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Stock Status Overview
|Northern Territory||Gulf of Carpentaria||ONLF||Sustainable||Stock Reduction Analysis, catch, catch effort|
|Northern Territory||North West Northern Territory||ONLF||Sustainable||Stock Reduction Analysis, fishing mortality, catch, catch effort|
- Offshore Net and Line Fishery (NT)
There are at least five Grey Mackerel biological stocks across northern Australia, with a possible additional stock in the north-east Gulf of Carpentaria1–5.
Here, assessment of stock status is presented at the biological stock level—Western Australia, North-west Northern Territory (Timor/Arafura), Gulf of Carpentaria, North-east Queensland and South-east Queensland.
North West Northern Territory
Assessments indicate that Grey Mackerel stocks in the Northern Territory declined substantially as a result of the high Taiwanese gillnet catches in the 1970s–80s, but have since recovered with the cessation of foreign fishing and more stringent management of the domestic fishery. The most recent assessment11 estimates that the biomass in 2011, was 81 per cent of the unfished level. The stock is not considered to be recruitment overfished. Furthermore, the current harvest rate is 12 per cent of that required to achieve maximum sustainable yield (MSY)11. Supporting this assessment is that catch per unit effort has increased over the past 10 years, while catches have remained relatively consistent11–13. This current level of fishing pressure is unlikely to cause the stock to become recruitment overfished.
On the basis of the evidence provided above, the North-west Northern Territory biological stock is classified as a sustainable stock.
Gulf of Carpentaria
Grey Mackerel in the Gulf of Carpentaria is primarily a commercial gillnet-caught species. Queensland and the Northern Territory share management of the Gulf of Carpentaria biological stock through the Queensland Fisheries Joint Authority. Queensland took the majority (88 per cent) of the commercial harvest in 2015 and has averaged 80–90 per cent of the harvest in recent years.
There has been a rising trend in commercial catch rate since targeted fishing for Grey Mackerel began in the Gulf of Carpentaria in the late-1990s. Queensland catches and catch rates reached record levels in 2010 and 2012, respectively. Although the Queensland catch rate dropped in 2013 (60 kg per 100 m net), it has steadily risen in 2014 (68 kg per 100 m net) and again in 2015 (86 kg per 100 m net)14. The most recent assessment estimates that the biomass in 2011 was 74 per cent of the unfished biomass11. The stock is not considered recruitment overfished. Stock reduction analysis of Grey Mackerel in the Gulf of Carpentaria, using Queensland and Northern Territory catches also concluded that the harvest rate is at 26 per cent of that required to achieve MSY11. The above evidence indicates the biomass of this stock is unlikely to be recruitment overfished.
Queensland introduced changes to the net fishery at the commencement of the 2012 season to reduce pressure on Grey Mackerel. These measures decreased the total length of available net by two-thirds, from 27–9 km in the offshore component of the fishery. Changes made for the Queensland inshore fishery (within 7 nautical miles of the coast) also reduced the capacity for boats to target Grey Mackerel. Commercial effort (days fished) and catch rates (kg per 100 m net) in 2015 were equal to the 5-year average for the Queensland component of the Gulf of Carpentaria stock. This level of fishing pressure is unlikely to cause the stock to become recruitment overfished.
On the basis of the evidence provided above, the Gulf of Carpentaria biological stock is classified as a sustainable stock.
Grey Mackerel biology7,16
|Species||Longevity / Maximum Size||Maturity (50 per cent)|
|Grey Mackerel||14 years; 1200 mm FL||Females: 2 years; 650–700 mm FL Males: 1–2 years; 550–600 mm FL|
Distribution of reported commercial catch of Grey Mackerel
|Hand Line, Hand Reel or Powered Reels|
|Hand Line, Hand Reel or Powered Reels|
|Fishery spatial closures|
|Total allowable effort|
|No limits on customary catch|
|8 in ONLF|
- Offshore Net and Line Fishery (NT)
|Commercial||410.66t in ONLF|
|Recreational||409 fish (<2 t), Approximately 10 t(2009–2010)|
- Offshore Net and Line Fishery (NT)
a Indigenous The reporting period for the Commonwealth (Torres Strait) and Queensland (east coast [Queensland]) is the 2012–13 financial year.
