One hand clinging to his boat's gunwale, Harun Muhammad submerges himself, eyes and ears wide open underwater as he "listens" for fish sounds emanating from the blue depths.
Harun is one of Malaysia's last "fish listeners," and he and his apprentice son Zuraini are believed to be the only active practitioners of this mysterious and dying local art.
"When you listen, it is like through a looking glass -- you can see mackerel, sardine," said Harun, 68, who has fished the Setiu lagoons on Malaysia's rural east coast his whole life.
"For us, we only look for gelama (a type of croaker). But in the schools of gelama, there will be other fish. The gelama is the king of fish."
Other fish listeners have passed away, retired or turned to modern fish-detection technology as the traditional practice has retreated in the face of dwindling catches and proliferating undersea noise.
Studies show Malaysian waters lost 92 percent of fishery resources between 1971 to 2007 due to overfishing.
"You can't copy our technique. You must gain the skill and learn the lay of the waters," said Harun.
"The wholesalers tell me, 'if you're gone, there will be no more gelama'," which fetches up to ten times the price of similarly sized fish.
"Pak Harun", as he is known locally -- "Pak" is a Malay honorific similar to "Uncle" -- finds it hard to describe exactly how fish sound, but likens it to pebbles being dropped into water.
"They have a voice. This sound is this fish, that sound is another. When someone is new, they can't tell one fish song from another."
Harun and his crew of a dozen can go nearly a week without hearing gelama -- which invites scepticism about the claimed fish-listening ability.
But experts in sonifery (fish sounds) say sailors have long heard sounds of whales and fish through boat hulls.
"Scuba divers often do not hear anything because their breathing and bubble exhaust makes so much noise. However free divers, or divers using quiet re-breathers, can hear much better," said US-based marine ecologist Rodney Rountree.
Former fish listeners describe a range of techniques. Some claim they can feel changes in water temperature.
For Harun, it is a multi-sensory experience requiring eyes wide open.
"After a while, it is as if you can see. Even though the fish is very far, you can sense it in that direction and you go there. Only when you get close, you can hear the fish clearly," he said.
Though he sports a slight paunch on his sun-darkened frame under a spiky white head of hair, Harun remains sprightly despite his years, deftly clambering in and out of his boat in search of fish sounds.
Once he pinpoints a school of gelama, his crew -- who have hung back with engines off -- motor forward, drop their nets and strike the sides of their boats to spook the fish into the mesh trap.
"You think it's just stupid fish but they can see you coming. When they hear the sound of the boat, they run. The fish cry or shout and then their friends swim away," he said.
Listening in vain
Landing a rich catch was easy when stocks were abundant, Harun said.
But after decades of overfishing, he now "listens" up to several dozen times under the scorching equatorial sun before catching a snippet of gelama song.
Modernisation, including sand dredging, aquaculture, factories and fishing trawlers have transformed the Setiu wetlands, a rich but threatened coastal ecosystem centering on a 14-kilometre (9 mile) long lagoon along the South China Sea.
The state of Terengganu is seeking to make it a protected park.
But Harun's catch is increasingly unpredictable, averaging about $2,000 per week gross, leaving little left over after all crew are paid, and fuel, maintenance, and other costs are deducted.
"Each year, the catch has reduced. But I'm not good at anything else, so I still have to do this," said his son and apprentice Zuraini.
Malaysia ranks among the top consumers of seafood in the world.
Intergovernmental industry researchers Infofish say Malaysians eat an average of 56.5 kilogrammes of seafood per person annually, more even than Japanese.
The global average is 20 kilos.
WWF-Malaysia chief Dionysius Sharma said overfishing threatens to leave Malaysian waters "vast and barren".
The organisation warns Malaysia's waters could run out of seafood by 2048.
Despite the long odds, Zuraini, 44, said someday he will train one of his own sons. "I don't want to see this practice die off," he said.