Britain’s enormous River Thames was declared “biologically dead” in the 1950s because it was so polluted and had no species living within it. Somehow, now almost 70 years later, 130 seal pups have been born on the river’s shores.
Researchers from the Zoological Society of London (ZSL) officially counted the seals born in the river, by analyzing hundreds of photographs taken from a light aircraft during last year’s pupping season. The river winds all the way from Gloucestershire, through Oxford and London, to the estuary, where it meets the North Sea.
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.
Since 2013, ZSL has been carrying out population estimates of the harbor seals and grey seals, both of which are hosted in the Thames. In 2017 there were 1,104 harbor seals and 2,406 grey seals, which confirms that the seal populations in the river are increasing and indicates that the river is providing the seals with a reliable food source. Although, conservationists don’t know whether it was due to resident seals having pups, or if adult seals arrived from other areas nearby where colony numbers are falling. This prompted ZSL to undertake a breeding survey of the harbor seals for the first time in 2018.
Both harbor seals and grey seals live in the Thames, but only the harbor seals breed there. Anna Cucknell, project manager, and leader of ZSL’s Thames conservation explained:
Incredibly, harbor 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.
In 1957, a Port of London Authority report declared no fish had been seen in this titanic 64 kilometers (40 miles) river from 1920-1956. The river was rendered biologically dead due to large stretches of water that were without oxygen. Today it is most definitely alive and thriving, with a rising population of seals, over 120 species of fish, two species of shark, short-sighted seahorses, endangered European eels, porpoises, dolphins, and even an occasional whale.
