New study reveals Alaska’s largest, most mysterious shark

The Pacific sleeper shark is the largest shark in Alaska and may be the largest predatory fish in the ocean. It is also one of the most vulnerable of all managed fish populations in Alaskan waters.

Yet its most basic biology is still poorly understood, said Beth Matta, a fisheries biologist at NOAA’s Alaska Fisheries Science Center.

A new collaborative study from NOAA Fisheries takes an important step toward better understanding and managing Pacific sleeper sharks. Researchers gather knowledge from a variety of sources to provide important new insights into its biology and ecology. They identified and prioritized research needs to better assess and manage the species.

Matta, who led the study, said we can’t manage what we don’t understand. We hope to create a one-stop shop for information about Pacific sleeper sharks that is a resource that others can use.

Slow growth and low yields lead to vulnerability

Pacific sleeper sharks, named for their slow movements, live throughout the Pacific Ocean. It has been found in shallow intertidal zones and has been spotted by submersibles at depths of more than a mile underwater. The most common situation encountered by humans is unnecessary bycatch on commercial fishing vessels.

Like many other sharks, Pacific sleeper sharks may be slow-growing, late-maturing, long-lived, and less productive. These characteristics make them highly vulnerable to overfishing.

Sustainable fishing rates for long-lived sharks are very low. For example, the white-spotted dogfish, a close relative of the Pacific sleeper shark that can live up to 100 years, has a catch rate of only 3 % about. Pacific sleeper sharks may take this situation to an extreme.

In Alaskan waters, most Pacific sleeper shark deaths are caused by fishery bycatch. Observed population declines in some parts of its range, coupled with its low productivity, have raised conservation concerns.this The North Pacific Fishery Management Council highlighted conservation concerns in its recent stock assessment review.

Assess and manage challenges

Despite its large size, wide range, interaction with humans and high vulnerability, the Pacific sleeper shark has been poorly studied until recently. This is due to its lack of commercial value, inaccessible habitats and the difficulty of safely landing and handling such large animals on boats.

Despite their size, Pacific sleeper sharks encountered by ships are almost always juvenile. Adult Pacific sleeper sharks are rarely seen. No pregnant females were retained.

This leads scientists to believe that mature sharks may live in deep-sea habitats at depths of 3,000-6,000 meters. Submersible cameras captured the giant shark, estimated to be 23 feet long, at great depths. No fishing or survey vessel has ever measured greater than 14 feet.

A large portion of the population remains undiscovered and unsampled, Tribuzio said.

Developing effective conservation and management strategies is challenging due to a lack of data on Pacific sleeper shark movements, reproduction, and population sizes.

We don’t have much to do in managing this species. Currently, they are managed based on historical catches. That’s not ideal, especially for highly vulnerable species, Tribuzio said. The more information we gather, the better we can develop and apply alternative methods to better assess this and other species for which data are limited.

Gather knowledge

Matas’s first step was to scour the existing literature for anything known that had nothing to do with Pacific sleeper sharks. The search uncovered many little-known resources. Some of them are more than 100 years old, Mata said.

The study borrowed some information from Greenland sharks. The two species are closely related, can interbreed, and are difficult to tell apart. The Greenland shark, however, is much more well-studied because it has a long history of being fished for its liver oil and meat.

Most recent data comes from research by the Alaska Fisheries Science Center.It is mainly accumulated through Cindy [Tribuzio]Mata said it took years of hard work and planning.

The researchers are also working with Fisheries and Oceans Canada, which provides additional data and a Canadian perspective.

Almost all of the research we have completed and are conducting is highly collaborative. “We work a lot with our fishing partners in particular,” Tribuzio said. Many of our studies would not be possible without their support and the measurements and samples they collect.

Improving our understanding of Pacific sleeping sharks

The study highlights trends and new findings that provide valuable information for the management and conservation of Pacific sleeper sharks.

For example, in recent decades, a decrease in Pacific sleeper shark populations has been observed in waters off Alaska and Taiwan, while an increase has been observed in Russian waters.

New genetic evidence suggests that Pacific sleeper sharks are a large group throughout the Pacific, from Alaska to the southern tip of the Southern Hemisphere. Matta said we once thought of three large species in the genus: the Pacific sleeper shark, the southern sleeper shark and the Greenland shark. We now know that southern sleeper sharks are not genetically unique.

Evidence also suggests that the Bering Sea is a potentially important habitat for Pacific sleeper sharks. The investigation found young sharks clustered together, and recent genetic evidence suggests the siblings in the area are related to each other.

Radiocarbon aging of the eye lens of a 10-foot-long Pacific sleeper shark shows that it grows very slowly. However, it’s still twice as fast as the Greenland shark, which can live up to 400 years.

Last summer, a 14-foot-tall dead female was luckily caught in the Aleutian Islands, providing a rare opportunity to study potentially mature female Pacific sleeper sharks. “Our eyes are as big as cantaloupes,” Tribuzio said. We hope to perform a bomb radiocarbon analysis of the lens of the eye to determine the age.

One apparently immature female was found to be at least 35 years old. All these factors taken together indicate that the potential for overfishing is high.

Future steps for better assessment and management

“Based on the information we gathered in this study, we were able to demonstrate the need to prioritize Pacific sleeper shark assessment efforts,” Tribuzio said. Given the species’ vulnerability and the challenges of assessment, we need to think outside the box on how to manage this species.

Ongoing research at the Alaska Fisheries Science Center will continue to fill knowledge gaps on Pacific sleeper sharks, including lifespan estimates, bioenergetics, locomotion and reproduction. Catch estimates have improved over the past decade thanks to teamwork by scientists and fishermen. Machine learning is used to process electronic surveillance video data. A new project is estimating the age of sharks based on their eye lenses. Tribuzio is exploring and pioneering the use of alternative methods to assess species for which data are severely limited to better inform decisions for their conservation.

These animals are truly fascinating biologically and very different from other animals we study. People care and they want to help. Now they are starting to see the results of their efforts, Tribuzio said. It’s very exciting to be able to translate the efforts of everyone involved into actionable information that informs species conservation.

Mata said the more we learn about these sharks, the more concerned we are about keeping them alive into the future. There is still much to learn.

The research was a collaboration between NOAA Fisheries’ Alaska Fisheries Science Center, Fisheries and Oceans Canada, Alaska Pacific University, University of Alaska Fairbanks and the University of Hawaii.