Using Salmon Ear Bones To Improve Fishery Management

May 19, 2017

The otolith, or "ear bone," is located just beneath a salmon's brain.
Credit Dr. Sean Brennan / University of Washington

A new study is using fish ear bones to trace where Kuskokwim king salmon are hatching to help managers better manage the fishery.

The ear bone is called the otolith. It’s small, white, and feels like a stone. If you were to cut it open, you’d see rings, similar to tree rings. Each ring shows the passage of time and carries clues to where the fish has swum. That’s because pieces of the environment, like chemicals dissolved in water that enter the fish’s bloodstream through the gills, collect in the otolith.

This summer, Dr. Sean Brennan of the University of Washington is using those clues to map where Kuskokwim king salmon are hatching to answer these questions:

“What parts of the watershed did those fish come from, and in any given year, which parts of the watershed were producing the most of the fish and how that varies through time,” said Brennan.

The idea is that if we can find out where the fish are hatching and when they’re arriving in the river, then we can fish in a way that doesn’t disproportionately impact one fish stock over another.

“Being able to unravel that," said Brennan, "[will] help management and research that is really focused and aiming at conserving the resource for future generations.”

The study has two parts. The first part is to collect water samples throughout the Kuskokwim River drainage and test those samples to determine the water chemistry at different parts of the river.

“Essentially what we’re going is mapping the chemistry that naturally occurs in each of the tributaries and mainstem channels of the Kuskokwim watershed.”

The second part involves taking all the king salmon the Alaska Department of Fish and Game catches in the Bethel Test Fishery and removing their otoliths. Then biologists will match the otoliths’ chemistry to the river’s chemistry to pinpoint where each fish hatched.

This means that the king salmon from the Bethel Test Fishery, distributed by ONC this summer, will look a little different.

“It’ll most likely look like a triangle of the top part of the head has been cut away.”

This study has been conducted in the Nushugak River in Bristol Bay and on the Yukon River here in the YK Delta for several years. It’s arriving on the Kuskokwim for the first time this summer.