Natural born navigators

Shortly after the salmon’s eggs hatch, the baby fish can navigate easily. They use the Earth’s magnetic field to navigate to traditional feeding grounds that have been used for generations, biologists from the Oregon State University discovered.

The scientific team of Nathan Putman put copper wires in water tanks, which they ruled differently and then put electricity through these wires to imitate a magnetic field. The scientists put hundreds of young Chinook salmons in these tanks to test how they reacted to different magnetic fields.

Artificial magnetic fields

“The fish behave like they have a map in their head that is based on the magnetic field of the Earth,” Putman explains. “When the salmon are placed in a magnetic field similar to a northern magnetic field, most fish swam south in order to reach their feeding grounds. When we created a typical southern artificial magnetic field, the fish swam north.”

Salmon not only navigate on one feature of the magnetic field, they use two. They use the strength of the magnetic field and combine it with the inclination angle. With these two aspects, the fish determine their position accurately and use it to find the most efficient route to their feeding grounds. A skill, the scientist conclude, is congenital. Similar observations by this team have been made on sea turtles and other marine animals.

The scientists discovered that the salmon navigation is prone to disturbances. “The changes in the magnetic field we applied during our study are so minimal that they would not appear on a normal compass. The natural compass of salmon is very sensitive which makes it likely to fail.” Large buildings of iron and concrete, like oil platforms, might disturb the salmon’s natural compass, the scientists say.