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This paper provides an update on yellowfin tuna (Thunnus albacares) otolith ageing activities in the western Indian Ocean that have occurred since Farley et al. (2021). Age estimates were obtained for 136 yellowfin tuna, using both daily (n=46) and annual (n=90) ageing methods. The youngest was aged 44 days and the oldest was 11.4 years. The new age data were combined with age data obtained in the ‘GERUNDIO’ project1 (Farley et al. 2021), providing a total of 386 age estimates for analysis. Four growth models were fit to the age and length data (von Bertalanffy (VB), Richards, VB log k, and 2-stage VB), with the 2-stage VB model providing the best fit, particularly for small fish (< ~55 cm fork length, FL). The length-at-otolith weight data (which is independent of the age estimation method) showed a change in otolith growth at ~55 cm FL, which is consistent with the length-at-age data and lends support to the 2-stage VB model. Overall, our analysis shows that fish grow rapidly after birth, reaching ~60 cm FL by age 1 and ~95 cm FL by age 2. Mean asymptotic length was estimated to be ~167 cm FL, slightly higher than estimated in Farley et al. (2021). The updated data analysis indicates that males reach larger sizes, on average, than females We continue to recommend that additional otoliths are collected from the northern and eastern regions of the Indian Ocean, and that these otoliths are aged to provide further information on growth and longevity of yellowfin tuna at the oceanic scale. These data will be useful for assessing whether there are regional differences in growth, and may also provide information regarding inter-annual variation in growth.
