Veterinary scientists at the University of Las Palmas de Gran Canaria in Spain recently reported finding two stranded Risso's dolphins that died from decompression sickness, commonly known to divers as "the bends." This was quite an odd finding, as dolphins' bodies are well-adapted to avoiding the malady. Decompression sickness is related to the formation of gas bubbles (often nitrogen) in the blood and tissues resulting from a rapid change in pressure, like when ascending from deep to shallow waters.

Professor of veterinary pathology Antonio Fernandez and his colleagues discovered the two stranded dolphins along the coast of Spain's Canary Islands. Both dolphins, a ten-foot male and a nine-foot female, were bloodied with lacerations to the skin. The male was the worst for wear. He had a squid's tentacle affixed to his mouth and numerous, round cuts from suckers. Clearly, both the male and female were battling squid around the times of their demises.

Necropsies revealed two undigested, almost entirely intact neon flying squid inside their stomachs (see image "d" below). Two long tentacles even ran up the esophagus of the male dolphin. Cuts pockmarked the esophageal tissue as if the squid was trying to climb its way out.

But both dolphins didn't die from suffocation by squid. When the scientists analyzed numerous tissue samples from the two dolphins, they spotted telltale signs of decompression sickness. There were gas bubbles in the liver, lungs, and even the brain (notice the clear bubbles in the figure below).

The scientists' best guess is that the predatory dolphins' frenzied pursuit of their squid prey was ultimately their undoing. The vigorous swimming, rapid diving, and ascending, coupled with the squids' single-minded and brutal fight to survive, overwhelmed the dolphins' "anatomical and physiological mechanisms for gas homeostasis, resulting in eventual lethal gas embolism."

To the best of the researchers' knowledge, this is the first time that any marine mammal has been found to die from decompression sickness unrelated to human activities like sonar or boat collision – a true forensic oddity.

Source: A. Fernandez et al. Deadly acute Decompression Sickness in Risso’s dolphins. Scientific Reports 7, Article number: 13621 (2017) doi:10.1038/s41598-017-14038-z