Pacific Salmon Rely On The Earth's Magnetic Field To Navigate

Brett Smith for redOrbit.com – Your Universe Online

Salmon have an uncanny ability to return to the river of their birth to spawn as adults and a new study in the journal Current Biology has found that these fish are born with an innate ability to sense Earth’s magnetic field – essentially a biological compass to guide them on their journey back.

To reach their conclusion, the study team executed a series of trials at the Oregon Hatchery Research Center in the Alsea River basin. Scientists subjected hundreds of young Chinook salmon to different magnetic fields that occur at the latitudinal ends of their oceanic range. The fish reacted to these “simulated magnetic displacements” by swimming in a way that would move them toward the middle of their marine feeding grounds.

“What is particularly exciting about these experiments is that the fish we tested had never left the hatchery and thus we know that their responses were not learned or based on experience, but rather they were inherited,” said study author Nathan Putman, a postdoctoral researcher at Oregon State University’s Oregon Sea Grant.

“These fish are programmed to know what to do before they ever reach the ocean,” he added.

In the study, the scientists built a large platform with copper wires working horizontally and vertically around the outside. An electrical current moving through the wires allowed the scientists to create a magnetic field and manipulate both the strength and angle of the field. Next, they placed 2-inch young salmon, called “parr,” in 5-gallon buckets and, after an adjustment period, recorded the direction in which they were swimming.

When the fish were presented with a magnetic field that resembled the northern edge of their range, they were more likely to swim to the south. Conversely, fish experiencing a southern-type field wanted to swim north. The scientists said this behavior is proof that these fish possess a “map sense” that allows them to determine where they are and which way to swim.

“The evidence is irrefutable,” said study author David Noakes a senior scientist at the Oregon Hatchery Research Center. “I tell people: The fish can detect and respond to the Earth’s magnetic field. There can be no doubt of that.”

While all of the fish in the study didn’t swim in the same direction, there was a clear desire by the fish to swim away from the magnetic field that was “wrong” for them, Putman said. A group of control fish that only experienced the magnetic field of the testing site were randomly oriented, which suggested that the orientation of the fish in the experimental group could only be explained by changes in the magnetic fields during the experiments.

“What is really surprising is that these fish were only exposed to the magnetic field we created for about eight minutes,” Putman pointed out. “And the field was not even strong enough to deflect a compass needle.”

As these salmon appear to be particularly sensitive to magnetic fields, Noakes noted that many structures contain weak magnetic fields associated with electrical wires or reinforcing iron, which could potentially affect the orientation of fish early in their life cycle.

“Fish are raised in hatcheries where there are electrical and magnetic influences,” Noakes said, “and some will encounter electrical fields while passing through power dams. When they reach the ocean, they may swim by structures or cables that could interfere with navigation. Do these have an impact? We don’t yet know.”

Putman added that magnetic fields may not be the only guide salmon use to navigate.

“They likely have a whole suite of navigational aids that help them get where they are going, perhaps including orientation to the sun, sense of smell and others,” Putman said.