When the normal intensity level for the Fraser River shifted to the north, the sockeye were more likely to choose a northern route for their return. When the field shifted slightly south, they chose a southern route.
This "field drift" accounted for about 16 percent of the variation in the migration route, Putman said, while variations in sea surface temperatures accounted for 22 percent. The interactive effect between these two variables accounted for an additional 28 percent of the variation in the migration route.
"Salmon are a cold-water fish, and all things being equal, they prefer cold water," said Putman, who earned his Ph.D. in biology from the University of North Carolina at Chapel Hill. "But the fact that they also demonstrate geomagnetic fidelity in choosing a route shows that this could be a major instrument in their biological toolbox to guide their way home."
Putman said that his previous studies of the Columbia River have shown that the magnetic intensity shifts less than 30 kilometers in either direction over a period of three years, which is about the length of time many salmon spend in the ocean.
"Salmon have to get it right because they only have one chance to make it back to their home river," Putman said, "so it makes sense that they may have more than one way to get there. The magnetic field is amazingly consistent, so that is a strategy that can withstand the test of time. But they may also use the sun as a compass, track waves breaking on the beach through infrasound, and use smell."
Putman and OSU fisheries biologist David Noakes plan to follow through with experiments on varying the magnetic field for
|Contact: Nathan Putman|
Oregon State University