Humpback, minke or fin? Identifying the whale stranded on the Kent coast | Cetacean Stranding Investigation Programme

This week Rebecca Lyal, our Cetacean Strandings Support Officer, reports on one of the latest whale strandings to receive media attention:

The first report I received of the phenomenal sea creature that had stranded in Kent was a post-it note left on my desk saying ‘Humpback whale, Kent’. My phone and inbox then buzzed with updates and enquiries from colleagues and news stations about an 11 metre whale that had washed up on the beach at Botany Bay near Margate. A characterless Wednesday morning had been transformed into a blizzard of curiosity that surrounded the seas’ most recent lost property. But this wasn’t a humpback whale (Megaptera novaeangliae), nor was it a minke whale (Balaenoptera acutorostrata) as was widely reported; it was in fact a fin whale (B. physalas).

11m long black whale, with white underside, stranded on beach, with mouth open. Long hairs of filter feeding apparatus visible.
Mistaken for a humpback whale, then a minke whale, this stranded fin whale was discovered on 14 October 2015. Credit: Maritime and Coastguard Agency (MCA).

The post mortem summary that was released by Cetacean Strandings Investigation Programme (CSIP) partner the Zoological Society of London (ZSL) reported that the whale had damage consistent with a ship strike, due to the parallel linear cuts and a pale appearance to the body that indicated the animal had lost a significant amount of blood from its wounds. But why was there confusion with the identification? Let’s find out…

[Warning: the next image in the post shows the damage to the fin whale’s body]

Fin whales are pelagic animals, living in open sea away from the coast or the bottom of the ocean. They feed on krill, small fish and squid and are rarely seen in the relatively shallow southern North Sea. They can however be seen in the Irish Sea and Bay of Biscay where they share the sea with ships traversing to and from Europe. Although they are fast moving whales, capable of maintaining a speed of 37 km/h, they may sometimes have trouble identifying the direction of a vessel due to the high levels of underwater noise pollution, which could result in a collision

Photo of Rob Deaville using measuring tape on the underside of fin whale.
Rob Deaville (ZSL) takes measurements between two wounds, suspected to have been inflicted by ship propeller blades. Credit: CSIP-ZSL.

Humpback, minke and fin whales are members of the largest group of baleen whales, called rorqual whales, which also includes the planet’s largest mammal, the blue whale (Balaenoptera musculus).  All rorqual whales have throat grooves that expand when the whale scoops up water to filter food; this was the first clue to identifying this particular specimen.

A curtain of ridges fringed with hair, trap crustaceans, fish and other sea critters as water is drawn over them. Known as baleen plates, these inbuilt filters grow from the top jaw of the animal and are made of keratin, the same material as that of our hair and nails. Each species of rorqual has a particular baleen plate colour which makes this feature ideal for species identification.

From the initial photos released of the Kent stranding, the baleen plates gave an appearance of being completely white, which is indicative of a minke whale, but as more images were released it became apparent the baleen was in fact greyish blue, which is indicative of a fin whale. It was recognising this distinction which led to the re-evaluation of the species identification from minke to fin whale.

Photo of the whale laid on the sand, with mouth wide open.
The greyish-blue baleen of the whale can be seen in this image, identifying it as a fin whale. Credit: Maritime and Coastguard Agency (MCA).

It’s been an unusual October with no less than three large rorqual whales stranded along the Eastern coastline: this fin whale and two minke whales. And the fin whale is also one of three to have stranded in the UK this year.

Rebecca Lyal is the Cetacean Strandings Support Officer at the Museum, one of the partnership organisations of the Cetacean Strandings Investigation Programme. The programme investigates the cause of death and the incidence of disease in the UK’s whale, dolphin and porpoise populations and relies on the public submitting their sightings of stranded marine fauna.

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