Fishes of Canada's National Capital Region
Species Accounts
Anguillidae - Freshwater Eels - Anguilles d'eau douce
Freshwater eels are found world-wide in temperate to tropical waters except for the south Atlantic Ocean and the whole eastern Pacific Ocean. There are 16 species with 1 occurring in Canada and the NCR.
The term eel-like is based on the body shape of freshwater eels and includes the muscular slipperiness associated with this fish and its mucus-producing skin. Both dorsal and anal fins are long and join the tail fin. The dorsal fin begins well behind the pectoral fin level. There are no pelvic fins and the pectorals, when present, are on mid-flank. Scales are absent or when present small, embedded and cycloid. There is a lateral line. Jaws are strong and toothed. The gill openings are small and just in front of the pectoral fins. The anterior nostril is tubular
The life cycle of eels was unknown until Johannes Schmidt published his 1922 study based on years of collecting. Where the adults went on their seaward migration and where the elvers ascending rivers came from were a mystery. These eels are catadromous, living in freshwater but migrating to the sea to spawn and die. In the North Atlantic Ocean spawning occurs in the Sargasso Sea. The young eels or leptocephali (= thin head larvae) are distinctive being transparent and leaf-like. A newspaper can be read through the body of a leptocephalus. In this form they drift to the shores of America and Europe, transform into elvers with the more familiar eel-shape and move into rivers and lakes to feed and grow.
The biology of eels is based almost entirely on the freshwater phase of their life. Adults in freshwater develop large eyes, the gut degenerates and coloration changes in preparation for the migration to the Sargasso Sea. Adults were only caught in the deep ocean, at nearly 2000 m near the Bahamas, in 1977. The Sargasso spawning ground is deduced from collections of larvae across the Atlantic Ocean - the smallest and youngest larvae are found around the Sargasso Sea. The spawning grounds are at about 400 m, at a 17°C temperature and in saltier water than usual sea conditions according to some authors but since spawning adults have never been caught this remains dubious.
The theory advanced by D. W. Tucker in 1959 maintained that European Eels lack the energy resources in their migratory, spawning phase to reach the Sargasso Sea 7000 km from Europe. They are presumed to be following an instinct to head out to sea, dating from an earlier geological age when the Atlantic Ocean was narrower before the separation caused by Continental Drift. All European Eels die at sea and Europe is restocked by larvae drifting there spawned from American parents. The American populations are closer to the Sargasso and can make the journey easily. Differences between American and European eels are merely the consequence of different environmental regimes in different parts of the Sargasso. This theory has not found general acceptance but, if true, means that all European Eels can be harvested for food without depleting stocks. Eels are valued as food, particularly in Europe and Japan, but are not used as extensively in North America.
American Eel / Anguille d'Amérique
Anguilla rostrata (Lesueur, 1817)
Taxonomy
Other common names include Common Eel, Atlantic Eel, Boston Eel, Snakefish, Silver Eel, Yellow-bellied Eel, Bronze Eel, Black Eel or Green Eel and Anguille argentée.
Key Characters
The American Eel is distinguished by its shape, confluent dorsal, caudal and anal fins, the toothed jaws, and the single gill opening. Lampreys have a similar shape and confluent fins but have no jaws (teeth are in a sucking disc) and there are 7 gill openings.
Description
Scales are small and embedded in the skin and not readily visible without close examination. The dorsal fin has about 240 rays, the anal fin somewhat fewer around 200, and the pectoral fin has 14-20 rays. Branchiostegal rays number 8-14 and vertebrae 103-112. The lower jaw projects and the mouth extends to the rear, or beyond, of the eye. The gill opening is a small slit in front of the pectoral fin. Migrating fish change colour and the eyes of males almost triple in size.
Colour
Freshwater adults are overall yellow, greenish, muddy or olive-brown with a dark back, sometimes yellow, green, orange or pink flank tinges and a creamy or yellowish-white belly. Such adults are called Yellow Eels. Adults migrating to the sea have a bronze to black back, a metallic sheen and a light to silvery belly. They are then known as Silver, Bronze or Black Eels. Colour will also change gradually to match the substrate. The larvae are transparent, the transformed elvers or glass eels are also transparent (with black eyes) but soon become grey-green to black, but only adults are found in the NCR.
Size
Reaches 1.52 m and 7.5 kg in females and 50.3 cm in males. Fish larger than 40 cm total length are almost always females. The world, all-tackle angling record weighed 3.88 kg and was caught at Cliff Pond, Massachusetts in 1992. A 5.1 lbs (2.32 kg), 38.5 inch (97.8 cm) long and 9.25 inch (23.5 cm) girth was caught in the Ottawa River on 30 July 2002 by Kyle Richards (www.ofah.org/Registry/fish.cfm?RecID=1, downloaded 14 May 2004).
Distribution
Found in the western North Atlantic from central Labrador south to Brazil. Also in freshwater drainages of the Mississippi and Great Lakes basins, the Hudson Bay drainage of Alberta and Saskatchewan (by introduction) and throughout Maritime Canada. Eels are reported from the Mississippi Lake and therefore can be expected to occur in the Mississippi River of the NCR as well as the Ottawa River.
Origin
This species entered the NCR from an Atlantic coastal refugium.
