Source: Patterson, H, Larcombe, J, Woodhams, J and Curtotti, R 2020, Fishery status reports 2020,S Australian Bureau of Agricultural and Resource Economics and Sciences, Canberra. CC BY 4.0.
The principal legal framework for the management of the fishery is specified in the Northern Prawn Fishery Management Plan 1995. The Northern Prawn Fishery is a multi-species fishery managed through input controls including limited entry, season length and individual transferable effort units – based on fishing gear size. The fishery relies on: a size and sex-based stock assessment model for brown and grooved tiger prawns; a biomass dynamic assessment model for blue endeavour prawns; and a quarterly age based biological stock assessment model for redleg banana prawns. There is currently no formal stock assessment for the white banana prawn fishery as the species is short lived and its abundance is driven by environmental factors, principally rainfall. The operational objective of the white banana prawn Harvest Strategy is to allow sufficient escapement to ensure an adequate spawning biomass of banana prawns (based on historical data), and to achieve the maximum economic yield from the fishery.
The Northern Prawn Fishery Management Plan 1995 was reviewed during the period and will be subject to some changes during 2019–20, primarily to reflect the revised Commonwealth Harvest Strategy Policy and Bycatch Policy. Overall the Plan remains effective for the management of the fishery.
Analysis of Performance
Performance – status of fish stocks
Tropical prawn species are very short-lived animals and their stock size is prone to wide inter-annual fluctuation with strong dependence on prevailing environmental conditions. For this reason, the assessment of prawn stock health is based on a five-year moving average of spawning stock abundance relative to a spawning stock abundance that produces maximum sustainable yield, which should not fall below the limit reference point of 50 per cent.
The last stock assessment for brown and grooved tiger prawns was completed in 2020 and determined that the stocks are not overfished and overfishing is not occurring. The assessment indicated that the five-year year moving average of spawning stock biomass was well above 100 per cent of spawning stock biomass at maximum sustainable yield, meaning that neither stock is overfished.
The management objective of maximising economic yield is also assessed against an annual target reference point, which is a spawning stock size equal to that which is estimated to produce maximum economic yield. Both brown and grooved tiger prawn spawning stocks were assessed as being close to or above the target in the 2020 assessment at 125 per cent and 99 per cent, respectively.
An additional in-season catch-rate trigger for pursuing maximum economic yield is also used in the fishery. The catch rate did not drop below the trigger in the 2019 tiger prawn season and the fishery remained open until the final day of the season on 30 November 2019. All 52 boat SFRs were utilised during the 2019 tiger prawn season.
As with the tiger prawn fishery, all 52 boat SFRs were utilised during the 2020 banana prawn season (1 April to 15 June 2019). Total catch in the 2020 banana prawn fishery was substantially lower than in 2019, decreasing from 5,640 tonnes to an estimated catch of 2,924 tonnes. This level of catch is below average and lower catches were likely impacted by lower rainfall. Changes in environmental conditions, such as rainfall, normally causes fluctuations in year-to-year stock size (and therefore catch) in this short-lived, tropical prawn species. The in-season catch-rate trigger for banana prawn season was breached this year prompting the early closure of the fishery on 10 June 2020. This trigger is designed to pursue Maximum Economic Yield within a season by triggering an early closure when catch rates drop below the annually agreed level.
The harvest strategy for redleg banana prawns is being reviewed to explore options that allow catch and effort levels to be progressively adjusted to levels that achieve maximum economic yield. A management strategy evaluation was completed in 2020 that provided several suitable control rules that would enhance management of redleg banana prawn. A decision on the preferred approach will be considered in late 2020 with changes to take effect in 2021.
During 2019, fishing catch and effort in the redleg banana prawn fishery was lower than in 2018 and similar to the relatively low effort of 79 and 76 boat days for 2015 and 2016 respectively. The total catch in 2019 was 47 tonnes across 75 boat days compared to 238 tonnes across 213 boat days in 2018. The fishing effort pattern in 2019 was unprecedented with almost all of the fishing effort in the second quarter, whereas in previous years the fishing effort was distributed in the second and third quarters (April-September). Although economic reasons may explain the change in fishing patterns, the first season catch per unit effort (CPUE-an index of relative stock abundance) indicates that the stock abundance in 2019 was below average.
The total annual spawning biomass trajectory predicted the prawn population to have declined after 2014 before reversing in 2018 with the CPUE trending back towards the target level. The latest CPUE data suggests that spawning biomass is again predicted to have decreased slightly. The 2019 stock size is estimated to be below the target level but above the limit reference point, although there is uncertainty with this prediction.
