Rare Sleeper Shark: One of Longest Living Animals at Risk Due to Overfishing [Study]

At least one species of shark is at risk due to overfishing. Only little is known about this rare and elusive sleeper shark because they spend most of their time in the deep.

Rare and Elusive Shark Is Heavily Threatened

In a new study from NOAA Fisheries, researchers learned that sleeper sharks are heavily threatened by overfishing. Beth Matta, a research fisheries biologist at the NOAA Fisheries Alaska Fisheries Science Center, also acknowledged that they only know very little about the shark's basic biology and they can't manage what they do not understand.

Their goal is to create a one-stop shop for information on Pacific sleeper sharks that will be a helpful resource for others. Pacific sleepers can grow up to 23 feet, but they are extremely slow-moving. They can survive for several centuries, making them one of the longest-living animals on the planet. However, it also takes decades to reach sexual maturity because they grow very slowly.

For instance, they studied a 14-foot female shark that was captured in the summer of 2023. It was discovered that the shark was still sexually immature despite being at least 35 years old.

"That indicates not only extreme longevity, but also delayed maturity," said study co-author Cindy Tribuzio, a researcher at the NOAA Fisheries Alaska Fisheries Science Center. "All those pieces together suggest a high susceptibility to becoming overfished."

Due to their lengthy lifespans and low birth rates, they are susceptible to population declines due to overfishing. Apart from inadvertent fishing bycatch, which frequently consists of juveniles, they are rarely observed by people.

For long-lived sharks, sustainable fishing rates are extremely low. The spiny dogfish, a relative of the Pacific sleeper shark with a 100-year lifespan, can only withstand harvest rates of roughly 3 percent. Potentially, Pacific sleeper sharks go too far with that.

The Pacific sleeper shark has not received much scientific attention until lately, despite its enormous size, wide range of habitat, and vulnerability. Its low commercial value, difficult-to-reach living quarters, and the difficulties of securely capturing and handling these big sharks aboard ships are the main causes of this dearth of research.

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What Are Pacific Sleeper Sharks?

Pacific sleeper sharks (Somniosus pacificus) are gigantic deep-water sharks that may grow to a length of 4.3 m for females and 4.4 m for males. This species may grow as tall as seven meters.

The blue-black fins of the Pacific sleeper shark give it a dark gray to black color. There are two equal-sized dorsal fins, a cylindrical body, and a short, rounded snout. Compared to the pectoral fins, the first dorsal fin is located closer to the pelvic fins. The caudal fin (tail) is asymmetrical with a well-developed ventral (lower) lobe, and there are small precaudal fins as well.

They can be found in the temperate waters between 70°N-47°S in the North Pacific from Japan to the Bering Sea, Baja California, southern California, and the Siberian coast. There are also recorded sightings in the South Pacific.

The Pacific sleeper shark inhabits waters in Australasia, ranging from the seamounts situated south of Tasmania to the Challenger Plateau in eastern New Zealand, and may reach Macquarie Island. Off the coast of Uruguay, they are visible in the southwest Atlantic.

This species favors living on slopes and continental shelves. The Pacific sleeper shark can be found in littoral (near the beach) and even intertidal environments at higher latitudes, at lower latitudes, and at least 2,000 meters below the surface.

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