During low tide in the lower estuary of Lourizan, Spain, groups of mostly women fan out into the wet sands of the inlet. Chatting and laughing, they wear rain boots and carry rakes and buckets. They are clam diggers, and call themselves "the peasant farmers of the sea."

Clam collecting in the expansive inlets of Spain's northwestern region of Galicia is a deep-rooted tradition, handed down from generation to generation. In times past, the women of the Lourizan village would trawl the wet sands while their husbands went to sea, often for several months at a time.

Two basic techniques are used to collect clams. One involves using a rake to scrape the mushy sand, and collect as many clams as possible in a bucket. Other collectors use neoprene waterproof or river-fishing clothing and wade waist-deep into the cold waters further out in the inlet. They use a rake linked to a metal cage to scrape and sift the sand from the seabed before bringing up their catch.

Each day, the diggers are allowed to bring home a total of about 10 kilograms (22 pounds) of two different types of clams. Tides and weather dictate when they can work, but there are also periods when water contamination forces a ban on collecting shellfish. These days, they say, clams of all types are much scarcer, possibly because of climate change.

The collectors sell their catch at the local fish market, from where it is distributed to fishmongers across the country before ending up as expensive dishes at restaurants and homes. Nowadays, their jobs are regulated and the women are guaranteed a wage of sorts, giving them some economic independence — so much so that there are waiting lists for permits that can take years to obtain.

The women relate that, decades ago, the job was much tougher, with no protective clothing and no social security to cover down periods. Many of them didn't even know how to swim. The clam diggers work about three hours a day over 15 or 16 days a month. On average they bring in €100 ($107) a shift, depending on market prices.

The clam fields are replenished constantly by sowing, or planting baby clams that can't be sold. Already-harvested areas are cordoned off to allow them to recuperate, maintaining a cyclical and sustainable industry.