Can Basking Sharks Breach?

Do basking sharks breach? 

The basking shark, Cetorhinus maximus, is the second largest shark in the world – and the largest to breach fully out of the water.

You may have seen the iconic footage of great white sharks propelling themselves through the air as they ambush prey from beneath, now basking sharks are definitely not launching an attack on plankton as they do this, so why exactly do they breach?

Firstly, it’s important to understand that breaching costs the animal a lot of energy, especially a slow moving animal like a basking shark who feeds exclusively on plankton. Unlike their faster relatives in the mackerel shark family, breaching is seemingly out of character for the basking shark and no one is certain why they do it.

Why do basking sharks breach?

Whilst we are not sure of the reason why basking sharks breach, we have some theories for this behaviour from research and known breaching behaviours of other species.

It was thought that basking sharks could be breaching to dislodge parasites, as seen in whales. Basking sharks are often sighted with parasitic lampreys, but research we contributed to discovered that parasites were not dislodged during breaching which makes this theory unlikely to be the reason.

Researchers from the University of Exeter deployed satellite tags on sharks in the Sea of the Hebrides which revealed some new insights into the breaching behaviour of basking sharks.

The three sharks tagged made 67 breaches in 41 days, which revealed the speed, repeatability and times of day that this occurred.

Some species breach as a visual signal, a way of communicating to others around that they may be ready to mate or to reunite with the group.  But basking sharks were found to breach both day and night, which suggests that if breaching is a form of communication it is most likely to be an acoustic signal. The noise made by such a large animal breaching can travel very far in water, it is known that whales use breaching as an acoustic signal communicating with others thousands of miles away, it is possible that basking sharks do the same.

Breaching behaviour is something we are lucky to encounter during the summer months in the Hebrides, this special area which attracts large aggregations of basking sharks each year is thought to hold some importance in basking shark courtship. It is not yet known where basking sharks mate, but new studies over the last few years have revealed some insights into what is believed to be pre-courtship behaviour, both here in Scotland and in the Irish Sea. Could breaching play some significance in this? It is definitely possible.

How often do basking sharks breach? 

Seeing a basking shark breach is very much a ‘right place, right time’ moment – and there are very few who have been lucky enough to capture this on film or camera. The University of Exeter team found from the three sharks they tagged that basking sharks could breach as often as 6 times in a day, sometimes these breaches could be in quick succession, one individual was recorded doing 4 breaches in 47 seconds!

The frequency of these recorded breaches in the Sea of the Hebrides MPA further supports how important this area is for basking sharks, another exciting step forward in learning more about this fascinating species!

Read the full paper here: https://www.nature.com/articles/s41598-021-84670-3