Nature Shock: Dolphin Murders

Channel 5, 8pm
Tuesday 28th Jan, 2008

The documentary series examining freak occurrences in the natural world continues. This programme focuses on a series of attacks on dolphins and porpoises in Virginia and Scotland. The victims all shared horrific internal injuries yet showed no sign of external trauma. Investigators on both sides of the Atlantic considered everything from underwater explosions to predation by other creatures in a bid to try and explain the deaths.

In 1997, marine biologists in Virginia were astonished to find the bodies of two dolphin calves with seemingly inexplicable injuries. Neither dolphin showed signs of injury on the outside, yet post-mortem exams revealed massive internal damage, including bleeding, shattered ribs and fractured organs. “We saw things like massive fractures of all the ribs on one side,” recalls biologist William McLellan. “It looked like the ribs had just been imploded.”

At the same time, Dr Ben Wilson, a marine biologist in Aberdeen, was puzzling over the corpse of a porpoise found in the Moray Firth. Although they belong to a different species, the porpoise is a similar size and shape to a dolphin calf. This creature appeared to have met with the same fate as the Virginian dolphins. “There was nothing obviously wrong with the animal,” Wilson recalls. “[But] the moment the animal is opened up, you realise it’s a mess inside... It looked like an animal that had been in a car crash.”

Establishing the cause of death would prove exceptionally difficult. Much of dolphin behaviour is poorly understood, as they spend 98 per cent of their lives underwater at depths of up to 1,000 feet. The presence of humans can also alter dolphins’ behaviour, making them extremely difficult to study. With no crime scene, no DNA evidence and no witnesses, the only clue for investigators to follow lay in the corpses.

The primary cause of marine mammal deaths is intensive fishing, yet there was no sign that the victims had been caught in fishing nets. Similarly, the physical evidence seemed to discount the possibility that they had been hit by a boat. “Boat strike is a common cause of mortality in marine animals but then again, you should have an injury that’s coming from one direction,” says military pathologist Colonel Dale Dunn. “These animals were obviously impacted from many directions.”

Investigators considered the possibility that the dolphins and porpoises were attacked by larger predators, such as killer whales or sharks, but with no bite marks, it was clear they were not hunted as food. Meanwhile, the body count continued to mount; over several months, nearly 30 victims appeared in both locations.

The next step was to look at environmental factors. These marine ‘murders’ had only been reported in two parts of the world, so the teams looked for common factors. They found that the Moray Firth is home to a number of oil rigs, which use air guns to detect hidden caverns. These guns produce sonic pulses akin to an underwater explosion. “Basically, a loud explosion underwater could shatter the ribs of a diver,” says Wilson. “So maybe that was happening to these marine mammals.” The Virginian dolphins, meanwhile, swam in waters that were used by the US navy. However, the forensic teams soon decided that the animals’ injuries were too focused to be consistent with the type of diffuse injury usually associated with ‘blast trauma’.

A breakthrough finally came when the US team discovered puncture marks on the dolphins’ lower jaws that matched the teeth of a bottlenose dolphin. For the first time, biologists had clear evidence that dolphins attack their own kind. Even more conclusive proof arrived in the form of shocking amateur footage that captured these attacks on film. But the question remained: why would these dolphins prey on their own helpless calves and the equally blameless porpoises?