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Sea Mullet (2023)

Mugil cephalus

  • John Stewart (New South Wales Department of Primary Industries)
  • Andrew Prosser (Department of Agriculture and Fisheries, Queensland)
  • Rodney Duffy (Department of Primary Industries and Regional Development, Western Australia)

Date Published: June 2023

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Summary

Sea Mullet is a sustainable species occurring in all coastal regions of WA, and on the east coast of Australia.

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Stock Status Overview

Stock status determination
Jurisdiction Stock Stock status Indicators
New South Wales, Queensland Eastern Australia Sustainable

Spawning stock biomass, Catch, Effort, CPUE, Length and age compositions, Stock Assessment

Western Australia Western Australia Sustainable

Catch, CPUE, length and age compositions, fishing mortality, spawning stock biomass

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Stock Structure

Sea Mullet (Mugil cephalus) was formerly regarded as a single species with a global distribution; however recent genetic evidence indicates that they are in fact a complex of many cryptic species. Sea Mullet along the west and east coasts of Australia are regarded as distinct species [Durand et al. 2012; Krück et al. 2013]. The population structure within Western Australia is yet to be fully examined but given the extensive coastline and wide latitudinal range, it is possible that this jurisdiction hosts more than one biological stock (or species). Given this uncertainty, Sea Mullet within each Bioregion are currently managed as separate units. Limited tagging and genetic studies [Thomson 1951; Watts and Johnson 1994] suggest mixing of fish throughout the West Coast Bioregion (WCB), where most of the catch is taken. Extensive tagging studies [Kesteven 1953] suggest a single east coast biological stock of Sea Mullet, extending from central Queensland to eastern Victoria. 

Here, assessment of stock status is presented at the jurisdictional stock level for Western Australia and the biological stock level for Eastern Australia.

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Stock Status

Eastern Australia

This cross-jurisdictional biological stock is fished in Queensland and New South Wales. Each jurisdiction monitors the part of the biological stock that occurs in its waters. The status presented here for the entire biological stock has been established using evidence from both jurisdictions.

The most recent stock assessment estimated that at the end of 2020 the Eastern Australia biological stock of Sea Mullet was at approximately 37% of unfished levels [Lovett et al. 2022], and above the limit reference point of 20%. The stock assessment used a two-sex, age-structured population model, fit to age and length data, and constructed within the Stock Synthesis modelling framework. Eight scenarios were run, covering a range of modelling assumptions. None of the model scenarios indicated that the biomass of Sea Mullet had declined to below the limit reference point of 20% of unfished levels at any time during the history of the assessment (1899 to 2020). The stock is not considered to be recruitment impaired. 

The total landed catch (New South Wales and Queensland combined) in 2020 was approximately 4102 t and below the estimated Maximum Sustainable Yield (MSY) of 5353 t [Lovett et al. 2022]. The relative biomass at 37% of unfished levels was above the estimated biomass at MSY, being 33% of unfished levels. This level of fishing mortality is unlikely to cause the stock to become recruitment impaired.

Since the final year modelled in the stock assessment (2020), nominal catch rates in the New South Wales estuary fishery have increased, whereas in the Queensland Ocean Beach Fishery they declined substantially, likely due to adverse weather conditions during the fishing season [Stewart 2023]. Harvest and fishing effort in New South Wales have been at historical lows. Recent age composition data for New South Wales show a strong year class moving through the fishery, first identified as 2-year old fish in 2018 through to 6 year old fish in 2022. The age compositions in the most recent years (2021 and 2022) show a good spread of ages in the fishery [Stewart 2023]. In Queensland recent harvest (918 t in 2021–22) was less than half the long-term average of 1,980 t (1988–22). This reduction may be due to a range of factors including management changes, licence buy backs, marine park expansion into historic fishing areas, introduction of TACC and subsequent reporting requirements in 2021, and an ageing demographic of fishers. Length and age frequency information from routine monitoring show stability in the sizes of fish being harvested and evidence of recent strong year classes. Nominal effort in the Queensland component of the fishery has reduced markedly from 7,563 days in 2015–16 to 2,503 in 2021–22, and the number of fishers reporting ‘Mullet - (unspecified)’ catch has reduced from 250 fishers to 164 fishers during the same period. These trends indicate that the stock and fisheries in both jurisdictions have not changed substantially since the final year in the last stock assessment, being 2020 [Lovett et al. 2022]. 

