Validation of Otolith Annuli of Bluegills in a Southeastern Thermal Reservoir

Abstract

Abstract Opaque bands on otoliths were validated as annuli for bluegills Lepomis macrochirus throughout their lives in Par Pond, a nuclear reactor cooling reservoir in South Carolina. Whole mounts of otoliths were suitable for age determination of young bluegills (less than 5 years old), but both whole mounts and otolith sections were necessary for age determination of older bluegills. Marginal increment analyses indicated that annulus formation began as early as February and was complete by June in bluegills of ages 1–9. Annulus formation began earlier in younger (age 1–2) bluegills than in older individuals. Similarity of observed and back-calculated sizes at age supported identification of opaque bands as annuli. Input of warm water from reactor operation occasionally produced opaque bands (false annuli) on otoliths; however, the faintness and incompleteness of such bands clearly distinguished them from true annuli. Identification of the first annulus of some otoliths was problematic due to the occurre...