02 Sep 2010: Report

A Steady, Steep Decline for
The Lowly, Uncharismatic Eel

The freshwater eel, which spawns in the middle of the ocean, was once abundant in much of the world. But the proliferation of dams, coastal development, and overfishing have drastically reduced eel populations, with few defenders coming to the aid of these fascinating — though still not fully understood — creatures.

by james prosek

In the early 19th century, freshwater eels — the only fish in the world that spends its adult life in freshwater and spawns in the middle of an ocean — were so abundant in New England’s rivers that residents described “slicks” of young, migrating eels moving up tidal creeks in spring, so thick they formed mats on top of the water. A century ago, America’s eels traveled up the Mississippi and its tributaries as far as Iowa, Ohio, Minnesota, and Illinois, in numbers large enough to support commercial fisheries. Eels once made up 50 percent of the inshore fish biomass of Lake Ontario at the head of the St. Lawrence River.

In England’s Thames River, a little more than a century ago, runs of young eels, each about two inches in length, formed a densely-packed column five inches wide that ran uninterrupted for miles. Indeed, the word for a young freshwater eel, elver, is thought to have come from a phenomenon in mid-May on the Thames that eel fishermen used to term the “eel fair.”

These days, however, an eel caught in the St. Lawrence, the Thames, or the rivers of America’s Upper Midwest is an aberration. The range of

Their sliminess and association with the snake and the phallus have made eels tough to champion.

American and European eels is shrinking dramatically and their total populations have fallen sharply. Populations of freshwater eels the world over — from South Africa, to Indonesia, to Australia — are in decline as the mysterious creatures have fallen victim to hydropower dams that macerate them on their downstream migrations, to coastal and river development that destroys or degrades their habitat, and to fisheries working to satisfy a robust demand for eels in Asia, especially in Japan.

As an international symposium on plummeting eel populations declared in 2003, “In recent decades, juvenile abundance has declined dramatically: by 99 percent for the European eel, Anguilla anguilla, and by 80 percent for the Japanese eel, Anguilla japonica. Recruitment of American eel, Anguilla rostrata, to Lake Ontario, near the species’ northern limit, has virtually ceased.”

The decline of the world’s eels mirrors crashing populations of many other magnificent marine creatures. But unlike the salmon, swordfish, or giant bluefin tuna — bold and magnificent emblems of the rivers and seas that have attracted funds to the coffers of conservation groups that support these charismatic creatures — the world’s eels have few defenders and are quietly slipping away. Their sliminess and association with the snake and the phallus, as well as a general tendency to stir human uneasiness, have made eels a tough species to champion.

In its own way, the freshwater eel is as remarkable as other great migratory fish. Unlike anadromous fish, such as salmon and shad, that spawn in freshwater and live their adult lives in saltwater, freshwater eels are catadromous, meaning they spend their adult lives in freshwater (on average 10 to 30 years) and spawn in the middle of an ocean. The American and European eels spawn in the same general area — the western part of the subtropical gyre of the North Atlantic Ocean between Bermuda and the Azores, a region of the Bermuda Triangle known as the Sargasso Sea. No one has witnessed an adult eel spawning in the ocean. The only reason we know they do is because eel larvae, days after hatching, have been caught in fine mesh nets drifting near the surface. A single female can carry thirty million eggs. To our knowledge, an eel spawns only once and dies, as adults have never been seen returning up rivers.

There are 14 other species of freshwater eels that make migrations from the rivers of other continents to spawning places (many of them unknown) in other oceans in the Indo-Pacific region, from east Africa to Polynesia and north to Korea and Japan. One of the more fascinating is the New Zealand longfin eel. It is not only the largest freshwater eel, reaching lengths of seven feet, but is the longest lived — individuals have been aged at over a hundred years; the indigenous Maori say they live much longer.

In earlier eras, the eels’ autumn exodus from freshwater to the ocean, as well as the spring migration of juveniles upstream, must have been one of the largest migrations of any creature on the planet, with naturalists describing processions of young eels swimming upstream for several straight days.

To this day, no one knows how the baby eels, all born in one place in the middle of an ocean, distribute themselves evenly throughout their vast range, which on the east side of the Atlantic historically extended from North Africa to all tributaries of the Mediterranean and north to France, England, and the Baltic Sea. Once in the rivers, the eels seemed to intuitively continue dividing their numbers, until the manna was disseminated.

But for a migratory fish such as the eel, the proliferation of hydropower dams worldwide was a major issue, perhaps the major issue, contributing to the species’ decline. For example, construction of the Beauharnois and Moses-Saunders hydroelectric dams on the St. Lawrence in the mid-20th

The construction of hydropower dams worldwide has been a major issue contributing to the decline.

century impeded the migrations of eels to and from what once comprised the single largest nursery for the American eel — Lake Ontario and its tributaries. Even if a juvenile eel was able to make it upstream of the dams via fish ladders, the downstream gauntlet was nearly insurmountable. The dams have turbines like giant window fans that spin horizontally as the water goes through, transforming the kinetic energy of falling water into electrical energy — and also grinding up the eels. Power companies have tried all kinds of ways to keep eels away from turbines in dams — screens, high-frequency sounds, lights— to no avail. The eels feel the pull through the penstock, the tube that funnels water to the turbine. The instinct to preserve energy for their long journey turns out to be deadly.

