by Dr. Sarah Treanor Bois, PhD
Director of Research & Education at the Linda Loring Nature Foundation
As spring weather finally begins to grace us here on Nantucket, we begin to look for our favorite signs of spring; cherry blossoms, daffodil blooms, spring peeper chorus, osprey returning, and…eels! That’s right, the annual spring migration of young eels is upon us, heralding the start of spring for the island.
The American eel (Anguilla rostrata) is a catadromous eel, meaning Atlantic eels spend most of their lives in freshwater or brackish tidal environments, found along the Atlantic coast. They only return to the ocean to spawn and then die. Their unique life cycle, spawning in the Sargasso Sea and migrating through both freshwater and saltwater, has also fueled both fascination and mystery surrounding their origins and behavior. For thousands of years, the origin of the eel and how and where it reproduces bedeviled a long list of thinkers and scientists. Parts of this life cycle (like what exactly happens in the Sargasso Sea) are still a mystery.
We know eels begin life as an egg with the odds of survival decidedly stacked against them. They hatch into willow leaf–shaped larvae (leptocephalus). Through a combination of natural forces, including currents and propulsion, the larvae slowly make their way to coastal waters. Those that survive their ocean journey transform into small, translucent glass eels several inches long. In the spring, glass eels migrate from the sea and enter brooks, streams, and ponds to feed and grow. We don’t often think of Nantucket as having rivers or streams but our estuaries, where the saltwater meets freshwater, serve that same function.
Upon reaching fresh water, the eel larvae gradually develop pigment and are known as “elvers.” After a few more color changes, they reach their final stage as full-grown adults with greenish, yellowish-brown or black-gray bodies with a white bellies and rounded tails. This is the stage most people think of when you say “eel.” Adult eels can live in fresh or brackish water from 5 to 20 years, consuming invertebrates, fishes, and carrion before they reach maturity and respond to a natural signal that it is time to breed. Mature eels, called neshaw by the Wampanoags, physically transform in preparation for their return to the ocean. Their eyes and pectoral fins enlarge, and they become black on the top and silver on the bottom. At this point they return to the Sargasso Sea to spawn and to die.
Eels have long been a part of the Nantucket tradition. They were part of the natural bounty for the Native Americans that first inhabited Nantucket, the Wampanoag. Later, English colonists relied on eels as an important part of their diet. During eel migrations, a series of nets called weirs were constructed in waterways like Madaket Ditch to trap the eels. In fact, Madaket Ditch was dug by Wampanoag and early colonists in an effort to increase fish runs like shad, herring, and eels. The Wampanoag shared their knowledge of these fish with the colonists. In winter, specially designed spears like barbed tridents were thrust through holes in the ice to catch dormant eels when fresh fish was hard to come by.
Fishing for eels has waned in recent decades and fewer people want to eat local eels. Today eels are primarily caught to be used as bait for larger target species. It’s illegal to harvest glass eels in Massachusetts, but fishing for adult eels (bigger than 9 inches) is permitted with a valid license.
The population of American eels has been declining since the 1970s. Their multi-stage life history has made American eels particularly susceptible to both over-fishing and habitat destruction or obstruction. In Massachusetts, eels appear to generally be widespread across coastal and inland waters, but little quantitative data exists regarding their population status. Climate change is further exacerbating declines, with sea surface temperatures and warming of the ocean currents – currents that swarms of glass eels rely on to get from the Sargasso Sea to the east coast and ultimately to places like Madaket Ditch and Folgers Marsh here on Nantucket.
With a new community science project, Nantucket Conservation Foundation’s (NCF) Jisun Reiner hopes to shed light on Nantucket eel populations and to help people understand more about these amazing creatures. The Nantucket Eel Project’s goal is to understand the migratory pattern of juvenile American eels on island and promote fish conservation. This community-focused science project is an opportunity for anyone on Nantucket to participate in valuable scientific research to help monitor eel populations.
Reiner is NCF’s Coastal Ecology Research Technician. She was inspired to bring this project to NCF after participanting in the Hudson River Eel Project as a high school student. Reiner hopes to elevate the community science aspect providing an opportunity for Nantucket that could mimic her own experience— the spark for science—with the community eel project. It’s more than just eels: it’s learning more about our waterways and natural areas. The methods for this project lend itself well to involving the community while also providing data that will be sent to the state.
The Nantucket Eel Project began as a pilot study in April of 2024, a little later than expected as they awaited state permits. At the time, they had no idea what to expect, but they quickly found eels in every sampling location. Traps (aka “eel mops”) were set at various locations across the island in “upstream” areas and where eels had suitable habitat and had often been seen.
According to the NCF website: The project uses eel mops, artificial habitats that passively collect eels, to catch, count, and release glass eels in select locations around the island. Counting eels will help us understand eels’ general presence or absence and their peak time of migration on Nantucket. We will also learn where the young eels spend their time and their different pathways from the ocean to freshwater. In turn, we will get a fuller picture of our waterbodies’ health and begin to study the influence of environmental conditions, such as water temperature and weather, on eel migration.
Isaac Hersh, Environmental Educator with NCF, has been part of the project from the beginning. Hersh notes: “It’s hands-on science that gets you out interacting with a live animal while collecting real and useful data. It’s a perfect marriage of community science, outreach, and data collection. It can be empowering for people to collect and contribute to research for a species that we don’t have a lot of info about. It’s a living mystery.”
Reiner and Hersh have brought the Nantucket Eel Project to school classrooms across the island, inspiring students of all ages. At the onset of each experience, kids are asked, “What do you think about eels?” Answers generally include comments such as slimy, like snakes, and creepy. Hersh notes that the answers usually change at the end of the experience reflecting enthusiasm for the eels and excitement about the project.
Only in its second year, Reiner and Hersh note that the project is just getting started and is meant to be a long-term community project to provide a decent data set for better understanding of Nantucket eels. So far, every location they put an eel mop has yielded eels. And 2025 is already showing greater numbers than last year. Reiner states, “The coolest thing about this year was to start at the beginning of the migration…to see where the eels have come in bigger numbers first.” Where the biggest swarms of glass eels arrive and when cause both Reiner and Hersh to think about the geography of the eel migration from the Sargasso Sea and how they get to Nantucket—how temperatures, currents, and geography affect the timing.
So why should we care about eels? Jisun Reiner boils it down to four primary reasons: 1. Eels are an important food resource historically and today; 2. They are culturally and spiritually significant in many cultures. Keeping eels alive helps keep those stories alive; 3. As predators, they help control populations of other creatures in our water bodies (namely aquatic insects, small fish, shrimp, etc.); 4. When harvested sustainably they play a pivotal role in aquaculture and are essential to aspects of the fishing industry.
But the real highlight of the project has been getting more people, especially local school children, involved in learning about eels, collecting real data on the Nantucket populations, and having an appreciation for their habitats.
To learn more about the Nantucket Eel Project or to participate, visit the NCF website at nantucketconservation.org/its-surreal-to-be-an-eel-on-nantucket
On Friday, May 2 at 5:30 pm NCF is hosting a talk at the Nantucket Atheneum with eel enthusiast and educator Chris Bowser of the NYS Department of Environmental Conservation. NCF scientists Jisun Reiner and Isaac Hersh will also talk about their research through the Nantucket Eel Project.
