Mass whale strandings: what is behind the recent spate of ‘suicidal’ urges?

Scientists are still puzzled by these tragic events, usually involving pilot whales. Vital clues, however, may lie in the tight-knit social ties that give each pod a unique culture

In July this year, responders scrambled to Traigh Mhor beach on the Isle of Lewis, off the west coast of Scotland, to reach a stranded pod of long-finned pilot whales. Most had already died. One was refloated and survived. The others were put down with a rifle.

It was one of the UK's largest mass stranding events (MSE), and the team retrieved samples from the organs and tissues of every pod member. Though exhausting and upsetting, the work revealed an unparalleled and puzzling insight into an entire whale community.

Most stranded cetaceans (whales, dolphins or porpoises) wash up alone and are already dead. MSEs are less common, and live mass strandings are rarer still, but there have been many in recent years. In the Scottish case, the primary cause of death was the stranding, according to Dr Andrew Brownlow, director of the Scottish Marine Animal Strandings Scheme (Smass), who was on Lewis, and spent months analysing the samples. As mammals, whales need to breathe, and most of these whales drowned, trapped in the surf and winds on the steep beach.

What puzzles Brownlow is what brought them there. Mass strandings have been recorded throughout history, he notes, from before we industrialised our oceans". Whales can strand while fleeing predators, become trapped by tides, weather and topography, or just get lost.