Uncertainty over 25% decline in seal pups at Donna Nook Nature Reserve near Louth

Wardens are unsure what has caused a big decline in the number of seals being born at a popular nature reserve.

Donna Nook, near Louth, sees thousands of pups enter the world every year — however last season’s numbers were down by about a quarter.

It is unclear what the cause of the decrease is, but it is suspected to be part of a wider slump across the entire east coast.

In its yearly summary, the warden said: “This is the first significant drop in the UK east coast colonies since monitoring began 40 years ago.

“The Sea Mammal Research Unit are undertaking a programme of research to understand the decline.”

In previous years, the pup numbers at the reserve have been stable at about 2,200 with mortality rates staying between 6.3% and 8.6%.

However, this season - which started on October 29 when the first pup was born and ended on December 22 when the last one was born - has seen a 25% decline from last year’s 2,207 to this year’s 1,649.

It is thought that the decrease could be due to some female seals just simply not giving birth or deaths of the mammal, however, Donna Nook has not seen a significant change in the number of dead seals washed up on the beach.

Despite the lower numbers, Donna Nook thanked its team of 68 volunteer wardens who recorded a combined 2,943 hours throughout the season - equivalent to 342 working days.