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Spanish Mackerel are widely distributed across several fisheries in WA, NT, Qld, NSW and the Torres Strait. Three of the five stocks are sustainable, the Gulf of Carpentaria stock is depleting, and the East Coast stock is depleted.

Genetic evidence indicates that there are three biological stocks of Spanish Mackerel across northern Australia [Moore et al. 2003]; however, evidence from otolith microchemistry, parasite analysis and limited adult movement (at scales greater than 100 km) indicates that there are likely to be a number of smaller biological stocks with limited interaction [Buckworth et al. 2007, Lester et al. 2001, Moore et al. 2003]. Each jurisdiction is likely to have multiple biological stocks within its boundaries; however, the difficulty in obtaining relevant biological, and catch and effort, information to assess each stock individually has meant that not all assessments are undertaken at the biological stock level. Those that are, are based on the populations that receive the highest harvest rates; their status can be assumed to be representative of the highest level of exploitation that occurs on any population within each management unit or jurisdiction.

Here, assessment of stock status is presented at the biological stock level—Torres Strait Spanish Mackerel Fishery and East Coast (Queensland and New South Wales); management unit level—Mackerel Managed Fishery (Western Australia), Gulf of Carpentaria (Queensland); and jurisdictional level—Northern Territory.

East Coast

This cross-jurisdictional stock has components in Queensland and New South Wales [Ovenden and Street 2007]. Stock status for the entire East Coast biological stock has been established using combined information from these jurisdictions. The most recent stock assessment [Tanimoto et al. 2021] base case scenario estimated that spawning biomass in 2020 was at 17 per cent (± 4 per cent) of the unfished (1911) level. 

Tanimoto et al. [2021] suggested that spawning biomass had declined as a result of high harvests during the 1970s, early 1980s and early 2000s. Most of the harvest is taken within Queensland waters (90.5 per cent) [Tanimoto et al. 2021] with a smaller catch during late summer–autumn in northern New South Wales waters [Stewart et al. 2015]. From 2016 to 2020, the total Spanish Mackerel annual harvest by all fishing sectors (515 tonnes (t)) has averaged approximately half the annual harvest compared to 1973–2004 [Tanimoto et al. 2021]. Estimated recreational catch in Queensland in 2019–20 (171 t) was lower than the previous recreational catch estimate in 2013–14 (231 t) [Webley et al. 2015, Teixeira et al. 2021]. The estimated recreational harvest in New South Wales during 2017–18 was highly uncertain, but likely to have been less than 3 000 fish [Murphy et al., 2020]. Queensland introduced a total allowable catch (TAC) and individual transferable quotas (ITQs) in 2004 for the commercial fishery. This coincided with the rezoning of the Great Barrier Reef Marine Park. Participation levels in subsequent years were substantially reduced and the lowest recorded for the previous 25 years. Fishing effort has varied since 2004 however the stock assessment indicated standardised catch rates have been declining for three decades for the fishery as a whole. Fishery-dependent sampling indicated that fish length and age frequencies in Queensland were annually variable, but also showed continuous recruitment into the fishery [Langstreth et al. 2018]. 

Fishing pressure for Spanish Mackerel has historically concentrated on a small area of important spawning grounds off the coast of Townsville [Tobin et al. 2013, Tobin et al. 2014]. Buckley et al. [2017] and Tobin et al. [2014] noted long term reductions in both the number of Spanish Mackerel spawning aggregations and in commercial catch rates in the region. O'Neill et al. [2018] estimated that fishing pressure for East Coast Spanish Mackerel from 2011–12 to 2015–16 was near a point equivalent to fully-fished. Fishing mortality in recent years, and for multiple historical periods, has exceeded levels to maintain Spanish Mackerel stock biomass above the limit reference point of 20 per cent. This level of fishing mortality is expected to prevent the stock from recovering from its recruitment impaired state. 
The range of biomass estimates from all models ranged between 14 per cent and 57 per cent, above and below the limit reference point of 20 per cent. However, four of the eight scenarios were < 20 per cent, two were ≤ 21 per cent, and only one scenario did not show evidence of significant decline. However, this scenario relied on implausible parameter values and did not account for hyperstability.

The stock is considered to be recruitment impaired. On the basis of the evidence provided above, the East Coast biological stock is classified as a depleted stock.

