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World’s Largest Fish and One Tiny Island: Studying Whale Sharks on St. Helena Island

Dr. Alistair Dove, director of research and conservation at Georgia Aquarium recounts his recent expedition to St. Helena Island studying the world’s largest fish – whale sharks.

A whale shark swims in the waters off St. Helena Island (Photo Credit: Georgia Aquarium)
A whale shark swims in the waters off St. Helena Island (Photo Credit: Georgia Aquarium)

Approximately 2,500 miles east of Rio de Janeiro and just over 1,200 miles west of the African country of Angola, lies St. Helena Island: one of the most remote inhabited islands in the world.  This stark volcanic peak juts up from the vast abyssal plain of the South Atlantic Ocean and covers just 47 square miles of rugged rocky terrain, but is home to a multitude of diverse animal, plant, and marine life. It has even been called the Galapagos of the South Atlantic.

This tiny island is over 6,000 miles away from Atlanta, Georgia, where I and a team of researchers from Georgia Aquarium started our journey to study the world’s biggest fish: the enigmatic whale shark. This species lives throughout the tropical and subtropical waters of the world, but encounters are rare and those places where whale sharks gather reliably have become figurative goldmines of scientific discoveries about this extraordinary filter feeding shark.

Just getting to St Helena is a huge challenge; we first flew to Cape Town, South Africa and then boarded the RMS St. Helena, which is the only form of regular transportation to the island and one of the last Royal Mail Ships in operation. We were aboard the St. Helena for five days as she steadfastly steamed to our destination across a seemingly endless plain of seabirds and flying fish. Talk about remote!  St Helena is so remote, in fact, that the island was chosen by the English as the location for Napoleon Bonaparte’s exile in 1815. He died there in 1821 and you can still visit his grave today.

Despite 500 years of this sort of exceptional maritime history, St. Helena has only recently come to scientific attention, not only as an important habitat for whale sharks, but as part of the United Kingdom Overseas Territories, a group of islands that is home to more than 90% of the UK’s biodiversity assets. With the help of the Darwin Initiative, Georgia Aquarium’s partners in the St. Helena Government, Mote Marine Laboratory, and the Marine Megafauna Foundation, we are so excited and proud to help study our flagship species in this beautiful and breathtaking location.

Georgia Aquarium is the only aquarium in the western hemisphere to display these elusive creatures and having them in this setting is an incredible research opportunity to complement our field research with studies of their growth, behavior, health, and genetics. This helps us improve our interpretation of their behavior seen in the natural setting, but there are still many tantalizing questions about whale sharks that we hope to answer.

We traveled to St. Helena once before, in December of 2014, and we ventured back again in December of 2015. We started these expeditions because we think St. Helena may play a vital role as a mating ground for whale sharks. The whale sharks of St Helena are an even split of adult males and females, which is different from the other places where whale sharks gather in numbers, where juvenile males dominate. This 50/50 mix of adults is incredibly important, because mating behaviors have never been documented in this species. Our main goal of the 2015-2016 expedition was to characterize these gentle giants in St. Helena, how they use the island habitats, and where they go when they leave, and of course to stay ever vigilant for signs of mating behavior. So how do we do all that?

We used a variety of techniques including computer-aided photographic identification, laser calipers to measure their size (and they can get big, over 35ft long), and several different types of tracking tags to help us figure out where they come from and where they go.  We also worked with local “saints” to install an acoustic array, which is a network of underwater hydrophones around the island that listens for tags we put on whale sharks and other species.  Over the weeks we spent in St. Helena we tagged over 30 whale sharks and photographed dozens more – all these are collected to assist in our understanding of where they go, how they grow, how they reproduce, and how St. Helena fits into a global population picture for this species, which the International Union for the Conservation of Nature lists as “Vulnerable”.

Another incredibly satisfying aspect of the expedition to St. Helena was working alongside some of our fantastic research partners. We work with members of the Marine Section of the St. Helena Government, and Mexican NGO Ch’ooj Ajail AC, in addition to Georgia Aquarium team members and other partners from the Marine Megafauna Foundation and Mote Marine Laboratory who couldn’t join us but materially supported our efforts. It was a demanding scientific agenda, but working with this talented crew made for a great trip. If you can measure the success of an expedition in the amount of data you generate, then we were certainly successful.

Up close with a whale shark in St. Helena. (Photo Credit: Georgia Aquarium)
Up close with a whale shark in St. Helena. (Photo Credit: Georgia Aquarium)

We’ve since returned from St. Helena and unpacked our gear and washed the salt out of everything, including our ears. What lies ahead is a daunting task of compiling all the data we’ve collected, including terabytes of video and photo data and thousands of laser measurements, so we can begin looking for the answers to the questions we’ve been asking. We still have not documented mating behaviors, but we continue to learn more about their migratory patterns through the tagging studies and to identify new whale sharks through the Wildbook global database of whale shark sightings. With whale sharks, though, the more answers you try to find, the more questions you end up raising! It’s an incredibly exciting time to be studying this extraordinary species, especially in such a special location, and you can join in the excitement. Some of the animals we tagged automatically tweet out their locations in real time, and you can follow along on Twitter @Wheres_Domino, and at whalesharkwatch.org. We continue to learn and discover things about this magnificent species and I know there will be even more things to uncover.  Anyone who says there isn’t amazing stuff still to discover in nature hasn’t put their head underwater lately, especially in places like St Helena.