Once Biologically Dead, London’s River Thames Rebounds – With Seahorses and Seals

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Pietro De Grandi

Once declared biologically dead, the Thames River flows as much with life as with water these days, and the first report on its health in 60 years is enough to make a Londoner cheer.

Perhaps 115 species of fish live in the river—providing food for not one, not two, but three species of shark which swim above a river bottom where seahorses and eels can be found.

The “State of the Thames” report highlights the gradual work in reduction of pressure on life in the river over the last 60 years, when pollution and sewage decimated it. Short and long-term phosphorus concentrations have fallen, while dissolved oxygen has increased.

“This report has enabled us to really look at how far the Thames has come on its journey to recovery since it was declared biologically dead, and in some cases, set baselines to build from in the future,” said Zoological Society London (ZSL) program lead for wetland recovery, Alison Debney.

ZSL has been working to restore the Thames as a tidal and estuarine ecosystem since 2003, and one of the best ways the look at progress is how river’s estuary is doing—specifically in the populations of the system’s top predators, grey and harbor seals.

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These furry, fish-seeking mammals have increased in numbers, indicating growing fish stocks despite competition from tope, starry smooth hound, and spurdog sharks.

Annual counts of both species of seal have taken place on the Thames Estuary every year since 2013 except during 2020, and they’ve increased from 797 harbor seals to 932, and from 2,866 grey seals to 3,243.

ZSL

“As top predators, (seals) are a great indicator of ecological health, so they tell us how the Thames is doing,” said conservation biologist Thea Cox, to the BBC. “People think the Thames is dead because it is brown, but the Thames is full of life—the water quality has improved so much.”

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It’s not just swimming things that are flourishing in the Thames, but flapping ones as well.

Several areas of the Thames are protected as native and migratory bird sanctuaries, and as a result the number of wading birds, for example the avocet, has doubled across a period from 1993 to 2017.

Additionally, the future is bright for the river, as while some measurements of life in the Thames are worsening, the report details a new “super sewer” that will divert 95% of all sewage from the waterway.

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“The new sewer, which is due to be complete in 2025, is designed to capture more than 95 per cent of the sewage spills that enter the River from London’s Victorian sewer system,” stated Liz Wood-Griffiths, Head of Consents at Tideway. “It will have a significant impact on the water quality, making it a much healthier environment for wildlife to survive and flourish.”

“A resilient future for both people and wildlife will depend on protecting remaining natural habitats, reconnecting and restoring habitats, and innovating new ways to maximize opportunities for wildlife in the urban environment,” Debney concluded.

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