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Species at Risk Act- Legal Listing Consultation Workbook, American Eel
Information on the species
Information on the species
Species biology and distribution
The American eel (Anguilla rostrata) is the only member of the genus Anguilla found in North America. Anguilla eels are termed “freshwater eels” although part of their life cycle occurs in the sea and some individuals complete the life cycle in salt water. Juvenile and adult American eels are long, snakelike fish with small, deeply-embedded scales. The species has historically been common or abundant throughout its range.
The American eel is widely distributed in fresh waters, estuaries and coastal marine waters of the western north Atlantic from Venezuela in the south to Greenland and Iceland in the north. Adults are found in oceanic waters of the Sargasso Sea where spawning occurs, and larvae are distributed in the western Atlantic Ocean as they move toward coastal and estuarine waters. In Canada the historic range includes all accessible freshwater, estuarine and coastal areas connected to the Atlantic Ocean, as far north as the mid-Labrador coast and as far inland as Niagara Falls in the Great Lakes. Continental shelf areas are also used by juvenile eels arriving from the oceanic spawning grounds and by adult silver eels returning to the spawning grounds.
All spawning adults of the species spawn together in the Sargasso Sea. Larvae (called “leptocephali” because of their leaf-like shape) drift and move to freshwater areas, and individuals undergo a series of changes in shape and ecological requirements through the life cycle. Life stages in coastal and freshwater areas are: glass eels (small, snakelike, transparent), elvers (small, snakelike, pigmented), yellow eels (larger, yellowish to brown, juveniles – the principal growth phase) and silver eels (mature adults migrating from coastal and freshwater areas to the spawning area in the open sea).
Maximum length of American eel observed in Canada is around 1 m, while maximum age observed is around 23 years. Sexual differentiation is considered complete at 270 mm total length. Mean observed age at the spawning migration is 19.3 yrs with a range of 12-23 years. Length at the spawning migration varies geographically, with individuals from the St. Lawrence River being larger at migration (840-1000 mm) than those from the Gulf of St. Lawrence and Atlantic regions (650-700 mm). Growth is faster in saltwater habitat than in freshwater, and in freshwater habitats is faster in rivers than in lakes.
Females are more abundant than males in most areas in Canada. Male silver eels are more common in areas south of the St. Lawrence River and Gulf and along the Atlantic coast of the USA but almost all individuals in Lake Ontario and the upper St. Lawrence are females. Individuals from the St. Lawrence/Great Lakes system may provide a high proportion of total reproductive potential for the species.
American eel is considered a single species without distinct sub-populations throughout its range -- that is, all individuals and sub-groups in the population are genetically the same. This is in contrast to many marine fish species which have well-defined populations which are genetically different from each other.
Last examination by COSEWIC
COSEWIC Reason for designation
Indicators of the status of the total Canadian component of this species are not available. Indices of abundance in the Upper St. Lawrence River and Lake Ontario have declined by approximately 99% since the 1970s. The only other data series of comparable length (no long-term indices are available for Scotia/Fundy, Newfoundland, and Labrador) are from the lower St. Lawrence River and Gulf of St. Lawrence, where four out of five time series declined. Because the eel is panmictic, i.e. all spawners form a single breeding unit, recruitment of eels to Canadian waters would be affected by the status of the species in the United States as well as in Canada. Prior to these declines, eels reared in Canada comprised a substantial portion of the breeding population of the species. The collapse of the Lake Ontario-Upper St. Lawrence component may have signficantly affected total reproductive output, but time series of elver abundance, although relatively short, do not show evidence of an ongoing decline. Recent data suggest that declines may have ceased in some areas; however, numbers in Lake Ontario and the Upper St. Lawrence remain drastically lower than former levels, and the positive trends in some indicators for the Gulf of st. Lawrence are too short to provide strong evidence that this component is increasing. Possible causes of the observed decline, including habitat alteration, dams, fishery harvest, oscillations in ocean conditions, acid rain, and contaminants, may continue to impede recovery.
Eel fisheries have existed in areas throughout the range in Canada, including Ontario (Lake Ontario and upper St. Lawrence River), Québec (Lac Saint-François, Lac Saint-Pierre and upper St. Lawrence estuary), the Gulf of St. Lawrence, Nova Scotia and Newfoundland. All fisheries have been for yellow and silver eels with the exception of fisheries for elvers which began on an experimental basis in the early 1990’s in Nova Scotia and Newfoundland, and are currently only active in Nova Scotia. Total harvests ranged between 500 and 1200 t/yr between 1961 and 2003; harvests declined from around 1100 t/yr in the late 1980’s to around 500 t/yr in 2003. Unreported catches are not thought to be significant. Fishing mortality estimates are relatively high in the few localities where these have been made but there are extensive areas in which no fisheries occur and total fishing mortality on eels in Canada is poorly known.
Presence of dams creates two potential impacts on eel populations: restriction of access to upstream habitat, and mortality in turbines during downstream passage. Although some estimates of mortality and losses due to dams exist for specific localities, there are no overall estimates of losses of spawners due to dams. For example, in the St. Lawrence River watershed over 8,000 dams restrict access to more than 12,000 km2 of freshwater habitat for eels, and dams could be reducing escapement of large female spawners by more than 800,000 in three tributaries alone. Downstream passage mortality of migrating silver eels is a function of eel size (larger individuals are killed more often than smaller eels), dam size (generally a higher fraction of eels is killed in smaller dams), turbine spacing, turbine type and operating conditions. Eels migrating downstream from Lake Ontario and the upper St. Lawrence are estimated to suffer at least 40% mortality due to passage through two power dams (Moses-Saunders and Beauharnois).
