A Well-Traveled Fish

A Well-Traveled Fish

by Michael Wisenbaker

A region of the North Atlantic that covers 2 million square miles of cobalt ocean known as the Sargasso Sea serves as sort of United Nations for eels. This sea, defined by the ocean’s clockwise circulation pattern, lies southwest of Bermuda between the West Indies and the Azores in the mid Atlantic. Drawn there for reasons we can’t fathom, these unlikely looking fish from eastern North America, Europe and the Mediterranean congregate to mate, spawn and eventually die.

Dr. George Burgess, a biologist at the Florida Museum of Natural History in Gainesville, explains that American eels and their relatives are catadromous. This means they spend most of their lives in brackish water or freshwater but return to the Sargasso Sea to spawn. In other words, you might think of them as “salmon in reverse.” These well-traveled fish are the only ones in the Americas that do this.

From the mysterious Sargasso. their offspring embark on a daunting sojourn to their respective haunts where they may remain for as long as 40 years before returning to their birthplace.
If not for their eyes, these eel larvae would be almost invisible. They resemble willow leaves more than fish. Scientists knew so little about these tiny transparent forms before 1900 that they classified them as a separate species known as Leptocephalus morrisi.
Finally, Johannes Schmidt, a Danish fisheries officer, resolved this issue. He discovered these animals were a larval form of eels. He also found that the animals gradually drift to the edges of the Sargasso Sea where currents eventually catch and carry them close to where they’ll spend most of their lives.

In the spring, about 15 months or so after they’re born, they have drifted near streams and estuaries along the continent. Known as glass eels at this stage – because you can still see through them – the creatures now have fins enabling them to swim and have taken the shape of adult eels.

Glass eels can assume characteristics of either gender and split into two groups upon approaching freshwater. While some stay in tidal areas along the coast and become males, others move upstream into creeks, rivers and lakes and become females.

After developing color, they are known as “elvers,” rarely reaching a length of more than 3.5 inches. They slowly evolve into “yellow eels,” characterized by a murky yellow-green color that grades into a pale underside. Yellow eels are what divers often see writhing about in Florida’s freshwater springs.

Within a decade or so, and some speculate for a much longer period, yellow eels undergo still another remarkable change, which includes developing special cells for riding their bodies of excessive sea salts and forming enlarged eyes. This prepares them for the long swim to the Sargasso Sea.

Their yellow-green covering changes into a metallic sheen, with their backs turning purplish black. Called “silver eels” at this stage, the new color scheme better camouflages them from oceanic predators. No longer freshwater creatures of the night, they have now become marine fish.

From late summer to November, most silver eels leave inland waterways. Males join females when the latter reach estuaries. Together, during the dark phases of the moon, they follow the siren call that draws them home.

By mid-winter, throngs of eels meet in the depths of the distant Sargasso Sea. After making this difficult voyage, they lay millions of eggs. Soon afterward, the silver eels die where they were hatched. Their offspring then begin this cycle anew.

American eels (Atigitilla rostrata) represent the only member of this genus in the western hemisphere. At least 14 other species of this fish occur elsewhere in the world.

American eels range from Greenland to northern South America. In Canada and the U.S., they may travel 1,000 miles or more up tributaries that flow into the Atlantic Ocean and the Gulf of Mexico. Eels scale dams, wriggle through aqueducts and navigate subterranean streams to reach their destinations. Sometimes they even crawl over dew-drenched fields – winding up in lakes with no links to the sea. These well-traveled fish occupy reservoirs, mats, of vegetation, spaces under rocks and limestone voids. Eels constitute one of a few fish species known as troglophiles that can live in underwater caves.

My curiosity about eels developed in the 1970s when I began noticing them in the caverns of our state’s freshwater springs. Generally, eels and yellow bullheads are the fish most often seen by divers in the dark zones of submerged labyrinths. These strange-looking fish often peer at you as you silently fin your way through serpentine passages and massive rooms of limestone. Eels often lurk in crevices and fissures on the floors, ceilings and walls, waiting until dark before they emerge and eerily undulate toward cave mouths.