Habitat
Eels are found in mud-bottomed rivers, streams and lakes. They can be seen looped over weeds in rivers but are usually nocturnal and lie buried in mud during the day. Their preferred temperature is 19.0°C. In winter they bury themselves in mud and are torpid. They can travel overland to reach isolated water bodies, using snake-like movements when the ground is wet. Elvers can climb short vertical, wet walls such as those at canal locks. The Moses-Saunders Hydroelectric Power Dam on the St. Lawrence River at Cornwall was a barrier to young eels migrating into Lake Ontario. An eel ladder (a trough and baffle system with rest pools crisscrossing an ice chute through the dam) was built and over 3 million eels used it in 4 years. There is some evidence of a homing ability to their river of origin if they are displaced. In Lake Ainslie, Nova Scotia, eels have been observed in clumps or eel balls of up to 30 fish found on the bottom or even breaking the surface. Eels can be heard making chirping or sucking noises in warm summer weather on Cape Breton Island. Silver Eels in Newfoundland migrate to sea at age 9-18 years. They leave Nova Scotian waters in late August to mid-November. Adults in Passamaquoddy Bay, N.B. are active by day and night in contrast to freshwater eels, and made frequent surface to bottom dives perhaps to sample geoelectric fields as orientation cues for migration. Migration is often nocturnal.
Age and Growth
Life span is at least 43 years, possibly 50 years or more. Males mature at about 28-30 cm and females at 46 cm. Females grow larger than males, as much as twice the length. The leptocephalus larva has a 1 year life span in the sea.
Food
In freshwater food is any bottom invertebrates, frogs and fishes. Smaller eels favour insects but large eels eat fish and crayfish as well as carrion. In New Brunswick eels are important predators of Atlantic Salmon in nets or traps. Elvers are cannibals. A wide variety of fishes and birds eat eels at various life stages. When they migrate back to the sea, they stop feeding.
Reproduction
Spawning in the Sargasso Sea is believed to occur from February to July but has not been observed. Egg numbers have been estimated as up to 20 million per female but the number released is guesswork as none have been found. The adults take 2-3 months to reach the Sargasso and the adults die after spawning. The Sargasso spawning grounds of the American Eel are to the southwest of the European Eel grounds although there is evidence for a more southern spawning ground. Leptocephali take 1 (perhaps more) year to drift to Canadian shores and transformation to a young eel or elver occurs at 60-65 mm during winter while drifting to or in nearshore waters. Glass eels near Saint John's, Newfoundland have been observed about 2 m below the surface drifting heads up and tails down. This may be done as camouflage from predators which swim horizontally, to counteract sinking, to escape vertically from predators and to facilitate vertical migration. The elvers enter estuaries in April and are 65-90 mm long. They are found in coastal rivers from May to July. The run lasts from a few days to several weeks depending on the river. In the northern Gulf of St. Lawrence young eels only move upstream in their second summer of stream residence. Temperature may be a factor in successful elver arrival. Males tend to stay near the coast in estuaries while females move up rivers sometimes as much as thousands of kilometres. All 356 eels sexed in Lake Champlain were female for example. Males also appear to be much rarer than females in northern waters. Males may have this distribution to ensure rapid maturation and return to the spawning ground. They do not need to be large to produce adequate amounts of sperm and estuaries are good feeding areas. Females require a delayed maturation as a larger body size results in more eggs. Cold northern and inland waters favour this. There are different stocks of eels in Canadian waters. Lake Ontario eels can be distinguished from those in St. Lawrence River tributaries and the Maritimes by the presence of mirex, a chemical used in insecticides. Pollutants are now a convenient method for stock identification but a sad reflection on the state of the environment.
Importance
Eels can be a nuisance to fishermen as they eat other fish caught in nets. They are used in physiological and other studies in laboratories and are easy to keep, surviving without food for up to 22 months. Adult eels are caught in Canada for export to Europe, particularly along the Gulf of St. Lawrence, using weirs, baited setlines, and pots, fyke nets, eel traps and hoop nets. Some are speared during winter when they are buried in mud. The catch in Lake Ontario reached 221,940 kg in 1978 and the total Quebec fishery for the same year was 527.9 tonnes and for the Maritimes about 320 tonnes. The total Canadian catch in 1988 was 1016 tonnes, worth about $2.3 million. Increased fishing pressure in Lake Ontario resulted in a decrease in average eel size. Elvers have been caught in Canada for raising in ponds in the U.S.A. and the Far East. Efforts to start such aquaculture in Canada have not met with extensive success but are potentially viable. Eels are exported live, on ice, or frozen. Live eels are used in making jellied eels which are popular in England. Smoked eel is an important, tasty and highly priced product. Eels should be cleaned with care as the blood has a neurotoxin which can affect humans but is destroyed in cooking. The Ontario Ministry of Natural Resources publishes a print and on-line "Guide to Eating Ontario Sport Fish" (www.mnr.gov.on.ca/MNR/) and has advisory limits for eating this species in the Mississippi River and Ottawa River. As these limits are apt to change, anglers consuming this fish should consult the most recent version.
Dymond (1939) records catches from 1881 onward in the general vicinity of the NCR but trends cannot be determined as fisheries data is recorded from different areas at different dates. For example, in 1898 the catch was 8172 kg in the Ottawa River from Carillon to Pontiac in Québec, the catch in 1933 from Hull, Labelle and Pontiac counties was 16,162 kg, and the catch in 1921 in Prescott, Russell, Carleton and Renfrew counties was 1800 kg, all the highest figures recorded. Generally catches were greater on the Québec side because there were more commercial fishermen there than on the Ontario side. Commercial fisheries for eels above and below Hull from the Québec side of the Ottawa River is documented by Pluritec (1982b). Lac Dollard des Ormeaux, the stretch of the Ottawa River form the Chaudière Falls to the Carillon Dam, had a harvest of 295 kg by Ontario commercial fishermen in 1999 but only 69 kg in 2000 (Haxton and Chubbock, 2002).
Blasting for a marina on the Ottawa River killed large eels around 1970.
© Brian W. Coad (www.briancoad.com)