The tale of Captain Ahab and the white whale has been invoked this week after a whale apparently attacked a yacht. How likely is an intentional whale attack? New Scientist has the answers.

What happened?          

On Sunday, a juvenile, 40-tonne right whale breached next to a 10-metre yacht sailing near Blouberg, off Cape Horn, South Africa. The animal struck the yacht, breaking the mast, before sliding back into the sea, reportedly leaving blubber and skin on the deck of the boat.

Why would the whale do that?

Probably it simply made a mistake, breaching near the boat without meaning to strike. Although there are many known cases of whales attacking ships, it is highly unlikely that this one meant to hit the yacht.

Juveniles are like teenage drivers – they are more likely to misjudge things and have accidents than adults, says marine scientist Robert Kenney of the University of Rhode Island in Narragansett. “In the studies of entanglement-scar acquisition in North Atlantic right whales, a large majority of entanglements happen to juveniles.”

In any case, right whales are not known to be particularly aggressive, says Giuseppe Notarbartolo di Sciara, founder of the Tethys Research Institute, a marine conservation organisation based in Milan, Italy, and a former International Whaling Commission representative for Italy. “At most, a juvenile may be inquisitive.”

For example, in 2001, in Hawaii, a 6-metre, 15-tonne baby humpback whale leaped onto the back of a whale-watching boat, breaking a passenger’s knee. At the time, the tour guide said: “Juvenile whales are pretty high-strung and they don’t know much yet.”

Are whales known to breach or jump out of the water to attack?

The function of whales’ jumping and breaching is not well understood. These acrobatics may signal aggression or irritation, but they may also simply be down to the exuberance of a youngster.

“Such behaviours may have meanings other than deliberate attacks,” says Giovanni Bearzi, president of Tethys. “If there was any aggressive intention, it remains to be seen why the whale reacted as it did – had it been harassed for too long?”

The South African Department of Environmental Affairs is investigating whether the yacht had been “harassing” the whale – repeatedly approaching the animal closer than the 300-metre legal limit. According to news accounts, the whale had been “lobtailing” – slapping the water surface with its tail – and breaching before the last breach when it landed on the sailboat.

So what does an intentional attack look like?

Cetaceans displaying aggressiveness towards a boat are more likely to ram it with the rostrum or give it a tail slap.

Perhaps the most famous example occurred in 1820 when the 218-tonne whaling ship Essex was rammed by a sperm whale and sank. The incident inspired Herman Melville to write Moby Dick.

Which species is most likely to attack?

The killer whale. In the news earlier this year when a captive orca attacked and killed its trainer, killer whales are highly territorial. If an approaching boat does not heed the whales’ warning signals, they may attack. In one dramatic case, six people were left adrift in a dingy for 38 days in the Pacific after killer whales sank their yacht.

Although it makes the news, it’s rare for a whale to attack a boat, let alone sink one, considering how often boats disturb and strike whales in virtually all oceans.

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.