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Of the nine Barramundi stocks across WA, the NT and QLD targeted by commercial fishers, eight are sustainable. The South-East Coast stock at the species' cool-water range limits in southern QLD is undefined.

Barramundi (Lates calcarifer; also known as Asian sea bass) are a large, predatory fish within the family Centropomidae, that are found across most of the Indo-West Pacific region, from the Arabian Gulf to China, Taiwan, Papua New Guinea and northern Australia [FAO 2020]. They are protandrous hermaphrodites (maturing as males first, then changing sex to female; Moore [1979]) that exhibit individual variation in habitat utilisation/migratory patterns during their life history [Crook et al. 2016], with the exception of spawning events, which always occur in highly saline estuarine or marine waters. 

The different life history contingents described by Crook et al. [2016] include: 1) an “estuarine” contingent, that remains in marine and estuarine habitats; 2) a “catadromous, sequential hermaphrodite” contingent, that enters freshwater reaches for a period of time, then migrates downstream and changes sex in marine waters; and 3) a “catadromous, delayed female spawning” contingent, that enters freshwater reaches and changes sex in this environment before migrating downstream. 

Genetic stock structure of Barramundi is complex. Keenan [1994] described 16 subpopulations of this species (through allozyme analyses) across most of its Australian range, with each subpopulation encompassing an individual catchment, or several adjacent catchments. More recently, Jerry et al. [2013] and Loughnan et al. [2019] described 21 distinct subpopulations (through microsatellite analyses) from samples collected over a wider geographic range than that of Keenan [1994]; noting that both recent works were based on the same set of tissue samples, many of which were initially collated by Keenan [1994].  

Difficulties in obtaining relevant biological and catch-and-effort information from each biological stock in Western Australia and the Northern Territory precludes individual assessments of these stocks. Therefore, the assessments for these jurisdictions were undertaken at the level of the management unit (Kimberley Gillnet and Barramundi Managed Fishery, Western Australia; and Barramundi Fishery, Northern Territory). 

The state of Queensland initiated a long-term monitoring program for Barramundi in 2000, with sampling regions following the boundaries of the six Queensland stocks described by Keenan [1994] [Fisheries Queensland 2010]. The assessment for Queensland Barramundi stocks presented here follows the same boundaries as Keenan [1994] and the abovementioned fisheries monitoring program, but also considers ‘vagrant’ fish, that venture south of 26⁰ South (and which were not sampled by Keenan [1994]), as a seventh biological stock. The seven biological stocks within Queensland are: Southern Gulf of Carpentaria, Northern Gulf of Carpentaria, Princess Charlotte Bay, North-East Coast, Mackay, Central East Coast and South-East Coast. 

It is acknowledged that the recent works of Jerry et al. [2013] and Loughnan et al. [2019] identified eight genetic stocks of Barramundi in Queensland, but there are practical limits on how many assessments can be conducted on this species. Additionally, tag-recapture information for Barramundi in Queensland indicates that the boundaries of the subpopulations identified by Jerry et al. [2013] and Loughnan et al. [2019] are somewhat porous, as individual Barramundi do move between subpopulations (Infofish Australia [2014, 2020]). This includes large female fish, that often move after flood events. The seven stock regions reported upon for Queensland capture most of the dynamics of the genetic subpopulations, which in Barramundi are thought to be highly responsive to regional climatic events [Staunton-Smith et al. 2004, Robins et al. 2005, Halliday et al. 2010, Halliday et al. 2012].

Extensive stocking of Barramundi fingerlings in catchments on the east coast of Queensland is unlikely to compromise the above stock structure as parents from the same genetic stock are used to produce fingerlings. The assessments of the individual management units encompassing Western Australia and the Northern Territory are based on the biological stocks that receive the highest harvest rates, and whose status is assumed to be representative of the highest level of exploitation that occurs on any biological stock within each unit. 

Here, assessment of stock status is presented at the management unit level—Kimberley Gillnet and Barramundi Managed Fishery (Western Australia), Barramundi Fishery (Northern Territory); and the biological stock level—Southern Gulf of Carpentaria, Northern Gulf of Carpentaria, Princess Charlotte Bay, North-East Coast, Mackay, Central East Coast and South-East Coast (Queensland).

Northern Territory

The most recent assessment of the Barramundi Fishery (Northern Territory) management unit (using data to the conclusion of 2019) indicated that this stock was impacted by high fishing pressure in the late 1970s and early 1980s, falling to 36 per cent of the unfished (1950) biomass [Grubert et al., unpublished]. However, there has been a strong recovery since that time, with the annual biomass as a proportion of virgin biomass exceeding 60 per cent for the last two decades, reaching 88 per cent by the end of 2019.

Monitored stocks have a broad length and age distribution, with little sign of a reduction in the proportion of older age classes, despite abundance surveys showing low levels of recruitment during recent, drier than average wet seasons [NTG 2018]. The above evidence indicates that the biomass of the stock is unlikely to be depleted and that recruitment is unlikely to be impaired.

The current (2019) fishing mortality rate, as a proportion of fishing mortality at maximum sustainable yield (MSY), was estimated at 19 per cent, roughly one fifth of the rate required to achieve MSY [Grubert et al., unpublished]. Recaptures from tagging programs also suggest that the annual harvest rate for all sectors combined is consistently below five per cent. The above evidence indicates that the current level of fishing pressure is unlikely to cause the stock to become recruitment impaired.

On the basis of the evidence provided above, the Barramundi Fishery (Northern Territory) management unit is classified as a sustainable stock.

Barramundi biology [Davis 1982]

Distribution of reported commercial catch of Barramundi

Western Australia – Recreational (catch) Boat-based recreational catch between 1 September 2015 and 31 August 2016 from Ryan et al. [2019]. Please note that catches of Barramundi are underestimates as shore-based and boat-based fishers that only operated in freshwater were out of scope of the survey.

Western Australia – Recreational (management methods) A Recreational Fishing from Boat Licence is required for the use of a powered boat to fish or to transport catch or fishing gear to or from a land-based fishing location.

Western Australia – Indigenous (management methods) Subject to application of Section 211 of the Native Title Act 1993 (Cth), and the exemption from a requirement to hold a recreational fishing licence, the non-commercial take by Indigenous fishers is covered by the same arrangements as that for recreational fishing.

Northern Territory – Indigenous (management methods) The Fisheries Act 1988 (NT), specifies that “…without derogating from any other law in force in the Territory, nothing in a provision of this Act or an instrument of a judicial or administrative character made under it limits the right of Aboriginals who have traditionally used the resources of an area of land or water in a traditional manner from continuing to use those resources in that area in that manner”.

Northern Territory – Charter (management methods) In the Northern Territory, charter operators are regulated through the same management methods as the recreational sector, but are subject to additional limits on licence and passenger numbers.

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

Commercial catch of Barramundi - note confidential catch not shown.

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