Western Trawl Fisheries

​​Chapter 6: North West Slope Trawl Fishery

J Woodhams and A Bath

FIGURE 6.1 Area fished in the North West Slope Trawl Fishery, 2015–16
TABLE 6.1: Status of the North West Slope Trawl Fishery
Status
Biological status
2015
Fishing mortality
2015
Biomass
2016
Fishing mortality
2016
Biomass
Comments
Scampi (Metanephrops australiensis, M. boschmai, M. velutinus)Not subject to overfishingNot overfishedNot subject to overfishingNot overfishedTrawl effort is low compared with historical levels, and nominal catch-per-unit-effort is relatively high.

Economic status
Estimates of NER are not available for the fishery, although the high degree of latent effort in the fishery indicates that NER are likely to be low.

Notes: NER Net economic returns.

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6.1 Description of the fishery

Area fished

The North West Slope Trawl Fishery (NWSTF) operates off north-western Australia from 114°E to 125°E, roughly between the 200 m isobath and the outer boundary of the Australian Fishing Zone. A large area of the Australia–Indonesia MOU box (an area off north-western Western Australia where Indonesian fishers may operate using only traditional methods) falls within the NWSTF (Figure 6.1).

Fishing methods and key species

The NWSTF has predominantly been a scampi fishery in recent years, using demersal trawl gear. The key species is Australian scampi (Metanephrops australiensis). Smaller quantities of velvet scampi (M. velutinus)and Boschma's scampi (M. boschmai)are also harvested. Mixed snappers (Lutjanidae) have historically been an important component of the catch. At the height of the fishery, in the late 1980s and early 1990s, deepwater prawns, particularly red prawn (Aristaeomorpha foliacea), were targeted and dominated the total catch. However, difficulties in maintaining markets for deepwater prawns led to a decline in the number of vessels operating in the fishery and a return to primarily targeting scampi.

Management methods

In 2011, the Australian Fisheries Management Authority (AFMA) updated the harvest strategy for the western trawl fisheries (NWSTF and Western Deepwater Trawl Fishery—WDTF; AFMA 2011). Given the relatively low levels of catch, the purpose of the harvest strategy is to allow fishing at current levels without additional management costs. The revised strategy uses historical catches and catch rates from 2000 to 2010 as the basis for triggers for further management actions, if fishing activity increases. An annual review determines whether these catch triggers have been reached. It is not clear whether the maximum catch over the chosen reference period (2000 to 2010) is a valid indicator of sustainable harvest levels, given the nearly 30 years of exploitation in this fishery, or whether catch rates over the reference period are representative of unfished biomass levels. However, the harvest strategy is designed to trigger management responses if fishing increases above recent historical levels. Given the recent boundary amendments to the Western Australia Offshore Constitutional Settlement arrangement, AFMA has commenced a review of the current harvest strategy with a focus on the triggers for mixed snapper species.

The 2010 stock assessment of scampi in the NWSTF (Chambers & Larcombe 2015) may provide information for refining catch and catch-rate triggers for these species.

Fishing effort

Fishing commenced in the NWSTF in 1985. The number of active vessels peaked at 21 vessels in 1986–87 and declined through the 1990s before increasing to 10 vessels in 2000–01 and 2001–02. Vessel numbers have since decreased to stabilise at one or two vessels each year since 2008–09 (Table 6.2). Historical effort, in trawl hours, in the fishery largely follows the trend in the number of active vessels (Figure 6.2). Fishing effort often increases when boats cease to operate in the Northern Prawn Fishery.

TABLE 6.2: Main features and statistics for the NWSTF
Fishery statistics a2014–15 fishing season2014–15 fishing season2014–15 fishing season2015–16 fishing season2015–16 fishing season2015–16 fishing season
Stock TAC
(t)
Catch
(t)
Real value
(2014–15)
TAC
(t)
Catch
(t)
Real value
(2015–16)
Scampi (Metanephrops australiensis, M. boschmai, M. velutinus)-33.4Confidential-33.0Confidential
Total fishery - 49.1 Confidential - 54.8 Confidential


