Thriving Seal Population Shows How Much Thames Have Improved Since it was Declared Dead

Hundreds of sleeping seals show how clean the River Thames has become since being proclaimed dead in the 1950s.

Seals During Molting Season

Seals spend much of their day on the sandbanks during molting season when they lose their coats and develop new ones. This makes it an ideal time for scientists to count them, with the Zoological Society of London (ZSL) conducting its annual seal survey over three days, utilizing boats and a specially leased light aircraft to obtain a bird's eye view.

Seals in the Thames

According to today's data, the survey found 574 harbor seals and 685 grey seals on the sandbanks and creeks downstream from London, spanning from Deal in Kent to Felixstowe in Suffolk. According to studies, roughly a quarter of grey seals and three-quarters of harbor seals are out onshore at this time of year. This suggests that the estuary has around 2,800 grey and 800 harbor seals.

Thea Cox, a ZSL conservation scientist, adds, "It's a very great tale for the Thames - it truly illustrates the rebound that the estuary has gone through." "Since the 1950s, we've gone a long way."

Biologically Dead

The Thames was deemed biologically dead in the 1950s, and the Guardian stated in 1959 that "the Thames tidal portions form a poorly managed open sewer." However, seals now have access to a diverse diet of over 100 fish species, including trout, plaice, and flounder. As a result, seals have a strong sense of belonging, and some have been here for five or six years.

"This is practically an all-inclusive holiday for them," says Barnes, who has been taking tours for a decade and talks warmly about their many personalities, including an albino seal he compares to a "funny old gentleman" and another who seems to be continually flaunting his abilities.

Why is the river still murky?

The Thames may appear nasty, but the browning is due to mucking being churned up from the ground by tides of up to seven meters. As a result, the estuary has a rich mix of fresh and saltwater, and the existence of keystone species demonstrates that the murky waters support a robust food web. Also found here are the highly endangered European eel, dover sole, and short-snouted seahorse.

River Seals

The seals lie still as people pass, save for the occasional turn of the head or wisp of a flipper, unconcerned about a boat of paparazzi aiming cameras at them. Despite their appearance, they spend up to 12 hours a day sleeping on the warm sand before flopping into the brackish water to eat.

They are fast swimmers who mingle freely with populations from all over the world. Researchers counted 138 seal pups born on the Thames in the first complete census in 2019. According to estimates, there were 3,243 grey seals and 932 harbor seals in the estuary that year. Unfortunately, due to the pandemic, the seal survey was canceled last year.

Growth in Population

The seal population has gradually increased since the ZSL census began in 2013. However, there has been a slight drop in harbor seals since reaching over 1,000 in 2017. Many reasons might account for this, including the fraction of seals present at the time of the census. "However, the key for us is in the long-term picture," Cox adds.

"When we do these surveys, we must keep in mind that we are taking a snapshot of a few days in the year, and there are also environmental elements at play," she adds. "It's about doing surveys regularly, observing what occurs over time, and tracking trends."

UK's Grey Seals

Controversial proposals to dredge the 10-mile-long Goodwin Sands, a popular sandbank for seals and a marine protected area off the Kent coast, are among the dangers. There are also fears that the phocine distemper virus would resurface, killing thousands of seals between 1988 and 2002.

The UK is home to 40% of the world's grey seals and about 33,000 harbor seals (the only ones that breed here), accounting for roughly 5% of the global population.

For the time being, it appears that these seals are in good health, and after a few hours of observing them, we return to the harbor, jealous of their carefree lifestyle. But, then, someone says, "For these lot, every day is Sunday."