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Researchers Tally Tern Relocation Impacts on Salmon

by Barry Espenson
Columbia Basin Bulletin - October 20, 2000

A spring 2000 strategy to reduce the number of migrating salmon consumed by Caspian terns in the Columbia River estuary produced some eye-catching results, though researchers say a few shifts in political will, and tern nesting locales, could have made an even greater salmon-saving impact.

The terns, though more numerous than in years past, ate 4.4 million fewer salmon during the late spring and earlier summer of 2000 than they did in 1999, according to preliminary estimates cited by Ken Collis, co-principal investigator for the research project. He and Dr. Dan Roby of Oregon State University provide technical assistance to a Caspian tern working group formed to develop strategies to reduce the tern impact on salmon populations.

Researchers estimate that 7.33 million salmon smolts were consumed in the estuary in 2000 as compared to 11.75 million in 1999.

The main focus of the 2000 Caspian Tern Management Plan devised by federal, state and tribal biologists was to eliminate tern nesting on Rice Island, roughly 40 miles inland from the river mouth. Over the years a colony of terns had settled on the sandy island, created as a depository for Corps of Engineers dredge spoils from the clearing of shipping channels.

The tern colony steadily grew to an estimated 8,000 breeding pairs by 1998 based on aerial photo surveys during the late spring-early summer peak incubation period.

In 1997 and 1998, Caspian terns nesting on Rice Island consumed between 6 million and 25 million, and 7 million and 15 million smolts (6-25 percent and 8-16 percent, respectively, of the estimated number of salmonid smolts to reach the estuary). Among those fish are 12 salmon and steelhead stocks listed under the Endangered Species Act.

A pilot study was conducted in 1999 to test the feasibility of colony relocation as a way to reduce the impacts of Caspian terns on the survival of juvenile salmonids in the Columbia River Estuary. Using habitat modifications and social attraction (i.e., tern decoys and audio playbacks) to encourage nesting on East Sand Island and grass planting, fencing, and harassment of terns to discourage nesting on Rice Island, researchers were successful in getting roughly 1,400 nesting pairs to relocate from Rice Island to East Sand Island in 1999.

It was believed that the relocation to East Sand, near the river mouth, would broaden the tern menu because of the presence of marine forage species and thus reduce the terns' intake of salmon.

As predicted, terns nesting on East Sand Island consumed roughly 40 percent fewer juvenile salmonids as compared to terns nesting on Rice Island.

Based on those results, regional fish and wildlife managers decided to pursue a long-term management plan to relocate terns nesting on Rice Island to East Sand Island and other restored colony sites outside the Columbia River Estuary to reduce smolt losses.

Facets of the plan were modified in mid-stream, but the impacts were even more dramatic in 2000 with the more intensive efforts to draw birds to East Sand Island and discourage nesting at Rice Island. The colony essentially flip-flopped, with 9,097 pairs nesting at East Sand and only 580 pairs counted at Rice Island during peak incubation. That compares to 1999, when 8,096 pairs camped out at Rice Island and 697 at East Sand.

As a result the researchers' "best estimate" is that 7.33 million salmon smolts were consumed in the estuary in 2000 as compared to 11.75 million in 1999 when the birds were concentrated at Rice Island and salmon were their principal foodstuff.

An estimated 44 percent of the East Sand terns' diet was estimated to be salmon this year as compared to 91 percent at Rice Island. The species composition in the Rice Island diet was also changed with terns eating the same proportion of steelhead and coho but far fewer chinook salmon, Roby said.

In a "theoretical scenario," Roby said the terns would have consumed 6 million more salmon this year had the entire colony been allowed to remain entrenched at Rice Island.

Nature's shifting forces had a hand in the reduced salmon consumption. Much ballyhooed "improved ocean conditions" have been credited with improving salmon ocean survival. Those cyclical ocean improvements also seemed to enhance populations of marine species such as sand lance, herring and anchovies on which the terns feed.

"There were a lot of things on the (terns') menu," Roby said. "We got lucky."

Total implementation of the 2000 management plan was met with resistance. The U.S. 9th Circuit Court of Appeals in San Francisco in May upheld a lower court injunction to stop harassment of terns on Rice Island as a means of discouraging nesting. Despite the pull-back on harassment activity, terns mostly stayed away from Rice Island and flocked to East Sand.

The Audubon Society, Defenders of Wildlife, Seattle Audubon Society and the American Bird Conservancy were parties in the lawsuit against the Corps. The groups asked that the Corps complete a formal Environmental Impact Statement analyzing other alternatives to moving the terns.

The success in shifting the bulk of the colony to East Sand was likely due to the fact that much of the plan had already been put into place when the injunction brought harassment to a halt. By late March, the Corps had made habitat on Rice Island as unfriendly to terns as possible by re-installing the silt fencing it used last year to pare down an eight acre nesting area to only a one acre sandy plot. At the same time, the Corps made East Sand Island attractive to terns by removing existing European beach grass to create four acres of sandy habitat that terns like for nesting. The Corps also placed lifelike tern decoys on the island, used tern-friendly sounds to attract more terns to the island.

Another key element of the plan, to lure some of the terns to nesting sites along the Washington coast, was also thwarted. It had been hoped that at least some of the terns could be drawn north to Cate Island in Grays Harbor, Wash., where terns have historically nested and where there are no listed salmon runs

Local protests gained the sympathies of state and county officials, who failed to produce the permits necessary to prepare the site to attract terns in search of a nesting site.

"The gains that were realized by this (the 2000 estuary strategy) were not as large as they could have been," Collis said.

Because of the Columbia River salmon consumption issues, "terns got a bad rep," Collis said. Efforts to locate potential sites for even experimental relocations are still coming up dry because of local concerns about impacts on fish populations.

"There's so much local or regional NIMBYism (not in my backyard)," Roby said.

He said state and federal officials need to sit down "and agree on where tern colonies should be restored."

A recent NMFS biological opinion judging that program's impacts on listed salmon specified that the Corps keep terns off all estuary manmade islands except East Sand.

The NMFS is charged with protecting federally listed salmon. The U.S. Fish and Wildlife is charged via the federal Migratory Bird Act with looking out for the welfare of the terns and also questioned the total disenfranchising of the Rice Island colony.

Researchers believe that a healthier solution, for salmon as well as the birds in the crowded East Sand (or Rice) Island colony, would be to establish small colonies along the coast or inland. Collis said they are trying now to win support for the establishment of experimental tern colonies, whose diet composition and reproductive potential can be evaluated.

The intent would be to create habitat, such as on stationary barges, that could be easily removed if the birds' impact is judged to be undesireable.

The need is heightened because the Columbia River estuary colony is growing by roughly 1,000 nesting pairs per year. Collis said researchers suspect that most of the colony's growth comes from birds that have wandered into the estuary when nesting grounds elsewhere became degraded.

"That draws attention to the importance of restoring lost tern habitat outside the estuary," Collis said.

Related Sites:

by Barry Espenson
Researchers Tally Tern Relocation Impacts on Salmon
Columbia Basin Bulletin, October 20, 2000

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