Hungry ducks feeding on tonnes of mussels from The Wash every day are a threat to local shell food farmers.
Feeding Eider ducks on the Wash are a threat to shell fishing
Fishermen say thousands of Eider ducks are now living on their mussel beds in The Wash bordering Lincs and Norfolk.
As a protected species they cannot be culled but consume up to 2.5kg each time they visit the mussel beds.
Matthew Mander of Eastern Sea Fisheries admits the birds are a nuisance but says culling is not an option in the short term.
A machine designed to keep the Eider ducks off the mussel beds in The Wash has, so far, proved to be ineffective and the birds are taking advantage.
As quickly as the fishermen seed the beds with new stock they are stripped by thousands of diving Eider ducks.
John Lake, a Wash shellfish farmer, said: "They feed 24/7 eating about 2.5 kilos and then come back for more."
"Some of the ducks are now so fat they cannot take off from the water after feeding."
Matthew Mander said: "The ducks are destroying the viability of the Wash mussel industry.
"It was bad in 2004 but even worse this year and the fishermen are now claiming it has reached a point where it is threatening their livelihoods as well as affecting the environment, structure and sustainability of the industry."
An evaluation of the problem is under way and the fishermen have applied to DEFRA for permission to cull the birds.
Fears of fishermen
Chris Durdin of the RSPB said: "An intensive mechanised shell fish industry is incompatible next to one of the most important areas in the UK for bird conservation."
Trials are underway to find a way for the industry to live comfortably alongside the birds and this might mean compensation for fishermen or a cull.
The fishermen fear that the large flocks of ducks may strip the mussel beds and then start on the cockles which live in The Wash as their staple diet is shellfish.
Conor Donnelly, English Nature's maritime conservation officer, said: "The latest surveys undertaken this week have shown 3,000 birds using the mussel beds.
"Eider aren't feeding 24/7 but confining feeding to low water when the mussels are covered by shallow water and the birds can feed quickly and efficiently by up-ending like dabbling ducks.
"The amount of mussel eider feed on depends on the size of the mussel and their energy requirements, and can range from less than 1kg per day to about 2.5kg."
The Wash is the most important wetland in the UK for waterbirds supporting an average population of more than 300,00 over winter.