The remarkable life cycle of the American Eel
American eels lead mysterious and unusual lives. For over 20 million years, their existence has begun when they hatch as leptocephali (eel larvae) in the Sargasso Sea. Leptocephali’s leaf-shaped, transparent bodies do not much resemble the creatures they will grow into, but are well suited to hitching rides on oceanic currents that help the leptocephali disperse across their sprawling range, extending north to Greenland and south to Venezuela.
After spending 7-12 months in the open ocean, leptocephali transform into glass eels, which look like small, translucent snakes, as they reach the continental shelf. Despite their small size, glass eels can cover up to 15 km a day, as they move into estuaries or river deltas. As glass eels age, their colour darkens and they become larger, entering the ‘elver’ stage of their life cycle. Elvers migrate up rivers en masse in the spring in order to reach the lakes, marshes, rivers or streams where they will mature into ‘yellow eels.’
American eels spend the majority of their lives in the yellow eel phase, which can last for well over a decade. In their final life stage, American eels ‘silver’ and leave their surroundings to return to the Atlantic Ocean where they return to the Sargasso Sea to breed and die. Neither spawning nor hatching has ever been observed and scientists remain unsure about where in the Sargasso Sea eels breed, or how they ensure synchrony.
The American eel population is in dire shape, especially in Lake Ontario
Until recently, the American eel was an integral part of Lake Ontario’s ecosystem. They were profusely abundant; constituting up to half of the near-shore biomass. Today, it is estimated that the abundance of the American eels in and around Lake Ontario has decreased 99% from historic levels.
Conservation efforts have been slow to respond to the decline
In Ontario, the American eel was finally listed as endangered in 2007. At this point, the commercial fishery had already collapsed (it was closed in 2004) and eels were virtually absent from Lake Ontario.
In 2013, the Ontario Ministry of Natural Resources released the Recovery Strategy for the American eel. The report presents an ambitious plan to re-establish the species across its historic range. The goal is not just to restore ecosystems, but also our cultural connection to the American eel.
Archaeological evidence from the Ottawa Valley shows that the Algonquin First Nation have relied on the eel as a food source for over 4000 years. The Recovery Strategy envisions a future in which the eel remains a landmark in Ontario’s cultural and ecological landscape. To achieve this, the report calls for Ontario to adopt a number of recovery objectives including:
- Restore access to all immediate tributaries of the Ottawa River, Lake Ontario and the upper St. Lawrence River by 2050
- Beginning immediately, increase American eel access to habitat by 10% every 5 years
- A 50% reduction in cumulative mortality rates at the watershed level by 2050
The report recognizes that the decline of the American eel is due to a host of problems, but singles out hydro electric dams as “the biggest threat to the continued survival and recovery of eels.”
Currently, regulations under Ontario’s Endangered Species Act allow hydroelectric generating stations to kill endangered species if they have entered into an agreement with the Minister of Natural Resources. According to the regulations, the agreement must state that the Minister is certain that “the operation of the station will not jeopardize the survival or recovery of the species.” This leaves the government with considerable discretion. If there is to be any hope of bringing back the eel, the Ontario government will want to ensure that any agreements they enter into are in accordance with the goals set by the recovery strategy.
Under Ontario’s Endangered Species Act the government is required to publish a statement that summarizes what actions the government intends to take in response to the recovery strategy. Yet, two years have passed since the publication of the eel recovery strategy, and the Ontario government has yet to issue a statement.
The Maritimes and Quebec
The American eel is also present in Quebec, Newfoundland, Nova Scotia, New Brunswick and Prince Edward Island. Although eel populations in these provinces have not experienced the same crash as the Lake Ontario population, there is evidence of widespread decline. The eel is listed as “Special Concern” in Newfoundland and “threatened” in New Brunswick, but for various technical reasons, it receives no formal protection in either province. Eel remains part of the commercial fishery throughout the maritimes. The only province that has taken some initiative towards eel conservation is Quebec, which got rid of (through a buy-back program) most of its commercial eel licences in the mid 2000s.
The United States
This fall, after a multi-year review the US Fish and Wildlife (USFAW) service decided not to list the American eel as threatened. The USFAW service argued that despite significant decline, American eels “remain widely distributed throughout a large part of their historical range.”
The decision has been criticized by some conservation groups that have suggested the USFAW service may have been influenced by the eel fishery, which campaigned against the proposed listing.
Since the collapse of Japanese and European eel populations, the price for glass eels has soared. In Maine, glass eels now sell for $2100 per pound, an increase from $100 per pound in 2009. Glass eels are sold to buyers from Asia, who raise them in aquaculture facilities and sell them for sushi. The persistence of a legal market for glass eels in the US will likely make illegal poaching harder to target.
The well-respected International Union for Conservation of Nature (IUCN) has not reached the same conclusion as the USFAW. The IUCN has listed the American eel as endangered, and after an extensive review of population trends concluded that “overall, despite regional variations, and in some cases, signs of stabilisation and/or recovery in the recent past, the general picture across the data-sets used, was that over the period of three generations analysed there had been a significant decline in recruitment across the species' range”.
Even though the eel may still be found throughout a large part of its historical range, the population is a fraction of what it once was. To ignore this trend is to ignore similar lessons in history. The abundance of the Atlantic cod and Passenger pigeon were taken for granted, until populations began to enter freefall. It’s hard to know when it becomes impossible to halt a species’ decline.
Canada (federal government)
The Federal government recently began a public consultation period to decide whether the American eel should be listed as a threatened species under federal legislation. Public consultation will last until March 18th, 2016.
If the federal government decides to list the American eel it could be a turning point for the eel. Federal listing would encourage Ontario to embrace its own recovery strategy, and it would help to address the lack of protection that exists in the maritimes and Quebec. If Canada is serious about protecting the American eel it could also work with the US to have the species listed under CITIES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora). This would restrict international trade and could help close or reduce commercial eel harvest in the US and Canada.
Panmixia: Problems and Possibilities
Panmixia is a biology term that comes from Greek – the direct translation would be “all mixing” pan (all) - mixis (mixing). Biologists will refer to a population as “panmictic” if all the individuals in the population are potential mating partners. In other words – a population will be panmictic if there are no barriers that prevent some individuals from mating with other individuals. This is rarely the case. Natural landscapes are full of barriers (think mountain, rivers, lakes). Distance itself can be barrier. A chipmunk in North Bay won’t be able to mate with a chipmunk in Rouge Park; chipmunks just don’t move around that much. And of course there are other non-physical barriers that can affect mating (e.g. temporal barriers, behavioural barriers).
Perhaps one of the most extraordinary attributes of the American eel population is that it may actually be panmictic. This is still a subject of debate, but there is recent genetic evidence that strongly supports the idea.
This means that an eel from Ottawa river might breed with an eel from Venezuela, or Greenland, or South Carolina or the Bay of Fundy. If the panmixia hypothesis is correct, it means that the American eel population is integrated and interdependent to a degree that is rarely seen at the species level.
From a practical perspective, panmixia means that conservation efforts need to be coordinated. The loss of eels in Lake Ontario will have population-wide consequences. Restoration efforts in Canada could be impacted by overfishing in the United States, or vice versa. This presents a problem.
Panmixia also creates possibilities. Eels aren’t like salmon; their offspring don’t always return to their parent’s watershed (their parents may well have come from different watersheds). If dams are removed and habitat is restored, some eels from somewhere will return.
The disappearance of American eels from Lake Ontario doesn’t have to be permanent. But the clock is ticking.