On the basis of the evidence provided above, the entire Eastern Australian biological stock is classified as a sustainable stock.itoring show stability in the sizes of fish being harvested and evidence of recent strong year classes. Nominal effort in the Queensland component of the fishery has reduced markedly from 7,563 days in 2015–16 to 2,503 in 2021–22, and the number of fishers reporting ‘Mullet - (unspecified)’ catch has reduced from 250 fishers to 164 fishers during the same period. These trends indicate that the stock and fisheries in both jurisdictions have not changed substantially since the final year in the last stock assessment, being 2020 [Lovett et al. 2022]. 

On the basis of the evidence provided above, the entire Eastern Australian biological stock is classified as a sustainable stock

Western Australia

Sea Mullet (Mugil cephalus) is primarily targeted by the commercial net fishing sector, with catches by the recreational sector and customary fishers likely to be low relative to commercial catches. The commercial catch of sea mullet in the South, West and Gascoyne Coast bioregions shows a gradual increase from 1941 to around 1980, peaking at just under 700 t. However, changes in management and market demand led to a reduction in effort and commercial targeting of sea mullet, and catches have since declined to their current annual level of around 200 t. Over the past five years, 62% of the catch was taken by haul netting, 19% by beach seining and 19% by gillnetting.

A stock assessment for Sea Mullet was completed in 2022 [Duffy et al 2022] using the Western Australian Department of Primary Industries and Regional Development’s risk-based Weight of Evidence approach. This assessment considered catch (including catch-MSY (maximum sustainable yield) analyses), effort, catch distribution, standardised catch per unit effort (CPUE), vulnerability and susceptibility to fishing (PSA) analysis, age and length composition data, catch curve estimates of (long-term average) fishing mortality, and a non-state space biomass dynamic model applied to nominal CPUE data. Based on a combination of relatively low recent annual catches, light-moderate truncation of age structures for fish from the Gascoyne region (assumed to be representative of the spawning stock) and estimates of current biomass and fishing mortality that were BMSY and below FMSY, respectively, the assessment concluded that the stock is sustainable. 

More recently, additional analyses for Sea Mullet in Western Australia involving the use of two more sophisticated (state space) biomass dynamics models, including ‘Just Another Bayesian Biomass Assessment (JABBA) [Winker et al. 2018] and ‘Surplus Production model in Continuous-Time’ (SPiCT) [Pederseen and Berg, 2018], applied to standardised CPUE (adjusted for assumed changes in fishing efficiency), yielded similar but slightly less optimistic results than produced in the previous assessment (DPIRD, unpublished data). Outputs from the recent analysis using the JABBA assessment model, for example, suggest that the current level of catch of approximately 200 t is well below the estimated Maximum Sustainable Yield (MSY) for the stock of 749 t (95% CLs: 515–1,808t). The JABBA point estimate for current biomass is at MSY (i.e. B/BMSY=1.0, 95% CLs: 0.67–1.45), and the estimate for current fishing mortality is well below FMSY (i.e. F/FMSY= 0.22, 95% CLs: 0.08–0.42).  Thus, these results from the recent biomass dynamics modelling indicate that the stock is sustainable, and that overfishing is highly unlikely to be occurring.

The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired. Furthermore, the current level of fishing mortality is unlikely to cause the stock to become recruitment impaired. 

On the basis of the evidence provided above, the Western Australia jurisdictional stock of Sea Mullet is classified as a sustainable stock.

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Biology

Sea Mullet biology [Virgona et al. 1998; Smith and Deguara 2002; Gaughan et al. 2006; Fisheries Queensland 2018]

Biology
Species Longevity / Maximum Size Maturity (50 per cent)
Sea Mullet

Western Australia 12 years, 790 mm FL; Eastern Australia 16 years, 640 mm FL

Western Australia Males and Females 370 mm TL;  Eastern Australia Males 300 mm TL, Females 330 mm TL

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Distributions

Distribution of reported commercial catch of Sea Mullet

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Tables

Fishing methods
Western Australia Queensland New South Wales
Commercial
Gillnet
Beach Seine
Haul Seine
Line
Net
Mesh Net
Various
Recreational
Hook and Line
Cast Net
Coastal, Estuary and River Set Nets
Beach Seine
Traps and Pots
Indigenous
Net
Unspecified
Various
Hook and Line
Traps and Pots
Charter
Hook and Line
Management methods
Method Western Australia Queensland New South Wales
Charter
Bag/possession limits
Gear restrictions
Seasonal or spatial closures
Size limits
Commercial
Gear restrictions
Harvest Strategy
Limited entry
Marine park closures
Seasonal or spatial closures
Size limits
Spatial closures
Temporal closures
Total allowable catch
Vessel restrictions
Indigenous
Bag limits
Customary fishing management arrangements
Gear restrictions
Recreational
Bag/possession limits
Gear restrictions
Licence
Marine park closures
Seasonal or spatial closures
Size limits
Spatial closures
Catch
Western Australia Queensland New South Wales
Commercial 179.36t 902.93t 1.77Kt
Charter Negligible
Indigenous Unknown Unknown Unknown
Recreational Insufficient data Negligible Unknown

