SCIENTIFIC COMMITTEE FOURTH REGULAR SESSION 11-22 August 2008 Port Moresby, Papua New Guinea PRELIMINARY STUDY OF AGE, GROWTH, AND SPAWNING ACTIVITY OF ALBACORE IN AUSTRALIA’S EASTERN TUNA & BILLFISH FISHERY

Executive Summary This report presents the results of a 1-year preliminary study to investigate the size, age and reproduction of albacore caught in the Eastern tuna and Billfish Fishery (ETBF) on Australia's east coast. The objectives of the study were to provided early information on key biological parameters including length-weight conversions, sex ratios, spawning frequency, batch fecundity, and a maturity schedule. Biological sampling of albacore was undertaken at three locations: Mooloolaba, Cairns, and the east coast of Tasmania. A total of 232 fish were measured for length (212 with sex identified), and 174 gonads, 149 otoliths and 189 fin spines were obtained. Although the sample size was small, the study found that longline catches off Queensland were dominated by adults (>80 cm FL) and the majority were male (70%), while recreational catches off Tasmania were dominated by juveniles (<75 cm) with a sex ratio of 1:1. Age was estimated independently using otoliths and fin spines for 100 albacore. Both structures had clear growth increments that provide reproducible counts. A direct comparison indicated very little bias in assumed ages 1-7 years, but otolith-based age estimates were generally higher than the spine-based estimates after age 7. Despite this, preliminary von Bertalanffy growth curves obtained from both structures were very similar, and both indicated growth and L∞ was greater in males than females. A maximum age of 14+ and 11+ years was obtained from otoliths and fin spines respectively. Analysis of 145 gonads collected from ~15-20ºS provided the first record of actively spawning albacore from the Coral Sea, and the high incidence of actively spawning fish during January/February suggests that this is an important spawning area/time. However, the presence of a number of post-spawning females during these months suggests that individuals may not spawn for an extended period. The relatively large number of regenerating females caught in June and July off Queensland also suggests that some females remain in the spawning area after spawning, while others move south as indicated by the presence of a regenerating female off Tasmania in April. Our study confirmed that albacore is a multiple batch spawner with indeterminate annual fecundity. Histological analysis of ovaries confirmed that females are capable of spawning daily, although the average mature female spawned every 1.3 days (in Jan/Feb). Batch fecundity estimated for 7 females ranged from 0.86 to 1.33 million oocytes. We suggest that gonads collected from the temporal window of January to …