ナショナルジオグラフィックさんのインスタグラム写真 - (ナショナルジオグラフィックInstagram)「It wasn’t long ago that swimmers splashed and surfers paddled along the beaches of Cape Cod with little thought that a great white shark might be on the hunt just feet away. But today, that reality is settling in among the popular seashore towns as white sharks return to an area they disappeared from decades ago for one simple reason: Their favorite prey, the gray seal, is back on the menu. Hunted nearly to extinction, the seal population began rebounding with the passage of the U.S. Marine Mammal Protection Act in 1972. So, just how many white sharks are out there? That number has been hard to come by, as counting the elusive and wide-ranging predators is complicated. But researchers with the Atlantic White Shark Conservancy finally have an answer, based on an innovative combination of acoustic tracking, photographic identification, and statistical modeling. The bombshell: Some 800 sharks—and possibly up to 900—swam the waters of Cape Cod between 2015 and 2018. The findings are striking not only because of the number of sharks, but the fact that they’re concentrated along just 560 miles of protected coastline. Read more about white sharks in Cape Cod and what scientists are doing to reduce the likelihood of shark-human encounters at the link in bio. Photograph by Brian J. Skerry (@brianskerry), Nat Geo Image Collection」7月7日 8時00分