BREWER, Maine >> Changes in the worldwide sushi industry have turned live baby American eels into a commodity that can fetch more than $2,000 a pound at the dock, but the big demand and big prices have spawned a black market that wildlife officials say is jeopardizing the species.

Law enforcement authorities have launched a crackdown on unlicensed eel fishermen and illicit sales along the East Coast.

Although not a well-known seafood item like the Maine lobster, wriggling baby eels, or elvers, are a fishery worth many millions of dollars. Elvers often are sold to Asian aquaculture companies to be raised to maturity and have become a linchpin of the sushi supply chain.

But licensed U.S. fishermen complain poaching has become widespread, as prices have climbed in recent years. In response, the U.S. Department of Justice, the U.S. Fish and Wildlife Service and other agencies are investigating clandestine harvesting and sales.

Operation Broken Glass, a reference to the eels’ glassy skin, has resulted in 15 guilty pleas for illegal trafficking of about $4 million worth of elvers. Two people are under indictment, and more indictments are expected.

In Maine, more than 400 licensed fishermen make their living fishing for elvers in rivers such as the Penobscot in Brewer and the Passagassawakeag in Belfast every spring. They say law enforcement is vital to protecting the eels and the volatile industry.

Randy Bushey, of Steuben, has been fishing for elvers since 1993. He said he saw his income balloon from as little as $5,000 per year in the 1990s to more than $350,000 in 2012. He said tighter quotas mean he’s earning less these days, and in the most recent season he made about $57,000.

“I’ve seen the best, and I’ve seen the worst,” Steuben said. “I want to see it preserved. I want to see it straightened out.”

The elvers are legally harvested in the U.S. only in Maine and South Carolina. The American eel fishery was typically worth $1 million to $3 million per year until 2011, when the economics of the industry changed. Asian and European eel stocks dried up, and the value of American eels grew to more than $40 million in 2012 because of demand in China, South Korea and other Asian countries.

Investigators also turned their eyes to poaching in 2011, the Department of Justice told the Associated Press. The investigation of people who catch, sell or export elvers illegally has ranged from Maine to South Carolina; a New York seafood distributor was among those netted.

In one case, federal prosecutors said, three men pleaded guilty in November 2016 to trafficking more than $740,000 worth of elvers harvested illegally from the Cooper River in the Charleston, South Carolina, area. In another, Richard Austin pleaded guilty in federal court in Norfolk, Virginia, to trafficking more than $189,000 in illegally harvested elvers from 2013 to 2015.

The federal agencies involved in the poaching investigations say there’s no end date for their probe. The Department of Justice declined to speculate on how many poachers there are and how many arrests are expected. A conviction for violating the Lacey Act, which prohibits illegal wildlife trade, can carry a penalty of up to five years in prison and a fine of as much as $250,000.

Investigators go undercover to track poachers, posing as people illegally fishing for elvers. They also follow eel migrations, hoping to catch illegal fishermen on the spot. Investigators also track catch records, which are required by states, to look for possible illegal fishing and selling along the supply chain.

The legwork is necessary because illegal trade in elvers jeopardizes the species’ long-term sustainability, said Jeffrey H. Wood, acting assistant attorney general with the Department of Justice’s environmental division.

Maine’s fishery for elvers is the biggest on the East Coast, making it the sole reliable source of the eels in the U.S. To prevent overfishing, fishermen are limited to catching them for only a few weeks every spring.

The eels hatch in the ocean waters of the Sargasso Sea, a weedy patch of the Atlantic Ocean between the West Indies and the Azores. They then follow currents back to rivers and streams from Greenland to Brazil. Mature eels that avoid hazards including fishermen’s nets, predatory fish and the turbines of hydroelectric plants will one day return to spawn in the Sargasso.

The baby eels are tiny at the time of harvest, weighing only a few grams when they are scooped with dip-nets or trapped with larger nets that resemble small soccer goals.

A well-managed eel fishery is critical to the health of the rivers and streams they swim in, said U.S. Fish and Wildlife Service Deputy Chief of Law Enforcement Ed Grace. Eels are important to the marine ecosystem because they serve as both predator and prey, feeding on fish and mollusks and serving as food for larger fish, seabirds and turtles.

“While the big charismatic animals like bears, big cats and eagles tend to grab all the public attention, it’s often the smaller, more obscure animals that are crucial to regional ecosystems and economies,” Grace said.

Some eels harvested in Maine eventually return to the U.S. as sushi dishes such as unagi. They’re also used for other food products, such as grilled eel dishes popular in Asia.

Sunny Chung, chef and owner at Yobo in Portland, gets Maine eels from American Unagi, the only American eel farm in the state. He described Maine eels as a top-notch product and “the only eel that we use.”

Going after scofflaw fishermen will help ensure the eels keep filling that commercial role, said U.S. Rep. Jeffrey Pierce, a Republican from Dresden who’s adviser to the Maine Elver Fishermen’s Association.

“We are committed to ending these problems,” Pierce said. “It behooves us to.”