In 2015 the Dutch Caribbean Nature Alliance started the Save Our Sharks project, focusing on the protection of sharks in the waters around Aruba, Bonaire, Curacao, Saba, St. Eustatius and St. Maarten. Shark populations in the Caribbean have shown decline, and we need to conserve these top predators to maintain the health of the reef and fish stocks around the islands. An integral part of the Save Our Sharks project is to introduce people to the sharks living in their waters, starting with one of the species you are most likely to observe in the vicinity of the reef.
When you go diving around the island, you might spot a docile looking shark with a light brownish colour lying still on the seafloor, hidden away between crevices or in a cave. This species is called the Nurse Shark. Despite a broad range of theories, the origin of its name remains unclear, but it does seem to fit the species’ gentle nature. The nurse shark is a harmless species, with whom no fatal encounters have ever been recorded. As a relatively large shark species that can grow to over three metres in length, it occupies a relatively high position in the food-web and its presence helps regulate the health of coral reefs and mangrove systems. But its size and slow reproductive rate make it particularly vulnerable to human threats. Therefore, it is important to find ways to avoid catches and assure an increased survival of nurse shark populations around the island in order to safeguard their presence for the future.
The nurse shark is one of the most common species around St. Maarten, Saba and Statia. It usually hides during the day, but at night will forage for small fish, molluscs and crustaceans between the seagrass beds, mangroves and coral reefs. To help speed this process along, the nurse shark uses two worm-like appendages on its snout called barbels with which it detects small movements under the sediment. Between the ages of 15 and 20, female nurse sharks start to reproduce once every two years. Following a six-month gestation period, they give birth to approximately 35 babies, who can fend for themselves from the minute they leave their mother’s womb.
Even though the nurse shark is relatively well studied, and we have some knowledge about its biological traits, reproductive system, and food habits, there are still large gaps in the knowledge about the species’ distribution, habitat use and population structures. From research, we do know that nurse sharks tend to stay within small geographical ranges, rendering them vulnerable to local extirpation from overexploitation. Therefore, the International Union for the Conservation of Nature (IUCN) has categorized the subpopulation of nurse sharks living in the Western Atlantic as near-threatened.
In the wider Caribbean region, the species is actively targeted in different fisheries for its meat and fins, but in Dutch Caribbean waters, fishermen typically only consider them a nuisance. Because the sharks swim around in shallow water, they are highly susceptible to fishing gear targeting other fishes, in which they get stuck. The action to free a nurse shark costs fishermen not only a lot of effort, but oftentimes their gear as well.
On a global scale, sharks (and closely related rays) are decreasing due to overfishing, the loss of suitable habitat to safely produce their offspring, and probably a decreasing supply of fish for them to feed on. In a recent study, researchers estimated that as much as one in four species is currently threatened with extinction. And moreover, almost half of all species are categorized as data deficient, which means all the available data are insufficient to assess their conservation status.
offered by Tadzio Boervets
