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American Eel

American Eel

Project Summary

Historically, the American eel had the largest geographic range of any fish species in the western hemisphere, and had a dominant position by numbers and biomass in many habitats it occupied. As such, American eel is a very important component of Canadian biodiversity, possibly playing a key role in habitats where it exists.

American eel have a long, slender, serpentine body, with a single dorsal fin running from about a third of the way down their back that continues into their caudal and anal fin. Their skin is covered in a protective slime layer, and they have a protruding lower jaw. Female American eel can grow to a size of about 1metre, while males are generally smaller. 

Committee on the Status of Endangered Wildlife in Canada has designated the American eel as threatened since May of 2012. Populations have declined by as much as 65% in the last 14 years in the St. Lawrence and Lake Ontario area. In parts of the Maritimes, substantial declines have been documented. Although the reasons for the decline are not completely known, key threats have been identified. These threats,both natural and anthropogenic, include fishing, dams and turbines, contaminants, environmental degradation, and a parasitic nematode that affects the swim bladder.

To date, no decision has been made as to the addition of American eel to the Schedule 1 list of SARA. There is, however, a National Management Plan for American Eel developed by the Canadian Eel Working Group. Coastal Action's “American Eel Habitat Assessment" project in Lunenburg County, NS specifically addresses 2 of the 8 listed objectives in this management plan: (Obj#2) “Achieve a net gain in abundance and escapement by ensuring access to and passage from quality habitats…” and (Obj#4) “Develop a decision support tool for identifying and prioritizing actions to improve habitat for eels”.

Coastal Action currently performs two studies involving American eel; an elver abundance study on East River, Chester and a silver eel study on East River, Chester and Oakland Lake, Mahone Bay. 

Life History

American eel are catadromous, meaning that they spawn in the ocean and return to freshwater systems to live and mature. Only when they are sexually mature do they begin their return to the ocean. This life cycle encompasses two very large and long migrations, one of which begins as a fertilized egg in the Sargasso Sea. The eggs hatch and the larvae produced are called leptocephalii. Leptocephalii are clear and willow leaf shaped. They are carried along by ocean currents for as long as one year before reaching the shores of North America. Once leptocephalii reach the continental shelf, they metamorphose into glass eel. Glass eel are typically 50-80mm long, unpigmented (clear), and resemble the shape of an adult eel. Glass eel begin to pigment as they grow at which point they are referred to as elvers. Elvers are defined under the Canada Fisheries Act as eels less than 10cm in length. 

Juvenile eels are referred to as yellow eel. Yellow eel have a dark brown to black back and a light yellow to dark green belly. American eel remain in this stage anywhere from 4 to upwards of 25 years. 

The final metamorphosis is one that accompanies sexual maturity and is called the silver eel phase. Silver eel are characterized by their black to dark grey back with a silver or white belly, as well as certain morphological and physiological changes. Morphological changes include the change in skin colour as well as integumental thickness, increased eye size, body length, and weight, as well as changes in the shape of pectoral fins and snout. Physiological changes include the degeneration of the digestive tract, visual pigment changes, skeletal muscle function and composition modifications, alteration of swim bladder structure, change in locomotory behaviour, a higher density of chloride cells in the gills, as well as gonadal development. These new characteristics prepare the eel for its long seaward migration. 

The Sargasso Sea has been designated as the eel’s spawning area due to the number of young larvae found floating in these waters. Spawning has not been observed, but due to no adult eel ever returning from the Sargasso Sea after spawning, it is assumed that silver eel die shortly after. 

American eel are thought to be a panmictic species, meaning that the species has a single, randomly mating population. Each year, during late summer or autumn, the silver eel leave their freshwater residences and migrate anywhere from 2000 to 6000 kilometers from North American shores to the Sargasso Sea. American eel meet in the Sargasso and undergo a mass spawning event.

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Species Importance

American eel are an important component to freshwater ecosystems. They are a top-order predator, which can help regulate the populations of other animals. Eels have a large array of food sources which includes other smaller fish, insects, amphibians, as well as decaying organic matter. Eels are also a significant food source for larger fish, mammals, and birds. 

American eel can also be used as a bioindicator for pollution, as they often remain in the same system their entire lives and they are long-lived. 

American eel are of great importance to Mi’kmaq people as they were once historically fished as a significant food source and continue to be fished. Eels are very nutritious and have a high fat and protein content. American eels also preserve well for travelling or long-term use after they are smoked or dried. Aboriginals also have important cultural meaning and practices associated with the American eel, which in Mi’kmaq language is termed Ka’t, including ceremonial and medicinal uses. 

Fishery

Fisheries exist in Canada for American eel elvers, yellow eel, as well as silver eel along the St. Lawrence River, and in New Brunswick, Nova Scotia, Newfoundland, and Prince Edward Island.

The elver fishery began in 1989 in response to demand for elvers in aquaculture for Asia. Most of the harvest of yellow and silver eels is exported to Western Europe. Live eels are preferred rather than frozen eels for the export market and silver eels are preferred to yellow eels because of their larger size and higher fat content. Due to the demand for live eels and their high value, airfreight is used to ship them to export markets. 

Large quantities of eels are smoked, jellied, or marinated. Tanned eel skins have also been used in high quality leather products. Elvers are primarily shipped to China and Taiwan for aquaculture purposes, while some are sent to Spain for consumption

The worldwide demand for eels is greater than can be supplied by natural means, therefore eel aquaculture has become a major source of eels for the market. Eel farming is widespread in Japan, Taiwan, and China and, to a lesser extent, in Holland, France, and Italy. In Canada, several attempts have been made for eel aquaculture but few have been successful over the longterm, mainly due to variable market conditions. 

With the large market for American eel elvers and adults, their large role in their ecosystem, as well as how meaningful they are to Aboriginals, it is clear to see their ecological and economical importance and why Coastal Action aims to learn more about them and to support a sustainable fishery.