HomeTechnologySome sharks return to the same sites to breed for decades

Some sharks return to the same sites to breed for decades

Some shark species return to the same breeding grounds for decades and live longer than previously thought, say scientists who study the animals in Florida.

Scientists at the New England Aquarium found that nurse sharks returned to the waters of the Dry Tortugas, 70 miles (113 kilometers) from Key West, to mate for up to 28 years. They also found that sharks’ lifespans appear to extend to at least 40 years, instead of 24 years as previously believed.

The researchers published their findings in October in the journal PLOS ONE as part of the world’s largest study of shark mating behavior. The research sheds new light on how sharks reproduce and the role their environment plays in their reproduction, said Nick Whitney, the aquarium’s senior scientist and co-author of the study.

“This is the first example that has shown long-term use of a breeding ground,” Whitney said. “For starters, observing the natural behavior of sharks in the wild is incredibly rare, and observing mating behavior is truly unusual.”

Scientists know that nurse sharks have used the waters of the Tortugas as a breeding ground since at least the late 19th century, but questions lingered as to whether the sharks returned to the area. Aquarium researchers tagged 118 sharks between 1993 and 2014 and found that more than two-thirds returned to breeding grounds in subsequent mating seasons.

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The scientists wrote that this evidence of long-term fidelity to a site “reveals the importance of identifying and protecting breeding sites for this and other” species.

Members of the research team said they did not believe the same animals would continue to mate at the site for years. Of all the sharks that returned to the site, almost 60% were monitored for more than 10 years and 13% were monitored for more than 20 years.

David Shiffman, a marine biologist at Arizona State University who was not involved in the study, said the work could open up new insights into sharks and how they migrate and make use of habitat.

That could be a key to helping conserve them, he said.

“Some of the best known shark species are highly migratory and regularly cross oceans. So learning that other species are home and use the exact same habitat year after year is fascinating,” Shiffman said.

Dry Tortugas is a remote group of islands in the Gulf of Mexico that is loved by divers and bird watchers. The area’s status as a breeding ground for nurse sharks could be compromised by a direct hit it suffered during hurricane ian in September, Whitney said.

Scientists have not yet been able to find out if their underwater monitoring stations withstood the storm, they said. They also don’t yet know if the sharks have returned. Female sharks come to the area’s shallow waters to prepare to give birth in September and October, said Ryan Knotek, the aquarium’s associate scientist and co-author of the study.

The vulnerability of the site is a good reason to protect both the sharks and their breeding grounds, Whitney said.

“These sharks clearly have a vested interest in returning to this state,” he said. “This was a shark that was once thought to be a sedentary shark. It turns out that they are much more active.”

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