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COSEWIC assessment and status report on the American Eel in Canada

Executive Summary

American Eel

Anguilla Rostrata

 

Species Information

The American eel, Anguillarostrata LeSueur 1817, is in the order Anguilliformes, family Anguillidae. Anguilla eels are termed freshwater eels, although some species (including the American eel) are able to complete their entire life cycle in salt water. Both the American eel and the European eel (Anguilla anguilla) spawn in the Sargasso Sea in the southern North Atlantic Ocean. American eels are considered to be panmictic, which means that all members of the species mate randomly as a single breeding population. However, the genetic analysis upon which this conclusion is based does not include samples from the upper St. Lawrence and Lake Ontario.

This report recognizes five zones, termed Freshwater Ecological Areas (FEAs), that are used by eels in Canada. These are 1) Great Lakes-Western St. Lawrence (Ontario and western and central Quebec); 2) Eastern St. Lawrence (eastern Quebec); 3) Maritimes (New Brunswick, Nova Scotia, Prince Edward Island, and the central and southern parts of Quebec's Gaspé Peninsula); 4) Atlantic Islands (Newfoundland); and 5) Eastern Arctic (Labrador).

 

Distribution

The continental distribution of the American eel ranges from northern South America to Greenland and Iceland. The historic Canadian range includes all accessible fresh water, estuaries and coastal marine waters connected to the Atlantic Ocean, up to the mid-Labrador coast. Continental shelves are used by juvenile eels arriving from the spawning grounds, and by silver eels returning to the spawning grounds. Niagara Falls is the natural distributional limit in the Great Lakes.

 

Habitat

American eels occupy salt water during their oceanic migrations. During the continental phase, eels occupy all salinity zones, including shallow and sheltered marine waters, estuaries, and freshwater rivers and lakes. Some eels remain in a particular salinity zone during the continental phase, while others move back and forth between fresh and marine waters. Eel densities in medium and large rivers typically diminish with distance from the sea. Maturing eels that descend rivers with hydroelectric dams risk mortality due to turbines. Eels in the continental growth phase are highly plastic in habitat use. They are primarily benthic, using substrate and bottom debris as protection and cover.

American eel habitat receives protection from the Canadian Fisheries Act and other legislation. Some areas of eel habitat have special protection (e.g. Marine Protected Areas), but such areas do not necessarily prohibit exploitation.

 

Biology

Spawning takes place in the Sargasso Sea. Hatched larvae develop a leaf-like shape and are termed leptocephali. American eel leptocephali drift westward towards the continental shelf, where they metamorphose into small, transparent glass eels, which have the serpentine shape of the adult form. As glass eels move into inshore waters, they develop pigmentation and become elvers. Elver arrival generally occurs in May and early June on the Atlantic coast of the Maritime Provinces, and in summer in the Gulf of St. Lawrence. Some elvers remain in shallow protected salt water, some move into estuaries, and some move into fresh water. Elvers become yellow eels, which have a dark back and a yellowish belly. Sexual differentiation occurs during the yellow phase. Sex determination appears to be controlled by environmental factors. Density appears to be the dominant influence, with high densities promoting the production of males. Eels in the upper St. Lawrence River and Lake Ontario are virtually all females. Females dominate in many locations elsewhere in Canada, but sex ratios are variable in rivers in the Maritime Provinces which flow into the Atlantic Ocean and the Bay of Fundy. Yellow eels in fresh water may continue to migrate for many years. Eels ascending the upper St. Lawrence in recent years are about 12 years old. Eels in brackish and salt water grow more rapidly than those in fresh water. Eels hibernate in mud in winter. Wintering habitat includes all salinity zones. Some, but not all, wintering sites have freshwater upwelling. When yellow eels reach a certain size, their bellies turn silver and they prepare for the spawning migration. In the upper St. Lawrence and Lake Ontario, the size at which silvering occurs is larger than elsewhere. These large eels are highly fecund and may make a major contribution to the species' total reproductive output. Generation time for these eels is about 22 years. Generation time is much shorter in eels reared in salt water (roughly 9 years), because of more rapid growth in this habitat. Because the American eel is a long-lived species, population indicators of any continental stage other than glass eels/elvers typically include numerous year-classes.

