Estimating Von Bertalanffy Growth Parameters From Mark-Recapture Data for Atlantic Bluefin Tuna (Thunnus thynnus)

Age-length relationships derived from hard parts and mark-recapture data are key assumptions in guiding management strategies aimed at rebuilding stocks of Atlantic bluefin tuna (Thunnus thynnus). While several growth curves have been proposed for this species, concern has been raised regarding the reliability of tagging data. We analyzed a large (>3000 recaptures) ICCAT database with records from 1963 to 2012. The resulting curves were consistent with past findings. Key issues in using the data were: some lengths were estimated, various length measurements were recorded, short term recaptures were sometimes associated with unreasonable growth increments, and growth may vary seasonally. When comparing data containing both measurements and estimates to data containing only measurements, we found that estimating lengths had no effect on resulting parameters. Only fork length measurements were used, which comprised 70% of total records. Excluding fish recaptured within 90 days eliminated most cases of unreasonable (negative) growth increments. Problems of seasonality in growth could be minimized by using fish at liberty for a whole number of years. These results suggest that tagging databases, when used sensibly, can provide insights about previously inferred growth curves and potentially produce growth parameters for species where no estimates are currently available.