Diving into deep sea sharks

Welcome back to the Whole Tooth, a podcast all about sharks, rays and the oceans. This week our host, Isla, is joined by deep-sea shark researchers Sofia Graça Aranha and Paul Clerkin to explore the depths, and meet some of the fantastical, alien-like and perfectly adapted sharks, rays and skates that live there. And, just how much they need our protection.

We start with Sofia and Paul’s most memorable ocean experiences [05.30]. Sofia takes us on a magical dive filled with sharks and a toothy treasure hunt, whereas Paul’s involves just one shark – but a very special one (how many people can say they’ve swam with a megamouth?!). We also learn how they got into deep-sea research [12.00]. Both Sofia and Paul were fascinated by sharks at a young age but discovered a passion for the rare, the weird, and the beautiful – leading them both to embark on careers studying the most unexplored places on earth.

And what is that place like? We talk about the deep ocean itself, and what you can find down there [17.10]. As Sofia tells us, some of the deep sea is vast, seemingly empty space, where dinner is hard to come by – but in some areas, there are habitats like hydrothermal vents, ocean ridges and fallen whale carcasses that provide refuge and food, and support communities of many different species. One of these is seamounts, which are almost like underwater mountains. Paul explains his research investigating the elasmobranchs that live around seamounts and talks about the importance of these ecosystems for not just sharks, but a huge diversity of marine life [20.33]. So, the deep sea might appear dark, cold and empty, but it is anything but!

That being said, it is a pretty challenging place to live. Low temperatures, immensely high pressure and limited food mean that you have to be specially adapted to thrive in such an environment [24.03]. Paul and Sofia tell us about some of the adaptations that deep-sea sharks have developed – including the ability to glow in the dark (bioluminescence) while at the same time being able to disappear into the shadows (counter-shading), as well as enormous eyes and some seriously powerful senses to enable detection of rare prey [24.44]. Some deep-sea sharks, like lantern sharks and goblin sharks, have taken these adaptations to the extreme [28.60]. The latter has a very long, pointed rostrum filled with ampullae of Lorenzini – tiny pits in the shark’s skin that allow it to detect bio-electrical impulses emitted by other animals – and jaws that act as a sling-shot, firing out at high speeds to engulf prey before it can escape…

We also discuss the potential ecological role of deep-sea sharks, which we’re still very much discovering [38.15]. Paul and Sofia explain that although these sharks look very different from the apex predators we’ve come to know closer to the surface, some deep-sea sharks most probably play a similar role as top predators. Paul tells us about one of the sharks he discovered, which he almost called ‘cutie-eye’, that has a not-so-cute life as a voracious predator. Sofia’s masters research also showed that deep-sea sharks can be both generalist and specialist feeders, and suggested that they can also be scavengers which makes sense – if food is hard to come by, you can’t afford to be picky. Either way, it appears that like many other sharks, deep-sea species play a vital role in the ecosystem.

So, we’ve established that the deep sea is a pretty difficult environment to live in…but does that mean it’s difficult to study as well? Equipment and expeditions can be pretty expensive, but one way Paul and Sofia reduce this cost is to work on board deep-sea fishing vessels and analyse what they bring up from the deep [42.35]. It’s a double-edged sword: on the one hand, you’re able to see species that in some cases have never been seen before, but on the other, many individuals don’t survive the drastic change in pressure and temperature. Through the DELASMOP project, Sofia is working with deep-sea crustacean trawlers to gain knowledge on the survival and condition of sharks, rays and skates brought on board, and is using that knowledge to improve management and handling practices [53.24]. Paul is also working to inform deep-sea fisheries management, through better information on species taxonomy and life-history traits [49.14]. Because if you don’t know what’s down there, and how they might be impacted by fishing activity, how can you adequately protect those species?

About our guests

Sofia Graça Aranha

Sofia holds an MSc in Marine and Coastal Systems and is a PhD candidate in Marine and Environmental Sciences at the University of Algarve and is a collaborator researcher at CCMAR and Ciimar. Her work, in collaboration with the Portuguese Institute of the Sea and Atmosphere (IPMA), consists of evaluating aspects of the biology, ecology and conservation of deep-sea sharks and skates and the possible interferences of bottom-trawl activities on their survival and condition. She is the project leader of the Delasmop project, entitled “Is it possible for deep-sea sharks and rays to thrive and survive in fishing grounds?” funded by the Save our Seas Foundation and is the scientific coordinator of the project entitled “The development of Electronic Monitoring and Reporting technology for fisheries in Portugal” funded by EEA Grants. 

Instagram: @sofiagracaaranha or @delasmop.pt

Paul Clerkin

Paul has a master’s degree from Moss Landing Marine Laboratories, California, and is currently working on his PhD at the Virginia Institute of Marine Science. He specializes in rare and deep-sea chondrichthyans and focuses on new species descriptions, taxonomy, life histories, genetics, and tagging of poorly understood shark species. His outside-the-box approach combines working with local fishers and high-tech innovative research techniques such as remotely operated vehicles (ROVs), specialized deep-sea cameras, and satellite archival tags. He has conducted deep-sea research aboard vessels all over the world and has discovered over a dozen species that are new to science. Paul also founded a non-profit called DeepBlue Foundation, which works to fund research and educate the public on deep-sea chondrichthyans.

Instagram: @paul_j_clerkin

Twitter: @PaulJClerkin