What do basking sharks eat?
This week, we’re plunging into the wild and mysterious world of the second largest species of shark on the planet – the basking shark! I popped down to basking shark HQ in Oban, on the west coast of Scotland, to nerd out about one of my all-time favourite species with fellow enthusiasts Shane Wasik and Rachel Brooks of Basking Shark Scotland. Every summer, they head out to a global basking shark hotspot, the Sea of the Hebrides, to see these animals in the wild and certainly know a thing or two about their ecology and behaviour. We had so much fun answering all your questions about the big beasties, and this episode touches on everything from filter-feeding to pointy-nosed babies and all things in between!
First, we learn a little about Basking Shark Scotland and Shane and Rachel’s role in the organisation [02.14 – 7.26]. Then, before embarking on our voyage into basking shark territory, we make a stop at Shane and Rachel’s most memorable ocean experience to meet Barney the humpback whale and a feeding frenzy [7.27 – 11.16] … Our journey then begins with the basics – what is a basking shark exactly [11.41]? We learn about their surprising family history and relation to white and thresher sharks in the order of Lamniformes [12.38- 13.06]. We also learn how big they can actually get [13.12], and discuss the differences between them and their one larger cousin, the whale shark [14.21].
Next, we talk about where we can find basking sharks [16.03]. Shane tells us that you can actually find basking sharks all over the world – they have a huge range – but that certain parts are ‘hotspots’ where they return to the surface in large numbers to feed on plankton blooms. One of these is the Sea of the Hebrides, where the Basking Shark Scotland operation is based. We also discuss the fact that the basking shark actually spends over 80% of its time in deep water, so what we see on the surface is only a very small fraction of its life cycle. Rachel tells us a little more about their migratory behaviour, or at least, what we know about it [17.59]. She explains that while some sharks stay within a relatively small boundary, data has also shown basking sharks undertaking huge transatlantic migrations, with one travelling from the UK to Canada!
So, with all that swimming, you definitely need to eat to keep yourself going…so what do basking sharks eat, exactly [20.10]? We learn about their favourite food, the copepod [21.54] as well as the filter-feeding mechanism they use to eat them with [24.00]. We find out that surprisingly, a basking shark has a mouth of a metre wide, but has a very tiny throat – so it couldn’t eat a human even if it wanted to! However, this brings on a debate about what a basking shark would do if you dressed up as a giant copepod and somehow got inside the mouth…a copepod gobstopper, anyone?
I then pitch Shane and Rachel some of your questions about the feeding habits of basking sharks. We learn how a basking shark gets enough food to sustain itself [27.20], which includes seeking out areas with a high abundance of plankton and utilising the ocean tides and currents to its advantage. We also debate how they avoid choking on larger items [31.24] – which if you think about it, could be a problem when you’re not a particularly picky eater! Our journey into the basking shark world then takes a much murkier, and more mysterious turn as we enter the realm of mating and reproductive behaviour [33.49]. We talk about how we don’t know much at all, and that no one has actually scientifically recorded these sharks mating or giving birth in the wild! More recently, we have learnt more about what could be pre-mating behaviour and Shane and Rachel tell us about the theories behind close-following [34.33], breaching [36.02], and a new circling behaviour called ‘torus’ where individuals circle closely while descending into the depths [39.03]. And, we look at a very recent study that suggested basking sharks might even hold fins before mating!
We bring our episode to a close by talking about some threats to basking sharks. First, we answer another listener question – do they have any natural predators [40.53]? Next, we discuss the intensive hunting of basking sharks for their very large and oily liver, which had a severe impact on the north Atlantic population until it was banned in the UK in 1995 [43.23]. We then chat about the more recent threat of microplastics [45.23] before rounding off our episode with a very topical threat, climate change [49.49] to answer some more listener questions about how this will impact their movements and behaviour.
As always, our final question covers which species of shark and ray Shane and Rachel would be – Rachel picks a graceful and glamorous species, whereas Shane chooses a stocky, hump-backed bottom-feeder…
About our guests
Owner and Skipper for Basking Sharks Scotland
Shane’s background is in Marine Biology, completing his honours degree in 2003. He attained scientific and commercial diving qualifications in 2001 but started diving as a wee laddie in 1996. His qualifications include BSAC First Class Diver and Advanced Instructor, along with technical and rebreather diving. He has worked in many different fields including fishery and environmental protection, aquariums, underwater and travel photography and shipwreck disaster response along with organising diving exhibitions. He also has a long list of boating qualifications including a Commercial Skippers Licence. His experiences with basking sharks have driven him to enable others to share the breathtaking experience of seeing these gentle giants in the wild. He also spends a lot of time in New Zealand where he lived for a number of years. He has travelled extensively around the world including much of the South Pacific.
Rachel is a Zoology graduate and scuba instructor who joined the Basking Shark Scotland team in 2020 as operations manager. She has been working in the dive industry since 2015 where she worked for five years overseas teaching and guiding dives in Queensland, Borneo, and the Ningaloo Reef before managing a dive centre in the Lembeh Straits. Here her interest in underwater photography really developed, seeking some of the world's strangest underwater critters and macro subjects. From the very small to the very large she is extremely passionate about all marine life, and is now enjoying introducing others to the waters of the Hebrides.
Rachel is also an internationally selling British wildlife artist. Her deep understanding of her subjects from time in the field and studies in Zoology have connected her to the field of scientific illustration. Rachel creates ink illustrations which celebrate the natural world and her work has been featured by organisations such as the RSPB and Shark Guardian. Her art is an account of her experiences and love for the ocean, with a mission to share that passion for conserving biodiversity to others.