Officials are taking "urgent action" to open part of a cockle fishery early to harvest cockles that could die.
Environment Agency Wales opened part of a bed for six days in the Dee Estuary, on the border of north Wales.
The agency said it was the first time such action had been taken.
There is concern densely-packed smaller cockles might not survive, particularly after the recent warm weather.
It is expected the beds will then open as normal on 1 July.
The agency is allowing 60 tonnes of the smaller cockles to be harvested from an area measuring 100m x 30m (328ft x 98ft).
It is thought the cockles left behind will migrate to this space, having more room to grow.This is all part of managing this fishery properly so the cocklers get a good, regular income from the beds David Edwell, Environment Agency Wales
The smaller cockles are expected to fetch about £200 per tonne, compared to an average price of £450 per tonne.
The agency said controls were in place to monitor the effect of the early opening on the amount and size of cockles throughout the season.
David Edwell, the agency's north Wales manager, said: "This action is vital as we do not want to see cockles struggling for space, especially in this heat.
'Ease the pressure'
"This will ease the pressure and give the cocklers an early financial boost ahead of the season.
"The fact we are gearing up for another open season for the fishery this year is also good news.
"Although the numbers of the bigger cockles are down at the moment, the early signs are that it will be a better year next year.
"We could also see these smaller, one year old cockles being ready for harvest later in the season.
"This is all part of managing this fishery properly so the cocklers get a good, regular income from the beds.
"The information that we gain will also help us inform our management of the other cockle fishery we now regulate in the Burry Inlet."
Last year, warm weather, barnacles and algae were blamed on a spate of cockle deaths.
At the time, the agency said warm weather was responsible for the highest number of deaths, with up to 20% on the densest part of the beds suffering "post-spawning heat-related stress".