The Ageing Laboratory ages about 2,000 fish per year using sagittal otoliths. Otoliths (ear bones) are located in the fish’s head behind the eye and directly below the brain.
Otoliths are used by the fish for orientation and to maintain balance, acting a lot like our middle ear, and are composed of calcium carbonate. Every year a layer of material is deposited. This process results in annual bands (i.e., annuli) forming on the otolith like the rings in a tree.
The otoliths among species vary in shapes and sizes. Some otoliths are large and chunky like those found in red drum and black drum while others are thin and fragile like the ones found in southern flounder and sheepshead.
Otoliths are removed, cleaned, and dried before they are stored. Later, a thin section is cut from the otolith using a Buehler low-speed Isomet saw with two diamond wafering blades and a spacer. A section is made through the core yielding a clear view of annuli formed in the otoliths.
By knowing the age of fish scientists can determine the age composition of the catch, age-at-maturity, age at capture in the fishery, and the maximum age that fish species lives. This yields information on the health of fish populations and the sustainability of the fisheries.
Some of the fish aged include: spotted seatrout, red drum, southern kingfish (whiting), Atlantic croaker, tripletail, sheepshead, and southern flounder.