I wrote some time ago about a species of bird, The Bar-Tailed Godwit, that migrates an astonishing distance every year.
Today, I am writing about a species of fish that engages in an equally arduous migration. The species is the European Eeel.
The Eel spends most of its life in fresh water, but when it reaches sexual maturity, it migrates back from its home body of fresh water to the ocean. This pattern of return to the ocean to spawn is the exact opposite of the life cycle and breeding action of the Salmon, which begins its life in freshwater, matures in the ocean, then returns to fresh water to spawn and (like the eel) to die.
What happens to migrating eels after their return to the ocean has never been entirely clear. In the late 19th Century, scientists finally established that juvenile eels were in fact the second larval stage of the species, developing from the first larval stage before the juvenile eels reached fresh water. By a process if extrapolation, scientists postulated that eels spawned in the Sargasso Sea, and that the larvae then traveled back to Europe via the Gulf Stream and other ocean currents.
This recent scientific paper, using modern tracking technology, largely confirms prior scientific theories about the reproductive process of the European Eel. Eels migrate up to 5000 km back to the ocean to spawn, living off stored food reserves. After spawning, they die, since they cannot feed any more.
