SIXTY years of surveying seals off the Northumberland coast is being marked today by the National Trust.

Since 1951, wardens have been counting and tagging seal pups born on the Farne Islands.

During this time, the number of pups born each year has grown from around 500 to last year’s 1,499, making it the largest English colony of Atlantic grey seals.

The 4,000-strong Farne Islands have 75% of England’s grey seal population.

But the pup mortality rate is around 50%, with most being lost to bad weather and storms.

In the 1970s, hundreds of adult seals and pups were shot in culls.

When the survey began, scientists knew little about seal behaviour so the early studies on the islands were groundbreaking.

The Farne Islands tagging and survey work is the longest-running study of grey seals in the world.

The seal colony is monitored throughout the autumn by a team of five National Trust wardens, led by David Steel.

He said: “Out here you’re really in the hands of nature. We can go a couple of weeks without seeing anyone else, it’s just us and the seals. The young pups can cry like human babies so it can be really eerie but after 11 years I’m used to it.

“One mother seal usually has her pup about 10ft from the door of where we live which makes life interesting.”

The results of the seal survey are collected by the Sea Mammal Research unit at St Andrews University. Senior research scientist Callan Duck said: “The Farne Islands are an integral feature in the Berwickshire and North Northumberland Coast Special Area of Conservation and the National Trust’s monitoring of grey seal pups provides as essential component of the information required by European conservation legislation for this area.”

Seal tagging was pioneered on the Farne Islands by members of the Natural History Society of Northumberland led by Ian Telfer and Grace Hickling.

The first stainless steel tags fitted to 10 pups on Staple Island were similar to cattle ear-tag clips.

Today tiny transmitters are glued to the seals’ fur.

Every time the animals surface, their location is sent back to the researchers, allowing them to pinpoint its movements.

Only a small number of seals are electronically tagged each year.

The rest are counted by hand – unlike most other seal surveys which use aerial photographs to estimate the number of newborn pups.