Gulf of Carpentaria

The Gulf of Carpentaria (Queensland) management unit for the Spanish Mackerel fishery has both commercial line and net components—the Gulf of Carpentaria Line Fishery and the Gulf of Carpentaria Inshore Fin Fish Fishery, respectively. The recreational fishery for this management unit is considered minor [Webley et al. 2015, Langstreth et al. 2018] and the Indigenous catch considered negligible. Harvests by sector are approximately 97 per cent commercial, 2 per cent recreational and 1 per cent charter [Bessell-Browne et al. 2020]. Of the reported commercial harvest, approximately 80 per cent is taken by line, the remaining 20 per cent by nets. A stock assessment of Spanish Mackerel in the Gulf of Carpentaria (based on 2018 data) estimated the stock was between 29 and 40 per cent unfished spawning biomass (median 32 per cent)[Bessell-Browne et al. 2020]. Model results suggested that biomass declined between 1940 and 1995 to 60 per cent of unfished spawning biomass and, although variable, has continued to decline. The downward trend in biomass since 2011 has been particularly steep prompting concerns for the stock. O'Neill et al [2018] recommended a more precautionary limit reference point (25–30 per cent of unfished spawning biomass, rather than the commonly used 20 per cent) for Spanish Mackerel on Queensland's east coast to account for risks associated with reduced spawning potential due to harvesting of large mature fish, and catch hyperstability. The lower estimate of spawning biomass of Spanish Mackerel in the Queensland Gulf of Carpentaria in 2018 reached the biological limit suggested by O'Neill et al [2018] and biomass was trending downwards. Standardised and nominal catch rates from 2011 to 2019 also indicate a declining trend.

Length and age frequencies from routine fishery-dependent monitoring of commercial line catches from 2007 to 2019 indicated relatively consistent recruitment and length and age compositions in the fishery in most years, with the majority of catches since 2007 comprising fish between 2–6 years of age [Langstreth et al. 2018]. However length and age structures in 2019 suggest limited recruitment into the fishery in 2018 and 2019. The Gulf of Carpentaria experienced a series of extreme ocean warming events during 2015 and 2016 [Benthuysen et al. 2018]. Extreme increases in water temperature can negatively impact the reproductive output of many tropical fish species [Pankhurst and Munday 2011]. The extreme climatic conditions observed in 2015-2016 may have exacerbated declines in biomass post 2017 once fish spawned in those years became vulnerable to fishing.

The most recent stock assessment [Bessell-Browne et al. 2020] estimates that biomass in 2018 was between 29 and 40 per cent of the unfished (1940) level. For the period (2011 to 2018) biomass declined, but the stock is not yet considered to be recruitment impaired.

The latest stock assessment model estimated that the overall population size of Spanish mackerel in the Queensland Gulf of Carpentaria is small (unfished biomass between 1150 to 1350 t), and only relatively small harvests are able to be sustainably maintained through time [Bessell-Browne et al. 2020]. The model results suggest an equilibrium maximum sustainable yield (MSY) biomass of 29 per cent of unfished spawning biomass at a harvest of 228 t per year (all sectors). Commercial harvests were above the estimated MSY for ten of the past 15 years (since 2005) [QFISH 2020]. From 2008 to 2018 there was a gradual decline in total commercial harvest, dropping to 176 t in 2018 and slightly increasing to 195 t in 2019. The majority of Spanish Mackerel harvest is taken by line. Participation (number of licences), effort (days fished) and catch rates in the line sector have shown a declining trend since the mid 1990s. Effort in the net sector has been generally increasing since 2013 however nominal catch rates have declined overall. The current level of fishing mortality is likely to cause the stock to become recruitment impaired.

On the basis of the evidence provided above, the Gulf of Carpentaria (Queensland) management unit is classified as a depleting stock.

Spanish Mackerel biology [McPherson 1992, McPherson 1993, QDAFF 2013]

Commonwealth – Commercial (active vessels) Total number of TIB licences; this is not an indicator of licence activity.

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

Commonwealth – Indigenous (a) The Australian Government does not manage non-commercial Indigenous fishing in Commonwealth waters, with the exception of the Torres Strait. In general, non-commercial Indigenous fishing in Commonwealth waters is managed by the state or territory immediately adjacent to those waters. In the Torres Strait, both commercial and non-commercial Indigenous fishing is managed by the Torres Strait Protected Zone Joint Authority (PZJA) through the Australian Fisheries Management Authority (Commonwealth); the Department of Agriculture, Fisheries and Forestry (Queensland); and the Torres Strait Regional Authority. The PZJA also manages non-Indigenous commercial fishing in the Torres Strait; and (b) Subject to the defence that applies under 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.

Western Australia – Recreational (catch) Western Australian boat-based recreational catch surveys from 1 Sept 2017–30 Aug 2018 [Ryan et al 2019]. Shore-based recreational catches are largely unknown.

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

Western Australia – Charter (catch) is an estimate based on numbers of fish caught multiplied by their average weight.

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 “…without derogating from any other law in force in the Territory, nothing in a provision of this Act or an instrument of a judicial or administrative character made under it limits the right of Aboriginals who have traditionally used the resources of an area of land or water in a traditional manner from continuing 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

New South Wales – Recreational (Catch) Murphy et al. [2020].

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

Commercial catch of Spanish Mackerel - note confidential catch not shown. Years shown on this graph are Australian financial years (e.g. 2015 refers to the financial year beginning 01 July 2014 and ending 30 June 2015).

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