Northern Prawn Fishery
Chapter 5: Northern Prawn Fishery
M Parsa, J Larcombe and R Curtotti
|Red-legged banana prawn|
|Uncertain||Not overfished||Uncertain||Not overfished||Low recruitment and declining catch rate; management is unable to constrain fishing effort. Spawning biomass is above the LRP of 0.5BMSY.|
|White banana prawn (Fenneropenaeus merguiensis)||Not subject to overfishing||Not overfished||Not subject to overfishing||Not overfished||High natural recruitment variability is primarily linked to environmental factors.Harvest strategy aims to provide for adequate escapement and for fishing effort to approximate EMSY.|
|Brown tiger prawn (Penaeus esculentus)||Not subject to overfishing||Not overfished||Not subject to overfishing||Not overfished||Effort is below EMSY, and catch is below MSY. Spawner stock size is above the LRP of 0.5SMSY.|
|Grooved tiger prawn (Penaeus semisulcatus)||Not subject to overfishing||Not overfished||Not subject to overfishing||Not overfished||Effort is near EMSY, and catch is below MSY. Spawner stock size is above the LRP of 0.5SMSY.|
|Blue endeavour prawn
|Not subject to overfishing||Not overfished||Not subject to overfishing||Not overfished||Catch is below the estimate of MSY. Spawner stock biomass is above the LRP of 0.5SMSY.|
|Red endeavour prawn (Metapenaeus ensis)||Uncertain||Uncertain||Uncertain||Uncertain||No current stock assessment.|
NER reached a high of $30.9 million in 2015–16, supported by a strong increase in tiger prawn catch, marking a fourth consecutive annual increase in NER. The performance in 2016–17 remained stable at $30.3 million. In 2017–18, lower gross value of production and higher unit fuel prices are expected to have a dampening effect on NER.
Notes: BMSY Biomass at MSY. EMSY Effort that achieves maximum economic yield. EMSY Effort that achieves MSY.
LRP Limit reference point. MSY Maximum sustainable yield. NER Net economic returns. SMSY Spawner stock size at MSY.
5.1 Description of the fishery
The Northern Prawn Fishery (NPF) extends from Joseph Bonaparte Gulf across the top end to the Gulf of Carpentaria (Figure 5.1). White banana prawn (Penaeus merguiensis) is mainly caught during the day on the eastern side of the Gulf of Carpentaria, whereas redleg banana prawn (Fenneropenaeus indicus) is caught during both day and night, mainly in Joseph Bonaparte Gulf. White banana prawns form dense aggregations (‘boils’) that can be located using spotter planes, which direct the trawlers to the aggregations. The highest catches are taken offshore from mangrove forests, which are the juvenile nursery areas. Tiger prawns (P. esculentus and P. semisulcatus) are primarily taken at night (daytime trawling has been prohibited in some areas during the tiger prawn season). Most catches come from the southern and western Gulf of Carpentaria, and along the Arnhem Land coast. Tiger prawn fishing grounds may be close to those of banana prawns, but the highest catches come from areas near coastal seagrass beds, the nursery habitat for tiger prawns. Endeavour prawns (Metapenaeus endeavouri and M. ensis) are mainly a byproduct, caught when fishing for tiger prawns.
Fishing methods and key species
The NPF uses otter trawl gear to target a range of tropical prawn species. White banana prawn and two species of tiger prawn (brown and grooved) account for around 80% of the landed catch. Byproduct species include endeavour prawns, scampi (Metanephrops spp.), bugs (Thenus spp.) and saucer scallops (Amusium spp.). In recent years, many vessels have transitioned from using twin gear to using a quad rig comprising four trawl nets—a configuration that is more efficient.
The NPF is managed through a series of input controls, including limited entry to the fishery, individual transferable effort units, gear restrictions, bycatch restrictions, and a system of seasonal and spatial closures. The fishery has two seasons: a predominantly banana prawn season that runs from 1 April to 15 June, and a longer tiger prawn season, running from the start of August to the end of November. Catch rates are monitored throughout the fishing seasons, and the season length can be shortened in accordance with harvest strategy decision rules (Dichmont et al. 2012).
The merits of input (effort) and output (total allowable catch) controls have been extensively evaluated in the NPF. In late 2013, mainly because of the difficulty in setting catch quotas for the highly variable white banana prawn fishery, the Australian Fisheries Management Authority (AFMA) determined that the fishery would continue to be managed through input restrictions and units of individual transferable effort. The NPF harvest strategy is being reviewed in 2019–2020, including management strategy evaluation for the redleg banana prawn subfishery.
