American Eel

Description

The American eel is an elongate, cylindrically shaped fish with small pectoral fins, long dorsal and anal fins, and no pelvic fins. The head is wedge-shaped with the mouth extending past the eyes, and with a small gill cover located farther down its body. Eels range in colour from transparent to yellow and from green to silver depending on their life stage. Mucus covers its body, making the American eel very slippery. Its scales are very small and are formed in irregular patterns. Female eels are larger than males and can reach lengths of 1 m. By comparison, male eels reach a maximum length of 40 cm.

Distribution and Habitat

The American eel can live in both salt and freshwater. It is found as far north as southern Greenland and as far south as coastal Venezuela and Guyana. In Canada, American eels are found in the waters of Atlantic Canada, southeastern Quebec and southeastern Ontario, including Lake Ontario. Depending on their life stage, American eels are found in rivers, lakes, estuaries and coastal areas. Most of the American eel’s life is spent hiding in substrate, under woody debris, or concealed in submerged vegetation. In the winter, American eels burrow into the mud of bays and estuaries. While they are known to spawn in the Sargasso Sea, east of the Bahamas and southwest of Bermuda, the specifics of this habitat remain a mystery. Despite often being described as catadromous (living in freshwater but spawning in saltwater water), the American eel can also complete its entire life cycle in salt water.

Reproduction and Development

All eels reproduce once then die. The eggs are fertilized externally and hatch as larvae, called leptocephali, that resemble small, transparent leaves. For up to a year, leptocephali are transported on ocean currents from the eels’ spawning area in the Sargasso Sea to the continental shelf of Canada. At this point, the leptocephali transform into their elongated eel shape but remain transparent — this is known as the glass eel stage. Glass eels begin to pigment and lose their transparency when they are about 55 to 65 mm in length. The pigmented eel, called an elver, continues to grow. When it reaches a body length of 30 cm, it is referred to as a yellow eel. The yellow eel stage is the longest stage of the eel’s life cycle. Size is the determining factor for when eels reach sexual maturity. While size at maturation is variable across Canada and different between female and male eels, male eels reproduce at a smaller size than females.

Once the eel reaches the silver stage, it not only takes on a lighter colour on its belly (the silvering), but its eyes and pectoral fins become larger to prepare for its oceanic journey. The eel’s digestive tract also degenerates, so it no longer feeds, among other physiological changes. At this point, the American eel migrates back to the Sargasso Sea to reproduce and die. Eels live 18 years or more before spawning.

Diet and Predation

American eels have a varied diet. Leptocephali eat plankton as they drift along oceanic currents. In brackish water, juvenile and adult eels are carnivorous and feed on small fishes, crustaceans, molluscs, and insects. In freshwater, they are known to eat small fishes, insect larvae, small invertebrates like worms, and molluscs. In the winter, feeding decreases then stops altogether as silver eels prepare for their spawning migration. The leptocephali and juvenile stages are especially vulnerable to predation from other fishes. Larger American eels are food for many large bird species, including bald eagles and seagulls, as well as many large fishes, such as sharks.

Behaviour

Much of the American eel’s behaviour is influenced by its foraging needs, the lunar cycle, and the temperature and level of the water it is in. Eels are most active at night when they are feeding. Some American eels undergo seasonal local migrations between summer feeding areas and overwintering areas. Eel activity diminishes when water temperatures fall to between 6^oC and 12^oC; it increases in water temperatures above 12^oC, when water levels are low, and when rainfall increases. While biologists are unsure of the reasons why, during the last quarter and dark phases of the moon, silver eels migrate downstream in rivers. Similarly mysterious is a behaviour known as an “eel ball.” An eel ball is a large congregation (up to 2 m in diameter) of eels lying motionless in lakes and rivers. Eels can survive out of water if they remain moist and are known to travel over wet areas to reach other water bodies.

Relationship with Indigenous Peoples

Indigenous peoples have a long history of fishing for American eels. They are valued as food and medicine, for cultural purposes, and for contributing to Indigenous peoples’ economies through trade and sale. Considered a gift from the creator, the eel is respected and held in high regard. Indigenous people often fed American eels to the ill to help ease the transition from life to death, as eating eels produces a feeling of relaxation. The Mi’kmaq would offer eels in ceremony so that people could survive harsh winters. Eel skins were used to set broken bones and were also fashioned into hair ties and bindings. The bindings were used for clothing such as moccasins and for tying spears and harpoons onto sticks. Oils from the eel were also used to treat earaches. The declining abundance of eels in Canada is concerning for Indigenous peoples, as Indigenous traditions and practices are connected to the eel.

Threats

Threats to American eels come from both natural and human causes. Commercial, recreational and Indigenous fisheries harvest adult eels and, more recently, glass eels as well. Since these fisheries harvest American eels before they have spawned, the opportunity for cumulative mortality is high even if annual mortalities from fishing or other threats is low. Infrastructure such as hydroelectric dams prevent American eels from migrating up and down river systems. Degraded water quality limits the American eels’ ability to survive. It is suggested that the swim bladder parasite, Anguillicoloides crassus, now common in many areas, may threaten the ability of the eel to reach its spawning destination. The parasite infects the organ needed to regulate buoyancy in the open ocean. The swim bladder parasite arrived through aquaculture imports from Asia and spread through transport of eels to other areas.

Status and Conservation

Overall, the American eel population is declining. In Canada, the Committee on the Status of Endangered Wildlife in Canada lists the American eel as “threatened.” In Ontario, eel fisheries are prohibited under Ontario’s Endangered Species Act. Conservation efforts to reduce eel mortality in the fisheries include increasing the minimum size at which an eel can be legally caught and reducing the amount of glass eels fisheries can harvest. Other measures include shortening the fishing season, eliminating the recreational winter eel spear fishery, and stricter reporting requirements. These measures differ by province and within each province. A stocking program developed for Ontario and Quebec between 2005 and 2010 to counteract local eel declines was suspended as concerns about negative impacts in stocked areas went unaddressed. Trap and transport projects to mitigate mortalities from hydroelectric dam turbines undertaken by Ontario Power Generation are ongoing.