Hatcheries able to disrupt steelhead navigation

GRANTS PASS, Oregon (AP) ― A new study suggests that steelhead trout can have trouble using the Earth’s magnetic field to navigate if they were raised in a hatchery, where the field can be distorted by iron pipes.

Scientists at the Oregon Hatchery Research Center in Alsea raised two sets of fish: one outside the hatchery with a natural magnetic field, and one inside the hatchery, where instruments showed the field was distorted.

Fish raised outside the hatchery oriented themselves to changes in the magnetic field, but fish raised in the hatchery’s distorted magnetic field did not.

The scientists found that when a field was created simulating the intensity and inclination of a spot in the ocean off California in the southern part of the steelhead’s range, most of the fish from the first group pointed northwest and out to sea. When the field was changed to simulate a location off Alaska, the northern part of their ocean range, most of the fish turned to point southeast, toward home. Fish raised in the distorted magnetic field did not orient themselves in any particular direction.

“I would not go out and tell hatchery managers to pull out all the iron pipes and replace them with PVC or aluminum,” said lead author Nathan Putman, a researcher at Oregon State University at the time of the study who is now at NOAA Fisheries Service in Miami working on fish migration questions.