what caused 77 healthy whales to die on a Scottish beach?

A mass stranding last week that left 77 pilot whales dead on the Orkney island of Sanday was the largest ever recorded on the British coast. Initially, 12 of the animals were thought to be alive on Tresness Beach – but sadly they did not survive.

The event came almost exactly a year after 55 pilot whales stranded at Tolsta Beach on the Isle of Lewis in the Hebrides on 16 July 2023. All but one of the 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 stranding in Orkney last week is very similar to what happened a year ago, in terms of the number of animals involved and their behaviour,” he said.

Brownlow’s research suggests a dramatic scenario: that mass strandings will increase exponentially – in numbers and events. There have been about 13 mass strandings of pilot whales since SMASS began in 1992, 10 of which have occurred in the last decade. Evidence suggests the situation will only get worse.

Long-finned pilot whales can grow to over 23 feet (7 meters) in length and are found in temperate waters around the world. These sleek, black animals are named for their apparent tendency to follow a leading or “pilot” whale – hence their almost suicidal tendency to escort a sick individual to shore. Pilot whales are often found in large numbers together and are among the most frequently beached cetaceans.

In the past, extreme weather, disease and solar storms have been blamed for disrupting the whales’ natural navigation system and tempting them to swim toward shore. But are these the reasons for the most recent strandings and the increase in occurrences over the years?

A team of 22 scientists from SMASS and the Institute of Zoology’s Cetacean Strandings Investigation Programme in London are working at the Sanday site, along with stranding officers from Cornwall and Wales, in a race against time – a kind of ‘CSI whale’.

Many were present at last year’s stranding, when they were unable to perform full necropsies on the animals due to delays and hot weather, which caused them to rapidly deteriorate.

Mariel ten Doeschate, one of the scientists, says that this time they were able to perform autopsies on 20 animals.

“With squid in their stomachs, it was clear that the animals had recently eaten,” she said. She ruled out illness as a reason for the stranding, explaining that these were “very healthy whales” that were not from one group but a “mixed clan aggregation … different groups coming together to breed.”

Among them were two calves of two or three weeks old, and at least one of the females appeared to be pregnant.

Crucially, Doeschate notes that their position on the beach was “clustered around the most important animals in the group”. This strongly suggests that they were afraid of coming ashore as a “stress response”.

They may have been fleeing predators – killer whales have been seen in the area, she says. But the scale of the Orkney beaching could prove long-held suspicions that extremely loud noises, made by humans, were responsible.

Evidence of such damage can be found in tiny hair cells embedded in the organ of Corti, which converts sounds into electrical signals that can be transmitted to the brain via the auditory nerve. These are the holy grail of whale biologists, embedded in the 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 enormous animals depends on such small things. The hair cells, which can be scarred by heavy sonic events, must be carefully extracted from the cochlea.

Unfortunately, the bone is so dense that samples must be softened in a chemical solution in a lab for up to a year before the hair cells can be examined. Doeschate says the team successfully retrieved six cochleas for analysis.

Brownlow sees the Scottish strandings as the result of a fateful combination of factors. First, warming waters around Scotland are bringing new prey for the pilot whales and other cetaceans to feed on; striped dolphins, more accustomed to Mediterranean temperatures, are now the most common oceanic dolphins seen off Scotland, Brownlow says.

Secondly, the pilot whales use these warmer waters to calve. Thirdly, and crucially, they do so off irregular coastlines that are dangerously unfamiliar to them.

It is a pitiful thought. The whales are lured to the waters by the promise of food and warm conditions to give birth, only to die en masse.

“Last year we had a lot of animals stranding that were pregnant or giving birth,” Brownlow said. “So they’re using these waters as calving grounds.

“But the problem with that is that when these waters are noisy, it poses a dangerous threat to animals that have a herd mentality, that are easily spooked. On top of that, you have some complex beaches that are difficult to get around and opaque to their sonar,” he says.

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Ironically, a fourth factor in this “perfect storm” of circumstances lies in our own success in ending most commercial whaling in 1982 and the subsequent increase in whale populations. Brownlow says, “While these whales were gone, we didn’t take our foot off the gas pedal. Now they’re back in a much more industrialized, much more dangerous arena than the one in which they evolved.”

Since the 1980s, researchers have pointed to the damaging effects of noise pollution on whales and dolphins, from seismic surveys for oil and gas to military sonar. But Brownlow advises caution, suggesting that natural earthquakes can have the same effect.

Whatever the reasons for the Orkney incident, the implications are serious, not just for cetaceans but for the health of our seas. Brownlow, a measured and careful scientist, nevertheless issues a stark warning: “We have to be very careful about what else we do in those waters.

“Otherwise,” he says, “this will become a terribly common occurrence.”