Tags unlock young salmon secrets

By Mark Kinver Science and environment reporter, BBC News

The tags gave researchers a unique insight into the behaviour of young salmon

Miniature tag technology has helped unlock the mysteries of the journey undertaken by juvenile salmon in the North-West United States and Canada.

A team of researchers fitted the novel devices to 1,000 of the young fish and tracked their progress from the Rockies through the Pacific to Alaska.

The scientists hope to use the tags in the future to learn more about the movements of other small fish species.

The study was part of a 10-year global project called Census of Marine Life.

Although tags have been used in the past to track mature salmon along their coastal migration, it is the first time the technology has been used on juveniles, otherwise known as smolt.

Jim Bolger, executive director of the Pacific Ocean Shelf Tracking (Post) project, said the findings were a major step forward in understanding the life cycle of the species.

The electronic and acoustic technology has demonstrated itself as a useful tool Dr David Welch, Kintama Research

"Until now, it has been difficult to follow small animals in vast oceans," he explained.

"It has only been possible to infer their movements using very indirect methods."

"But thanks to new sound-emitting tags, about the size of an almond, combined within an extensive coastal network of underwater detectors from Alaska to California, several mysteries of fish migration may soon start to unravel."

More questions

Writing in the online journal Plos Biology, a team of US and Canadian scientists explained how they tagged 1,000 smolt in 2006 in two rivers - the Columbia and Fraser.

Researchers worked quickly to tag the juvenile salmon

One of the factors they wanted to examine was whether there was a difference in mortality rates between the heavily dammed Columbia and the dam-free Fraser.

By using the data gathering via the tags and receivers, the researchers found that the average mortality in both rivers was similar - between 70% and 80%.

However, co-author Carl Schreck, a professor of fisheries and wildlife at Oregon State University, urged caution about assuming that the study contradicted the long-held view that dammed rivers adversely affected fish populations.

"Despite the obvious comparison, it would be overly simplistic to say that dams have no impact on smolt survival," he said.

An array of receivers gathered data from the tags

"There may be some delayed mortality of Columbia River smolts caused by the stress of passage through the hydro-system that is not manifested until the fish reach the ocean."

He added one factor could be that the fish channel their energy into navigating and surviving the series of dams rather than investing the energy in growing bigger.

But the researchers added that the tagging technology had proved to be a valuable tool in terms of gaining a clearer picture on what was happening under the water.

Analysis of the data revealed that two tagged juveniles had taken three months to complete a 2,500km (1,550-mile) migration from a tributary of the Columbia River into the Pacific Ocean, and north to Alaska.

"The electronic and acoustic technology has demonstrated itself as a useful tool for obtaining unique scientific data of importance in a number of public policy arenas," said lead author Dr David Welch from Kintama Research, British Columbia.

Victor Gallardo, Census of Marine Life's vice-chairman, added: "These results from North America have global implications and will be of interest in Chile, Russia, Japan, India, Ireland - indeed every nation where fish migrate between freshwater and saltwater."

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