On a pale blue dawn on the Irrawaddy River in Myanmar (Burma), Maung Lay crouched at the front of his canoe, rapping the gunwale with a short stick. He then made a throaty, high-pitched purr, like the ringtone of an old telephone: his call for assistance.

On cue, the shiny gray flipper of a dolphin broke the surface and waved—dolphinese for: "We're ready to cooperate."

Standing up, Maung Lay pulled a pleated net over his right elbow and shook the lead weights woven into its hem against the hull. At the other end of the 15-foot (5-meter) boat, an assistant splashed the water with an oar.

More dolphins arrived, exhaling heavily as they breached the surface, their mission to corral schools of fish around the canoe. After about a minute, a dolphin flicked its tailfin out of the water, a sort of aquatic thumbs up. Maung Lay responded by casting his net in a wide arc into the tea-brown water.

But when he hauled the net back in, it was empty—not a single fish.

Such scenes are increasingly common on the Irrawaddy River. That's because of "electro-fishing"—a new, and illegal, technique in which rogue fishermen send an electric current through the water to stun fish, making them easier to scoop up in bunches.

The tactic is depleting the fish stocks that feed the already endangered Irrawaddy dolphins and is thought to have inadvertently killed two dolphins. It also seems to have made some dolphins wary of helping legitimate fishermen round up fish, a longtime tradition on the river.

View Images Lauren James, NG Staff Sources: IUCN; Ministry of Environmental Conservation and Forestry 2013

Irrawaddy dolphins (Orcaella brevirostris) live in rivers, lakes, and seas from the northwest Bay of Bengal, in India, to northeastern Australia. In Myanmar, they're critically endangered. Two years ago, 82 dolphins were counted in the Irrawaddy River; today there are no more than 60.

Conservationists say that the increasing threat electro-fishing poses to Irrawaddy dolphins is reminiscent of what happened to the baiji dolphins in China's Yangtze River. Those dolphins were declared extinct eight years ago, in part, it seems, because of electro-fishing.

You Scratch My Back, I'll Scratch Yours

People along the Irrawaddy have fished cooperatively with dolphins for generations. The dolphins take their share of the catch by snapping up fish that try to wriggle free from the net as it's pulled up.

A 2007 report by the Wildlife Conservation Society (WCS) estimated that a good net haul with dolphin assist was about 60 pounds (27 kilograms). Without help from dolphins: a meager 11 pounds (five kilograms).

Maung Lay has been working with dolphins for more than 30 years, but he says the relationship is fraying. "There used to be trust between the dolphins and fishermen—they're no longer obeying our calls as they used to."

View Images An Irrawaddy dolphin breaches the surface of the river. The dolphins are highly endangered and now number no more than 60. Photograph by Minzayar

During the past few months, I've spent several days on a patrol boat run jointly by the WCS and Myanmar's Ministry of Livestock, Fisheries, and Rural Development. We've been reconnoitering a 40-mile (72-kilometer) reach of the river north of Mandalay that has been set aside as a protected area, where fishing with certain types of dragnets and gill nets is banned.

There was a time when the dolphins would wake a sleeping Maung Lay with a squirt of water to start the night's fishing. He would call out their names—Thangina and Thandima were his favorite dolphins.

These days the dolphins seem reluctant to heed Maung Lay's calls, and they rarely come anywhere close to his canoe.

I spent several frustrating hours watching Maung Lay cast his net in vain. Even at night, when the fish swim to the surface to feed, his catch was scanty—a fraction of what he routinely caught a decade ago.

"When I was young, I was happy—there were so many fish," he said.

View Images Village dogs greet Maung Lay, a self-styled dolphin whisperer, at the end of a day's fishing. Maung has been teaching his son (in the canoe) how to fish with help from dolphins before that long-held tradition is lost. Photograph by Minzayar

A New Way to Fish

The first electro-fishing boats appeared on the Irrawaddy around than ten years ago. Fishermen used small batteries and wire wound around bamboo poles to create a shock, whose radius was not much more than a yard. Even so, the method zapped a lot of fish and was cheap, and it spread like a virus along the river.

During the past three years, violent gangs of fishermen have been stalking the Irrawaddy. Their more sophisticated technique is to thread copper wires through trawling nets, and then connect the wires to banks of car batteries and high-voltage transformers. The heavy doses of electricity sent into the river by this method stun a whole lot more fish.

A significant part of the problem is the way the regional government parcels out fishing concessions on a year-by-year basis through competitive bidding, creating an incentive to pull a lot of fish out of the river as quickly as possible.

"It's clearly not a sustainable fisheries system," said a conservationist who asked to remain anonymous. Under that system, the conservationist said, "fishermen are trying to maximize their catch before their concession ends."

"When I started fishing in 1984, it was easy," Maung Lay told me. "There were many fish, and the water was clean. Since 2005, I haven't caught so many. It's electro-fishing."

Electro-fishing is illegal in Myanmar, carrying a three-year prison sentence and a fine, but those penalties aren't enough to stop the battery-powered marauders.

The "electro-fishermen" (who come from the same riverside villages as people like Maung Lay) often use the traditional calls to dolphins. If the dolphins respond and go to work rounding up fish, they get stunned too—and worse.

View Images These fishermen use electric current to stun fish. The method, called electro-fishing, is illegal on the Irrawaddy and is so efficient that it's depleting fish stocks. Photograph by Minzayar

On December 4, 2014, two dolphins, a young male and female, were found dead in a protected stretch north of Mandalay, not far from Maung Lay's village.

"We saw no injury or sign of them becoming entangled in nets," said Kyaw Hlay Thein of the WCS, flicking through photos of the dolphins' carcasses on his cell phone. "We found no sign of toxics."

