Growth of Atlantic Bluefin Tuna (Thunnus thynnus): Analysis of Tag Recapture, Direct Aging and Size Frequency Data

We analyzed >3000 recaptures of tagged Bluefin tuna from 1963 to 2013. Key issues were: some lengths were estimated, various length measurements were recorded, short term recaptures sometimes had unreasonable growth increments, and growth may vary seasonally. We dealt with each issue to determine the best subset of data for estimating von Bertalanffy growth parameters. With Fabens’ (1965) method, the estimates were close to past findings but the issue of seasonality remained unresolved and influential. Francis’ (1988) model allowed us to incorporate seasonality parameters, which resolved the issue, and allowed estimation of growth variability and measurement error. The growth curve currently used in the stock assessment is based solely on direct aging and length-frequency data. The comparability of von Bertalanffy growth curves derived from tagging and age-length data, an issue raised by Francis, was addressed for Atlantic bluefin tuna. Since each source of data has its own strengths and limitations, we combined all three types in an integrated model based on maximum likelihood estimation. The resulting estimates make full use of the available information, thus providing more comprehensive estimates of growth for Atlantic Bluefin tuna.