Cheryl-Samantha Owen

Lying in Wait For Oceanic Sharks But All We Find is Emptiness 

Our fresh fruit supply has dwindled to nothing, the last extremely over-ripe banana was cooked a few days ago, the Seychellois school kids who won a privileged visit to Aldabra have wiped out the chocolate supply from the island tuck shop (a sight I foresaw but was too slow to beat them to it), the bait is smelling extremely rotten, and someone forgot the energy bars… but we are all talking big fish, photography and watching new footage every evening – so we are still full steam ahead keeping our fins wet and on the look out for Aldabra’s large shark species.

Co-incidentally I am here in 2008, the International Year of the Reef, ten years after the record high sea temperatures and coral bleaching event, when the coral polyps lost their symbiotic zooxanthellae, that wiped out 40% of Aldabra’s corals. On our mission to film and photograph the marine life and shark species in particular we have been diving on fringing reefs along the rim and in coral gardens up the Atoll’s indigo channels almost to the azure heart of the lagoon. Coral reefs are the most diverse and productive ecosystem on our planet, far more so than tropical rainforests, and as such are critical indicators of the global marine ecosystem’s health. Despite slopes and valleys of coral rubble, the aftermath of coral bleaching, it is refreshing to see and photograph healthy coral reefs, teaming with a profusion of fish, boasting more than 200 coral species and bursting with new life. It is recovering well from the 1998 mortality.

Reading a recent study of coral reef organisms, that covered everything from microbes to sharks, I can understand why the Aldabra reefs are so healthy and why they are proving so resilient. The answer is simple; they are teaming with reef sharks. Predators accounted for 85% of the total fish weight in the study’s pristine reef site, a complete reversal of life on reefs across the world today where most of the sharks have ended up dead on rows of baited hooks and where the reefs are depleted of life.

Sharks are essential to coral reef health because they are the pinnacles of the food chain, and if they are removed from the ecosystem the whole ocean tilts off balance. Sharks have a very slow reproductive rate and do not recover well from exploitation. Over fishing sharks sets of a domino effect throughout the reef: fewer sharks leads to an increase in their prey, large carnivorous fish such as grouper, who in turn decrease the number of important plant-grazing herbivorous fish, such as parrotfish. Once this happens the reef is in danger of shifting from coral to algae domination and it is less able to withstand other human disturbances such as rises in water temperatures.

At the end of a long dive this morning photographing on the reefs I was greeted by a gigantic yet weary lemon shark. Perhaps one day this regal predator will be given the respect it deserves as guardian of the reefs, until then at least the inshore waters here are a welcome sanctuary.

Aldabra’s formation as a massive seamount rising from the dark depths of the ocean floor means there is a sharp gradient along its edge, allowing deep open water to lick the Atoll’s outer rim. With the deep open ocean comes the large pelagic (oceanic) species of sharks, and we only had to venture out to sea 2km on the other side of the rim to enter waters where we thought we had a good chance of finding such species. Despite gargantuan efforts to attract them, our cameras came back with empty memory cards and blank videos. Out there sharks such as oceanic white tip, tiger, and great hammerheads are beyond the protection of Aldabra’s reefs and vulnerable to fishing in almost every part of the ocean they travel. The big blue is looking very much like an empty ocean.

Visit http://www.saveourseas.com to learn more about SOSF, the marine environment and to read my daily blog of the Aldabra Expedition