The American eel is at very high risk of extinction in the wild, the International Union for Conservation of Nature (IUCN) announced last month. The organization added the eel to its Red List, where it joins the endangered Japanese eel and critically endangered European eel.

In this first assessment of the American eel, the IUCN saw a troubling trend: a drop of around 50 percent in the population in the past several decades. The decline, abetted by sky-high demand from Asian markets, placed the species in the IUCN’s endangered category. The American eel has only recently become a sought-after fish, since the 2011 tsunami in Japan wiped out eel stocks and Europe banned eel exports a year later. “We saw a big shift from the European eel to the American eel to meet demand in Asia,” says postdoctoral researcher David Jacoby of the Zoological Society of London, who was involved in the American eel assessment. “This set off alarm bells during our assessment.”

The IUCN’s listing, which is not legally binding, echoed a federal commission’s decision last month to curtail eel fishing in the U.S. The commission passed several conservation measures, including lowering the cap on Maine’s glass eel fishery from a quota of 11,000 pounds down to 9,688 pounds for the entire fishery. Glass eels are the juvenile life stage of the American eel, and over the past few years they have brought a fortune to Maine fishermen who have sold the tiny eels to Asian dealers for as much as $2,600 per pound. Maine is one of two states that allow glass eel harvesting, and until last season it had no quota for the fishery. At its high point in 2012, Maine’s glass eel catch represented a $38-million industry.

Maine glass eel fishermen protest the commission’s decision. “A lot of fishermen are upset because we’ve taken a hell of a cut [in our catch],” says fisherman Darrel Young. He attended the commission’s meeting on eel regulations and felt that Maine’s representative did not speak up for fishermen’s interests. “We could have kept (the quota) we had, but the state rep gave in,” he says. Yet fishermen are also somewhat optimistic because the commission voted to let states open a glass eel fishery—or in Maine’s case, raise its quota—in exchange for restoring American eel habitat. This move means fishermen can harvest more eels if Maine reduces its river pollution or knocks down dams to open spawning habitat.

But conservation efforts will need to be extraordinary to bring the eel population back to health. Both the federal commission and the IUCN say that the American eel faces many threats—fishing, dams, water pollution, parasites—but it is unclear how much each threat harms the species. “No one really knows how those threats combine to cause population declines,” Jacoby says. “That’s what makes the conservation piece so tricky.”

Climate change makes the picture even more complicated since it could alter ocean currents. The American eel depends on consistent currents to carry its young from birthing grounds in the Sargasso Sea to inland freshwater habitat where eels mature. Scientists have little idea what might happen to the eel when ocean currents change. “There’s very little data on how this could influence population trends,” Jacoby says, “so we can only really acknowledge that climate change is another possible threat.”