The NPF developed rapidly in the 1970s, with effort peaking in 1981 at more than 40,000 fishing days and more than 250 vessels. During the next three decades, fishing effort and participation were reduced to the current levels of around 8,000 days of effort and 52 vessels. This restructuring of the fishery was achieved through a series of structural adjustment and buyback programs, and the implementation of management measures to unitise and control fishing effort. Total catches also fell during this period, but by a much smaller percentage, illustrating the clear transformation of the fleet to more efficient vessels.
Total NPF catch in 2018 was 6,778 t, comprising 6,675 t of prawns and 103 t of byproduct species (predominantly squid, bugs and scampi). Annual catches tend to be quite variable from year to year because of natural variability in the banana prawn component of the fishery.
Fishery statistics a
2017 fishing season
2018 fishing season b
Other catch (prawns)
Other catch (not prawns)
Banana season: 2,304 shots
Banana season: 2,506 shots
Crew member observers: 1,169 days (15.8%)
Crew member observers: 1,255 days (15.7%)
Primary landing ports
Darwin (Northern Territory); Cairns and Karumba (Queensland). Much of the catch is offloaded onto motherships at sea.
Input controls: individual tradeable gear units, limited entry, gear restrictions
Domestic: fresh and frozen
Northern Prawn Fishery Management Plan 1995 (amended 2012)
a Fishery statistics are provided by fishing season, unless otherwise indicated. Value statistics are by financial year. Therefore, changes in catch may appear to be inconsistent with changes in value.
b Fishing season predominantly for banana prawns: 1 April – 15 June; predominantly for tiger prawns: 1 August – 30 November.
Notes: GVP Gross value of production.
5.2 Biological status
Redleg banana prawn (Fenneropenaeus indicus)
Line drawing: FAO
Redleg banana prawn is widely distributed across the Indo-West Pacific Ocean. In Joseph Bonaparte Gulf, a single stock is assumed for assessment purposes.
Most of the NPF redleg banana prawn catch is taken in Joseph Bonaparte Gulf, with a smaller proportion taken in the wider NPF to the east. A small amount of catch is also taken in regions adjacent to the NPF. The catch of redleg banana prawn usually contributes a relatively small component of the total banana prawn catch in the fishery. The highest catch reported was 1,005 t in 1997 (Figure 5.2). Since then, most reported catches have been below the average of 482 t, except in 2014 (886 t). The lowest reported catches were in 2015 and 2016, both below 50 t. In 2018, the catch was 269 t.
Estimates of maximum sustainable yield (MSY) and its corresponding spawning biomass level (BMSY) are difficult to derive for short-lived, variable stocks such as redleg banana prawn. Typically, yield is determined largely by the strength of annual recruitment, and therefore annual sustainable yields can be expected to fluctuate widely around deterministic estimates (Plagányi et al. 2009).
The most recent accepted assessment for the stock was in 2018 (Plagányi et al. 2018). Catch rates (the index of abundance) for 2015 and 2016 were excluded from the base-case model because they poorly represent fishing effort in these years. Data from 2017 (when effort increased again) were included. The assessment model uses quarterly time steps of catch and effort. As a result, outputs from the model depend on the distribution of effort across fishing seasons, and sensitivity to this has been explored in the past. The updated assessment showed that spawning biomass declined substantially between 2014 and 2017 to below BMEY (biomass at maximum economic yield) (Figure 5.3), before increasing slightly at the end of 2017 to a level below the BMEY target but above the biomass limit (0.5BMSY). The assessment concluded that the biomass declines were likely due to the combined impact of fishing and major environmental anomalies (discussed further below).
The Northern Prawn Resource Assessment Group (NPRAG) analysed the anomalously low Joseph Bonaparte Gulf catches of redleg banana prawn in 2015 and 2016 (Plagányi et al. 2017). One hypothesis is that recruitment or availability was lower in 2015 and 2016 as a result of anomalous environmental factors. Preliminary work by Plagányi et al. (2017) found an association between catch rates and different combinations of El Niño conditions (Southern Oscillation Index) and seasonal rainfall. The model predicted low catch rates in both 2015 and 2016 as a result of El Niño conditions and below-median rainfall.
