Table 1: Stock status determination for Deepwater Flathead
Jurisdiction |
Commonwealth |
Stock |
Great Australian Bight
(CTS, GABTS, WDTF) |
Stock status |
|
Sustainable |
Indicators |
Biomass |
CTS = Commonwealth Trawl Sector; GABTS = Great Australian Bight Trawl Sector (Commonwealth); WDTF = Western Deepwater Trawl Fishery (Commonwealth)
The biological stock structure of Deepwater Flathead is unknown; however, it is considered a single biological stock for management purposes. Hence, stock status is reported at the level of the individual biological stock. Stock assessments for Deepwater Flathead have been completed only for the Great Australian Bight part of the biological stock1. Since the Great Australian Bight Trawl Sector (Commonwealth) accounts for the majority of catch taken from this biological stock, the stock status for the entire biological stock is based on assessments and catch from this area.
Great Australian Bight biological stock
The most recent quantitative assessment1 estimated the spawning biomass at the start of 2011 to be 62 per cent of the unfished (1978) level. This assessment is generally consistent with previous assessments and fishery-independent surveys2–3. The updated assessment estimated that the spawning biomass was progressively fished-down in the mid-2000s, but the biological stock had recovered by the start of 2010. This was most likely a result of lower fishing pressure in recent years, combined with at least one substantial recruitment event. The biological stock is not considered to be recruitment overfished.
The biologically derived total allowable catch (TAC) for the Great Australian Bight Trawl Sector (Commonwealth) for the 2010–11 fishing season was 1100 tonnes (t), which was subsequently adjusted to 1240 t to account for undercatch and overcatch. Landed catch of Deepwater Flathead from this fishery in the 2010–11 fishing season was 921 t, which was below the TAC. 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.
Table 2: Deepwater Flathead biology3–7
Longevity and maximum size |
Females: ~26 years; 82 cm TL Males: ~19 years; 59 cm TL |
Maturity (50%) |
Females: 5–6 years; 43 cm TL Males: 4–5 years; 43 cm TL |
TL = total length
Figure 1: Distribution of reported commercial catch of Deepwater Flathead in Australian waters, 2010
- Deepwater Flathead are primarily caught by demersal otter fish trawl, with some Danish-seine fishing.
- A range of input and output controls have been implemented across the fisheries that target Deepwater Flathead:
- Input controls include limited entry, gear restrictions and spatial closures in the Great Australian Bight Trawl Sector (Commonwealth), Commonwealth Trawl Sector and Western Deepwater Trawl Fishery (Commonwealth).
- Output controls include a TAC, with apportionment of catch assigned as individual transferable quotas in the Great Australian Bight Trawl Sector (Commonwealth).
- In the Great Australian Bight Trawl Sector (Commonwealth), 4 demersal otter trawl vessels and 1 Danish-seine vessel caught Deepwater Flathead in 2010–11. Eleven vessels caught Deepwater Flathead in the Commonwealth Trawl Sector, and no vessels caught Deepwater Flathead in the Western Deepwater Trawl Fishery (Commonwealth).
- Total commercial catch of Deepwater Flathead in 2010–11 was 995 t, comprising 961 t from the Great Australian Bight Trawl Sector (Commonwealth), 34 t in the Commonwealth Trawl Sector and 0 t in the Western Deepwater Trawl Fishery (Commonwealth). This species is not targeted by recreational or Indigenous fishers.
a)
b)
Figure 2: a) Commercial catch of Deepwater Flathead in Australian waters, 1986–2011 (calendar year);
b) percentage of unfished biomass, 1978–79 to 2011–12 (financial year)
Deepwater Flathead catches in the Great Australian Bight Trawl Sector (Commonwealth) decreased substantially from a peak of 2365 t in 2004 to 817 t in 2008. This decrease corresponds with a substantial decline in biomass to around 25 per cent of unfished biomass in 2005–06 and 2006–071. Catch per unit effort (CPUE) declined from 84 kg/trawl hour to 38 kg/trawl hour over the same period. Biomass had recovered to 62 per cent of unfished biomass by 2010, with CPUE increasing to 56 kg/trawl hour by 2010. Despite more than doubling of biomass since 2005–06, catch has remained below 1000 t as a result of decreases in both the TAC and effort. Effort in the Great Australian Bight Trawl Sector (Commonwealth) decreased from 30 387 trawl hours in 2006 to 15 887 trawl hours in 2010.
- The Great Australian Bight Trawl Sector (Commonwealth), Commonwealth Trawl Sector and Western Deepwater Trawl Fishery (Commonwealth) catch non-target species (bycatch). These fisheries have bycatch and discarding workplans or bycatch catch triggers in place to reduce interactions with non-target species and minimise environmental impacts8–10.
- Changes in ecosystem structure and function associated with changes in the climate may affect larval recruitment of Deepwater Flathead11.
a Australian Bureau of Agricultural and Resource Economics and Sciences
b Institute for Marine and Antarctic Studies, Tasmania