EVALUATION OF ATLANTIC BLUEFIN TUNA OTOLITH AGEING PROTOCOLS

Abstract

An otolith ageing bias for juvenile Atlantic bluefin tuna was detected at the 2017 population assessment. Consequently, revised reading criteria were proposed to reduce this ageing bias. To evaluate standardized and revised reading criteria, age estimates were compared to reading and radiocarbon age estimates. Age estimates showed a lack of bias and adequate level of precision for most readers, indicating that reading criteria are adequate. No bias was detected in the ageing of juveniles, contrary to the 2017 assessment findings. This may be due to the fact that one-year biases may not be noticeable given the wide age range and small sample size used in this study. Some readers showed lower age estimates for older individuals (20+) as compared to radiocarbon age estimates. Furthermore, age estimates were consistently higher than the Ailloud et al. (2017) growth curve for samples aged over 20 years, likely due to the lower mean asymptotic length of the growth curve using the Richards fitting. In terms of methodology, a potential section effect on identification of false annulus and edge type was noted.