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Follow that Fin!

"The American eel is, in many respects, a force of nature - a creature whose lifecycle profoundly influences the lives of countless other creatures."

George Schuler, scientist, The Nature Conservancy in New York

The American eel is a slippery, slimy creature that, despite its unglamorous appearance and lowly stature, is one of the world’s greatest — and most mysterious — travelers.

With a vast migratory route that spans thousands of miles, a lifespan of over 20 years, and mating behavior that has never been witnessed by science, the American eel (Anguilla rostrata) is a vital and fascinating link in our natural world.

But they are also in trouble; in some areas, the American eel population is estimated at less than 1 percent of historic levels.

Never one to pass up a mystery or a challenge, scientists from The Nature Conservancy in New York have devised a new tool to track — and ultimately protect — these elusive travelers: a sonar beam.

Take Me to the River

While many details about the private life of the eel still remain a mystery, it is known that they begin their lives deep in the Sargasso Sea, a nebulous region in the center of the Atlantic Ocean.  After hatching, the young eels ride ocean currents for up to a year, eventually moving along coastlines and up freshwater rivers from South America to Greenland. 

It is within these rivers that the eel spends most of its life before migrating back to the Sargasso Sea to mate, spawn and die.

The Delaware River Watershed, just two hours from New York City, is a rare, pristine oasis brimming with life. The largest un-dammed river east of the Mississippi, the Delaware is one of New York’s purest sources of drinking water. It’s also a haven for migratory fish, including the American eel.

For this reason, scientists from The Nature Conservancy’s Eastern New York Chapter have targeted the Delaware River Basin and the nearby Neversink River to learn more about the American eel and their mysterious travels. Their goal is to collect baseline and long-term population data in order to develop a comprehensive conservation plan for these elusive creatures.

Counting up the Eels

To set things in motion, Conservancy ecologist Mari-Beth DeLucia and scientist George Schuler have enlisted the high-tech help of Mark Grooms from Ocean Marine Industries, Inc.

Using new technology in the form of Dual Frequency Identification Sonar (DIDSON), Grooms and Conservancy scientists are devising a way to census the eels on their annual migration down the Neversink River, en route to the Sargasso Sea.

A small device placed in the middle of the stream projects sonar beams into the water. The beams reflect back off of the target object — in this case an eel — and produce an image that can then be recorded. The tool allows Conservancy scientists to generate video-like images that will be analyzed to identify, count and measure the length of migrating fish.

Previous attempts at surveying migrating eel populations, whether by the construction of eel weirs or tagging individual fish, have proven to be difficult, time consuming and very labor intensive. DeLucia and Schuler hope that the new sonar technology will provide a more efficient, accurate and practical way to record eel population numbers and migration movements.

Filling in the Gaps

Research by Conservancy scientists in the Upper Delaware River Basin has shown that the American eel is a significant component not only of the local but the global natural community.  As they travel across vast surfaces of our planet, eels influence the lives of countless other creatures.

But in recent decades, eel numbers have declined precipitously. In some places, the freshwater population has declined by 99 percent.  In 2006, the American Eel Management Board of the Atlantic States Marine Fisheries Commission recommended that they be listed as federally endangered or threatened under the Endangered Species Act.  Commercial landing of eels in the United States has declined from 1.8 million pounds in 1985 to 649 thousand pounds in 2002. While 2002 is the latest year when complete data is available, most of fishery managers seem to think that commercial landings have declined even further since then.

By utilizing this new monitoring technology, The Nature Conservancy hopes to fill in important scientific and population gaps about the American eel — and bring back a force of nature from the brink of collapse.

The Nature Conservancy — with its focus on both local communities and global issues — is uniquely situated to bring together the people and institutions necessary to successfully protect migratory animals throughout their global journey.

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