The mass pilot whale stranding on the Isle of Lewis is the biggest one ever in Scotland, an expert has said.

Dr Andrew Brownlow from the Scottish Marine Animal Stranding Scheme (SMASS) told BBC’s Good Morning Scotland on Monday, the 55 whales that were washed ashore at Traigh Mhor in North Tolsta on Sunday was one of the biggest mass strandings the organisation had ever dealt with.

Marine rescuers were called to the scene on the Isle of Lewis to reports that dozens of the mammals were in difficulty there at around 7am on Sunday.

Initial reports suggested there were around 55 animals consisting of both adults and calves, however it was soon discovered that only 15 were still alive.

Attempts were made to re-float two of the most active whales, but by 3.30pm on Sunday, it was decided that the remaining whales should be euthanised on welfare grounds, despite a multi-agency rescue attempt.

Dr Brownlow said: “In terms of the number of casualty animals, this is the biggest one we’ve had. This is one of the biggest pilot whale mass strandings we’ve ever dealt with.”

On Monday, work will be undertaken to determine the cause of the pod’s death by SMASS and led by Dr Brownlow.

While the exact cause is currently unclear, Dr Brownlow said SMASS had a “fairly clear idea” the whales could have come onto a “very shallow” beach in quite bad weather.

He added: “Because they’re pilot whales, they form very strong social bonds.

“So if one animal goes on to the beach for whatever reason then it can be that the entire pod will follow and that is basically what happened in this case.”

Dr Brownlow said there was still a backlog of post-mortem examinations to take place on animals from previous mass strandings and that determining the cause of death will be a “monumental task”.

He said: “What we will try and do is triage these animals.

“We will select the animals we think best represent the rest of the pod and make sure we take samples and as much data from those as we can. Then it’s simply a race against time, energy and weather.

“We will do the most we possibly can to find out what’s going on here.”

The whales will be taken to a landfill site in Stornoway to be worked on and Dr Brownlow said they would be buried after the post-mortem examinations were complete.