Nature Matters: Alewife and Eel – Part 2

By John L. Turner

This is part two of a two-part series on a remarkable pair of fish.

The life cycle of the American eel is a little more complicated than that of the river herring and consists of six stages: egg, larva, glass eel, glass eel, yellow eel and silver eel.

Mature adults spawn only once in their lifetime, with all eels emanating from the east coast unfailingly migrating to the Sargasso Sea where mass spawning takes place. (The Sargasso Sea, located south of Bermuda, has no land boundaries but is unique in that it is bounded by four strong ocean currents, including the Gulf Stream, resulting in calm waters drawn into the gyre; here masses of Sargassum abound, providing shelter for many marine species, including young sea turtles).

Shortly after spawning here, the adult eels die. An adult eel releases up to several million eggs and these hatch within a week. At first, leptocephali do not resemble eels, being transparent and flattened, described as resembling a willow leaf; they are carried north by currents, including the Gulf Stream.

American eel. Wikipedia picture

After about six months, they metamorphose into “elvers”, still transparent but in the shape of baby eels, and this is the stage, together with the stage of the lightly pigmented elver, which arrives at the mouths of the streams of Long Island. They wriggle up vertical faces and across wetlands to make their way into freshwater ponds and lakes (although some spend their adult lives in the brackish waters of Long Island estuaries).

While living for decades in ponds and lakes, they go through a few more color stages, including yellow and silver eels. Here they become fully integrated members of the local food web, feeding on a variety of different aquatic prey while being preyed upon by many other animals, including ospreys and bats. eagles (stay tuned: June’s Nature Matters!).

Eels are also food for humans (remember one of Long Island’s most famous paintings — William Sidney Mount’s 1845 “Eel Spearing at Setauket”?). Eventually, an internal trigger “tells” these decades-old fish to head out to sea and back to the Sargasso Sea to create a new generation of eels. To help them on their long journey, their bodies change a bit — their eyes get bigger as well as their pectoral fins.

Eel is managed by the Atlantic States Marine Fisheries Commission (ASMFC), beginning in 2006 with the first species management plan. The Commission sets harvest quotas for all age classes of eel, including those intended for use as bait and intended for direct consumption. The news has not been good over the past few decades with eel abundance declining and the ASMFC currently classifying the eel stock as ‘depleted’.

How to increase abundance? Reduce all causes of eel mortality, especially in young animals, adults trying to navigate the perils of hydroelectric dam turbines, and increase opportunities for eels to migrate to freshwater areas where they can survive , becoming mature adults over time.

The Seatuck Environmental Association has been at the forefront of documenting migratory occurrences of Long Island alewife and eel through its surveys of herring and eels in the river and has for decades worked to protect the existing tracks while facilitating others. If you would like to help research new gaspereau or eel migration sites or document more fully what is happening at existing sites, please visit the Seatuck webpage.

In pre-colonial times, before the advent of dams and other barriers, many, if not all, streams and rivers on Long Island were likely teeming with alewife and eel in the spring. They, in turn, provided food for many species of wildlife, from otters to ospreys to eagles. However, today’s Long Island is a very different place, with so many cut or frayed eco-yarns. The reduced abundance of these fish illustrates the widespread loss of ecological connectivity that has occurred on Long Island over the past few centuries. The good news? Many individuals, organizations and government agencies are working to improve connectivity here – to reconnect the cut ecological wires – through the installation of additional ladders and walkways, and better yet, the removal of more dams, all steps to give these remarkable animals a chance to recover and maybe even thrive.

I hope you will get to know them.

A resident of Setauket, John Turner is conservation chair of the Four Harbors Audubon Society, author of “Exploring the Other Island: A Seasonal Nature Guide to Long Island” and president of Alula Birding & Natural History Tours..

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