The five dead whales washed up on the beaches of Lincolnshire and Norfolk represent the biggest mass sperm-whale stranding in British waters for 20 years. Twelve sperm whales also washed up dead off Germany and Holland earlier this month and others could follow: at least one more of these colossal cetaceans has been spotted off the Norfolk coast.
Are these deaths natural or the result of human interference in the last great wilderness – the ocean?
Sperm whales have died in the southern North Sea for centuries: Dutch etchings record 17th-century strandings. According to Peter Evans, the director of Sea Watch Foundation, the North Sea acts as a trap. Young male sperm whales head north in search of deep-sea squid, but won’t find much suitable food in the North Sea. Used to navigating in depths of 2,000 metres, they are disoriented by the North Sea’s 20-30-metre depths and the lack of “landmarks” on its gently sloping seabed. It’s virtually impossible for them to find their way out through the narrow English Channel. The whales become dehydrated because they obtain their water from squid.
But the dead Dutch and German animals were found to be well-fed, according to Andrew Brownlow, a Scottish pathologist who helped conduct the necropsies. It is still possible they succumbed to a virus or became disoriented and beached once in shallow water, their own bodyweight can crush their internal organs.
What about human impacts? Four large bombs exploded underwater by the Royal Navy killed 19 pilot whales off Scotland in 2011, and the extent of the damage caused to cetaceans by US navy tests of “low-frequency active sonar” – said to be the loudest sound ever put into the seas – is controversial and not yet fully known.
“Military exercises using mid-frequency sonar have been linked quite clearly to the disorientation and death of beaked whales,” says Evans. But big naval exercises in UK waters are unusual in midwinter. “When there’s a mass stranding, it’s always wise to look at a possible human effects,” says Evans. “But, at the moment, I don’t see anything pointing in that direction.”
Sperm-whale strandings around Britain increased in the 1980s from an average of one a year to about seven. This may be positive: since hunting was banned, the number of mature males has increased, pushing juvenile males further north into the North Sea. Reports of increased squid catches – influenced by climate change – may also be encouraging more sperm whales into the area.
Knowledge of sperm whales’ even most basic biology remains a mystery. And the cause of these deaths may remain just that, too, despite the best efforts of pathologists and scientists.