Fishery-level statistics
2014–15 fishing season2015–16 fishing season
Effort115 days; 2,137 trawl hours117 days; 2,241 trawl hours
Fishing permits45
Active vessels12
Observer coverage8 days (7%)16 days (14%)
Fishing methodsDemersal trawlDemersal trawl
Primary landing portsDarwin (Northern Teritory), Point Samson (Western Australia)Darwin (Northern Teritory), Point Samson (Western Australia)
Management methodsInput controls: limited entry, gear restrictions
Output controls: harvest strategy contains catch trigger for scampi, deepwater prawns and some finfish (redspot emperor and saddletail snapper)
Input controls: limited entry, gear restrictions
Output controls: harvest strategy contains catch trigger for scampi, deepwater prawns and some finfish (redspot emperor and saddletail snapper)
Primary marketsDomestic: Perth, Sydney and Brisbane—frozen
International: Singapore, Hong Kong, China and Japan—frozen
Domestic: Perth, Sydney and Brisbane—frozen
International: Singapore, Hong Kong, China and Japan—frozen
Management plan North West Slope Trawl Fishery and Western Deepwater Trawl Fishery statement of management arrangements (AFMA 2012) North West Slope Trawl Fishery and Western Deepwater Trawl Fishery statement of management arrangements (AFMA 2012)

a Fishery statistics are provided by fishing season, unless otherwise indicated. Fishing season is 1 July to 30 June. Real-value statistics are by financial year.
Notes: TAC Total allowable catch. – Not applicable.

6.2 Biological status

Scampi (Metanephrops australiensis, M. boschmai and M. velutinus)

Scampi (Metanephrops australiensis, M. boschmai and M. velutinus) 

Line drawing: FAO

Stock structure

The NWSTF targets several species of scampi. The stock structure of these species (predominantly M. australiensis, M. boschmai and M. velutinus)is not known, and they are grouped into a multispecies stock for management and assessment purposes. Scampi in the NWSTF are therefore assessed as a single stock.

Catch history

Trends in total catch have largely followed trends in active vessels and fishing effort (Figure 6.2). Scampi catch in recent years has been relatively stable at around 30 t. Total catch has primarily consisted of scampi, with the exception of 2011–12, when mixed snapper accounted for a large proportion of the catch (32 t of snapper and 21 t of scampi).

FIGURE 6.2 Catch and effort for scampi in the NWSTF, 1985–86 to 2015–16
Source: Australian Fisheries Management Authority
Stock assessment

In 2010, the scampi stock (predominantly M.australiensis, M.boschmai and M.velutinus) was assessed using surplus production models (Chambers & Larcombe 2015). This assessment indicated that scampi biomass at the end of 2008 was most likely between 65 per cent and 85 per cent of unfished biomass. The fishing mortality rate in recent years was estimated to have been well below the rate that would achieve maximum sustainable yield.

Wallner and Phillips (1995) noted that scampi catch rates in the NWSTF tended to decline quickly in response to fishing but recovered after grounds were rested for relatively short periods. They suggested that scampi might spend a greater proportion of time in burrows after the grounds have been trawled, temporarily reducing their catchability. If scampi respond to fishing in this way, catch-per-unit-effort (CPUE) should decline more quickly than abundance (‘hyperdepletion'). Stock assessments based on CPUE would tend to be precautionary (that is, the stock would be less depleted than indicated by CPUE).

Scampi CPUE has been close to historical highs since the 2010 stock assessment, suggesting that biomass remains high. Trawl effort has been at low levels over the same period (Figure 6.2), which suggests low levels of fishing mortality during this time.

The possible conservative nature of CPUE indices used in stock assessments suggests that, provided scampi remain a primary target for the fishery, use of nominal (unstandardised) CPUE and annual catch is probably adequate for assessment purposes. Standardised CPUE series should be produced every 3–5 years, and assessment models fitted to periodically update relative biomass estimates. Analysis of the mean carapace length of Australian scampi measured by observers could provide a comparative indicator of total mortality.

Stock status determination

Chambers and Larcombe (2015) assessed the scampi stock as not overfished and not subject to overfishing in 2008–09. Since then, catch and effort have remained low (Figure 6.2), and nominal catch rates are reasonably high compared with historical levels. Based on these indicators and information from the previous stock assessment, scampi in the NWSTF are classified as not overfished and not subject to overfishing.

6.3 Economic status

Key economic trends

Economic surveys of the NWSTF have not been undertaken. The gross value of production for the fishery has been confidential since 2006–07 because five or fewer vessels have been active in the fishery. Five fishing permits were issued for the 2015–16 fishing season, and two vessels were active in the fishery. The low number of active vessels indicates that there is latent effort in the fishery and suggests potentially low net economic returns (NER), because fishers are not fully using their right to fish. The volume landed of the high-value scampi species was mostly unchanged from 2014–15 to 2015–2016; however, overall catch in the fishery increased by 12 per cent. The increase in catch and relatively smaller increase in effort (5 per cent increase in trawl hours) suggest that there may have been some improvement in NER from 2014–15 to 2015–16.

