Why Are So Many Sperm Whales Becoming Stranded In The North Sea?

One of the 30 sperm whales to have washed up around Northern Europe. CSIP/ZSL.

In less than a month, dozens of sperm whales have washed up along the shores of Northern Europe. Almost all were dead when discovered, and despite efforts to save the creatures, the two that were found alive died shortly afterward.

This highly unusual stranding event began on January 12 when five of the toothed whales were found beached on The Netherlands’ Texel Island. Over the next few weeks, the animals began popping up along the shores of the U.K., Germany, the German islands of Wangerooge and Helgoland, and France. As of February 9, the tally has reached 30, according to the BBC.

Beachings are not uncommon. But there has only been 82 events documented since the ‘90s, making this year's occurrences unprecedented. It's only thanks to continual monitoring and investigations by groups like the U.K. Cetacean Strandings Investigation Programme (CSIP) that we know this particular event is abnormal.

“We have a strong baseline for mortality rates,” CSIP project manager Rob Deaville told IFLScience. “We normally see 600 strandings of all cetaceans each year, and of those we expect to see 2 to 5 sperm whales on average.

“While we have historically had mass strandings in the U.K., they’ve tended to be in Scotland. There has been nothing in this order on the England coast for 100 years. It’s markedly unusual.”

So, this begs the question: What is going on?

One of the whales stranded in the U.K. Credit: CSIP/ZSL

Given that the whales were all male and of a similar age, it’s likely that they all belonged to the same bachelor pod. While females tend to stay in the tropics or subtropics year-round, breeding and caring for young, males will journey to higher latitudes during the winter.

But the North Sea is a dangerous area for these animals. It’s scarce in their main food source – squid – and relatively shallow. As they need deeper waters for their echolocation to work, which is used for navigation and perhaps hunting, it’s possible they became confused and ended up stuck. This, combined with a lack of food, could explain why they ended up stranded. Indeed, when the stomach of one of the whales was analyzed, it was virtually empty and stained with bile, indicative of an absence of food for some time.

What this doesn’t explain, however, is why the animals ended up in this area in the first place. “There has been a lot of speculation on what might have brought them,” said Deaville. “The strandings have been linked with wind farm activity, naval sonar, and even climatic factors that may have had an impact on prey distribution and sea surface temperature.

“While it’s too early to say at this stage, we will be looking into this in the weeks and months ahead, gathering what data there is out there and trying to tie things together.”

Another possibility, Deaville says, is that there could be an underlying disease, perhaps a virus called morbillivirus that naturally infects cetaceans. Analyses of the carcasses might tell us more, which are currently underway, but getting enough information is perhaps easier said than done when they have a tendency to explode due to all the gases that get released as they decompose.

Sperm whale found in Skegness, Lincolnshire. Credit: CSIP/ZSL.

Although the stranded animals have appeared in quick succession, that doesn’t necessarily mean this is a one-size-fits-all situation. There could be different drivers for each event, and it’s possible we are seeing strandings from different pods that entered the North Sea independently.

While devastating by anyone’s standards, there could be a flip side. Sperm whales are classified as a vulnerable species, but there is evidence that some of their populations are increasing in size, which could be a factor in the current event. If there are more sperm whales out there, then more strandings may occur. But until we know more about their populations, this again is unfortunately hand-waving at the moment. 

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