The total annual spawning biomass trajectory predicted the prawn population to have declined after 2014 before reversing in 2018 with the CPUE trending back towards the target level. The 2019 stock size is estimated to be below the target level but above the limit reference point. The low level of catch and effort in 2019 is unlikely to take the stock to below its limit reference point. Variability in biomass is to be expected for short-lived species such as prawns, but as the biomass levels are estimated to have been below the target level for a number of recent years, additional management measures are being implemented to reduce the risk of further declines. The harvest strategy is being reviewed to explore options that allow catch and effort levels to be progressively adjusted to levels that achieve maximum economic yield.
Performance – status of bycatch
Following the great progress reducing small fish bycatch through the Northern Prawn Fishery Bycatch Strategy 2015–18, new bycatch reduction devices (BRDs) are being implemented from the 2020 tiger prawn season. The new BRDs have been demonstrated through scientific trials to achieve up to 44 per cent reduction in bycatch compared to the standard device (the square mesh panel) previously used in the fishery. The newest device known as ‘Tom’s Fisheye’ creates an area of low pressure in the trawl net as it is pulled through the water, increasing access to a gap in the net for fish to escape. There will be a choice for Northern Prawn Fishery trawl boat operators to use one of four more effective devices from 2020. The Northern Prawn Fishery fishers, led by the NPFI, continue to demonstrate commitment to reducing bycatch through design and trial of new equipment and technology. It is important that fishers can use an effective device that will suit different operating conditions.
An updated Bycatch Strategy is under development for the Northern Prawn Fishery and will be published during 2020. The new strategy will continue to build on previous achievements with bycatch reduction and respond to updated guidance from the Commonwealth Fisheries Bycatch Policy 2018. The strategy will have a focus on improving information on interactions with sawfish species, including identifying how sawfish interact with the fishing gear, particularly around the Turtle Excluder Devices that are used in all fishing nets.
Performance – economic returns
During the most recent financial year (2018–19) the Northern Prawn Fishery GVP was $117.6 million and the Northern Prawn Fishery was the highest valued Commonwealth managed fishery.
The fishery is broadly (across the two key species groups – banana and tiger prawns) managed to pursue maximum economic yield. Overall fishing effort limits (fishing gear and season lengths) are set on the result of outputs from the bio-economic model for tiger and endeavour prawns. Additionally, season length is further controlled through catch-rate triggers in the banana and tiger prawn sub-fisheries to account for annual variability in these stocks. Recent assessments of economic performance by ABARES indicates that the level of fishing effort in the fishery is close to maximum economic yield targets.
Net economic returns in the Northern Prawn Fishery reached a peak of $32.1 million in 2015–16. Economic performance remained stable at $30.9 million in 2016-17 but was forecast to dampen in 2017–18 on the back of lower gross value of production and higher unit fuel prices. Based on previous net economic returns and relatively stable economic conditions, it is anticipated that the economic performance of the Northern Prawn Fishery will have remained positive in 2017-18 and 2018-19. While further economic assessment has been undertaken, results are not available for this report.
The management of the fishery is certified as sustainable by the Marine Stewardship Council. A surveillance audit was conducted in February 2020 and confirmed the fishery continues to meet the Marine Stewardship Council Fisheries Standard.
Throughout 2019-20, there has been continued investment into prawn aquaculture, with increased interest in the Northern Prawn Fishery as a source of black tiger prawn (P. monodon) as aquaculture broodstock. Aquaculture businesses can access black tiger prawn broodstock through three fishing permits issued to trawlers to specifically target black tiger prawns outside of the main fishing seasons of the fishery, or through a commercial arrangement to purchase or lease Northern Prawn Fishery SFRs. During 2019-20 we have seen increased use of commercial arrangements to use Northern Prawn Fishery SFRs to target black tiger prawns for broodstock, and between these arrangements and the three dedicated permits, the fishery met demand throughout the year.
The increased demand (and indications of greater needs in the future) present several management challenges for AFMA and the fishery. The minor role that black tiger prawns have played in the fishery in the past has led to there being a generally poorer understanding of the stock status than for other targeted prawn species and the key drivers of that status. A stock assessment commenced in late 2019 with results expected later in 2020. This is a foundational assessment and while there are some data challenges, we expect the results will inform updated arrangements to apply in 2021.
Detailed stakeholder consultation, innovation and commercial relationships will also be essential in order to find the right balance between the needs of the aquaculture industry and the existing management arrangements with SFRs in the Northern Prawn Fishery.