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Fantastic Breaches & Where to Find Them

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 commonly be sighted in British waters! And not only are they often seen in the UK, but they have even been known to put on fantastic displays - 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 can really jump (Image Source: Rudd et al, 2021)

Basking Sharks are Gentle Giants

Reaching enormous sizes up to 12 metres in length and weighing in at as much 16 tonnes, basking sharks are truly huge! Yet, basking sharks are not voracious predators! Like whale sharks (Rhincodon typus) and megamouths (Megachasma pelagios), basking sharks are filter feeders. Cruising at a leisurely 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 such as white sharks (Carcharodon carcharias), shortfin makos (Isurus oxyrinchus) and common thresher sharks (Alopias vulpinus), commonly jump out of the water (this is known as "breaching") when they are hunting prey. But basking sharks do not require these surprise attacks with great bursts of speed to get their food (Compagno, 1984). So why do these sharks jump?



Do They Jump to Communicate?

It has been suggested that basking sharks may use breaching to communicate with other sharks.

Communication between animals involves sending a signal, or “cue”, which can be detected by a "conspecific" (individual of the same species) or a “heterospecific” (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) and are able to detect 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). It might be a basking shark's way of communicating with other sharks about foraging opportunities or to find a mate (Hawkes et al, 2020 & Rudd, 2020 & Rudd et al, 2021).


Do Basking Sharks Breach to Dislodge Parasites?

It is also possible that basking sharks use breaching for the maintenance of their health. 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 (Hawkes et al, 2020 & Rudd, 2020 & Rudd et al, 2021). Maybe they even just jump for fun!


To try to answer these question, 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)


Scientists are now attaching cameras to study why basking sharks breach (Rudd et al, 2021)


What Does Breaching Mean?

It is very important to understand why basking sharks breach because it can tell a lot about where their critical habitats are. For example, if basking sharks breach when they are feeding, this would suggest that an area is important foraging habitat. 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)



Basking sharks can be seen in the Sea of Hebrides (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!


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.


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.


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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