Jessica Farley, Paige Eveson and Naomi Clear

Session 2, Talk 1, 18/1/16 @ 1330 hrs

Our understanding of the population biology and life-history of southern bluefin tuna (SBT) (Thunnus maccoyii) has increased substantially over the past two decades through the collection of high quality, multi-sourced data on the age, growth and reproduction. The collection of these data, using a combination of targeted research and collaborative long-term monitoring work, was driven by the need for this information for quantitative population assessment and effective management of the highly depleted species. Here we provide a synthesis of the data and resulting information obtained, and highlight its use in models to assess population abundance and stock status.

Growth rates of juvenile SBT increased between the 1960s and 1990s, possibly as the result of population decline, but appear to have stabilized since. After 10 years of age, males grow faster than females, which may account for the bias observed in the sex ratio of SBT whereby males become progressively more dominant above ~170 cm. A comparison of the length-at-age of fish caught on and off the spawning ground suggests that size may be the primary determining factor in timing of maturation for both males and females. Although the maturity schedule for SBT remains poorly defined, size related trends in other reproductive parameters such as batch fecundity, spawning frequency and the duration of spawning and non-spawning episodes are available. These biological data and parameter estimates have been central to the development and refinement of the CCSBT Operating Model used for assessing the status and productivity of the stock and evaluating alternative management procedures, as well as to the construction of models for close-kin abundance estimation. Priorities for future research include targeted sampling and analysis to improve estimates of size and age at maturity (and senescence) and of duration on the spawning ground, and continued monitoring of growth rates through the rebuilding period.

Contact: J. Farley, CSIRO Marine Laboratories, Australia, This email address is being protected from spambots. You need JavaScript enabled to view it.