Thousands of seals make the estuary their home

As revealed by the Zoological Society of London (ZSL), which runs London Zoo, there are currently almost 600 harbor seals and 3,000 gray seals living in the Thames Estuary.

Taking to the air and sea, ZSL carried out research, observing seals from boats along the estuary and from RAF training flights over the coastline between Suffolk and Kent.

Hannah McCormick, from ZSL, who led the study, said: “During the 2024 seal survey we counted 431 harbor seals and 714 gray seals lying on sandbanks along the Thames.

“By combining this data with the estimated number of seals that remained in the water during the count, we can estimate a total of 599 harbor seals and 2,988 gray seals alive.”

“Seals are playful but shy creatures, so using a long-range lens to take photos from a distance allows us to maximize count accuracy while minimizing any disruption, helping us best understand how these native species fare in the wild. Thames and emphasizing the importance of protecting this ecosystem.”

The counting was carried out over several days in August, during the moulting period of harbor seals.

During these weeks, the seals spent most of the day basking on the sandy banks of the estuary, which made it easier for the research team to spot them.

The Thames is home to both harbor and gray seals, although harbor seals are the only two that breed in the area.

This year’s study was consistent with the results of several recent studies, which estimated there would be 692 harbor seals and 3,134 gray seals in 2021.

Ms McCormick explained: “We have seen an incredible improvement in the situation for seals in the UK since the early 2000s, when high rates of distemper virus led to a sharp decline in seal numbers.

“Results since 2018 suggest that harbor seal numbers have declined, which has also been observed in other harbor seal colonies in eastern England.”

She added: “While the causes of these declines remain unknown, experts are investigating potential factors and monitoring these changes closely.

“We will continue to improve our understanding of seals in the Thames, while also contributing to long-term regional and national seal data.”

A report led by ZSL previously revealed that although the Thames was declared “biologically dead” in 1957, conservation efforts have led to it once again becoming home to a wide range of British wildlife including seals, seahorses and critically endangered eels.