A shark that walks in water instead of swimming might sound like a creature straight out of a science fiction thriller. However, that is precisely how the four new species of the fish — found in the tropical waters of the Indo-Australian archipelago — move across the seafloor. The unique ocean dwellers were discovered by a team of scientists, led by Dr. Christine Dudgeon from Australia's University of Queensland, during a 12-year global conservation study.
The newly-found species belong to the genus Hemiscyllium, the same family as the previously known five species. The sharks have all evolved to survive in low oxygen environments, enabling them to hunt during low tides. The researchers believe their ability to use their fins to walk across the water affords the sharks a substantial advantage over the unsuspecting smaller animals they prey on. Though they are an apex predator in their shallow coral reef habitat, the tiny sharks are harmless to humans.
"At less than a meter (3.2 ft) long on average, walking sharks present no threat to people, but their ability to withstand low oxygen environments and walk on their fins gives them a remarkable edge over their prey of small crustaceans and mollusks," says Dudgeon. Team member Dr. Mark Erdmann, a coral reef ecologist at the California Academy of Sciences, adds, "They're incredibly cute little animals and are really more like a gecko walking around than a shark."
A DNA analysis of skin samples from the live fish suggests that walking sharks broke away from their gliding brothers and sisters about nine million years ago and became a distinct species. Though that may appear to be a long time ago, it is relatively recent given that sharks have been around for more than 400 million years. In fact, Dudgeon and her team believe walking sharks are the youngest kind of sharks on Earth!
"Data suggests the new species evolved after the sharks moved away from their original population, became genetically isolated in new areas, and developed into new species," says Dudgeon. "They may have moved by swimming or walking on their fins, but it's also possible they 'hitched' a ride on reefs moving westward across the top of New Guinea, about two million years ago. We believe there are more walking shark species still waiting to be discovered."
The researchers, who published their findings in the Marine and Freshwater Research journal on January 21, 2020, say that the sharks' small numbers and shallow habitat makes them extremely vulnerable to natural disasters and overfishing. Three of the nine walking shark species, all of which live in the waters off Northern Australia, eastern Indonesia, and near the island of New Guinea, are currently on the International Union for Conservation of Nature Red List, which lists species at risk. Dudgeon and her team believe sensible conservation management plans are urgently needed to protect the walking sharks and other endangered animals from further threats.
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