River Currents: The American eel — a peculiar fish

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The American eel (Anguilla rostrata) is a peculiar fish. First, although eels breathe with gills underwater, they can survive out of water for several hours breathing through their skin. Their migration cycle is backwards from other migrating fish in the Connecticut River as they come into the river as juveniles and leave as adults on their way to spawn in the Sargasso Sea.

The American eel is not a loveable creature. Adults are three to four feet long. Despite one long dorsal fin that extends more than half of the body and two smaller pectoral fins, they look and move like snakes. They are muscular with a girth of the size of your forearm. Their ample body slime does make them "slippery as an eel."

They are a top predator and they will chomp anything they can feed on or that annoys them, including anyone who inadvertently hooks one while fishing. If they cannot swallow a meal whole, they bite into their prey with their un-fish like array of sharp pointed teeth and then spin their bodies tearing pieces from their quarry. They do not even benefit from a cute baby factor, because no one sees the returning juveniles as they are less than four inches long, are nearly transparent, and travel at night.

The eel is an ancient fish living on earth for 100 million years, outlasting most of their fellow species from that era. Eels live in freshwater, females for up to 40 years, before returning to the sea.The 80 species of eel worldwide are scattered in the Americas, Europe, the Pacific Rim and the Caribbean. For these locales, the spawning grounds are in different oceans around the world. Until 2015, no one had ever tracked an American eel to where it spawns but now a team of Canadians satellite tracked an adult female 1,500 miles from Nova Scotia to the Sargasso Sea.

The ensuing life stage changes into adulthood are remarkable. The female lays up to 20 million buoyant eggs and, once fertilized, the eggs hatch within a week becoming transparent leptocephalus larva that drift toward coastal waters for up to 18 months. At sea, they consume plankton, insects, and floating dead tissue. As they cross the continental shelf, leptocephali metamorphose into glass eels that are still transparent but now have the elongated eel shape.

Upon reaching estuary waters, they change into elvers as they enter our river, one to four inches long and are nearly transparent. All eels beyond the leptocephalus stage are voracious feeders, aggressive swimmers and are primarily active at night. As elvers, they become avid carnivores.

As other migrating species are swimming up river to spawn, the juvenile eels swim up river to grow into adults. The elvers have never been in the Connecticut River before yet they select the Connecticut as their returning river. The fish does have a small spot of magnetite in its head so they sense magnetic direction but no one knows if this directs the eel to a particular river. In the elver phase, the sex of the eel is still undetermined. The elver stage lasts up to twelve months and while becoming adults, they are busy migrating further up river.

In river, they transform into Yellow eels, the sexually immature adult stage, as they begin to identify their sex. Species density influences sexual differentiation, the higher the density of eels the more males. These life phases are clearly peculiar.

In 20 to 40 years, in their last metamorphosis, they become silver eels and spawning time has come. Like all fish that migrate, the change is more profound than color with internal changes that prepare eels to migrate to the Sargasso Sea. Their digestive tract shrinks, the pectoral fins enlarge to increase swimming capacity, the skin thickens, the composition of their body fluid changes, their swim bladder increases in size, eye diameter and retina expand as a necessary adaption to ocean colors, and egg, and sperm production begins.

For thousands of years, people worldwide consider the eel a tasty fish. The largest consuming nation is Japan where they even make a "unagi inu," grilled eel cooked then placed on a bread bun, their equivalent of our hot dog. The fishery for glass eels and elvers is huge in Maine and South Carolina, the two east coast states that allow it, fetching $2,500.00 per pound. Part of the glass eel catch supports eel farming now underway in Japan and China. Yet, the eel cannot win for losing. Major eel consuming nations still prefer wild eel, so the fishing pressure remains strong.

Once the most common finfish in the Connecticut River watershed, and be they loveable or not, restoring historic population levels of eels is a concern in the FERC relicensing of the mainstem hydroelectric dams. In recent river history, we have invested in passage for salmon, shad, Sea Lamprey, and blue backed herring but none of the passage methods works well for eels. Continued blockage of the mainstem and the tributaries could mean the failure of eels as a species in our watershed but with success in our call for effective eel passage, we hope to increase the numbers and distribution of this peculiar fish of the Connecticut River, the American eel.

David L. Deen is River Steward for the Connecticut River Watershed Council. CRWC is celebrating 60 years as a protector of the Connecticut River. The opinions expressed by columnists do not necessarily reflect the views of the Brattleboro Reformer.


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