Northern Australian biological stock
This cross-jurisdictional biological stock has components in the Northern Territory and Queensland. Each jurisdiction assesses that part of the biological stock that occurs in its waters. Status presented here for the entire biological stock has been established using evidence from both jurisdictions.
The Northern Territory manages the commercial harvest of Saddletail Snapper and Crimson
Snapper together as red snapper. Over the past 10 years, Saddletail Snapper has averaged around
78 per cent of the Northern Territory commercial red snapper harvest. For the Northern Territory part of this biological stock, the most recent assessment4 estimated that the biomass of the red snapper group in 1990 was 24 000 tonnes (t). This estimate took into account high fishing pressure from foreign fleets (1970–1989), which peaked at 4200 t in 1989. Stock reduction analysis conducted
in 1996 indicated that, for the biological stock to be reduced to 24 000 t in 1990, the unfished biomass would have been approximately 50 000 t. Hence, biomass in 1990 was estimated to be
45–50 per cent of the unfished level.
Licensed activity by foreign fleets in northern Australian waters ceased in 1991, and total catch of red snapper in the Northern Territory decreased substantially between 1991 and 1995 (to less than 100 t annually). Over the past 15 years (1995–2010), domestic effort in the Arafura Sea, where more than
80 per cent of red snapper is taken, has been minimal compared with pre-1991 levels. The most recent estimate of annual sustainable yield for Saddletail Snapper is 2900 t4–5. In 2010, the total commercial catch of Saddletail Snapper was 1041 t.
It is assumed that, as a result of the reduced effort since 1990, further reductions in biomass are unlikely. Hence, the Northern Territory part of the biological stock is not considered to be recruitment overfished, and fishing mortality is unlikely to cause this part of the biological stock to become recruitment overfished.
For the Queensland part of the biological stock, commercial catch in 2010 was 193 t. Since no information is available on biomass, there is insufficient information to confidently classify the status of this part of the biological stock.
Since the Northern Territory part of the biological stock constituted the majority of the total catch in
2010, the status of this part of the biological stock is indicative of the entire biological stock. Hence, the biological stock is classified as a sustainable stock.
East coast Queensland biological stock
Since the quota management system was introduced in 2004, commercial harvest has dropped to around 50 t per year. Current biological information is unavailable. Uncertainty also exists around the biological stock structure, and no stock assessment has been completed. Insufficient information is available to confidently classify the status of this biological stock; as a result, the biological stock is classified as an undefined stock.
North West Shelf biological stock
Saddletail Snapper is exploited primarily on the north-west coast of Western Australia as a component of the Pilbara Demersal Scalefish Fisheries (Western Australia) and Northern Demersal Scalefish Fishery (Western Australia)6. Saddletail Snapper is assessed on the basis of the status of several indicator species (e.g. Red Emperor, Lutjanus sebae) that represent the inshore demersal suite of species (30–250 m depth). The major performance measures for these indicator species relate to spawning stock levels. The target level of spawning biomass is 40 per cent of the unfished level. The limit level is 30 per cent of the initial spawning biomass. Data analysis using an integrated age-structured model determined that the spawning biomass levels of the indicator species were greater than 40 per cent of the unfished level in the Pilbara Demersal Scalefish Fisheries (Western Australia) and the Northern Demersal Scalefish Fishery (Western Australia) in 20077. The biological stock is not considered to be recruitment overfished.
The fishing mortality (F)–based assessments7 indicated that the fishing levels on the indicator species were either lower than the target level or between the target and threshold levels. These fishing mortality–based assessments use reference levels based on ratios of natural mortality (M) for each species, such that Ftarget = 2/3M, Fthreshold = M and Flimit = 3/2M. This level of fishing mortality is unlikely to cause the biological stock to become recruitment overfished.
On the basis of the evidence provided above, the biological stock is classified as a sustainable stock.
Total commercial catch of Saddletail Snapper remained stable at around 1000 t until 2006, when catches began to rise steadily from around 1200 t to around 1500 t in 2010. This was a result of increased harvest in the northern Australian biological stock. Catch in the Queensland-managed sector of the Gulf of Carpentaria was less than 1 per cent of the northern Australian harvest in 2000, but has gradually increased, accounting for around 16 per cent in 2010. In 2009, a record 229 t of Saddletail Snapper was reported in the Gulf of Carpentaria Developmental Fin Fish Trawl Fishery (Queensland). Catch in the Northern Territory–managed sector of the northern Australian biological stock has also increased, from around 800 t in 2006 to around 1000 t in 2010.
The east coast Queensland harvest decreased from more than 100 t in 2000 to 7.5 t in 2005. The catch remained low until 2007, when it began to increase again. This may have been the result of changes to reporting requirements. In 2007, a more detailed logbook was introduced to the Coral Reef Fin Fish Fishery (Queensland), and reporting of 'nannygai-unspecified' dropped from 18 t in
2006–07 to less than 100 kg in 2009–10.
The catch of Saddletail Snapper in Western Australia has been stable at 198–203 t over the past three years (2008–10), despite variation in effort allocation levels across multiple fisheries.