Urgent action is being taken to try to save the cockle beds off Gower.
The Environment Agency said its officers and other specialists confirmed the shellfish have started to die again this year in the Burry Inlet.
It has opened the beds for harvesting early to gather smaller cockles and has doubled the cockle gatherers' daily allowance.
It is hoped that by thinning the beds of the smaller cockles it will give the larger ones a better chance to survive.
Investigations were ongoing into the cause of the cockle deaths which have hit the industry hard over the last few years.
But the agency said an interim study has not found any evidence to link the problem to pollution.
John Hogg, environment manager for the agency, said: "The steps we are taking, initially, are to make sure that in the difficult circumstances of cockle mortalities these cockles aren't wasted and the cocklers can get a return on their licence fee.
"What it will also help us to do is see how the cockles respond to this kind of thinning of the beds.
"It may be that it will give the other cockles in the beds that are un-fished a better chance of survival and give us a clearer signal as to why they are dying.
"It will also make sure that local bird life of this special area still have enough shellfish to eat."