Salmon homing behavior

Powered by magnetism

Eugene M. McCarthy

Eugene M. McCarthy - 10/21/2015

sockeye salmon face
Sockeye salmon (Oncorhynchus nerka), coming home after years spent at sea. Credit: Current Biology, Putman et al

sockeye salmon face
Sockeye salmon spawning. Credit: Current Biology, Putman et al.

sockeye salmon Sockeye salmon are famous for their homing behavior

Fraser river map The mouth of Canada's Fraser River lies behind Vancouver Island, so salmon have to choose one of two routes to reach it.
Salmon homing behavior is made possible, at least in part, by an ability to sense the earth's magnetic field, says a new study based on data collected over a 56-year period. The research is published in the online journal Current Biology.

"To find their way back home across thousands of kilometers of ocean, salmon imprint on the magnetic field that exists where they first enter the sea as juveniles," said Nathan Putman of Oregon State University. "Upon reaching maturity, they seek the coastal location with the same magnetic field."

It has long been believed that many sea creatures, including not only fish, but also seals and sea turtles, can sense the local intensity of the earth's magnetic field and use it as a guide. But establishing this fact has been exceedingly hard to do.

In a new study, Putman and his colleagues examine salmon homing behavior by looking at sockeye spawning in British Columbia's Fraser River Watershed, one of the most important salmon-producing regions in the world (see map at right). These particular salmon lend themselves to resolving the magnetism question, says Putman, because returning fish encounter a major obstacle, Vancouver Island, which blocks direct access to their river.

"So the fish must make a choice," he says, "Do they use the northern inlet or the southern inlet in their detour?"

In designing their study, Putman and his colleagues reasoned that if these salmon do follow magnetic fields, then their behavior would vary in predictable ways, because of geomagnetic field drift (the Earth's magnetic field changes gradually over time).

Both fish movements and magnetic changes over the last 58 years are known, and Fraser sockeyes would be expected show a greater tendency in any given year for the passage around Vancouver Island that most closely matches the magnetic value of the Fraser River when they first emerged into the ocean. Comparison of available data collected agreed well with a model salmon homing behavior based on this reasoning.

So it seems sockeyes do use magnetic fields to find their way around, a discovery that will, no doubt, be useful to conservationists.

"If you want to predict the distribution of salmon, then having information on their mechanisms of navigation is really important," Putman said.

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This story was based on information obtained from the AAAS.

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