Apparently Everything We Knew About Whale Sharks Was Wrong

In 2015, Conservation International launched a tagging program in Indonesia’s Cenderawasih Bay to learn more about the behaviors of the largest fish species in the ocean: whale sharks. Whale sharks are often caught in nets and become victims of bycatch in the region. Now, a year later, scientists have learned a lot of new information about the large fish, and much of what they’ve found is rather shocking.

Scientists Tag World’s Largest Fish, Whale Sharks | Shark Week – Conservation International (CI)

Watch researchers tag whale sharks, the biggest fish in the ocean. Whale sharks grow to over 40 feet long and weigh as much as 20 tons. Conservation International has partnered with the Indonesian Ministry of Marine Affairs and Fisheries, the State University of Papua and the Cenderawasih National Park Authority to tag whale sharks with fin-mounted satellite tags in Indonesia’s Birds Head Peninsula.

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The fin-mounted tags gave researchers information about the whale sharks’ locations, their depth under water and the temperature of the water they were swimming in. Over the course of the year, it became apparent to scientists that, like oceanic manta rays, whale sharks are homebodies for the most part. That means they don’t typically have large migrations and instead feed on the local fish supply year round.

Nevertheless, some whale sharks were observed taking a few short, seemingly random “road trips,” but researchers are still trying to figure out the motivations for the trips.

Whale shark sucks fish out of hole in fishing net – Conservation International (CI)

On a recent expedition to Indonesia’s Cendrawasih Bay, Conservation International’s Mark Erdmann learned how whale sharks often congregate around bagan (lift net) fishing platforms to eat the small silverside baitfish that the fishers are targeting. The sharks have also learned how to “suck” the fish out of holes in the nets!

“We have no idea why they went so far — one shark covered 4,000 kilometers (2,485 miles) before returning to the bay — for such short periods of time,” explains Conservation International’s Dr. Mark Erdmann in a blog post. “Although we suspect that the journeys of some of the larger males might be related to mating, several of these traveling sharks have actually been juvenile males under 4.5 meters (15 feet), leaving us scratching our heads!”

The most shocking discovery about the gentle giants, though, has to do with depth. Whale sharks tend to stay above a 330-foot depth, as it’s where most of the fish they eat are. However, scientists observed some of the tagged whale sharks diving as deep as 6,000 feet below the surface — and they have no idea why!

Scientists Tag World’s Largest Fish, Whale Sharks | Shark Week – Conservation International (CI)

Watch researchers tag whale sharks, the biggest fish in the ocean. Whale sharks grow to over 40 feet long and weigh as much as 20 tons. Conservation International has partnered with the Indonesian Ministry of Marine Affairs and Fisheries, the State University of Papua and the Cenderawasih National Park Authority to tag whale sharks with fin-mounted satellite tags in Indonesia’s Birds Head Peninsula.

The baffling discoveries drive home how much more there is to learn about whale sharks (including where the females and babies are). Luckily, the tags will last another year so scientists can collect even more data. The more they can learn, the better equipped they’ll be to learn how to protect the vulnerable species.

Scientists free a whale shark from a fishing net | Shark Week – Conservation International

In Indonesia’s Cendrawasih Bay, whale sharks often congregate around bagan (lift net) fishing platforms to eat the small silverside baitfish that the fishers are targeting. Sometimes the sharks swim right into the nets and become entangled. Local fishermen are considering modifying the lift net design in a way that prevents the sharks from entering.