More than 700 seals have been spotted in the Thames Estuary in the first ever count carried out by air, land and water.
Conservationists and volunteers recorded 708 grey and harbour seals along the Thames in a survey stretching up the estuary to Tilbury, the Zoological Society of London (ZSL) said.
The survey involved recording seals spotted from boats, from the air or by teams on the ground investigating small creeks and rivers, with the GPS co-ordinates of sightings noted.
The aerial survey enabled researchers to count seals on the outer sandbanks of the estuary where colonies of up to 120 seals were recorded in remote and undisturbed spots away from people and boats.
Boats were used for surveying areas of the Medway and Swale estuaries, while researchers on foot were able to get to spots the boats could not reach.
It is the first such complete assessment of the seals in the Thames following a boat survey by ZSL last year.
The survey was timed to coincide with the annual seal moult, when harbour seals shuffle onto sandbanks to shed their coats and grow a new layer in time for the winter, making them easier to spot.
The scientists estimate there were around 500 harbour seals and 200 of the larger grey seals, although the exact figures need to be confirmed through further analysis.
– Joanna Barker, ZSL's conservation scientist
We knew there were a lot of seals in the Thames but 708 is pretty incredible. In previous results there's been a good few hundred in the Thames, but it's great to have a figure we can use as a baseline. Now we know the numbers and where they are, it can help with conservation.
The presence of so many seals is good news for the Thames Estuary, which was declared biologically dead in the 1950s as a result of heavy pollution, but has since largely recovered.