work, Roby said the terns may not continue to use some of the sites, which have recently suffered from severe drought conditions.

"The Army Corps has decided that as of this past breeding season, they are out of the Caspian tern management business, completely," he said. And with about half of the funding from BPA, it's not yet clear what aspects of the Caspian tern management project will continue, he said.

But, he said, further reducing their nesting area is not likely, even though the actual work to reduce the area from one acre to two-thirds of an acre could be done relatively cheaply and quickly. But the work would also require a new environmental analysis, and none of the agencies appear willing to do that work, he said.

Roby said so far, monitoring has shown that their work to reduce Caspian tern nesting has had significant impacts on seven Endangered Species Act-listed stocks, including four Chinook populations, and three steelhead runs.

Before the project began, these terns ate an average of 22.2 percent of the Snake River steelhead smolts that made it to the Columbia River estuary, and today, they consume about 9.5 percent. Rates for upper Columbia steelhead dropped from 17.2 percent to 9 percent, and for middle Columbia steelhead from 14.9 percent to 9.3 percent.

Other stocks that saw significant reductions in Caspian tern predation rates include Snake River spring/summer Chinook, which dropped from 4.8 percent to 1.5 percent; upper Columbia spring Chinook which dropped from 3.9 percent to 1.6 percent; Snake River fall Chinook which dropped from 2.5 percent to 0.8 percent; and upper Willamette River spring Chinook, which dropped from 2.5 percent to 1 percent.

He said recent studies are beginning to show that controlling Caspian tern predation is having a direct impact on not only smolt survival, but also smolt-to-adult return rates. "As Caspian tern predation goes up, smolt-to-adult survival rates go down, and they go down significantly," he told the Council.

In addition to the Caspian tern colony on East Sand Island, other efforts to control predation by birds in the Columbia River Basin include the management of Caspian terns that nest on Goose and Crescent islands in the Columbia Plateau, and of double-crested cormorants that nest on East Sand Island.

Other native birds that prey on salmon and steelhead in the basin, including American white pelicans and a variety of gull species, are currently unmanaged. -K.C. Mehaffey

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