"It certainly is high, and it's somewhat higher than some work that was done by some colleagues of mine about 10 years ago using similar tags, but without the predation detecting capability," says David Hardie, a marine biologist with the Department of Fisheries and Oceans.

Each spring for the past three years Hardie has implanted 50 salmon smolts with predation tags before they run to the ocean.

The tag is equipped with a small dab of polymeric coating that, once eroded by the stomach acids of a predator, changes the signal emitted by the tag.