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The five stocks of Grey Mackerel assessed across Australia’s northern waters are all sustainable.

Grey Mackerel (Scomberomorus semifasciatus) are found in southern Papua New Guinea and northern Australia from Shark Bay, Western Australia, to northern New South Wales. At least five Grey Mackerel stocks have been identified for management purposes across northern Australia as determined by otolith stable isotopes chemistry and parasite abundance: Western Australia, North West Northern Territory, Gulf of Carpentaria, East Coast North and East Coast South. Four of these stocks have been confirmed as genetically distinct biological stocks: Western Australia, North West Northern Territory, Gulf of Carpentaria and the East Coast of Queensland. Research suggests that a sixth stock potentially occurs in the north-east Gulf of Carpentaria [Welch et al. 2009; Charters et al. 2010; Newman et al. 2010; Broderick et al. 2011; Welch et al. 2015]. However, the presence of this stock has yet to be confirmed; therefore, it was not included in the assessment.

Here, assessment of stock status is presented at the biological stock level—Western Australia, North West Northern Territory, Gulf of Carpentaria, and at the management unit level for North East Queensland and South East Queensland.

Gulf of Carpentaria

Grey Mackerel in the Gulf of Carpentaria is primarily a commercial gillnet-caught species. Over 90% of the reported catch was captured by Queensland operations (2021–22 data). The majority of the remaining catch is reported from the Northern Territory by operators in the Offshore Net and Line Fishery (ONLF).

In Queensland, the 2021–22 Grey Mackerel catch of 987 tonnes (t) was the highest recorded and exceeded the 10-year average of 657 t (2011–12 to 2020–21). However, effort in the Queensland region has shown a decreasing trend from 2017–18, dropping from 1,276 to 827 annual fishing days in 2021–22, the lowest recorded since 1995–96. The nominal catch rate has shown an increasing trend, however due to difficulties in distinguishing effort from co-targeted species, the trend is uncertain. The Queensland Grey Mackerel effort footprint appears to have contracted over 2017 to 2021 with operations focusing more on northern Gulf regions. Although some effort may have shifted in response to the introduction of marine park closures in 2018 [Parks Australia 2018], the reasons behind the recent shift northward are not certain and it is difficult to ascertain if this is driven by operational/economic considerations or due to changes in regional biomass levels. However, it is notable that this region is a possible additional management unit (distinct adult stock) due to differences in parasite abundance [Welch et al. 2015], which suggests that concentrated fishing in this area could contribute to localised depletion in the long term. Particularly noting that grey mackerel aggregating behaviour makes them more susceptible to targeted fishing pressure [Pidd et al. 2021].

Outside of commercial fishing, the fishing pressure exerted on Grey Mackerel by other sectors in the Gulf of Carpentaria is limited. Recreational catch for this stock is likely to be low, with the species registering combined state-wide catch of 16 t [Teixeira et al. 2021]. Grey Mackerel catch rates in the charter sector are unknown but thought to be low in Queensland. Charter vessels in the Northern Territory recorded less than 1 t of Grey Mackerel catch in 2021–22. 

While there is no recent assessment of the risk of the fishery on Grey Mackerel in the Gulf of Carpentaria, a 2021 Ecological Risk Assessment (ERA) assessed Grey Mackerel as medium risk on the east coast of Queensland and aspects of the assessment such as life history traits would apply to all stocks [Pidd et al. 2021]. The ERA suggested grey mackerel have life history traits that are highly productive, including low age at maturity, high fecundity, and a broadcast spawning reproductive strategy [Pidd et al. 2021]. Productive species may be more resilient to higher fishing pressure; however Grey Mackerel on the east coast of Queensland are susceptible to hyperstability due to predictable aggregating behaviour [GBRMPA 2012], which may make this species more susceptible to targeted fishing pressure in the Gulf of Carpentaria. 

Grey Mackerel catch in the Gulf of Carpentaria (Queensland and Northern Territory data) was subject to a catch-MSY model-assisted catch-only assessment based on catch data to 2021 [Martell and Froese 2013]. This analysis detected a declining trend in regional Grey Mackerel biomass. However, the model also indicated that biomass levels were more than likely above the reference limit point in 2021 [Northern Territory Government, unpublished]. The analysis also suggests fishing mortality is more likely to be below the limit reference point, although mortality was estimated to show an increasing trend [Northern Territory Government, unpublished]. This indicates that the current level of fishing is unlikely to cause the stock to become recruitment impaired in the short-term. However, the assessment estimated that recent harvests have exceeded FMSY and are beyond that which would be considered sustainable in the long term. The notable caveat being that catch-MSY modelling has a higher degree of uncertainty and should not be solely relied on to make inferences about long-term biomass trends. The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired. 

On the basis of the evidence provided above the Gulf of Carpentaria biological stock is classified as a sustainable stock.

