By Mary Kate McCoy
November 20, 2024
Climate change charts a dangerous course for the world's largest fish
7 min
Warmer oceans are putting two giants of the sea on a collision course. Even at the size of a school bus, whale sharks — the world’s largest fish — are no match for cargo ships in busy shipping lanes: When the two collide, the sharks always lose.
The study, published in Nature Climate Change, found that in every future climate scenario, the risk of fatal collisions rises: If greenhouse gas emissions surge unabated, that risk could increase by up to 43 percent by 2100.
The study’s results offer other insights into whale sharks, whose populations have struggled in recent decades. Erdmann said the findings are helping scientists piece together what’s behind their decline — and what the future may hold for this endangered species.
Where did all the whale sharks go?
Today, whale sharks are protected in nearly every country within their range. Yet despite decades of protection, their populations continue to decline.
“Scientists were scratching their heads wondering what the heck was going on,” Erdmann said. “That’s when we began to suspect that something more insidious was going on that we weren’t seeing.”
“Satellite tags would be happily pinging on whale sharks — then they would swim into a shipping lane and suddenly they’re gone,” Erdmann said. “Those ships move at high speeds and can be the size of a football field. It’s likely they’re mowing over whale sharks without even knowing it.”
Though collisions happen with other species, such as whales and dolphins, whale sharks are uniquely vulnerable, he said: They’re slow and they like to linger near the surface to feed on plankton.
Slow moving and surface feeders, whale sharks are uniquely vulnerable to collisions with large ships.
A clear solution
Thankfully, Erdmann said, there is a clear solution to the problem — and it’s already helping protect endangered whale species: Slow down.
“If we can get industrial ships to slow down in areas with a high risk for collisions, we can make a big difference,” he said. “And we already have a template. It’s been done to protect whales for many years.”
The 2022 study found that restricting speeds to less than 10 knots (19 kilometers per hour) reduced the likelihood of whale shark fatalities by more than 50 percent. Researchers hope the findings from both studies will help enact similar policies to protect whale sharks, Erdmann said.
Countries have the power to enforce speed limits in designated areas of their waters, Erdmann said. And in some cases, adjusting the location of the shipping lane by 10-15 kilometers (6-9 miles) could significantly reduce collisions.
“This study is further proof that climate change can make human-caused problems even worse for wildlife,” he said. “We have the data and the tools to change the outcome. Now, we must act."
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