When we talk about large sharks, most people usually think of far-off places... tropical destinations, with coral reefs and secluded islands. So it might surprise you to learn that, in fact, the worlds second largest shark can be found in the cold and rainy waters of Great Britain! And not only are they often seen in the UK, but they have even been known to put on quite a show - launching their enormous bodies completely out of the surface of the water! Why on Earth do basking sharks Cetorhinus maximus) jump around like that? And (more importantly) where can we go see it!?
Basking Sharks are Gentle Giants
Reaching enormous sizes up to 12 metres in length and weighing in at around 5 metric tonnes, basking sharks are truly huge! Yet, basking sharks are the not active, voracious predators you might picture when you think of a big shark. Like whale sharks (Rhincodon typus) and megamouths (Megachasma pelagios), basking sharks are filter feeders. Cruising at a leisurely 1-3 km an hour with their mouth open, they can filter 500 tons of water each hour through their gills, sifting out “zooplankton” (tiny animals such as crustaceans, and eggs and larvae of larger animals) to eat (Compagno, 1984).
Active predatory sharks like white sharks (Carcharodon carcharias), shortfin makos (Isurus oxyrinchus) and common thresher sharks (Alopias vulpinus), often jump out of the water when they are hunting prey. This is known as "breaching". But basking sharks do not need to use these surprise attacks with great bursts of speed to get their food (Compagno, 1984). So why on Earth do basking sharks jump?
Do They Jump to Communicate?
Some scientists wonder if basking shark might using breaching to communicate with other sharks. Communication between animals involves sending a signal, or “cue”, which can be detected by another shark - either a "conspecific" (an individual of the same species) or a “heterospecific” (an individual of a different species). These cues can take many forms, including visual signals (like dancing), chemical attractants/ deterrents (like pheromones) or auditory signals (such as singing or roaring). A cue may say, “I am bigger than you, back away from my food” or “I am a healthy, sexy male, we should have babies”.
Sharks have all 5 senses that humans can relate to (sight, hearing, touch, taste, smell), but also have 2 other senses through which they can receive cues! Sharks are able to detect electromagnetism through the “Ampullae of Lorenzini” - gelly-filled organs in their snout. They can also sense the movement of water and changing pressure through their “lateral line” - a short-range mechanosensory structure which runs along the centre-line on both sides of the body from nose to tail. You can see this organ if you look on each side of any fish you have in a home aquarium!
The action of jumping and landing back on the surface of the water might communicate size to other sharks through visual cues (a large splash), auditory cues (a loud sound as the shark hits the water) or water displacement (movement of water particles caused by the shark landing). So breaching might be a basking shark's way of communicating with other sharks about foraging opportunities or to find a mate (Gore et al, 2018, Hawkes et al, 2020, Rudd, 2020, Rudd et al, 2021).
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Do Basking Sharks Breach to Dislodge Parasites?
It is also possible that basking sharks use breaching as a personal hygiene routine. Spinner dolphins (Stenella longirostris) jump to dislodge parasites, as the force of their bodies against the surface knocks pests from the surface of their skin. Basking sharks are plagued by lampreys (a jawed fish with a toothed, sucking mouth, which bore into flesh to suck blood), so it is very possible they breach to get rid of these parasites (Hawkes et al, 2020, Rudd, 2020, Rudd et al, 2021).
Jumping into the Future
In truth, we have more work to do to certain of the function of breaching. It is very possible that the behaviour has several functions depending on the context. Basking sharks might breach competitively when they are foraging, but they may also use it for signalling during mating rituals and also when they need to remove parasites. Maybe they even just jump for fun (Gore et al, 2018, Hawkes et al, 2020, Rudd, 2020, Rudd et al, 2021).
To try to answer these questions, scientists are now making the most of modern technology to learn more about breaching. Using underwater cameras that follow sharks or are even attached to the animal via a tag, we can now actually get a shark's-eye-view of these spectacular jumps! (Rudd et al, 2021).
What Does Breaching Mean?
It is really important to understand why basking sharks breach because it can tell us a lot about where their critical habitats are. For example, if basking sharks breach when they are feeding, this would suggest that the place where they are jumping is an important foraging area. On the other hand, if they breach during courtship displays, this would suggest the area may act as a mating site (Rudd, 2020).
As basking sharks are currently classified as 'Endangered' by the International Union for Conservation of Nature (meaning their numbers are declining globally), protection of basking sharks’ critical habitats will be vital to ensure their survival for future generations to enjoy!
Where Can You Go See Jumping Sharks?
In British waters, if luck is on your side and you know where to go, you can witness these spectacular breaches in person! Basking sharks are commonly sighted in the Irish sea during the spring, at hotspots along the south coast from Cork to Kerry and on the north coast at Mayo, Slingo and Donegal. In fact, it seems their numbers may be increasing in the area (Hawkes et al, 2020).
Recent research is focusing on an area in the Sea of Hebrides, off the coast of the islands of Coll and Tiree. This site is now a proposed Marine Protected Area (MAP). If this bid is successful, it would mean that human activity within the MPA would be restricted; potentially limiting fishing and controlling boat moorings, in order to protect marine life from disruption. This could help basking shark populations to continue to recover (Hawkes et al, 2020).
If you would like to see a basking shark jump, your best chances will be in Cornwall, The Isle of Man, western Scotland and the Isles of Scilly between mid May and July. Head over to Ireland Wildlife learn more. To get up close and personal with basking sharks in the water, it is best to book a tour with a reputable company, like Basking Shark Scotland. Remember, whilst basking sharks are considered to be harmless to humans, they are still a very large wild animal... so NEVER approach them closely and give them the respect they deserve!
To learn more about other jumping sharks, you can check out Pretty Fly for a White Shark and Jumping the Shark.
References
Compagno, L.J. V. (1984). "CETORHINIDAE – Basking sharks". In: Sharks of the World: An annotated and illustrated catalogue of shark species known to date. Food and Agriculture Organization of the United Nations.
Gore M, Abels L, Wasik S, Saddler L & Ormond R (2018). Are close-following and breaching behaviours by basking sharks at aggregation sites related to courtship? Journal of the Marine Biological Association of the United Kingdom, 3:99, 681-693. Access online.
Hawkes LA, Exeter O, Henderson SM, Kerry C, Kukulya A, Rudd J, Whelan S , Yoder N & Witt MJ (2020). Autonomous underwater videography and tracking of basking sharks. Animal Biotelemetry, 8:29. Access online.
Rudd JL (2020). ‘Fantastic breaches and where to find them: first insights into basking shark breaching behaviour’. In: The role of accelerometry in the conservation of two coastal marine vertebrates. Masters degree thesis, University of Exeter, Exeter, UK, pp. 24- 58. Access online.
Rudd JL Exeter OM, Hall J, Hall G, Henderson SM, Kerry C, Witt MJ & Hawkes LA (2021). High resolution biologging of breaching by the world’s second largest shark species. Scientific Reports, 11:5236. Access online.
By Sophie A. Maycock for SharkSpeak
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