Vertebrae reveal industrial-era increases in Atlantic bluefin tuna catch-at-size and juvenile growth

Abstract

Climate change and size-selective overexploitation can alter fish size and growth, yet our understanding of how and to what extent is limited due to a lack of long-term biological data from wild populations. This precludes our ability to effectively forecast population dynamics and support sustainable fisheries management. Using modern, archived, and archaeological vertebrae dimensions and growth rings of one of the most intensely exploited populations, the eastern Atlantic and Mediterranean bluefin tuna (Thunnus thynnus, BFT), we estimated catch-at-size and early-life growth patterns from the 3 rd century bce to the 21 st century ce to understand responses to changes in its environment. We provide novel evidence that BFT juvenile growth increased between the 16 th–18 th, 20 th, and 21 st centuries, and is correlated with a warming climate and likely a decrease in stock biomass. We found it equally plausible that fisheries-induced evolution has acted to increase juvenile BFT growth, driving earlier maturation as a result of size-selective exploitation. Coincidently, we found limited evidence to suggest a long history of large ( >200 cm FL) BFT capture. Instead, we found that the catch-at-size of archaeological BFT was relatively small in comparison with more intensive, 20 th and 21 st century tuna trap fisheries which operated further from shore. This complex issue would benefit from studies using fine-scale biochronological analyses of otoliths and adaptation genomics, throughout the last century especially, to determine evolutionary responses to exploitation, and further disentangle the influence of temperature and biomass on fish growth.

Isotopic life‐history signatures are retained in modern and ancient Atlantic bluefin tuna vertebrae

“…(1983) and Andrews et al . (2023), where 1 year pertained to one groove (summer growth) and one ridge (winter growth).…”

“…The 35th vertebra was selected for consistency between specimens and due to the fact that annuli (growth rings) are often more clearly interpreted in these vertebrae. The authors estimated the age of specimens by counting annuli (Figure 1a) on the posterior centra of the 35th vertebra for each specimen, without staining and with illumination only, following Lee et al (1983) and Andrews et al (2023), where 1 year pertained to one groove (summer growth) and one ridge (winter growth).…”

“…Note. Age was estimated by counting annuli followingLee et al (1983) andAndrews et al (2023), as described in the methods. Height, width and length correspond to 35th vertebra measurements on the posterior centra as perAndrews et al (2022a).…”