Nature Notes: The Journey of the Eel
On Friday afternoon I witnessed something for the first time in my 75 years. I was standing with a companion on Alewife Brook Road at the edge of Cedar Point County Park, looking at the water from Scoy Pond in the Grace Estate rushing out of the iron culvert under the road into Ely Brook Pond. We were looking at some killifishes swimming in three or four inches of water on top of the pipe end, when my companion pointed to something different swimming in the same spot. “Isn’t that an eel?” he asked. I got closer for a better look, and yes, it was an eel, a small one, an “elver” about four inches long but only barely discernible because it was as thin as a spaghetti strand.
As our eyes adjusted to the tiny sinusoidal swimmer, we began to see more elvers, as many as 15, swimming around and on top of the culvert opening. A few were actually entering the culvert, moving upstream against the current. We wondered, would any actually be able to make it through the 30 feet of corrugated steel to the other side? They were all pigmented. If they were still “glass eels,” the metamorphic stage before elver, which they assume before leaving the Gulf Stream to head toward the estuary in search of freshwater sources, we wouldn’t have been able to see them at all.
A few minutes later we were standing at the edge of Scoy Pond surveying the beaver damage of a few years back and watching the water pour out into Scoy Run. After a few minutes of staring at the rushing water, there came a few elvers heading up stream. They had fought the current through the culvert and were a mere 20 feet from the pond where they would spend the next 10 to 20 years growing up. To make it into the pond they would have to hug the bottom and swim-sidle up the incline at a 30-degree angle. But elvers have been doing just that for longer than humans have been on Long Island. They can even wriggle over land, as long as it is wet, to get to where they are going.
These elvers belonged to the American eel species, Anguilla rostrata, one of several Anguilla species throughout the world. They are practically identical worldwide and they all have the same astonishing life history. When reproductively mature and packed with fat, they take on a silvery appearance and begin a long journey to spawning areas in the ocean depths. In the case of the American eel, the ones that grow up in Scoy Pond will have to travel more than 1,000 miles south to reach the sacred spawning ground somewhere in the Sargasso Sea south of Bermuda and east of the Bahamas. No one other than the eels themselves knows the exact spot. It’s a one-way journey, a year of fasting. Their digestive systems are metabolized along with their fat reserves. They’re not coming back. All is sacrificed for reproduction and continuing the species.
They’re not so different from Pacific salmon that die after spawning, except the salmon leave saltwater to spawn in freshwater, while the eels do exactly the opposite. The salmon is anadromous, it goes up to spawn, like the shad, sea-run trout, anchovy, sturgeon, and a host of others that leave the sea to reproduce in rivers, lakes, and ponds. The eel is the only fish that does it the other way around, it is catadromous, it goes down.
Three years ago Japanese scientists found the spawning area for Anguilla japonicus, near the Mariana Trench in the western Pacific Ocean. Two species of New Zealand eels, long and short fin, go to near New Caledonia to spawn. The European eel, Anguilla anguilla, the first to be studied in depth going all the way back to the time of Aristotle, who postulated they came from worms and wet earth, also spawns in the Sargasso Sea, more westerly so than its American cousin.
A mature female eel can be four feet long and have more than a million eggs. After fertilization, the eggs develop into leptocephalus, “thin-headed” larvae that are transparent and flat from side to side, in the shape of a cherry leaf. It was the Danish ichthyologist Johannes Smith at the turn of the 19th century who figured out the mysterious whereabouts of European eels’ spawning area. His expeditions started in the latitude of the British Isles and ended near the Sargasso Sea. He caught smaller and smaller leptocephalus larvae drifting north in the Gulf Stream as he proceeded south-southeast.
Twenty years earlier, the very odd looking leptocephalus was considered a species all its own, Leptocephalus brevirostris. It looked nothing like what it would eventually become. It wasn’t until Yves Delage kept a leptocephalus in a tank and watched it turn into a round elver, that it became known to the scientific world that, indeed, leptocephalus and eels were one and the same species.
Even Sigmund Freud got into the act 10 years earlier while still a neophyte researcher in Austria. He looked for the reproductive organs in hundreds of small eels, but gave up in despair. He couldn’t find any. He went on to study a much easier subject. Eels are long livers, but only reproduce once in a lifetime. Elvers become “yellow” eels as they grow longer and wider, but don’t become sexual until spending many years in fresh water. As they get ready to reproduce and their sexual organs become mature they become “silver” eels and head for the sea in late summer and early fall, especially after rains.
Having such a complicated life story, it is no wonder that eels are becoming scarce the world over. They are harvested for food, bait, even, skins. I’m sure you’ve heard of “eelskin” accessories. Largemouth bass and other fish, as well as diving birds, eat them. The American and European eels have been in a downturn spiral for 20 years now. Obstructions such as water gates, dams, and hydroelectric turbines prevent or injure eels going upstream and downstream, respectively.
An Asian parasitic nematode, Anguillicola crassus, that arrived on the Atlantic and European coasts in the mid-1990s, has added to their difficulties. It attacks the swim bladder, an organ in many fishes which regulates buoyancy and which is certainly of great value in the long trek from northern waters to the Sargasso Sea.
North Fork and South Fork creeks and streams, save for culverts, don’t have dams and other barriers preventing eels from reaching fresh waters in which to mature. The new fishway at Grangible Park in Riverhead where the Peconic Estuary meets the Peconic River is probably just as negotiable by eels as it is by alewives. What’s good for the goose is also good for the gander.