Species Spotlight: American Eel

Fish Biologist
Published April 30, 2015
A group of glass eels, which are collected and bred at the District's St. Stephen Powerhouse grounds.

A group of glass eels, which are collected and bred at the District's St. Stephen Powerhouse grounds.

There are approximately 800 species of eels worldwide. The American eel (Anguilla rostrata) is common in South Carolina and found at the Cooper River Rediversion Project at St. Stephen. The life history of American eel and their European counterparts is not completely understood, but what is known about their spawning migration is quite astounding. Eels have long been considered a delicacy in Asian and European cultures, and due to harvest and a number of other factors, their populations are declining.

Many species of fish, such as salmon and shad, are anadromous, meaning they live their adult lives in saltwater and move into freshwater to spawn. The members of the genus Anguilla are the most well-known of the catadromous species, fish that grow to adults in freshwater and move into saltwater to spawn. Every mature American and European eel migrates to the Sargasso Sea to spawn… one area for all of them. For those from Europe, that can be a 3,700 mile trip!

The eel lifecycle is a series of changes, or metamorphoses. The first life stage is known as a leptocephalus, which is a clear, ribbon-like form. Leptocephali may remain in that stage for a couple of years as the currents move them up the Atlantic coast and, in the case of the European eel, around to the eastern Atlantic. When they begin to move into freshwater rivers and streams, they become ‘glass eels,’ which look like very small versions of adults, but with no color. This life stage moves up into freshwater to grow and mature, often encountering dams, culverts, and other manmade structures that impede their path. Glass eels can scale vertical walls and climb over rocks, as long as there is a tiny trickle of water.

Eels are called ‘elvers’ when they begin to gain their pigment, or color. From elvers, they transform into the yellow eel life stage, which is the sexually immature adult stage. The yellow eel stage may last up to 15 years. At the completion of their maturation process, yellow eel metamorphose into silver eel and they return to the Sargasso Sea to spawn.
A benchmark stock assessment by the Atlantic States Marine Fisheries Commission in 2012 found “…the American eel population is depleted in U.S. waters. The stock is at or near historically low levels due to a combination of historical overfishing, habitat loss, food web alterations, predation, turbine mortality, environmental changes, toxins and contaminants, and disease.” The US Fish and Wildlife Service is currently reviewing a petition to protect the species under the Endangered Species Act.

At St. Stephen, biologists from the South Carolina Department of Natural Resources have been collecting elvers since 2003, using a simple ‘eel ramp.’ The aluminum frame extends from well-above the top of the high water level to a sill which supports the fishlift wingwalls. The bottom of the two-foot-wide tray is covered with a material that provides a climbing surface for the glass eels. A small pump provides a small flow of water. Even when the turbines are not operating and the water level is low in the tailrace, glass eels swim up that small flow out of the canal and ‘climb the ramp’ to the collection area. SCDNR biologists check the ladder daily from February – May and every other day throughout the remainder of the year. Captured eels are measured, weighed, and released into the intake canal where they move into the lake system to mature. Some are tagged to monitor movement and growth patterns.

Through the Cooper River Rediversion Project, the Charleston District and the SCDNR are doing their part to help these tiny animals move around the dam to grow into adults. The general public is invited to visit the Cooper River Rediversion Project to see the eel ladder and the Visitor Center where, during the spring fish migration, thousands of American shad and blueback herring may be seen passing through the fishlift.