Expanded marine protected areas (MPAs), created and maintained to be aquatic no-fishing zones, have been found to be effective in protecting grey reef sharks, a near-threatened species.
For their study, published in the latest issue of Biological Conservation, researchers at Stanford University's Hopkins Marine Station investigated both sharks and fishing vessels in the U.S. Palmyra Atoll National Wildlife Refuge, a large MPA about 1,000 miles, or 1,600 kilometers, south of Hawaii.
Marine protected areas have been around for decades but they've mostly been near the coasts and rather small, with 1 square mile, or 2.6 square kilometers, being a typical size. Recently, much larger MPAs have been established in waters far from large human populations, the largest being the Ross Sea Protected Area in Antarctica, designated by 24 countries, including the United States, and the European Union.
Originating 423 million years ago, sharks are a group of predators that span 490 species and play crucial roles within their ecosystems. They mature slowly, they don't have high numbers of offspring, and they're under serious threat due to the value of their fins.
The researchers used both conventional numbered tags and satellite-enabled tags to monitor the movement of the sharks. The first method is cheap and can cover large numbers of sharks, but relies on the return of tags, 262 of them, to the researchers by fishers who catch the sharks, which is a rare occurrence. The second method allows the researchers to track the sharks' movement by satellite, but each tag is very expensive. They attached satellite tags to 11 sharks.
Devices called automatic identification system (AIS) transceivers helped the researchers identify the movement of distant fishing vessels. Boats are equipped with these devices in order to let each other know their identities and locations in order to avoid collisions. They can also transmit additional information, such as the size and type of boat. By collecting this publicly available data and applying an algorithm previously developed by Global Fishing Watch, a partnership between Oceana, SkyTruth and Google, the researchers figured out where and when each vessel was likely to be fishing.
The combination of these tools meant that the researchers could track shark and fishing activity throughout the large, remote reserve.
What they found suggests that the expanded MPAs are working. There were more sharks in the MPA than outside and the majority stayed within its limits. Fishing vessels almost exclusively sat outside the boundaries but they were there in unexpected abundance, nearly 200 ships from 12 countries over the course of two years.
Another discovery was that one of the grey reef sharks, so-named because they are considered reef dwellers, swam more than 575 miles, or 925 kilometers, from the atoll where it was tagged and spent 97 percent of its time in open water. Additional tags recovered at various islands further suggested that grey reef sharks may swim longer distances than previously thought.
"These techniques showed for the first time that large MPAs are effective tools for protecting declining shark populations and other mobile marine predators that are not adequately protected by smaller, coastal MPAs," Fiorenza Micheli, professor of marine science at Hopkins Marine Station and co-author of the paper, was quoted as saying in a news release from Stanford University.
As the researchers believe preserving sharks has benefits for both ocean-dwellers and people, they plan to continue to study this area of the Pacific.
