[3] Region Creates One Of World's Biggest Bird Feeders
The survival benefits to salmonids from moving a colony of Caspian terns further down the Columbia River may have been lost because the lower estuary cormorant population has doubled in the past few years, according to researchers from Oregon State University and Real Time Research of Bend, Ore.
In a draft report available on their web site, the researchers say that the largest cormorant colony in North America now inhabits East Sand Island, about 12,500 pairs of double-crested cormorants, along with about 8,800 pairs of terns. Together, the terns and cormorants consume about 10 million smolts annually.
The transplanted terns, about the same sized-colony as once hung out at Rice Island further upstream, now eat an estimated 3.6 million juvenile salmonids at their new nesting grounds on East Sand Island. That's 9 million less salmonids than they consumed in 1998 at the other location, according to the study, which was released in early February.
And though cormorants do have a varied diet, juvenile salmonids only make up about 5 percent of it, and their sheer numbers have made total consumption by the two species similar to the numbers consumed by the terns alone in 1998.
The U.S. Fish and Wildlife Service has already developed a plan that calls for moving two-thirds of the East Sand tern colony to other West Coast sites. And with cormorant numbers still expanding into the "foreseeable future," researchers are studying the feasibility of relocating some of the cormorants as well.
Through a combination of tactics that included blaring loudspeakers and habitat modification, the scientists were highly successful at relocating the terns to a place where their diet focused less on salmonids. Before the move, it was estimated that the tern colony consumed about 13 percent of the nearly 100 million smolts migrating past in the spring of 1998.
More than 36,000 PIT tags from juvenile salmonids were recovered from the colony at Rice Island. It showed that nearly 14 percent of all the PIT-tagged steelhead detected at Bonneville Dam ended up in a tern that year.
Recent PIT tag detections at East Sand Island show that in 2005 the terns consumed about 11 percent of the hatchery steelhead and 8 percent of the wild steelhead passing though the estuary, with less than a 2 percent impact on spring chinook. The birds nailed about 6 percent of the hatchery coho and .6 percent of the wild coho passing by.
By actually observing bill loads from nesting terns, the report says about 23 percent of their diet was made up of salmonids, while most consisted of sardines, herring, shad, anchovies, smelt and surfperch. About 42 percent of the juvenile salmonids consumed by the terns were hatchery coho, about 27 percent were spring chinook, 20 percent were steelhead, 10 percent fall chinook, and 1 percent were sockeye.
Upriver, the terns are even more of a problem for salmonids migrating down the Snake River, because they make up about 65 percent of the terns' diet. Nearly 500 nesting pairs at Crescent Island, near the confluence of the Snake and Columbia, chomped an estimated 440,000 smolts in 2005, mainly steelhead. And it gets worse in low-flow years like 2004 and 2005, says the report.
The researchers say PIT tag recoveries at Crescent Island show that 2004 was especially bad for steelhead, since about one-third of them were picked off by the terns. In 2005, predation on migrating steelhead was about half that. Luckily, about 95 percent of these steelhead were transported in barges in those years.
However, BiOp judge James Redden has ordered more spill this coming spring, which would reduce the number of steelhead that will be barged. Luckily, there is little habitat available for the Crescent Island tern colony to increase in size.
A nearby cormorant colony (300 pairs) picked off fair numbers of salmonids early in the 2005 migrating season, said the researchers, consuming about one-quarter of the number of smolts that the tern colony had eaten.
Investigators also found that the 500 pairs of white pelicans didn't seem very interested in eating salmonids. Only 600 PIT tags were counted in their nesting area, compared to 16,000 tags counted at the tern colony and 4,100 at the cormorant colony.
The cost of dealing with the birds is increasing. For the 2007-09 budget, nearly $2.5 million has been proposed for research in BPA's fish and wildlife program, with another $4 million projected in shared-cost proposals in the 2007 budget for more monitoring and creating new nesting habitat for terns at other West Coast sites.
If agencies decide that cormorants must be removed to relieve predation on ESA-listed salmonids, then another EIS must be completed. -B. R.
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