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Annual seal survey highlights Thames’ importance

Marine biologists from ZSL (Zoological Society of London) have been scanning the shorelines and sandbanks of the Thames Estuary as part of their annual seal survey.

Every August a land, sea, and air count is conducted to assess the current population of harbour and grey seals while also highlighting the Thames’ importance as an ecosystem.

Thames Seal Survey 2021 (c) ZSL

ZSL has been monitoring the grey and harbour seals in the Greater Thames Estuary since 2013, and this year’s count has revealed an active population. 

According to the latest seal survey, it is estimated that the Thames estuary is home to 2,866 grey and 797 harbour seals, showing that the iconic river is a key ecological hotspot for these species. 


Thames Seal Survey 2021 (c) ZSL

To conduct the count, the ZSL team took aerial photographs of the seals from a light aircraft and used boat trips on the estuary for closer observations where needed. The images were then analysed to confirm numbers and determine species of seal, helping scientists to monitor the impacts of emerging threats such as wildlife disease and competition between seals for food and habitat.  


Thames Seal Survey 2021 (c) ZSL

Since beginning their survey, nearly a decade ago, ZSL has shown how valuable the Thames estuary is as a habitat, not just for seals, but for several other species, including the European eel, Dover sole and the short-snouted seahorse.


ZSL is now  urging policymakers to put nature at the heart of all decision making to tackle climate change and biodiversity  loss and  will be calling on  leaders to make this commitment at COP26 in Glasgow in November. To find out more, visit


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