An estimated 708 seals have been spotted by conservationists in the Thames Estuary. The study was conducted by the Zoological Society of London (ZSL).

Harbor seals or common seals (Phoca vitulinaare) are usually found in the waters of the north Atlantic and north Pacific Oceans. About five percent of the world's seal population lives in Britain.

BBC had earlier reported the disappearance of seals in the United Kingdom. The population of seals in some parts of the U.K. is falling at a rate of ten percent per year.

In the present study, researchers estimated the number of seals present along Thames by recording seal sightings. Local residents were also encouraged to report seal sightings at the Society's website.

"Recently, we have seen drastic declines in numbers of harbour seals across Scotland, with populations almost disappearing in some areas. Reasons behind the decline are unclear, but other seal populations may also be vulnerable," said Joanna Barker, ZSL's conservation scientist.

This is the best time to count seals. During the annual seal moult, the creatures venture into sandbanks to shed their old coat and grow a new coat for winter.

"The harbour seal population in south-east England is the least understood in the country. As well as the survey, we are urging members of the public to report sightings of seals and other marine mammals to us," said Stephen Mowat, ZSL's Thames Projects Manager, according to a news release.