18 years on, how are sharks faring in French Polynesia’s shark sanctuary?

TAHITI — From their perch on the side of a small boat, three divers tip backward into the sea. Once underwater, shoals of fish, including small red-and-grayish humpback red snapper (Lutjanus gibbus), seem to fly above the divers’ heads, while a titan triggerfish (Balistoides viridescens), yellow and blue with a big mouth, forges its own path in the opposite direction. Inside craggy corals caves, fishes small and large play hide and seek.

Suddenly, large tails and caudal fins appear. They’re right there, nestled in a dark cave on the sandy ground. The diving instructor places his right hand above his head, fingers together like a fin: Shark. Three of them.

Diving in French Polynesia means encountering sharks. In 2006, the government of this French overseas territory designated its entire exclusive economic zone as a sanctuary for sharks and rays: 5.5 million square kilometers (2.1 million square miles), an area half the size of Canada, where it’s illegal to kill sharks and rays. French Polynesia is one of the last oases for sharks worldwide, and it has become one of the best places to observe them.

After nearly two decades as a shark haven, however, a lack of data has made it hard to confirm whether the sanctuary has had its intended effect. Although sharks still face challenges in French Polynesia, mainly from illegal and accidental capture, scientists recently published the first evidence that sharks may indeed be flourishing there.

Vulnerable sharks

On this early April afternoon, the divers pause, bewitched by the trio of sharks in the coral cave. They’re tawny nurse sharks (Nebrius ferrugineus), napping to prepare for hunting after dark. After a few minutes, the youngest one moves quickly. Bubbles from the diving gear might have spooked it, or perhaps a noise. Sharks are sensitive and fearful around humans.

At this time of year, tawny nurse sharks are common in this diving spot off the island of Tahiti’s eastern shore, called the Diadème because of its location right in front of the crown-shaped mountain by the same name, according to Thibaut Molina, co-manager of Scubatek, a local diving school. “From March until June, we know we see a lot of them,” Molina tells Mongabay. “We assume they come here, from deep down, to reproduce in warmer waters. But we can’t be sure.” Scubatek is helping scientists investigate this hypothesis through a citizen-science research program that started this year.

Tawny nurse sharks are classified as vulnerable in the latest IUCN assessment from 2020, which indicates a decreasing global population. “Nurse sharks are extremely forgotten by conservation measures although they are pretty charismatic, big and not dangerous to humans,” Clémentine Séguigne, founder of the Institute for Research on Mesophotic and Deep Ecosystems, a private research institute based in Tahiti, and the scientist working with Scubatek on the nurse shark research, tells Mongabay. “They’re sort of the diver’s best friend, but the species is still very vulnerable.”

Tawny nurse sharks are one of the 20 species of sharks living in Polynesian waters and benefiting from protections here.

A sanctuary for sharks

In April 2006, a new law declared French Polynesian waters a sanctuary for all shark and ray species except the shortfin mako shark (Isurus oxyrinchus). This made French Polynesia the first state to ban shark fishing across its entire marine territory. Since then, other jurisdictions in the Pacific Ocean, such as Hawai‘i, have followed suite.

In traditional Polynesian knowledge, sharks are sacred animals that represent gods and the link between the present and the past. “I think sharks are even better known than dolphins in our culture,” Matahi Tutavae, environment and cultural consultant for various organizations, tells Mongabay. “Some myths talk about sharks as being guardians and navigators. Our ancestors observed sharks in order to find different islands.”

Six years after the sanctuary’s inception, the shortfin mako was finally included for protection, making the shark and ray sanctuary complete. The designation of the sanctuary aimed to maintain the good health of Polynesian shark populations by eliminating the major threat of overfishing, especially since the animals are facing a rapid decline worldwide, with 37% of species threatened with extinction, according to the IUCN. The sanctuary legislation prohibits all lethal capture of sharks and the trade of any shark parts.

“In the same way as for measures to protect whales and turtles, French Polynesia aims to set an example in terms of preserving biodiversity essential for maintaining the proper balance of its rich coral ecosystem, which is vulnerable to the challenges posed by climate change,” Séguigne says, speakinge, which manages the sanctuary. The directorate didn’t respond directly to Mongabay’s requests for comment, instead authorizing Séguigne’s response.

Although the shark sanctuary has been in place for nearly 20 years, it’s been unclear whether it’s effectively protecting French Polynesian shark populations. A key metric would be whether populations have changed since the sanctuary’s inception. However, due to the difficulties of surveying such a large area, there was no baseline shark population data for the territory before the sanctuary was established, and no comprehensive scientific surveys have been done since, leaving questions about the sanctuary’s efficacy unanswered.

