Cambodia’s concrete ‘reefs’ thwart trawling and create new homes for marine life

Choeurn Hong, 46, was a longtime fisherman on Koh Sdach, King Island, just two miles long off the coast of Cambodia. But now, his bright orange wooden boat is packed with neon life jackets and snorkeling gear for visitors.

Hong switched to working in tourism a few years ago, when he could no longer support his family through fishing.

“I noticed the number of fish declining about seven years ago when there was a lot of illegal trawling at the time,” Hong said.

In June, countries — including the UK and Ghana — committed to bans on the destructive practice of bottom trawling, in which weighted nets are dragged across the ocean floor to scoop up large catches of sea life. But in Cambodia, the island community on Koh Sdach is using a more tangible strategy than the law: Locals are dropping large cement blocks in near-shore waters, lying in wait to snag a trawling boat’s fishing net. The blocks can also help promote biodiversity and increase fish populations by serving as artificial reefs. 

Hong anticipates that the blocks will improve fish stocks and the marine ecosystem around Koh Sdach. He brings tourists on his boat to must-see spots around the island, above coral reefs where floating snorkelers can observe schools of colorful butterflyfish, sea turtles and even a rare seahorse species.

“I want to preserve more coral reefs in my community to attract tourism,” he said.

Industrial trawlers have been coming into community fisheries like the one near Koh Sdach at night, dragging up loads of fish and other marine life. Cambodia’s fishermen reported their catches declined by 40% to 60% from 2017 to 2022, according to the Asian Development Bank.

More than two-thirds of the catch coming from Cambodia’s largest coastal provinces were caught by trawlers, according to government data from 2023. 

The Cambodian government has faced criticism for a lack of enforcement and allegations of accepting bribes to turn a blind eye to illegal fishing. The Ministry of Environment and the Ministry of Agriculture, Forestry and Fisheries did not respond to requests for comment. 

Cambodian trawling boat owner Ta Ngee said he has seen fisheries enforcement officers while on the water, but that his boat does not fish in protected areas.

“I don’t know what else I could do to make a living, this is like farming rice on the ocean for us,” he said. “Yesterday, my boat didn’t make any profit because I spent so much on diesel.”

Ngee took out a bank loan to purchase his vessel. Some days, he struggles to break even because so many trawling boats are competing for fish on the water.

And there are serious costs if one of his trawling nets gets caught on something underwater, including on cement anti-trawling blocks. The net will snap when crew members pull it up, ripping the mesh in multiple directions and leaving it beyond repair. A new one can cost upwards of $1,500.

In Koh Sdach, local fishermen have often gone out on late-night patrols to try and stop the trawlers. But residents are now taking a safer approach, with a project supported by the Cambodian Fisheries Administration and the international conservation NGO Fauna & Flora. 

Kieran Murray, project manager for Marine Species and Ecosystems with the NGO, was part of the team that implemented the project, dropping a row of hollow cement blocks on the sea floor two years ago.

He and Deputy Commune Chief Srenh Sorn took a boat out to locate the blocks dropped two years ago. Once the vessel reached the GPS location of one block, a crew member dropped the anchor to stop the boat, down seven meters (about 23 feet) deep. Twelve concrete blocks, each weighing over a ton, were deployed along a corridor where fishermen say trawlers have been spotted.

“[Concrete] is just really tough and heavy. It’s nothing too complicated,” Murray said. “You have a really heavy piece of concrete that will last a long time. Salt water is corrosive and over time it will degrade all kinds of really tough materials.”

The concrete blocks may also have another side benefit. They can act as a home for new sea life.

“Organisms such as corals can seed onto it and then grow from there. Then you are creating more complexity that more organisms can use as shelter to promote biodiversity,” he added.

While their team has yet to dive to see what is growing on the blocks, seagrass meadows have regrown near cement structures deployed in nearby Kep province, spearheaded by the organization Marine Conservation Cambodia. Data collected by the NGO shows that trawlers began avoiding areas where those blocks were placed in 2018. Cambodia is currently working to deploy 5,000 underwater cement structures along its coast, part of a $104 million initiative to restore the country’s near-shore fisheries.  

Fishermen on Koh Sdach are hopeful they can see those positive results. 

“Coral reefs can last for centuries as long as nothing disturbs them,” said Lorn Lay, a 57-year-old retired fisherman who still goes out on the water.

He has noticed more fish in areas close to the shore, and thriving coral reefs, after the blocks were dropped. He knows that’s good for the local economy, both for tourism and the fishing industry.
Additional reporting and translation by Eung Sea and Vutha Srey. This story was supported by Internews’ Earth Journalism Network.