Almost 3,600 seals have been counted in the Thames Estuary showing the habitat is still healthy, conservationists said.

The Zoological Society of London (ZSL) teamed up with military helicopter pilots based at RAF Shawbury this year for its annual grey and harbour seal survey across the Greater Thames Estuary.

The team counted the number of mammals laying out on sandbanks and estimated how many may be in the water, concluding a total of 599 harbour seals and 2,988 grey seals living in the Thames Estuary.

Hannah McCormick, the ZSL conservationist who led the survey, said the numbers help to paint a picture of how these two apex predator species are faring and what that means for the wider habitat.

She said: “A flourishing ecosystem has enough food, shelter and space for all of its inhabitants, and although we still have a way to go in terms of improving the health of this important habitat, as top predators, this seal population shows us that there is good habitat available to the species that call the Thames home.”

Ms McCormick said issues like plastic and sewage pollution still pose a threat to wildlife in the area.

“Pollution coming into our rivers and into our estuaries and into the ocean are just going to have a huge knock-on effect for everything living there,” she said.

She urged members of the public not to litter and to continue to put pressure on decision-makers to tackle pollution and discharge.

“Everything that lives here is an argument for reducing that as much as we possibly can,” she said.

“It is vital that the health and recovery of our waterways is a key government priority.”

Over the last two decades, UK seal numbers have recovered after the distemper virus decimated the population in the early 2000s.

ZSL said this year’s survey was consistent with the strong results from the last few surveys, with 692 harbour seals and 3,134 grey seals being estimated in the last count in 2021.

But results since 2018 also suggest there has been a decline in harbour seals, a trend which has been seen in other seal colonies in the east of England.

“While the causes of these declines remain unknown, experts are investigating potential factors and by keeping a close eye on these changes; we will continue to build our knowledge of seals in the Thames while contributing to long-term regional and national data on seals,” Ms McCormick said.

As part of the survey, the team observed seals from boats along the estuary but also joined training flights with RAF Shawbury’s No 1 Flying Training School to cover the coastline between Suffolk and Kent.

The count took place in the first two weeks of August during moulting season for the harbour seals, when they spend much of their day basking on sandbanks.

The RAF was also able to practice using infrared cameras, which can detect heat from enemy troops and engines, to spot signs of seals before the team used long-range lens cameras to confirm the individual seals.

One of the pilots, Major Karl Cooper said the RAF was “very proud and happy” to be able to help with the seal count.

“We’ve been able to develop core skills in regards to working in different areas, different airspace, and then the niche skills of using the camera.”

He added that while a lot of training is “for training’s sake”, on this occasion they felt they were also making a difference.

“To do this and actually have an impact while having the training benefit was a lovely use of our time and aircraft,” he said.

The information gathered by the survey will ultimately feed into St Andrew’s Sea Mammal Research Unit’s database working to understand the status of seals across the UK.

A ZSL-led report previously revealed that although declared “biologically dead” in the 1970s, conservation efforts have led to the Thames once again becoming home to a wide variety of British wildlife including seals, the short-snouted seahorse, the critically endangered European eel as well as sea grass and salt marsh.

The public can support ongoing work by reporting live sightings to the Thames Marine Mammal Survey, avoiding disturbing seals on land or in the water, and reporting dead seal sightings to the ZSL-led Cetacean Strandings Investigation Programme.