Spanish Mackerel Scomberomorus commerson

Torres Strait (Commonwealth) biological stock

A formal stock assessment of Spanish Mackerel in the Torres Strait Spanish Mackerel Fishery (Commonwealth) was conducted in 2006, informed by data to 2003 ⁴. The assessment uses a sex-specific age-structured population dynamics model to estimate biomass. A range of biological and effort reference points were assessed to evaluate various potential management strategies for the fishery. The assessment estimated that biomass in 2006 was 37 per cent (range 26–67 per cent) of the unfished level. Results of the assessment indicated that the base-case maximum sustainable yield (MSY) for Spanish Mackerel in the Torres Strait was 169 tonnes (t) per year, and annual catches of around 150 t per year would achieve a fishing mortality target of half natural mortality. The stock assessment concluded that the stock was likely to be harvested at levels near or exceeding MSY up to 2003. Catches since 2007–08 have been below both the base-case (169 t) and lower risk estimates of MSY⁵. The stock is therefore not considered to be recruitment overfished ⁶, and the current level of fishing mortality is unlikely to cause the stock to become recruitment overfished⁶.

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

East coast (Queensland) biological stock

The east coast biological stock extends from Cape York in Queensland waters to its southern extent in northern New South Wales⁷, although New South Wales catches are limited⁸. The most recent stock assessment⁹ indicated that the 2009 estimate of biomass ranged from 36 to 54 per cent of the unfished level. Recent research, using commercial catch-and-effort data, describes a contraction in the spatial and temporal presence of spawning aggregations on the main commercial fishing grounds¹⁰, which may be a result of the vulnerable nature of transient spawning aggregations that form each year¹¹. Potential serial depletion of these spawning aggregations may be a concern for the reproductive potential and size of the stock. However, the overall evidence indicates that the biological stock is unlikely to be recruitment overfished.

Total landings for the combined commercial and recreational catch for Queensland and New South Wales over the past few years have been below the lowest sustainable yield estimate (yield that sustains 1.2B_MSY in the hyperstable model case) of 956 t, as well as below the lowest risk management yield estimate of 715 t⁹. In Queensland, introduction in 2004 of a total allowable catch and individual transferable quotas for the commercial fishery substantially reduced participation; in 2013, fishing effort was around the lowest level recorded in the past 25 years. Fishery-dependent monitoring data indicate a varied but continuous pattern of recruitment, and the estimate of total mortality rate in 2012–13 is less than twice the natural mortality rate¹². This level of fishing mortality is unlikely to cause the biological stock to become recruitment overfished. However, given the proximity of stock levels to relevant reference points, the fact that an average of only 51 per cent of available quota has been harvested in the past 9 years, and uncertainty around the levels of recreational harvest, future harvests will need to be closely monitored.

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

Gulf of Carpentaria (Queensland) management unit

The Gulf of Carpentaria (Queensland) management unit has a line and net component—the Gulf of Carpentaria Line Fishery and the Gulf of Carpentaria Inshore Fin Fish Fishery, respectively. Catch rates for both fisheries have continued to increase since the mid-1990s. Age-composition data from routine monitoring of line catches since 2007 are now available. The data indicate relatively consistent recruitment and age composition in the fishery, with the majority of line catches since 2007 comprising fish between 2 and 6 years of age. This evidence indicates that the biomass of the stock is unlikely to be recruitment overfished.

Total commercial landings are within historical harvest levels (238 t in 2013), with the majority taken by the line fishery (76 per cent in 2013). Landings in the line fishery have been relatively stable over the last 2 years; there have been stable catches in the net fishery over the past 4 years. Fishing effort in the line fishery has decreased substantially to a historical low in 2013. This evidence indicates that 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 management unit is classified as a sustainable stock.  

Northern Territory

Spanish Mackerel stocks have been assessed at a territory-wide level, including information up to 2011. The results indicated that stocks declined substantially because of high Taiwanese catches in the 1970s and 1980s, but have since recovered as a result of more stringent management. In 2011, egg production was estimated at around 85 per cent of unfished levels, which is well within sustainable limits for a species such as Spanish Mackerel, and it was suggested that increases in catch could occur^13,14. This assessment is supported by increased catch rates over the past 10 years, with the 2012 value being the highest recorded in the fishery¹⁵. The evidence provided indicates that the biomass of this management unit is unlikely to be recruitment overfished and the current level of fishing mortality is unlikely to cause this management unit to become recruitment overfished.

On the basis of the evidence provided above, Spanish Mackerel in the Northern Territory is classified as a sustainable stock.  

Mackerel Managed Fishery (Western Australia) management unit

Fishing effort throughout the Mackerel Managed Fishery (Western Australia) has been relatively stable since 2006, following reductions due to management changes. The high catch rates for the two main fishery areas, both near record levels, indicate a relatively high abundance of Spanish Mackerel in these management areas. Catch rates in other areas have remained stable at relatively high levels since 2007. As the minimum legal size for Spanish Mackerel is 900 mm total length, which is similar to the size at maturity for this species¹⁶, the spawning stock is essentially the same as the exploited stock. Therefore, the status of the Spanish Mackerel spawning stock is measured using the catch rates for each area of the fishery. Catch rates are either continuing to increase or are stable at relatively high levels within each management area, suggesting that the overall spawning stock is increasing. Additionally, the total catches of Spanish Mackerel remain within the target range. Spanish Mackerel in Western Australia 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 management unit is classified as a sustainable stock.