A sperm whale which died on Monday after washing up on the island of Raasay had been entangled in ropes.

It was the latest in a series of whale entanglements off the Scottish coast in the last few months.

What is behind such incidents and how common are they?

The 15m-long (49ft) sperm whale was spotted off Skye last Thursday.

It was entangled in ropes, some of them trailing up to 20m (66ft) behind it.

Volunteers from wildlife charity British Divers Marine Life Rescue (BDMLR) managed to reach the whale in a small boat on Saturday.

They successfully freed it of five ropes, but others remained wrapped around its head.

On Monday, the whale was discovered stranded on the shoreline near Oskaig, on Raasay, a small island off Skye’s east coast.

BDMLR said a rope was found tightly wrapped around the whale’s mouth.

It said this would have prevented it from feeding and it was likely to have been malnourished for some time.

Sperm whales are a deep-diving species and prey on large squid.

BDMLR had hoped that, once free of all the remaining ropes, the whale would refloat on a rising tide. But it died later on Monday.

Rescuers said it appeared to take its last breath moments after being disentangled.

Entanglements can involve creel fishing gear or ghost gear – rope and nets that have been lost or abandoned by fishing boats.

A sperm whale that died after stranding on the Isle of Harris in November 2019 had a 100kg “litter ball” in its stomach.

Fishing nets, rope, packing straps, bags and plastic cups were among the items discovered in a compacted mass during an investigation by Scottish Marine Animal Strandings Scheme (Smass).

And a humpback whale that died after coming ashore near Thurso, in Caithness, in 2019 may have become entangled in fishing gear thousands of miles away.

Scientists who examined the carcass said it was tightly wrapped in creel rope.

A buoy attached to the rope had contact details for a fisherman in Nova Scotia, Canada.

Since Christmas, the Scottish Entanglement Alliance (Sea) has recorded five humpback entanglements – in addition to the incident involving the sperm whale.

Only one of the previous five died.

Of the others one was disentangled by BDMLR, two were freed by fishermen and one had no material on it but it did have scars on it suggesting it had been involved in a serious entanglement.

The project’s co-ordinator Ellie MacLennan said: “It’s unusual to see this number over such a short space of time.”

She said the increase could be due to a number of reasons, including that whale populations are recovering following the end of commercial whaling in the 1980s.

Ms MacLennan said: “It could be their distribution is changing so they are moving more into inshore water where they are more likely to overlap with fishing gear.

“That might be down to prey availability and factors to do with climate change and warming seas.”

She added: “This time of year we wouldn’t expect to see humpbacks hanging around for so long.

“We know there have been humpbacks in the Inner Sound area of Skye since October last year.

“That’s quite unusual.”

Ms MacLennan said an incident in January when a humpback got into difficulty at a Skye fish farm was particularly unusual.

“An entanglement in a fish farm is very rare,” she said.

“I think it was only the second one we’ve had in Scotland.”

The entanglement alliance has been working with the inshore fishing industry for a number of years to raise awareness.

It encourages people in the industry to report incidents and to find out how they might be able to assist in disentanglements through workshops.

Ms MacLennan said: “These animals can pose a financial threat to fishers if these whales take off with their gear or damage their gear.”

It has also been working with the fishing industry on possible solutions.

Whales can become caught in rope that runs between shellfish creels on the seabed to a buoy on the surface.

Trials have been done using “ropeless creels” which have the main line in a container along with a buoy and these are lowered to the seabed with the creels.

The buoy is released electronically and rises to the surface, bringing the rope with it when the creels need to be retrieved.

The technology was developed initially for fisheries in the US and Canada where endangered North Atlantic right whales have died in entanglements.