*

Australian Bonito are a highly mobile species found in the western Pacific Ocean around south-eastern Australia, Norfolk Island and northern New Zealand. The Eastern Australia biological stock is classified as sustainable.

Australian Bonito Sarda australis occurs in the western Pacific Ocean where it is restricted to waters around south-eastern Australia, Norfolk Island and northern New Zealand [Collette and Nauen 1983]. Australian Bonito range from south-eastern Queensland southwards to northern Victoria. Little is known about stock structure within this range; however Australian Bonito are highly mobile and commercial landings exhibit consistent seasonal patterns in availability in terms of both abundance (peaking during summer and autumn) and sizes [Stewart et al. 2013].  Due to the latitudinal distribution along eastern-Australia, and influence of the prevailing southerly flowing Eastern Australian Current in this area, Australian Bonito are considered a single biological stock in this region.  Here, assessment of stock status is presented at the biological stock level—Eastern Australia.

Eastern Australia

The Eastern Australia biological stock has components in Commonwealth, Queensland and New South Wales waters off eastern Australia. The catch of Australian Bonito by Commonwealth fishers is extremely low, averaging less than 200 kg per financial year since 2012–13. Australian Bonito in Queensland is managed under the East Coast Inshore Fishery Harvest Strategy [QDAF 2022]. Nominal commercial catch in Queensland peaked at 52 t in 2006–2007, dropping to an average of 12 t from 2012–2021. In 2021–22, commercial catch decreased further to 2 t. A similar pattern is observed in nominal effort in Queensland, suggesting the decrease in catch is associated with fisher behaviour rather than a decrease in biomass. Nominal effort (fishing days per year) averaged 317 from the period 2012–2021 and decreased to 52 days in 2021–22. Catch in the Queensland recreational sector is unknown, although it is likely to be low. Together, Commonwealth and Queensland fisheries have contributed less than 1% of the total annual harvest since 2012–13 and are considered minor components of this stock. Consequently, the stock is assessed using data from New South Wales.

Results from surplus production modelling using NSW commercial catch data from 1990–91 to 2021–22 and standardized catch rates from 1997–98 to 2021–22 produced imprecise estimates of depletion; however even the lowest trajectories during the time period remained above the limit reference level of 0.2 of the unfished biomass [Stewart 2023]. The median depletion level in 2021–22 was estimated to be 0.53 (CIs 0.28 to 0.88) which is well above the limit reference level of 0.2. Standardized catch rates for line fishing methods between 1997–98 and 2021–22 fluctuated substantially, likely a reflection of highly variable abundance of Australian Bonito as a result of their life history traits including extremely fast growth, early maturation, high mobility and variable recruitment [Stewart et al. 2013].  The absence of obvious overall trends in catch rates suggest that the biomass is not declining [Stewart 2023]. The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired.

Estimated Fishing mortality (F) from surplus production modelling was below that required to achieve maximum sustainable yield (MSY) with a high degree of certainty (Stewart 2023]. Fishing is therefore unlikely to cause the stock to decline [Stewart 2023]. Landed commercial catch during the late 2000s and early 2010s approached 350 t per year and exceeded the estimated MSY of approximately 200 t per year.  Catch in recent years has been well below the estimated MSY and fishing effort on Australian Bonito has been relatively stable with slight recent declines during the previous decade [Stewart 2023]. A change in length compositions from being bimodal during the 2000s to mainly the smaller mode from around 2010–11 onwards is potentially concerning and may indicate either a greater abundance of younger cohorts in more recent years, or alternatively excessive fishing of larger fish during the preceding high catch years. Given that these ‘bi-modal’ length composition years were generally lower catch years, and that the recent years of higher landings were associated with mainly the smaller mode of fish, the former hypothesis is most likely. Estimates of mortality derived from length-based catch curves and an estimated maximum age of 4 years indicate that total mortality (Z) is unlikely to exceed 2 x natural mortality (M) with a high degree of certainty [Stewart 2023]. The above evidence indicates that the current level of fishing mortality is unlikely to cause the stock to become recruitment impaired. 

On the basis of the evidence provided above, the entire Eastern Australian biological stock is classified as a sustainable stock.

Australian Bonito biology [Collette and Nauen 1983; Stewart et al. 2013]

Distribution of reported commercial catch of Australian Bonito

Commonwealth – Commercial (Management Methods/Catch). Data provided for the Commonwealth align with the 2021–22 financial year.

Commonwealth – Recreational. The Commonwealth does not manage recreational fishing in Commonwealth waters. Recreational fishing in Commonwealth waters is managed by the state or territory immediately adjacent to those waters under its management regulations. 

Commonwealth – Indigenous. The Australian government does not manage non-commercial Indigenous fishing in Commonwealth waters, with the exception of Torres Strait. In general, non-commercial Indigenous fishing in Commonwealth waters is managed by the state or territory immediately adjacent to those waters.

New South Wales – Recreational (Catch). Murphy et al. [2022].

New South Wales – Indigenous (management methods). (https://www.dpi.nsw.gov.au/fishing/aboriginal-fishing

Queensland – Recreational Fishing (Catch). Data with high uncertainty (Residual Error >50 %) have been excluded and listed as unknown. More information available at: https://www.daf.qld.gov.au/business-priorities/fisheries/monitoring-research/monitoring-reporting/statewide-recreational-fishing-surveys  

Queensland – Indigenous (Management Methods). For more information see https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing 

Queensland – Commercial (Catch). Queenslandcommercial and charter data have been sourced from the commercial fisheries logbook program. Further information available through the Queensland Fisheries Summary Report at: https://www.daf.qld.gov.au/business-priorities/fisheries/monitoring-research/data/queensland-fisheries-summary-report  

Queensland – Commercial (Management Methods). Harvest strategies are available at: 

https://www.daf.qld.gov.au/business-priorities/fisheries/sustainable/harvest-strategy

Commercial catch of Australian Bonito - note confidential catch not shown

1. Collette, BB and Nauen, CE 1983, Scombrids of the World. An Annotated and Illustrated Catalogue of Tunas, Mackerels, Bonitos and Related Species Known to Date. Rome, FAO: 137 pp.
2. Murphy, JJ, Ochwada-Doyle, FA, West, LD, Stark, KE, Hughes, JM and Taylor, MD 2022, Survey of recreational fishing in NSW, 2019/20 – Key Results, NSW DPI – Fisheries Final Report Series No. 161, ISSN 2204-8669.
3. Queensland Department of Agriculture and Fisheries, 2022, Harvest Strategies, Fisheries, QLD.
4. Stewart, J 2023, NSW Stock Status Summary 2021/22 – Australian Bonito – (Sarda australis), NSW Department of Primary Industries. Fisheries NSW, 16 pp.
5. Stewart, J, Robbins, WD, Rowling, K, Hegarty, A, and Gould, A 2013, A multifaceted approach to modelling growth of the Australian bonito Sarda australis (Family Scombridae). Journal of Fish Biology, 64: 671-678.