Evaluating otolith increment deposition rates in bigeye tuna (Thunnus obesus) and yellowfin tuna (T. albacares) tagged in the Atlantic Ocean: Suppl. Fig. 2

Abstract

— A recent Atlantic- wide tag- recapture experiment run by the International Commission for the Conservation of Atlantic Tunas was an opportunity to directly validate otolith increment deposition rates for bigeye tuna ( Thunnus obesus ) and yellowfin tuna ( T. albacares ) in the region. Age and time at liberty were estimated by using annual and daily increment counts for sectioned otoliths from sampled fish previously injected with oxy- tetracycline and later recaptured. The use of annual increment counts resulted in g reater age estimates than those from daily increment counts for fish >55 cm straight fork length (SFL). Use of daily increment counts led to underestima- tion of time at liberty for fish >55 cm SFL at recovery, compared with known times at liberty. In contrast, predictions based on annual increment counts are accurate across the entire size range of sampled fish, validating the notion that increments are deposited annually. We therefore recommend that counting annual increments be the preferred method for aging yellowfin and bigeye tuna from the Atlantic Ocean and that the use of daily increments for aging be limited to young of the year. Aging fish accurately is important for stock assess- ments in which data on age and growth play an increasingly essential role in examining population dynamics. It is crucial that otolith reading practices and analyses based on age data reflect the most up- to- date recommendations for age estimation.