 

Population Sizes and Trends

FEA1 - Great Lakes and Western (Upper) St. Lawrence (Ontario and western and central Quebec)

Juvenile eels have been counted at a fish ladder at the Moses-Saunders dam at Cornwall Ontario since 1974. Mean age of ascending eels rose from 5.6 years in the mid-1970s to 11.9 in the 1990s. Most ascending eels are destined for Lake Ontario. The count index peaked in 1982-1983, and then fell sharply. The index in recent years is about 3 orders of magnitude below its peak level. The decline in Lake Ontario, as indicated by an electrofishing survey and a trawl index in the Bay of Quinte, closely matches the decline of the Moses-Saunders index, when suitable time lags are applied. Eel counts at Moses-Saunders and at passage facilities at the Beauharnois dam on the St. Lawrence River and the Chambly dam on the Richelieu River have shown some increases in recent years.  Recruitment to Lake Champlain via the Richelieu River is a small fraction of former levels, despite the restoration of eel passage. The Moses-Saunders index in the last 2 decades is negatively correlated with the North Atlantic Oscillation Index (NAOI), when appropriate time lags are applied. Silver eels caught in the St. Lawrence estuary fishery are principally from FEA1. Eel fisheries have been closed in the upper St. Lawrence River and Lake Ontario and fishing effort has declined in the St. Lawrence estuary. Reported estuary landings decreased from 452 tonnes in 1980 to under 82 tonnes in 2004. Commercial catch per unit effort (CPUE) declined from the beginning of the series in 1985 to the late 1990s. An experimental trap located near Quebec City has showed no consistent trend since the 1970s, but catches in a nearby commercial trap fished with constant effort declined substantially over the same period. The run of silver eels exiting the St. Lawrence was estimated at 488,000 in 1996 and 397,000 in 1997. The exploitation rate on these eels was estimated at 15% in 1996 and 26% in 1997.

FEA2 - Eastern St. Lawrence (eastern Quebec)

Counts of juvenile eels migrating upstream on the Petite Trinité River in the northwestern Gulf of St. Lawrence in 1982-1985 and in 1993-1996 showed no consistent trend with time. An index of year class strength has been derived from counts of juvenile eels migrating upstream in the Sud-Ouest River, which drains into the south shore of the St. Lawrence estuary. The index declined substantially over the time series, which runs from 1999 to 2005. No trend is apparent in electrofishing densities of eels in the Bec-Scie River, Anticosti Island, from 1988 to 1996, but densities in a tributary of the Bec-Scie declined.

FEA3 - Maritimes (New Brunswick, Nova Scotia, Prince Edward Island, and the central and southern parts of Quebec's Gaspé Peninsula)

The only indices of elver arrival in Canada are from two rivers on the Atlantic coast of Nova Scotia. Arrivals fluctuated without trend between 1989 and 2002. Eel densities estimated from electrofishing surveys in the Restigouche River, between New Brunswick and Quebec, showed an isolated peak in 2001 and 2002, but subsequent densities are below the long-term mean. Eel densities estimated from electrofishing in the Miramichi River in eastern New Brunswick are the longest non-fisheries data series for the American eel. Densities varied irregularly in the 1950s and 1960s, peaked in the early 1970s, declined to a minimum in the late 1980s, and have since been increasing.

Eel densities on the Margaree River on Cape Breton Island peaked strongly in the early 1960s, weakly in the 1970s, and subsequently declined to very low levels. A CPUE of the Prince Edward Island (PEI) commercial fyke net fishery has increased between 1996 and 2004.

FEA4 - Newfoundland

Electrofishing survey results for the Northeast Brook on Trepassey Bay suggest a decline from the early 1980s to the mid-1990s. A similar downward trend is found in densities in the Highlands River on Newfoundland's west coast.

FEA5 - Labrador

Eels are found as far north as Hamilton Inlet and Lake Melville. Small numbers have recently been found north of this, in the English River. There are no quantitative abundance series for eels in Labrador.

Canadian Eel Components in the North American Context

Relative contribution of eels reared in FEA1 and elsewhere in Canada to total spawn output of the American eel can be crudely estimated by two methods. The discharge method is based on the assumption that the number of young eels recruiting from the ocean is a direct function of freshwater discharge. This method also takes into account regional variation in fecundity and sex ratio.  The discharge method indicates that the St. Lawrence River basin (including the western part of FEA2) contributes 59.2% of the spawn output of the species if the species range is considered to exclude the Mississippi Basin, and 48.8% of the spawn output if range includes the Mississippi. The landings method indicates that FEA1 produces 26.4% of spawn output. Both the discharge and the landings methods rest on unproven assumptions, and their interpretation must consider the major uncertainties inherent in these analyses.

