WASHINGTON — They were two of the 1,000 juvenile salmon implanted with almond-sized transmitters as they headed out of the Rocky Mountains , down the Snake River bound for the sea.
Their remarkable three-month, 1,500-mile journey of survival to the Gulf of Alaska was tracked by an underwater acoustic listening network that has wired the West Coast from just north of San Francisco to southeastern Alaska . The tracking network could provide a model for a global system.
A salmon's life in the ocean has always been one of nature's best kept mysteries.
However, scientists using the Pacific Ocean Shelf Tracking network have made some startling discoveries that challenge long-held beliefs about salmon survival and raise new cautions about how global warming may affect salmon and other marine species.
"I hope it will be a revolution in the way we do marine science," said David Welch , the president of Kintama Research Corp. in Nanaimo, British Columbia , who was one of the founders of the tracking system. "I think we will make discoveries that are incredibly important and unexpected."
The transmitters, which are becoming increasingly sophisticated, smaller and cheaper, have been implanted in a dozen species, including coho, sockeye and chinook salmon, along with green sturgeon, white sturgeon, sixgill shark, salmon shark, market squid, cutthroat trout, steelhead, dolly varden and black rockfish. Eventually, scientists think they'll be able to implant the transmitters in marine animals as big as whales and as small as herring.
Signals from the transmitters are picked up by nearly 300 receivers on the ocean floor as the fish swim by. The information is eventually retrieved from the listening devices by scientists who routinely visit the eight lines of acoustic receivers by ship. The receivers don't transmit the data by satellite.
Listening lines are off Washington state's Willapa Bay , in the Strait of Juan de Fuca between Vancouver Island and Washington's Olympic Peninsula , in British Columbia's Strait of Georgia , Queen Charlotte Strait , Howe Sound and off the northern tip of Vancouver Island , along with Point Reyes, north of San Francisco , and Graves Harbor in southeastern Alaska .
Two major Northwest rivers, the Columbia and Fraser, are also wired with receivers that can keep track of salmon movements from the river mouth to hundreds of miles inland.
"This is a revolution in being able to study marine animals that travel vast distances," said Fred Goetz , a fish biologist with the U.S. Army Corps of Engineers who's been studying Puget Sound chinook, steelhead and bull trout. "This is a big breakthrough."
Goetz said an effort is under way to permanently establish an acoustic listening line in Puget Sound near Admiralty Inlet.
Scientists are convinced the marine environment is changing because of global warming. However, no one yet understands how the changes are linked to such weather patterns as El Nino, La Nina and the Pacific Decadal Oscillation, a shift in the weather that occurs every 20 to 30 years in the northern oceans.
Tracking marine life could help document these shifts and the effects they are having on the oceans.
"Now we are getting virtually real-time information," said Jim Bolger , the executive director of the tracking network. "We are answering questions we couldn't before."
Among the findings:
— Previously, it was thought that the highest mortality rates for salmon were in the freshwater streams and rivers as they headed to the saltwater ocean. But using the acoustic tracking system, researchers found that within the first few weeks of entering the ocean, 40 percent of the salmon died. Meanwhile, billions of dollars have been spent to increase in-river survival rates of salmon through projects such as habitat improvements in spawning areas and the modification of hydroelectric dams.
— A study by Welch, which has touched off a major scientific debate, found dams may have less of an impact on salmon survival rates than previously thought. The study found juvenile salmon from the Columbia River , with its string of massive hydroelectric dams, survived their downstream migration equally or better than those migrating downstream in the dam-free Fraser River in British Columbia . Some environmentalists have insisted the only way to restore the Columbia River runs is by breaching four dams on the lower Snake River , a major tributary of the Columbia .
— It's long been thought green sturgeon from the Sacramento and Klamath rivers in California migrated into the ocean but didn't go far. Now, using the acoustic tracking system, the green sturgeon have been found congregating off the north end of Vancouver Island at certain times of the year and then heading into the North Pacific. They've also been found in Puget Sound .
"We are taking a black box which is the ocean and trying to shed some light on it," said Jonathan Thar, the network's research coordinator.
The tracking system has also helped researchers confirm the incredible speeds at which juvenile salmon can travel, said Cedar Chittenden, a doctoral student at the University of British Columbia .
Juvenile coho salmon, about five inches in length, can travel almost 20 miles a day in the ocean and nearly 40 miles in rivers, or about 200,000 body lengths a day, she said. An average-sized person swimming at the same rate would cover nearly 220 miles a day in the ocean and almost 435 miles in a river, Chittenden said.
Using the tracking system, Chittenden said, researchers also found that wild juvenile salmon take less time to enter the ocean than hatchery fish, perhaps because the hatchery fish tend to be heavier and slower. And wild fish adapt faster to saltwater than hatchery ones.
The tracking system may also help scientists determine whether salmon runs, because of rising ocean temperatures, may be relocating further north. Chittenden said there is some evidence thermal blocks, or areas of warm water, have hindered salmon as they seek to return to their home rivers to spawn, and instead the fish may head to different rivers.
"We can actually track individual fish," she said. "We couldn't do these things without POST," the Pacific Ocean Shelf Tracking network.
The network, which has cost about $7 million , is run by a nonprofit organization hosted by the Vancouver Aquarium and funded by various foundations. It is also one of 14 field projects under the Census for Marine Life , a group of scientists and researchers from more than 60 universities and colleges around the world who are spending 10 years cataloging every marine species.
Eventually, the Census for Marine Life hopes to establish a global Ocean Tracking Network, or OTN, that would cover 14 areas in the Pacific, Atlantic, Indian and Arctic oceans, along with the Mediterranean Sea .
Efforts to establish such networks are already under way in eastern Canada , South Africa and Australia . In Australia and South Africa , the networks could also be used to alert authorities when sharks are near swimming beaches.