Marine protected areas (MPAs) are proven to provide refuge for smaller species that stay close to their reef home. But whether they protect creatures that roam beyond their borders has been up for debate. A recent study from Stanford University shows promise for such species, with an MPA south of Hawaii providing protection for wide-ranging grey reef sharks.

The establishment of MPAs has surged in recent years and they currently cover about three percent of the world's oceans, protecting these areas from fishing and other human activity in the name of conservation of many threatened species, including sharks, turtles, seabirds and marine mammals. The largest and most recent marine park is the Ross Sea Protected Area in the Antarctic designated in October of 2016 and encompassing 1.55 million sq km (600,000 sq mi).

"Some of these protected areas are twice the size of Texas and they've been very recently established, so they hold great conservation potential," said Tim White, a Stanford PhD student in biology at the university's Hopkins Marine Station and lead author of the study. "But we're not sure of the effects that these marine protected areas will have on a range of species."

For the study, the Stanford team tracked near-threatened grey reef sharks at the 54,000-sq km (20,850-sq mi) U.S. Palmyra Atoll National Wildlife Refuge, which is located 1,000 miles (1,600 km) south of Hawaii in the Pacific Ocean. Reef shark populations in particular continue to decline despite the establishment of MPAs.

Researchers Kosta Stamoulis of Palmyra Atoll Research Consortium and University of Hawaii and Tim White of Stanford's Hopkins Marine Station measuring a grey reef shark(Credit: Palmyra Atoll Research Consortium)

"Many reef shark populations have recently declined throughout the world, driven in large part by demand for shark fin soup," White told New Atlas. "In some cases, reef shark population declines have even occurred within large MPAs, which has fueled uncertainty about whether or not large MPAs can effectively protect these important species."

White explains that reef sharks are important predators that help support healthy coral reef ecosystems, as well as generating hundreds of millions of ecotourism dollars, "so it is crucial that we figure out if current conservation strategies are effective," he says. Reef sharks are also susceptible to fishing pressure since they reach sexual maturity at a relatively late age and don't have many offspring.

The team tagged 262 reef sharks with conventional number tags that relied on fishing boats to report when they'd caught one, while very expensive satellite tags were used on 11 sharks to track their movements via satellite. The researchers found the majority of sharks stayed within the boundary of the refuge, though one shark swam more than 575 mi (925 km) from the atoll, while other tags were retrieved at various islands, suggesting reef sharks swim longer distances than previously thought.

White says the reason most of the sharks stayed within the protected region was because the MPA boundaries are currently quite large. Before the boundaries of Palmyra Atoll National Wildlife Refuge were expanded from 12 nautical miles to 50 nautical miles, nearly all sharks moved outside the smaller boundary, suggesting that large MPAs can be very beneficial to these sharks and other wide-roaming species.

To further bolster their conclusions, the researchers were able to compare the protected Palmyra MPA against an unprotected reef a few hundred kilometers away. "They've found that protected reefs support substantially more sharks than the nearby, unprotected reef," says White.

Another goal of the researchers was to track fishing activity in the region, which they did by collecting publicly available data via automatic identification system (AIS) transceivers equipped on all boats (for safety and identification).

"Fish don't know where we have drawn management lines on the vast, blue regions of the globe," says White. "But as it turns out, many fishermen do. The fact that virtually all fishing vessels that we observed remained outside the MPA is good news for marine conservation, as it suggests that MPAs can effectively reduce fishing pressure throughout immense regions of the ocean."

The findings were published in the journal Biological Conservation.

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