Investigating the Population of Blacktip Reef Sharks in Mohéli, Comoros.
In early April this year, Clare Thouless, my fellow researcher at CORDIO, joined me in Comoros to investigate the waters of Mohéli, scoping out blacktip reef sharks. This was undertaken as part of the Strengthening Ocean Protection in Comoros program (from the French RPOC, Renforcement de la Protection des Océans aux Comores), where CORDIO East Africa is contributing to the increase of knowledge on marine biodiversity across the Comoros marine National Parks.
Having worked on elasmobranchs for some years, my curiosity about the presence of sharks and rays was immediately piqued when I arrived in Comoros over a year ago now, as there is barely any existing data on these species in the country. Fishermen from Mohéli had quite a lot of interesting information. On top of catches of tiger, hammerhead, and silky sharks, the mention of small ones with a black patch on the dorsal fin also caught my attention. They would find them in small groups in shallow sandy or rocky areas and by mangroves within Mohéli National Park. These habitats are known to be used as nurseries and feeding grounds by juveniles blacktip reef sharks (Carcharhinus melanopterus). Therefore, in light of the regular catches of juvenile blacktip reef sharks, already listed as Vulnerable on the IUCN Red List, investigating their habitat use and identifying potential nursery areas, as well as their movement along the coast is critical to developing effective conservation and management measures with the parks’ managers.
Accompanied by several park staff from the Mohéli National Park, Clare and I went on a quest to mark blacktip reef sharks using conventional “spaghetti” tags (Hallprint), small tags placed externally at the base of the dorsal fin of the animal. Each tag has a unique ID number, allowing us to keep track of the animals’ movements in space and time pending their recapture. By day, we were snorkelling and flying a drone in search of the sharks in their preferred habitats; by night, we were trailing fishermen to check their catch. If a shark was caught, we would untangle it, quickly take some morphometric measurements, tag it, and then set it free. In the span of a week, our team was able to tag 12 sharks. Also looking at the healing status of the umbilical scar of each shark, we were able to confirm that some of them were recently born and others young-of-year. The course is now set for the design of an extensive study across the whole park.
My highlight of the week? That mystical night ride out to sea. The ocean’s bioluminescence made sparked as our boat cut through the water, the night sky glittered with a blanket of stars and, in the distance, lightning ripped through a plume of clouds before a giant orange moon rose over the horizon. “Yep, I sure know why I am doing this job!”, I reflected excitedly.
Check back for when we resume the study.
As the 2023 bleaching season comes to an end, the Western Indian Ocean (WIO) region can breathe a sigh of relief. Over the past three
Exploring the frontiers of marine research My thesis studied the connections between shallow reefs (0-30 m) and deeper reef habitats (30-150 m) in the Indian