2 shark species in Seychelles keep peace by social distancing, study finds
The sicklefin lemon shark and the blacktip reef shark peacefully coexist in the shallow lagoon of the Seychelles’ remote St Joseph Atoll by giving each other space, a new study found.
In a communique last week, the Save Our Seas Foundation said that although both species use the whole atoll overall, small differences in where they are and when actually mean that blacktips and lemons are in the same place only about 25 percent of the time.
The chief executive of the Foundation at the D’Arros research centre, James Lea, said that “what is exciting about this research is that it shows us how these species have adapted to exist together in a really confined space, essentially through social distancing, without outcompeting each other. It is a powerful example of how animals carve out specific niches, enabling them to function together within an ecosystem.”
The research was made possible by the Foundation’s network of 88 acoustic receivers placed around the atoll. The array is significant as it is the only one of its size and kind in the Amirantes.
The Foundation said that even on the sand flats, where the sharks come at high tide to forage for food and find safety from larger predators, their overlap is only about 35 percent.
“Similar behaviour has been seen in animals that share space on land: lions, leopards, cheetahs and African wild dogs are all predators that hunt in the same areas. They have developed various methods of minimising competition with one another, the most significant of which is to use the same habitat at different times of day,” it added.
Lea said that the study highlights the importance of St Joseph Atoll as a critically important habitat for blacktip and lemon sharks, and also raises concerns about climate change.
“Over thousands of years, these animals have found ways to exist together under present environmental conditions. Given the narrow tidal range at St Joseph, we have to ask ourselves what would happen if a small increase in sea level made the sand flats habitat available at all tides. How would this affect the finely tuned ecological balance of the animals that have learned to thrive here?,” he added.
St Joseph is part of the D’Arros group of islands in the outer islands of the Seychelles archipelago in the western Indian Ocean. The group became an officially protected nature reserve under the Nature Parks and Conservancy Act in July 2014. In March 2020, the ecological value of the atoll was recognised by the Seychelles’ government, which declared it as a Marine Protected Area within the nation’s larger Marine Spatial Plan Initiative.
The ecology of the atoll is largely sculpted by the rising and falling of the tides. This is particularly true for adult sharks, which swim onto the sandy flats as they become flooded at high tide in order to hunt and seek shelter. The sharks then return to the deeper waters of the lagoon when the tide retreats.
The work of the D’Arros Research Centre is part of the Save Our Seas Foundation’s bigger mission to safeguard sharks and rays around the world through research and communication.
Abdulmohsen Abdulmalik Al-Sheikh, the founder of the Save Our Seas, said, “Seychelles has been at the core of the foundation from the beginning, and our strong history of supporting marine and education projects here aims to help protect the natural heritage of the islands for generations of Seychellois to come.”
So far, the Foundation has initiated 28 research projects on D’Arros, focusing mainly on threatened species.