River of life: zoo’s yearly count finds seals thriving on Thames

Stuart Barnes, the boat skipper, describes it as a sushi conveyor belt. We watch the customers and dozens of harbour seals resting on the sandbanks at Thames estuary's mouth, just 15 minutes from Ramsgate marina.
August is the moulting season. Seals shed their fur and grow new coats. They spend a lot of time on the sandbanks during this period. It is a great time to count seals, and the Zoological Society of London (ZSL), which conducts its annual seal survey over three days, uses boats and a light aircraft specially chartered to provide a view from the sky.

Today's results reveal that 574 harbour seals were spotted along with 685 grey seals on the creeks and sandbanks running downstream from London. They can be found from Deal, Kent, to Felixstowe, Suffolk. Research suggests that almost a quarter of grey seals, and three-quarters harbour seals, are found on land at this time of the year. This means that the estuary has approximately 2,800 grey seals and 800 harbour seals.

This is a fantastic story for Thames, it really shows the recovery that the estuary underwent, according to Thea Cox (ZSL conservation biologist). Since the 1950s, we've made a lot of progress.

The Thames was declared biologically dead in the 1950s. In 1959, the Guardian reported that the Thames tidal reaches were a poorly managed open sewer. Now, seals can enjoy more than 100 species, including plaice, trout and flounder. Some seals have been in the area for more than five years.

They are basically on an all-inclusive vacation, according to Barnes. He has been doing tours for over a decade and speaks with warmth about the different characters of each seal, including one albino seal that he compares to a funny old man and another who is constantly showing off.

This is a fantastic story for Thames. It demonstrates how the estuary has recovered through Thea Cx, ZSL conservation biologist

Although the Thames may look grimy, it actually looks brown due to the seven-metre high tides that churn up mud. The estuary has a rich mixture of freshwater and saltwater. Keystone species are a sign that there is a healthy food chain in these murky waters. Here are the critically endangered European eel and dover sole, as well as the short-snouted seahorse.

We cruise by the seals, and they remain still, with the exception of occasional head swivels or flipper wisps. They are unaffected by the boat of paparazzi shooting at them. They spend 12 hours a days lying on the warm sand, then dipping into the cold water to feed.

They can swim well and mix easily with other species. Researchers recorded 138 seal pups on the Thames in 2019, the first complete count. Researchers estimated that there were 3243 grey seals and 932 harbour sealing pups in the estuary at that time. Due to the pandemic, the seal survey didn't take place last year.

Seals sleep on sandbanks. The pinnipeds, despite their incontinence on land are agile in water and can swim long distances despite being awkward. Photograph: Courtesy ZSL

The ZSL count was started in 2013. Since then, the seal population has steadily increased. However, it has seen a slight drop in harbour seals since 2017. This could be explained by many factors, including the number of seals at sea during the count. Cox says that the important thing is the long-term picture.

When we conduct these surveys, it is only a snapshot of the year. There are also environmental factors to consider. It's about conducting surveys on a regular schedule, monitoring trends over many years, and seeing what happens.

There are also concerns about plans to dredge Goodwin Sands (10 miles long), off Sandwich Bay, Kent coast. This is a popular sandbank area for seals as well as a marine protected zone. Concerns are also raised about the possibility of the phocine dystemper virus returning to the area that decimated thousands of seals between 1988 and 2002.

UK is home of 40% of world's grey seals, and 33,000 harbour seals. These are the only ones that breed in the UK, which accounts for about 5% of all global populations.

It seems that all is well for these seals at the moment. After a few hours watching them, we drive back to the harbour envying their relaxed lifestyle. Someone comments that Sunday is every day for these seals.

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