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New tool to save salmon: isotope tracking

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Posted May 11, 2015

Salmon carry a strontium chemical signature in their “ear bones” that lets scientists identify specific streams where the fish hatched and lived before they were caught at sea. The new tool may help pinpoint critical habitats for fish threatened by climate change, industrial development and overfishing.

A cross-section of a salmon otolith, also known as a fish ear stone or fish ear bone.  Image credit: Sean Brennan, University of Washington

A cross-section of a salmon otolith, also known as a fish ear stone or fish ear bone. Image credit: Sean Brennan, University of Washington

“Using this method, we can trace where the salmon were born and where they moved while they were growing in the rivers and streams,” says University of Utah geochemist Diego Fernandez, a co-author of the study published May 15 in the journal Science Advances.  “This could be useful for protecting fish and understanding how many salmon we can take from nature.”

Genetic studies of salmon caught in saltwater previously determined the watershed where fish hatched, but not sets of streams and not where they spent time as they grew, says Thure Cerling, also a University of Utah geochemist and co-author.

In the new study, researchers from the universities of Utah, Washington and Alaska Fairbanks and the U.S. Geological Survey analyzed strontium isotope ratios in otoliths – also known as ear stones or ear bones – from 255 chinook salmon caught in southwestern Alaska’s Bristol Bay. The study determined where the fish hatched and spent time in seven different sets of two to five streams within the watershed of the Nushagak River, western Alaska’s third-largest river.

Wild salmon worldwide are under pressure by many interests: mining, logging, hydroelectric dams, hatcheries, industry, and commercial, sport and subsistence fishing.

“Disturbances to salmon populations can range widely from large-scale disturbances due to a rapidly changing climate to smaller-scale disturbances such as habitat loss or contamination from industrial development of the freshwater streams that are the spawning grounds of salmon,” says the study’s lead author, Sean Brennan, a 2007 University Utah biology graduate and now a postdoc at the University of Washington.

“Without knowing which habitats are producing fish and what habitats are used by fish during critical periods of their lives, it is very difficult to understand how populations might respond to some disturbance and to design effective conservation strategies,” says Brennan, who ran the study as a doctoral student at the University of Alaska Fairbanks and a visitor at the University of Utah, where the lab work was done.

He says the study could have important implications in understanding how habitat loss and contamination could affect salmon if the proposed Pebble Mine is built in the headwaters of the Nushagak. Development of the copper, gold and molybdenum mine is opposed by fishers and hunters, environmentalists, local residents and federal regulators.

Source: University of Utah

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