The deceased is aged between 1 and 4 years old. Laid out on a metallic table in a small, white-tiled laboratory at London Zoo, it displays no signs of external physical damage or trauma, potentially signifying that its end was not a violent one. Initial necropsy findings indicate that it was nutritionally challenged but had recently fed.

This isn't a plot extract from a surreal Nordic noir crime story, but notes relating to a harbor porpoise — the UK's most common cetacean — found washed up lifeless on a Welsh beach.

It is the latest animal to be examined as part of the Cetacean Strandings Investigation Programme (CSIP), a UK government-funded group that was established in 1990 and operates from the Zoological Society of London (ZSL).

Through a network of partner organizations and volunteers, it monitors strandings of cetaceans, turtles and basking sharks on the country's thousands of miles of shoreline.

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A number of corpses are available for post mortem every year, and in performing necropsies on them, the investigators — in this instance biologists Rob Deaville and Matt Perkins — hope to get a long-term idea of numbers, distribution and what contaminants or other factors  are impacting cetaceans' health.

"One stranding a year won't tell you much. But 15,000 stranding events, 4,000 post mortems, that builds up to an internationally significant archive of information," Deaville says of the approximate number of necropsies conducted since CSIP launched. "One animal fits into a wider context."

Canary in the mine 

The CSIP's acronym, and the comprehensive scientific work they do, lend themselves nicely to the hashtag CSIoftheSea, but the tools they use are a little less sophisticated than those featured on the popular US TV crime series.

"You can get more expensive ones," Deaville says, brandishing a pair of garden shears over the motionless porpoise. "But these more than do the job."

The porpoise has only recently been removed from the deep freeze and its smell overpowers the small room where a scalpel, hacksaw and the ominously named "brain bucket" are also waiting to be used.

For Deaville and Perkins, it's just another day at the office. Collectively, they have more than 25 years' experience at ZSL and have conducted over 1,000 necropsies in labs or, in the case of large marine animals, on beaches and in fields.

Porpoises account for almost half the average 600 to 700 strandings reported in the UK annually. And it's harbor porpoises that Deaville describes as the CSIP's "bread and butter."

"In many ways they're the canary in the mine when it comes to what's going on in the water," he explained.

Nicola Hodgins, head of science with Whale and Dolphin Conservation (WDC) says CSIP offers "one of the only ways" to gain a real insight into whales, dolphins and porpoises.

"You can start to build up a picture, potentially looking at a life history, so you can look at age, you can look at whether they're able to reproduce, you can look at contaminant levels. We are learning so much from the strandings program," she said.

Whodunnit

That said, it is not always possible to establish the reasons for beachings, which have been happening since time immemorial.

"When you get a stranding, people always want to know why and they want to know who, and there isn't always a who," Deaville says.

"It would be nice to say that this porpoise died because it was hit by a boat, and this one died because it's old." Hodgins agrees, "Sometimes you just can't tell."

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In early 2016, areas of coast in England, Holland and Germany became cetacean graveyards, with 30 huge young sperm whales beached there.

Such a large number of animals from a species uncommon to the North Sea was highly unusual. Investigations and post-mortems were carried out, and significant amounts of plastic and waste  were found in some of the whales' stomachs.

"The plastic or marine litter or pollution burden in the animals was quite surprising to us," says Ursula Siebert, the head of the Institute for Terrestrial and Aquatic Wildlife Research at the University of Veterinary Medicine Hannover, whose team examined the sperm whales in Germany.

"We couldn't associate any lesions with those findings or lesions that are assumed to be lethal to the animals but it was taken as a warning how much those animals take in marine litter while looking for their food or just swimming around."

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A more recent and puzzling case is the discovery of 58 dead whales, the majority Cuvier's beaked whales, on the Western Seaboard of Scotland and Ireland.

Figures from the Scottish Marine Animal Stranding Scheme (SMASS) indicate that more of the elusive, deep-diving species have stranded in the last four weeks than in the whole of the last decade.

"We attended about six or seven of the beached whales," Hodgins says, adding that most of them looked like a big blob of blubber and would be hard to identify as whale were it not for the smell. 

"It's completely unusual that you have that many animals stranding, it's just not normal. Something has happened out at sea, somewhere. We just need to find out what."

Unsolved mystery

The juvenile  porpoise , now sawn into various separate bloody parts, may be a gruesome sight. But there are clues emerging from its three stomachs and its lungs.

Deaville lifts the lungs and reveals that while left is a pinky color, the right is much darker, similar to a human liver. This indicates hypostasis, in which the blood would have seeped down into one lung as the porpoise died on land on its right-hand side.

Further tests indicate the presence of a fungus in the lung, meaning the young male may have simply succumbed to infection.

This porpoise's fate will probably never be fully explained. But for all that, his story will form part of the wider narrative of the oceans.