Age and growth of three coastal-pelagic tunas (Actinopterygii: Perciformes: Scombridae) in the Florida Straits, USA: blackfin tuna, Thunnus atlanticus, little tunny, Euthynnus alletteratus, and skipjack tuna, Katsuwonus pelamis

Abstract

Background. Understanding the life history of a species is essential for fully understanding its role within an ecosystem.  However, many of the fish species of high ecological value have not been studied due to their less prominent roles in local recreational and commercial fisheries in comparison to other targeted species.  These valuable fishes are also important trophic linkages between small neritic fishes and large, economically valuable apex predators.  This study describes for the first time the yearly age and growth patterns of three small tuna species inhabiting South Florida (USA) waters: blackfin tuna, Thunnus atlanticus (Lesson, 1831); little tunny, Euthynnus alletteratus (Rafinesque, 1810); and skipjack tuna, Katsuwonus pelamis (Linnaeus, 1758). Materials and methods. Tuna specimens were collected in two ways: via donations obtained from various fishing tournaments and charter captains in the areas of the Florida Straits as well as hook-and-line catches performed especially for this project.  Age determination was based on sagittal otolith hyaline deposition patterns.  Marginal increment analysis was used as an indirect validation method.  Growth parameters were determined by comparison of the fish fork length and the hyaline band measurements. Results. Two hyaline bands formed each year in all three species—one in winter and one in summer.  The von Bertalanffy growth equation produced a growth rate for each species: blackfin tuna, L¥ = 95.34 cm, K = 0.28, and t0 = –1.53; little tunny, L¥ = 77.93 cm, K = 0.69, and t0 = –0.69; and skipjack tuna, L¥ = 112.76 cm, K = 0.24, and t0 = –1.70.  Parameters of each resulting von Bertalanffy equation were compared among species showing that little tunny grew the fastest, but skipjack had the largest estimated size.  Results were also compared with growth rates currently used in stock assessments by fisheries management organizations, such as the International Commission for the Conservation of Atlantic Tunas (ICCAT). Conclusion. Sectioned otoliths indicate two bands a year for these three species in the Florida Straits.  Results were comparable to other studies, with a similar finding of two bands per year in hard parts for these species.  Further knowledge of these populations will aid in stock assessments for these species and the ongoing shift to ecosystem-based management plans.