http://www.sciencemag.org/news/2018/08/biological-passports-help-researchers-track-world-s-biggest-fish

The world’s largest fish is something of a homebody, rarely wandering far from its favorite feeding waters, a new study reveals. And that has big implications for efforts to protect endangered whale sharks (Rhincodon typus), which have seen their numbers fall by half over the past 3 decades.

The behemoths typically glide slowly through the world’s oceans, grazing on plankton. They grow to 20 meters long and 40 tons. Previous research revealed they can swim more than 10,000 kilometers in a year, and dive to 2000 meters beneath the surface. And genetic studies suggested the whales are divided into distinct regional populations.