Are eels nocturnal?

One of our patrons was reading George R.R. Martin’s A Song of Ice and Fire fantasy series, on which the HBO television series Game of Thrones is based. Presumably to give things a more fantastical flavor, Martin made up his own system of telling time, having characters refer to times such as “the hour of the bat,” “the hour of the wolf,” and “the hour of the eel.” “I understand the wolf and the bat,” our patron said, “because they’re both associated with night. But why the eel? Are they nocturnal?”

While we can’t explain why Martin makes the writing decisions he does, we could find information about eels. We looked them up first in the World Book Encyclopedia. It didn’t tell us anything about when they were active, but we did learn that they undergo several metamorphoses over the course of their lives. American and European eels travel to the Sargasso Sea to lay their eggs. The eggs hatch into transparent larvae shaped like willow leaves. The larvae change into small transparent eels, called glass eels. By the time they reach the coast, the small eels have developed a greenish-brown color. No longer baby glass eels, they’re now juvenile eels, called elvers. The elvers travel inland and grow into yellow eels (though they’re more yellow-green or yellow-brown). During this stage, which can last many years, they reach their full size, three to five feet for females and around one-and-a-half to three feet for males. Eventually, they reach sexual maturity and turn black and silver. Now, they’re called silver eels. They fatten up for their journey back to the Sargasso Sea to mate. (They don’t eat on their voyage, and their digestive system actually starts to break down.) After mating, they die. Because they are born in the ocean, grow up in fresh water, and then go back to the ocean to spawn, eels are catadromous, and they’re the only such fish in North America.

As interesting as this is, it didn’t answer our question. We found that information on the U.S. Fish and Wildlife Service website. Freshwater eels are indeed nocturnal, at least during their yellow phase. They come out at night to eat crabs, fish, insects, eggs, clams, and frogs. They have small teeth and weak jaws, so to break off pieces of food that’s too big to swallow whole, they’ll grip it in their mouths and spin their bodies. They can spin up to fourteen times a second, almost three times as fast as an Olympic ice skater. Eels can move just as well forward and backward, and they can move over land through wet grass and mud because they’re able to absorb oxygen through their skin.

For more information on eels, James Prosek’s fascinating Eels: An Exploration, from New Zealand to the Sargasso, of the World’s Most Mysterious Fish is available through CLEVNET. George R.R. Martin’s books that inspired this question (as well as the television series inspired by the books) are both available at the Newton Falls Public Library or through CLEVNET.