Facebook
Twitter
Pocket
Reddit
Email
In the blue expanse of the world’s tropical waters, whale sharks glide like gentle giants. Stretching upward of 60 feet in length, these endangered creatures are the largest fish in the ocean.
Known for their distinctive spotted skin, truncated snouts, and wide, flat heads stretching up to 5 feet across, whale sharks earn their names in part from their massive size and filter-feeding behavior, which resemble that of baleen whales. But their cartilage skeletons and five pairs of gill slits give them away as belonging to the shark family.
Conservation biologist Freya Womersley, a postdoctoral research scientist at the University of Southampton in the United Kingdom and the Marine Biological Association, became fascinated with whale sharks after her first encounter with one while diving near the island of Mahé in the Seychelles with a local marine conservation society. She was impressed by their slow, cumbersome grace.
But when Womersley began to study the creatures not long after that, she noticed something else. “One of the things that struck me early on was how many of these whale sharks had injuries,” she recalls. These were deep lacerations down the sides of their bodies, blunt trauma, and in some cases, partial fin amputations.
Though capable of diving to depths of more than 3,000 feet when migrating or foraging, whale sharks often linger near the surface, where plankton, small fish, and other food sources thrive. Despite their deep-diving abilities, they spend much of their lives in these sunlit waters, making them more visible to humans. Unfortunately, this surface feeding behavior also places them in harm’s way, as their habitat frequently intersects with busy shipping lanes, leaving them vulnerable to collisions with the propellers of large ships.
One of the things that struck me early on was how many of these whale sharks had injuries.
It’s about to get even worse: According to a recent study co-authored by Womersley, as climate change warms the ocean and makes certain core habitats inhospitable for the creatures, they are likely to migrate poleward into areas that overlap even more closely with major shipping routes. The researchers’ findings suggest that the species’ range is likely to shift some 7.5 miles a year, but the picture is worse if ocean temperatures continue to warm at current rates.
To build their model, Womersley and colleagues used satellite-tracking data from 348 whale sharks, mapping their movements in relation to current and future ocean temperatures under various climate scenarios. Under the worst-case scenario, where global temperatures could rise by more than 3 degrees Celsius by the end of the century, the sharks’ core habitats in regions like Asia could shrink by more than half. At the same time, new, more suitable habitats would open up in areas heavily intersected by shipping lanes, such as parts of the Eastern China Seas near Japan, and off the coast of California. The models showed that even if shipping traffic remains at current levels, the overlap between whale sharks and large vessels would still dramatically increase.
Whale sharks aren’t the only species on this collision course. The study reflects a broader trend of climate-driven species redistribution, a phenomenon already being observed as all kinds of animals begin to move poleward in search of cooler temperatures, with redistributions projected for over 12,000 species across the globe. But marine creatures are especially vulnerable and are moving poleward as much as six times faster than land dwelling animals, with a network of effects throughout the marine food web.
“That study is fascinating and important,” says Amber Sparks, a marine biologist and co-founder of the Blue Latitudes Foundation, who was not involved. “It highlights a trend that marine scientists have been tracking for some time, marine species shifting poleward in search of cooler waters as ocean temperatures rise. This migration is essentially a biological escape route from climate stress, but it brings cascading impacts.”
For whale sharks, those impacts could include increasing battle scars—and the risk of fatal strikes by ships. 
Lead photo by Connor Holland / Ocean Image Bank
Get the Nautilus newsletter
Cutting-edge science, unraveled by the very brightest living thinkers.
