Slithering along the bottom of Prince Edward Island freshwater ponds, estuaries, and nearshore saltwater environs is a uniformly olive-colored, long, tubular creature called the American eel (Anguilla rostrata). The story of A. rostrata is one of conflict with man; they’re a case study in how man’s desires (needs?) often butt heads with the requirements of wildlife.
American eels are fish, though perhaps they don’t really appear like your traditional fish. They are a member of the Order Anguilliformes, which consists of some 791 species of eels including the moray eels (Muraenidae) that many of us are familiar with. Fish in this Order inhabit all sorts of habitats from deep seas to freshwater lakes and ponds.
Anguilliformes swim with a whole-body, undulating motion, a style named after the Order itself. The only other fishes to swim like this are lampreys (Petromyzontiformes) and hagfishes (Myxiniformes). A propulsive waves runs backward down the body of the fish, generated by the snaking S-shaped body movements. The propulsive wave gets progressively larger as it moves down the body until finally the forces are transferred to the water at the tail fin, displacing water and moving the fish forward. Undulating the entire body, though, causes water to be displaced side-to-side and wastes energy. Normally, these reactive forces might slow the body down, but because the bends are so large the lateral forces cancel out. Still, eels are relatively slow swimmers with moderate swimming efficiencies (tunas, mackerels, billfishes, and lamnid sharks like makos and great whites are the most efficient).
American eels feed on a variety of things. The adults are omnivorous, feeding on everything from plants to fish. They are benthic dwellers that ply the bottom for whatever they can find.
But perhaps one of the most interesting aspects of American eels is their life history strategy. A. rostrata begin life at sea, specifically in the Sargasso Sea, and spend much of their early developmental stages drifting in currents. These currents will eventually push them toward the coast as little transparent, “glass” eels. As they continue to develop into what’s termed elvers they move farther into freshwater. An interesting little factoid is that the juvenile elvers can move up and over rocks and other obstructions by using surface tension to adhere they bodies to surfaces and climb over things. Once in ponds, lakes, or inland rivers they will develop into adults (known as yellow eels). Eventually, the adults will out-migrate from August to December (usually at night) back to the ocean to spawn. This life history strategy is known as catadromy, and is the opposite strategy to anadromy that Pacific and Atlantic salmon use.
One caveat to their life history strategy is that they don’t necessarily have to go into freshwater to develop into adults. The coastal waters around Prince Edward Island is a perfect example of this. My limited excursions with a mask and snorkel have yielded a surprising number of eel sightings. This is encouraging because American eels are a threatened species…
Eels are threatened because humans have a voracious appetite for them. Stewed, barbecued, baked, or pan fried, the sweet, white flesh of American eels is considered a delicacy to many. Our desire (again, need?) to dam rivers and prevent them from reaching upstream feeding areas has created a powerful double-whammy that has led to population declines across their range. There are still fisheries for them, including here on PEI, but these are tightly managed. Conditions at sea and little or missing information on recruitment dynamics makes them difficult to manage.
These fish are fascinating to watch underwater and I had the great pleasure of doing so in a relatively open environment late yesterday evening. I’m looking forward to more time spent with these creatures!