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NMFS Report: Estuary Terns Hinder ESA Fish Recovery

by Barry Espenson
Columbia Basin Bulletin - October 7, 2002

Caspian terns that settle in each spring on an island in the Columbia River estuary and prey on passing salmon and steelhead smolts do hinder Endangered Species Act fish recovery efforts, according to a report released Sept. 26 by the National Marine Fisheries Service.

"Caspian tern predation on juvenile salmonids reduces salmon population growth rate and thus recovery, however, removing all tern predation will not, by itself lead to full recovery of any listed salmon and steelhead stock," according to the report's executive summary.

"It's not jeopardizing the continued existence of the fish, but it is impairing recovery," NMFS' Ben Meyer said of the attempt to analyze the impacts terns have on listed salmonids and the benefits that could be derived by moving the bird to other habitats.

The tern predation on salmon and steelhead juveniles "is one of many things in the basin that is impairing recovery," Meyer and the report stress.

The extent to which tern predation in the estuary impacts listed salmon and steelhead populations has become a major point of contention. State, federal, tribal and private entities have since 1996 been working on plans to reduce tern predation, pointing to estimates that the birds consume millions of the young fish as they migrate toward the ocean.

Bird conservation groups say tern predation on salmonids is a natural event and maintain that the federal agencies have not proven that terns impede recovery. The latest report fails again to prove that point, according to Gerald Winegrad, the American Bird Conservancy's vice president for policy.

"Tern predation at dams and hatcheries as well as predation by other birds needs to be evaluated in the context of the major problems facing salmon recovery -- hydro, harvest, hatcheries, and habitat -- the FOUR H's," Winegrad said. "Habitat, hydro power, harvest, and hatchery issues, rather than bird predation, are widely and officially recognized as the primary causes for the listing of various Columbia River runs of salmonids for protection under the ESA. Focusing limited resources on birds eating fish will likely yield no discernible increases in salmon recovery."

The report, "Caspian Tern Predation on Salmon and Steelhead Smolts in the Columbia River Estuary," is one of three reports called for in the settlement of a lawsuit filed by bird conservation groups. The lawsuit against the U.S. Fish and Wildlife Service and Corps of Engineers challenged the tern management plan.

The National Audubon Society, Defenders of Wildlife, Seattle Audubon Society and the American Bird Conservancy's successful lawsuit this past spring threatened to prevent continued implementation of the plan to relocate what is considered the world's largest Caspian tern colony. The goal was to shift the birds from their favored site, Rice Island, to a site nearer the Pacific Ocean, East Sand Island. It was believed, and the theory has been borne out during the past three years, that the terns would consume fewer juvenile salmon and steelhead and more marine fishes at East Sand.

The plan shifted most of the birds in 2000 and all of the birds nested at East Sand in 2001 and 2002, reducing smolt consumption from an estimated 11.7 million in 1999 to 7.3 million and 5.9 million respectively in 2000 and 2001. The birds fly north in April to nest at the site and rear their young. The overall percentage of salmonids included in the terns' diet dropped drastically for birds nesting at East Sand.

Since 1991, 12 different stocks of salmon and steelhead have been listed under the Endangered Species Act. The NMFS report says that, in 1999 "roughly 6 million listed smolts entered the estuary along with over 80 million unlisted smolts (primarily of hatchery origin)." Researchers estimate that Caspian terns, then largely still settled on Rice Island, ate between 6 to 14 percent of the migrating juvenile salmonids that reached the estuary.

Regardless of the location, the terns seemed to have the greatest impact on steelhead and the least impact on wild yearling chinook, according research cited in the NMFS report. The data was produced by retrieving PIT tags on the islands that had been implanted in juvenile fish. The birds also ate a higher percentage of hatchery produced smolts than wild fish.

Those numbers need to be updated and validated, Meyer said.

"Additional PIT tag data needs from East Sand Island in 2001 and 2002 has yet to be analyzed," the report says. "This data should provide a better evaluation of any changes in predation rates that may have been realized by relocating the colony to East Sand Island."

The NMFS used two approaches to evaluate salmonid mortality resulting from tern predation -- analysis of the PIT tags detected at the colonies and the use of a bioenergetics model to estimated tern predation based on data from observed salmonid consumption.

The agency then used a life cycle model that was developed under the auspices of the Cumulative Risk Initiative to assess the impact tern predation would have on the fish stocks' population growth rate -- called lamda.

In an example in the report, a hypothetical predation rate of 5 percent for Snake River steelhead was plugged into the model.

"a maximum potential improvement in population growth rate of 1.077 percent would be realized if this mortality could be completely eliminated. If the predation rate was reduced by 50 percent, the impact on that ESU specific population growth rate would improve approximately .530 percent," the report said of the hypothetical example.

