Scientists tracking mysteries of salmon
Written by Tri-City Herald   
Tuesday, 25 April 2006 06:30

Scientists hope to unravel one of the great mysteries surrounding Northwest salmon by installing a network of sophisticated acoustic receivers off the coast to track fish implanted with tiny transmitters as they journey through the Pacific Ocean.

Eventually, the network could include 2,000 listening devices at 30 locations stretching from Baja California to the Bering Sea to track not only salmon, but also sharks, rockfish, sturgeon and other fish and marine mammals up to and including blue whales.

Already, 200 receivers have been installed in Puget Sound, including at the Tacoma Narrows and Hood Canal Bridge, to monitor South Sound coho salmon, steelhead from the Nisqually, Puyallup and Green rivers, bull trout, sharks and Pacific squid. They even have detected a green sturgeon from Oregon and California's Klamath River that was implanted with a transmitter several years ago and seven-gill sharks from Willapa Bay that carry transmitters.

"I was studying a single juvenile bull trout in a single stream 15 years ago and thought that was cool," said Fred Goetz, a fish biologist with the Army Corps of Engineers. "Now we are following fish all over Puget Sound and all the way to Alaska. My vision of the world has exploded."

For now, much of the emphasis is on salmon and the mysterious two or three years they spend in the ocean before returning to freshwater to spawn. While scientists are starting to understand the effects of stream flows, dams and habitat on salmon, they know next to nothing about the time the fish spend in the ocean.

An earlier federal plan for protecting salmon observed ocean survival was the "greatest uncertainty" in their life cycle and ocean impacts could "dwarf" other factors.

"It's a big black box," said David Welch, a Canadian marine biologist whose company, Kintama Research, is spearheading the effort to install the ocean tracking system.

Welch's three-year, $4.5 million plan will involve salmon from the Columbia and Snake rivers, Puget Sound and British Columbia. A smaller-scale demonstration program over the past two years already has shown the tracking system will work, he said.

The network will be financed by the Bonneville Power Administration, several private foundations and Canadian government fisheries agencies.

The acoustic devices have been placed or will be placed in a half- dozen locations, including the mouth of the Columbia River, Grays Harbor, the Strait of Juan de Fuca, off both the west and east coasts of Vancouver Island and as far north as the Alaska panhandle.

The devices will be anchored by 500-pound cement blocks and bob 15 to 30 feet above the seabed so they aren't covered by sand dunes that travel across the ocean floor. About 20 or 25 of the devices are arranged in a precise geometric pattern, or acoustic line, providing coverage over 15 or 20 miles on the relatively narrow continental shelf where most of the young salmon travel in what Welch called a "smolt highway."

Signals from the salmon's transmitters can be detected up to two-thirds of a mile away.

The transmitters, or tags, which are about the size of the last joint in a human pinky finger, are surgically implanted in the abdomen of young salmon or smolt before they head for the ocean. The operation is done in a specially designed "field hospital."

First, the fish are calmed using a sedative and then fully anesthetized. During the operation, the fish's gills are kept moist, its eyes protected from UV light and its vital signs monitored. The fish are kept in a darkened holding tank after the surgery, then released at dusk to reduce the risk of being eaten by predators.

The transmitters send out a small pulse or buzz that is picked up by the acoustic tracking devices. The serial number of the fish's tag is recorded along with the date and time; scientists eventually download the information and analyze it. The electronic pulse can be heard by a dog or a cat, but not by a human or a fish.

"It's kind of like E.T. can phone home wherever they go," Welch said.

Five years ago, when he first proposed an ocean tracking system, major U.S. and Canadian fisheries agencies were skeptical, Welch said.

"They thought it was pie in the sky," he said. "No one thought we could do this. But there has been a technological revolution."

Eventually, up to 1,500 salmon will be tagged annually. Once the entire West Coast system is completed in 2010, it should be able to monitor 250,000 tagged fish and marine mammals.

Currently, salmon headed for the ocean are tracked through the dams on the Columbia and Snake rivers with smaller transmitters knows as PIT tags. The tags' broadcasting range is at best a foot or two, which works fine as the salmon are channeled through and around dams that are equipped with detectors.

"We've done a masterful job of tracking them as they go through the hydrosystem," said Todd Ungerecht, a scientist with the National Marine Fisheries Agency. "But we need to look at their entire life cycle. If we could unlock what happened to them in the ocean, it would be very helpful."

Scientists believe each salmon run heads to a different location in the ocean, with the fish traveling roughly 15 miles a day. They believe the fish stay close to the continental shelf, though there is anecdotal evidence of steelhead being caught by Japanese squid fleets more than 1,000 miles offshore.

"Once they get in the ocean, we don't have a clue what happens to steelhead," said Barry Berejikian, a fisheries biologist with NMFS who studies Hood Canal steelhead.

Welch speculates some of the Snake River runs could be depleted because they congregate in ocean areas where the food is not as plentiful as in areas where other, healthier runs head. No one knows how many salmon die at sea, though Welch said the tracking system already has shown more survive their initial two or three months in the ocean than previously thought.

In addition to the advances in technology, the cost of the receivers has fallen from $5,000 to $10,000 apiece to as low as $1,000 each, Goetz said.

"Five years ago, professional biologists were saying we know everything we need to know (about salmon in the ocean)," Welch said. "I was surprised. We now feel we can put the technical infrastructure in place. We should be able to track anything."

 
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