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Ear bones divulge an eel's true age

NSF Award:

REU Site: Research Experience for Undergraduate Minorities in Marine and Environmental Sciences.  (South Carolina Department of Natural Resources)

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Want to know how old a fish is? Check its ear bones. The bones, called otoliths, have growth rings just like growth rings in a tree, and many fish add one growth ring to their ear bones every year. During an NSF-sponsored Research Experiences for Undergraduates summer internship, James White wondered if eel ear bones add one growth ring every year. He spent the summer studying eel otoliths at the Department of Natural Resources in Charleston, S.C.

After looking at many eel otoliths, White determined that American eels in South Carolina add one growth ring to their ear bones each year. This is important because researchers can use the ear bones to figure out how long eels are living as well as the location of old and young eels. American eel fisheries are important contributors to commercial fisheries on the East Coast, but the number of eels is declining. Research suggests that understanding the eel life cycle and learning the best ways to track them will help to increase their numbers.

American eels live most of their lives in fresh water along the East Coast, but they swim into the middle of the Atlantic Ocean to lay their eggs and die. The eggs hatch in the ocean and develop into young eels that migrate back to the freshwater streams and rivers when they are about a year old. Adults can live to up to 25 years. 


  • a slice of an eel ear bone
A slice of an eel ear bone.
James White and Stephen Arnott, Marine Resources Research Institute

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