Another hypothesis for the low Joseph Bonaparte Gulf catch and effort is the potential existence of more favourable fishing opportunities in other parts of the multispecies NPF, particularly for tiger prawn in the Gulf of Carpentaria, thereby leading to low fishing effort in Joseph Bonaparte Gulf. Predictably, preliminary analysis found that, when revenue-per-unit-effort is lower in Joseph Bonaparte Gulf than in the Gulf of Carpentaria, operators will preferentially fish the Gulf of Carpentaria (AFMA 2017a). This would contribute to low effort in Joseph Bonaparte Gulf during years of unfavourable environmental conditions, as explained above. Thus, low Joseph Bonaparte Gulf effort and catches may, in part, result from a combination of poor environmental conditions in Joseph Bonaparte Gulf and better fishing opportunities elsewhere.
The redleg banana prawn harvest strategy uses a proxy limit reference point (LRP) based on 0.5BMSY, which correlates with a catch of 390 kg per vessel per day. The LRP is deemed to have been breached if catch rates fall below 390 kg per vessel per day in August, September and October, and there have been at least 100 days fishing over the full fishing year. In this scenario, the fishery will be closed for the first three-month ‘season’ the following year. The fishery will also be closed if catch rates fall below 390 kg per vessel per day in each of two consecutive years and there have been at least 100 days fishing activity in the fishery in each year. In this scenario, the fishery would be closed for all of the following year. Under the harvest strategy, when effort is below 100 days, the fishery remains open in both seasons of the following year, regardless of whether catch rates fall below 390 kg per vessel per day in August, September and October. There is no precedent for two consecutive years with such low fishing effort. Consequently, in late 2016, NPRAG recommended reviewing the decision rules for redleg banana prawn under the NPF harvest strategy (AFMA 2016), including potentially modifying the season opening for years with fewer than 100 fishing days and considering environmental conditions (AFMA 2017b). The current harvest strategy requires two full years of very low catch rates (effectively two overfished years) together with sustained fishing effort before there is a management response of closing the fishery for a whole year. The harvest strategy has no mechanism to adjust catch or effort levels to achieve the BMEY target, or to progressively reduce catch or effort as biomass approaches the limit.
In November 2018, NPRAG determined that a management strategy evaluation would assess the effectiveness of a range of alternative decision rules in achieving management objectives before revising and incorporating the rates into the new harvest strategy.
Stock status determination
The most recent assessment (2018) estimated that biomass had declined substantially between 2014 and 2017. Although this decline is a cause of concern, the estimated biomass remained above the LRP in 2017. The biomass status of the redleg banana prawn stock is therefore not overfished.
The current harvest strategy for redleg banana prawn is poorly suited to the current low biomass level of the stock, providing no direction for a progressive reduction in effort as the stock approaches the LRP. Although management has previously advocated to the fishing industry that effort be constrained in the redleg banana prawn fishery, any such response would be voluntary. A lack of control over fishing effort, together with the recent variability in annual recruitment and declines in catch rates, makes it difficult to determine whether current fishing mortality will result in the biomass falling below the LRP. As a result, the level of fishing mortality of redleg banana prawn is classified as uncertain.
White banana prawn (Penaeus merguiensis)
Line drawing: FAO
The stock structure of white banana prawn is uncertain. In the NPF, there is some evidence of substock structuring associated with significant river catchments and their annual flow regime, but, in the absence of clear information on biological stock structure, status is reported at the fishery level.
Catch in 2018 was 4,439 t (Figure 5.4). Seasonal catch is highly variable and is associated with rainfall in some areas (Venables et al. 2011).
The environmentally driven variability of this resource means that a robust stock–recruitment relationship cannot be determined. Because annual yields are largely dependent on annual recruitment and recruitment is closely associated with seasonal rainfall, it has not been possible to develop a stock assessment for white banana prawn. To see whether total allowable catches could be implemented for the fishery, CSIRO modelled the relationship between historical catch and rainfall, to investigate whether the next year’s catch could be predicted based on the most recent wet-season rainfall. Unfortunately, large uncertainties remain because the model cannot accurately predict catch levels in some years, particularly in recent years (Buckworth et al. 2013).