b Queensland – Commercial (catch) With reference to the East Coast Inshore Fin Fish Fishery; in Queensland, under the Fisheries Act 1994 (Qld), Indigenous fishers are able to use prescribed traditional and non-commercial fishing apparatus in waters open to fishing. Size and in possession limits and seasonal closures do not apply to Indigenous fishers. Further exemptions to fishery regulations may be applied for through permits.
c Queensland – Commercial (catch) With reference to the East Coast Inshore Fin Fish Fishery; Queensland east coast stock only—limits applied to the combined catch of the two east coast stocks.
d Queensland – Commercial (catch) With reference to the East Coast Inshore Fin Fish Fishery; includes minor levels of catch from the Bowen region which is not considered part of the North-east Queensland and South-east Queensland biological stocks.
e Western Australian – Recreational (catch) Western Australian boat-based recreational catch from 1 May 2013–30 April 2014 9.
Commercial catch of Grey Mackerel - note confidential catch not shown
Effects of fishing on the marine environment
- Commercial gillnets have almost no impact on coastal habitat and are selective with high proportions of fish being caught marketed, with bycatch making up only a small proportion of the catch18. However, commercial gillnets do interact with threatened, endangered and protected (TEP) species. Although reported interactions are low, the impact on the populations of TEP species is unknown. Mitigation measures include spatial closures to protect ecological significant areas, fisher voluntary code of conduct (Northern Territory Offshore Net and Line Fishery [ONLF] and Queensland Gulf of Carpentaria), training of fishers in endangered species awareness (Queensland) and net attendance regulations (Northern Territory and Queensland). Bottom set gillnets are banned in the ONLF, to reduce turtle interactions.
- The targeted fishing method of trolled lines used exclusively in Western Australia and by fisheries in other jurisdictions has very little direct impacts on the marine environment and results in little bycatch or TEPs interactions13,19,20.
Environmental effects on Grey Mackerel
- The duration and magnitude of the wet season is likely to impact the overall biomass of coastal stocks like Grey Mackerel that are dependent on nearshore waters for breeding and feeding21,22. The fine-scale stock structure evident on the Queensland east coast may limit adaptability to changing environmental conditions, if stocks are unable to move in response to changing conditions21.
- 1 Broderick, D, Ovenden, J, Buckworth, R, Newman, S, Lester, R, and Welch, D 2011, Genetic population structure of grey mackerel Scomberomorus semifasciatus in northern Australia, Journal of Fish Biology, 79: 633–661.
- 2 Charters, R, Lester, R, Buckworth, R, Newman, S, Ovenden, J, Broderick, D, Kravchuk, O, Ballagh, A, and Welch, D 2010, The stock structure of grey mackerel Scomberomorus semifasciatus in Australia as inferred from its parasite fauna, Fisheries Research, 101: 94–99.
- 3 Newman, S, Wright, I, Rome, B, Mackie, M, Lewis, P, Buckworth, R, Ballagh, A, Garrett, R, Stapley, J, Broderick, D, Ovenden, J, and Welch, D 2010, Stock structure of grey mackerel, Scomberomorus semifasciatus (Pisces: Scombridae) across northern Australia, based on otolith isotope chemistry, Environmental Biology of Fishes, 89: 357–367.
- 4 Welch, D, Buckworth, R, Ovenden, J, Newman, S, Broderick, D, Lester, R, Ballagh, A, Stapley, J, Charters, R, and GribbleN 2009, Determination of management units for grey mackerel fisheries in northern Australia, Fisheries Research and Development Corporation project 2005/010, Fishing and Fisheries Research Centre Technical Report 4, Fishing and Fisheries Research Centre, James Cook University, Townsville, Australia.
