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 thousands of miles 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 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 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 have even 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 U.S. 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 rivers and streams 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 they 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 affecting endangered and threatened runs.
“It’s a big black box,” said David Welch, a Canadian marine biologist whose company, Kintama Research, is spearheading the effort to install an 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 listening devices have been placed or will be placed in half a dozen locations: 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 the Alaska panhandle.
The devices will be anchored by 500-pound blocks of concrete and bob between 15 and 30 feet above the seabed so they aren’t covered by the 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.”
The signals from the salmon transmitters can be detected up to two-thirds of a mile away.
The tiny transmitters, or tags, are surgically implanted in the abdomen of young salmon or smolts before they head for the ocean.
The operation is done in a specially designed “field hospital” and follows guidelines of the Canadian Council for Animal Care.
First, the fish are calmed using a sedative, and then fully anesthetized. During the operation, the fish’s gills are kept moist, its eyes are protected from UV light and its vital signs are monitored.
The fish are held in a special darkened holding tank after the surgery before being released at dusk to reduce the risk of being eaten by predators.