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.