First pigeons, now sockeye salmon. It seems more animals are using cues radiating from the earth to navigate. While homing pigeons are now thought to use infrared sound waves to find their way over hundreds of miles, salmon returning from the Pacific to their freshwater breeding grounds may be using the earth’s magnetic field as a guide.
In a new Current Biology study, researchers looked at 56 years’ worth of federal fishery records, watching whether salmon returning to British Columbia’s Fraser River took a route on the north side of Vancouver Island or the south, as fish tended to frequent both. They also looked the geomagnetic field, which moves over time, but always in a predictable pattern. The field will be stronger in one place and weaker in another, then shift over the years.
They found that the salmon remembered what the magnetic field was like when they left the Fraser River for the open ocean, two years before spawning. The followed the course that was the most magnetically similar to that younger, simpler time.
But how do the fish even sense the magnetic field? According to research done last year, scientists believe the salmon nose has magnetite crystals that help the fish navigate the field. However, this isn’t believed to be the end-all-be-all of salmon navigation. It’s already well known that the fish use smell to follow their course upstream once they reach the river and researchers think the sun and water temperature could play a role in finding their way as well. As for us, we’ll just have to stick with Google Maps.