Age validation of yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tuna of the northwestern Atlantic Ocean

Abstract

Estimates of age and growth of yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tuna remain problematic because validation of growth zone deposition (opaque and translucent) has not been properly evaluated. Otolith growth structure (zone clarity) can be poorly defined for tropical tunas, but the use of bomb radiocarbon dating has validated age estimates to 16–18 years for yellowfin and bigeye tuna. Use of the radiocarbon decline period — defined by regional coral and otoliths — provided valid ages through ontogeny. Yellowfin tuna aged 2–18 years (n = 34, 1029–1810 mm FL) and bigeye tuna aged 3–17 years (n = 12, 1280–1750 mm FL) led to birth years that were coincident with the bomb radiocarbon decline. The results indicate there was no age reading bias for yellowfin tuna and that age estimates of previous studies were likely underestimated for both species.

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

“…Yellowfin Tuna age and growth were successfully estimated in the U.S. GOM and western Atlantic Ocean using direct annual aging methods from otoliths that were largely obtained from fishery-dependent recreational sources. The aging criterion was supported by 14 C bomb radiocarbon validation (Andrews et al 2020) and otolith edge analysis, and the APE among age readers (8.1%) was less than the threshold of 10% set for similar, difficult-toage pelagic fish species, such as Atlantic Bluefin Tuna (Secor et al 2014;Busawon et al 2015). The ability to reliably age Yellowfin Tuna by using otoliths has resulted in the age-at-length data being used in the most recent ICCAT Yellowfin Tuna stock assessment (ICCAT 2019b).…”

“…Daily age enumeration from otoliths (Stequert et al 1996;Shuford et al 2007) and annual aging of spines (Lessa and Duarte-Neto 2004) resulted in extremely high L ∞ estimates (2,307-2,727 mm SFL), an implausible situation given that L ∞ is intended to represent the average maximum (asymptotic) lengthnot the maximum length of the largest individual observed in the population (ICCAT 2019a). The high extrapolated L ∞ estimates were likely caused by using aging methodologies (i.e., daily otolith increments and spines) that are known to underestimate the ages of older individuals (Williams et al 2013;Andrews et al 2020). In the current study, the L ∞ estimated from the VBGM was 1,589 mm CFL (1,533 mm SFL), which was reasonable given that the standardized residuals were normally distributed around L ∞ .…”

“…However, there have been several studies estimating the growth of tuna species, such as South Pacific Albacore T. alalunga (Farley et al 2013), Bigeye Tuna T. obesus (Farley et al 2006;Schaefer and Fuller 2006), Pacific Bluefin Tuna T. orientalis (Ishihara et al 2017), and western Atlantic Bluefin Tuna T. thynnus (Neilson and Campana 2008), using validated otolithbased annual aging methods. Additionally, the annual age-reading criterion currently used for Yellowfin and Bigeye tunas in the GOM was recently validated using 14 C bomb radiocarbon techniques (Andrews et al 2020) and is recognized by ICCAT as an acceptable aging method (ICCAT 2019a(ICCAT , 2019b.…”

“…Since annual aging from otoliths of fish older than age 1 is considered the most accurate method for tropical tuna species (Williams et al 2013;Farley et al 2019) and has been recently validated for Yellowfin Tuna in the GOM (Andrews et al 2020), there was a need to undertake a comprehensive aging study to improve the growth information for Yellowfin Tuna stock assessments. The goals of this study were to derive ages using annual growth increments in otoliths, to determine both pooled sex and sex-specific growth model parameters using a multi-model approach, to investigate otolith weight as a tool to predict age, and to estimate mortality of Yellowfin Tuna in the U.S. GOM and western Atlantic Ocean.…”

Early overcounting in otoliths: a case study of age and growth for gindai (Pristipomoides zonatus) using bomb 14C dating

“…Comparison of measured 14 C values at their respective birthdates, and relative to the regional 14 C references, provided a baseline for interpreting the validity of age estimates from the Scofield (2013) study ( Supplementary Material 1). Alignment or misalignment of the calculated birthdate -determined as the date of collection minus the age estimate -with the years and 14 C levels of the post-peak 14 C decline (more recent than ~1980) can validate or invalidate the age estimates (See Andrews et al (2020b) for an example of age scenario elimination using the post-peak bomb 14 C decline period). The reference records used in this study were two coral and otolith 14 C data sets: 1) Kure Atoll of the Northwestern Hawaiian Islands (NWHI), and 2) Kona of Hawaii Island of the main Hawaiian Islands (MHI; Andrews et al, 2016b; Fig.…”