Eels and connectivity in aquatic ecosystems

Eels / Conservation

The chief difficulty in evaluating the possible endangered species listing of the American Eel (Anguilla rostrata) is the somewhat bizarre life-cycle of the organism. Although the eel is chiefly a freshwater fish, in order to reproduce it travels from the freshwater waterways where it makes its home, and every eel in America makes its way in the ocean to the Sargasso Sea, a region of the Atlantic Ocean in what is popularly known as the "Bermuda Triangle" (south of the Bahamas and east of Bermuda). From this centralized oceanic spawning-ground, the eggs are fertilized and hatch into miniscule larval eels which then travel back to the freshwater ecosystems where the eels spend most of their adult life apart from this mating ritual.

The possibility of the eel being overexploited by commercial fishing is definitely worth considering, when a host of other factors have conspired to deplete the numbers of American eels, including the destruction of their habitats, changes in their food supply, predation, environmental toxins and contamination, and diseases. However, the ability to measure the population of American eels is made difficult by the strange life cycle described above: the population of the species ranges over the entirety of the continental United States, but is nonetheless a consistent population with a single genetic pool based on the actual mating habits. The Atlantic States Marine Fisheries Commission notes that "from a biological perspective much is still unknown about the species" ("American Eel" 2014). This is because the migratory habits make the species difficult to monitor, and the actual abundance of the species is somewhat obscure; however it is possible to note that the numbers are indeed vastly depleted, significantly enough to warrant possible government intervention to protect the species. But the difficulty would be in how to establish this intervention.

Based on the present status of eel fisheries, there is one obvious and immediate recommendation that could be put into place. Currently eels are harvested at different stages of the life cycle: obviously adult freshwater eels are caught by specific fishing methods, since the adult eel can be used for food. But the greater concern in terms of population depletion is the harvesting of the larval young, known as "glass eels" in their second stage of development after hatching in the Sargasso Sea. The reason for special consideration of the harvesting of the juvenile "glass eels" is that the return of the juveniles from the Atlantic spawning grounds to the freshwater inland North American habitats marks the only time besides the actual oceanic spawning in the Sargasso Sea when the eel population is localized in one place, thus making them easier to harvest on a larger scale. This particular type of fishing, therefore, is arguably capable of doing greater damage to the population dynamics than any commercial fishing of the adult eel, simply because it involves a larger number at a more vulnerable developmental stage. Thus the outright ban on the harvesting of juvenile eels would be the most obvious form of conservation effort that could be enacted immediately.

Otherwise more data and creative solutions would be required in order to get some sense of how to maintain eel populations. The notion of doing a population survey in the Sargasso Sea is tempting, although it is difficult to see how this would be accomplished. Perhaps serious monitoring efforts on the return of the juveniles -- taking the place of harvesting of these juveniles -- could give some sense of the abundance of the species on a yearly basis. Otherwise a fishing ban or limit on the adult eel could be enacted if the numbers are as seriously depleted as is feared. But obviously the unusual life cycle makes the commercial farming of eels extremely difficult, as they do not mate in captivity. If this could somehow be accomplished, it would be a useful way to raise the numbers of the species.