The photos show two slate-gray dolphins with bulbous heads and the signature dolphin grin being examined, then buried in the sandy riverbank. Their skin had already begun to peel away, revealing pink flesh underneath.

According to Kyaw Hlay, autopsies indicated that the dolphins were victims of electro-fishing.

"When they died, it felt like a member of the family was gone," Maung Lay said.

As the waterborne mafia has become more organized and aggressive, electro-fishing has become more lethal and widespread. Locals who try to stop electro-fishermen by reporting them to the police do so at their peril.

In U San Win's village, people tried to stop the electro-fishermen. "They threatened to burn down our whole village," he said. "We couldn't persuade them to stop, and now we're afraid to report them to authorities."

"The collaborative fishing will completely disappear if something isn't done," Kyaw Hlay told me.

Our patrol boat captain was too afraid to stop at one village where, after he informed authorities, several electro-fishermen had recently been arrested.

Maung Lay says he's concerned that the electro-fishermen don't realize—or care—that their unchecked avarice is pushing the dolphins toward extinction. "Regret always comes too late," he said.

View Images Fish prices at this market in Mandalay have risen dramatically in recent years, as stocks in the river have plummeted. Environmentalists blame overfishing, chiefly by electro-fishermen. Photograph by Minzayar

Cooperative Covenant

Villagers along the river revere Irrawaddy dolphins, which are woven into their folktales. The animals are integral to their culture and identity.

The late dictator Ne Win, who was Burma's head of state from 1962 to 1981, is said to have bathed in dolphin blood to keep him youthful.

Records show that cooperative fishing with dolphins has been going on in Myanmar for at least 150 years. And the dolphin-fisherman bond has been so close that particular dolphins came to be associated with certain villages.

An 1843 edition of Zoologist: A Monthly Journal of Natural History notes that fishermen sometimes sued one another to recover their share of a catch in which "a plaintiff's dolphin [was] held to have filled the nets of a rival fisherman."

Over a lunch of rice and fermented fish paste in the village of Shein Makar, Maung Lay told me how, according to local mythology, this extraordinary relationship began.

There was once a Buddhist monk in Bagan, the ancient capital of what was to become Myanmar, who made it rain gold and silver. At the time, some struggling local fishermen were sleeping and missed the rain.

One day a wife of one of the fishermen was crying by the riverbank and said to her friend, "How can we feed our children and make enough money to send them to school if there aren't any fish?"

A pair of dolphins overheard the commotion and asked why she was crying. They made a covenant with the woman: "We will help find fish for you, but you have to be faithful and must not betray or harm us."

From that day forward, the dolphins have helped more than triple the size of the average catch of net fishermen on the Irrawaddy.

View Images A girl fetches water from the Irrawaddy River, eulogized as the "Road to Mandalay" in Rudyard Kipling's 1892 poem, "Mandalay." Photograph by Minzayar

Other Threats to the Dolphins

Electro-fishing is a grave threat, but dolphin-watchers also worry about logging, dredging, and gold mining.

Since the early 1990s, when Western governments imposed economic sanctions on Myanmar after the junta failed to recognize the landslide election of democracy icon Aung San Suu Kyi, the government intensified exploitation of teak and rosewood forests.

According to the United Nations Food and Agriculture Organization, in two decades one-fifth of the nation's forest cover was stripped. Soil erosion increased, and silt washed into the Irrawaddy.

"There's more erosion and turbidity, which indicates how much mud is in the water," explained Myo Aung, a river dolphin expert for the government. "This kills the small fish and affects the food chain the Irrawaddy dolphin feeds on."

Meanwhile, river dredging to keep the waterway open for barge traffic and gold mining in government and rebel-held territory upstream of the protected area have added to the river's sediment burden.

Early last year, I visited a gold mine controlled by the Kachin Independence Army, a rebel group opposed to the central government, about 300 miles (500 kilometers) northeast of Mandalay. The bleak, treeless landscape looked like a World War II battlefield, and milky red water seeped into the local stream.

The water's burgundy color is a side effect of the extraction process, in which water under high pressure is used to free fragments of gold from the red-brown earth.

Worse still, mercury, used to amalgamate gold, is released into the river. Once there, it's ingested by fish and gradually accumulates at the top of the food chain, inside dolphins and people.

Spectrum, a local extractive industries watchdog group, stated in a 2014 report that although mercury levels for fish in the Irrawaddy are not known, it's highly likely that they carry "large proportions of mercury."

View Images People offload stacks of wood from a boat at the jetty in Mandalay, Myanmar's second largest city and last royal capital. Photograph by Minzayar

Can the Irrawaddy Mafia Be Stopped?

Electro-fishing gangs, ever more brazen, have begun working in teams of up to a dozen boats, equipped with bigger engines, that can easily outrun river police and conservation patrols.

They've been known to attack officials with catapults loaded with sharpened nails and have even seized back electro-fishing equipment confiscated during raids.

Fishermen from several villages claimed government officials have even sold equipment back to busted gang members.

Han Win, a government dolphin expert, says that too often the gangs plunder the river unchallenged, and that even when electro-fishermen are arrested, they rarely get the maximum jail time. Local judges "aren't giving harsh-enough sentences," he said.

There's some reason for optimism, perhaps. A specialist river police team was established recently to combat a separate spate of river piracy around Mandalay. The police, the WCS, and the fisheries ministry have started patrolling together.

Over the longer term, Han Win told me, ecotourism may offer the best hope for the last surviving Irrawaddy dolphins. Dolphin-watching excursions will put tourist dollars into the pockets of villagers and, he suggested, help end behavior that threatens the dolphins.

A pilot program has already sent six groups of tourists upriver, giving them an intimate dose of local culture and cuisine.

"Even electro-fishermen may swap their livelihood for ecotourism," Han Win said, "because I don't believe they want to live on the dark side."