Devon: Reporter enjoys swimming with seals near Lundy Island
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A team of researchers from the Zoological Society of London (ZSL) identified that the Thames has 2,866 grey seals and 797 harbour seals living in it following the recent pupping season. Conservationists have said that this is proof that there is plenty of life in the capital’s river, even though there has been a slight dip in numbers over the last two years.
Marine biologists say that stable numbers of seals, who are apex predators, means that the river is healthy, with a high water quality and reliable stocks of fish.
While seals remain a protected species, they face a lot of threats which includes marine litter, disease and they can get tangled in ghost nets.
Ghost nets refer to abandoned shipping gear, and if they get caught in this they run the risk of being hit by ship traffic.
They also face the threat of being disturbed when they are having their pups, especially from dogs without leads, members of the public who are intrigued and other water users like canoeists and kayakers.
Seals in the Thames have been counted every year (apart from 2020 due to the pandemic) since 2013. In 2019, the researchers found 3,243 grey seals, easily recognizable from their longer snouts, compared to 932 harbour seals.
In 2002, the seal population was struck by an outbreak of the distemper virus.
This virus causes a number of symptoms such as rashes, conjunctivitis and can lead to a bout of pneumonia which often results in death.
Researchers monitor the seal population by comparing the seals with photographs taken from a light aircraft of different haul-out spots in the Thames Estuary over a three-day time frame.
The numbers get added up and the final figure gets adjusted to account for the fact that some of the seals will go out to sea.
Although there has been a drop in the seal population over the last two years, the research team at ZSL said it was not complete proof that the two populations of seals are going through a difficult period.
Conservation biologist Thea Cox said: “It is the long-term picture that is most significant, and that’s why it is important to do these surveys on a regular basis.
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“Changes in number can be down to a few factors, such as the variability in the proportion of seals at sea whilst the survey is taking place, but this is something we want to keep a close eye on.
“As top predators, [seals] are a great indicator of ecological health, so they tell us how the Thames is doing.
“People think the Thames is dead because it is brown, but the Thames is full of life – the water quality has improved so much.”p
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