North East Queensland

The North East Queensland management unit is managed as part of the East Coast Inshore Fishery (ECIF) and is primarily targeted using commercial gillnets [Bessell-Browne et al. 2019]. The take of Grey Mackerel in this fishery is primarily managed through the 250 t total allowable commercial catch (TACC) limit for the Queensland east coast and Individual Transferable Quotas (ITQs). ITQs were introduced on 1 September 2021 and are applied at a regional level. The ECIF has five management regions [Queensland Department of Agriculture and Fisheries 2022].

The most recent stock assessment (using 2018 data) did not detect any trend in Grey Mackerel abundance that might indicate overfishing on the Queensland east coast-wide and/or evidence to support a downward amendment of the TACC. The assessment did recommend a slightly lower equilibrium MSY for the east coast [227 t; Bessell-Browne et al. 2019]. The stock assessment indicated that the North East Grey Mackerel stock was at or around 48% (range 37–58%) of unfished biomass. 

Current harvest levels (33 t) are below the equilibrium MSY level and the longer-term target of 60% of unfished biomass for each stock. Of notable importance, the North East stock has been fished at lower levels since the introduction of the ECIF-wide 250 t TACC. Prior to the introduction of the TACC, nominal fishing effort (days when Grey Mackerel were caught) in the North East averaged 1,020 annual net fishing days between 2004–05 and 2008–09. This average decreased to 516 annual net fishing days between 2009–10 and 2018–19. In 2021–22 annual net fishing days reduced further to 207 days. The reduction in effort may be associated with the introduction of ITQs. The above evidence indicates that the biomass of this stock is unlikely to be recruitment depleted and that recruitment is unlikely to be impaired.

Outside of commercial fishing, the fishing pressure exerted on regional Grey Mackerel stocks is more limited. Recreational catch for this stock is likely to be low, with the species registering combined state-wide catch of 16 t [Teixeira et al. 2021]. Grey Mackerel catch rates in the charter sector are unknown. Charter catch levels though are likely to be low.

On the basis of the evidence provided above, the North East Queensland biological stock is classified as a sustainable stock.

South East Queensland

The South East Queensland management unit is managed as part of the East Coast Inshore Fishery (ECIF) and is primarily targeted using commercial gillnets [Bessell-Browne et al. 2019]. The take of Grey Mackerel in this fishery is primarily managed through the 250 t TACC limit for the Queensland east coast and ITQs. ITQs were introduced on 1 September 2021 and are applied at a regional level. The ECIF has five management regions [Queensland Department of Agriculture and Fisheries 2022].

The most recent stock assessment (using 2018 data) did not detect any trend in Grey Mackerel abundance that might indicate overfishing on the Queensland east coast and/or evidence to support a downward amendment of the 250 t TACC [Bessell-Browne et al. 2019]. However, the report did recommend a slightly lower equilibrium MSY for the east coast of 227 t. This stock assessment indicated that the South East Grey Mackerel stock was at or around 51% (range 40–61%) of unfished biomass. 

Current harvest levels (36 t) for the 2021–22 season are below the equilibrium MSY level and the longer-term target of 60% of unfished biomass for each stock. This reduction in fishing pressure is attributed to the introduction of regional ITQs. Fishing pressures for this stock though have been lower since the introduction of the ECIF-wide 250 t TACC. Prior to the introduction of the TACC, nominal fishing effort (days when Grey Mackerel were caught) in the south east averaged 1,427 annual net fishing days between 2004–05 and 2008–09, after which it decreased to an average of 792 annual net fishing days between 2009–10 and 2018–19. In 2021–22 nominal effort reduced to 346 annual net fishing days, a reduction which may be associated with the introduction of ITQs. The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired.

Outside of commercial fishing, the fishing pressure exerted on regional Grey Mackerel stocks is more limited. Recreational catch for this stock is likely to be low, with the species registering combined state-wide catch of 16 t [Teixeira et al. 2021]. Grey Mackerel catch rates in the charter sector are unknown. Charter catch levels though are likely to be low.

On the basis of the evidence provided above, the South East Queensland biological stock is classified as a sustainable stock.

Grey Mackerel biology [Cameron and Begg 2002]

Western Australian – Recreational (catch). Western Australian boat-based recreational catch survey from 1 Sep 2017–30 Aug 2018 [Ryan et al. 2022]. Shore based recreational catch (if any) largely unknown.

Western Australia – Recreational (Management methods). Western Australian boat-based recreational licence required.

Northern Territory – Charter (management methods). In the Northern Territory, charter operators are regulated through the same management methods as the recreational sector but are subject to additional limits on license and passenger numbers.

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.”

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

Queensland – Recreational Fishing (Catch). Data based at the whole of Queensland level and derived from state-wide 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 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  

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