Let us consider doing a vast experiment on the waters of our state. This experiment will be especially risky because, once it is begun, it cannot be stopped by anyone. The aquatic environment could be irreparably damaged in ways we can only imagine
Let us consider doing a vast experiment on the waters of our state. This experiment will be especially risky because, once it is begun, it cannot be stopped by anyone. The aquatic environment could be irreparably damaged in ways we can only imagine, and the experiment has absolutely no perceivable benefits. There is no way to predict the experiment's outcome because nothing quite like it has been done before.
Few people would condone such a misguided venture. Yet, this very experiment is currently underway in Georgia. It began with the release of an exotic species, the Asian Rice Eel, Monopterus albus, into the Chattahoochee River system. Exotics are species that are not native to an area, and, as a result, can greatly upset the balance of a natural ecosystem. The Asian Rice Eel, probably released from a pet-owner's aquarium, has the potential to do just that.
The Chattahoochee Nature Center, with its peaceful woods, winding nature trails, log cabin-style visitor's center, and three picturesque ponds, is an unlikely setting for an experiment with peril. Located north of Atlanta adjacent to a wetland along the north bank of the Chattahoochee River, the center is a valuable island of beauty lodged between the rapidly growing urban centers of Atlanta, Roswell, and Marietta. In this increasingly crowded urban area, the center plays an increasingly important role as a place for school children to visit and learn about nature. They can walk the trails, feed the ducks, collect tiny invertebrates from the ponds with dip nets, see bald eagles, view interpretive exhibits, and learn about nature. And now, too, perhaps they can learn important lessons about a newcomer to this peaceful scene.
While visiting the Nature Center in September 1994, a tiny, eel-like creature, barely 2 inches long and swimming in a shallow dish, came to our attention. Puzzling over the dish, we learned that the little creature had been dipped from the smallest of the three impoundments at the center by a youngster earlier that day. We also learned that, on rare occasions, others had been dipped from the pond over the previous four or five years. Barely thicker than a pencil lead, details of the mystery animal were difficult to discern. Any fins, legs, gill slits, mouth shape, or other characters that might give a hint of its identity were scarcely if at all visible without the aid of a microscope. It clearly was not a worm or a snake but rather a fish or amphibian. But was it a very young eel or lamprey, or a tiny eel-like salamander, such as a siren?
In much of Georgia, an eel would seem a good bet. The American Eel, Anguilla rostrata, is a freshwater species that penetrates far into the continental waters of North America. All true eels spawn at sea, even though a few, including the American Eel and its kin on other continents, enter freshwaters. The American eel spawns in the ocean, somewhere near the Atlantic's vast Sargasso Sea, and has a semitransparent, ribbonlike larval stage, termed a leptocephalus. These larvae drift hundreds or thousands of miles before transforming into a transparent juvenile stage, called a glass eel, as they finally near coastal waters. Leptocephali may reach over 3 inches but actually shrink to a length closer to 2 inches upon transformation.
As the young eels near or enter the mouths of rivers, they darken into a grayish elver stage before, at about 4 inches, becoming the more familiar yellowish color that they maintain as juveniles and most of their adult life. They may remain in freshwaters or estuaries for as long as 20 years before reaching full maturity. During this time, while many individuals remain in lower reaches of rivers or estuaries, many others penetrate far inland to the headwaters of Atlantic and Gulf tributary rivers.
After total sexual maturation occurs, the eels turn a silvery color, their eyes become much larger, and a spawning migration to sea occurs. A few of the largest may exceed 3 feet in length. Adults ostensibly die after spawning. This reverse spawning migration, the opposite of the more familiar anadromous spawning migrations of salmon, shad, or striped bass, that live as adults in the sea but enter rivers to spawn, is termed a catadromous migration.
Although most true eels, other than the American Eel and its kin on other continents, do not enter freshwaters, all spawn at sea and have the unique leptocephalus stage. This life cycle is important to remember for discussions that follow. Eels are extremely diverse, with about 15 families and nearly 750 species known. Some, like the American Eel and its kin, have paired pectoral fins, while others, such as the familiar morays, have none.
While American Eels are renowned for their prowess at surmounting obstacles in the paths of their upstream migrations, few if any have been able to negotiate the several large dams on the Apalachicola and Chattahoochee rivers in recent decades and reach the Atlanta area. This fact, and the very small size of the squirming little creature in the dish, greatly reduced the probability that it was an American Eel that had somehow made its way to this scenic little locale so far removed from the coast. So, as we worked to identify the creature, lamprey or amphibian were our other logical choices among critters native to this region of Georgia.
Lampreys are ex