Table 1: Stock status determination for Common Jack Mackerel
Jurisdiction |
Tasmania, New South Wales, Commonwealth |
Tasmania, Commonwealth |
Stock |
Eastern stock
(CTS, NSWCF, SF, SPF, VIT) |
Western stock
(CTS, GAB, SET, SF, SPF) |
Stock status |
| |
|
Sustainable |
Sustainable |
Indicators |
Catch, effort and CPUE trends, spawning biomass, ecosystem modelling |
Catch, effort |
CPUE = catch per unit effort; CTS = Commonwealth Trawl Sector; GAB = Great Australian Bight Trawl (Commonwealth); NSWCF = New South Wales Commercial Fishery; SF = Scalefish Fishery (Tasmania); SPF = Small Pelagic Fishery (Commonwealth); VIT = Victorian Inshore Trawl Fishery (Commonwealth)
There is evidence of at least two biological stocks of Common Jack Mackerel in Australian waters: one off eastern mainland Australia, including eastern Tasmania, and the other extending from western Tasmania through to southern Western Australia. A separate biological stock also exists in New Zealand waters. These conclusions are based on morphological and meristic differences between fish from the Great Australian Bight and eastern Australia1, genetic differences between fish from the Great Australian Bight and New Zealand2, and a lack of genetic difference between fish from eastern Tasmania and New South Wales3. While not conclusive, the above evidence was considered sufficient for the Common Jack Mackerel in the Small Pelagic Fishery (Commonwealth) to be managed as separate eastern and western biological stocks4, and they are assessed as such in this chapter.
Eastern biological stock
Two studies have estimated the adult biomass of the eastern Common Jack Mackerel stock. The first, based on an ichythoplankton survey conducted in 2002, used the daily egg production method and estimated the spawning biomass to be in the range 114 900–169 000 tonnes (t)5. The second study used two ecosystem-based modelling techniques to examine the plausible biomass required to support the shelf ecosystem of south-eastern Australia. These models estimated the biomass to be in the order of 130 000–170 000 t, and suggested that there would not be any broadscale restructuring of the marine ecosystem should the total allowable catch (TAC) for the Small Pelagic Fishery (Commonwealth) eastern stock (10 000 t in the 2012–13 fishing season) be taken 6.
The low market value of this species, reduced demand for fish meal, and a recent moratorium on the operation of large-scale factory trawlers has meant that fishing activity has been minimal, and the TAC has not been taken in recent years. The most recent stock assessment for the eastern biological stock of Common Jack Mackerel4 reported that, since 2011, catches in all fisheries have been at historically low levels and collectively less than 100 t. Further, there has been a general decline in the number of vessels operating within the eastern zone of the Small Pelagic Fishery (Commonwealth) over the past 15 years4. The above evidence indicates that the current level of fishing pressure is unlikely to cause the stock to become recruitment overfished7. Relatively high biomass estimates6 and voluntary decreases in fishing effort, unrelated to Common Jack Mackerel abundance, also indicate that the biomass of the stock is unlikely to be recruitment overfished4,7.
On the basis of the evidence provided above, the biological stock is classified as a sustainable stock.
Western biological stock
No daily egg production method survey or estimate of spawning biomass has been conducted for the western Common Jack Mackerel stock. Aerial surveys in the 1970s suggested a biomass off western Tasmania of at least 80 000 t8. Catches peaked in 2006–07, when they were less than 1 per cent of the biomass estimate and 9 per cent of the current TAC (5000 t) for the Small Pelagic Fishery (Commonwealth). Catches in recent years have been low; the current catch is close to zero. The above evidence indicates that the stock is unlikely to be recruitment overfished and that the current level of fishing pressure is unlikely to cause the stock to become recruitment overfished.
On the basis of the evidence provided above, the biological stock is classified as a sustainable stock.