Harvest rates for white banana prawn in the fishery are understood to have been high (>90% of available biomass) in some years (Buckworth et al. 2013), but banana prawns are believed to be resilient to fishing pressure, and recruitment appears to be more closely associated with seasonal rainfall than with fishing mortality. The harvest strategy for the stock includes an objective to allow enough escapement to ensure an adequate spawning biomass and subsequent recruitment (Dichmont et al. 2012). This is achieved by closing the season when catch rates fall below a trigger level. The trigger is also designed to achieve an economic outcome by closing fishing when catch rates fall to an uneconomical level (based on an annual trigger that is computed using estimates of fuel costs and prawn prices for that year).
Stock status determination
With the adoption of the harvest strategy, a relatively small fleet and a lack of evidence of recruitment overfishing, this stock is classified as not subject to overfishing and not overfished.
Alan Specketer, AFMA
Brown tiger prawn (Penaeus esculentus)
Line drawing: FAO
Brown tiger prawn appears to be endemic to tropical and subtropical Australian waters. Some genetic evidence indicates that there are separate stocks on the east and west coasts (Ward et al. 2006). However, the biological stock structure in the NPF is uncertain, and the population in the Gulf of Carpentaria is assumed to be a single stock for management purposes.
Brown tiger prawns are caught primarily in the first season in the southern and western Gulf of Carpentaria, but also in waters westward towards Joseph Bonaparte Gulf. Catch of brown tiger prawn in 2018 was 366 t (Figure 5.5).
The stock assessment for the tiger prawn fishery uses a multispecies approach, with a weekly, sex- and size-structured population model for brown and grooved tiger prawns, and a Bayesian hierarchical production model for blue endeavour prawn (Metapenaeus endeavouri). It is integrated with an economic model that calculates maximum economic yield (MEY). Full assessments are undertaken every two years, with data collected continuously in intervening years. The most recent tiger prawn fishery assessment (Deng et al. 2018) also included a Bayesian hierarchical biomass production model as a scenario testing model for red endeavour prawn (M. ensis).
The base-case estimate of the size of the brown tiger prawn spawner stock at the end of 2017 as a percentage of spawner stock size at MSY (S2017/SMSY) was 78% (range across sensitivities 69–79%; Deng et al. 2018). The base-case estimate of the size of the spawner stock as a percentage of stock size at MEY (S2017/SMEY) was 75% (Figure 5.6) (range across sensitivities 67–76%). These results indicate a substantial decline in biomass compared with the 2015 assessment (Figure 5.6). This decline appears to be largely due to poor recruitment in recent years (Deng et al. 2018), which is of some concern, particularly if this trend continues. However, the abundance indices are within the range of historical variability (Deng et al. 2018), and the 2019 recruitment survey showed that recruitment increased in 2019 (Roy Deng [CSIRO], 2019, pers. comm). For the most recent assessment, the estimate of effort in 2017 as a percentage of effort at MSY (E2017/EMSY) was 52%. The estimate of effort in 2017 as a percentage of effort at MEY (E2017/EMEY) was 42%. Catch of brown tiger prawn has remained substantially below the base-case estimate of MSY (1,083 t) since the assessment (see Figure 5.5).
FIGURE 5.6 Spawner stock size as a proportion of SMEY for brown tiger prawn, 1970–2017
SMEY Spawner stock size at maximum economic yield.
Source: Deng et al. 2018
Stock status determination
Effort in recent years has been less than the level associated with MSY and MEY, but shows an increasing trend since 2005. Catches in recent years have been less than MSY. The latest assessment shows a significant recent decline in biomass; however, the five-year moving average estimate of spawner stock biomass for the base-case model (and all other sensitivities) remains above the LRP (0.5SMSY) in the most recent assessment. Therefore, brown tiger prawn in the NPF is classified as not subject to overfishing and not overfished.
Grooved tiger prawn (Penaeus semisulcatus)
Line drawing: Karina Hansen
Grooved tiger prawn ranges across northern Australian waters, the Indo-West Pacific Ocean and the Mediterranean Sea. The biological stock structure is uncertain, but the population in the Gulf of Carpentaria is assumed to be a single stock for assessment purposes.
The annual catch of grooved tiger prawn, which is primarily taken in the second season, peaked in the early 1980s at more than 2,500 t and has shown a declining trend since then (Figure 5.7), except for the 2015 catch of 2,405 t. Catch in 2018 was 1,097 t.
