Radio Tags Shed Light
by Mark Hume
VANCOUVER - Every spring millions of young Pacific salmon leave the rivers where they hatched and begin a miraculous journey that takes them through rapids, past huge dams and out to sea.
Despite a century of study, scientists still aren't clear exactly what route those fish take as they migrate along the coast, into the Gulf of Alaska and on to the north Pacific, before returning four years later as adults.
But some of the gaps were filled in this year when a team of researchers for the first time tracked radio-tagged salmon down the Fraser River, in British Columbia, and the Columbia River, in Oregon.
The Pacific Ocean Shelf Tracking project followed 1,000 juvenile Chinook salmon that began their journeys deep in the interior, near the Rocky Mountains.
Most of those salmon were lost along the way - but two continued to send back signals over more than a three-month period, until they vanished beyond the end of the ocean tracking sensors in the waters of southeast Alaska.
By the time the small salmon finally blinked off the tracking screens, they had travelled more than 2,500 kilometres.
"That's a pretty extensive journey," said Jim Bolger, POST Executive Director. "We're excited about it because it really illustrates the usefulness of this tool, not just for salmon but for a lot of species, in understanding where they live and where they die."
Mr. Bolger said it's the first time small juvenile Pacific salmon have been tracked over such an extensive time and distance.
"Up until now it has been difficult to follow small animals in vast oceans, and it has only been possible to infer their movements using very indirect methods," said Mr. Bolger.
Until now the best way to trace the outward migration routes of young salmon has been to set nets at various points along the west coast, and use tags or DNA samples to identify the fish and link them to their rivers of origin.
The POST method relies on an extensive network of underwater detectors that are strung along the coast, and in the Fraser and Columbia Rivers.
The sensors pick up signals from small transmitters that are surgically placed inside the body cavities of young salmon.
For the study, published today by the Public Library of Science, young fish were fitted with transmitters in the Thompson River, a tributary of the Fraser, and the Snake River, a tributary of the Columbia.
The Columbia fish had to by-pass eight huge dams on their way to the river's estuary, near the Oregon-Washington State border.
In the Fraser, which has not been dammed, the fish had to overcome thundering rapids including one daunting section known as Hell's Gate.
Some of the fish simply vanished along the way, but between mid-April and the end of May, most fish made their way out of the rivers to the sea.
One surprising finding was that the rate of survival for young salmon in both the dammed and un-dammed rivers was about the same.
It has long been speculated that the dams on the Columbia were responsible for killing large numbers of young salmon, but this research suggests otherwise.
Mr. Bolger said the study did not determine what happened to salmon that stopped transmitting either in the river or later at sea. Some undoubtedly died, but others might have migrated outside areas monitored by the POST underwater detectors, or the batteries that power the transmitters could have expired before they reached the final line of sensors. The batteries have a life span of about four to eight months.
The two Chinook that survived the journey down the Snake and Columbia Rivers, sent signals from April 17 until August 7, when they moved past the last line of underwater detectors, strung along the coast of Southeast Alaska.
In recent weeks a new line of detectors has been set up in Prince William Sound, extending the northern range of the study deep into the Gulf of Alaska.
Mr. Bolger said as more detectors are established off the West Coast, it will be possible to track salmon with greater detail, perhaps allowing researchers to determine if there are "choke points" where salmon are dying off.
One of the mysteries researchers are faced with is the failure of any of the Fraser River fish to make it beyond the north end of Vancouver Island.
"What happened to them? We don't know. They say good research often creates more questions....so that is the follow up research we'll be seeing," said Mr. Bolger.
Co-authors of the paper were David Welch, of Kintama Research; Erin Rechisky, Michael Melnychuk, Carl Walters and Scott McKinley, University of B.C.; Aswea Porter, Kintama Research; Shaun Clements, Benjamin Clemens and Carl Schreck, U.S. Geological Survey and Oregon State University.
Biodiversity: Unraveling the Mysteries of Salmon Migration by Stephen Leahy, Science Daily, 10/31/8
Do Dams Make A Difference? IPS News, 10/30/8
Salmon Study Yields Surprise Result by Jeff Barnard, Capital Press, 10/30/8
Readers Discuss POST article by Reader Discussion, The Oregonian, 10/29/8
Salmon: No Dam Difference? by Editorial Board, The Oregonian, 10/29/8
Track the Salmon in California by Editorial Board, Contra Costa Times, 10/29/8
New Study Finds Fish Do as Well on Dammed Rivers by Editorial Board, Walla Walla Union-Bulletin, 10/29/8
Dams Appear to Have No Impact on Salmon by Michael Reilly, Discovery News, 10/29/8
Salmon Smolt Survival Similar in Columbia and Fraser by Mark Floyd, Eureka Alert, 10/27/8
Salmon Study Under Fire for Minimizing Effect of Dams by Warren Cornwall, Seattle Times, 10/27/8
Research Hints Dam Improvements Helping Salmon by Michael Milstein, The Oregonian, 10/27/8
Dams Not Main Cause of Salmon Collapse, Study Says by James Owen, National Geographic News, 10/27/8
Study Shows More Salmon Survive West's Dammed Rivers Canadian Press, 10/27/8
Radio Tags Shed Light on Salmon Migration Routes by Mark Hume, Globe and Mail, 10/27/8
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