Table 1: Stock status determination for Tropical Rocklobster
Jurisdiction |
Commonwealth, Queensland |
Stock |
North-eastern Australia
(CSF, TRLF, TSTRLF) |
Stock status |
|
Sustainable |
Indicators |
Biomass, fishing mortality, stock assessment |
CSF= Coral Sea Fishery (Commonwealth); TRLF= Tropical Rock Lobster Fishery (Queensland); TSTRLF= Torres Strait Tropical Rock Lobster Fishery (Commonwealth)
The Tropical Rocklobster populations in northern Queensland (managed by Queensland), the Coral Sea (managed by the Commonwealth) and the Torres Strait (managed under the Torres Strait Protected Zone Joint Authority) are thought to comprise a single biological stock, as a result of the mixing of larvae in the Coral Sea1. Stock assessments have not been carried out for the complete biological stock, but have been conducted on the various parts of the biological stock.
North-eastern Australia biological stock
Stock status for the entire Tropical Rocklobster biological stock has been established using evidence from the Queensland, Coral Sea and Torres Strait parts of the biological stock.
For the Torres Strait part of the biological stock, the most recent assessment2 estimated that biomass in 2010 was 75 per cent of the unfished (1973) level. This part of the biological stock is not considered to be recruitment overfished. The model generated a nominal total allowable catch (TAC) for 2010 of 853 tonnes (t), with 763 t caught3. Therefore, the level of fishing mortality is unlikely to cause this part of the biological stock to become recruitment overfished.
For the Queensland part of the biological stock, the most recent stock assessment4 estimated that biomass at the start of 2008 was 60–70 per cent of the unfished (1988) level. The commercial catch since 2009 has been less than the conservatively set TAC (195 t in 2010)5. As a result, this part of the biological stock is not considered to be recruitment overfished, and current fishing mortality is unlikely to cause this part of the biological stock to become recruitment overfished.
No formal stock assessments have been carried out for the Coral Sea part of the biological stock, but there is only limited targeting of Tropical Rocklobster in this area. Estimates of density on Coral Sea reefs, inferred from fishers’ catch rates, suggest that lobster abundance is likely to be many times higher than would be required to support the total historical catch (<10 t)3. This part of the biological stock is not considered to be recruitment overfished. Additionally, no commercial catch was recorded in 2010. Therefore, fishing mortality is unlikely to cause this part of the biological stock to become recruitment overfished.
On the basis of the evidence provided above, the biological stock is classified as a sustainable stock.
Other potential stocks
Although Tropical Rocklobster is present in both the Northern Territory and northern Western Australia, it is not commercially fished in either jurisdiction or in Queensland waters of the Gulf of Carpentaria. Biological stock structures in these regions have not been studied.
Table 2: Tropical Rocklobster biology6–8
Longevity and maximum size |
3–5+ years; >15 cm CL |
Maturity (50%) |
2–3 years; ~10 cm CL |
CL = carapace length
Figure 1: Distribution of reported commercial catch of Tropical Rocklobster in Australian waters, 2010
- Tropical Rocklobster is predominantly a dive-based, hand-collection fishery, using surface-supplied air (hookah). However, some lobsters are collected at night on shallow reef flats, and some are collected using hand-held implements (e.g. snare, net or spear).
- A range of input and output controls are in place for the Tropical Rocklobster biological stock:
- Input controls include seasonal closures, area closures and gear restrictions.
- Output controls include TACs, and size and bag limits, although with differences in each jurisdiction.
- Two commercial sectors operate within the Australian area of the Torres Strait Tropical Rock Lobster Fishery: the Traditional Inhabitant Boat sector and the Transferable Vessel Holder sector (non-Islanders). In 2010, 11 Transferable Vessel Holder sector vessels and 270 Traditional Inhabitant Boat sector vessels were active. In addition, 7 cross-endorsed Papua New Guinean vessels fished in Australian waters of the Torres Strait. The number of Papua New Guinean vessels fishing the same stock in Papua New Guinean waters of the Torres Strait in 2010 is not known. Within the Queensland-managed fishery, there were 10 active vessels. A number of the Queensland vessels were dual-endorsed to fish also in the Torres Strait. No fishing was reported from the Coral Sea in 2010.
- Total commercial catch of Tropical Rocklobster across Australia in 2010 was 893 t, comprising 763 t in the Torres Strait and 130 t on the Queensland east coast. Recreational catch was likely to be comparatively small. It was last estimated in Queensland in 2005 at 20 000 ± 6000 (standard error) lobsters9. Indigenous non-commercial harvest was also thought to be small but socially important. An Indigenous catch survey conducted in Australia in 2001 estimated an annual take of 13 000 lobsters in Queensland10.
a)
b)
Figure 2: a) Commercial catch of Tropical Rocklobster in Australian waters, 2001–10 (calendar year);
b) spawning stock biomass estimates from the Commonwealth-managed Torres Strait region, 2001–10
Commercial catch of Tropical Rocklobster peaked in 2005 at approximately 1300 t (estimated whole weight) and has since declined to an average of approximately 800 t per year over the period 2006–10. Fluctuations in yearly catch of Tropical Rocklobster may be explained by fluctuations in recruitment and/or in economic drivers, such as input prices (e.g. fuel) and demand for rocklobster, particularly in major export markets3,5.
There is no indicator that covers the entire biological stock. However the integrated stock assessment model for the Torres Strait provides an estimated biomass each year for the following three years2. Estimated spawning stock biomass results show the variability expected, given the known dependence of the Tropical Rocklobster’s life cycle on environmental conditions. However, there were no significant trends in the spawning biomass for the period 2001–102.
- Fishing for Tropical Rocklobster has little direct impact on the marine environment or other fish species, since hand-collection fishing methods allow careful selection of catch3.
- The abundance of Tropical Rocklobster is highly influenced by environmental conditions, which affect settlement and recruitment. Ocean current and wind patterns affect transport of larvae and create variability in abundance. These variations should be taken into account in setting TACs1,7.
a Department of Agriculture, Fisheries and Forestry, Queensland
b Australian Bureau of Agricultural and Resource Economics and Sciences
c Department of Primary Industry and Fisheries, Northern Territory