GREAT BAY--A new scientific study examining sharks and rays across the Dutch Caribbean has found that Caribbean reef sharks become less common in coastal areas affected by heavier development and intensive diving activity, findings with direct relevance for St. Maarten as the country continues to balance tourism, coastal development and protection of its marine environment.
The research, published in the Journal of Applied Ecology, examined reef shark and ray distribution across Aruba, Bonaire, Curaçao, Saba, St. Eustatius, St. Martin and the Saba Bank. Researchers carried out 995 baited remote underwater video deployments across the region and recorded 455 sharks and rays. The Caribbean reef shark was the most frequently recorded shark species.
St. Martin was one of the most extensively sampled locations, with 189 underwater video deployments conducted in 2015. Importantly, the study treated the Dutch and French sides of the island together as one research location, meaning the St. Martin results should not be interpreted as measurements of the Dutch side alone.
The St. Martin surveys recorded Caribbean reef sharks, nurse sharks and tiger sharks. The mean relative abundance for all sharks was 0.27 per deployment, compared with 0.47 for St. Eustatius and the remote Saba Bank, 0.29 for Saba, 0.19 for Aruba, 0.18 for Bonaire and 0.04 for Curaçao. The researchers stress that the MaxN measurement used in the study is a conservative measure of relative abundance and is not a direct estimate of the total shark population.
St. Martin also stood out for its rays. The study found a mean ray relative abundance of 0.30 per deployment, the highest among the locations surveyed. Southern stingrays accounted for most of the ray observations around the island, while spotted eagle rays were also recorded. Researchers found that southern stingrays and rays overall had higher relative abundance on St. Martin than at the other study locations.The wider finding, however, concerns the relationship between human activity and sharks. Across populated coastal reefs, shark abundance declined as coastal building density and diving activity increased. Caribbean reef sharks in particular were less common in areas with greater coastal development, heavier diving activity and locations closer to shore. They were most frequently detected farther offshore and along windward coasts.
The findings do not suggest that simply having established dive sites causes shark numbers to fall. Researchers actually found more sharks near areas with a greater number of designated dive sites, which they believe may be because dive operators tend to select high-quality, structurally complex reefs that naturally support more marine life. The important distinction was between the presence of a dive site and the intensity with which it is used. Heavy diving activity showed the negative relationship with shark abundance.
For St. Maarten, coastal development is another point of interest. The study measured the percentage of the nearest kilometre of coastline covered by buildings within 100 metres inland. Across the combined St. Martin study area, building density ranged from zero to 31 percent, the highest maximum recorded among the populated islands included in the research. The average was 4.6 percent.
Researchers said coastal development can affect sharks through several pathways. Development can contribute to sedimentation and pollution, degrade reef habitat and affect the availability of prey. Human presence can also alter shark behaviour and lead animals to avoid otherwise suitable areas. The study found that Caribbean reef sharks were less common around heavily disturbed coastal sites even where appropriate habitat remained available.
The contrast with the Saba Bank was particularly significant. With minimal tourism-related disturbance, shark distribution there was primarily influenced by natural conditions such as reef complexity and water depth rather than human activity. This gave researchers a relatively undisturbed reference point against which the populated islands could be compared.
The study recommends that governments and marine managers consider tourism intensity and coastal development as part of marine spatial planning rather than relying solely on protected-area boundaries. Possible measures identified by the researchers include limiting diver numbers at sensitive locations, rotating heavily used dive sites, temporary closures during important periods such as mating or pupping seasons, and buffer zones around sensitive reefs.
Researchers also called for sustained long-term monitoring developed with local stakeholders, noting that the findings demonstrate the importance of managing both the location and intensity of human activity around reef habitats. The Nature Foundation St. Maarten was among the organisations acknowledged for assisting with planning and fieldwork.
The study is based on surveys conducted between 2012 and 2017, with the St. Martin fieldwork carried out in 2015. Its findings therefore provide scientific evidence on the relationship between human disturbance and shark distribution rather than a current count of sharks around St. Maarten. For an island where tourism, diving, coastal construction and the marine environment are closely connected, the research adds another consideration to how future coastal and marine development is managed.
