Abstract

The periodicity of otolith growth rings from adult red snapper was examined through a mark and recapture study. In 2005 - 2007, red snapper (n = 251) were caught hook-and-line, injected with oxytetracycline, and released 15-40 km south of Dauphin Island, Alabama. Fish were recaptured up to 2.5 years after release (n = 12). Sagittal otoliths were dissected, sectioned, and the number of growth rings past the OTC mark was compared to time at liberty of the fish. Preliminary findings support an annual periodicity of growth ring formation, however, all recaptured fish were less than 10 years of age and validation of older red snapper (> 10 years) is still needed. Otolith shape analysis was applied to otoliths taken from hatchery reared known-age red snapper. Morphological shape indices were able to distinguish among age-0, age-1 and age-2 otoliths. Significant differences in the aspect ratio, box x/y, and radius ratio showed juvenile red snapper otoliths grew faster along the anterior-posterior axis compared to the dorsal-ventral axis. A discriminant function analysis and cross-validation showed an age classification success of 70% based on shape variables alone. The addition of otolith weight to the discriminant function increased classification success to 93%. Based on these data, we believe otolith shape analysis is a potential new method for ageing young red snapper at least to age-2.

PDF Preview