During the fall migration on the St. Lawrence, the accumulated mortality from the turbines of both dams was about 40 percent, according to John Casselman, a biologist at Queen’s University in Ontario. That didn’t account for the fish that were wounded and weren’t in good enough physical condition to make the long journey to the Sargasso Sea. “Unfortunately,” Casselman said, “since the dams on the St. Lawrence are run-of-the-river and use all the flow, there is little or no likelihood that the eels can get by any other way.”

The population of young eels coming up the fish ladder at the Moses-Saunders hydroelectric dam has dropped from nearly a million in the 1980s, to a hundred thousand in the early 1990s, to less than ten thousand in the late 1990s, and virtually to zero in 2000. Hydroelectric dams have similarly hurt eel populations worldwide.

The international trade in eels — a multibillion-dollar industry driven largely by Japan’s appetite for the rich, fatty flesh — has also taken a heavy toll. By the 1970s, populations of native Japanese eels had fallen to a level

The international trade in eels led to overfishing that has also taken a heavy toll.

where they could not satisfy the domestic market. Buyers started looking elsewhere to meet the demand. Dealers discovered that similar eels lived in Europe and North America. The most efficient way to import them was as juveniles, known as glass eels, and then raise them in farms. By the mid-1990s the Japanese eel population had fallen so precipitously it sent prices for American glass eels to levels never before seen— an event that fishermen and conservation officers alike refer to as the eel "gold rush."

Despite alarming declines in numbers of adult eels, fishing continues; the eel trade remains dependent on the capture of wild fish, because no one has figured out how to reproduce eels in captivity in an economically viable way.

In recent years, the evidence of a drastic decline in global eel populations has become irrefutable. No longer are enough eels being born in the Sargasso Sea to spread to the extremes of the fish’s historical range. In the U.S., plenty of eels still exist in South Carolina, Virginia, and Maryland, closer to the spawning grounds, but in places such as the St. Lawrence in Canada or in the Mississippi, eels hardly show up anymore. Likewise, in Europe, populations are still somewhat healthy in the rivers of France and England closer to the eels’ birthplace in the Sargasso, but beyond the strait of Denmark in the Baltic Sea, or at the eastern end of the Mediterranean Sea ̉— and up the Nile — there are far fewer. In 2007, fisheries scientists reported that the European eel population was “outside of safe biological limits.” Last March, the Belfast Morning Telegraph reported that virtually no glass eels were returning to the lakes of Northern Ireland, including such famous fisheries for eels as Lough Neagh.

Willem Dekker, a biologist at the Netherlands Institute for Fisheries Research, said the steep decline in eel populations threatens the livelihoods of more than 25,000 European fishermen. But he said the causes of the drop are not fully understood. “The eel stock is dangerously close to collapse,” Dekker wrote in the newsletter of the International Council for the Exploration of the Sea. “Without better, coordinated assessments and an international management plan, the future looks bleak for these ocean travelers.”

The global response to rapidly diminishing eel populations has been feeble. The European Union has threatened to shut down the commercial fishery for eels in Europe, but has never actually done so. Some European countries have taken action on their own, including Ireland, which, in response to rapidly dwindling populations, shut down its commercial and recreational eel fisheries until June 2012.

In 2000, in the U.S., the Atlantic States Marine Fisheries Commission issued an extensive Interstate Fishery Management Plan for the American eel, recommending necessary steps to save the species. Despite evidence in the report of a “very serious” decline along the U.S. Atlantic coast, the proposed plan was never put into effect. In 2004, the U.S. Fish and Wildlife Service ruled that the eel, though threatened, was not in immediate danger of extinction and therefore should not be listed under the Endangered Species Act. That decision did not sit well with some scientists, including John Casselman of Queens University, Ontario, who first reported on the decline in eel reproduction in the St. Lawrence River. “It is truly a crisis,” said Casselman.

The concern among scientists is that freshwater eel numbers are declining to the point where populations will not possess the critical mass necessary to carry on migration and reproduction. In the nineteenth century, the North American population of passenger pigeons was estimated to be over six billion, representing 25 percent or more of the total bird biomass of the continent. Even though millions of passenger pigeons were being killed every year, it seemed the resource could never be exhausted. The species went extinct in 1914.

Similarly, it was once widely believed that the superabundant eel population of the St. Lawrence could never be diminished, with the New York Times describing the eel fishery in 1880 as “the most productive in the world.”

But in the first decade of the 21st century, the warning shots have been fired. In the St. Lawrence and elsewhere, the eels are disappearing.

POSTED ON 02 Sep 2010 IN Biodiversity Climate Oceans Policy & Politics Asia Europe North America 

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