Table 1: Stock status determination for Blue Grenadier
Jurisdiction |
Commonwealth |
Stock |
CTS |
GABTS |
Stock status |
|
|
Sustainable |
Sustainable |
Indicators |
Spawning stock biomass, fishing mortality |
Current and historical fishing pressure |
CTS = Commonwealth Trawl Sector; GABTS = Great Australian Bight Trawl Sector (Commonwealth)
Comparative analysis of otolith chemistry and shape indicates two separate biological stocks of Blue Grenadier: one in the region of the Great Australian Bight Trawl Sector (Commonwealth) and the other in the region of the Commonwealth Trawl Sector1. There is some evidence that Blue Grenadier from the western Tasmanian and eastern Bass Strait regions of the Commonwealth Trawl Sector may constitute separate substocks, but these are currently assessed and managed as a single Commonwealth Trawl Sector stock2.
Commonwealth Trawl Sector biological stock
Blue Grenadier in the Commonwealth Trawl Sector and the Gillnet, Hook and Trap Sector (Commonwealth) of the Southern and Eastern Scalefish and Shark Fishery (Commonwealth) is managed under a multiyear total allowable catch (TAC). The Commonwealth Trawl Sector accounts for the majority of the catch from these two sectors. Given the small catch from the Gillnet Hook and Trap Sector, the biological stock is referred to in this report as the Commonwealth Trawl Sector biological stock.
In 2013, the Blue Grenadier stock assessment was updated using acoustic and egg survey indices, and new catch-at-age and catch-rate data up to 2012 3. The assessment estimated a large recruitment event in 2010. The stock was assessed as being above the target reference point at 77 per cent of unfished biomass in 2012, and trending upwards, indicating that the biological stock is not recruitment overfished4.
Blue Grenadier has been managed under a 3-year TAC, first implemented in 2011–12. After adjustment for uncaught quota and carryover from the 2012–13 fishing season, the TAC for the 2013–14 fishing season was set at 5704 tonnes (t)5. Total commercial catch in 2013 was 3828 t, and the 2013–14 fishing season catch was below the TAC, at 3847 t. This level of fishing mortality is unlikely to cause the biological stock to become recruitment overfished4.
The 2013 assessment3 provided recommendations for increased multiyear recommended biological catches. The South East Management Advisory Committee accepted a recommendation for a 3-year recommended biological catch of 8810 t for the 2014–15, 2015–16 and 2016–17 fishing seasons. After application of the large change limiting rule and proposals for a phased increase to facilitate stability, the agreed TAC was set at 6800 t for the 2014–15 fishing season6.
On the basis of the evidence provided above, the biological stock is classified as a sustainable stock.
Great Australian Bight Trawl Sector (Commonwealth) biological stock
There have been no stock assessments for the Great Australian Bight Trawl Sector (Commonwealth) biological stock of Blue Grenadier, and no estimates of fishing mortality or biomass have been made. A catch trigger of 400 t is in place; if this is exceeded, data collection and the development of an assessment plan are required. A cease-to-fish catch trigger of 500 t also applies7.
