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Marine Mammal Survey

Marine Mammal Survey

The PLA has joined with the Zoological Society of London (ZSL) to assist in a survey of marine mammals in the tidal Thames. Seals have been spotted in the Thames as far up as Richmond Lock. They feed on a wide range of fish in the estuary and can sometimes be seen resting on the sandbanks in the outer Thames at low tide. There has been a dramatic global decline in the numbers of common harbour seals; populations have decreased by more than 50% since 2000. Marine mammals are known to visit the Thames estuary but, until now, sightings have not been formally recorded.  This survey  is operating in the tidal Thames area, between Teddington upriver to Shoeburyness and Sheerness in the outer estuary, it is on going and will address this information gap.

The Zoological Society of London (ZSL) has launched the Thames Marine Mammal Sightings Survey and is appealing for people fortunate enough to spot dolphins, porpoises and seals in the Thames to participate in the survey. PLA staff have been issued with guidance on the different types of marine mammals that may visit the Thames and are asked to inform the PLAs Environment team detailing the details of date, time, species and number of individuals. This information is sent on to ZSL.

The data collected will help to develop patterns and trends in species distribution, behaviour and habitat use.  Findings will also be fed into national databases.  

If you would like to help - please display information (such as survey forms) on your vessels, and keep your eyes peeled!  Check out www.zsl.org for more information, posters and survey forms.

Common Name:

The Grey Seal

The Common Harbour Seal

Latin Name:

Halichoerus grypus

Phoca vitulina


Parallel nostrils

V-shaped nostrils


Flat head profile

Concave (curved) head profile


Elongated muzzle

Short muzzle 

Male Size & Weight:

Males: 2.5m, 300kg

Males: 1.8m, 100kg

Female Size & Weight:

Females: 1.8m, 175kg

Females: 1.5m, 80kg


Cetaceans in the Thames


ZSL are the lead for any stranding in the river Please follow the link on this website:  http://ukstrandings.org/


Code of Conduct:

The British Divers Marine Life Rescue has produced a Code of Conduct for watching cetaceans (dolphins, porpoises etc). Click here to view the code (pdf file - 44kb)  

Useful Links