CORVALLIS, Ore. The mystery of how salmon navigate across thousands of miles of open ocean to locate their river of origin before journeying upstream to spawn has intrigued biologists for decades, and now a new study may offer a clue to the fishes' homing strategy.
In the study, scientists examined 56 years of fisheries data documenting the return of sockeye salmon to the Fraser River in British Columbia and the route they chose around Vancouver Island showed a correlation with changes in the intensity of the geomagnetic field.
Results of the study, which was supported by Oregon Sea Grant and the National Science Foundation, were published this week in the journal Current Biology.
"What we think happens is that when salmon leave the river system as juveniles and enter the ocean, they imprint the magnetic field logging it in as a waypoint," said Nathan Putman, a post-doctoral researcher at Oregon State University and lead author on the study. "It serves as a proxy for geographic location when they return as adults. It gets them close to their river system and then other, finer cues may take over."
Earth has a predictable, consistent geomagnetic field that weakens as you move from the poles toward the equator. The magnetic North Pole has an intensity gradient of roughly 58 microtesla, while the equator is about 24 microtesla.
Salmon originating from Oregon that have spent two to four years in the northern Pacific Ocean off Canada or Alaska would return as adults, the scientists speculate, journeying southward off the coast until they reached a magnetic field intensity similar to that of their youth.
"That should get them to within 50 to 100 kilometers of their own river system and then olfactory cues or some other sense kicks on," said Putman, who conducts research in OSU's Department of Fisheries and Wildlife.
Vancouver Island provides a natural laboratory for the study of salmon, the rese
|Contact: Nathan Putman|
Oregon State University