Although little studied to date, entrainment (“capture” of eels when water is taken in for industrial or other purposes) in municipal water intakes, industrial water intakes, and thermal generating stations is a potentially significant source of eel mortality.
Eels accumulate chemical contaminants, since they are relatively long-lived, bottom-living, and are high in fat content (which favours accumulation of chemicals which are soluble in fats, such as PCBs, pesticides, dioxins and furans). This chemical build-up can result in lesions, affect egg, embryo and larval development and impede swimming ability. While contaminant levels have been reduced in many areas of eel habitat, it is the accumulation of these contaminants that could have a negative effect on the American eel’s capacity for survival throughout its range.
Many rivers in the southern uplands area of Nova Scotia (southern and southeastern parts of the province) are affected by acid precipitation, and acidic conditions in these rivers may limit survivorship of American eels. Agricultural runoff has increased substantially in recent years with the increase of intensive agriculture (especially maize) in eastern Canada, and this may affect eels.
The swim bladder parasite Anguillicola crassus was first discovered in North America in South Carolina in 1995 and has subsequently been found in eels in the Chesapeake Bay, the Hudson River, Massachusetts and Maine. The parasite has not been found in Canada to date but its arrival may be imminent. Heavy infections can lead to swim bladder shrinkage or collapse, skin ulcers, reduced appetite and reduced swimming performance.
In 2004 the Minister of Fisheries and Oceans announced a goal of reducing eel mortality by 50% within 2 years and called on stakeholders and jurisdictions to take the necessary measures to reach this goal. A Canadian Eel Working Group has been formed to bring together federal and provincial agencies responsible for eel conservation and management, and this group is currently leading development of a Management Plan for American eel in Canada addressing all threats to the species.
In 2005 representatives from government agencies and hydroelectric industries from Canadian and US jurisdictions in the Lake Ontario/upper St. Lawrence area developed a “Decision Analysis” aimed at identifying the key threats to American eel from dams in this area, and the best short-term and long-term measures to address these threats. Short-term measures included stocking to maintain depleted populations, reducing fishing mortality, research into means of reducing downstream passage mortality, and basic research to improve population information. Long-term measures included trapping eels upstream of dams and transporting them downstream, and research into effective dam bypass mechanisms.
Stocking of young American eels into areas in the Great Lakes/St. Lawrence watershed began in 2001 and intensified in 2005 and 2006, with young eels (elvers) from Atlantic Canada stocked into the Richelieu River and Lake Ontario. Funding for stocking has been provided by power generation companies. All commercial fisheries for American eel were closed in Ontario in 2004, and Ontario recreational fisheries were closed in 2005. Fishery removals have been reduced in Québec, and also in Atlantic Canada through shorter seasons and increased minimum sizes. Negotiations with power companies in Ontario and Québec are under way to finalize an overall plan to address dam-related mortalities. One option under such an agreement would be further reductions in Québec fishery removals over the next 5 years through a combination of licence buyback and releasing live harvested eels downstream from the fishery. Research on population dynamics, trap and transport methods, and monitoring continues.
Potential impacts on stakeholders
Listing of American eel as Special Concern would not bring automatic prohibitions on killing or harming the species, so there would be no automatic impacts on stakeholder activities if the species were listed.
Management measures needed to reduce eel mortality, halt the decline in abundance and promote recovery of the species have been outlined in a draft Management Plan for American eel. The Management Plan, to be in compliance with SARA requirements, will be finalized in spring 2007. The Management Plan outlines a series of long-term and short-term objectives, and management actions associated with each of these. The objectives identified in the Management Plan are as follows:
Rebuild overall abundance of American eel in Canada to its level in the mid-1980’s, as measured by the key available abundance indices, in particular
· Ensure presence of American eel in all areas throughout its historic distribution
· Sustainable fisheries for elvers and large eels are producing economic benefits for fishermen in all areas where fisheries were historically present
Reduce eel mortality from all sources by 50% relative to the 1997-2002 average
1. Develop a detailed implementation plan, based on Identifying priority actions, for reducing eel mortality from all sources by 50%
2. Achieve a net gain in abundance and escapement by ensuring access to and passage from quality habitats:
· ensure no net loss of habitat from new facilities
· ensure a net gain in habitat through modifications to existing facilities; specifically, provide upstream and downstream passage to an additional 10% of lost eel habitat in each jurisdiction every 5 years
· continue action to reduce contaminant and pollution impacts
3. Ensure that mortality due to fisheries is consistent with the overall goal of reducing mortality from all sources by 50%
4. Develop a decision support tool for identifying and prioritizing actions to improve habitat for eels
5. Maintain and, where required, develop fishery-independent abundance indices.
6. Ensure presence of eels in areas where abundance has collapsed by stocking young eels
7. Develop a binational management plan
8. Explore setting up a binational Commission for eel conservation and management
Consistent with the objectives in the draft Management Plan, potential new measures to reduce eel mortality could include further requirements for dam operations, construction of eel ladders on dams to allow upstream passage, further reductions in chemical discharges, further reductions in fishery catches, or offsetting measures such as stocking.
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