Using electronic and archival tags, we have discovered new insights into the migration patterns and feeding behaviour of southern bluefin tuna in the Great Australian Bight, which contributes to a larger dataset spanning 30 years.

The challenge

Understanding the movement and behaviour of southern bluefin tuna

Southern Bluefin Tuna being tagged

Southern Bluefin Tuna being tagged.

Southern bluefin tuna (SBT) are one of Australia's most valuable fisheries, and 95 per cent of the commercial catch is from the Bight. However, little is known about the response of SBT, or highly mobile fish in general, to noise caused by oil and gas operations.

SBT consistently use the Bight from summer to autumn. Possible impacts on SBT from human activities could include shifts in their distributions or changes in their diving or feeding behaviour while they are in the Bight. Such changes could in turn affect the annual aerial surveys that contribute abundance estimates to support SBT management and the efficiency of fishing operations in the Bight.

Our response

Electronic tagging of SBT

CSIRO has developed improved statistical methods for estimating positions, behaviours, and feeding patterns of individual SBT using electronic and archival tags.

Southern Bluefin tuna beneath the surface of the ocean.

The data from 110 archival tags (from 1998-2011) and 125 electronic tags deployed during the period of exploration (2013-2017) provide new insights on the movement, migration and behaviour of SBT.

This provides a basis for establishing the spatial dynamics and ecological role of juvenile SBT as an apex predator in the Bight, in the context of oil and gas exploration and extraction, and will build on 30 years of historical data.

We found that the proportion of time that juvenile SBT spend in surface waters in the Great Australian Bight varies, with most occurring at depths of 50 metres or less throughout the day and night. Most feeding occurs around dawn in shallow depths. The timing of feeding suggests that SBT track their prey visually.

The results

Managing SBT for the Australian community

Results from this study will benefit all stakeholders interested in the region, such as Commonwealth and state regulators and governments, commercial users and academic, research and local communities.

Southern Bluefin Tuna aerial survey.  ©Jim Dell, CSIRO

Information on key habitats for SBT in the Bight, variability in those habitats and linkages with population dynamics has provided information on areas that are most important for the juvenile component of the population to better understand their movement and behaviour.

This is important for planning and managing human impacts to make sure these have no long-term impacts on the SBT population.

This research will have long-term benefits for the fishing and aquaculture industry, the Bight ecosystem, and the broader Australian community.

The Great Australian Bight Research Program was a collaboration between BP, CSIRO, the South Australian Research and Development Institute (SARDI), the University of Adelaide, and Flinders University.

What to do if you catch a tagged fish

We offer rewards for the return of tags and information about the fish and its capture. Please contact us at tags@csiro.au as soon as possible after the catch. The return of tags as well as information about the recapture of the fish is important to our research.

NOTE: most tags are on the outside of the fish but some are inserted inside the fish.

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