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NATURE Basking sharks leap from Achill waters

Outdoor Living
Basking shark

One giant leap

Marine Life
John Paul Tiernan

In the month of May, there is one animal which grabs all the attention in the waters off Mayo: basking sharks. This is so even if sightings of them, exhilarating as they are, are sporadic and fleeting when they do occur. 
Every year seems to bring a steady increase in the amount of basking sharks seen off our coast. Some say this is a sure sign of their increasing populations in our waters, others will point out that we simply have more time on our hands these days, and that we are choosing to spend it by the coast, hence we see more.
Whether or not they are seen is also down to weather; the settled seas and clear skies of April meant lots of sightings around Achill, whereas this May, an almost three-week run of dark skies and constant wind and swell meant sightings were down somewhat.
Some of the sightings that did occur this year, however, were quite impressive. To watch a 15-ton animal burst clear from the water and flip in mid air, acrobatic despite its enormity, is an unforgettable sight – almost unbelievable in fact. But the people from Blackfield Surf School (see in Achill have photographic evidence, taken by a customer of theirs a few weeks ago. Such activity is called ‘breaching’ and is usually associated with whales and dolphins where it has a mainly social function. But why would a large, often solitary, slow-moving shark, which unlike whales and dolphins doesn’t need to come to the surface to breathe, make such sudden, energetic leaps into the air?
Some scientists hypothesise that the sharks breach to remove parasites, which include another enigmatic creature of the sea – the flesh-sucking lamprey eel, from their skin. This is an enormous energy investment for the shark, however, and scientists aren’t too convinced that this is the true motivation.

A basking shark breaching, photographed by a customer of Blackfield Surf School in Achill. Pic courtesy of David Corr.
A basking shark breaching, photographed by a customer of Blackfield Surf School in Achill. Pic courtesy of David Corr.

Another theory which has more support is that breaching behaviour is related to mating. Scientists have noted that sharks only tend to breach when in groups of three or more. Rather than being a competitive display between males however, it is females that have been recorded breaching on the few occasions that scientists have come close enough to be sure, and is thought to be a signal from the females that they are ready to mate.
Regardless of the reason, there is not likely to be a more spectacular scene off our coasts this month. If you’ve seen a basking shark, breaching or otherwise, I’d love to know about it – email me at

John Paul Tiernan, Louisburgh, runs, a website dedicated to the creation of knowledge of our marine ecosystems. He is currently studying for an MSc in Marine Science.