Humpback whales are getting stranded in the southern North Sea

Environment | Oceans

By Hannah Corsini, Freelance Writer

Published October 1st, 2022

In 2021, a humpback whale, nicknamed Humpy, washed up on the coast of Blyth Beach, Northumberland, from the North Sea. Humpy was dead when they found him, wrapped up in the rope from a lobster pot. The Scottish and UK Humpback Catalogue, a whale monitoring group, remarked that this would spark discussion about the risk of the entanglement of whales off the Northumberland coast.

Humpback whales (Megaptera novaeangliae) are cetaceans—aquatic mammals—known for their extraordinary migration patterns, with one whale managing to swim 9,800 kilometres from breeding areas in Brazil to breeding areas in Madagascar. Despite this, the southern North Sea has never been thought to be of particular migratory importance to these whales.

Young male humpback whales, Moorea, French Polynesia. | Ron Watkins / Ocean Image Bank

In previous decades, humpback whale sightings in the southern North Sea were rare, with only one adult and a calf reported in the thirty-five year period from 1970 to 2005. However, since then, the humpback whale has transformed into an annual visitor, with a significant increase in sightings in recent years, particularly in European waters.

The good news is that the increase in humpback whale sightings is likely linked to a global recovery of the species after a commercial whaling ban was imposed in 1986, which saved the species from extinction. Their populations, although short of what they once were, have been steadily increasing since the 1990s, bringing them into a global conservation status of ‘Least Concern.’

The bad news is that with this increase in spottings comes an increase in strandings. I have a vivid memory of reading ‘This Morning I Met A Whale’ by Michael Morpurgo in my childhood, a story in which a young boy befriends a whale that swims up the Thames. Morpurgo based his work on the real-life cases of whales being stranded in the Thames, including a humpback whale that was washed ashore in Dartford in 2009; a young male assumed to have died from starvation.

Fortunately, humpback whale strandings in the southern North Sea are relatively rare. The very first recorded stranding occurred in 1982 and there have been 19 strandings since the year 2000. However, the UK Cetacean Strandings Investigation Programme suggests that strandings of cetaceans are increasing, meaning that tragedies like the death of Humpy may become more common.

A dead humpback calf, stranded on the Alaskan coast. Photo taken in 2005. | NOAA Photo Library / Flickr

What causes strandings?

The North Sea is rich in fish diversity, many of which provide sustenance for humpback whales, including sprat, herrings and sandeels. However, the former two species have declined significantly in abundance since the 1960s, meaning that sandeel is now one of the most abundant fish species in the North Sea.

Consequently, many cetacean species in these regions are dependent on the sandeel as a staple of their diet. Warmer sea temperatures spell trouble for sandeel populations, and in turn, negatively impact cetacean species such as the humpback whale.

That is not all they have to worry about. Humpback whales are particularly subject to disturbance, given their tendency to swim close to shores and around harbours. Typically, the whales make ‘calls’—low to mid frequency vocalisations—to communicate with other humpback whales around them for a variety of reasons such as breeding, foraging, and other social communication.

However, loud anthropogenic noises, such as blares from boats, have the capability of ‘masking’ these calls and ensuring that they go unheard. Maritime industries like oil and gas extraction, shipping, transportation and tourism are commonly encountered by humpback whales, making vessel noise a prominent risk.

In October 2020, NATO military exercises took place in Gare Loch, Scotland, despite concerns raised by the British Divers Marine Life Rescue (BDMLR) over the presence of whales in the area. Earlier that year, researchers in Australia had released a paper implying a link between military sonar and mass whale strandings based on statistical correlation between the two. This suggests that military practices serve as another potential threat to whales.

There is also always the possibility that, like poor Humpy, they will face the fate of entrapment in fishing gear, the largest source of anthropogenic mortality and injury for humpbacks in the western North Atlantic Ocean.

Humpback whales, Reunion Island. | François Baelen / Ocean Image Bank

How will climate change impact the humpback whale?

Studies suggest that climate change is having an impact upon the behaviours and health of marine mammals, as oceanic temperatures change and Arctic sea ice retreats. This is another possible factor explaining the spike in sightings of humpback whales in the North Sea.

As climate change grows more severe, we can expect to see further drastic changes in whale migration, as well as in distribution, prey abundance, trophic relationships and community structure. Ultimately, this puts the future survival of marine mammals in peril.

The resurgence of the humpback whale is undoubtedly a good thing, and their presence in southern North Sea waters could potentially be a positive sign. However, to ensure the long-term safety and survival of the species, we need to mitigate the harm of certain human activities in hope to avoid unnecessary deaths, like that of Humpy.

Featured Image: Silas Baisch | Unsplash

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