Seals are breeding on the banks of the Thames ZSL/Tony Thomas
London’s River Thames is usually thought of as an urban environment – but it’s also home to a surprising array of wildlife. That includes harbour seals, which had a successful breeding season last year.
The first breeding survey, carried out by the Zoological Society of London, found 138 pups had been born in the Thames estuary in 2018.
Seals spend more than half their time on land, so can often be seen around the British coastline, and there are regular sightings of them in the Thames as far inland as central London. As well as harbour seals, the Thames is also home to grey seals, with a combined population of about 3000 individuals.
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Only harbour seals can breed in the estuary, though, because its sandy or muddy banks tend to get completely submerged at high tide. Newborn grey seals take weeks before they can enter the sea, and so to give birth, the females have to travel to beaches that do not get covered by the tide. But harbour seals are able to swim within hours of being born, and slip into the water on the first high tide.
Adult seal numbers in the Thames estuary have been increasing for a while, but it was unknown if this was due to resident animals having pups or adults migrating in from other regions. So last June, the Society carried out its first breeding survey, by taking photos of the pups from a light aircraft over three days.
Their numbers are “a really good sign about the rest of the ecosystem,”, says the Society’s Anna Cucknell. Seals prey on fish, crabs, mussels and squid. “A lot of people think the Thames is still dead when they see the brown water. But it’s now a really thriving environment.”
The estuary is also home to harbour porpoises, seahorses, and two kinds of shark.
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