Semester of Graduation

Spring 2022


Master of Oceanography and Coastal Sciences (SOCS)


Oceanography and Coastal Sciences

Document Type



Tunas are highly migratory species that are ecologically and economically important components of oceanic ecosystems worldwide. Unfortunately, life history information for the smallest true tuna (genus: Thunnus), blackfin tuna Thunnus atlanticus, is scarce despite the fact that it is the most abundant tuna found throughout much of the western Atlantic. In this study an otolith-based aging approach was used to evaluate age and growth relationships, examine sexual dimorphism in growth, and derive mortality estimates for blackfin tuna in the Gulf of Mexico. Age and growth relationships were evaluated using two models commonly applied to age-at-length data for tunas: the von Bertalanffy growth model and Richards growth function. Blackfin tuna were aged to 13 years old, representing a considerable increase over previous estimates of longevity for the species. The Richards growth function provided a better fit (L ∞ = 907 mm, k = 0.112 y-1, a = 1.05, b = 0.25) to the data compared to the von Bertalanffy growth model (L∞ = 824 mm, k = 0.365 y-1, t0 = -0.96; ∆AICC = 82.27), and was characterized by rapid growth during the first two years of life. Differences in sex-specific growth were also observed, with males reaching a higher L∞ than females (907 mm vs. 857 mm curved fork length, respectively). Similar to other tunas, otolith mass was a strong predictor of age (r2 = 0.91) in blackfin tuna. Finally, estimated instantaneous total (Z = 0.532 y-1) and natural (M = 0.467 y-1) mortality rates for blackfin tuna in the GOM were low relative to previous estimates in the southwestern Atlantic. These results represent critical baseline estimates of size-at-age, longevity, and natural mortality at relatively low levels of exploitation that can be used to inform future assessments.

Committee Chair

Dance, Michael



Available for download on Saturday, March 22, 2025