Changes in American eel data series were evaluated between years prior to 1980, and 2000-2005. The interval between these periods represents about three times the approximate generation time of female American eels. Series included reported landings and research survey indices. Percent change between the early and recent periods ranged from -99.5% to +74.8%. All four landings series, and five of the six survey indices, were negative. The sole U.S. series (reported landings) was negative (‑67.5%). Landings may be influenced by many factors other than abundance.  It is possible that abundance in the 1970s, when much of the early data was collected, was bolstered by favourable conditions of the North Atlantic Oscillation, thereby emphasizing the decline in comparison to recent times.

 

Rescue Effect

If Canadian eel components collapse, eels whose parents were reared in the United States or elsewhere, may re-colonize Canadian waters. However, the benefits of the rescue effect may be limited if components elsewhere collapse concurrently, particularly if migration is density dependent.

 

Limiting Factors and Threats

American eels are subject to natural and anthropogenic mortality factors. Changes in ocean current systems may interfere with the ability of leptocephalus larvae to reach continental waters. Estimated disappearance rates due to natural mortality and emigration to the spawning ground range from 15% to 26% per year.

Dams may prevent access to upstream growth habitat, and turbines in hydro dams kill some downstream migrants. There are two large hydro dams on the St. Lawrence River, but eels can bypass these by fish ladders and also by navigation locks. Most major tributaries of the St. Lawrence have impassable hydro dams. The Richelieu River is an exception; the two dams on this system have eel passes and no turbines. There are few dams in rivers flowing into the Gulf of St. Lawrence drainages of New Brunswick and Nova Scotia. There are numerous non-hydro dams on PEI, and there are numerous hydro dams on the Fundy and Atlantic drainages of New Brunswick and Nova Scotia, and in Newfoundland and Labrador. Risk of turbine mortality varies with turbine design and eel size; larger eels have a higher chance of being sliced by blades. Cumulative turbine mortality due to the two dams on the St. Lawrence main stem above Montreal is about 40%. All continental life stages are commercially fished in at least some parts of Canada. Reported Canadian commercial catches decreased in the 1990s. The formerly large yellow eel fishery in Lake Ontario was closed in 2004 due to conservation concerns. Eels are fished in the main stem of the St. Lawrence, and the large silver eel fishery occurs in the estuary. Eels are fished extensively in tidal waters in eastern New Brunswick and on PEI. Elsewhere in the Atlantic Provinces, fisheries may occur in either salt or fresh water, but large areas of eel habitat are unfished. In the 1970s and 1980s, toxic chemicals in the St. Lawrence system impacted eels there. Since that time, concentrations of major toxins have decreased in Lake Ontario. The swim-bladder parasite, Anguillicola crassus, has the potential to cause significant damage to eels. It has not yet been detected in Canada but is documented 40 km from the New Brunswick border.

Stocking is a potential way to reduce the sharp decline of eels in FEA1. The net benefit of stocking to total reproductive output depends on several factors which are poorly known, including effects of translocation on sex ratio, ability of translocated eels to find migration routes to the spawning grounds, the survival rates of eels that are stocked relative to the survival rates of the same eels if they had been left in their natural habitat, and the uncertainty whether stocked eels would spawn successfully.

 

Special Significance of the Species

The American eel has the greatest range of any fish species in North America and has supported major commercial, recreational, and Aboriginal fisheries. Eels were fished by Aboriginals, both in the pre-historic and historic periods. The upper St. Lawrence was a major eel fishing area for Aboriginals. Eels were an important food source for Mi'kmaqs in the Maritime Provinces.

 

Existing Protection or Other Status Designations

Fishing regulations are established by the Ontario and Quebec governments, and by the Department of Fisheries and Oceans in the Atlantic Provinces. American eels in Canada are not currently listed by the IUCN and have not been assessed by COSEWIC prior to 2006.

COSEWIC HISTORY

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list.  On June 5th 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

 

COSEWIC MANDATE

 The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC MEMBERSHIP

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species. 

DEFINITIONS

(2006)


Wildlife Species: A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and it is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X): A wildlife species that no longer exists.

Extirpated (XT): A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E): A wildlife species facing imminent extirpation or extinction.

Threatened (T): A wildlife species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)*: A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at Risk (NAR)**: A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data Deficient (DD)***: A category that applies when the available information is insufficient (a) to resolve a species' eligibility for assessment or (b) to permit an assessment of the species' risk of extinction.

*       Formerly described as "Vulnerable" from 1990 to 1999, or "Rare" prior to 1990.
**     Formerly described as "Not In Any Category", or "No Designation Required."
***   Formerly described as "Indeterminate" from 1994 to 1999 or "ISIBD" (insufficient scientific information on which to base a designation) prior to 1994. Definition of the (DD) category revised in 2006.

Environment                Environnement
Canada                       Canada

Canadian Wildlife         Service canadien
Service                       de la faune

The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.