Management arrangements

Under the harvest strategy, the fishery is managed through input controls and catch triggers. As higher catch triggers are reached, the harvest strategy may require more sophisticated stock assessment techniques to be applied (AFMA 2011). Such stock assessments would inform potential changes to management arrangements for the fishery, including a change to output controls, if catch increased sufficiently to justify such considerations.

Performance against economic objective

The fishery's performance against the economic objective is uncertain because there is no explicit economic target or supporting analyses. However, the relatively low value of the fishery justifies the low-cost management approach currently applied, given the low levels of effort.

6.4 Environmental status

The NWSTF is included in the List of Exempt Native Specimens under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and is exempt from export controls until 22 December 2017.

Chondrichthyans and teleosts caught in the NWSTF and the WDTF have been assessed to level 3 of the AFMA ecological risk assessment framework (Zhou et al. 2009). None of the species assessed were found to be at high risk at the current level of fishing effort.

AFMA publishes quarterly summaries of logbook reports of interactions with protected species on its website. No interactions with species protected under the EPBC Act were reported in the NWSTF in 2016.

6.5 References

AFMA 2011, Harvest strategy for the Western Deepwater Trawl Fishery and North West Slope Trawl Fishery 2011, Australian Fisheries Management Authority, Canberra.

—— 2012, North West Slope Trawl Fishery and Western Deepwater Trawl Fishery: statement of management arrangements, AFMA, Canberra.

Chambers, M & Larcombe, J 2015, ‘North West Slope Trawl Fishery scampi assessment', in J Larcombe, R Noriega & I Stobutzki (eds), Reducing uncertainty in fisheries stock status, ABARES research report, Canberra.

Wallner, BG & Phillips, BF 1995, ‘Development of a trawl fishery for deepwater metanephropid lobsters off the northwest continental slope of Australia: designing a management strategy compatible with species life history', ICES Marine Science Symposium, vol. 199, pp. 379–90.

Zhou, S, Smith, T & Fuller, M 2009, Rapid quantitative risk assessment for fish species in seven Commonwealth fisheries, report to AFMA, Canberra.

Boxed scampi
Mike Gerner, AFMA

Chapter 14: Western Deepwater Trawl Fishery

J Woodhams and A Bath

FIGURE 14.1 Area fished in the Western Deepwater Trawl Fishery, 2005–06 to 2015–16
Note: 2013–14 was the last year when there was catch in the fishery.
TABLE 14.1 Status of the Western Deepwater Trawl Fishery
Status
Biological status
2015
Fishing mortality
2015
Biomass
2016
Fishing mortality
2016
Biomass
Comments
Deepwater bugs (Ibacus spp.)Not subject to overfishingUncertainNot subject to overfishingUncertainNo fishing effort in 2015–16. No reliable estimate of biomass.
Ruby snapper (Etelis carbunculus, Etelis spp.)Not subject to overfishingUncertainNot subject to overfishingUncertainNo fishing effort in 2015–16. No reliable estimate of biomass.

Economic status
No fishing activity occurred in the fishery during the 2015–16 fishing season. Estimates of NER for previous years are not available, but a decline in effort and a low number of active fishing permits in recent years indicate that NER have been low.

Notes: NER Net economic returns.

Trawl net and haul
Tamre Sarhan, AFMA

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14.1 Description of the fishery

Area fished

The Western Deepwater Trawl Fishery (WDTF) operates in Commonwealth waters off the coast of Western Australia between the western boundary of the Southern and Eastern Scalefish and Shark Fishery in the south (115°08'E) and the western boundary of the North West Slope Trawl Fishery (NWSTF) in the north (114°E; Figure 14.1).

Fishing methods and key species

Operators in the fishery use demersal trawl, and catch more than 50 species in waters seaward of a line approximating the 200 m depth contour, in habitats ranging from temperate–subtropical in the south to tropical in the north. Catches in the WDTF were historically dominated by six commercial finfish species or species groups: orange roughy (Hoplostethus atlanticus), oreos (Oreosomatidae), boarfish (Pentacerotidae), eteline snapper (Lutjanidae: Etelinae), apsiline snapper (Lutjanidae: Apsilinae) and sea bream (Lethrinidae). Between 2000 and 2005, deepwater bugs (Ibacus spp.) emerged as the most important target species, although fishing effort (and consequently catch) has decreased substantially in recent years.

Management methods

The fishery is managed under the same harvest strategy as the NWSTF (AFMA 2011; see Chapter 6).