Table 2: Common Jack Mackerel biology9–11
Longevity and maximum size |
17 years; 470 mm FL |
Maturity (50%) |
5–6 years; 315 mm FL |
FL = fork length
Figure 1: Distribution of reported commercial catch of Common Jack Mackerel in Australian waters, 2013 (calendar year)
Table 3: Main features and statistics for Common Jack Mackerel fisheries in Australia, 2013 (calendar year)
Jurisdiction |
Tasmania |
New South Wales |
Commonwealth |
Fishing methods |
Commercial |
Purse seine |
✓ |
✓ |
✓ |
Midwater trawl |
|
|
✓ |
Beach seine |
✓ |
|
|
Gillnet |
✓ |
|
|
Demersal otter trawl |
|
✓ |
✓ |
Recreationala |
Gillnet |
✓ |
|
|
Rod and line |
✓ |
✓ |
|
Indigenousb |
Rod and line |
|
✓ |
|
Unknown |
✓ |
|
|
Management methods |
Commercial |
Limited entry |
✓ |
✓ |
✓ |
Vessel restrictions |
✓ |
✓ |
✓c |
Catch limits |
✓ |
|
✓ |
Mesh size regulations |
✓ |
✓ |
|
Spatial closures |
✓ |
✓ |
|
Recreationala |
Bag limits |
✓ |
✓ |
|
Spatial closures |
✓ |
✓ |
|
Indigenousb,d,e |
Bag limits |
✓ |
✓ |
|
Spatial closures |
|
✓ |
|
Section 37(1)(c1), Aboriginal cultural fishing authority |
|
✓ |
|
Active vessels |
|
5 in SF |
<6 in NSWCF |
2 in GAB
23 in CTS
3 in SPF
2 in VIT |
Catch |
Commercial |
0.25 t in SF |
Confidentialf in NSWCF |
0.1 t in GAB
36.1 t in CTS
0 t in SPF
0.3 t in VIT |
Recreationalb |
1 t (2007–08) |
Unknown |
|
Indigenousc |
Unknown |
Unknown |
|
Markets |
Domestic |
✓ |
✓ |
✓ |
Export |
|
|
|
CTS = Commonwealth Trawl Sector; GAB = Great Australian Bight Trawl (Commonwealth); NSWCF = New South Wales Commercial Fishery; SF = Scalefish Fishery (Tasmania); SPF = Small Pelagic Fishery (Commonwealth); VIT = Victorian Inshore Trawl Fishery (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.
c Historically, no restrictions on vessel hold capacity have been in place in the Small Pelagic Fishery (Commonwealth). However, in 2012, an interim declaration was made to prevent factory trawlers greater than 130 metres in length with on-board fish processing facilities, and storage capacity for fish or fish products in excess of 2000 t, from entering this fishery for a 2-year period.
d The Aboriginal Fishing Interim Compliance Policy allows an Indigenous fisher in New South Wales to take in excess of a recreational bag limit in certain circumstances—for example, if they are doing so to provide fish to other community members who cannot harvest themselves.
e The Aboriginal cultural fishing authority is the authority that Indigenous persons can apply to to take catches outside the recreational limits under the New South Wales Fisheries Management Act 1994, section 37(1)(c1) (Aboriginal cultural fishing authority).
f Confidentiality clauses prevent reporting of fishery statistics for fewer than six vessels in New South Wales.
Figure 2: Commercial catch of Common Jack Mackerel in Australian waters, 2000 to 2013 (calendar years)
Of the three main fishing methods used to target Common Jack Mackerel (purse seine, midwater trawl and beach seine), only beach seine interacts with the benthos. Studies in New South Wales have shown that purse-seine nets have a negligible impact on seagrass habitats12. Both purse-seine and midwater trawl fisheries interact with marine mammals, including seals and dolphins. Purse-seine nets remain open to the surface. Studies in the Northern Hemisphere have shown that, although interactions with dolphins (Bottlenose and Common dolphins occur in Australia) can be common, these species are rarely caught by purse seine and, when caught, usually survive13. Mortalities of both seals and dolphins have been recorded during midwater trawl operations in this fishery14. Dolphin encounters appear to be very rare; however, underwater cameras have revealed that seals commonly enter and forage in midwater trawl gear, with some mortalities14. Seal excluder devices in the trawl nets have had some success in reducing, but not eliminating, lethal interactions14.
Common Jack Mackerel play a role in the pelagic food chain as a link between primary and secondary producers and top predators, including tunas, sharks, marine mammals and seabirds. Recognising this important ecological role, the harvest strategy adopted in the Small Pelagic Fishery (Commonwealth) restricts catches to conservative levels of below 20 per cent of current spawning biomass estimates. These are consistent with levels internationally recommended for the sustainable management of forage fisheries15.
A decrease in the presence and size of surface schools of Common Jack Mackerel in Tasmanian waters during the 1990s was initially considered to be due to the effects of heavy fishing pressure during the 1980s and 1990s by the Tasmanian Jack Mackerel (purse seine) Fishery. However, there is evidence that strengthening of the East Australian Current has altered the swarming behaviour and abundance of Australian krill (Nyctiphanes australis), a major prey for Common Jack Mackerel, and this contributed to the reduction in surface schools16. Associated with this ocean warming has been an apparent increase in the abundance of Redbait (Emmelichthys nitidus), a species that predominantly preys on small copepods17, which may have increased in abundance with the strengthening of the East Australian Current 18.
a Institute for Marine and Antarctic Studies, University of Tasmania
b Australian Bureau of Agricultural and Resource Economics and Sciences
c Department of Primary Industries, New South Wales