A body washes up on a beach in eastern England. Then another. And another. Soon, people living in two coastal communities have five deaths on their hands.

Things take a further macabre twist when it emerges that more than a dozen bodies are littering the shores of the Netherlands and Germany. What could possibly link the deaths? A CSI team, dispatched to hunt for clues, faces a race against time. Scavengers and saltwater will devour the carcasses and destroy potentially vital evidence.

No, it’s not a plot lifted from the latest series of The Bridge. This is life at the gory end of zoological research. The CSI team are not crime scene investigators, but members of the Cetacean Strandings Investigation Programme, a specialist team based at the Zoological Society of London in Regent’s Park, whose work was thrown into sharp relief last week when five sperm whales were found stranded on beaches in Hunstanton, Norfolk, and Skegness, Lincolnshire.

“We weren’t the ones who gave it the name; it’s entirely fortuitous that the initials are CSI,” said Rob Deaville, the programme’s project manager. “But there is a degree of truth in it. You’re trying to find what happened to bodies on a beach.”

Set up in response to a 1988 virus that killed thousands of European seals, the CSIP – cetacean is the collective noun for aquatic placental mammals – is celebrating its 25th year. It continues work begun by the Natural History Museum in 1913 in response to a mass stranding of 50 sperm whales in Cornwall.

At least 21 dolphins died in a mass stranding in the Percuil river, Cornwall, in 2008. Photograph: Barry Batchelor/PA

Now, with more than a century’s worth of data to draw on, the programme has become a zoological treasure trove. In the quarter of a century it has been operating, the CSIP has recorded almost 13,000 strandings of porpoises, whales, turtles, seals and basking sharks, conducted 3,500 postmortems, and collected 80,000-plus samples.

Funded by the Department for the Environment and the Scottish and Welsh governments, the programme carries out between 100 and 150 post-mortems on the 600 or so strandings that occur each year around the UK shoreline. Selecting which creatures to examine depends on several factors.

“Thankfully, everyone now has camera phones,” Deaville said. “We try to ascertain what it is and ask whether it is in a fresh enough condition. Can we access it safely? Often they are stranded in inaccessible locations.”

In the latest strandings, Deaville and his team were able to examine four of the sperm whales. A fifth was too far out on mudflats which may have been littered with ordnance from a nearby military range. But this was not the only explosive risk to the team, Deaville explained. The whale carcasses, insulated by blubber, were storing a potentially dangerous buildup of gases.

“Sperm whales are like pressure cookers; they keep everything locked in. Two of the ones in Skegness were so distended we were concerned about the risk to us and the public.”

The programme’s chief remit is to establish causes of death, but Deaville said that, as distressing as it is to see the carcass of a whale or porpoise washed up on a beach, much good can come from it. “We use the opportunity to learn more about species which are incredibly hard to study in the wild. The sperm whale is a case in point. They spend a fraction of their life at the surface, most of it at depth. So although it’s a tragic event, it does give us a great chance to collect a range of material.”

This can yield important breakthroughs. An examination of porpoise carcasses found the presence of specialist chemicals used to make sofas flame-retardant. This led to a ban on the chemicals in 2004. Other work has suggested dolphins may be subject to decompression syndrome and that whales are affected by the use of military sonar, research that has led to paradigm shifts in how zoologists think about cetaceans.

A sperm whale in the Caribbean Sea. Photograph: Reinhard Dirscherl/Visuals Unlimited/Corbis

Often there are prosaic explanations for why whales and dolphins end up stranded – they may have been caught in fishing gear or been struck by a vessel. But it is the strandings of seemingly healthy creatures that pose the biggest challenge to investigators.

“In terms of the sperm whale events, we will have discussions with our Dutch and German colleagues,” Deaville said. “We’ll look at what may or may not have been going on. It may be that after months of research we are none the wiser as to what caused them to come into the North Sea in the first place. I suspect this is a strong possibility.”

Investigators will check for marine earthquakes with the British Geological Survey and examine underwater noise levels to see if these could have been triggers. They will also study whether there was a change in the distribution of prey that might have encouraged the whales to come into UK waters.

That the amount of strandings remains fairly stable each year seems reassuring, but the number masks wide variations in the fortunes of different species. Humpback whale strandings were unheard of for 80 years, but in 1986, following a ban on large-scale commercial whaling operations, the population started to increase.

“The corollary is that we see strandings; it’s terrible for the individual, but good news –it means there are more of them out there,” Deaville said.

Indeed, it is the species that the CSIP never encounter which cause the most concern. In the UK there is now only one small population of killer whales, off Shetland. Once the species was observed off Wales and England too. But harmful chemicals known as PCBs – which, despite being banned, are still present in the world’s oceans – have had a severely limiting effect on the species’ ability to reproduce.

More recently the CSIP has been concerned by a spate of turtle strandings along the Atlantic coastline. These include several Kemp’s Ridley turtles, the most endangered marine turtle in the world. In the 1960s the species had 40,000 nesting sites around the world. This was down to just 200 by the 1980s. Man-made climate change is to blame, Deaville believes.

“The probable driver [of the turtle strandings] was the extreme weather over Christmas. They’ve been around for hundreds of millions of years and we are having a big impact on them.”

But a century’s worth of research into cetacean strandings continued by the CSIP offers hope that humankind’s relation with the creatures of the sea can change. Ten years ago this month, tens of thousands of people flocked to central London to see a five-metre northern bottlenose whale swim up the Thames.

“If the whale had come up the Thames 60 years ago, there would not have been the same response,” Deaville said. “London used to be at the centre of the whaling industry. They’d tow them up the Thames and boil them up to power the streetlights. It’s really not that long ago since we moved from being a nation of whalers to whale conservationists.”

The CSI Programme can be contacted on 0800 652 0333.

Most common cetacean strandings in British waters between 2003 and 2007

1,924

Harbour porpoises





685

Short-beaked common dolphins





76

Minke whales

72

Atlantic white-sided dolphins

52

Long-finned pilot whales

48

Striped dolphins

43

Bottlenose dolphins

40

Risso’s dolphins

37

White-beaked dolphins

28

Sperm whales

• This article was amended on 1 February 2016. An earlier version referred to the Shetland Islands rather than Shetland.