For the most recent assessment (Deng et al. 2018), the base-case estimate of the size of the grooved tiger prawn spawner stock at the end of 2017 as a percentage of spawner stock size at MSY (S2017/SMSY) was 74% (range across sensitivities 69–84%). The base-case estimate of the size of the spawner stock as a percentage of spawner stock size at MEY (S2017/SMEY) was 63% (range across sensitivities 58–64%), indicating a substantial decline in biomass compared with the 2015 grooved tiger prawn assessment (Figure 5.8). This decline appears to be largely due to poor recruitment in recent years (Deng et al. 2018).
For the most recent assessment, the estimate of effort in 2017 as a percentage of effort at MSY (E2017/EMSY) was 49%. The estimate of effort in 2017 as a percentage of effort at MEY (E2017/EMEY) was 71%. The 2018 catch of grooved tiger prawn (1,097 t; Figure 5.7) was below the base-case estimate of long-term average MSY (1,654 t).
Stock status determination
Catches of grooved tiger prawns in the past six years were below MSY except in 2015 when recruitment was higher than average. The estimated spawning stock biomass for the base-case model is below the biomass levels associated with MSY and MEY; however, the five-year moving average estimate of spawn stock biomass for the base case (and all other sensitivities) remains above the LRP (0.5SMSY) in the most recent assessment. Grooved tiger prawn in the NPF is therefore classified as not subject to overfishing and not overfished.
Blue endeavour prawn (Metapenaeus endeavouri)
Line drawing: FAO
Blue endeavour prawn ranges across northern Australia waters and parts of the Indo-West Pacific Ocean. The biological stock structure is uncertain, but the population in the NPF is assumed to be a single stock for management purposes.
Annual catches of blue endeavour prawn peaked in the early 1980s at more than 1,500 t, and again in the late 1990s at 1,000 t (Figure 5.9). Since 2002, annual catches have averaged around 300 t, with 283 t caught in 2018. Blue endeavour prawn is a byproduct of the tiger prawn fishery, and so catches are linked to changes in effort targeting tiger prawns.
The stock is assessed using a Bayesian hierarchical biomass dynamic model, within the same overall bio-economic model system used for the two tiger prawn species (Deng et al. 2018).
The base-case estimate of the size of the blue endeavour prawn spawner stock at the end of 2017 as a percentage of stock size at MSY (S2017/SMSY) was 41% (range across sensitivities 41–62%). The base-case estimate of the size of the spawner stock as a percentage of stock size at MEY (S2017/SMEY) was 44% (range across sensitivities 39–61%), indicating a substantial decline in biomass compared with the 2015 blue endeavour prawn assessment (Figure 5.10). Similar to the two tiger prawn stocks, the recent decline in biomass is thought to be associated with poor recruitment, which in turn may be related to environmental factors (Roy Deng [CSIRO], 2019, pers. comm).
The 2018 catch of blue endeavour prawn (283 t; Figure 5.9) was substantially less than the base-case estimate of MSY (752 t).
SMEY Spawner stock size at maximum economic yield.
Source: Deng et al. 2018
Stock status determination
The catch in 2018 was well below the estimated MSY, and the estimate of spawner stock size (five-year moving average) for the base case was above the LRP (0.5SMSY). Blue endeavour prawn in the NPF is therefore classified as not subject to overfishing and not overfished.
Red endeavour prawn (Metapenaeus ensis)
Line drawing: FAO
Red endeavour prawn ranges across northern Australian waters and parts of the Indo-West Pacific Ocean. The biological stock structure is uncertain, but the population within the NPF is assumed to be a single stock for management purposes.
Annual catches of red endeavour prawn have been variable over the history of the fishery, with peak annual catches exceeding 800 t in 1982 and 1997 (Figure 5.11). Since 1998, catches have been below 400 t, with 209 t caught in 2018. Red endeavour prawn is a byproduct of the tiger prawn fishery.
A preliminary assessment of red endeavour prawn, using a Bayesian hierarchical biomass dynamic model as a scenario test model, was undertaken in 2018 (Deng et al. 2018) to explore whether the model could provide a preliminary indication of the stock status of this species. Since the sensitivity of the outputs of the model has not been significantly tested against different model input scenarios, the assessment results were not considered reliable for determining the stock status of red endeavour prawn.
Catches in recent years have been quite low compared with historical highs. This is most likely related to the overall decline in fishing effort directed at tiger prawns, and the closure of some areas and time periods where red endeavor prawn was historically targeted, rather than being an indication of a fall in red endeavour prawn biomass (which is also the case for blue endeavor prawn).
