Scientists from the Zoological Society of London (ZSL) undertook the first ever comprehensive count of pups in the Thames, taking hundreds of photos during the pupping season in 2018.


After analysing the images, they have now tallied up a total of 138 common seal pups, which they say is clear evidence that the species is breeding in the river.

“We were thrilled to count 138 pups born in a single season,” says Thea Cox, a conservation biologist at ZSL. “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.”

Photos were taken from a light aircraft as the seals rested, ensuring they would not be disturbed and enabling the team to take an accurate count.

ZSL has undertaken a count of the Thames’ seal population every year since 2013, and the figures show that the population has been increasing.

However, scientists are unsure if this rise is due to new pups, or from adults migrating to the Thames from other regions.

The introduction of the breeding survey will complement the existing survey and allow scientists to better understand changes in seal numbers.

The Thames is home to both common and grey seals, but only the former breeds there. Common seals are also known as harbour seals. How to tell the difference between the two species.

“The restored ‘Mother Thames’ (as we call her) is an essential nursery habitat and home to many animals – more than 100 species of fish, including two species of shark, short-snouted seahorses and the Critically Endangered European eel,” says Anna Cucknell, ZSL’s project manager.

“Incredibly, common 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.”


Main image: Common seal and pup. © Graham Mee/RSPB