Seal of approval for citizen scientists

Joanna Barker

Many people are surprised when they meet a marine biologist that lives and works in London. They expect stories of diving in coral reefs or surveying crystal blue waters, however I’m far more used to donning a dry suit or a pair of waders! 

I’ve dedicated my three years at ZSL to conservation in the Thames Estuary. Whilst it may not sound quite as exotic, there is an amazing variety of marine life swimming through the heart of London, including seals, porpoises and even whales. 

Thames seal by Tim MacQuillin
This seal image was submitted by citizen scientist Tim MacQuillin

And it’s not just me that gets excited about encounters with marine life in the Thames. Ten years ago we launched our Thames Marine Mammal Sightings Survey (TMMSS). Since then, an amazing 1,317 people have sent us their marine mammal sightings. We rely on public sightings to understand where marine mammals are present in the Thames Estuary and use this information, in collaboration with other organisations, to decide what measures are needed to conserve them.

I wrote this blog and the report published today  to thank all the citizen scientists who have given up the time to let us know when they’ve spotted a marine mammal. With your help we have reached the ten year mark much better equipped to protect marine mammals in and around London.

The results

We received 1,317 sightings in total, with harbour seals being by far the most commonly reported animal. They are likely visiting central London as they follow their fish prey upstream - one seal was even sighted as far up as Hampton Court Palace! We’re pleased to see that harbour seals are often spotted in the Thames as their numbers have dramatically declined in some parts of Scotland. As we’ve collected data on harbour seals in the Thames through public sightings, annual population surveys  and tagging research, we know the South East is an important area for the conservation of this species.

Seal at Chiswick Pier by Lorraine Conterio
This seal was spotted at Chiswick Pier by Lorraine Conterio.

I’m often asked where the best place to spot a marine mammal in central London is. Our analysis points to one area where you’d probably not expect – London’s financial heartland, Canary Wharf. This area had the greatest density of sightings in the whole estuary – perhaps due to the large number of people working in glass-fronted offices facing the Thames or due to the proximity to Billingsgate fish market. Seals are clever animals and will not miss out on a free meal – one affectionately named ‘Sammy ’ by ’The Friends of The Dockland Seal’ is often seen waiting for scraps!

Check out our infographic below for an overview of the key statistics, or you can read the full report here: PDF icon Thames Marine Mammal Sightings Survey Ten Year Report 2004-2014 (2.59 MB)

Key numbers from ten year report of Thames Marine Mammal Survey
Key numbers from our ten year marine mammal sighting report.

Why sightings are so important

From tourists spotting seals as they walk along the Southbank, to city workers seeing porpoises from their high-rise offices and Londoners encountering marine mammals as they undertake their daily commute – we rely on public sightings to understand how marine mammals use the Thames.

The Thames Estuary is a busy urban waterway used for leisure, transport and industry – but it also is a biodiverse ecosystem that needs to be protected. By gathering information on the distribution of marine mammals, we can work with other organisations in London to design conservation and management measures, to ensure their populations are protected.

How can I get involved?

We’d urge anyone who spots a marine mammal in the Thames to log their sighting on our interactive map and to raise awareness of this project with their colleagues, friends and family. When you do see a marine mammal, please follow our marine mammal code of conduct to avoid any disturbance.

It can be difficult to tell the difference between harbour and grey seals, so here’s a quick guide to help:

  European harbour seal Atlantic grey seal
Size Smaller at 1.3-1.7m Larger at 1.8-2.1m
Weight Can weigh up to-100kg Can weigh up to 300kg
Colour Varies between dark brown, pale grey and even chestnut red. Lighter colouring on stomach and chest than back. Often have mottled coats.  Varies from near black to creamy white, adult males often darker than females. Both sexes have lighter colouring on stomach than back. Pups have white fur when born.
Head shape Pronounced forehead, stout nose, eyes near front of head Long flat nose, eyes mounted midway between nose and back of head


Share your stories

Help us spread the word about the survey by sharing our blog and infographic on social media, and stories of your own marine mammal encounters, using #inthethames.  Whether your encounter happened in the Thames or elsewhere, we’d love to hear about it and see your photos and videos.

And be sure to report any sightings on our Thames marine mammal map.



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