On my hundreds of dives into springs and sinkholes, I’ve never had any unpleasant encounters with them, except when they careened off my faceplate. Other divers have also seen them nipping at the chrome on tank valves and regulators.

Dr. Jan Hoover, an ichthyologist who works for the U.S. Army Corps of Engineers Waterways Experiment Station in Vicksburg, Mississippi, says eels have small, setiform (bristlelike) teeth that grasp but cannot cut. This means that they have to attack larger prey by chomping down on them and then spinning the victims, just as crocodiles do. In so doing, the eels extract a plug – or a fish McNugget as Jan put it. He recalls one eel specialist saying that these fish can spin at a rate greater than that of the fastest figure skater. In short, unless you are worried about being gummed to death, divers have little to fear from eels.

Arecent study of eels at Vortex Spring about 100 miles west of Tallahassee, shed light on their feeding habits. It revealed that mature eels fed at night and were idle during the day. At dusk, like aquatic vampires, they came out of the spring7s cavern and tunnel to forage around the surface pool before returning to their shadowy haunts at dawn. Conversely, younger eels fed at the mouth of the spring during the day. The researchers believe that as eels grow older their vision in low light improves -thus allowing them to feed at night.

At a glimpse, they look more like snakes than fish -being long and round, with ribbon-like rins fused into one along their backs and tails. Until the turn of the last century, even scientists thought eels were, some type of snake. American eels may reach lengths, of 4 feet, although males rarely exceed 2 feet, and weigh up to 7 pounds.
Their ability to secrete a heavy white mucous when upset may lend to their reputation of being slimy. Those who often handle them, though, say they feel like soft velvet.

Eels have one of the most highly developed senses of smell among animals. This, might explain how they survive even in the dark, far reaches of caves. They devour living or dead creatures such as insects (larvae and adults), smaller fish, worms, mollusks, crustaceans and salamanders.

While many Americans view them as “trash” fish, eels have been a highly prized food since the days of the Roman Empire. They are eaten in parts of Asia, Europe and Latin America.

Many Japanese believe that eating eels rejuvenates the spirits worn down by the heat of summer. So they began celebrating an annual festival that features gorging on eels.

Gourmets in Germany, Holland and England delight their palates with smoked eel, but the fish must be delivered live to European eateries where this delicacy is served.

Though you’re unlikely to catch many eels with a hook and line, commercial fishers who know when and where to rind eel runs capture them by the thousands with nets and traps. One eel fishery in Quebec has exported 350 tons of eels to various parts of the world annually. Some complaints have arisen that eels are being over fished along the east coast from Chesapeake Bay to Canada’s maritime provinces. If this should turn out to be a serious problem, a solution may be at hand. Eel farms have existed throughout the world for more than 2,000 years.

Eels provide much more than just food for human consumption. The skins of American eels once were a source for quality book bindings and buggy whips. In Japan, shoes, wallets and brief cases are sometimes made from eel hides. Eels also serve as animal fodder, fertilizer and an ingredient in some glues.

We’ve learned a lot about eels since Aristotle proclaimed them sexless beings that arose from the “entrails of the sea7′ and Pliny the Elder insisted that they reproduced by rubbing against rocks. Medieval folk tales even led some to believe that larval eels came from the hairs of horses’ tails or the dews of May mornings.

Yet many facts about the only species of this well-travel’ed fish found throughout Florida’s freshwaters remain one of nature’s best kept secrets. For as Johannes Schmidt opined in 1912, “the whole story of the eel has come to read almost like a romance, wherein reality has far exceeded the dreams of fantasy.”

(Michael Wisenbaker is a Tallahassee-based writer who frequently covers nature.)

Woodville Karst Plain Project