Natural Curiosities: The Slippery Question of Eels

On cool autumn evenings when rains swell rivers on America’s eastern seaboard, one of nature’s strangest mysteries unfolds. Freshwater eels by the thousands rouse themselves from hiding places in streams, lakes, and ponds. Driven by instinct, they push downriver seeking the open sea. Along the way, the eels spontaneously become sexually mature and begin prepping for life in the ocean as if a hormonal switch has been flicked. Eels that might be decades old grow sex organs for the first time, change in color from yellowish brown to silver, and become a solid tube of rippling muscle. Already tolerant of salinity, their digestive system adapts to salt water consumption.  A river within a river, the eels pour into the Atlantic, then make for their breeding grounds far offshore in the warm waters of the Sargasso Sea.

Like, all eels do this. As far as science knows, that patch of ocean is the only place American eels, as well as