Oceanographic synopsis of the Southern Bluefin Tuna spawning ground in the Eastern Indian Ocean

The only known spawning ground of the Southern Bluefin Tuna (Thunnus maccoyii) occurs in the Eastern Indian Ocean between north-west Australia and Indonesia. This study examined environmental features of this spawning ground... [ view full abstract ]

The only known spawning ground of the Southern Bluefin Tuna (Thunnus maccoyii) occurs in the Eastern Indian Ocean between north-west Australia and Indonesia. This study examined environmental features of this spawning ground using remote sensing and in-situ archived oceanographic data relative to the habitat requirements of the Southern Bluefin Tuna. Environmental data (sea surface temperature, sea level height anomaly, surface chlorophyll a and XBT sections) were extracted from the IMOS portal and used to establish a spatial and temporal oceanographic synopsis of the area. In addition, CSIRO Atlas of Regional Seas data (CARS; temperature, salinity, oxygen, silicate, nitrate and phosphate) and ARGO data (temperature and salinity) were extracted to supplement the remotely-sensed data. The SST data show significant upwelling (4 degrees Celsius less than the surrounding ocean) along the coastline of Java and Sumatra during the monsoon, about two months before the summer Southern Bluefin Tuna spawning season. This upwelling drives biogeochemical processes that support the pelagic ecosystem in the region. Southern Bluefin Tuna are fast growing; juveniles are voracious predators on macro-zooplankton and small nekton and migrate southwards in the Leeuwin Current to their cool temperate habitat in the Southern Ocean. These fish form the basis of the Port Lincoln tuna ranching industry in South Australia and the longline tuna fishery off New South Wales. It is anticipated that the understanding of the oceanographic features of the spawning ground will provide an important link into the year class strength for this extremely valuable, yet severely depleted, apex fish species.