Table 1: Stock status determination for Dusky Flathead
Jurisdiction |
New South Wales |
Queensland |
Victoria |
Stock |
EGF |
ECIFFF |
GLF |
Stock status |
|
|
|
Sustainable |
Sustainable |
Sustainable |
Indicators |
Commercial catch rates, age and length, mortality |
Commercial catch rates, age and length |
Commercial and recreational catch rates, length |
ECIFFF = East Coast Inshore Fin Fish Fishery (Queensland); EGF = Estuary General Fishery (New South Wales); GLF = Gippsland Lakes Fishery (Victoria)
The biological stock structure of Dusky Flathead populations is not known. As a result, status assessments of the potential individual biological stocks have not been completed. Some assessments of Dusky Flathead have been completed at a jurisdictional level. In the absence of information on biological stock boundaries, status is reported at the jurisdictional level.
New South Wales
Commercial landings of Dusky Flathead have been relatively stable for the past four decades, fluctuating between 150 and 200 tonnes (t) annually1. For the past decade, commercial catch per unit effort for Dusky Flathead has been steady2. In addition, long-term length-frequency distributions of commercial landings appear stable, although some temporal and spatial variability has been reported in the length composition of landings1. Reported estimates of annual total mortality were temporally and spatially variable between 1995 and 1997, ranging from 0.45 to 1.641. For the fishery to be sustainable, it is considered that fishing mortality should not exceed natural mortality. This evidence indicates that the biomass of Dusky Flathead in New South Wales is not considered to be recruitment overfished, and the current level of fishing mortality is unlikely to cause the Dusky Flathead to become overfished.
On the basis of the evidence provided above, Dusky Flathead in New South Wales is classified as a sustainable stock.
Queensland
The most recent stock status assessment for Dusky Flathead in the East Coast Inshore Fin Fish Fishery (Queensland) was completed in 20113. The assessment used a weight-of-evidence approach to assign an exploitation category; it considered information from biological monitoring (length and age), commercial catch and effort information from logbooks, and recreational catch data from surveys in 2000 and 20054,5. Commercial gillnet catches and catch rates decreased slightly in 2010, but are within historical levels dating back to 1993 and are considered stable. A commercial catch performance measure (a change of more than 30 per cent over three years) was not triggered in 2010. Biological monitoring of Dusky Flathead indicates a spread of lengths and ages within the catches of both commercial and recreational sectors from 2007 to 2010. This evidence indicates that the biomass of Dusky Flathead in Queensland is unlikely to be recruitment overfished.
The commercial and recreational fishery predominantly harvests female fish because of minimum and maximum legal sizes that are in place. The current minimum legal size (40 cm) protects most male fish from harvest, while the maximum legal size (75 cm) protects large fecund female fish. An in-possession limit of five Dusky Flathead per recreational fisher is also in place. The current management regime for Dusky Flathead means that the allowable level of fishing mortality is unlikely to cause Dusky Flathead in Queensland to become recruitment overfished.
On the basis of the evidence provided above, Dusky Flathead in Queensland is classified as a sustainable stock.
Victoria
The most recent fishery assessment for the Gippsland Lakes, Victoria, which included Dusky Flathead, was completed in 2011 (J Kemp, pers. comm, August 2012.). The assessment of Dusky Flathead uses a weight-of-evidence approach that assesses commercial and recreational catch rates, and length-frequency distributions. Commercial and recreational catch rates are highly variable. Following a peak in commercial mesh-net catch rates in 2005–06, there has been a decrease in recent years. Similarly, there has been a decrease in catch rates of Dusky Flathead by recreational anglers for the past four years. Despite these decreases, catch rates by commercial nets for the past four years have been higher than those recorded from 1986–87 to 2004–05. There is no compelling evidence to suggest that the reduction in commercial catch rates since 2005–06 is a result of the species being recruitment overfished in Victoria. Fluctuations in the indicators are instead likely to be the result of environmental conditions affecting spawning success and/or recruitment to the fishery. This evidence indicates that the biomass of Dusky Flathead in Victoria is unlikely to be recruitment overfished. The catch of Dusky Flathead in 2010 was less than the average catch for the period 2002–09. The current level of fishing mortality is unlikely to cause Dusky Flathead in Victoria to become recruitment overfished.