This Blue Grenadier biological stock is targeted on the upper continental slope (around 200–700 m depth). Fishing effort on the Great Australian Bight continental slope has decreased since 2005 because of the targeting of shelf species rather than slope species. There are large areas of slope habitat across the Great Australian Bight and Western Australia, with fishing generally limited to a small area. It is therefore likely that parts of this biological stock remain unfished. Commercial catches of Blue Grenadier are typically low in the Great Australian Bight Trawl Sector (20 t in 2013, with a peak commercial catch in 2005 of 421 t). The above evidence indicates that the biomass of this stock is unlikely to be recruitment overfished. In addition, the low 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: Blue Grenadier biology1
Longevity and maximum size |
25 years; ~1100 mm TL, weight 6 kg |
Maturity (50%) |
4–5 years; females 640 mm TL, males 570 mm TL |
TL = total length
Figure 1: Distribution of reported commercial catch of Blue Grenadier in Australian waters, 2013 (calendar year)
Table 3: Main features and statistics for Blue Grenadier fisheries in Australia, 2013 (calendar year)
Jurisdiction |
Commonwealth |
Fishing methods |
Commercial |
Demersal trawl |
✓ |
Midwater trawl |
✓ |
Demersal longline |
✓ |
Dropline |
✓ |
Recreationala |
Rod and line (electric reel) |
✓ |
| Indigenousb |
|
|
Management methods |
Commercial |
Limited entry |
✓ |
Total allowable catch (CTS) |
✓ |
Trigger limits (GABTS) |
✓ |
Spatial closures |
✓ |
Recreationala |
| |
|
Indigenousb |
| |
|
Active vessels |
|
35 in CTS
3 in GABTS |
Catch |
Commercial |
3828 t in CTS
20 t in GABTS |
Recreationala |
|
Indigenousb |
|
Markets |
Domestic |
✓ |
Export |
✓ |
CTS = Commonwealth Trawl Sector; GABTS = Great Australian Bight Trawl Sector (Commonwealth)
a The Australian Government does not manage recreational fishing in Commonwealth waters. Recreational fishing in Commonwealth waters is managed by the state or territory immediately adjacent to those waters, under its management regulations.
b The Australian Government does not manage noncommercial Indigenous fishing in Commonwealth waters, with the exception of the Torres Strait. In general, noncommercial Indigenous fishing in Commonwealth waters is managed by the state or territory immediately adjacent to those waters.
Figure 2: Commercial catch of Blue Grenadier in Australian waters, 1979 to 2013 (calendar years)
In the Commonwealth Trawl Sector, commercial catch increased from 1999 to 2004, with a corresponding increase in effort. Commercial catch and catch per unit effort have been relatively constant over recent years.
Commercial catch of Blue Grenadier in the Great Australian Bight Trawl Sector (Commonwealth) has historically been low, only exceeding 50 t from 2004 to 2007, as a result of increasing fishing effort on the continental slope over this period. Fishing effort on the slope has dramatically decreased since this period, with catches not exceeding 10 t since 2008.
There can be a substantial level of bycatch in the fish trawl sector. In 2006, mandatory requirements for otter trawls to use 90 mm square-mesh codend panels were introduced to reduce the catch of small species and juvenile fish8.
Interactions also occur with animals protected under the Environment Protection and Biodiversity Conservation Act 1999, including marine mammals (dolphins, seals and sea lions), seabirds, some shark species and seahorses and pipefish (syngnathids). These interactions are reported quarterly by the Australian Fisheries Management Authority9 and on-board observer programs are used to validate the reporting in commercial logbooks.
In 2007, the South East Trawl Fishing Industry Association released an industry code of practice that aims to minimise interactions with fur seals, as well as addressing the environmental impacts of the fishery more generally10. Operators have developed other mitigation protocols that have further reduced seal mortalities, including using breakaway ties that keep the net closed until it is below depths that seals regularly inhabit, adopting techniques to close the trawl opening during recovery to minimise opportunities for seals to enter the net, switching off gantry lights that are not required during night trawling to avoid attracting bait species and seals, and dumping offal only when the boat is not engaged in deploying or hauling gear10.
In 2011, AFMA mandated individual vessel seabird management plans11. The seabird action plans are used in the Commonwealth Trawl Sector to mitigate the impacts of trawling on seabirds. Seabird mitigation measures include warp deflectors (‘pinkys’), bird bafflers (a system of ropes and PVC piping that protects the warp cable) and seal excluder devices.
The effects of trawl fishing on the marine environment are assessed through an environmental risk assessment and risk management framework and mitigated through spatial closures, and the implementation of bycatch and discard workplans in the Commonwealth Trawl Sector and Great Australian Bight Trawl Sector fisheries.
- Changes in ecosystem structure and function due to changes in climate may affect larval recruitment of Blue Grenadier12. Stock assessments indicate substantial interannual recruitment variability, with occasional years of very high recruitment, which are probably environmentally driven3.
a Australian Bureau of Agricultural and Resource Economics and Sciences