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Scientists are finding that even the world’s largest fish can hide in the vastness of the ocean.
Or at least, they’re hoping that’s the case. The other option is that adult whale sharks are disappearing.
In a new study published Wednesday in the journal Royal Society Open Science, researchers at the University of Western Australia raised concerns about where the world’s largest whale sharks have gone, as the size of the biggest sharks observed in recent years pale in comparison to those recorded more than a decade ago.
Whale sharks measuring between 43 and 49 feet were observed in oceans around the world in 1995, from India to Belize. In more recent years, reports have shown that aside from two populations of adult female sharks in the East Pacific, most locations consisted only of juvenile sharks measuring less than 23 feet in length.
Ana Sequeira, a research associate at University of Western Australia and the study’s lead author, started looking at whale sharks around the coral reefs of Western Australia’s Ningaloo Coast and subsequently expanded the study worldwide.
“The majority of whale sharks seen at Ningaloo were juveniles with mean lengths of around six meters (20 feet),” Sequeira said in a statement. “Given the fact that the fish reach maturity when they are about nine meters long (29 feet), it prompts the question: Where are the adults?”
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The answer remains a mystery, because researchers still don’t have a firm grasp on the species’ global populations or why they sometimes gather in groups close to shore. There are also knowledge gaps in understanding how often whale sharks breed and how many offspring they produce.
Study coauthor Mark Meekan of the Australian Institute of Marine Science suggests tagging and satellite tracking some of the larger whale sharks left around Ningaloo to learn more about their population and where they roam.
Whale sharks are listed as threatened by the International Union for Conservation of Nature and protected by governments in Australia, Mexico, and China. But they are still illegally hunted for their fins and oil in other parts of the world. Their slow growth rates—whale sharks can live for up to 80 years—make the species particularly vulnerable to overexploitation.
“Understanding the whereabouts of the biggest whale sharks will also help us understand how human activity, such as industrial developments, fisheries, and boat strikes, might impact the animals,” Meekan said.
