Thursday, June 5, 2014

Hatcheries May Be Wrecking Fishes’ Sense of Direction

Salmon and ocean-going trout are famous for their ability to return to the streams of their birth after years at sea. Growing evidence suggests the fish use the earth’s magnetic field to find their way home. That could be a problem for fish raised in hatcheries, according to a new study. It finds that common construction materials like iron and steel can throw off the fishes’ navigation.

The earth’s magnetic field runs in long, arcing contours from the north to south pole. The closer it gets to the poles, the stronger the magnetic pull. “The earth’s magnetic field varies in a predictable way. It has a couple components that are useful for telling an animal where it is,” says Nathan Putman, a fisheries biologist at the Oregon Research Hatchery Center, and the lead researcher on the new study.

He believes salmonids (which include ocean-going trout like the steelhead trout used in this study) and other marine creatures use magnetic intensity to gauge how far north or south they are from their home stream. He also thinks it’s possible for the fish to use another magnetic property—inclination, which is the field’s angle relative to the earth’s surface—to map their position to the east and west. In graduate school, Putman was part of a different team that showed sea turtles have this ability, but says he still needs to do more experiments to confirm that salmonids can do it as well.

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