Dusky Flathead Platycephalus fuscus

Jason McGilvraya, Faith Doyleb and Corey Greenc


Dusky Flathead from side
Dusky Flathead from above

Table 1: Stock status determination for Dusky Flathead

Jurisdiction

Queensland

New South Wales

Victoria

Stock

Queensland
(ECIFFF)

New South Wales
(
EGF)

Victoria
(GLF)

Stock status

 

 

Sustainable

Sustainable

Sustainable

Indicators

Commercial catch and CPUE, length and age composition, mortality rate (Z)

Commercial catch and CPUE, length and age composition, mortality rate (Z)

Commercial catch and CPUE, length frequency

CPUE = catch per unit effort; ECIFFF = East Coast Inshore Fin Fish Fishery (Queensland); EGF = Estuarine General Fishery (New South Wales); GLF = Gippsland Lakes Fishery (Victoria); Z = total instantaneous mortality rate


Stock Structure

The biological stock structure of Dusky Flathead populations is unknown. However, the biological information on populations within each of the jurisdictions is well known and this coupled with the unknown stock structure dictates that assessments of Dusky Flathead stocks be completed at a jurisdictional level1–5.


Stock Status

Queensland

Nominal commercial catch rate has been stable since 19936. Fishery-dependent monitoring from 2007 to 2013 indicates that both the commercial and recreational fishery sectors are harvesting Dusky Flathead across a spread of lengths and ages6. Fishery-dependent monitoring of length and age indicates that Dusky Flathead populations have variable recruitment, with no evidence of a decline through time6. The evidence indicates that the biomass of this stock is unlikely to be recruitment overfished.

In the commercial fishery, nominal effort continues to decrease (5408 days fished in 2009; 4100 days fished in 2013)6. Recreational anglers were estimated to have targeted Dusky Flathead on more days in 2013 (163 580 days) than in 2000 (147 580 days). Commercial and recreational fishers predominantly harvest female fish because of the minimum and maximum size limits that are in place. The minimum size protects most male fish, and the maximum size protects large female fish6. Possession limits are in place for the recreational sector. Mouth-hooked Dusky Flathead have high post-release survival7. Estimates of total mortality (from catch curves) are high—the fishing mortality rate (F) is greater than the natural mortality rate (M)—but show no clear trends upwards or downwards since 20076. The estimates do not take into account older fish, which are known to exist in the population but are protected by the upper size limits in place. The current level of fishing effort is unlikely to cause this stock to become recruitment overfished.

On the basis of the evidence provided above, Dusky Flathead in Queensland is classified as a sustainable stock.  

New South Wales

Median commercial catch rates (nominal) of Dusky Flathead in New South Wales have been relatively steady for the past 5 years, and slightly higher than those observed in the previous 11 years (1997 to 2013)8. There is some temporal and spatial variability in the length compositions of the landings for this species, which is indicative of a stock with variable recruitment. This pattern has been the same since the 1960s. The above evidence indicates that the biomass of this stock is unlikely to be recruitment overfished.

Landings in New South Wales in 2013 (93.84 tonnes [t]) were lower than the long-term annual average (152.32 t). Summed across all methods in the Estuarine General Fishery, about 15 113 fisher-days were reported during 2013. This was the lowest annual effort for that fishery on record8. The size composition of fish measured during the 2012–13 financial year was similar to previous years, suggesting no large changes to the size frequency of the stock8. Although this species is likely to be primarily harvested by the recreational sector in New South Wales, recent estimates of recreational catch or effort are unavailable. The above evidence indicates that the current level of commercial fishing pressure is unlikely to cause this stock to become recruitment overfished, notwithstanding the unknown effects of recreational fishing pressure.

On the basis of the evidence provided above, Dusky Flathead in New South Wales is classified as a sustainable stock.  

Victoria

Most Dusky Flathead caught in Victoria are taken from the Gippsland Lakes. The most recent assessment for Dusky Flathead in the Gippsland Lakes was undertaken in 2011. The assessment indicated that commercial and recreational catch rates for Dusky Flathead are highly variable, but there was no evidence of a long‐term decline. Commercial mesh-net catch rates in 2009–10 were above both the long‐term and the 10‐year averages4. The above evidence indicates that the biomass of this stock is unlikely to be recruitment overfished.

Commercial catches of Dusky Flathead dropped from 17 t in 2012 to 6 t in 2013; however, this level of annual catch is still double the size of commercial catches from the early 2000s. The trend in the 5‑year moving average of recreational catch rates is stable4. Available recreational monitoring data (2005, 2006, 2009 and 2010) suggest that recreational fishers in the Gippsland Lakes rarely take Dusky Flathead greater than 50 cm total length 4. In November 2013, Victoria introduced a slot limit for recreationally caught Dusky Flathead of 30–55 cm. The number of licensed commercial fishers in Victorian waters was reduced by two-thirds between 1986–87 and 2010–11. The majority of the licence removals occurred as a result of voluntary licence buyback schemes conducted in 1999–2000 and 2005–06. The above evidence suggests 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, Dusky Flathead in Victoria is classified as a sustainable stock.


