Univ. of Idaho researchers study salmon ear bones

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MOSCOW, Idaho (AP) — Researchers at the University of Idaho are looking at the ear bones of salmon to help discover just how close the fish get to returning to the spawning beds where they emerged as fry.

Brian Kennedy, an associate professor at the university's College of Natural Resources Department, began studying the geochemistry of the fish ear bones, or otoliths, in the late 1990s. The bones are made up of thin layers of calcium carbonate and proteins, and a new layer gets added every day. The composition of each layer changes based on the temperature and chemistry of the surrounding water and, like tree rings, those layers can help researchers determine the history of a fish.

Kennedy told the Lewiston Tribune ( ) that he's been using the layers to track migratory history of salmon, spending long hours examining remote stretches of tributaries of the Middle Fork Salmon River with specialized equipment. Some parts of the Big Creek tributary, nestled in the Frank Church River of No Return Wilderness, are accessible only by horse, boat or foot.

"It's not exactly Lewis and Clark, but it's some of the more challenging science I've done," Kennedy said. "You have to put in a little extra effort."

Kennedy and graduate student Ellen Hamann looked at four years of water samples and other data collected from Big Creek and other tributaries along with otoliths collected from juvenile chinook salmon and from the carcasses of 76 adults found in six different spawning bed locations.

They looked at two types of strontium isotopes found in many types of rocks. By comparing the ratios of the two isotopes present in the rocks along the waterways, they were able to create a kind of map, which they matched to the isotope ratios found in the different layers of salmon ear bones.

The data allowed Kennedy and Hamann to identify where along Big Creek each of the 76 adult Chinook were reared and compared that with where they actually spawned and died.

The researchers found that while most salmon do go home again, they don't necessarily return to the exact neighborhood where they were hatched.

Overall, the study found 55 percent of returning adults spawned within a kilometer, or just over a half mile, of where they were born, while 87 percent came within 10 kilometers, or just over six miles. That meant 45 percent strayed a little and 13 percent strayed a lot.

Males were about 12 times more likely than females to stray from their home waters, and fish that moved around a lot as juveniles — because of food supply, habitat quality, fish density or other reasons — were more likely to stray as adults.

"It's an interesting ecological result," Kennedy said. "It suggests that when times are good, when there's high fish density, it might increase juvenile dispersal, which in turn selects for higher straying. That could be one way salmon spread out to colonize new habitat. As density increases, juveniles are more likely to disperse and that leads to more straying as adults."


Information from: Lewiston Tribune,

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