Grey Mackerel Scomberomorus semifasciatus

Central-east Queensland biological stock 

The central east Queensland biological stock is managed as part of a Queensland east coast–wide fishery. The most recent stock assessment⁶ did not detect any trend in east coast Grey Mackerel abundance that might indicate overfishing at the east coast–wide level, or find evidence to advocate against the current fishery-wide total allowable commercial catch (TACC) of 250 tonnes (t). The stock assessment (2011 data) for the central east Queensland stock estimated the maximum sustainable yield (MSY) at approximately 90 t (80 per cent confidence interval: 70 to 130 t) and recommended a TACC of 70 t. Grey Mackerel is primarily a commercial net-caught species⁶; an average of 3 per cent of catches each year since 2003 have been taken by line fishing. The stock assessment estimated that the biomass of the central east Queensland stock in 2011 was equal to the biomass associated with MSY (B_MSY). Harvest levels for the commercial net fishery since 2011 (57 t in 2012; 53 t in 2013) were lower than the estimated MSY and the recommended TACC. Given this evidence, the biomass of the stock is not considered to be recruitment overfished.

Fishing pressure (days fished) on the central east coast has been low in recent years following the introduction of the current fishery-wide TACC of 250 t (an average of 93 net-fishing days from 2003 to 2009, and 61 days from 2010 to 2013). Fishery-dependent biological monitoring of central east Queensland Grey Mackerel indicates consistent recruitment in the fishery, with stable length and age frequencies^6,7 . Estimates of fishing mortality are below natural mortality. This suggests stable levels of fishing pressure since 2008⁶. This level of fishing pressure is unlikely to cause the stock to become recruitment overfished.

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

North-east Queensland biological stock 

The north-east Queensland biological stock is managed as part of a Queensland east coast–wide fishery. The most recent stock assessment⁶ did not detect any trend in east coast Grey Mackerel abundance that might indicate overfishing at the east coast–wide level and found no evidence to advocate against the current fishery-wide TACC. However, uncertainty in the model outputs, particularly for the north-east Queensland stock, prompted the authors to suggest a conservative approach to sustainable yield estimates and subsequent TACC for this stock. The stock model estimated that MSY for the north-east Queensland stock ranged from 100 to 150 t and recommended a TACC of 100 t. The authors also indicated that there was flexibility in the proposed TACC, given the level of model uncertainty. The stock assessment estimated that the biomass of the north-east Queensland stock in 2011 was at levels close to B _MSY (noting the uncertainty in the model outputs). Commercial net harvest levels in 2013 (126 t) were above the recommended TACC but within the range of MSY, and average annual harvest levels since 2010 (113 t) of the north east Queensland biological stock have been close to the recommended TACC, following the introduction of the fishery-wide TACC of 250 t on 1 July 2009⁷. Given this evidence, the biomass of the stock is not considered to be recruitment overfished.

Fishery-dependent biological monitoring indicates that length and age frequencies in the north-east stock have been stable since monitoring commenced in 2008⁶. Estimates of total mortality have been below the threshold (double the natural mortality) since 2009. This suggests stable levels of fishing pressure since 2008⁶, and it is unlikely that the current level of fishing pressure will cause the stock to become recruitment overfished.

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

Gulf of Carpentaria biological stock 

Grey Mackerel in the Gulf of Carpentaria is primarily a commercial net-caught species. Queensland and the Northern Territory share management of the Gulf of Carpentaria biological stock through the Queensland Fisheries Joint Authority. Queensland takes the majority of the commercial harvest (average 80–95 per cent).

There has been a rising trend in commercial catch rate since targeted fishing of Grey Mackerel began in the Gulf of Carpentaria in the late 1990s. Queensland catches and catch rates reached record levels in 2010 and 2012, respectively. Although the Queensland catch rate dropped in 2013, the rate (54 kg/100-m net) was still above the previous 10-year average (52 kg/100-m net)⁷. A stock reduction analysis of Grey Mackerel in the Gulf of Carpentaria, using Queensland and Northern Territory catches, concluded that the biomass in 2011 was at 74 per cent of the unfished biomass, and the harvest rate was 26 per cent of that required to achieve MSY⁸. The biomass of this stock is not considered to be recruitment overfished.

Queensland introduced changes to the net fishery at the beginning of the 2012 season to reduce pressure on Grey Mackerel. The measures decreased the total length of available net for the Queensland component of the stock by two-thirds, from 27 km to 9 km, in the offshore component of the fishery. Changes to the Queensland inshore fishery (within 7 nautical mile of the coast) also reduced the capacity for boats to target Grey Mackerel. Commercial catches and catch rates in 2013 were below the 5‑year average for the Queensland component of the Gulf of Carpentaria stock. Given this evidence, the current allowable level of fishing pressure is unlikely to cause the stock to become recruitment overfished.

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

North-west Northern Territory biological stock 

Grey Mackerel has been assessed at the jurisdictional level for the north-west Northern Territory stock⁸. Assessments indicate that Grey Mackerel stocks in the Northern Territory declined substantially as a result of high Taiwanese catches in the 1970s and 1980s, but have since recovered, with the cessation of foreign fishing and more stringent management of the domestic fishery. In 2010, egg production was estimated at 74 per cent of unfished levels, which is well within sustainable limits for productive species such as Grey Mackerel⁸. Supporting this assessment is that catch per unit effort has increased over the past 10 years, while catches have remained relatively consistent^8–10. Grey Mackerel in the north-west Northern Territory stock is not considered to be recruitment overfished, and the current level of fishing mortality is unlikely to cause the stock to become recruitment overfished.

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

Western Australian biological stock 

Grey Mackerel is exploited as a component of the Mackerel Managed Fishery of Western Australia⁵. The primary target species of the Mackerel Managed Fishery is Spanish Mackerel (Scomberomorus commerson). Grey Mackerel is therefore assessed on the basis of the status of the indicator species (Spanish Mackerel), which represents the pelagic suite of species. A stock assessment of Spanish Mackerel—examining catch-and-effort data, biological information, biomass and yield per recruit modelling—indicated that this stock is sustainable¹¹. In addition, Grey Mackerel are fast growing and have a young age at sexual maturity (less than 2 years) ^4,12,13, indicating some resilience to fishing pressure.

Grey Mackerel catch levels in the Mackerel Managed Fishery from 2000 to 2013 have been relatively low and stable, ranging between 10 and 24 t, with catches reported from only a small area of the Grey Mackerel range¹¹ . This level of catch is well below the TACC (60 t for each of the three management areas) for Grey Mackerel. The low levels of catch are likely to reflect the gear limitations (line only) that apply to the fishery. The biomass of the stock is not considered to be recruitment overfished, and the level of fishing mortality is unlikely to cause the stock to become recruitment overfished.

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