On the basis of the evidence provided above, Dusky Flathead in Victoria is classified as a sustainable stock.
Table 2: Dusky Flathead biology6–7
Longevity and maximum size |
Females: 16 years; 120 cm TL Males: 11 years; 62 cm TL |
Maturity (50%) |
Varies according to location. The most recent study in New South Wales reports 32 cm TL for males and 57 cm TL for females. |
TL = total length
Figure 1: Distribution of reported commercial catch of Dusky Flathead in Australian waters, 2010
- Commercial catch of Dusky Flathead is predominantly taken using gill (mesh) and hauling (seine) nets. Recreational catch is typically by rod and reel using bait or lures.
- A range of input and output controls are in place across jurisdictions:
- Input controls include limited entry to the commercial fishery, gear restrictions, spatial closures, temporal closures and size limits (commercial and recreational).
- Output controls include recreational bag limits.
- In 2010–11, commercial Dusky Flathead catch was reported from 232 net vessels and 15 line vessels in Queensland, 393 vessels in New South Wales and 13 vessels in Victoria.
- Total commercial catch of Dusky Flathead across Australia in 2010 was 196.6 t, comprising 117.8 t in New South Wales, 59.5 t in Queensland and 19.3 t in Victoria. Recreational catch of Dusky Flathead is thought to be considerably greater than commercial catch. The most recent estimates of the recreational catch of Dusky Flathead include 415 000 fish in Queensland in 20055, and 597 t (all flathead species) in Victoria in 20004. In New South Wales, total flathead catch (all species) was estimated at 570–830 t in 20004. The only estimate of Indigenous catch was 2384 fish in Queensland for 20004.
Figure 2: Commercial catch of Dusky Flathead in Australian waters, 2002–10 (calendar year)
Commercial catches in New South Wales fell in the early 2000s, after which total landings have been relatively stable and within historical records (since the 1960s). The decline in commercial catches after 2000 was associated with commercial licence buy-outs during the creation of recreational fishing havens and marine parks. Catch rates of Dusky Flathead in New South Wales from commercial gillnets have remained relatively stable over the past 10 years. In Queensland, commercial catch and catch rates decreased slightly in 2010; however, these are within historical levels back to the early 1990s. Catch fluctuations in Victoria in recent years are likely to be associated with environmental conditions affecting stock dynamics. There has been a decline in large Dusky Flathead (≥50 cm total length) taken by recreational anglers in Mallacoota Inlet and Lake Tyers, Victoria; this is currently being monitored8.
- Commercial coastal, river and estuary set gillnets have been shown to have minimal impact on the environment in Queensland and are quite selective in their harvest9. Bycatch levels using these types of gillnets in Queensland inshore waters are generally low compared with the retained harvest.
- Specifically designed flathead gillnets are used to target Dusky Flathead in three estuaries in New South Wales, but they also catch other byproduct and bycatch species, particularly undersized juveniles of other key species10–12. In all other estuaries, general gillnets are used to catch a wide variety of species, including Dusky Flathead. These nets have specific bycatch issues, including the capture of undersized conspecifics of key species12–13.
- Dusky Flathead is dependent on estuarine and inshore coastal habitats throughout its life cycle. Physical impacts on coastal marine vegetation, subsurface topography and water quality are likely to influence the resilience, productivity and recruitment variability of Dusky Flathead populations at local scales.
a Department of Agriculture, Fisheries and Forestry, Queensland
b Department of Primary Industries, New South Wales
c Department of Primary Industries, Victoria