The American Eel:
A Journey Of Glass And Silver

It’s springtime and the world is on the move. Amphibians gather in vernal pools, rivers teem with herring, and chirping osprey crowd the sky. Another migration is a bit harder to see: the marvelous journey of the surprisingly superlative American eel. 

The American eel, Anguilla rostrata, is one of two eels to be seen in Massachusetts; the other being the marine conger eel. Of all the fish in the world, Anguilla eels occupy the most diverse habitats. American eels range from Venezuela to Greenland and Iceland, living everywhere from the open ocean, to rivers, lakes, and swamps. More mobile than other fish, they can access seemingly isolated bodies of water, moving as far inland as Wisconsin and Ontario. Prior to river damming, overfishing, and industrial pollution, estimates suggest they accounted for 25-50% of freshwater biomass in some waterways.

The far flung populations of these creatures is even more amazing considering that, unlike other freshwater fish, they start their lives in the ocean. Fish that move between freshwater and saltwater to reproduce are diadromous. Most of these, like herring, are anadromous; they mature in the ocean and swim upstream to lay eggs. American eels are North America’s only catadromous fish, meaning they do that in reverse. Their journey begins in the Sargasso Sea surrounding Bermuda. The only full oceanic sea, it sits in the Atlantic Subtropical Gyre, an enormous eddy in which floats Sargassum seaweed. The “rainforest of the Atlantic,” this is a nursery for many creatures, including our eel’s counterpart, the European eel, which has a similar life cycle.

Anguilla eels have long been an important food source for people on both sides of the Atlantic, but their life-cycle was a mystery. The question of these eels’ origins was solved in 1923, by trawling the Atlantic for smaller and smaller eels until converging on the Sargasso Sea. We know they begin their lives as tiny, leaf-shaped zooplankton, called leptocephali, that float on the currents. It takes them 8-12 months to reach the shore, by which time they have grown more eel-shaped. Less than 4” long and transparent, these are dubbed “glass eels.” Between 4-8” long they acquire pigment, and are called “elvers”. The glass and elver stages are what we will see migrating upriver.

As they settle into their freshwater homes, they become “yellow” eels. Unlike herring, they stay upstream for a long time, around 15-20 years. The oldest found in the wild was 40 years old; one even reached 88 in captivity. After their long freshwater stay, they migrate downstream in the fall as “silver” eels. The females can be up to 4 feet long, though males are usually under 8 inches. It is believed that they do not eat on their return to the Sargasso Sea, where they will spawn and die. Questions remain: attempts to track adults on their ocean migration have failed; adult eels have never been seen in their spawning grounds. In 2008, scientists at Umass Dartmouth managed to coax eels to lay eggs which successfully hatched. Though too intensive of a process to be viable for farming, this was a major milestone for understanding Anguilla rostrata.

Eels hold another record: due in part to their popularity in Asian cuisine, they are the most poached animal, accounting for about half of all the value of poaching globally. Since we don’t know the specifics of how they reproduce, they cannot be farmed like other fish. Instead, young eels are caught and raised to adult-hood. In 2010, Europe banned the export of elvers for conservation purposes. In 2011, the devastating tsunami off of Japan destroyed much of the Asian eel infrastructure. These two factors caused the price of American eels to jump from $25 a pound to more than $2,000. This sudden price increase gave rise to a massive international poaching ring, culminating in a multi-state sting called Operation Broken Glass, which resulted in hundreds of arrests.

Thanks to conservation efforts and their own tenacity, local eel populations have largely stabilized. Dam removals, like at Red Brook, and eel passes, such as one on the Wankinco River by the old Tremont Nail Company, help eels navigate altered waterways. Though small, with a careful eye and some luck, you can witness their incredible journey.

By Justin Cifello, Land Trust Member and Volunteeer