What’s killing the world’s biggest fish?

“The largest fish on Earth is a shark. Capable of reaching a length of up to 60 feet — roughly the height of a four-story building — whale sharks, named for their size, are so large that they make great whites look like minnows.
But even giants can disappear. Over the last several decades, more than half of all whale sharks have vanished from the ocean. Some populations have fallen by more than 60 percent.”

“A study in the journal Proceedings of the National Academy of Sciences reveals that cargo ships are likely a leading cause of whale shark deaths. Often, where you find high densities of these endangered fish, you also find shipping traffic, the authors found, and ships are already known to strike and kill these animals.”

“Whale sharks are not the only roadkill. Vast cargo vessels harm many species of marine giants, such as the endangered North Atlantic right whales, and some smaller creatures, like sea turtles. Ships also emit loud noises that disrupt marine life and spew planet-warming carbon dioxide into the atmosphere.
“Shipping is a serious problem for giants of the sea,” said Robert Harcourt, a marine ecologist at Macquarie University in Australia who was not affiliated with the study. “We have an economy that’s derived from moving things around the world in a way that’s not taking into account the cost to the environment.””

“A good step toward decreasing collisions is figuring out where animals are most at risk, and that’s where this new whale shark study comes in. Large ships are required to report their locations, and the authors compared those points to the movement of hundreds of whale sharks, which they had previously tagged with satellite trackers. (This is no easy feat: “You’ve gotta have some nice long fins, a good pair of lungs, and sprint after it underwater,” said David Sims, a marine ecologist at the University of Southampton and a study co-author.)
The results revealed just how vulnerable these fish are: More than 90 percent of the ocean’s surface area that whale sharks use overlaps with the routes of tankers, passenger ships, and fishing vessels. Whale sharks tend to congregate near the coast, where shipping is especially busy”

“many of the sharks’ tracking devices stopped working when the animals entered busy shipping lanes, perhaps because they were killed by ships. (Some trackers even showed sharks swimming into dense shipping routes and then sinking slowly to the seafloor — “the smoking gun for a lethal ship strike,” as Womersley and Sims wrote in The Conversation.)”

“Making oceans safer for marine giants is conceptually simple, and one option is to route ships away from animal hot spots.”

“Even just slowing ships down can make a huge difference. The chance that a cargo ship will kill a whale falls to below 50 percent when it’s moving at around half speed (10 knots, or 11.5 miles per hour), compared to nearly 100 percent when it’s moving more quickly, according to one 2006 study.”

“there’s a big drawback to ships slowing down or going on a different route: It takes longer to deliver goods. That’s one reason studies like this don’t always translate into shipping restrictions. That drawback also makes alternative approaches, such as designing quieter ships or adding wildlife deterrents or propeller guards, appealing (although the benefits of these technologies aren’t well established).”
https://www.vox.com/down-to-earth/23064401/cargo-ships-killing-whale-sharks-ocean-animals

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