Queensland – Indigenous (Management Methods). For more information see: https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing

Queensland – Commercial (Catch). Queensland commercial and charter data have been sourced from the commercial fisheries logbook program. Further information are available through the Queensland Fisheries Summary Report: https://www.daf.qld.gov.au/business-priorities/fisheries/monitoring-research/data/queensland-fisheries-summary-report 

Queensland – Commercial (Management Methods). Harvest strategies are available at: https://www.daf.qld.gov.au/business-priorities/fisheries/sustainable/harvest-strategy

New South Wales – Indigenous (Management Methods). https://www.dpi.nsw.gov.au/fishing/aboriginal-fishing

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Catch Chart

Commercial catch of Sea Mullet - note confidential catch not shown

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References

  1. Duffy, R, Harris, D, Fisher, E, Smith, K, Johnston, D, Denham, A, Hesp, A, Hodgson, B, Quinn, A and Newman, M 2022, South-West Estuarine and Nearshore Finfish Resource Part 1: Sea Mullet and Yellowfin Whiting Mullet and Yellowfin Whiting, Fisheries Research Report No. 322.
  2. Durand, JD, Chen, WJ, Shen, KN, Jamandre, BW, Blel, H and Diop, K 2012, Systematics of the grey mullets (Teleostei: Mugiliformes: Mugilidae): molecular phylogenetic evidence challenges two centuries of morphology-based taxonomy, Molecular Phylogenetics and Evolution, 64 73–92.
  3. Fisheries Queensland 2018, Fisheries Queensland monitoring data 1999–2018, Monitoring our fisheries, Queensland Department of Agriculture and Fisheries.
  4. Fowler, AM, Smith, SM, Booth, DJ and Stewart, J 2016, Partial migration of grey mullet (Mugil cephalus) on Australia’s east coast revealed by otolith chemistry, Marine Environmental Research, 119: 238–244.
  5. Froese, R, Demirel, N, Coro, G, Kleisner, KM and Winker, H 2017, Estimating fisheries reference points from catch and resilience, Fish and Fisheries, 18: 506-526.
  6. Kesteven, GL 1953, Further results of tagging sea mullet, Mugil cephalus Linnaeus, on the eastern Australian coast, Australian Journal of Marine and Freshwater Research, 4: 251–306.
  7. Krück, NC, Innes, DI and Ovenden, JR 2013, New SNPs for population genetic analysis reveal possible cryptic speciation of eastern Australian sea mullet (Mugil cephalus), Molecular Ecology Resources, 13: 715–725. doi:10.1111/1755-0998.12112.
  8. Lovett, R, Prosser, A and Stewart, J 2022, Stock assessment of Australian east coast sea mullet (Mugil cephalus) with data to December 2020, Technical Report. State of Queensland, Brisbane, 48pp.
  9. Pedersen, MW and Berg, CW 2017, A stochastic surplus production model in continuous time. Fish and Fisheries, 18(2), 226–243.
  10. Smith, KA and Deguara, KL 2002, Review of biological information and stock assessment for the NSW sea mullet resource, NSW Fisheries Resource Assessment Series No. 12, New South Wales Fisheries, Cronulla.
  11. Stewart, J 2023, NSW Stock Status Summary 2021/22 – Sea Mullet (Mugil cephalus). NSW Department of Primary Industries, Fisheries. 13 pp
  12. Stewart, J, Hegarty, A, Young, C and Fowler, AM 2018, Sex-specific differences in growth, mortality and migration support population resilience in the heavily exploited migratory marine teleost Mugil cephalus (Linnaeus 1758), Marine and Freshwater Research 69: 385–394.
  13. Thomson, JM 1951, Growth and habits of the sea mullet, Mugil dobula Gunther, in Western Australia, Australian Journal of Marine and Freshwater Research, 2: 193–225.
  14. Virgona, JL, Deguara, KL, Sullings, DJ, Halliday, I and Kelly, K 1998, Assessment of the stocks of sea mullet in New South Wales and Queensland Waters, Final Report Series No. 2, New South Wales Fisheries, Cronulla.
  15. Watts, RJ and Johnson, MS 2004, Estuaries, lagoons and enclosed embayments: habitats that enhance subdivision of inshore fishes, Marine and Freshwater Research, 55: 641–651.
  16. Winker, H, Carvalho, F, and Kapur, M 2018, JABBA: Just Another Bayesian Biomass Assessment. Fisheries Research, 204, 275–288.

Downloadable reports

Click the links below to view reports from other years for this fish.