European Eels: Fresh/Salty Water Species of the Week (for World Oceans Day)

European eels are highly endangered. Photo: Ron Offermans, Wikimedia Commons


Today is World Oceans Day, so we decided to take a look at a species that straddles both fresh and salty water. Consider the eel, specifically the European eel (Anguilla anguilla). 

The species was historically a significant food source for many Europeans (including the famous jellied eels of East London), but pollution, over harvesting, and river impediments have resulted in a crashed population, which numbers less than 10% of previous levels. The eels are catadromous, meaning they live much of their lives in freshwater, but travel out to sea to spawn.

For centuries, the precise rhythms of the eels were unknown, but scientists think the mature adults swim several thousand miles out to the Sargasso Sea, where they breed and then die. Larvae drift back towards Europe over about 300 days, until they enter rivers as tiny “glass eels.” The pint-sized animals swim upstream and grow bigger (eventually becoming the adorably named “elvers,” then “yellow eels,” followed by “silver eels,” due to changing hues with age).

freshwater species of the weekThe eels live for five to 20 years in freshwater rivers before they head to sea to reproduce. In captivity, they are known to live much longer.

Interestingly, recent research suggests they can swim four to six times more efficiently than non-eel like fish, which helps explain how the adults are able to make it so far out to sea.

Also for World Oceans Day, the group  One World One Ocean has just released a new animated video, “The Ocean We Want To Know,” which happens to be set to one of my favorite recent songs — Gotye’s haunting “Somebody That I Used To Know.”

According to One World rep Molly Malloy, the video “takes you on a trip around the world to some of the ocean’s most special places, singing a song of ocean celebration…  The goal in creating this video was to really engage younger audiences, the majority of which have no idea that World Oceans Day even exists — using stunning facts about the blue planet. From Yosemite to the Mariana Trench to the Arctic, ‘The Ocean We Want To Know’ aims to do just that in a fun and unique way.”

Check it out:


Did you do anything for World Oceans Day?


Brian Clark Howard is an Environment Writer and Editor at National Geographic News. He previously served as an editor for and E/The Environmental Magazine, and has written for,,, Yahoo!, MSN, Miller-McCune and elsewhere. He is the co-author of six books, including Geothermal HVACGreen Lighting and Build Your Own Small Wind Power System.