GPS: Salmon have an app for that

Without ever having migrated before, juvenile Chinook salmon innately know where to go.

An Oregon State University researcher revealed that salmon have a sort of built-in GPS system, which allows them to strategically locate their position by swimming in accordance with the earth’s magnetic fields.

Nathan Putman, postdoctoral research scholar in the department of fisheries and wildlife at OSU, and his research team were seeking to understand how it is possible for the salmon to find a location that they have never visited before.

“How do they know where to go?” Putman asked and sought to answer.

Based on Putman’s recent results studying juvenile salmon, it looks like magnetic fields are quite an important cue for the fish.

It certainly has been one of those things that has gone unnoticed — it appears to be a major part of their sense of direction and location, according to Putman.

When salmon go out to sea after a couple of months in the rivers, they go to somewhat specific foraging grounds. Different populations go to different places — they don’t seem to disperse at random.

Other juvenile animals go on long migrations, but are often accompanied by adults or other experienced migrants within flocks or herds. Salmon don’t have this parental relationship and guidance — they are all alone.

“We were curious whether these little guys might come programmed to know which way to swim based on what magnetic field they were in,” Putman said.

If the magnetic field is really important for fish, researchers should be able to keep the fish in the rivers of the Alsea River, let them have a full view of the sky and their other surroundings and just change the magnetic field around them in order to mimic that which exists out in the North Pacific Ocean, according to Putman.

“There are multiple ways to try to figure out where you are, but if the main way you use is the earth’s magnetic field, then depending on what magnetic field you are in, that’s where you will think you are located,” Putman said.

Thousands of fish were tested in the study. The experiments with each fish lasted 18 minutes. Researchers placed the fish into a plastic bucket and let them sit for 10 minutes to calm them down following potential stressors.

After about eight minutes, researchers began changing the magnetic field around the fish. Snapshots of the fish were taken with a GoPro camera braced onto beams from above at 10-second intervals. The fish were then removed from the buckets and sent on their way.

According to Putman, it’s a nice assay because it causes minimal stress to the animal and most importantly — it doesn’t kill them.

“Not many people care what you do with hatchery fish,” Putman said. “However we could do this (test) with many different populations, some of those populations may be of a conservation concern — it’s not very invasive.”

The field strengths that researchers are testing are the most extreme magnetic fields the fish would encounter in nature.

According to Putman, the extreme sensitivity to magnetic fields the fish require to do this kind of work is seemingly hard for most people to wrap their heads around.

“The fields that we are producing wouldn’t deflect a compass needle,” Putman said. “They are about 50 times less strong than a refrigerator magnet, and yet the fish respond to it.”

The test fish had always been at the OHRC. They had never been given the opportunity to build up a sense of how magnetic fields should behave.

By only changing the one variable of the magnetic field, researchers were able to show that this is how the fish derive their position.

If the magnetic field is changed around the fish, it will change its swimming direction. Fish do this in predictable and sensible ways, according to Putman.

“The fact that this can come programmed into a fish is pretty neat and opens up a lot of other interesting questions to try to look into,” Putman said.

Components like iron pipes and reinforcements within the tanks of the fish hatcheries or iron reinforcements or rebar distort the magnetic field and are perceptible by these fish, according to Putman.

Putman is now investigating whether these components surrounding the fish within a traditional hatchery setting may disturb or distort the fish’s sense of mapping.

“When we were trying to find places to form these experiments, we brought a magnetometer (a devise that measures magnetic fields) and it was a struggle to find a place that had a pristine sort of natural magnetic field that a wild fish would be able to develop in,” Putman said.

Shortly, Putman’s team expects to see whether being reared in a more traditional hatchery setting — in a tank that is placed above an iron pipe — ultimately poses problems for the fish.

If it proves to disrupt the fish’s ability, this might explain the high stray rates of adults not returning to spawn and the low numerical return of fish to fisheries.

If a distortion were present within the magnetic field, the fish would presumably be less efficient at navigating and being able to find optimal ocean foraging grounds.

“It’s a tough world out there,” Putman said. “It really leaves them susceptible to predation and increases their chances of not getting enough food and starving.”

Putman worked with senior scientist and director of OSU’s Oregon Hatchery Research Center David Noakes, Michelle Scanlan, a masters of science candidate in the fisheries and wildlife department, and Eric Billman, a postdoctoral scholar in fisheries and wildlife. The team began its research in summer 2012 at OHRC in the Alsea River Basin.

“(Putman) is the first researcher to ever demonstrate that salmon can detect the earth’s magnetic field,” Noakes said. “That is an enormous breakthrough.”

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