Scientists at the Alaska Fisheries Science Center collect a variety of information about fish that aids in the effective management of commercially-important fish stocks. Knowing the age composition of commercially exploited fish populations is critical to understand how healthy fish populations are and set sustainable catch limits each year. For instance, if a fish stock has a range of old and young fish it is indicative of a more healthy fish population.
To determine how old fish are, scientists collect and analyze fish otoliths (a calcium carbonate structure found in a fish’s ear). Otoliths contain annual growth zones that are deposited each year. Counting otolith growth zones to estimate fish age is analogous to counting tree rings. More than 20,000 otoliths are read by AFSC scientists each year.
Otoliths are collected from NOAA Fisheries surveys, fisheries observers, foreign fisheries agencies and state agencies. Current species studied include: walleye pollock, sablefish, Pacific cod, Atka mackerel, yellowfin sole, Pacific ocean perch, salmon, and various other flatfish and rockfish species.
To confirm the accuracy of age estimates, the Alaska Fisheries Science Center’s Age and Growth Program use a number of age validation techniques including stable isotopes, the novel use of bomb radiocarbon ( 14 C) derived from above-ground atomic bomb testing, and other validation methods.
Thomas Hesler, program manager