It’s well known that Pacific salmon return to the stream they were born when it’s time for them to spawn and die. When they get close, they might be able to smell their home stream, but how do they know which way to go in the first place? It’s been suspected since the 1960s that salmon migrate successfully in part through detecting the earth’s magnetic field.
Nathan Putman is a professor at Oregon State University. The work he and his colleagues have done in recent years showed that sea turtles, sockeye salmon, and now in a new study, king salmon, all basically have built in compasses.
“In this most recent study of ours 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.”
Putman said his team used very weak magnetic fields in their laboratory studies, but they were strong enough to influence the salmon’s migratory behavior:
“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.”
Putman says the ability to navigate is based not just on magnetic intensity, but the angle of the field as well.
“We know they can tell the difference between far north, far south, and the center of their range, which is sort of the home area. But whether they’re doing anything more specific with it, those are the experiments we’ll be doing in the coming year trying and figure that out.”
The earth’s magnetic field is not fixed – it moves around quite a bit in geologic time, and could be a reason salmon pioneer new areas, are late, or never return home.
“We’ve actually seen some evidence for that with sockeye salmon down in the Fraser River. Whether fish are coming in from the northern or southern end of Vancouver Island seems to be dependent on how the magnetic field is at any particular time.”
Putman said the study showed that the salmon’s navigational skills seem to require no prior life experience – that they are born knowing north from south. He said their sensitivity to magnetic fields should be kept in mind when hatchery-rearing salmon in unnatural environments built of concrete and iron rebar.