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Cobia are widespread in tropical and subtropical oceans globally. In Australia, the two biological stocks of Cobia (Northern and Eastern Australia) are sustainable.

Photo: Rosenstiel School of Marine and Atmospheric Science

Cobia has an almost worldwide distribution in tropical and sub-tropical waters, except in the Eastern Pacific Ocean [Fry and Griffiths 2010]. In Australia, Cobia is found from Cape Naturaliste in Western Australia, across and around northern Australia to Botany Bay in NSW [Hoese et al 2006].

The stock structure of Cobia across Australia is not known and the determination of population subdivision in large mobile marine pelagic fish species is often challenging due to a range of factors including large effective population sizes, high dispersal capacities, and lack of apparent physical barriers to gene flow.

In Australia, Cobia is not commonly encountered in large numbers and is not currently a specific target species in any state or Commonwealth fishery. It is therefore difficult to collect the relevant biological and catch and effort information to assess any putative individual stocks. Consequently, we have taken the conservative step of separating Cobia into two functional management units. This is based on a parsimonious separation at Torres Strait, based on the separation of populations of pelagic species at the Torres Strait biogeographic barrier, resulting from the Torres Strait land bridge between continental Australia and New Guinea that persisted through much of the late Pleistocene and separated Indian and Pacific Ocean taxa (e.g. Spanish mackerel [Moore et al. 2003], grey mackerel [Broderick et al. 2011].

In addition, fishing mortality is fairly equivalent across each management unit (low), therefore undertaking an assessment at the management unit scale is justified.

Here, assessment of stock status is presented at the management unit level—Northern Australia (Western Australia, Northern Territory, QLD Gulf of Carpentaria, and Commonwealth) and Eastern Australia (Queensland East Coast, NSW, and Commonwealth).

Eastern Australia

Cobia is a popular recreational species in Queensland with estimated recreational catches generally higher than the commercial sector. Whole of Queensland recreational harvest was estimated to be 19 t in 2019–20 [Webley et al. 2015; Teixeira et al. 2021]. In the commercial sector, Cobia is a byproduct species in the East Coast Inshore Fishery (ECIF), and subsequently the commercial catch is low, peaking at 40 t in 2008–09 and averaging 14 t for the last 10 years to 2021–22. The New South Wales commercial catch from 2015 to 2022 averaged approximately 1.5 t per year, and Cobia is not a major component of recreational landings [West et al. 2015; Murphy et al. 2020; Murphy et al. 2022]. Commonwealth commercial catch of Cobia averaged less than 1 t per year during 2017–18 to 2021–22 financial years and was less than 1 t in the 2021–22 financial year. Commonwealth fishing is unlikely to be having a negative impact on the stock. There have been no significant catches by Victorian fisheries, not surprising given this species is at the end of its southern range in this jurisdiction. The last reported catch in Victoria was in 2013–14, and less than 0.05 t was taken in any preceding year.

A preliminary assessment using Queensland recreational, commercial and charter catch data applied to a modified catch-MSY model (developed by Martell and Froese [2013] and modified by Haddon et al. [2018]), estimated that the 2019 biomass of Cobia was 76% of unfished levels [Saunders et al. 2020a]. This indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired. Similarly, the fishing mortality in 2019 was 0.06 which was well below the limit reference point indicating that the current level of fishing mortality is unlikely to cause the stock to become recruitment impaired. Catch-MSY modelling has a higher degree of uncertainty and should not be solely relied on to make inferences about long-term biomass trends. However, Cobia has life history traits that are highly productive, including low age at maturity, high fecundity, and a broadcast spawning reproductive strategy [van der Velde et al. 2009]. Productive species may be more resilient to higher fishing pressure and given the low and consistent catch over the last decade, recruitment is unlikely to be impaired.

On the basis of the evidence provided above, Cobia in Eastern Australia is classified as a sustainable stock.

Northern Australia

Total catch of Cobia across WA over the last 10 years (2013–22) has ranged from 15.7–24.1 t, with a mean annual catch of 20.7 t. This is similar to the average catch for this species during the previous 10 years at 21.3 t. During the past 10 years when reliable annual catch estimates are available for the recreational and charter sectors, their combined catches have been relatively low compared to commercial catches, i.e. at approximately 20% of total annual catches.

Cobia is not targeted by any fisheries in the Northern Territory. The majority of catch is landed as by-product in the Demersal Fishery trawl sector and, to a lesser extent, the Spanish Mackerel and Offshore Net and Line fisheries. Total commercial catch over the last 10 years (2012–13 to 2021–22) in the Northern Territory has ranged from 7.9 t to 19.7 t, at an annual average of 12.9 t.

Queensland commercial (net and line) catches of Cobia in 2021–22 were minor (3 t), and similar to the previous 20-year annual average of 4 t. There are no reliable estimates of recreational or indigenous harvest of Cobia in the Queensland component of the stock.

