What happened on Sunday at Traigh Mhor on the Isle of Lewis was the most lethal mass stranding of whales in living memory in Scotland. Despite the volunteer efforts of British Divers Marine Life Rescue who rushed to the scene, 54 pilot whales tragically died. Only one was saved.

Whilst other strandings have seen as many whales beached - in the Kyle of Durness, for instance, seventy were stranded in 2011, but most were refloated - none have resulted in so many deaths.

“We believe this has been essentially the biggest loss of life in a pilot whale stranding for about 100 years,” said Colin McFadyen, Scotland Coordinator for the British Divers Marine Life Rescue.

The cause of the stranding is not yet to be confirmed, but, he said, there is already a working theory. “There was a very young calf on the beach and female with prolapsed womb. The assumption is that she was clearly in difficulties and the pod stayed in shallow water helping her to stay afloat, essentially helping her to recover, until either they were too tired to escape the tide or the water went out from under them.”

A key reason so few were saveable was the amount of time they spent on the beach before the stranding was spotted. The whales washed up in the middle of the night and were therefore not observed and reported till many hours later.

Mr McFadyen said: “Time on the beach is the biggest factor in terms of survival, and that can be influenced by how remote the stranding is, how likely it has been for someone to find the stranded whales, and time of day. These whales were stranded on a relatively remote part of the beach in a relatively remote part of the country sometime during the night.”

The whales were seen in the water sometime after 7pm on Saturday night and their stranding was reported at 7.15am. “That,” he said, “is a relatively large window and given how embedded in the sand some of them were it seemed clear they were not freshly ashore.”

“Assuming that they were all healthy when they hit the beach, then how long they were lying there with crush injuries building up is what would affect how likely they were to be able to leave the beach.”

By the time the rescue team arrived and were able to make assessments, there were only 15 left alive. Attempts were made to refloat some of these, but by 3.30pm, the local vet along with the Coastguard, Fire and Rescue, and a forensics vet, came to the conclusion that the conditions made it too unsafe to refloat the remaining animals. They were then euthanased.

Pilot whales are particularly prone to mass stranding - and if this one proves the result ofa whale in difficulty in labour, then this would not be the first time in Scotland.

“One of the last mass strandings,” said Mr McFadyen, "was at Staffin on Skye in 2015 and it again it was a female in labour, in a quiet shallow bay”.

21 animals washed ashore, and 18 were refloated, though some of these later beached again and a further nine died.

Such strandings are often the result of the high level of social care and seemingly selfless cooperation the species exhibits. "However," said Mr McFadyen, “I’m not entirely sure – and this is just my own view – that the whales necessarily understand the danger that they put themselves in. Because they are deep sea animals, pilot whales don’t understand what beaches are and that the water can shallow out and disappear.”

“From what I’ve seen they do whatever they can to assist their pod-mates, but they don’t necessarily know that by doing that they are putting themselves in lethal danger – until the water goes away and they suddenly can’t swim anymore.”

“It is,” he said, “absolutely a selfless act, but I don’t think it’s necessarily the almost suicidal selfless act that we would see it as.”

Though it looks likely that this stranding has a biological cause, there have, he observed also been strandings in the past that have been the result of human activity: "whales scared by a noise or explosions.”

McFadyen who had not been able to attend the rescue, paid tribute to the enormous efforts of the volunteers, who had arrived from across the islands.

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READ MORE Mass pilot whale stranding on Isle of Lewis is ‘biggest one ever in Scotland’

At Traigh Mhor this weekend, these volunteers worked throughout the daylight hours to tend to the animals and to gather samples, of blood, skin and other tissues.

A veterinary team from  Scottish Marine Animal Stranding Scheme has since been carrying out full necropsies.

“My understanding,” Mr McFadyen said, “is that the whales have been taken to a landfill for these necropsies,  which is a bit more sheltered. These necropsies usually involve looking at the brain, the inner organs and possibly looking to see whether they can retrieve the ears.

"If they are able to do that then that will tell whether there has been any sonar or seismic to the animals the past – and therefore hearing loss."