Updated growth models for bigeye tuna (Thunnus obesus) in the Atlantic Ocean

Abstract

The International Commission for the Conservation of Atlantic Tunas (ICCAT) concluded the Atlantic Ocean tropical Tuna Tagging Programme (AOTTP) in 2021. This project had the objectives of enhancing food security, stimulating economic growth, and improving management through research on tropical tuna resources in the Atlantic Ocean, including bigeye tuna (Thunnus obesus). Here, we combine tagging data and otolith data from the AOTTP program, Panama City Lab and the Pelagic Fisheries Lab at the University of Maine with historical tagging data and otolith data from ICCAT and other sources to fit integrated growth models with the goal of providing the most complete growth curve (in terms of data inclusion and validation of age-at-length) for bigeye tuna in the Atlantic Ocean. Both Richards and von Bertalanffy growth models were fitted. A variety of models were fitted to subsets of the data to investigate the consistency of growth information. In all cases for the integrated model, the Richards and von Bertalanffy models were very similar with the von Bertalannfy model being preferred for parsimony. The preferred model, based on fit to old fish, was the von Bertalanffy curve based on length-age pair data from multiple sources. The addition of tagging data to create an integrated model showed patterns of lack of fit to both the tagging and otolith data suggesting conflict between the tagging and otolith data. The preferred model (length-age pair data only) gave the estimates: asymptotic length L∞ (fork length) equals 161.21 cm (95% bootstrap CI 154.39, 166.84), growth parameter K equals 0.392 yr−1 (95% bootstrap CI 0.355, 0.441), and the time-axis intercept t0 equals − 0.239 yr (95% bootstrap CI –0.306, −0.175). For the best fitting integrated model, the asymptotic length L∞(fork length, in cm) was estimated to be 185.78 (SD 6.298), the growth parameter K was 0.252 yr−1 (SD 0.014), and the time-axis intercept t0 was − 0.524 yr (SE 0.025). The value for asymptotic length L∞ from the integrated model was larger than the lengths of all the old fish in the sample whereas the value for the curve based on otoliths passes through the cloud of points for old fish.