In a white-tiled lab at London Zoo, just across the street from the giraffes, two investigators are slowly and painstakingly dissecting a porpoise.
Rescue workers recovered the stranded animal on a beach in Somerset a week before. It was maimed by brutal red gashes – from a boat’s propeller, they thought.
Investigators Rob Deaville and Matt Perkins are not so sure. Over the next two hours, they will try to uncover what killed this particular porpoise. They will also look for clues to a much bigger puzzle, one that involves all of marine life, answering questions like: what is the state of our oceans? What are the biggest threats? And what can we as humans do to help?
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Deaville and Perkins conduct post-mortems on more than a hundred porpoises, dolphins and whales a year for the Zoological Society of London. Their work has uncovered surprising threats, from long-banned chemicals lingering in the water to the devastating impact of fishing nets. But it has also revealed good news about the power of policy change and the return of endangered species.
“We use a dead body on a beach to shed light on its life, not just its death,” says Deaville, who leads the UK’s Cetacean Strandings Investigation Programme – or CSIP for short – at the Zoological Society.
Cetaceans are dolphins, porpoises and whales, and the UK’s waters host an incredible range of them. About a quarter of the world’s known species have been found here, from bus-sized, singing humpback whales, to sleek, leaping bottlenose dolphins.
Some 600 cetaceans wash up on UK shores every year. CSI scientists have systematically examined 4,000 of the strandings since 1990, more recently adding large sharks to their remit to deepen our understanding of sea life.
In the lab, surrounded by intriguing jars labelled “penguin” and “mountain chicken”, Deaville and Perkins are taking a closer look at this particular porpoise’s wounds. The tools they use are basic – a scalpel, tweezers, a pair of garden shears – but having seen hundreds of bodies, they quickly form a view of how the porpoise died.
The injuries are too shallow for propeller damage; pecking seagulls are probably to blame. Deaville gently slices off a strip of skin and blubber to be tested later for accumulated chemicals. A putrid, rotten smell rises from the body. I realise now why I was asked before the post-mortem if I had a strong stomach, and warned that some observers faint.
“As we’ll go through this, you’ll see a lot of similarities between us and them, because they are mammals,” Deaville says as he lifts out the dark purple liver. “But you’ll see differences as well.”
The most obviously familiar features are the porpoise’s eyes. They are dog-like and friendly-looking, not flat and glassy like those of fish. But soon, more curious traits emerge. Porpoises have multiple stomachs, like cows, and are indeed related to them. They don’t have two large kidneys, but hundreds of tiny ones. Their adrenal glands tend to be enlarged, possibly because life as a porpoise is rather stressful. They are smaller than dolphins and whales and face many predators, including seals, who can pull them down by their tails and drown them.
Added to these natural threats are the man-made ones. The main killer of sea mammals in the UK is bycatch – that is, unintended entanglement in fishing nets and lines. They suffocate in the nets and often sustain terrible injuries, losing flippers or breaking bones as they try to wriggle free.
“Bycatch is a very unpleasant way to die,” says Sarah Dolman, senior policy manager at Whale and Dolphin Conservation, a charity that campaigns for better protection of cetaceans. I call Dolman after the post-mortem – or necropsy, as it is properly called – to hear more about this clash between our appetite for fish and the cetaceans’ fight for survival.
Both Dolman and Deaville are quick to point out that no fisherman wants to catch a dolphin, as dolphins are a protected species along with whales and porpoises. Indeed, a 2017 report for the UK government notes fishermens’ high levels of compliance with EU regulations on reducing bycatch. These include the use of ‘pingers’ that emit a sound that drives porpoises away. But even with these measures, more than 1,000 harbour porpoises were estimated to have died in nets off the UK’s coast in 2016 alone – and that just covers the UK fleet.
One of the difficulties in reducing bycatch is the UK’s astonishing marine diversity. The range of different species here – not just dolphins and whales, but also sea birds – and many different types of fishing gear mean that no single solution will work.
In Scotland, for example, about half of minke whales that wash up dead were entangled in the fishing lines of pots for catching lobster, langoustines or crabs. Humpback whales even have been spotted dragging fishing gear with them through the sea. Off the coast of southern England, hundreds of common dolphins are caught in ordinary fishing nets every year.
Meanwhile, my shopping habit of checking tuna tins for the ‘dolphin-friendly’ label may not be as helpful as I thought. Dolphin-friendly means the fishing fleet makes an effort to avoid dolphins, but they may still accidentally catch them. The only way to really avoid bycatch is to buy hand-caught ‘pole-and-line’ fish, according to Dolman – meaning when fishermen pull their catch out of the water one by one. Still, she remains hopeful: “Bycatch is not an easy problem to solve, but it’s solvable.” She believes the UK’s strategy to reduce bycatch could pay off in the next few years.
“I think we’re in a very positive place in UK,” she says. “It’s high on the political agenda, and there’s a lot of public support.”
The porpoise in the lab did not die in a net. About an hour into the inquest, Deaville has taken apart its liver, lungs, stomach and ovaries, and determined that the animal is young, female and rather undernourished. He found parasites, some abscesses and a stomach ulcer. He suspects that she may have suffered from an infection that left her too weak to hunt. Or perhaps she could not find enough food, and in her weakened state caught an infection.
The exact cause of death is often difficult to establish, but even a slightly inconclusive necropsy can yield fascinating results.
Perhaps the most surprising finding is the presence of a long-banned toxic flame-retardant known as polychlorinated biphenyls, or PCBs, in stranded whales, dolphins and porpoises. Outlawed in the 1980s, PCBs still seep into the sea from landfill sites.
They have been linked to infertility in sea mammals, and are thought to be driving the last pod of orca whales in Scotland into extinction: only eight of the distinctive black-and-white whales remain. Last year, the stranded body of one, nicknamed Lulu, was described as “one of the most contaminated animals on the planet” in terms of its PCB load.
“It’s a really sad situation,” says Dolman. “They’re not having youngsters, so they’re probably going to die out.”
On the upside, Deaville’s work has shown that policy change can be remarkably effective. One study on the blubber of harbour porpoises found that levels of PBDE, another toxic flame retardant, have fallen since the compound was phased out in the 2000s. And a moratorium on whaling has prompted a rise in the number of humpback whales – which also means more of them wash up.
“Strandings are not always bad news,” Deaville says. “It’s the species we don’t see that we worry about.”
The necropsy is almost over. Last, we inspect the inside of the porpoise’s head, including the parts that facilitate so-called echolocation – the cetaceans’ famous ability to hunt guided by sound alone. The remains are dropped into yellow plastic bags to be incinerated later.
I leave the lab and return to the outside world, passing blossom-covered trees and chattering groups of schoolchildren, while thinking of the drama that unfolds along our shores every day – unseen and unnoticed, until a body on a beach reveals it all.
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