A whale has washed up dead on a Scottish island with a belly filled with fishing nets, plastic bags, ropes, and a selection of other plastic trash.

Experts from the Scottish Marine Animal Strandings Scheme (SMASS) dissected the juvenile male sperm whale this weekend on Luskentyre beach along the Isle of Harris after it became stranded and died on November 28.

During an “explosive” necropsy, the team discovered the 100-kilogram (220 pounds) ball made up of “net, bundles of rope, plastic cups, bags, gloves, packing straps and tubing.”

“By the time we got to it had been dead for 48 hours and pretty much most of the guts blew out of the side when we stuck a knife in it,” SMASS said in a Facebook post.

“Animals this size are so well insulated that even though the temperature outside barely got above freezing, they don’t cool down and hence decompose incredibly quickly,” they explained.

It isn’t yet clear whether the swallowed trash was directly responsible for the whale’s death as it appeared to be in remarkably good health and they found no evidence of the debris obstructing its intestines. They did, however, note the quantity of debris in its stomach must have at least "compromised digestion". 

Nevertheless, the experts argue the death clearly demonstrates how prevalent the threat of plastic pollution and discarded fishing gear has become.

After the dissection, the coastguard and Western Isles Council helped SMASS bury the carcass in the surrounding dune ecosystem, primarily because they were unable to move the 20-tonne animal elsewhere or even tow it out to sea.

Sperm whales (Physeter macrocephalus) can grow up to 20.5 meters (67 feet), making them the largest of the toothed whales. While there are a number of baleen whale species that have a larger body, sperm whales hold the record for the largest brain of any species. According to the IUCN Red List, the species is considered vulnerable to extinction. 

Sperm whales are known to have a “cosmopolitan range,” meaning they can be found throughout most of the planet’s oceans and seas. In fact, they can be found in all marine waters deeper than 1,000 meters (3,280 feet) that are not covered by ice. 

Whale strandings can occur for a number of reasons and it’s not possible to speculate how this one occurred, although the SMASS is hoping to investigate the death further. 

"This whale had debris in its stomach which seemed to have originated from both the land and fishing sectors, and could have been swallowed at any point between Norway and the Azores," SMASS wrote in their post.

“We are looking in more detail to see if we can work out quite why this animal ended up with so much of it in its stomach.”

Occasionally, human activity is to blame for whale strandings, such as the sonar of ships or military exercises confusing the whales’ echolocation senses. There are often natural explanations too, from rough weather, weakness due to poor health, or simply navigational errors. One particularly interesting theory says that some cetacean strandings might even be caused by solar storms.