- 5 Welch, D, Newman, S, Buckworth, R, Ovenden, J, Broderick, D, Lester, R, Gribble, N, Ballagh, A, Charters, R, Stapley, J, Street, R, Garrett, R, and Begg, G 2015, Integrating different approaches in the definition of biological stocks: A northern Australian multi-jurisdictional fisheries example using grey mackerel Scomberomorus semifasciatus, Marine Policy, 55:73-80.
- 6 Fletcher, W and Santoro, K (eds.) 2014, Status Reports of the Fisheries and Aquatic Resources of Western Australia 2013/14: The State of the Fisheries, Department of Fisheries, Perth.
- 7 Cameron, D and Begg, G 2002, Fisheries biology and interaction in the northern Australian small mackerel fishery, final report to Fisheries Research and Development Corporation, projects 92/144 and 92/144.02, Department of Primary Industries, Queensland.
- 8 Great Barrier Reef Management Authority 2012, A Vulnerability Assessment of the Great Barrier Reef - Grey mackerel, Great Barrier Reef Management Authority, Townsville.
- 9 Ryan, KL, Hall, NG, Lai, EK, Smallwood, CB, Taylor, SM, Wise BS, 2015, State-wide survey of boat-based recreational fishing in Western Australia 2013/14, Fisheries Research Report 268, Department of Fisheries, Western Australia.
- 10 Ryan, K, Wise, B, Hall, N, Pollock, K, Sulin, E, and Gaughan, D 2013, An integrated system to survey boat-based recreational fishing in Western Australia 2011/12, Department of Fisheries, Western Australia.
- 11 Grubert, M, Saunders, T, Martin, J, Lee, H, and Walters, C 2013, Stock Assessments of Selected Northern Territory Fishes, Fishery Report 110, Northern Territory Government, Australia.
- 12 Northern Territory Government 2012, Fishery Status Reports 2011, Fishery Report 111, Northern Territory Government.
- 13 Northern Territory Government 2014, Fishery Status Reports 2012, Fishery Report 113, Northern Territory Government Department of Resources, Darwin, Northern Territory.
- 14 Department of Agriculture, Fisheries and Forestry 2014, Queensland Stock Status Assessment Workshop 2014, 5–6 June 2014, Brisbane, Queensland Department of Agriculture, Fisheries and Forestry.
- 15 Lemos, RT, Wang, Y-G, O'Neill, MF, Leigh, G, and Helmke, S 2014, East Queensland Grey Mackerel Stock Assessment, Brisbane.
- 16 Department of Agriculture and Fisheries 2016. Grey Mackerel Update. www.daf.qld.gov.au/fisheries/monitoring-our-fisheries/commercial-fisheries/species-specific-programs/monitoring-reporting/grey-mackerel-update
- 17 West, L, Lyle, JM, Matthews, SR, Stark, K, and Steffe, AS 2012, Survey of Recreational Fishing in the Northern Territory, 2008-10, Fishery Report 109, Department of Primary Industry and Fisheries, Northern Territory, Darwin.
- 18 Halliday, IA, Ley, JA, Tobin, A, Garrett, R, Gribble, NA, and Mayer, DG 2001, The effects of net fishing: addressing biodiversity and bycatch issues in Queensland inshore waters, Fisheries Research and Development Corporation project 97/206, Department of Primary Industries, Queensland.
- 19 Department of the Environment, Water, Heritage and the Arts 2009, Assessment of the Western Australia Mackerel Fishery, DEWHA, Canberra.
- 20 Queensland Department of Primary Industries and Fisheries 2005, Report on the bycatch and byproduct risk assessment for the East Coast Spanish Mackerel Fishery, DPIF, Brisbane.
- 21 Robins, JB, Halliday, IA, Staunton-Smith, J, Mayer, DG, and Sellin, MJ 2005, Freshwater flow requirements of estuarine fisheries in tropical Australia: a review of the state of knowledge and application of a suggested approach, Marine and Freshwater Research, 56: 343–360.
- 22 Cameron, DS and Williams, LE 2002, Grey Mackerel in LE Williams (ed.), Queensland’s fisheries Resources - Current condition and recent trends 1988 - 2000, Department of Primary Industries Queensland, Brisbane, 139-143.
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