Fishing effort

The number of vessels active in the fishery and total hours trawled have fluctuated from year to year. Notably, total hours trawled were relatively high for a brief period during the early 2000s when fishers targeted ruby snapper (Etelis carbunculus and Etelis spp.)and then deepwater bugs. Total fishing effort has been comparatively low since 2005–06, although still variable, and mostly targeted at deepwater bugs. No vessels were active in the 2015–16 fishing season.

Catch

Total catch has generally remained below 100 t, apart from peaks in the early to mid 1990s, when it reached 378 t, and in 2001–02, when it reached 347 t. The peak in catch in the early to mid 1990s consisted mostly of orange roughy, while the peak in catch at the turn of the century consisted mostly of orange roughy, deepwater bugs and, to a lesser extent, ruby snapper.

Total catch has been relatively low in recent years, consisting mostly of deepwater bugs, with minimal catch of finfish. There was no catch or effort in 2015–16 (Table 14.2; Figure 14.2).

TABLE 14.2 Main features and statistics for the WDTF
Fishery statistics a2014–15 fishing season2014–15 fishing season2014–15 fishing season2015–16 fishing season2015–16 fishing season2015–16 fishing season
Stock TAC
(t)
Catch
(t)
Real value (2014–15)
TAC
(t)
Catch
(t)
Real value (2015–16)
Deepwater bugs0000
Ruby snapper0000
Total fishery 0 0 0 0

Fishery-level statistics2014–15 fishing season2015–16 fishing season
Effort00
Fishing permits1111
Active vessels00
Observer coverage0 days (0%)0 days (0%)
Fishing methodsDemersal trawlDemersal trawl
Primary landing portsFremantle, CarnarvonFremantle, Carnarvon
Management methodsInput controls: limited entry (11 permits), gear restrictionsInput controls: limited entry (11 permits), gear restrictions
Primary marketsDomestic: Perth, Sydney, Brisbane—frozen, chilled
International: United States, Spain, Japan—frozen
Domestic: Perth, Sydney, Brisbane—frozen, chilled
International: United States, Spain, Japan—frozen
Management plan North West Slope Trawl Fishery and Western Deepwater Trawl Fishery: statement of management arrangements 2012(AFMA 2012) North West Slope Trawl Fishery and Western Deepwater Trawl Fishery: statement of management arrangements 2012(AFMA 2012)

a Fishery statistics are provided by fishing season, unless otherwise indicated. Fishing season is 1 July to 30 June. Real-value statistics are provided by financial year, which is also 1 July to 30 June.
Notes: TAC Total allowable catch. Not applicable.

FIGURE 14.2 Total catch in the WDTF, 1992–93 to 2015–16
Source: Australian Fisheries Management Authority

14.2 Biological status

Deepwater bugs (Ibacus spp.)

Deepwater bugs (Ibacus spp.) 

Line drawing: FAO

Stock structure

The WDTF catches several species of deepwater bugs. Stock structure of these species is not known, and they are grouped into a multispecies stock for status assessment.

Catch history

The catch history of deepwater bugs in the WDTF is characterised by four years of relatively high catches from 2001–02 to 2004–05, peaking at 160 t in 2002–03 (Figure 14.3). Apart from this brief period, annual catches of deepwater bugs have been less than 20 t. There was no catch in 2015–16.

FIGURE 14.3 Deepwater bug catch in the WDTF, 1992–93 to 2015–16
Source: Australian Fisheries Management Authority
Stock assessment

A formal stock assessment for deepwater bugs has not been done, and little information is available with which to assess stock status. The low fishing effort, low catch levels and sporadic targeting of key commercial species make it difficult to assess stock status.

Stock status determination

There was no fishing in the WDTF in 2015–16 (Figure 14.3). As a result, deepwater bugs are classified as not subject to overfishing.There is currently little empirical data that would inform status for this stock. As a result, the stock is uncertain with regard to the level of biomass.

Ruby snapper (Etelis carbunculus and Etelis spp.)

Ruby snapper (Etelis carbunculus and Etelis spp.) 

Line drawing: FAO

Stock structure

Stock structure of ruby snapper caught in the WDTF is not known, so the stock is assessed here at the fishery level.

Catch history

Catches of ruby snapper in the WDTF peaked in 2000–01, with a smaller peak in 2008–09. Catches have been negligible since 2010–11, with no effort in the fishery in 2015–16 (Figure 14.4).

