Salmon researchers have proven it takes more than a good nose for the fish to find their way home to spawn. The salmon have built in compasses and it’s the earth’s geomagnetic field that gets credit for salmon returns.
“We’re actually able to show this does occur. That the fish are able to figure out where they are based on the magnetic field they’re in.”
Nathan Putman is a senior scientist at LGL Ecological Research Associates co-lead author on the salmon studies being done at Oregon State University and the Hatchery Research Center.
“We changed the magnetic field around the fish to simulate one that exists sort of north of their oceanic range, and even though they’re sitting in rural Oregon, they act like they’ve been displaced somewhere up near Alaska. And they swim to the south. Give them a magnetic field that exists in the southern end of their range, and they act like they’re there – they swim to the north.”
The ability to navigate is based not just on magnetic intensity, Putman says, but also the angle of the field as well.
Now newer studies show magnetic are critical to tiny fish.
In tests, a low electric current was run through coiled copper wires to precisely control the magnetics. It revealed that the fields are critical for baby Chinook salmon to find their way to surface waters after they emerge from their gravel nests.
The scientists said the salmon use the geo- magnetics for three-dimensional orientation – as a map, a compass and an indication of which way is up.
That sensitivity should be kept in mind, they said, when rearing salmon in hatcheries built of concrete and iron rebar which can disrupt the fishes’ ability to orient direction appropriately.
The study is published in the journal Biology Letters. 
