Isotope Tracking May Reveal Critical Habitats for Salmon Threatened by Climate Change

There may be a new tool to help save salmon: isotope tracking. Scientists have found that the strontium chemical signature in salmons' "ear bones" could reveal critical habitats for fish threatened by climate change, industrial development and overfishing.

"Using this method, we can track where the salmon were born and where they moved while they were growing in the rivers and streams," said Diego Fernandez, co-author of the new study, in a news release. "This could be useful for protecting fish and understanding how many salmon we can take from nature."

Previous genetic studies revealed the watershed where fish hatched, but not the sets of streams and not where they spent time as they grew. In the new study, the researchers analyzed strontium isotope ratios in otoliths, which are the "ear bones" in salmon. In all, the scientists examined the otoliths from 255 chinook salmon caught in southwestern Alaska's Bristol Bay. This revealed not only where the fish hatched, but also where they spent time in seven different sets of two to five streams.

"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," said Sean Brennan, one of the researchers, in a news release. "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."

The findings are published in the journal Science Advances.

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