The fisherwomen at the heart of Europe's shellfish industry in northwest Spain have been reporting a worrying die-off that is hitting just when holiday season demand is soaring. 

The nutrient-rich silt of Galicia's chilly Atlantic estuaries — known as rias — is normally fertile ground but not after extended periods of heatwaves and abnormally heavy rainfall.

Around 4,000 people, almost all women, work as traditional shellfish catchers known as "mariscadoras" in the inlets that criss-cross the region's rugged coastline.

"In the 42 years I have gathered shellfish, I have never seen a year as bad as this," Juana Maria Martinez told AFP.

Working at the small beach on the island of Arousa near the city Santiago de Campostela, she wore dishwashing gloves and carried a long-handled spade used to dredge up shellfish.

In recent weeks these shellfish collectors report that at some beaches 60-80 percent of the shellfish they find are dead, sparking concerns for their livelihoods.

Across the region "there's the same problem, there's nothing… the Christmas season is going to be a total disaster," said Carmen Suarez, who scrolled through photos of dead shellfish on her phone.

"These are the clams under the bridge. You can see perfectly that they have their mouth half open and their little tongue out. That means that there is no turning back, they are dead."

Heavy rainfall in October and November has caused the salinity in the region's estuaries to be abnormally low, making it hard for shellfish to survive.

In addition, the seawater temperature is abnormally high at the end of a year marked by several heatwaves.

Scientists say heatwaves have become more likely due to climate change, which has also disrupted rainfall patterns.

"What scientists are telling us is that the warming of the air, the warming of the water and pollution directly influence the shellfish, which become weaker" and eventually die, said 57-year-old shellfish catcher Sandra Amezaga.

A spokesman for the Galician Federation of Fisherman's Associations told AFP that while the mortality figures "vary a lot from place to place" there are "tonnes and tonnes of dead shellfish".

The fisheries minister in the Galicia's regional government, Alfonso Villares, pledged at the end of November to ask that Spain's central government declare a state of emergency for the areas affected. 

"This is a truly exceptional situation," he told the regional parliament, adding the regional government would "take the necessary measures" to help workers in the sector.