American Eel

(Anguilla rostrata)

Status: Endangered (ESA 2008), Threatened (COSEWIC 2012)

Table of Contents:

Species Identification
Diet
Habitat and Range
Biology and Behaviour
Threats/Reasons for Being at Risk
Conservation and Recovery Strategies
How You Can Help

Species Identification:

The American Eel is a fish species with a long, snake-like body. Females can reach lengths of over a metre while males grow to less than 40 cm. Their fins extend down their backs to the tail and around the underside. They have large lips and their lower jaw is slightly larger than their upper jaw, giving them an underbite appearance. Adults are grey with a white or cream underbelly, and juveniles are yellow-green or brown in colour.

Diet:

The American Eel’s diet changes as they grow and depends on which habitat they are in. In the initial larval stage, American Eels will filter feed on particles like algae and bacteria from the surrounding water. As they mature, they will feed on small insect larvae or invertebrates. Once they reach their primary habitat where they will spend most of their lives, American Eel will nocturnally hunt for fish, molluscs, crustaceans, insect larvae, worms, and plant matter.

Map taken from Hinterland Who’s Who: https://www.hww.ca/en/wildlife/fish-amphibians-and-reptiles/american-eel.html

Habitat and Range:

American Eel will begin their lives in the Sargasso Sea in the North Atlantic Ocean. From there, they will travel along the east coast of the United States and up into Canada, in search of freshwater. Their Canadian historical range consisted of any freshwater connected to the Atlantic Ocean, but today they exist in small patches from Niagara Falls to the Labrador coast. In Ontario, American Eels have a very small population, but they can be found as far as Algonquin Park. Once the Eels are sexually mature at 10-25 years, they will migrate back down to the Sargasso Sea to mate and spawn.

Because American Eels have such a far migration, they use a variety of habitats. Some researchers believe that they have the most diverse habitats of any fish species around the world. They start in saltwater and travel up the coast as they mature, heading to freshwater habitats. They occupy all freshwater habitats up to 15 m deep, which includes rivers, lakes, streams, ponds, wetlands, rivulets, and especially tributaries.

Biology and Behaviour:

Life for the American Eel begins in the Sargasso Sea, where females can lay between 500,000 and 4 million eggs. Larger females have been known to be more fertile and can lay the most eggs. Males will come along and fertilize the eggs, but only a small percentage will actually hatch. Spawning areas in the Sargasso Sea are massive, reaching across several thousand square kilometres. It is unknown exactly where American Eels lay their eggs or how they hatch, but eggs will generally hatch within a week. Eel larvae are translucent and resemble a willow leaf. They use the sea currents to drift north in the Gulf Stream for up to 7 to 12 months. Once out of the larval stage, American Eels will turn into glass eels, which look like small regular eels, only translucent and under 1 cm long. They will swim closer to the shoreline and get darker in colour as they age. Glass eels will reach the mouth of the St. Lawrence river in May, and they will move onto the next growth stage, which is an elver. Elvers are slightly larger and pigmented eels. They will continue their journey north and inland for another 3-12 months depending on their destination. They will grow into immature eels usually when they reach their destination. This life stage is called a yellow eel, and this is where they will grow the most. American Eels in yellow eel form that are still in brackish or saltwater will mature much faster (about 9 years) but be much smaller. Freshwater yellow eels can take much longer to mature and grow much larger, up to about 50 years.

They will spend much of this time buried in the sediment of lakes and rivers, foraging for food at night and burrowing under the mud during the day. During the winter, American Eels will remain buried in the mud of shallower waters to hibernate. Once they become sexually mature, they reach the silver eel stage where they are ready to head back to the Sargasso sea to lay or fertilize eggs and then die. Silver eels will actually undergo another physical change in order to make travelling these huge distances much easier. Their digestive system will shut down, their fins and eyes will grow larger, allowing them to travel faster and prepare for saltwater conditions. Silver eels can be anywhere from 10-50 years old at this point, but the average age of American Eels in Canada is about 22 years. The Canadian population will travel up to 5,500 km to get back to the sea, and migration generally happens from spring to late fall. Spawning will begin from late winter to early spring, and the process starts all over again. American Eels do not have too many predators as they are thought to be near the top of their food chain, but they can still be preyed upon by large fish, Gulls, Eagles, and Ospreys.

Threats/ Reasons for being at Risk:

1. Habitat fragmentation and loss: Dams are one of the greatest threats to the American Eel, as they create habitat fragmentation and may prevent Eels from migrating inland or lead to mortality. There are thousands of man-made dams in watersheds along the St. Lawrence river, many of which completely block access to historical American Eel ranges. Studies have shown that the further inland female Eels travel, the larger they grow and the more eggs they are able to lay. American Eels are also at risk for mortality when exposed to dam turbines, but this is less of a threat than the habitat loss dams create initially.

2. Fisheries: Commercial and recreational fishing of all life stages of the American Eel has led to population losses presently and historically. American Eels take about 20 years to reach sexual maturity, and they only mate once at the end of their life stage. This makes the population unstable when they are exploited in commercial fishing activities. Recently most provinces have set catch limits in order to reduce mortalities by 50%.

3. Changes in our water systems: There have been dramatic ecological changes to our fresh and saltwater ecosystems in the last few decades. Changes in productivity, food webs, as well as the introduction of the Round Goby, Zebra and Quagga Mussels has made vast changes to our water systems and has impacted many important native species. An Eel stocking experiment occurred in 2005, where researchers attempted to raise American Eels to the yellow eel stage and release them into lakes and rivers. This however, created unforeseen negative effects between the domestic and wild populations.

4. Climate change: The initiation of reproduction and migration may be influenced by temperature changes in the water. Climate change has been warming both freshwater and saltwater ecosystems which may tamper with both timing and food supply for the American Eel. Climate change has also created a great deal of uncertainty when it comes to weather, as sudden cold snaps and extreme weather events increase.

Conservation and recovery strategies:

The American Eel is considered an indicator species, which means that their presence or absence in an area can indicate how healthy and normal an ecosystem is. Now that populations are declining, it is hard to determine ecosystem health in our water systems and whether they are partially the cause of American Eel decline. Even though this species is designated as Threatened in Canada, there are no protections in place for them. However, since they are Endangered in Ontario, Ontario’s species and their habitats are protected. There are also limits set in place for the fisheries industry, but more needs to be done to help raise the population. There is still a lot that we don’t know about the American Eel, so more research needs to be conducted to determine best practices for recovery and conservation. Researchers also have created “eel ladders”, which may help them be able to cross dams in Ontario. Researchers and local governments have also been in talks with Indigenous people to find out more about the American Eel and how we can help this species.

How can you help?

Report any American Eel sightings to The Land Between, iNaturalist or your local natural resources office.
Avoid using harmful chemicals near water bodies on your property.
Do not release any invasive species into the wild, and make sure you are not relocating any aquatic invasive species when travelling from one area to another.

Quick Facts:

American Eels were an important food source for Indigenous people, especially during the winter and while travelling
The American Eel is the only fish species in North America that is “catadromous”, which means they start in saltwater habitats and travel to freshwater, which is the opposite of how Salmon migrate
American Eels are able to absorb oxygen through their skin as well as their gills. This gives them the ability to survive temporarily out of water if they need to cross land to get to other water bodies when migrating
The term “slippery as an Eel” comes from the mucous layer that they excrete when threatened, which makes them nearly impossible to hold