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

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 the majority 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.

Western Australia

The current assessment of Sea Mullet in south-west WA is primarily based on estimates of biomass. This performance indicator is periodically (at least every five years) compared to reference levels based on estimates of Maximum Sustainable Yield (MSY). The estimated biomass expected to achieve MSY (B_MSY) is considered as the threshold reference level for the stock, and 50 per cent B_MSY is set as the limit reference level. 

A Catch-MSY model (CMSY; Froese et al. 2017) was fitted using catch data for Sea Mullet in south-west WA to estimate the MSY for the stock. Whilst outputs from the CMSY model were uncertain, the results suggest that annual catches have largely remained below the estimated MSY of 642 t over the history of the fishery. The model indicate that stock biomass gradually decreased from 1941 to the early 1980s as a result of increasing catches and exploitation up to, and briefly exceeding, the level expected to achieve MSY. A subsequent reduction in catches has resulted in the biomass rebuilding to 86 per cent of the unfished level in 2018. As the estimated value of this performance indicator is above the threshold, the stock is considered not to be depleted to a level at which recruitment could be impaired. 

The fishing mortality of the stock in 2018 was estimated to be at 19 percent of the estimated fishing mortality at MSY (F_MSY) of 0.31 year-1, with an estimated probability of 100 percent that it is below this threshold reference level. 

The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired. The above evidence also indicates that 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 is classified as a sustainable stock.

Sea Mullet biology [Virgona et al. 1998, Smith and Deguara 2002, Gaughan et al. 2006, Fisheries Queensland 2016]

Distribution of reported commercial catch of Sea Mullet

Queensland – Indigenous (management methods) for more information see https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing

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

1. Durand, JD, Chen, WJ, Shen, KN, Jamandre, BW, Blel, H, Diop K, et al. 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.
2. Fisheries Queensland 2018, Fisheries Queensland monitoring data 1999–2018, Monitoring our fisheries, Queensland Department of Agriculture and Fisheries.
3. 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.
4. Froese, R., Demirel, N., Coro, G., Kleisner, K.M., Winker, H. (2017). Estimating fisheries reference points from catch and resilience. Fish and Fisheries, 18: 506-526.
5. Gaughan, D, Ayvazian, S, Nowara, G and Craine, M 2006, The development of a rigorous sampling methodology for a long-term annual index of recruitment for finfish species from south-western Australia, Final report, Fisheries Research and Development Corporation project 1999/153, Fisheries Research Report 154, Western Australian Department of Fisheries, Perth.
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, RA, Prosser, AJ, Leigh, GM, O'Neill, MF and Stewart, J. 2018. Stock assessment of the Australian east coast sea mullet (Mugil cephalus) fishery 2018. Technical Report. Department of Agriculture and Fisheries. Brisbane, Queensland
9. QFish, Department of Agriculture and Fisheries, www.qfish.gov.au
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 2020. Status of Australian Fish Stocks 2020 – NSW Stock status summary – Sea Mullet (Mugil cephalus).
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.