Age and growth of the spiny butterfly ray G ymnura altavela ( E lasmobranchii, G ymnuridae) in the S outhwest A tlantic (in situ) and under human care in a public aquarium (ex situ): Plasticity and population patterns

Abstract This study provides the first age and growth assessment of the endangered spiny butterfly ray, Gymnura altavela (Linnaeus, 1758), in the Southwest Atlantic, while also updating the growth parameters (asymptotic disc width—DW ∞ and growth coefficient— k ) estimated in an ex situ a marine aquarium setting. In situ growth was assessed by analyzing the vertebrae of 95 individuals captured off the southeastern coast of Brazil. The Centrum Edge and Marginal Increment analyses indicated an annual annuli formation cycle. After applying a multi‐model approach, the Gompertz model was selected as the most appropriate for describing the in situ growth of both females (DW ∞ = 201.0 cm and k = 0.100 year −1 ) and males (DW ∞ = 139.4 cm and k = 0.170 year −1 ). In turn, ex situ growth was assessed by periodically measuring seven individuals kept in a marine aquarium for 8 years (2018–2025). The von Bertalanffy model modified by Fabens was used to estimate ex situ growth parameters for females (DW ∞ = 212.1 cm and k = 0.132 year −1 ) and males (DW ∞ = 120.1 cm and k = 0.255 year −1 ). A well‐marked sexual size dimorphism was observed in both in situ and ex situ, with females growing more slowly but reaching larger sizes than males. G. altavela grew faster in the controlled environment (ex situ). However, reaching the maturity size earlier may not necessarily result in anticipated reproduction events and it may also have a negative effect on longevity. Comparing the growth parameters and curves estimated in situ and ex situ provides valuable insight into how this population may respond to future environmental changes and impacts.