Background
Yellowfin tuna (Thunnus albacares) support some of the world's largest tuna fisheries and are of major economic and food security importance to Pacific Island countries and territories. Reliable reproductive parameters are essential inputs for stock assessment models, yet for yellowfin tuna in the Western and Central Pacific Ocean (WCPO), the most recent WCPO-wide estimates are nearly 30 years old. This study provides updated estimates of length and age at maturity across the WCPO.
Methods
A total of 1,634 female yellowfin tuna collected between 2005 and 2025 from 21 Exclusive Economic Zones were examined histologically to assess maturity. Logistic models were used to estimate length and age at 50% maturity (L50 and A50), investigate spatial variation in maturity, and evaluate the influence of gonad preservation method.
Results
The WCPO-wide L50 was estimated at 90.76 cm, compared with the previously accepted estimate of 104.57 cm. This difference is largely explained by the use of an updated histological classification that improves identification of regenerating mature females. The estimated A50 was 1.83 years. Frozen preservation had little effect on maturity estimates, producing L50 and L95 values only 3.0% and 7.3% higher than those obtained from formalin-preserved samples. Strong variation in length at maturity was observed across WCPO, with L50 lowest in the Archipelagic region (73.29 cm) and highest in the Southern region (101.96 cm). Regional differences in spawning seasonality were also evident, with spawning occurring throughout most of the year in equatorial waters but showing a distinct peak in the Southern region.
Conclusions
This study provides the first WCPO-wide update of yellowfin tuna maturity estimates in almost three decades. The results demonstrate clear spatial variation in maturity and provide updated parameters for future stock assessments.