Stock status determination
Given the preliminary nature of the 2018 stock assessment, red endeavour prawn is classified as uncertain with regard to fishing mortality and biomass status.
5.3 Economic status
Key economic trends
The gross value of production (GVP) for the NPF fluctuated during the decade to 2017–18, peaking at $129 million in 2015–16 and reaching a low of $73 million (in 2017–18 dollars) in 2011–12 (Figure 5.12). During the same period, the average GVP per active vessel increased by 5% to $1.78 million (in 2017–18 dollars).
Notes: GVP Gross value of production. 2017–18 data are preliminary.
Since the early 1990s, ABARES has used data from economic surveys of the NPF to estimate the net economic returns (NER) earned in the fishery. The most recent survey in 2017 provided survey-based estimates of NER for the 2014–15 and 2015–16 financial years, and forecasts for 2016–17 (Mobsby, Curtotti & Bath 2019).
Real NER in the NPF have varied considerably during the period 2006–07 to 2016–17 (Figure 5.13). In 2006–07 and 2011–12, real NER were negative, estimated at –$3.7 million and –$4.0 million (in 2017–18 dollars), respectively. NER have followed an increasing trend since 2011–12, reaching a peak of $32.1 million in 2015–16, supported by a strong increase in tiger prawn catch and good prices. The NER improvement in 2015–16 was the fourth consecutive annual increase in NER. The strong performance in 2015–16 was forecast to be repeated in 2016–17, following a strong increase in banana prawn catch in 2016–17, albeit slightly lower, at ($30.30 million). In 2017–18, which comprises the 2017 tiger prawn season and 2018 banana prawn season, lower GVP and higher unit fuel prices are expected to have a dampening effect on NER.
Increasing profitability during this period is likely to stem from a combination of factors, including favourable market conditions and management changes that have occurred in the fishery in recent years. Favourable market conditions include a lowering of the Australian dollar exchange rate and fuel prices after 2012–13. Management changes include targeting of MEY in the tiger prawn component of the fishery from 2004–05; implementation of the Securing our Fishing Future structural adjustment program (which concluded in 2006–07), resulting in a 50% reduction in the fleet; and the adoption of quad trawl gear. The structural adjustment program removed 43 class B statutory fishing rights from the fishery, reducing the already declining active vessel numbers from 86 in 2005–06 to 55 in 2007–08. Since then, active vessel numbers have declined slightly, to 52 in 2017. Together, these changes are likely to have improved the economic performance of the fishery.
Total factor productivity (a measure of fishers’ ability to convert inputs into outputs over time) in the fishery increased from 2005–06 to 2010–11, at a rate robust enough to offset declining terms of trade from declining prices and high fuel costs (Mobsby, Curtotti & Bath 2019; Figures 5.14 and 5.15). This trend was largely driven by growth in outputs and a slightly declining inputs index. Most of the increase in the outputs index coincides with increases in banana prawn catch per vessel; however, targeting MEY in the tiger prawn component of the fishery would also have supported this improved productivity at a time of declining terms of trade. Because the productivity index was not adjusted for stock effects, productivity growth also reflects favourable environmental conditions at the time, which allowed increases in catch, particularly for banana prawns, rather than just changes in efficiency measures and technology adopted by fishers. From 2010–11 to 2015–16, total factor productivity generally declined, but the negative impact of this on NER has been more than offset by a strongly positive trend in terms of trade, largely as a result of improved prices for banana and tiger prawns, and lower fuel costs since 2013–14. The positive trend in terms of trade has largely driven the steady rise in NER during the period.
FIGURE 5.14 Total factor productivity index, 2005–06 to 2015–16
FIGURE 5.15 Terms of trade index, 2005–06 to 2015–16
The NPF is managed using input controls. The main control is individual tradeable gear units, which limit the length of headrope on trawl nets. Controls on season length, spatial closures and other gear restrictions are also applied.
An assessment of the impact of the structural adjustment program by Vieira et al. (2010) suggested that, for the benefits of the program to be preserved, management arrangements in fisheries targeted by the program need to be set in ways that prevent a repeated build-up of fishing capacity. In recent years, AFMA has sought to better align banana prawn catch levels with the MEY objective. In 2014, an MEY catch-rate trigger for banana prawn was introduced to the fishery (AFMA 2015).
