Across their lifetime, sharks can swim enormous distances, but how they completed annual migrations without getting lost hadn’t been definitively proven. Like turtles, homing pigeons and dogs, it was thought that magnetoreception played a part, and that sharks were able to find their way using the Earth’s magnetic field. Now, new research published in the journal Current Biology has found some of the first solid evidence for the magnetoreception skills of sharks.
While the concept was not new to science, it’s one that’s proven difficult to test in sharks. It turns out, they’re quite a tricky test subject. "To be honest, I am surprised it worked," said Save Our Seas Foundation project leader Bryan Keller, also of Florida State University Coastal and Marine Laboratory in a statement. "The reason this question has been withstanding for 50 years is because sharks are difficult to study."
The study selected bonnethead sharks (Sphyrna tiburo) for the study, as they needed a species that wasn’t too enormous and was known to return to specific locations that might require the sort of magnetic reception they were testing for. Bonnetheads travel thousands of miles annually and can reliably return to estuaries every year, demonstrating they have some concept of “home” and how to get there.
They placed the wild-caught baby sharks (do do do do do do) in a tank and exposed them to magnetic conditions that mimicked those of remote locations from the testing site. The researchers predicted that, if the sharks were reading the field for navigation, they would swim in a direction to correct their displacement and return to the magnetic conditions of the testing site. Imagine you’re driving north to get to your home, but suddenly your satnav says you’ve overshot by a mile. You’re going to turn the car around to correct the displacement. The same response was expected to be exhibited by the sharks, orienting themselves in a way that would correct the sudden change. Sure enough, they did.
As well as means of getting around, the researchers believe that sharks’ magnetoreception could reveal new insights into the genetic difference between wild populations. “Our finding that bonnetheads derive spatial information from geomagnetic cues may have important implications for understanding their current migrations and biogeographic patterns,” wrote the study authors.
“One such example is that genetic differences between populations of sharks may be predicted by spatial variation in the [geomagnetic field]. Population structure can be a function of geographic distance, and in an isolation by distance model, populations will be more diverged if separated by greater differences. Likewise, environmental conditions can affect components of genetic variation with organisms in disparate habitats experiencing reduction in gene flow.”
The team hopes next to investigate if anthropogenic factors could soon (or perhaps are already) influencing these magnetic fields, and what effect that might have on these animals. They also hope to explore if these navigation skills come into play for more than just enormous annual migrations, and perhaps are a part of everyday shark life.