The 2 GPS' of the sea
Many sea animals, such as sharks and turtles, travel huge distances throughout the year as part of their migration. They are able to go across the whole ocean and yet still not get lost. In fact, sea turtles almost always are able to find the exact same beach they were born on, after traveling thousands of miles away. How do they do this? Both animals use the Earth's magnetic field.
To make sure that sharks used the Earth’s magnetic field, Bryan Keller of Florida State University Coastal and Marine Laboratory experimented on bonnethead sharks, a relative of hammerhead sharks. He captured a few wild bonnethead sharks in the Gulf of Mexico and put them in tanks surrounded with a cube and copper wire. The magnetic field of the tank could be changed by changing the amount of power running through the wires.
When the sharks were exposed to the same magnetic field of the place they were caught, the sharks swam randomly in various directions. When they were exposed to a magnetic field 375 miles south of their capture site, they attempted to swim north so they could reorient themselves. However, when they were exposed to a magnetic field 375 miles north of their capture site, they did not know where to swim.
The researchers hypothesize that their confusion comes from the fact that they have never been to the place 375 miles north of their habitat, as that area was actually on land. The area 375 miles south was in the Gulf of Mexico, a place they could have had a chance to explore. Therefore, it means that sharks may have to learn some of their magnetic fields- it is not all inherited in genes.
Another experiment about shark navigation was conducted in San Diego by Andrew Nosal, a postdoctoral researcher at the Scripps Institution of Oceanography. He and his team wanted to test whether sharks relied on their keen sense of smell for navigation. So, he and his team captured a group of wild leopard sharks and brought them 6 miles away from their capture site. Half of the sharks had their nostrils clogged with cotton, while the others did not.
In the end, both groups of sharks made it to their original place, but the sharks with cotton balls in their nostrils took a longer time and also wandered meaninglessly for some time. It can be hypothesized that sharks do rely slightly on their sense of smell, but it cannot be for certain because there is a chance that the sharks were annoyed by the cotton and therefore, were not focused on getting back home.
Besides sharks, sea turtles also use the Earth’s magnetic field. Many species of sea turtles migrate far away the instant they are born because their instinct tells them to swim for the sea and go to a feeding place. After years, most of them are able to find the exact same beach they were born on and lay eggs there.
One of the experiments conducted on sea turtle navigation was Luschi et al. To test out whether turtles truly use the Earth’s magnetic field, researchers used adult female green sea turtles in the Indian Ocean. They captured a group of sea turtles and split them into 3 groups. One group of sea turtles had a magnet strapped on top of their heads, and the magnet’s field was stronger than the Earth’s. The other group had a non-magnetic brass disk strapped on top of their heads, just to make sure that the group with a magnet on a top was not behaving differently only because there was a weight on their heads. The last group of sea turtles did not get anything on their heads. Then, the sea turtles were brought to somewhere 100-200 kilometers away from their capture site and set free to see if they could find their way back.
All sea turtles were able to make it back to their original site, but sea turtles that had nothing on their heads were able to make it back the fastest. This means that sea turtles do rely on the Earth’s magnetic field to some extent, but may also use other factors.
The research being done into how these animals navigate the ocean are becoming increasingly helpful towards conservation, as we are learning more about them. Scientists are continuing to experiment on sea animals to find out how weather and the position of the sun may also affect navigation.