Precision of age estimation in red snapper (Lutjanus campechanus)

The validation of aging methods is an important step in estimating growth and longevity and has been accomplished for red snapper. However, routine age interpretation remains largely subjective. A reference collection of 300 red snapper otoliths was circulated among seven external laboratories in the Gulf of Mexico region to compare ages against our internal laboratory determinations. A precision benchmark of average percent error (APE; estimate of precision) ≤5% has been suggested for moderately long-lived species such as red snapper. APE ranged from 2.5 to 6.0% for six facilities with no apparent bias in estimates as age increased. One initial estimate was notably higher with an APE of 11.6% and bias was evident. Beyond the need for initial training to recognize annulus patterns in decades-old fish, common differences between readers were related to interpretation of the otolith edge type and to interpretation of the first annulus. Precise measurement of annulus distances and identification of otolith edge patterns aided by light reflectivity measurements indicated that annual rates of transition from translucence to opacity were consistent. However, annual differences in the seasonal timing of otolith zone transition occurred on the order of a few months (this study and others). The degree of opacity varied in the first annulus, but the distance from the core to the distal edge of the first annulus was consistently around 1 mm (mean = 1.05 mm; S.D. = 0.11). By recognizing possible variations in these patterns and with use of periodic reader training and a reference collection, our expectation is that a 5% APE precision target can be readily achieved and improved upon.