Age and growth estimation of bigeye tuna, Thunnus obesus (Teleostei: Scombridae) in the southwestern Atlantic

Abstract

The purpose of the current study was to supply the first information on age and growth for Thunnus obesus caught in the equatorial south-western Atlantic using dorsal spines, an approach that has been successfully employed for ageing tuna species. The study was conducted using a multi-model inference based on information theory for back-calculated and observed length-at-age data. Uncertainty associated with the parameter estimation was verified and results were compared to other accounts on the species, considering both the statistical and methodological contexts. Samples were collected in Natal city (Rio Grande do Norte State, Brazil) from February 1999 to January 2000, of tuna vessels and from surveys, aimed at providing information on the Brazilian Exclusive Economic Zone (EEZ) in the area around São Pedro and São Paulo Archipelago. Validation using marginal increment indicated that one ring is deposited per year. Mean length-at-age ranged of 54.3 to 177.5 cm (fork length) for ages 1 to 9 years. Von Bertalanffy, Richards, and Gompertz models were considered suitable for the bigeye tuna. Hence, the model-averaged asymptotic length ¯L&#8734; was estimated. The averaged model generated in the present study by back-calculation was considered appropriate for describing the growth of T. obesus.<br>A proposta do presente estudo foi fornecer a primeira informação sobre idade e crescimento de Thunnus obesus, capturado no Atlântico sudoeste equatorial usando espinhos dorsais, uma abordagem que tem sido utilizada com sucesso na determinação de idade de espécies de atuns. O estudo foi conduzido usando uma inferência de multi-modelos baseada na teoria de informação avaliada para dados de comprimento por idade retrocalculados e observados. Incertezas associadas aos parâmetros foram verificadas e os resultados foram comparados aos de outros estudos realizados para esta espécie, considerando os contextos estatísticos e metodológicos. As amostras foram coletadas na cidade de Natal (estado do Rio Grande do Norte, Brasil) de fevereiro de 1999 a janeiro de 2000, provenientes de embarcações comerciais e também prospecções, cujo objetivo foi prover informações sobre a Zona Econômica Exclusiva (ZEE) na área do entorno do Arquipélago de São Pedro e São Paulo. A validação usando incremento marginal indicou a deposição de um anel anual. Os comprimentos médios por idade variaram entre 54.3 a 175.7 cm (comprimento furcal) para idades de 1 a 9 anos. Os modelos Von Bertalanffy, Richards e Gompertz foram considerados adequados para a albacora bandolim e, desta forma, o comprimento assintótico para um modelo médio (¯L&#8734;) foi estimado. O modelo médio gerado no presente estudo a partir dos comprimentos retrocalculados foi considerado apropriado para descrever o crescimento de T. obesus capturada no Atlântico

Growth of bluefin tuna (Thunnus thynnus) in the North-eastern Atlantic and Mediterranean based on back-calculation of dorsal fin spine annuli

“…Growth back-calculations from fin spines have been a suitable approach for large pelagic species (Tserpes and Tsimenides, 1995;Lessa and Duarte-Neto, 2004;Kopf et al, 2011;Duarte-Neto et al, 2012). The implementation of a wide array of methods for estimating length-at-age from different calcified structures allows corroborating age and growth information of a species (Ballagh et al, 2011;Kopf et al, 2011).…”

Direct ageing of Thunnus thynnus from the eastern Atlantic Ocean and western Mediterranean Sea using dorsal fin spines

“…This process, known as nucleus vascularization, is the greatest disadvantage of using this calcified structure for ageing purposes, as it might result in significant age underestimation and growth overestimation (Panfili et al , ; Drew et al , ; Kopf et al , ). Nucleus vascularization has been reported in several tuna species with frequent use of the method developed by Hill et al () to replace lost annuli (Compeán‐Jimenez & Bard, ; Tserpes & Tsimenides, ; Chiang et al , ; Zaboukas & Megalofonou, ; Duarte‐Neto et al , ; Farley et al , ). This method relies on the assumption that the annulus of a particular age class forms at approximately the same radius for each individual in the population; nevertheless, very little has been published regarding the quantification of obscured annuli due to vascularization in most of these species including T .…”

Effectiveness of Large-Scale Marine Protected Areas in the Atlantic Ocean for Reducing Fishing Activities

“…To meet global MPA commitments and in recognition of the relatively poor development of protected areas associated with the marine realm in Brazil, the Ministry of the Environment declared two sets of large-scale MPAs in the Southwestern Atlantic Ocean in early 2018: (i) two MPAs surrounding the São Pedro and São Paulo Archipelago (SPSP), which is formed by rocky islands in the mid-Equatorial North Atlantic Ocean (0 • 55 N; 29 • 20 W), distant about 1,000 km from the mainland; and (ii) two MPAs surrounding the Trindade Island and the Martin Vaz Archipelago (TMV), which is formed by the emerged part of the Vitória -Trindade submarine chain in the southwestern tropical Atlantic Ocean (29 • 18 S; 20 • 30 W), distant 1,160 km from the mainland (see Supplementary Figure 1 for detailed zoomed views of both regions). These islands have among the highest fish biomass across Brazilian reefs (Morais et al, 2017), notable endemism (Simon et al, 2013;Pinheiro et al, 2020), and globally threatened fauna (Almeida et al, 2011;Duarte-Neto et al, 2012). Despite their biodiversity significance, both regions are also threatened by commercial fisheries and climate change (Magris et al, 2020).…”