| 英文摘要 |
To understand the age and size structure of southern bluefin tuna (SBT, Thunnus maccoyii) across central Indian Ocean, we examined the fishery dependant data as well as the observer data. We also examined 56 SBT otoliths collected by the observers. The fishery dependant data show similar size and age composition of the total catch compared with the total catch in previous years. However, the observer data confirm that 1999 - 2001 are weak year class. To study the migratory life history of SBT, we analyzed stable oxygen isotope composition of SBT otolith. The results indicate that the hatched SBT stay in the tropical ocean for about 1.5 month, followed by the southward migration and arrive in the temperate area about 1 year. In addition, we also cloned and sequenced the mitochondrial DNA cytochrome b gene of 22 Thunnus orientalis collected in Don-Gang and 28 SBT collected in central Indian Ocean. The results show evident genetic variation between 2 bluefin tuna species. This genetic method can be applied to species identity if morphological characaters are not available or cannot work. |