March 16, 2004

Critical to fisheries management is being able to assign an age to fish that are sampled.  Fortunately for biologists, many fish are cooperative in that they record their growth – and age – on their bones.  Scales, opercles (gill plates), and fin rays all record fish growth in a manner that allows age interpretation.

Like a tree, fish lay down one annular ring, or annulus, on otoliths ever year.  Fortunately, non-lethal scale sampling can be used to age fish, although they require more interpretation as they lay down numerous circuli every year.  Knowing the age of fish sampled in fisheries assessments makes it possible to determine annual mortality rates, the size of a given year class, and to assess how successful a stocking program is, to name just a few.