Séguigne’s doctoral thesis, published in the journal PLOS ONE in 2023, was the first study to offer a partial answer. With colleagues from the Island Research Center and Environmental Observatory (CRIOBE), where she worked at the time, and the Polynesian Shark Observatory, both based on the island of Moorea, she looked at data the latter institution had gathered by enlisting divers and dive centers throughout French Polynesia to collect data on the sharks they encountered. In all, she analyzed data from more than 13,900 dives at 43% of French Polynesia’s 118 islands between July 2011 and April 2018. The data included the number and species of sharks observed per dive, the locations and environmental parameters, such as temperature and current direction, and whether sharks were being offered food to attract them to the site — a common practice in French Polynesia to promote shark tourism.

The results indicate a tentative increase in shark abundance in some places. “We could see that there was an extremely high diversity of species. There were also some places where there was an abundance of species considered globally endangered, which is important: Rangiroa or Tikehau where we found hammerhead sharks, which are critically endangered,” Séguigne says.

But she also warns about the shortcomings of the data. The observations didn’t necessarily adhere to scientific methodology because they were collected by citizens and only in diving spots. “It’s an indicator but not enough to prove the effectiveness of the sanctuary,” Séguigne says.

Sharks still threatened

Bycatch, when sharks are accidentally caught on fishing gear, remains a big source of mortality in French Polynesia. A recent study found that 20,000 sharks are victims of bycatch on longline tuna fishing gear annually within the territory. And there’s another threat: people who flout the sanctuary’s rules.

Some boats, mostly foreign-flagged vessels, still fish sharks illegally in Polynesian waters. “We have filed numerous complaints about this,” Winiki Sage, president of FAPE, a network of French Polynesian environmental organizations, tells Mongabay. “Fortunately, sometimes some illegal fishermen are arrested, which is good.”

According to Séguigne, with the Westernization of Polynesian society, fear of sharks has increased. In a recent study she led, half of the 300 French Polynesia residents her team interviewed said they believed sharks are potentially dangerous. And even though the sanctuary’s establishment didn’t raise any opposition, its existence and rules aren’t well known. “We observed a certain ignorance about the protection measures that have been established, especially in the faraway islands,” Séguigne says.

Various associations offer awareness sessions about sharks and the importance of protecting them. A new project slated to start in 2025 aims to make sea users more aware of the sanctuary and better understand why shark protection is important for their activities. CRIOBE has been working to convince fishers that sharks are worth more alive than dead by calculating how much tourism income they bring: one lemon shark (Negaprion brevirostris) can bring in around $300,000 annually, according to CRIOBE’s math.

Even though sharks are considered sacred, conflicts often arise between local fishers and sharks over fish. Fish parks are a traditional method of trapping fish in corrals made of stones or wood and nets. Sharks occasionally become stuck in the traps and eat the other fish inside, according to Séguigne. This upsets the fishers and poses a danger for them to enter the fish parks to release the sharks, she says, adding that she’s heard around 100 sharks are killed annually in fish traps.

In Rangiroa, a major atoll in the Tuamotu archipelago, local fisher Siméon Wong Sang confirms that the shark population brings conflicts, and that not everyone’s happy with the sanctuary rules.

“The sanctuary is very good, but at the same time, there was no consultation with the local population before it was put in place,” he tells Mongabay. “And now, for example, in one of the most important fishing spots in Rangiroa, there are many sharks and it’s becoming more and more difficult to coexist with them. The sharks are there all the time and eat our fish. So the fishers get tired, and sometimes kill sharks … I think there should be discussions to review the sanctuary’s rules.”

In Tuamotu, Séguigne and other scientists, in partnership with local fishers, are planning to test a new method to prevent sharks from entering fish parks. It’s another attempt to optimize the sanctuary and help sharks and people live in harmony.

Banner image: A shark in French Polynesia. While sharks are feared and threatened in many parts of the world, French Polynesia decided to protect them. Image by Hannes Klostermann / Ocean Image Bank.

Maps of sharks’ journeys show marine protected areas alone won’t save them

Citations:

Aminian Biquet, J., Tixier, P., Richard, G., Soehnlen, M., Thellier, T., Carzon, P., … Guinet, C. (2024). Toothed whale and shark depredation and bycatch in the longline fishery of French Polynesia. Fisheries Research, 271, 106928. doi:10.1016/j.fishres.2023.106928

Séguigne, C., Bond, M. E., Goyaud, A., Heithaus, M. R., Siu, G., Torrente, F., & Clua, É. (2024). Stakeholder perception of the danger posed by sharks in the world’s largest shark sanctuary. Marine Policy, 164, 106127. doi:10.1016/j.marpol.2024.106127

Clua, É., Buray, N., Legendre, P., Mourier, J., & Planes, S. (2011). Business partner or simple catch? The economic value of the sicklefin lemon shark in French Polynesia. Marine and Freshwater Research, 62(6), 764-770. doi:10.1071/mf10163

Séguigne, C., Mourier, J., Clua, É., Buray, N., & Planes, S. (2023). Citizen science provides valuable data to evaluate elasmobranch diversity and trends throughout the French Polynesia’s shark sanctuary. PLOS ONE, 18(3), e0282837. doi:10.1371/journal.pone.0282837

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