Surveying sharks in Cape Verde

Tom Letessier

ZSL's Tom Letessier shares his experience of using underwater baited cameras (mid-water BRUVs) to survey sharks in Cape Verde. 

whale shark
A whale shark came up to our tenders in Cape Verde and stayed around for around 15 minutes

I have just returned from a six-day marine expedition in Cape Verde, and I realise that few things get me as excited as going out to sea. As a child I used to run around rock-pools, and as a youngster I used to scour the Norwegian coasts trying to capture something to call dinner. Later, in my teens, I couldn’t wait to get my SCUBA certificate, which opened a world that I had only been able to explore superficially. But it was only in my early twenties, as a PhD student, that I was able to board a vessel and join a research expedition as part of a team of scientists (to study krill, the stuff whales eat). Ten years later, I still recall these early moments of excitement. 

Tom Letessier onboard the Yersin
Tom Letessier onboard the Yersin

This trip to Cape Verde, in collaboration with MARBEC, marked the first leg of perhaps the most exciting field project I have ever participated in to date: a three-year global circumnavigation (2017-2020) as part of Monaco Exploration on board the RV Yersin. In addition to visiting icons of natural history such as the Galapagos and the Seyschelles, the Yersin will reach truly remote locations such as shallow banks and deep seamounts far from any harbours. 

Our purpose, and my main reason for participating, is to identify the last pockets of marine predators, like sharks, tuna and other megafauna. Shark and other marine predators are under considerable fishing pressures, and many populations are depleted to the point of functional extinction: remote sites may contain the last remaining strongholds.

A marlin, caught on our mid-water BRUVS
A marlin, caught on our mid-water BRUVS. The bait canisters seen in the middle of the shot attracts big predators, that we can then film and survey

In Cape Verde we used underwater baited cameras (mid-water BRUVs), which survey sharks and predators. This trip was in many ways a trial run for the team. We were therefore very happy to see that we could work well with the vessel, and its hardworking crew. 

We now can look forward to a potential of three more years of BRUVs sampling. Our work on mid-water BRUVs is part of a collaboration with the Centre for Marine Future at the University of Western Australia. This collaboration has taken me to many remote parts of the world, such as Pitcairn, Easter Island, and the Chagos Archipelago. The Yersin circumnavigation enables both the addition of new site whilst re-visiting previously sampled sites, and is therefore of great scientific value. 

Tom onboard one of the Yersin tenders
Tom onboard one of the Yersin tenders, getting the mid-waters BRUVS ready for deployment

My research is funded by the Bertarelli Foundation as part of the Bertarelli Programme in Marine Science.  This multi-year, collaborative programme supports science to advance our understanding of oceanic processes, and importantly, to improve the management of the Chagos Archipelago in the British Indian Ocean Territory (BIOT) marine reserve.

Monaco Exploration follows a trend of resurging interest in ocean exploration and seafaring, in line with the Malaspina Expedition and the Tara Expeditions. Circumnavigation from capable vessels using strategic sampling design and oceanographic methods enable scientists to collect data on key marine characteristics and processes. This increases our ability to respond to rising environmental threats in the global ocean, and to understand the global context of large marine reserves like BIOT. For us scientists, it is an exciting time, with new opportunities for science, and to rekindle child-like wonders. I look forward to being a small part of it. 

Follow Tom on Twitter for more updates from the field.  

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