FIGURE 14.4 Ruby snapper catch in the WDTF, 1992–93 to 2015–16
Source: Australian Fisheries Management Authority
Stock assessment

The only stock assessment for ruby snapper was published in 2002 (Hunter et al. 2002). However, the reliability and accuracy of outputs from this assessment were weakened by the poor quality and limited quantity of data. The assessment identified biological characteristics that potentially increase the species' vulnerability to overfishing: the species is relatively long lived, has a high age at maturity, has a slow growth rate and aggregates in restricted continental-shelf habitats. Hunter et al. (2002) showed that fishing for ruby snapper in the WDTF was historically restricted to the area of the continental-shelf region from Shark Bay to North West Cape. Commercial catch-per-unit-effort has been highly variable—it was initially around 400 kg/hour in January 1997, peaked at 900 kg/hour in September 1997 and declined to less than 200 kg/hour towards the end of the study period in mid 2001. Although Hunter et al. (2002) could not conclusively identify the cause of the decline in catch rates, they concluded that it probably resulted from a combination of changes in stock abundance and fleet movements.

Status determination for ruby snapper in the WDTF is further complicated because the same stock is also harvested by fishers operating inshore from the WDTF—in state fisheries that are under the jurisdiction of the Western Australian Department of Fisheries. Additionally, recent multivariate analyses of otolith morphology suggest that records of historical ruby snapper catch have actually comprised distinct species (E. carbunculus and Etelis spp.)that are almost indistinguishable apart from differences in otolith shape (Wakefield et al. 2014). The Western Australian Department of Fisheries is currently undertaking a stock assessment to estimate recent fishing mortality of ruby snapper in the Pilbara demersal fishery (Stephen Newman, Western Australian Department of Fisheries, 2015, pers. comm.). The results of this assessment may provide an improved basis for future assessments of the status of ruby snapper in the WDTF.

Stock status determination

A weight-of-evidence approach based on catch and landing data since the 1992–93 fishing season (Figure 14.4), together with information published with the 2002 stock assessment (summarised above), has been used to determine stock status. There was no catch of ruby snapper in the WDTF in 2015–16. As a result, ruby snapper is classified as not subject to overfishing.The absence of a reliable estimate of population size and the stock's relatively long history of exploitation result in the stock biomass being classified as uncertain.

14.3 Economic status

Key economic trends

Fishing is opportunistic in the fishery, and catch levels have been variable in the past. Since 2003–04, catch has not exceeded 100 t. Eleven permits were held for both the 2014–15 and 2015–16 seasons; however, there were no active vessels in the fishery for either season. The limited effort, relatively low catch and small number of active fishing permits in previous years indicate that net economic returns have been low. For 2015–16, the lack of any fishing activity indicates that fishers expect limited economic return from operating in the fishery.

Management arrangements

The fishery has the same harvest strategy as the NWSTF (Chapter 6). The WDTF is managed through input controls (11 permits with a five-year duration).

Performance against economic objective

The fishery's performance against the economic objective is uncertain. Fishing has been opportunistic, with a range of species caught in low volumes, typically generating low overall value. Given these characteristics and no fishing activity during 2014–15 and 2015–16, low-cost management arrangements are appropriate.

14.4 Environmental status

The WDTF is included in the List of Exempt Native Specimens under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and is exempt from export controls until 22 December 2017.

The Western Trawl fisheries (NWSTF and WDTF) have been assessed to level 3 of the Australian Fisheries Management Authority (AFMA) ecological risk assessment (Zhou et al. 2009). No species were found to be at high risk at the current level of fishing effort.

AFMA publishes quarterly summaries of logbook reports of interactions with protected species on its website. As there was no fishing effort, no interactions with protected species listed under the EPBC Act were reported in the WDTF in 2016.

14.5 References

AFMA 2011, Harvest strategy for the Western Deepwater Trawl Fishery and North West Slope Trawl Fishery, Australian Fisheries Management Authority, Canberra.

—— 2012, North West Slope Trawl Fishery and Western Deepwater Trawl Fishery: statement of management arrangements, AFMA, Canberra.

Hunter, C, Dichmont, C & Venables, B 2002, Ruby snapper stock assessment (Western Deepwater Trawl Fishery), CSIRO, Brisbane.

Wakefield, CB, Williams, AJ, Newman, SJ, Bunel, M, Dowling, CE, Armstrong, CA & Langlois, TJ 2014, ‘Rapid and reliable multivariate discrimination for two cryptic eteline snappers using otolith morphometry', Fisheries Research, vol. 151, pp. 100–6.

Zhou, S, Fuller, M & Smith, T 2009, Rapid quantitative risk assessment for fish species in seven Commonwealth fisheries, report to AFMA, Canberra.

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Last reviewed:
09 Feb 2018