Thames harbour seals

A harbour seal photographed in the Thames The harbour seal (also known as the common seal) has seen a dramatic fall in population size, with their numbers declining by over 50% since 2000. The reason for this decline is unknown and may be as a result of climate induced changes, shifting prey species, disease, disturbance or competition with the grey seal. Harbour seal populations are also shifting south, and the waters of the Southern North Sea including the Thames Estuary are increasingly important for their survival.

The regional population status and baseline ecology of the local population of seals is one of the least understood in the entire British Isles. Over the last few years, the East coast of England appears to have become regionally more important for the harbour seals and is therefore considered an area of European importance for this population – the UK has 40 percent of the European population. Understanding the range of the species in terms of its foraging, the seasonal use of the foraging area and the extent to which the population is local or migratory are key areas of research that have practical implications for management. As such, the research is fundamental to the conservation of UK harbour seals.

On-the-ground data collection

Data is collected out in the Thames by ZSL in two ways:

Marine Mammal Sightings Survey: ZSL is asking the public to send in any sightings and photographs of the seals as part of our city-wide marine mammal sightings initiative. We welcome sightings of any marine mammals as part of this project, including porpoises and (if you are one of the lucky ones) dolphins. In the case of harbour seals we are combining this valuable data with that of several other organisations to get a wider picture of seals in the Thames. If you spot one of these visitors to the Thames please send us as much info as you can via our online form, and if you want to know more check out the project page .

Population counts: ZSL Marine and Freshwater staff also carry out an annual visual population count. By targeting the main ‘haul-out’ sights where seals are known to rest at low tide, a more accurate estimate of total populations can be gained. These surveys are conducted partly from boats, but also include shore-based counts in collaboration with organisations such as the Kent Marine Mammal group, Kent and Essex Wildlife Trusts, Chalkwell Redcap swimming club and other community groups.

Satellite Telemetry

In January 2012 ZSL, along with the Sea Mammal Research Unit (SMRU) of St. Andrews University deployed ten satellite tags on Harbour seals in the inner Thames estuary. Five seals were tagged in each of two colonies near Southgate and Margate Sands. Important measurements were also taken from the seals in order to monitor health and gain insight into their diet.

The GPS mobile phone tags, which report directly to a mobile phone, accurately show the position of the animal in ‘real-time’ and can record haul out behaviour with a wet/dry sensor. Depth sensors will allow detailed dive data to be gathered that allows foraging behaviour to be monitored. With this suite of information ZSL hope to vastly broaden our knowledge of the zones seals use within the estuary, what they use each area for and ultimately advise on potential conflicts and how they may be avoided or reduced.

Thanks to funding from the BBC Wildlife fund and the SITA Trust, preliminary maps such as those shown below have lent detailed information that, once collated and analysed, will act as an important resource for conservation planning, development and mitigating human-wildlife conflict in this busy waterway.

Satellite Tag

Seal movement in the Thames estuary
An individual seal's movement