A mass stranding last week that led to the deaths of 77 pilot whales on the Orkney island of Sanday was the largest ever recorded of the species on the British coast. Initially 12 of the animals at Tresness beach were still alive – but unfortunately did not survive.
The event took place almost exactly a year after that the stranding of 55 pilot whales on Tolsta beach on the Isle of Lewis in the Hebrides on July 16, 2023. All but one of those whales died. According to Dr Andrew Brownlow, director of the Scottish Marine Animal Stranding Scheme (SMASS) at the University of Glasgow, this may not be a coincidence.
“The Orkney stranding last week has so many parallels to what happened a year ago, in terms of the number of animals involved and their behaviour,” he says.
Brownlow’s research suggests a drastic scenario: that mass strandings increase exponentially – in the number of animals and events. There have been approximately 13 mass strandings of pilot whales since SMASS was started in 1992, 10 of which were in the past decade. Evidence suggests that the situation is only going to get worse.
Longfin pilot whales can grow to over 7 meters in length and are found in temperate waters around the world. These sleek black animals are named for their apparent propensity to follow a pilot or “pilot” whale—hence their near-suicidal urge to accompany a sick individual ashore. Often found together in large numbers, pilots are among the most likely cetaceans to become stranded.
In the past, severe weather conditions, disease and solar storms have been blamed for disrupting the whales’ natural navigation system and tricking them into swimming to shore. But are these the reasons for the most recent stranding and increase in events over the years?
A team of 22 scientists from SMASS and the Cetacean Strandings Research Program from London’s Institute of Zoology, is working with stranding officers from Cornwall and Wales at the Sanday site in a race against time: a “CSI whale” of sorts.
Many attended last year’s stranding, when due to delays and hot weather causing rapid decay, they were unable to complete post-mortem examinations of the animals.
However, Mariel ten Doeschate, one of the scientists, says that this time they were able to carry out post-mortem examinations on 20 animals.
“With squid in their stomachs, it was clear that the animals had recently fed,” she says. She rules out disease as a reason for the stranding, explaining that these were “very healthy whales”, which did not consist of one pod, but a “mixed family aggregation … several different pods coming together to breed”.
Among them were two calves two or three weeks old, and at least one of the females was found to be pregnant.
Doeschate notes that their position on the beach was “clustered around key animals in the group”. This strongly suggests that they were afraid to come ashore as a “stress response”.
They may have been fleeing predators – orcas have been seen in the area, she says. But the scale of the Orkney stranding may prove a long-held suspicion: that extremely loud noises, caused by humans, were responsible.
The evidence for such damage is found in tiny hair cells embedded in the organ of Corti, which convert sounds into electrical signals that can be transmitted to the brain through the auditory nerve. It’s the holy grail of whale biologists, embedded in the animals’ walnut-sized ear bones, or cochleas, which are themselves buried deep within the whale’s skull.
It is a paradox that the fate of these great animals can come down to such small things. The hair cells, which can be scarred by severe sonic events, must be delicately extracted from the cochlea.
Unfortunately, the bone is so dense that samples will have to soften in a chemical solution in a laboratory for up to a year before the hair cells can be examined. Doeschate says that the team successfully obtained six cochlea for analysis.
Brownlow sees the Scottish strandings as the result of a fatal combination of factors. First, the hot water around Scotland, bringing in new prey for the pilot whales and other whales to feed on; striped dolphins, more used to Mediterranean temperatures, are now the most common oceanic dolphins seen off Scotland, says Brownlow.
Second, the pilot whales take advantage of those warmer waters to calve there. Third, and crucially, they do so along irregular coastlines with which they are dangerously unfamiliar.
This is a deplorable idea. The whales are lured into waters by the promise of food and warm conditions to give birth, only to die en masse.
“In last year’s stranding there was a significant number of animals that were pregnant or in the process of giving birth,” says Brownlow. “So they use this water as calving areas.
“But the problem with that is, if these waters are noisy, then it’s a dangerous hazard for animals that have a herd mentality, that startle easily, and you have some complex beaches that are difficult to navigate around and opaque for their sonar,” he says.
Ironically, a fourth factor in this “perfect storm” of conditions lies in our own success most commercial whaling ceased in 1982 and the subsequent increase in whale populations. Brownlow says: “While these whales were away, we didn’t take our foot off the accelerator. Now they have come back into a much more industrialized, more dangerous arena than the one in which they evolved.”
Since the 1980s, researchers have noted the harmful effects of noise pollution on whales and dolphins, from seismic surveys for oil and gas to military sonar. But Brownlow advises caution, pointing out that natural earthquakes can also have the same effect.
Whatever the reasons for the Orkney event, the consequences are serious, not just for whales, but for the health of our seas. Brownlow, a measured and cautious scientist, nevertheless delivers a sharp warning: “We have to be very careful about what else we do in those waters.
“Otherwise,” he says, “it’s going to become a terribly common occurrence.”
