Salmon Sense Magnetic Forces in River, Swim Upstream 4,000 Miles

A new study published in the issue of Current Biology and partly funded by the National Science Foundation suggests that salmon find their home by sensing the rivers' unique magnetic signature.

A study encompassing data from over 56 years of catches used salmon fisheries to identify routes that salmon had taken from their most northerly destinations, which were probably near Alaska or the Aleutian Islands in the Pacific Ocean, near the mouth of the river-the Fraser River in British Columbia, Canada. This data was compared to the intensity of the Earth's magnetic field at pivotal locations in the salmon's migratory route.

As the earth has a magnetic field that weakens the proximity to the equator and distance from the poles, it gradually changes on a yearly basis. The intensity of the magnetosphere in any particular location is unique and differs slightly on a year to year basis.

The fishing community has long wondered how salmon find their way home over rivers. Yet sockeye salmon typically swim up to 4,000 miles into the ocean, navigating back to the upstream years later to spawn their young. But how exactly do they do it?

Results from the study concluded that the intensity of the magnetic field determined which route the salmon would choose. The salmon were more likely to take whichever route had a magnetic signature that most closely matched that of the Fraser River years before, when the salmon initially swam from the river into the Pacific Ocean.

"These results are consistent with the idea that juvenile salmon imprint on (i.e. learn and remember) the magnetic signature of their home river, and then seek that same magnetic signature during their spawning migration," said Nathan Putman, a post-doctoral researcher at Oregon State University and the lead author of the study.

Research shows that this study provides the first evidence of magnetic imprinting in animals and represents the discovery of a major new phenomenon in behavioral biology.