The Question: I recently I saw an eel-like fish while swimming in the sea in Rockport, MA. It looked around 3 feet (1 meter) long and was white/grey with black stripes (running from nose to tail, not vertically). It moved like an eel. We were in water that was around 3 feet (1 meter) deep, no snorkeling/diving mask. It was very sandy, no rocks at all. Not sure how many stripes exactly – my impression was that it was black stripes on a silver/white body…perhaps 12 or so thin stripes running nose to tail. We saw it three times (or maybe different individuals). I would love to know what it was.
The Short Answer: I thought at first Kathryn might have seen an American eel (Anguilla rostrata), but the description of stripes bothered me. I asked two fisheries biologists who both came back with the same answer: striped bass (Morone saxatilis). When I asked Kathryn how tall the fish was, she said it was more like six inches (15 cm) than three inches (7.5 cm), which pretty much clinched it. That measurement suggests much more of a striped bass shape than the thin shape of an American eel.
Ken Oliviera, associate professor of biology at the University of Massachusetts Dartmouth, and an expert on American eels, said he has never seen a striped pattern on an American eel, and the location suggests striped bass to him. He also said it was probably multiple fish, since striped bass school.
Brad Chase, aquatic biologist for the Massachusetts Division of Marine Fisheries, was also bothered by the stripes. He pointed out that American eels are typically nocturnal and they prefer habitat with rocks and other hiding places. His guess agreed with that of Ken Oliviera in that the size, stripes, and location point to striped bass.
So I think that’s your mystery fish, a school of striped bass.
The Interesting Science: It just so happens that striped bass and American eel have something in common. They both breed in one type of water and live in another. Striped bass are “anadromous” which means they breed in fresh water, but spend most of their lives in salt water. Salmon, of course, are famous for this, but they are hardly the only fish that goes up rivers to breed and then moves into the ocean to grow. The American eel, however, is “catadromous” which means it breeds in salt water, and then moves to fresh water. This is a far less common lifestyle. For a long time the breeding location of the American eel was unknown. But we now know they breed in the Sargasso Sea, an area of relative calm in the Atlantic Ocean. Once they reach about 2.5 inches (6 cm), young American eels are carried by the Gulf Stream to the Atlantic shore. It was once thought that all American eels then return to fresh water, but we now know that it’s mostly females that move into fresh water and only when conditions are good. Once the eels reach a certain size, they move back to salt water. When they reach adult size, they return to the Sargasso Sea to breed.