ILWACO - With an ample supply of marine prey fish available, salmon consumption in the Columbia River estuary by the world's largest Caspian tern colony last spring and summer dropped to an all-time low since research on the birds' diet began in 1997.
However, a burgeoning population of double-crested cormorants that shares East Sand Island residence with the terns filled the salmon consumption gap. The percentage of salmon and steelhead in the big-bodied cormorants' diet was quite small, but their overall intake in 2004 surpassed that of the terns for the first time.
"A system-wide assessment of avian predation using the available data indicates that the most significant impact to juvenile salmonids occurs in the estuary, with terns and cormorants nesting on East Sand Island combining to consume (around) 10 million smolts in 2004," according to the draft 2004 season summary released last week. The research was launched in 1997 to investigate the impact of piscivorous colonial waterbirds on Columbia River basin salmonids.
The terns fly northward in the spring to find suitable nesting habitat. The colony initially established a foothold on Rice Island in the 1980s, where populations blossomed. In 1998 it was estimated that the 17,000 nesting terns on Rice Island, created with spoils from dredging of the river's navigation channel, ate approximately 12.4 million salmonids or 13 percent of the 96.6 million outmigrating smolts that reached the estuary. That represented 74 percent of the terns' diet.
Twelve of the basin's salmon and steelhead stocks are listed under the Endangered Species Act.
In an attempt to reduce tern salmon consumption, a multi-agency team developed a management plan in which nesting was discouraged at Rice Island and suitable habitat was prepared at East Sand Island, 16 miles nearer the ocean. It was theorized that the proximity to the ocean, and marine fish species, to help diversify the terns diet.
The plan to draw terns to East Sand has been a success. With all terns shifted to East Sand, the percentage of salmon in their diet dropped steadily from 72.7 percent in 1997-98 and 76.5 in 1999 at Rice Island to 46.5 in 2000, 32.5 in 2001, 31.1 in 2002, 24.1 in 2003 and then only 16.8 percent of the East Sand colony's diet in 2004. That 2004 salmon consumption is about 3.5 million smolts or roughly 29 percent of the total consumed in 1998 at Rice Island.
"There's lots of alternative prey, though that won't necessarily be the case forever," said Ken Collis, an independent consultant and co-principal investigator for the research project. Principal investigator is Dan Roby of Oregon State University. The research is funded by the Bonneville Power Administration and U.S. Corps of Engineers.
Collis theorized that the birds, now long-established at East Sand, have also perfected their methods for preying on the marine species. Cyclical ocean conditions now seem to favor the proliferation of marine species such as Pacific herring, anchovies, smelt and surf perch.
The draft report notes that Caspian tern numbers in the Columbia River estuary have remained stable over the past eight years while the numbers of double-crested cormorants nesting at East Sand has nearly tripled to about 12,000 pairs. An estimated 9,500 Caspian terns flew north to nest at East Sand last year.
Salmon and steelhead represented only a small percentage of the cormorants' overall diet - about 5 percent. But because of the large colony size, and the larger food requirements of the big birds, their salmon consumption of about 6.4 million smolts surpassed that of the neighboring tern colony. The most common salmon target for the cormorants in 2004 was subyearling chinook. The salmon consumption totals are midpoints of an estimated range.
The report notes that the cormorants last year continued to experience high nesting success with an average of 2.05 young per breeding pair.
"The colony is expected to continue to expand for the foreseeable future, perhaps posing an increasing risk to juvenile salmonid survival," the draft says.
The only other large tern aggregation on the lower-to-mid-Columbia is at Crescent Island, just below the confluence of the Snake and Columbia. About 530 breeding pairs settled there last spring, roughly the same size colony as the previous year.
That inland colony focused on salmonids, eating an estimated 470,000 smolts. That represented 70 percent of the birds' diet.
The salmon consumption was relatively small in comparison to the estuary colony but it did raise some red flags for researchers. The terns ate an estimated 23 percent of the passing Snake River steelhead smolts and 3 percent of the Upper Columbia steelhead smolts. The wild Snake River steelhead are listed as threatened and the Upper Columbia wild stocks are listed as endangered.
The impacts of the high predation rate on the Snake River steelhead is offset to a great degree by the fact that few of the migrating fish remain in the river at McNary pool. The vast majority are collected at three lower Snake River dams and transported for release below Bonneville Dam, the lowermost hydro project in the system.
The toll on juvenile salmon and steelhead remains the greatest in the estuary, a reach both in-river and transported smolts must pass.
"For these reasons, management of terns and cormorants on East Sand island has the greatest potential to benefit Columbia River salmonid populations across the basin, when compared to potential management of other bird populations," the report says.
New twists in that management are planned via the preferred alternative in a Environmental Impact Statement completed in January by the U.S. Fish and Wildlife Service in January with the help of the Corps and other agencies. It calls for dispersing of two-thirds the estuary tern colony to seven alternate sites in Washington, Oregon and California by gradually reducing the East Sand habitat as new habitat is made available.
The primary goal of the plan is to reduce the number of young salmon eaten by terns as the fish migrate past the colony on their way to the Pacific Ocean. The plan is also expected to benefit the terns. The large breeding concentration leaves the population vulnerable to disease, human disturbance, predation and storms.
The EIS was prepared as the result of a court settlement in a lawsuit by bird conservation groups who have sought assurances that the long-term health of the terns is paramount in management decision-making.
Implementation of the management plan/Final Environmental Impact Statement was to be launched via an official USFWS record of decision by Feb. 28 but an 11th-hour agreement between litigants allowed that deadline to be stretched until, perhaps, April, according to Nanette Seto of the USFWS.
The extra time was needed to resolve environmental compliance issues, including consultation with NOAA Fisheries regarding potential impacts on listed salmon stocks at tern relocation sites. NOAA is expected to produce a biological opinion on potential impacts.
"We can't implement anything until the ROD is done," Seto said. Site planning, permitting, funding decisions and other issues lie ahead. The agency had said it would like to implement the preferred alternative over a 3- to 5-year span.
The bird groups that brought the lawsuit "are not pleased" with the EIS despite basic agreement dispersing some of the terns to suitable habitat elsewhere is desirable, according to Gerald Winegrad of the American Bird Conservancy.
"We are very displeased with the poor science on which bird management is based," Winegrad said. The bird groups say federal agencies have failed to prove that the terns' salmon consumption was a factor in pushing the fish stocks onto the ESA list.
"If the terns are eating so many salmonids that it's a problem, why are they (the salmon) returning in record numbers," Winegrad said of increased salmon returns to the Columbia over the past five years. The listings of the Columbia Basin salmon stocks began with the Snake River sockeye in 1991 and the Snake River spring/summer chinook and steelhead stocks in 1992.
A new federal action agency "updated proposed action" for Columbia/Snake hydro operations and NOAA Fisheries biological opinion that sanctions the UPA say the tern management plan is a key tool for improving salmon survival.
Winegrad said the federal agencies should "declare victory" with the steep drop salmon consumption achieved in the estuary and concentrate the money and effort on fixing the true causes of the salmon's demise - hydrosystem-caused mortality, degraded habitat, harm from hatchery process and harvest.
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