Investigating the Mysterious Whale Sharks of Mafia Island | National Geographic

[Music] The fishermen and the tourism operators here, they were only seeing whale sharks for a few months a year, over the summer. When we started tagging the sharks, though, with small acoustic tags, and we've got a network of receivers out here in the bay, we started finding that actually the whale sharks don't leave; they just move slightly further offshore and slightly deeper, and they don't come to the surface quite as [Music] often.

One of my jobs while I'm here in Mafia is to take tissue samples with the whale sharks. Usually, those bits of tissue are less than 1 gram, so it's a very small amount, and the sharks very rarely react. Some of the things that the tissue samples can tell us about is that they can actually give us an idea of the location of the sharks and where they spend most of their time. For example, the profiles from the fatty acid analysis have shown that although the sharks do mostly feed on the shrimp here, they also have other diet preferences out in deeper water and at night.

So we can actually use it to show that the sharks often stay in an area such as Mafia, and we can prove that by [Music] chemically. Even though whale sharks are quite a popular species with divers and scientists, there's still a lot we don't know about them, and some of the stuff we don't know is really fundamental. We don't know how old they are when they become adults; we don't know how old they get here.

We can get to know individuals, so we can learn a lot about what whale sharks are doing over their lifespan. It's pretty crazy in that the whale sharks here often look like a mobile ecosystem. There's loads of other species of fish that are feeding on the same stuff; they'll often associate with the whale shark.

So you'll get this huge cloud of fish biomass just moving around, often almost completely blocking the shark from view. [Music] I'm very proud to see the largest fish in the world, very important for the ecosystem because they serve as a sign for the fish we call the mael, and sometimes the tuna fish. [Music]

The issues are likely to be if the fishermen accidentally get the whale shark in the net, and it can be quite difficult and quite dangerous to free such a large animal. So one of the things we're working at here is just helping the fishermen to be able to safely release them and, as much as possible, trying to avoid catching them in the first place.

As a conservation biologist, one of the things that particularly motivates my research is that whale sharks are now globally endangered species. Since 2016, we think the populations have declined over the last few decades, and that's purely due to human influence. So we've got to make sure that places like this remain a sanctuary for the whale sharks because they spend so much time here.

We've really got to try and minimize the human threats and just help them recover as a species. [Music]