Commonwealth commercial catch averaged less than 1 t per annum during 2017–18 to 2021–22 financial years and was less than 1 t in the 2021–22 financial year. Commonwealth fishing is unlikely to be having a negative impact on the stock.

While Cobia is caught by recreational fishers, they generally represent < 1% of the total catch of this species in this stock [e.g. West et al. 2012; Matthews et al. 2019; Ryan et al. 2019].

The majority of the commercial catch of Cobia in WA is landed by the Pilbara Fish Trawl Managed Fishery. They have also been landed in small quantities in the Gascoyne Demersal Scalefish Managed Fishery, Northern Demersal Scalefish Managed Fishery, Pilbara Line Fishery, Pilbara Trap Managed Fishery, West Coast Demersal Gillnet and Demersal Longline Fishery, and the West Coast Demersal Scalefish Interim Managed Fishery. Cobia is assessed on the basis of the status of several indicator species (including, for example, Red Emperor, Rankin Cod, and Bluespotted Emperor in the Pilbara region, and Red emperor and Goldband Snapper in the Kimberley region) across the North Coast Demersal Resource (NCDR) that represent the entire inshore demersal suite of species occurring at depths of 30–250 m [Newman et al. 2018]. The indicator species in the Pilbara and Kimberley have been classified as sustainable [Wakefield et al. 2023]. The level of risk associated with the sustainability of Cobia in the NCDR is assessed as low. This assessment of Cobia is also supported by the results of a data-limited Catch-MSY assessment, where recent catches are compared to model predictions for maximum sustainable yield (MSY).

Results of analyses using a Catch-MSY model applied to data on annual WA catches for this species (1993–2022), show that the annual catches since 2006 have remained below the median model prediction for maximum sustainable yield (MSY), after having been above the 95% CI of MSY for the period of 1998–2004. This is also consistent with the predicted values for biomass in recent years being above predicted BMSY, and fishing mortality remaining below FMSY. However, it is important to recognise that Catch-MSY is a data-limited technique with strong assumptions, dependent on user inputs. For this assessment, these included specified ranges for initial depletion (0.4–0.8), based on likely catches from foreign fishing fleets prior to the start of the time series, final depletion (0.15–0.7), based on recent catches relative to the maximum recorded annual catch and the non-targeted nature of fishing for this species, and medium resilience (r=0.3–0.8, consistent with species longevity, of approximately 13 years). Given consistent catch levels across multiple fisheries, recent catches of this species being less than the predicted MSY, and status of the indicator species for the NCDR, it is considered unlikely that the biomass of Cobia in Western Australia is depleted.

An assessment using catch data to 2019 from Western Australia, Northern Territory and Queensland commercial fisheries was applied to a modified catch-MSY model (developed by Martell and Froese [2013] and modified by Haddon [2018]). The results indicate that the estimated biomass exceeds the limit reference point, with the 95% confidence intervals positioned above the limit and the mean value in excess of the target reference point [Saunders et al. 2020b]. The estimated fishing mortality level in 2019 was 0.12, well below the limit reference point of 0.2. Similarly, as Cobia is broadly distributed beyond the effort footprint of the above fisheries, the stock likely has access to refuge from fishing pressure. 

While there is recognised uncertainty in the outcomes of data limited approaches such as catch-MSY, the results indicate that the stock is unlikely to be depleted and that recruitment is unlikely to be impaired. Further, the current level of fishing mortality is unlikely to cause the stock to become recruitment impaired.

On the basis of the evidence provided above, Cobia in Northern Australia management unit is classified as a sustainable stock.

Cobia biology [van der Velde et al. 2009; Fry and Griffiths 2010]

Distribution of reported commercial catch of Cobia.

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

Queensland – Recreational Fishing (Catch). Data are based at the whole of Queensland level and derived from statewide recreational fishing surveys. Where possible, estimates have been converted to weight (tonnes) using best known conversion multipliers. Conversion factors may display regional or temporal variability. In the absence of an adequate conversion factor, data presented as number of fish. 

Queensland – Commercial (Catch). Queensland commercial and charter data has been sourced from the commercial fisheries logbook program. Further information is available through the Queensland Fisheries Summary Report 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  

Northern Territory - Indigenous (management methods) The Fisheries Act 1988 (NT), specifies that: “Unless expressly provided otherwise, nothing in this Act derogates or limits the right of Aboriginal people who have traditionally used the resources of an area of land or water in a traditional manner to continue to use those resources in that area in that manner.”

Western Australia – Recreational (Catch). Boat-based recreational catch is from 1 September 2020–31 August 2021. These data are derived from those reported in Ryan et al. [2022].

Western Australia – Recreational (management methods). A Recreational Fishing from Boat License is required for the use of a powered boat to fish or to transport catch or fishing gear to or from a land-based fishing location.

Western Australia – Indigenous (management methods). Subject to application of Section 211 of the Native Title Act 1993 (Cth), and the exemption from a requirement to hold a recreational fishing licence, the non-commercial take by Indigenous fishers is covered by the same arrangements as that for recreational fishing.

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

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

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

Commercial catch of Cobia

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