Performance against economic objective
The tiger prawn component of the fishery has explicit MEY targets (across two tiger prawn stocks and one endeavour prawn stock), and a bio-economic model is used to estimate annual fishing effort required to move towards SMEY. Stocks are assessed every two years. Spawning stock sizes of both stocks of tiger prawn were below SMEY at the end of the 2017 season (Deng et al. 2018). Spawner stock size of blue endeavour prawn for the same period was also estimated to be below SMEY. Effort levels as a proportion of effort at MEY for brown tiger prawn and grooved tiger prawn were estimated to be below effort at MEY. Current effort limits in the fishery are based on outputs from the fishery’s bio-economic model, and are designed to achieve an MEY (optimal profit at the fleet level) target over a seven-year projection period (noting that the target changes with every assessment because of changes in biological and economic parameters).
Recruitment for all stocks is variable, particularly for white banana prawn, for which recruitment is closely associated with rainfall. Therefore, no BMEY target is defined for white banana prawn. Instead, an MEY-based catch-rate trigger was implemented for the 2014 banana prawn season, with mechanisms in place to adjust total annual effort levels to ensure that the fishery remains sustainable and profitable (AFMA 2015).
An updated assessment of redleg banana prawn, primarily caught in Joseph Bonaparte Gulf, indicates that spawning stock biomass fell to below the BMEY target but remained above the LRP (0.5BMSY) between 2014 and 2017.
Targeting MEY in the fishery is consistent with the economic objective of maximising economic returns, and could be expected to increase NER in the fishery. Targeting MEY of the tiger prawn component of the fishery began in 2004–05. Despite declining terms of trade from 2004–05 to 2010–11, productivity and NER improved. Although the targeting of MEY over this period is likely to have supported these improvements, other factors, such as the structural adjustment program and improved banana prawn catch, also contributed. The banana prawn catch trigger targeting MEY has only been in place since 2014, so it is too early to determine its effect on NER.
5.4 Environmental status
The NPF was reaccredited under part 13 of the Environment Protection and Biodiversity Conservation Act 1999 in December 2018. The current approval of a wildlife trade operation (part 13A) expires on 6 January 2024. Three recommendations accompanied the strategic assessment, relating to the management and monitoring of sawfish and sea snake species.
The NPF was certified as a sustainable fishery by the Marine Stewardship Council in November 2012 and recertified in January 2018.
Ecological risk assessment (ERA) of the NPF has assessed 9 target species, 135 byproduct species, 516 discard species (chondrichthyans and teleosts only), 128 protected species, 157 habitats and 3 communities (AFMA 2008). Following review of the level 2 Productivity Susceptibility Analysis (PSA) risk rankings, using residual risk guidelines (AFMA 2008), 26 species remained at high risk. During and following the level 2 PSA work, selected taxonomic groups were the subject of level 2.5 studies (Brewer et al. 2007). Milton et al. (2008) estimated temporal trends in abundance of sea snakes in the NPF to provide a quantitative assessment of trawling on populations. Although most populations had been relatively stable, two species (spectacled seasnake [Hydrophis kingii] and large-headed seasnake [H. pacificus]) showed evidence of decline on the trawl grounds. Results from a level 3 Sustainability Assessment for Fishing Effects analysis of elasmobranchs in the NPF (Zhou & Griffiths 2011) indicate that, of the 51 species considered, fishing impacts may have exceeded the maximum sustainable fishing mortality harvest rate for 19 species, although these estimates were highly uncertain. Based on these risk assessments, three species are currently considered to be at high risk in the NPF: porcupine ray (Urogymnus asperrimus) and two species of mantis shrimp (Dictyosquilla tuberculata and Harpiosquilla stephensoni). The ERA is currently being updated.
AFMA publishes quarterly logbook reports of interactions with protected species on its website. In the NPF in the 2018 calendar year, 621 sawfish interactions were reported, of which 425 were released alive, 193 were dead and the remainder were injured; 11,048 sea snakes were caught, of which 8,593 were released alive, 2,107 were dead and 348 had an unknown life status; 169 seahorse and pipefish species were caught, of which 118 were released alive and the remainder were dead; and 78 turtle interactions were reported, with all but 4 being released alive. Reports also indicate that one dolphin was caught and released alive.
The fishery has had a bycatch management plan for many years, and NPF Industry has been leading projects on bycatch reduction devices with the aim of reducing bycatch in the fishery by 30%.
AFMA 2008, Residual Risk Assessment of the level 2 ecological risk assessment species results, report for the Northern Prawn Fishery, Australian Fisheries Management Authority, Canberra.
