Assessing the effectiveness of Curieuse Marine National Park in the protection of sicklefin lemon sharks

The global population of the sicklefin lemon shark (Negaprion acutidens) is classified as vulnerable by the International Union for the Conservation of Nature due in part to its coastal preference and susceptibility to human-induced stressors. Furthermore, the species has a minimal habitat range and limited movement patterns, threatening its survival, mainly because fishers can harvest them throughout their habitat. Understanding the movement patterns and habitat preferences of these small sharks during different life stages is crucial for their protection.

The Curieuse Marine National Park (CMNP), established in 1979, spans an area of 2.9 square kilometers and is located north of Praslin Island. It is a key tourism site within the inner islands. A shallow fringing reef, seagrass beds, and a healthy strand of mangrove forests surround the island, making it an ideal habitat for sea turtle feeding and nesting and a nursery for N. acutidens.

The Global Vision International (GVI)–Seychelles studied the spatial ecology of N. acutidens by installing an acoustic receiver on both the north and east coasts of Curieuse Island and tagging 20 newborn sharks. Then, their movements were monitored over six months. The project’s overall outcome aims to collect data on the movements of neonate N. acutidens within the marine park and help assess whether the park’s area covers sufficient range to protect the species.

Other project objectives include refining population estimates of N. acutidens within CMNP and developing local capacity by training at least ten Seychellois stakeholders and marine protected area practitioners in shark research techniques. The project also did its part to contribute to national biodiversity protection efforts by identifying critical habitats in and around the CMNP used by neonate sharks and informing conservation of N. acutidens.

In the span of 18 months, the project successfully tagged 19 sharks and logged a total of 292,107 shark detections, mostly happening within the Turtle Pond area. The findings confirm the hypothesis that these sharks tend to wander only around a relatively small area in shallow waters. As such, the current size of the conservation area was deemed sufficient enough to protect the species fully.

In addition to its original scope, the project further observed a significant emigration rate of N. acutidens, with supply estimates ranging from 200 to 250 individuals per year from CMNP to surrounding habitats. Hence, more than just a sanctuary for juvenile N. acutidens, the marine park also potentially protects the species’ survival at a larger scale by being a breeding ground for sicklefin lemon sharks.