A team of international researchers recently introduced the world to four new species of "walking sharks" discovered in waters off northern Australia and New Guinea. The find comes after a 12-year study and almost doubles the number of known species of walking sharks, bringing the total to nine. 

While their name conjures up images of sharks strolling along the sandy shore, these ornately patterned fish lack the physiology for life outside the water. Although they are known to "walk" on land, they are more adept at using their fins to pull themselves along shallow reefs – a trait that helps them catch small fish and invertebrates.

"At less than a metre 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 molluscs,” University of Queensland's Dr Christine Dudgeon explains in a press release. "These unique features are not shared with their closest relatives the bamboo sharks or more distant relatives in the carpet shark order including wobbegongs and whale sharks."

The new "walkers" belong to the Hemiscyllium genus, and were linked to the five existing members of the category courtesy of genetic analyses. "We estimated the connection between the species based on comparisons between their mitochondrial DNA which is passed down through the maternal lineage," says Dudgeon.

The Halmahera bamboo shark (Hemiscyllium halmahera), one of nine species of walking shark known to inhabit the waters around Australia and the island of New Guinea. (© Conservation International/photo by Mark Erdmann)

Walking sharks appeared about 9 million years ago, which is relatively recently when compared to the first sharks that emerged some 400 million years ago. Although it's tricky to grasp exactly how the walking sharks came to be, it's likely that environmental factors like changing sea levels, new landforms, the emergence of reefs, and the spread of sharks to new areas played a vital role in shaping the genus.

Sharks in the Hemiscyllium genus are believed to have moved away from their ancestral populations and adapted to new tropical habitats, eventually becoming genetically distinct. "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 2 million years ago," Dudgeon explains.

As a result of their limited range in northern Australia, New Guinea and parts of Indonesia, walking sharks are threatened by habitat destruction and overfishing. "A global recognition of the need to protect walking sharks will help ensure they thrive providing benefits for marine ecosystems and to local communities through the sharks’ value as tourism assets," Mark Erdmann, a co-author of the paper from Conservation International, said in a press release. "It’s essential that local communities, governments, and the international public continue working to establish marine protected areas to help ensure our ocean’s biodiversity continues to flourish."

Header image: © Citron