American eels are washing up dead on the shores of northern Lake Champlain, and biologists are investigating what may be killing them.
Vermont Fish and Wildlife Department fisheries biologist Bernie Pientka said people started seeing the eels over the past few weeks, with about 15 of the creatures reported dead on the lakeshore from Swanton south to Milton. It's not yet clear what's causing the die-off, he said.
“We really don't know — we're looking to try to get some samples over the next period of time," he said. “The challenge is that often when we get the reports of them washing up, they're pretty far decomposed, which makes kind of figuring out why pretty challenging.”
An invasive nematode has harmed eel populations in the U.S. Southeast, so that may be a cause, Pientka said. He said other fish species in the lake do not seem to be affected, so low oxygen levels or pollution are likely not factors.
Adult eels have a complicated life cycle. They grow up to three feet long, and then migrate to the Sargasso Sea in the Atlantic Ocean in the late summer and fall to spawn. The migrating eels undergo physiological changes to adapt to salt water and the ocean depths.
“They are thought to use some of the deep water currents to get to the spawning areas, so they have to basically adjust to that higher pressure,” Pientka said.
"The challenge is that often when we get the reports of them washing up, they're pretty far decomposed, which makes kind of figuring out why pretty challenging." — Bernie Pientka, fisheries biologist
Eels are rugged creatures, and can even survive on land for a time when migrating. "They're able to actually go around some areas on land in wet weather," he said. Biologists have found the eels "multiple lakes" up the watershed from the ocean, Pientka said.
"It's kind of amazing that they can get up that far," he said.
Their numbers around the country have been reduced by pollution and dams that block their migration from ocean to freshwater. Lake Champlain once supported a commercial eel fishery, although the population declined in the 1980s and 1990s. But after eel ladders were upgraded on the Richelieu River – which flows north from Champlain to the St. Lawrence River –the population rebounded, Pientka said.
“Right now, when we do our fishery surveys, it’s fairly common for us to encounter these eels,” he said.
The American eel is actually an ancient species of fish, but it’s hard to mistake them for anything else in the big lake. Mature eels are long, slender and are covered with a layer of mucus.
Pientka asked that anyone who sees dead eels to contact the Fish and Wildlife Department at its offices in Essex.
“We’re just trying to figure out what’s going on. It’s a situation in progress,” he said.
