Monitoring UK Marine Mammals

Harbour Seal in the Thames

The UK is home to 24 species of cetacean (whales, dolphins and porpoises) and 2 species of seal (harbour and grey seal). ZSL set up the Cetacean Stranding Investigation Programme in 1990 to coordinate the investigation of all cetacean, marine turtle and basking shark strandings around the UK coastline. Since 2004, ZSL has also closely monitored the number of marine mammals in the Thames Estuary, using a public marine mammal sightings survey and in 2011, ZSL set up the Harbour Seal Conservation Project in the Greater Thames Estuary. All of these projects provide vital data to help us better understand the marine mammal population in the UK and what threats they are facing to inform conservation and management. 

Public Marine Mammal Sightings

The Thames Estuary is home to harbour seals, grey seals, harbour porpoises and sometimes even dolphins and whales. Since 2004, ZSL has been collecting public sightings of these marine mammals, to help us understand how they use the Thames Estuary. If you are lucky enough to see a marine mammal, please report a sighting.

Cetacean Strandings

More than 3,400 cetaceans have stranded on UK beaches over the past six years. ZSL runs the collaborative UK Cetacean Strandings Investigation Programme (CSIP) that investigates stranded whales, dolphins, porpoises, marine turtles and basking sharks across the UK. As well as documenting each individual stranding, CSIP also retrieve a proportion for post-mortem investigation, to allow us to establish a cause of death. Find out more here.

We are dependent on the public to notify us about any new strandings. If you see a stranding, please call: 0800 6520333

Thames Seal Programme

The Thames Estuary is home to 670 harbour seals, but they are one of the least understood seal populations in the country. ZSL use an annual harbour seal population survey to estimate the number of seals in the Thames Estuary and completed a telemetry (tagging) study to collect vital information on harbour seal movements, foraging areas and haul out areas. We have set up the Greater Thames Seal Working Group to coordinate research, management and conservation of seals in the Thames Estuary.

Find out more about the Thames Seal Programme

Marine Mammal Code of Conduct

The marine mammal code of conduct for the Thames Estuary was jointly developed by ZSL and the Greater Thames Seal Working Group, to provide advice on what to do when you see a marine mammal in the water or on land. 


Interactive Seal/Marine Mammal Map Screenshot

Marine mammal sighting survey

Interactive marine mammal map to record sightings

Partners and Sponsors

Key Species

  • Harbour porpoise
  • Harbour (common) seal
  • Grey seal
  • Bottlenose dolphin
  • Common dolphin

Partners and Sponsors

  • SITA Trust Ltd
  • BBC Wildlife Fund
  • Sea Changers
  • Bramley Associates

Partners and Sponsors for CSIP

  • The Scottish Government
  • Welsh Assembly Government
  • Joint Nature Conservation Committee
  • Natural History Museum
  • Marine Environmental Monitoring
  • Scottish Agricultural College