—— 2015, Northern Prawn Fishery: directions and closures 2015, AFMA, Canberra.
—— 2016, ‘Northern Prawn Fishery Resource Assessment Group (NPRAG) meeting minutes: 17–19 November 2016’, AFMA, Canberra.
—— 2017a, ‘Northern Prawn Fishery Resource Assessment Group (NPRAG) meeting, minutes, 4–5 December 2017’, AFMA, Canberra.
—— 2017b, ‘Northern Prawn Fishery Resource Assessment Group (NPRAG) meeting, minutes, 11 May 2017’, AFMA, Canberra.
Brewer, DT, Griffiths, S, Heales, DS, Zhou, S, Tonks, M, Dell, Q, Taylor, BT, Miller, M, Kuhnert, P, Keys, S, Whitelaw, W, Burke, A & Raudzens, E 2007, Design, trial and implementation of an integrated, long term bycatch monitoring program, road tested in the Northern Prawn Fishery, final report on Fisheries Research and Development Corporation project 2002/035, CSIRO, Cleveland, Queensland.
Buckworth, RC, Ellis, N, Zhou, S, Pascoe, S, Deng, RA, Hill, FG & O’Brien, M 2013, Comparison of TAC and current management for the white banana prawn fishery of the Northern Prawn Fishery, final report for project RR2012/0812 to AFMA, CSIRO, Canberra.
Deng, RA, Hutton, T, Punt, A, Upston, J, Miller, M, Moeseneder, C & Pascoe, S 2018, Status of the Northern Prawn Fishery tiger prawn fishery at the end of 2017 with an estimated TAE for 2018 and 2019, report to AFMA, CSIRO, Brisbane.
Dichmont, CM, Jarrett, A, Hill, F & Brown, M 2012, Harvest strategy for the Northern Prawn Fishery under input controls, AFMA, Canberra.
Milton, DA, Zhou, S, Fry, GC & Dell, Q 2008, Risk assessment and mitigation for sea snakes caught in the Northern Prawn Fishery, final report on FRDC project 2005/051, CSIRO, Cleveland, Queensland.
Mobsby, D, Curtotti, R & Bath, A 2019, Australian fisheries economic indicators report 2017: financial and economic performance of the Northern Prawn Fishery, ABARES, Canberra.
Plagányi, É, Dennis, D, Kienzle, M, Ye, Y, Haywood, M, Mcleod, I, Wassenberg, T, Pillans, R, Dell, Q, Coman, G, Tonks, M & Murphy, N 2009, TAC estimation and relative lobster abundance surveys 2008/09, AFMA Torres Strait Research Program, final report, AFMA project 2008/837, AFMA, Canberra.
——, Hutton, T, Kenyon, R, Moeseneder, C, Deng, R, Miller, M, Pascoe, S & Upston, J 2017, Environmental drivers of variability in Joseph Bonaparte Gulf red-legged banana prawn (Penaeus indicus) fishery, preliminary progress report for the Northern Prawn Fishery Resource Assessment Group, AFMA Canberra.
——, Deng, R, Upston, J, Miller, M, Hutton, T & Moedeneder, C 2018, Preliminary assessment of the Joseph Bonaparte Gulf red-legged banana prawn (Penaeus indicus) fishery in 2017, with TAE recommendations for 2018, AFMA, Canberra.
Venables, WN, Hutton, T, Lawrence, E, Rothlisberg, P, Buckworth, R, Hartcher, M & Kenyon, R 2011, Prediction of common banana prawn potential catch in Australia’s Northern Prawn Fishery, AFMA, Canberra.
Vieira, S, Perks, C, Mazur, K, Curtotti, R & Li, M 2010, Impact of the structural adjustment package on the profitability of Commonwealth fisheries, Australian Bureau of Agricultural and Resource Economics research report 10.01, ABARE, Canberra.
Ward, R, Ovenden, J, Meadows, J, Grewe, P & Lehnert, S 2006, ‘Population genetic structure of the brown tiger prawn, Penaeus esculentus, in tropical northern Australia’, Marine Biology, vol. 148, no. 3, pp. 599–607.
Zhou, S & Griffiths, S 2011, Sustainability Assessment for Fishing Effects (SAFE): a new quantitative ecological risk assessment method and its application to elasmobranch bycatch in an Australian trawl fishery, CSIRO Marine and Atmospheric Research, Brisbane.