The same CRI model projected that hydrosystem passage improvements called for in NMFS 2000 biological opinion, if implemented, would increase the population growth rates by approximately 1 to 2 percent for Snake River spring/summer-run chinook salmon and nearly 5 percent for the Snake River fall chinook. The report cautions that the calculations assume there is no compensatory mortality later in the life cycle and that any reduction in tern predation is fully realized.

Winegrad says that is an important distinction.

"Such an assumption is highly unrealistic and NMFS notes that their population growth rates for salmon with elimination of the tern colony or reduction of it by 50 percent should be considered the maximum potential improvements, conceding it is likely less than assumed," Winegrad said. "Further, NMFS acknowledges that it is difficult to substantiate with data how much a change in colony size will affect predation rates, but they make such an assumption, nonetheless, of a 50 percent reduction in predation rates with a 50 percent reduction in colony size. This house of cards collapses under scientific scrutiny."

He said the final document is not a step forward from a draft presented for review at mid-summer.

"Despite the learned comments of leading scientists who peer reviewed the original draft, NMFS continues to hypothesize that since terns eat salmonids, they therefore adversely affect adult returns and impede recovery," Winegrad said. "They then use biological voodoo to justify their conclusion, despite the near total lack of scientific evidence that terns inhibit recovery. They go so far as to attribute specific percentage declines in populations of salmon runs that are due to tern predation of young salmon in the estuary. This is scientific chicanery."

Seven experts on terns and/or bird predation were enlisted by the bird conservation groups to review the draft document. Comments from the scientists roundly criticized the scientific methods used and the draft's conclusions.

Meyer defended the report's scientific approach and tools.

"The CRI model has been vetted and looked at" extensively, he said. The methods for assessing tern predation on the salmonids are also solid scientifically.

"What science don't we have?" he asked rhetorically.

"The intent of this document is to summarize what is known about Caspian tern predation impacts to salmonids in the Columbia River estuary," according to the report, which is absent of any management recommendations.

The report is intended to guide the region's policy makers -- provide a tool to assess potential impacts on tern predation from any management scenario that is considered.

The bird conservation groups said that fish-eating birds are a natural part of the ecosystem. They challenged the scientific basis for the plan and said the tern management plan developed by federal, state, tribal and private entities did not take into account the long-term welfare of the birds.

U.S. District Court Judge Barbara Rothstein agreed in large part. In an August 2001 injunction, Rothstein prohibited any harassment of the birds in the estuary or manipulation of habitat. The injunction threatened implementation of the management plan this year.

The Corps and USFWS had appealed the decision to the Ninth Circuit Court of Appeals, which steered the two sides toward settlement negotiations. The Corps is in charge of the dredging activities that created Rice Island. The USFWS has responsibility to protect the migratory birds that fly north to nest and rear their young during the late spring and summer. NMFS is charged with protecting and restoring listed salmon and steelhead.

Rothstein ruled that the Corps and USFWS acted illegally when they initiated a plan to turn the terns away from their preferred nesting site without the benefit of a full environmental impact statement. She also said the federal agencies provided almost no information as to whether reducing tern predation would affect the number of salmon returning to the estuary.

The three reports called for in the settlement agreement include: (1) Avian predation analysis to determine levels of predation that do not impede salmon recovery; (2) Status Assessment of Caspian Terns; and (3) Feasibility study of potential Caspian Tern nesting sites in the Pacific Northwest.

The first two reports are now complete. The nesting site survey will be completed later this fall, said Tara Zimmerman of the USFWS. The USFWS will take the lead in preparing a long-term management plan and an environmental impact statement for Caspian terns in the Columbia River estuary. Initial scoping begins next spring. The draft is due out no later than Oct. 1, 2004, according to the agreement.

The ideal scenario, and one favored by all involved, is to find, restore and/or create alternative nesting sites so the huge colony -- an estimated 25 percent of the North American population -- could disperse naturally. The tern status assessment completed in late August for the USFWS says that the concentration of birds at one site -- nearly 10,000 breeding pairs this past season -- leaves them vulnerable to disease outbreaks, severe storms, disruption by predators or human disturbance, oil spills or other calamities.

The settlement agreement charges the USFWS, in cooperation with NMFS and the Corps, with initiating National Environmental Policy Act scoping in April 2003 on Caspian tern management in the Columbia River estuary through publication of a notice in the Federal Register.

Related Sites:
Predation report:
Tern status report:'s_new.htm

Barry Espenson
NMFS Report: Estuary Terns Hinder ESA Fish Recovery
Columbia Basin Bulletin, October 7, 2002

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