Age and Growth of Yellowfin Tuna in the U.S. Gulf of Mexico and Western Atlantic

Abstract

AbstractAge, growth, and mortality were estimated for Yellowfin Tuna Thunnus albacares from the U.S. Gulf of Mexico and western Atlantic Ocean. During 2004–2017, 3,443 Yellowfin Tuna were sampled, primarily from recreational landings off the coast of Louisiana (90%). Based on reading otoliths, ages ranged from 1 to 18 years, with younger fish (<4 years) representing the majority (78%) of the age‐classes. Otolith weight was allometrically related to fish age (r2 = 0.91), which suggests that it may be a useful tool in indirectly estimating age given the challenges associated with directly aging tropical tunas. Based on Akaike’s information criterion (AIC), the Richards growth model had the most parsimonious fit to the length‐at‐age data (average maximum length L∞ = 1,658 mm, growth coefficient k = 0.23 year−1, a = 1.04, b = 0.45) compared to the von Bertalanffy growth model (L∞ = 1,589 mm, k = 0.36 year−1, theoretical age at zero length t0 = −0.8 year; AIC difference = 26.21), which had a relatively poor fit. The size‐modified Richards model, which assumed a truncated error structure at the minimum size limit (686 mm curved fork length [CFL]) in fishery‐dependent collections, improved the fit in the smallest individuals and was therefore the preferred model. Males and females had similar maximum ages (18 and 17 years, respectively) but showed significant differences in growth, with males reaching a larger L∞ than females (size‐modified Richards: 1,706 versus 1,568 mm CFL, respectively). Baseline natural mortality (M) using a maximum age of 18 years was 0.346 and was then scaled across age‐classes. These growth and mortality estimates and the individual age data have been used in improving stock assessments for Yellowfin Tuna to support scientific management.