magnets... but I am not even kidding. they include a tiny bit of magnetic material in their ear. but it must be a genetic construct that informs them what to

magnets... but I am not even kidding. they include a tiny bit of magnetic material in their ear. but it must be a genetic construct that informs them what to do with north, they use it to move to particular undersea canyons out in the ocean they have never been to.