Friday, September 26, 2014

Black Tip Reef Shark Breeding

We have been observing some very odd behaviour from our adult Black Tip Reef Sharks (Carcharhinus melanopterus) recently in the shallow water between the Spa and Jetty 2. Groups of up to 32 individuals have been observed within a small area being very active; chasing each other, almost beaching themselves, and making a huge commotion in the shallows! These groups are actually breeding aggregations, and we have been lucky enough to get some video footage of this very under studied event, which we have posted below! Credit goes to Sophon, our Spa Manager.




This species has black tips to all fins, most obviously the dorsal and caudal fin
It's not uncommon to spot large Black Tips from the jetty!
A small shark attaining lengths of around 1.8m with characteristic black tips to each fin which give them their name, these Black Tip Reef Sharks are usually seen on the reef flat and near the drop off in shallow water where they feed on small boney fishes, squid, and crustaceans. Despite a conservation status allocated by the IUCN as “Near Threatened”, it is not uncommon to spot Black Tips here at Gili, whether you’re snorkeling or just strolling along the jetties. With 37 different species of shark recorded in Maldives, and no recorded shark attacks since records began, we are lucky enough to be in one of the safest places in the world for snorkeling and diving with these beautiful creatures!

The life history of the Black Tip is a little bit of a mystery, with lots of conflicting data, which mostly reflects geographical ranges. Here at Gili, we observe mating behaviour around twice per year. This year, however, I was lucky enough to witness one such event from start to finish first hand! The sharks began to aggregate in water only 1m deep at about 10am, moving very slowly between each other at first, and building in numbers over a period of about 45 minutes. After approximately 1 hour, I could clearly see males following females very closely, attracted by chemicals she releases. All the sharks began to swarm quickly into a smaller area, where I could count ~32 within about 20 square meters!! After this courting behaviour, the male sharks bite the females’ pectoral fins and push her head against the shallow sand and mating begins. It lasts a few minutes, and once complete, all the sharks disperse and continue with their usual daily behaviour: Patrolling the reef.
Black Tip pups congregate in the shallow lagoon at 
Gili Lankanfushi

Studies suggest Black Tip gestation period is somewhere between 9 and 16 months, at which point our females will give birth to 2-5 live pups.  Black Tip Reef Sharks have high site fidelity, meaning these individuals will remain on Gili’s reef for many years. We will have to check back from next June and see if we can find any small pups hiding in the shallows! In the mean time- watch out for big pregnant females!!

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