Counting eels has helped scientists understand that American eel populations are increasing. Hudson River nets caught an average of 17 eels a day in 2008. In 2020, they caught an average of 504. That’s great news for these mysterious nocturnal animals, listed as endangered by the International Union for nature conservation, partly due to habitat loss and dam construction.
“We still have a long way to go before we reach historic levels,” says Mount. But thanks to habitat restoration and other work, “we are moving in a positive direction.”
There are 19 species of freshwater eels, and they all start their lives in the Sargasso Sea. It is part of the Atlantic Ocean, off the coast of North America and the Bermuda Islands. A female eel spawns in lush sargassum, a type of seaweed. Its millions of larvae are swept out to sea by strong ocean currents and head west (American eels), further west (Japanese eels) or east (European eels), for example. The American eel is the only catadromous fish species in North America. In other words, they live in fresh water and return to salt water to spawn.
By the time the baby eels reach the mouth of the Hudson River in New York, the Chesapeake Bay in Maryland or the Mississippi River in Louisiana, they have been in the water for a year. They are two inches long, translucent, and extremely strong and sinewy. They then develop into glass eels, then into yellow eels. Around the age of 20, they grew into four-foot silver eels.
By then they will have swum to the muddy bottom of the streams that have become their longtime homes. The males will die there. Females, which live longer than males, travel more than 1,000 miles to the Sargasso Sea. They reproduce, then die.
Back on the Hudson, Mount and his volunteers open the bottom of the fyke net tunnel and carefully remove the eels. They place them in a bucket and count them: 74 glass eels today. Volunteers weigh the eels and place them in a resealable plastic bag filled with water. They give the eels a lift upstream, bypassing hungry fish and a waterfall that would take a lot of effort to climb. Although, says Mount, “eels are a really resilient species. They can swim on land to circumvent barriers, as long as their skin is moist.
Mount hopes that resilience will keep eel numbers growing for years to come. And that his work with eel counters will help scientists solve many of the remaining mysteries, such as their migration routes, how they spend their days, and where they breed in the Sargassum. “They have very complex life cycles,” says Mount. And there’s so much more to learn about them and how to save the species from extinction.