Wednesday, May 8, 2013

The Mystery of Salmon Migration and Magnetism

by KellyC, This post originally appeared at the Future Science Leaders blog.

During spawning season, salmon somehow swim thousands of kilometers from the sea to the rivers where they were born. It has long been a mystery as to how they are able to navigate such an enormous distance, and with startling accuracy, yet a new study indicates that magnetism may play a role in guiding salmon home.

This study, published recently in Current Biology, finds that salmon sense rivers’ magnetic signature to help guide them. The researchers in the study used data spanning 56 in order to identify the migration routes taken by the salmon, and comparing them to the intensity of the Earth’s magnetic fields at important points in their migratory route. The intensity of the Earth’s magnetosphere differs at every point, and changes over time. Researchers observed how migratory patterns could be predicted based on the strength of the magnetic signature of the routes, and found that in all 56 years, salmon were more inclined to take the path that had the magnetic signature that most closely resembled that of the Fraser River when they first swam out from that river into the Pacific Ocean. Surprisingly, the researchers found that the migratory routes taken by salmon relied entirely on the magnetism of the routes, not on the distance of the route.
“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.
Researchers say that they still don’t know exactly when, how early or how often salmon are able to check the Earth’s magnetic field in order to situate them during their migration home. However, Putman says,
“For the salmon to be able to go from some location out in the middle of the Pacific 4,000 miles away, they need to make a correct migratory choice early–and they need to know which direction to start going in. For that, they would presumably use the magnetic field,” which implies that salmon must use magnetism early in their journey home. 
He also says, “As the salmon travel that route, ocean currents and other forces might blow them off course. So they would probably need to check their magnetic position several times during this migration to stay on track. Once they get close to the coastline, they would need to hone in on their target, and so would presumably check in more continuously during this stage of their migration.”
Previous studies suggest that salmon use their sense of smell to find the tributary in which they were born, and Putman agrees with this. However, he points out that over long distances, magnetism would be more beneficial than odors because unlike odors, it can be continuously detected over great distances.
This study is ground-breaking because scientists have never before shown an animal’s ability to learn the magnetic field through individual observation, like when the salmon somehow remembered the magnetic signature of the Fraser River as they left it to swim to the sea, and how they used this information to guide them back to their home river. This is the first study that shows evidence of magnetic imprinting in animals, and reveals valuable new concepts in the field of behavioral biology.
Also, this study suggests that the migratory patterns of salmon could be predicted using geomagnetic models, which has major implications for conservation and management.
About this contributor: Kelly is an ocean lover and high school student, and is particularly fascinated by whales. She enjoys being outdoors, writing, traveling and meeting new people.

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