Sea cucumbers, or 'janitors of the sea', scour and clean the seafloor, allowing other animals to thrive. In the Philippines, a group of women stand guard to help them multiply.

Aweng Caasi, a 61-year-old widow, often sits for hours in a wooden hut towering over waist-deep waters in Bolinao, a small town some 300km (190 miles) north of the Philippines' capital of Manila.

The hut serves as a guard post for fisherfolk protecting a sea ranch filled with sea cucumbers. These unique-looking bulbous brownish-green animals have taken them years to raise.

Caasi's late husband, Ka Artem, was the leader of the fisherfolk group in the village of Barangay Victory in Bolinao that worked with scientists to build the ranch almost two decades ago. They hoped to replenish the supplies of these pickle-like creatures, which once swarmed these waters. Today, Caasi carries on this legacy.

People in the Philippines have been plucking these chunky, leathery-skinned animals, locally known as balat or balatan, out of the sea for at least a century, and their harvesting in Asia goes back to ancient times. Sea cucumbers are from the same family as starfish and sea urchins, and are popular in East Asia for both culinary and medicinal reasons. In Chinese cuisine, they are even regarded as treasure. A kilogram of the most valuable species of dried sea cucumber, the Japanese Apostichopus japonicus, is valued at an average $1,782 (£1,400).

For the Holothuria scabra or sandfish species that the Bolinao ranch produces, prices can vary from $220 to $1080 (£160-790), depending on their size.

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When Caasi was still in her teens, the Philippines was the top producer of wild sea cucumbers – between 1985 and 1993, it exported some 3,000 to 4,000 tonnes. But overexploitation and overfishing led to a sharp decline in stocks. In the 1980s, fisherfolk in Bolinao and its neighbouring island town Anda were collecting up to 100kg (220lb) of sea cucumbers per person a day. The daily per person catch plummeted to just 25kg (55lb) a decade later, and by 2002, to a measly 2.55kg (5.6lb).

The waters around Caasi's home, once crowded with the cucumbers, had become barren.

"We don't care much about harvests, since we care more about increasing their population," Caasi tells me as we sit next to each other in the hut, watching over the sea ranch. "When I was a child, I used to see loads of them, but now that I'm older, they've become so little. We want to restore them so they can multiply."

Apart from their economic value, sea cucumbers provide benefits for the environment. Commonly referred to as the janitors of the sea, they clean sediments in the seafloor by eating bacteria and decaying organic matter, and recycle nutrients that benefit ecosystems. Their presence has even recently been found to suppress diseases among corals. Bolinao and its neighbouring towns are known for their rich marine life, which includes a 200 sq km (77 sq mile) coral reef area that provides benefits to residents through shoreline protection, fisheries, aquaculture and tourism.

Annette Meñez, a marine invertebrate ecologist at the University of the Philippines Marine Science Institute (UPMSI), reached out to the Bolinao fishing communities in the early 2000s to ask if they would like to try co-designing a system to restore the town's sea cucumbers. Meñez has been researching marine invertebrates with UPMSI since the 1980s, including how to help Bolinao's fishing communities replenish their stocks of

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