Blasket islander was spot on about long-finned pilot whale

SOME 350 pilot whales frequent the deep food-rich waters between Tenerife and La Gomera, writes Richard Collins.

Although these ‘blackfish’ approach the coast occasionally, they are seldom seen from the shore. Nor is it easy to find them in the vast ocean but, with excellent visibility and calm seas last week, our boat soon homed in on a pod.

Unlike dolphins, pilot whales don’t approach boats or ride bow-waves, though they’re not afraid of people and don’t flee when approached. The whales accepted our intrusion; a trusting female came right up to us but the big males ignored the boat as it drifted silently among them.

Another group of islands, the Blaskets, came to mind as I watched. A hundred years ago Tomas Ó Criomhthain, in An tOileánach, described a stranding incident there. The victims, he wrote, were dolphins “with their great fins sticking up out of the water, all of them close together”. This description suggests that they were pilot whales, a species which occasionally becomes stranded on Irish beaches.

Ó Criomhthain wasn’t wrong; the long-finned pilot whale is actually a large dolphin. Males can be over seven metres in length, females a metre or two less. The pectoral fins are unusually long; hence the creature’s full name. You couldn’t mistake a pilot for a bottle-nosed or common dolphin; the dorsal fin is sickle-shaped and curved backwards.

The blunt bulging forehead houses the creature’s extraordinary echo-location system; in 2014, HS Mortenson and colleagues claimed a typical pilot whale has about 37,200,000,000 neo-cortical neurons. Human females have 19,000,000,000 and men have 23,000,000,000. ‘For the first time, we show that a species of dolphin has more neocortical neurons than any mammal species studied to date, including humans’, they wrote. The pilot whale’s ‘songs’ squeaks and buzzing sounds are much studied but still not understood.

The highly sociable ocean wanderers move in tight formations led by a leader, the ‘pilot’ which gives the species its name. It’s said the whales sleep so close to each other that their pectoral fins touch. Pods usually have 15 to 200 members, although schools of up to 3,000 have been reported. I couldn’t say how many were around our boat off Tenerife, perhaps a few dozen.

Females seem to rule the roost. Although males remain members of the pod in which they were born, they seldom breed with females of their own group. A sort of ‘incest taboo’ dictates they visit other pods to consort with females in ‘love-them-and- leave-them’ encounters. This arrangement promotes genetic diversity and ensures incest is avoided. The females of only three mammal species undergo menopause; humans, orcas and pilot whales.

The pilot probably decides where the pod goes. Dictatorship, alas, has its weaknesses; a ‘dear leader’, despite the adulation of his or her subjects, can get things wrong. Was ‘pilot error’ responsible for the disaster described by Ó Criomhthain and countless other such incidents. Nobody knows why these tragedies occur but difficulty navigating in shallow waters seems to be a factor. Pilot whales, deep-water creatures, may be ‘out of their depth’ when venturing too close to shore. If a confused leader takes a wrong turning or two, the entire pod may end up beached.

Parasites or ear infections might impair a leader’s judgement. Submarine detection systems, or depth-charges detonated in naval exercises, could produce sounds loud enough to damage a whale’s sensitive hearing. Pollution may also be implicated; toxic substances have been detected in whale tissues.

However, human factors may not be entirely responsible; strandings were recorded since 1704. Evolution has provided the pilot whale with remarkable abilities but it seems also to have saddled it with a fatal ‘design fault’.

Mortensen HS et al. Quantitative relationships in delphinid neocortex. Frontiers in Neuroanatomy. 2014.