The way we count seal pups is changing at England's largest grey seal colony

The first grey seal pup was spotted at Blakeney National Nature Reserve in 1988. Since then, the site has grown to become England’s largest grey seal colony, with the numbers born increasing from just 25 pups in 2001 to 3,399 in 2019 due to low levels of disturbance and mortality during the first few key weeks of life and a lack of natural predators.  

And this year, rangers are anticipating around 4,000 new arrivals, with the first pup spotted at the end of October. Did you know that global numbers are estimated to be around 300,000 with British and Irish waters supporting about 40 per cent of the grey seal population?

The colony at Blakeney has now become so large that it is almost impossible to record the number of pups precisely. 

The way we count the pups is changing

Until now, the pups were counted individually by rangers and volunteers walking carefully through the colony, but from this year, numbers of newborns and weaned pups - which will have moulted their white fur but will be much smaller than the adults - will be recorded in just one specific area. 

The change in the number of pups recorded in this area from one year to the next will give an indication of what is happening across the whole colony – for example whether or not the colony is still increasing in size and if so, how quickly.  This new approach will also give staff the opportunity to look in-depth at the behavior of the animals, including how long the pups are fed by their mothers.  

National Trust Ranger, Leighton Newman, said, “When the seals first started pupping here it was really important to count the pups to help us monitor the health of the colony. More recently, however, the density of the colony has increased hugely and walking through the colony is now not safe for staff or for the seals. 

“Changing the way we do things recognises that methodologies need to change over time, in response to changes to both the colony itself and the techniques available to help us study it. Over the coming years we can hopefully push forward with this new approach but also work with experts and scientists to keep up with any other new or improved methods of monitoring this important colony.” 

Working with the Sea Mammal Research Unit

This information will be fed into the Sea Mammal Research Unit (SMRU) at St Andrew’s University in Scotland, which estimates grey seal productivity for the whole of the UK.

Chris Bielby, Countryside Manager for the National Trust on the North Norfolk Coast said: “Counting the colony only provides a fairly basic overview of the seal colony so we are going to work with the SMRU to do more in-depth research to better-understand why Blakeney has become such an important habitat, and to look at their behaviour to get a greater understanding of these curious creatures.”

The team is also planning to work with SMRU in 2021, when they plan to do an aerial count of the seal colony. 

Chris concluded: “It will be exciting to get an accurate picture of just how large the colony is and see if by counting just one area we can infer whether or not the colony is increasing in size.”