Could wind farm survey or navy sonar have caused whale deaths? 

Scientists are investigating whether naval activity or offshore wind farm surveys are responsible for the largest mass whale stranding in the UK in almost a century.

About 80 long-finned pilot whales died after washing up on a beach on the isle of Sanday in Orkney on Wednesday. Despite efforts to refloat them, the decision was reluctantly taken to euthanise them due to their deteriorating condition.

Whale experts from around the UK are arriving in Orkney to carry out post-mortem examinations. Specialists from the Scottish Marine Animal Stranding Scheme (SMASS) and UK Cetacean Strandings Investigation Programme (CSIP) will use tissue samples to establish the cause of the deaths.

Last summer another smaller pod of long-finned pilot whales washed up on the Isle of Lewis in the Western Isles. At that time it was suggested that seismic surveys, carried out to locate potential locations for offshore wind farms, were potentially responsible. There was fresh speculation that similar acoustic activity had been carried out along the seabed west of Orkney.

Dr Andrew Brownlow, director of SMASS, said they were looking for answers. “Pilot whales can form very large groups, superpods of many tens, when they are subject to disturbance such as noise or the threat of killer whales,” he said.

“We want to know what acoustic activity was taking place in the hours and days before this latest stranding. Man has made our oceans noisier and these activities are having an effect – so we need to get a better understanding of what’s happening and the impact on creatures like whales.”

Brownlow said he was still awaiting information from an acoustic buoy that may contain vital clues over last year’s mass stranding at Tolsta Beach on Lewis. An entire pod of 55 pilot whales died. The stranding of a large pod of pilot whales in July 2011, at the Kyle of Durness, Sutherland, was blamed on the underwater detonation of bombs by the Royal Navy.

Sonar waves can frighten deep-diving whales, forcing them to surface too quickly and leading to symptoms similar to decompression sickness, also known as the bends, in humans.

“The Royal Navy takes its responsibilities in safeguarding the environment very seriously and, when at all possible, operators take avoidance actions should animals be detected before or during sonar operations,” a Ministry of Defence spokesman said.

Emma Neave-Webb from British Divers Marine Life Rescue said removing the whales from the beach at Orkney was a massive undertaking. “Quite often you feel quite helpless because it’s not a safe environment,” she said. “The animals were very closely packed together with alive animals next to dead animals, they were moving around quite a bit, thrashing their tails occasionally so it was a really dangerous situation.”

The pod included male whales, measuring up to seven metres (23ft) long as well as females, calves and juveniles.

A spokesman for the wildlife charity Whale and Dolphin Conservation said: “The whales had been out of the water for too long and, after sinking into the soft sand, could not refloat on the incoming tide. A team will now try to examine as many bodies as possible to try to find out what caused this terrible and heartbreaking loss of life.”