Direct Ageing of South Atlantic Swordfish (Xiphias gladius)

Studies of swordfish growth provide essential biological parameters for stock assessment and fisheries management, informing both conventional population models and the evaluation of different management strategies. The present study aims to provide insight into the dynamics of the South Atlantic Ocean stock growth patterns. The sampling is the most complete to date in the literature, with a wide geographical distribution and in every month of the year. The analysis included 788 anal fins. Biometric relationships between different anal fin spine measurements and fish size were found. Some variation in the size of annulus one and vascularisation hiding some internal bands was found in larger specimens. Marginal increment ratio (MIR) and edge type analyses showed an annual band formation in the austral winter (July to September), thereby confirming the hypothesis of one annulus formation per year. Growth parameters were calculated using different growth models. The Gompertz model yielded the most reliable parameters (L∞ = 341 cm LJFL, k = 0.13 yr−1, T = 2.83 yr). The tagging and recapture data corroborated the selected model. Results were compared with other growth curves published.