Age, growth, and mortality of Blackfin Tuna in the Gulf of Mexico

Objective

An otolith-based aging approach was used to evaluate age and growth relationships, sexual dimorphism in growth, and derive mortality estimates for Blackfin Tuna Thunnus atlanticus in the Gulf of Mexico (GOM).

Methods

Blackfin Tuna (n = 395) were sampled from recreational fisheries and aged from 0 to 13 years, representing an increase over previous estimates of longevity for the species.

Result

Rapid growth was exhibited during the first two years of life, and the Richards growth function provided a better fit (L_∞ = 907 mm, k = 0.112 /year, a = 1.05, b = 0.25) to the data compared with the von Bertalanffy growth model (L_∞ = 824 mm, k = 0.365/year, t₀ = −0.96). Sexual dimorphism in growth was observed, with males (907 mm) reaching a larger L_∞ than females (857 mm), and otolith mass was a strong predictor of age in both sexes. Estimated instantaneous total (Z = 0.532/year) and natural (M = 0.467 year) mortality rates for Blackfin Tuna in the GOM were low relative to previous estimates in the southwestern Atlantic, where fishing mortality (F) is likely much higher.

Conclusion

Results represent critical baseline estimates of size-at-age, longevity, and natural mortality for Blackfin Tuna at relatively low levels of exploitation that can be used to inform future assessments.