Table 2: Dusky Flathead biology1,9

Longevity and maximum size

Females: 16+ years; 1200 mm TL
Males: 11+ years; 620 mm TL

Maturity (50%)

Females: 570 mm TL
Males: 320 mm TL

TL = total length


/reports/PublishingImages/2014_data/DuskyFlathead.jpg
Figure 1: Distribution of reported commercial catch of Dusky Flathead in Australian waters, 2013 (calendar year)



Table 3: Main features and statistics for Dusky Flathead fisheries in Australia, 2013 (calendar year)

Jurisdiction

Queensland

New South Wales

Victoria

Fishing methods

Commercial

Gillnet

Seine net

Tunnel net

Recreational

Rod and line

Spearfishing

Indigenousa,b,c

Management methods

Commercial

Limited entry

Size limits

Fishing gear and method restrictions

Spatial closures

Temporal closures

Recreational

Size limits

Bag limits

Possession limits

Fishing gear and method restrictions

Spatial closures

Licence

Indigenousa,b,c

Active vessels

239 in ECIFFF

333 in EGF

10 in GLF

Catch

Commercial

51 t in ECIFFF

93 t in EGF

<7 t in GLF

Recreational

149 t 10 (2010–11)

886 t 11 (2000–01)

Unknown

Indigenous

Unknown

Unknown

Unknown

Markets

Domestic

Export


ECIFFF = East Coast Inshore Fin Fish Fishery (Queensland); EGF = Estuarine General Fishery (New South Wales); GLF = Gippsland Lakes Fishery (Victoria)

a In Queensland, under the Fisheries Act 1994 (Qld), Indigenous fishers in Queensland are able to use prescribed traditional and noncommercial fishing apparatus in waters open to fishing. Size and possession limits, and seasonal closures do not apply to Indigenous fishers. Further exemptions to fishery regulations may be applied for through permits.

b In New South Wales, Indigenous fishers are able to use traditional and noncommercial apparatus to take double the recreational bag limit. Further exemptions to fishery regulations can be obtained through permits.

c In Victoria, regulations for managing recreational fishing are also applied to fishing activities by Indigenous people. Recognised Traditional Owners (groups that hold native title or have agreements under the Victorian Traditional Owner Settlement Act 2010) are exempt (subject to conditions) from the requirement to hold a recreational fishing licence, and can apply for permits under the Fisheries Act 1995 that authorise customary fishing (e.g. different catch and size limits, or equipment). The Indigenous category in Table 3 refers to customary fishing undertaken by recognised Traditional Owners. In 2012–13, there were no applications for customary fishing permits to access Dusky Flathead.


Figure 2: Commercial catch of Dusky Flathead in Australian waters, 2002–10 (calendar year)
Figure 2: Commercial catch of Dusky Flathead in Australian waters, 2000 to 2013 (calendar year)



Effects of fishing on the marine environment
  • In Queensland, coastal-, river- and estuary-set gillnets have been shown to have minimal direct impact on the environment and are quite selective in their harvest12. Levels of bycatch are generally low compared with the harvest of the target species12. Fishers using tunnel nets operate under an industry-developed code of best-practice guidelines13. Marine turtles are released with minimal difficulty, and a high proportion of undersized or unwanted catch is returned to the water alive.

  • In New South Wales estuaries, Dusky Flathead is targeted using gillnets, which also catch other species, including undersized individuals targeted in other key fisheries14–18. These impacts can be minimised by using specifically designed Dusky Flathead gillnets that target fish above the minimum legal size16.

  • In a similar manner to the tunnel net fishery in Queensland, the New South Wales estuarine beach-seine fishery operates in a manner that allows a proportion of nontarget species to be released alive19.

  • Fishers in the Victorian Bays and Inlets Fisheries Association have adopted responsible fishing practices20. It is likely that fishing activities have minimal direct impact on the environment.

  • Seabirds and other marine life often become entangled in discarded recreational fishing tackle21. In south-east Queensland, a Fishing Line Recovery Bin program was instigated in 2012 to minimise the occurrence of discarded tackle at popular shore-based fishing locations.


Environmental effects on Dusky Flathead
  • Dusky Flathead are dependent on estuarine and inshore coastal habitats throughout their life cycle. Variable recruitment has been observed in all three states, and is thought to be environmentally driven4. Physical impacts on coastal marine vegetation, subsurface topography and water quality are likely to influence the resilience and productivity 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