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Survey proves harbour seals are breeding in London’s river

In 2018, scientists at conservation charity ZSL conducted the first-ever count of seal pups born in the Thames. The results have just been published and show an incredible 138 arrived in one season, proving that harbour seals are breeding in London’s river.

To carry out the research, hundreds of photos were taken from a light aircraft during summer pupping time as the seals rested, undisturbed on the sandbanks and creeks below.  Researchers found it much easier and more accurate to count the seals in photos instead of trying to monitor the constantly moving, playful creatures.

The survey forms part of UK-wide seal monitoring initiative and although the Thames is home to both harbour seals and grey seals, it is only the harbour seals that breed here.

Conservation Biologist, Thea Cox said: “We were thrilled to count 138 pups born in a single season. The seals would not be able to pup here at all without a reliable food source, so this demonstrates that the Thames ecosystem is thriving and shows just how far we have come since the river was declared biologically dead in the 1950s.”

Project Manager, Anna Cucknell, who leads ZSL’s Thames conservation explained: “The restored ‘Mother Thames’ – as we call her – is an essential nursery habitat and home to many animals including more than 100 species of fish, including two species of shark, short-snouted seahorses and the Critically Endangered European eel.

“Incredibly, harbour seal pups can swim within hours of birth which means they are well adapted to grow up in tidal estuaries, like the Thames. By the time the tide comes in they can swim away on it. Grey seals, on the other hand, take longer to be comfortable in the water, so breed elsewhere and come to the Thames later to feed.”

ZSL has carried out Thames seal population surveys each year since 2013. The most recent results, from 2017, recorded 1,104 harbour seals and 2,406 grey seals across the estuary. Although ZSL’s surveys show that seal numbers in the Thames are rising, it’s not yet known if this is due to resident seals having pups or from adults migrating from other regions where colonies are known to be dwindling.

Image credit: Graham Mee

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