The river Thames is home to a staggering 2,866 grey seals and 797 harbour seals following the most recent pupping season, researchers from the Zoological Society of London (ZSL) said today.
The Thames’ healthy seal population is a promising sign the river is teeming with life, conservationists have said, despite a dip in numbers over the past two years.
The number slightly decreased from 2019, where 932 harbour seals and 3,243 grey seals were counted.
Aside from 2020, when the survey was paused due to the pandemic, the seals have been counted every year since 2013.
Marine biologists use the mammals as an indicator of the health of the river, with stable numbers suggesting good water quality and reliable stocks of fish.
Even the seals are a protected species, they still face a number of threats, including disease, marine litter, becoming entangled in “ghost nets” – abandoned fishing gear – and being hit by ship traffic.
As well as being vulnerable to disturbance when having their pups, such as from curious members of the public, or water activities.
To monitor the population, researchers compared the seals from photographs taken from a light aircraft of different haul-out spots in the Thames Estuary over a period of three days.
The numbers are counted and the final figure adjusted to allow for the fact a number of seals will always be out at sea.
Despite the decline in numbers, the research team said it was not definitive proof that the two populations of seals are facing difficulties.