The American Eel
© Parks Canada
Parks Canada works to protect the ecological integrity of our national parks and has a responsibility to protect and conserve species at risk, with a proven track record for their effective recovery. In 2006, after dramatic population declines of up to 99% in Lake Ontario and the upper St. Lawrence River, the American eel (Anguilla rostrata) was assessed as a species of Special Concern by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).
In Atlantic Canada, the eel is found in seven national parks and is of great cultural value to Aboriginal communities. The eel's recent declines in other regions and its potential for becoming a species at risk prompted Parks Canada to work with Aboriginal communities and other partners to embark on a multi-year project both to assess the status of the American eel in Atlantic Canada and to educate Canadians about this fascinating species.
What is it?
Adult eels are known as “yellow eels” and are olive-green to brown on their back and pale green or yellow on their sides and underneath. Adult female eels are usually 60 to 90 cm in length whereas adult males are typically 35-40 cm. Their dorsal and anal fins are long and joined to the tail fin and there are two small pectoral fins behind the gills. Spawning (sexually mature) eels are dark brown or black on top and silver underneath, hence they are called “silver eels”. At this final stage of their life cycle, the American eel's eyes will enlarge and they will stop eating as their digestive system begins to shut down to allow for increased growth of their reproductive organs. To aid in swimming back to the sea to spawn, their pectoral fins will also increase in size.
Where is it?
Range and Distribution
The range of the American eel extends from northern South America to Greenland. In Atlantic Canada, they have been found in all freshwater habitats, as well as estuaries and coastal marine areas connected to the Atlantic Ocean all the way north to central Labrador. This large-scale distribution of a single population is referred to as panmixia, which means that all members of the species mate randomly within a single breeding population.
© Parks Canada
Reproduction and Life Cycle Habitat
Although adult American eels can be found over a very large geographic range, they all spawn in a single location: the Sargasso Sea, a large expanse of the Atlantic Ocean east of Bermuda. It is thought that a single female may release up to 20 to 30 million eggs. After these hatch, eel larvae, called leptocephali, may drift for months on the currents of the Gulf Stream before finally making their way to coastal areas. By the time they reach the coast of North America, they are 5-7 cm in length and have changed into the next life stage in which they are called glass eels, so named because they are completely transparent. Once they enter freshwater estuaries (where rivers meet the sea), they begin to gain colouration and they develop into the next life stage, known as elvers. Elvers may settle in coastal bays or estuaries, or migrate into freshwater rivers, ponds, and lakes. Here they transform into yellow eels as adults, and then, from 4 to 25 years later, into maturing silver eels that migrate back to the Sargasso Sea to spawn and die. The oldest captive eel on record lived for 88 years.
© Ontario Ministry of Natural Resources
Eels are catadromous, meaning they live in freshwater as juveniles and adults, and spawn in the ocean once mature. Yellow eels occupy every type of accessible freshwater habitat, as well as estuaries and sheltered bays. As they grow into yellow eels, individual adult eels will often migrate between salt and fresh water, inhabiting estuaries and bays in the summer, and then moving back up rivers and lakes in the winter. Eels bury themselves in the mud during the daytime in summer, and around the clock in winter.
Larval eels appear not to have a functional digestive system, and may acquire food by absorbing dissolved nutrients. Small yellow els eat invertebrates, but larger ones rely mostly on fish. Once they begin to metamorphose into silver eels and return to the sea, they will no longer eat, forgoing energy spent on feeding in favour of conserving resources for the development of their sexual organs.
For the Mi'kmaq, Wolastoqiyik and Passamaquoddy, the American eel (Katew) is considered a spiritual being and is referred to in Mi'kmaw legends. In addition to its spiritual significance, the American eel was and still is an important food source with medicinal properties and is a ceremonial figure and symbol. In the past, Katew was a staple food source throughout the year; however, it was especially important during the onset of winter and spring when environmental conditions prohibited the Mi'kmaw community from harvesting other fish. One of the various medicinal properties of the eel has to do with the characteristics of its skin. Given its unique ability to be tightened considerably without tearing, eel skin was often used to wrap sprains. It was also worn next to the skin to provide relief from cramps, rheumatism, headaches and lameness. Katew was also used to create decorative ornaments such as a string to tie around hair, described in the legend “Sakklo'pi'k” as being made from eel skin, porcupine quills and sinew.
Why is it in danger?
In recent years, the American eel population has declined by 99% in Lake Ontario and the upper St. Lawrence River. Hydroelectric dams are considered the primary threat to the American eel as they prevent many elvers from entering the Great Lakes, while largely preventing silver eels from migrating to their spawning grounds. Other threats may include overfishing, habitat loss, and an invasive swim bladder parasite. As larvae, American eels have many aquatic predators; however as adults, their predators are fewer and may include avian predators, such as osprey and gulls.
The swim bladder parasite, Anguillicoloides crassus, is a relatively new threat for American eels in Atlantic Canada. This invasive parasite has been steadily expanding its range northward from Texas, and it has been known to spread very easily from one eel to another. A. crassus infects the swim bladder of host eels, causing potential irritation and/or inflammation to the swim bladder and resultant problems with buoyancy. The ultimate effects of A. crassus on its host are unknown, and the parasite is currently being investigated to determine its role in the decline of eel populations.
What is Parks Canada doing?
As the American eel is part of one large spawning population, there is mounting concern in Atlantic Canada that the dramatic declines in American eel populations seen in Lake Ontario may signal decreases throughout their entire range of distribution. However, to date, such declines have not been observed in Atlantic Canada. Given that there is little baseline data on the abundance of eels across Atlantic Canada at any life stage, it is becoming necessary that we begin to collect this data across the region in order to properly assess their status.
The American eel is found in seven national parks in Atlantic Canada, from the west coast of Newfoundland to southern Nova Scotia, and in the Gulf of St. Lawrence and the Bay of Fundy. This presents an excellent opportunity for collaboration. Parks Canada is working with multiple partners, including Aboriginal communities, other federal departments and universities to assess the population status of the American eel in Atlantic Canada. Along with its partners, Parks Canada has initiated a multi-park, multi-partner project to:
- gain a better understanding of the biology of eels in our rivers — including habitat, distribution and life history—through a combination of Aboriginal Traditional Knowledge (ATK) and scientific study, thereby providing much needed baseline data;
- strengthen partnerships with First Nations communities and enable them to aid in both ATK and scientific data collection; and
- increase Canadians' knowledge of this extraordinary species, using its fascinating life history to encourage Canadians to take an interest in protecting American eels and working with us to collect scientific data.
- Kerry Prosper, Mary Jane Paulette. The Mi'kmaq relationship with Kat (American eel), Social Research for Sustainable Fisheries, March 2002
- COSEWIC Assessment and Status Report on the American eel (Anguilla rostrata) in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa.