c h a p t e r 6 North West Slope Trawl Fishery 119

c h a p t e r 6

6 North West Slope Trawl Fisherya Sampaklis, m chambers and t Pham

F i g u r e 6 .1 Relative fishing intensity in the North West Slope Trawl Fishery, 2005–06 to 2008–09

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ta B l e 6 .1 Status of the North West Slope Fishery

Fishery status 2008 2009 Comments

Biological status Overfishing Overfished Overfishing Overfished

Deepwater prawns (6 spp.) Prawn stock modelling indicates a biomass recovery. Fishing mortality was low.

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

Non-equilibrium surplus production models indicate stock is not overfished. Catches are considered sustainable.

Economic statusFishery level

Estimates of net economic returns not available Economic status uncertain. High latency and low gross value of production indicate total net economic returns low.

not overfiShed / not Subject to overfiShing overfiShed / overfiShing uncertain not aSSeSSed

ta B l e 6 . 2 Main features and statistics of the North West Slope Trawl Fishery

Feature Description

Key target and byproduct species

Australian scampi (Metanephrops australiensis)Boschma’s scampi (Metanephrops boschmai)Velvet scampi (Metanephrops velutinus)Red prawn (Aristaeomorpha foliacea)Royal red prawn (Haliporoides sibogae)Giant scarlet prawn (Aristaeopsis adwardsiana)Red striped prawn (Aristeus virilis)Red carid prawn (Heterocarpus woodmasoni)White carid prawn (Heterocarpus sibogae)

Other byproduct species Goldband snapper (Pristipomoides multidens)Redspot emperor (Lethrinus lentjan)Saddletail snapper (Lutjanus malabaricus)See Table 6.4 for a list of other byproduct species.

Fishing methods Demersal trawl

Primary landing ports Darwin, Port Hedland, Broome

Management methods Input controls: limited entry (7 permits), gear restrictions (codend mesh size ≤50 mm)

Management plan AFMA statement of management arrangements 2004 (AFMA 2004)

Harvest strategy Western Trawl Fisheries Harvest Strategy—North West Slope Trawl Fishery (NWSTF) and Western Deepwater Trawl Fishery (WDTF) (AFMA 2007)

Consultative forums The Western Trawl Fisheries Management Advisory Committee was disbanded on 1 July 2009 and replaced by a small consultative panel tasked with focusing on strategic issues in the NWSTF and Western Deepwater Trawl Fishery.

Main markets Domestic: Perth, Sydney and Brisbane—fresh and frozenInternational: United States, Spain, China and Japan—frozen

EPBC Act assessments:—listed species (Part 13)—international movement of wildlife specimens (Part 13A)

Current accreditation dated 28 September 2005Current accreditation (Wildlife Trade Operation) expires 15 November 2010

Ecological risk assessment Level 1: Scale Intensity Consequence Analysis (SICA) completed on 157 species (AFMA unpublished)Level 2: Productivity Susceptibility Analysis (PSA) completed on 7 species (AFMA unpublished)Level 2.5: REsidual Risk Assessment (AFMA 2010)Level 3: Draft Sustainability Assessment of Fishing Effects (SAFE) assessment completed (Zhou et al. 2009)

Bycatch workplans North West Slope Trawl Fishery Bycatch and Discarding Workplan (31 October 2008–1 November 2010) (AFMA 2008)

Table 6.2 continues over the page

c h a p t e r 6 North West Slope Trawl Fishery 121

Feature Description

Fishery statisticsa 2007–2008 fishing season 2008–2009 fishing season

Fishing season 1 July 2007–30 June 2008 1 July 2008–30 June 2009

TAC and catch by species—scampi—deepwater prawns

TACNoneNone

Catch (tonnes)14.43.5

TACNoneNone

Catch (tonnes)33.7Zero

Effort 2022 hours of trawling 2449 hours of trawling

Fishing permits 7 7

Active vessels 3 2

Observer coverage 53 trawl hours (2.6%) 0 trawl hours (0%)

Real gross value of production (2008–09 dollars)

Confidential (<5 vessels) Confidential (<5 vessels)

Allocated management costs $0.11 million $0.14 million

EPBC Act = Environment Protection and Biodiversity Conservation Act 1999; ERA = ecological risk assessment; NWSTF = North West Slope Trawl Fishery; TAC = total allowable catch

a Fishery statistics are provided by fishing season unless otherwise indicated.

ta B l e 6 . 2 Main features and statistics of the North West Slope Trawl Fishery C O N T I N U E D

6 . 1 B a c k g r o u n d

The North West Slope Trawl Fishery (NWSTF) operates off north-western Australia from 114°E to about 125°E, between the 200-metre isobath and the outer boundary of the Australian Fishing Zone, taking into account Australian–Indonesian maritime boundaries (MOU Box; Fig. 6.1). The NWSTF has traditionally targeted scampi and deepwater prawns (Tables 6.2, 6.3).

Offshore Constitutional Settlement (OCS) arrangements between the Commonwealth and Western Australian governments specify management jurisdictions. Under the terms of the OCS, the Commonwealth via the Australian Fisheries Management Authority (AFMA) has management responsibility for all marine species taken by trawl in waters deeper than 200 m, while the Western Australian Government via the Department of Fisheries has responsibility for species taken with non-trawl methods in these waters (except tunas) and for all trawling in inshore waters. The OCS arrangements are currently under review; a temporary area closure implemented in 2007 was considered again in October 2009 and extended until December 2010 while this review takes place.

The Western Trawl Fisheries statement of management arrangements 2004 (AFMA 2004) aligns fishing seasons with financial years, and specifies a maximum of seven fishing permits, each valid for five years. Different vessels may fish on the same permit, provided that only one vessel is fishing at any time.

Scampi PHOTO: GAVIN KEWAN, AFMA

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ta B l e 6 . 3 History of the North West Slope Trawl Fishery

Year Description

1985 Fishing commenced in the NWSTF.

1987 Management of the Western Trawl Fisheries commenced on 1 July with the first of a series of annual development plans.

1987 to 1990 Fishing effort peaked at 18 600 trawl hours and prawn catch (predominantly red prawn) peaked at 876 t.

1987 to 1992 Substantial decline in scampi and prawn catch rates.

1991 to 1996 Catch comprised largely deepwater prawns (mainly royal red prawns), with squid (mostly Hawaiian flying squid—Nototodarus hawaiiensis) an important byproduct. A shift towards targeting of scampi subsequently occurred because markets for deepwater prawns had become less profitable and catch rates had fallen. Since 1993–94, scampi has accounted for more than 70% of the total reported catch by weight in the fishery, and on average the fishery accounts for around 70% of Australia’s total scampi production.

1996 Limited entry enforced through the issue of seven fishing permits.

1998 Recovery of scampi stocks confirmed through stock assessment.

2004 Western Trawl Fisheries statement of management arrangements (AFMA 2004) commenced in lieu of a management plan.

2005 A stock assessment by Lynch & Garvey (2005) indicated a decline in scampi stocks.

2006 to 2008 Targeted fishing of finfish (tropical snappers) saw the catch of scampi as a proportion of total catch by weight reduce to 33% and 19% from 2006 to 2008, respectively.

2007 Western Trawl Fisheries Harvest strategy adopted by AFMA. AFMA issued a direction that precluded fishing from areas in the north of the fishery <200 m for two years to reduce targeting of finfish such as goldband snapper, saddletail snapper and redspot emperor, and to amend the OCS boundaries.

2009 Western Trawl Fisheries Management Advisory Committee disbanded and replaced by a small consultative panel. The area closure in the north of the fishery extended until 31 December 2010. Consequently, the NWSTF has returned to a scampi-dominated fishery—in 2008–09, approximately 95% of the total reported catch was scampi.

AFMA = Australian Fisheries Management Authority; OCS = Offshore Constitutional Settlement; NWSTF = North West Slope Trawl Fishery

6 . 2 h a rv e s t s t r at e g y

A combined Western Trawl Fisheries Harvest Strategy (HS), which applies to the NWSTF as well as the Western Deepwater Trawl Fishery (see Chapter 19), reflects the mixed-species composition and opportunistic nature of the two fisheries. The HS acknowledges that there are no target reference points in terms of maximum economic yield (MEY). It aims to strike a balance between precautionary management arrangements and allowing industry to capitalise on fishing opportunities, while emphasising the need to collect biological data.

There are three catch trigger rules to initiate management actions that progressively increase requirements on the fisheries for data collection and analysis (Levels 1 and 2) and establish limit reference points for the target stocks (Level 3). Separate triggers and control

rules apply to vulnerable species identified through the ecological risk assessment (ERA) process; the Level 1 and Level 2 ERA results have not yet been published by AFMA.

The HS prescribes species-specific multilevel catch thresholds that initiate alternative management arrangements, such as catch limits and spatial closures. In the absence of other information or assessments, the triggers for target species are based on the highest historical catch. Level 1 is half the highest historical catch, Level 2 is the highest historical catch, and Level 3 is double the highest historical catch. In the case of the NWSTF, zone-specific trigger levels (based on relative historical catch) may in future be applied across three longitudinal areas.

The Level 1 trigger initiates an investigation to reveal why the trigger has been reached. This is undertaken through analysis of logbooks and examination of

c h a p t e r 6 North West Slope Trawl Fishery 123

some of which also fish in the Western Deepwater Trawl Fishery and the Western Australian State fisheries (Table 6.3).

The closure of the north-east extremity of the fishery in late 2007 (Fig. 6.1) resulted in a reduction in landings of tropical snappers and other finfish to negligible levels (<100 kg).

deepwater prawns

Deepwater prawns have previously been considered a target in this fishery, with catches in the late 1980s accounting for most of the total landings by weight. It would appear that deepwater prawns have not been seriously targeted since the early 1990s, and these species are now classified as byproduct. Annual reported prawn catch has typically been less than 1 t in recent years, and no catch of deepwater prawns was recorded in 2008–09. Observer reports from the fishery suggest that the quantity of discarded prawn bycatch might be substantially higher than the recorded catch (AFMA pers. comm.).

Scampi

Total scampi catch (33.7 t) in the fishery in 2008–09 was more than double the catch recorded in the previous year. This is likely to be due in part to fishing effort being targeted at scampi rather than finfish. In addition, total trawl effort increased and catch rates were high relative to the previous 10 years.

standardised catch per unit effort (CPUE) data. It may also result in expert consultation and a possible revision of limit reference points. The Level 2 trigger results in stock assessments using biological parameters, such as size-specific fishing mortality, natural mortality, growth and reproduction. A revision of trigger values is also undertaken. Exceeding the Level 3 trigger results in a cessation of targeted fishing effort, pending a stock assessment and expert consultation.

The trigger values for target species in the NWSTF are:

Level 1: scampi 50 t, prawns 9 t•Level 2: scampi 100 t, prawns 18 t•Level 3: scampi 200 t, prawns 36 t.•

The HS also specifies control rules for species identified as high risk under the ERA framework. The measures include 50 animal move-on provisions for high-risk chondrichthyans (sharks). High-risk teleosts (bony fish) and crustaceans have two trigger levels: an intermediate trigger of 2 t (in effect initiating the same management responses as the Level 1 trigger for target species) and a catch limit of 4 t (Level 2).

6 . 3 t h e 2 0 0 9 F i s h e ry ( 2 0 0 8 – 0 9 F i s h i n g s e a s o n )

key target and byproduct species

Two vessels were active in the fishery in 2008–09 and predominantly targeted scampi (Table 6.2). A total of 33.7 t of scampi were landed in 2008–09, but no deepwater prawns (Figs. 6.2, 6.3). Fishing effort in 2008–09 was approximately 2400 hours, roughly 20% higher than in 2007–08, but still much less than the peak of 18 600 hours in 1987–88.

In the past, vessels based in the Northern Prawn Fishery (NPF) have fished opportunistically in the NWSTF. This has not been the case in the past two years, and effort in the fishery has been dominated by vessels based in Western Australia,

Boxed scampi PHOTO: GAVIN KEWAN, AFMA

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model in the Western Australian Northern Demersal Scalefish Managed Fishery, adjacent to the NWSTF, indicated that breeding stock levels of tropical snappers were adequate to maintain the stock above limit reference points; there have been recent concerns about effort levels (Newman & Skepper 2007). The stock assessment is currently under review (Newman & Skepper 2009).

In order to reduce fishing pressure on tropical snapper stocks, AFMA implemented the closure in the north-east of the NWSTF in depths less than 200 m. The area closure lapsed in October 2009 but was renewed to 31 December 2010. Trigger limits for goldband snapper and red emperor were introduced through the HS review process to ensure sustainability of these species. An assessment of the extent and variety of byproduct (notably finfish) is among the most pressing research needs for the NWSTF, together with the collection of biological data for assessment purposes.

minor byproduct speciesThe combined catch of finfish in 2008–09 (1.5 t) was substantially lower than in 2005–06 and only a small amount of sharks were landed (approximately 0.1 t). A total of 22.6 t of finfish were landed over the period 2005–06 to 2008–09 (Table 6.4). Reductions in catch of goldband snapper (Pristipomoides multidens), redspot emperor (Lethrinus lentjan) and saddletail snapper (Lutjanus malabaricus) were particularly pronounced, owing to the temporary closure of depths below 200 m in the north-east of the fishery (implemented in 2007). Observer reports suggest that total discards might account for a large proportion (perhaps more than 80%) of total catches by weight; however, observer coverage in this fishery is low (zero in the 2008–09 fishing season) (Table 6.2).

Stocks of finfish in the area of the fishery were not assessed in 2009. An assessment of goldband snapper and redspot emperor in 2002 using an age-structured stock assessment

ta B l e 6 . 4 Minor byproduct stocks in the NWSTF

SpeciesTaC or trigger

2005–06 to 2008–09 catch (tonnes)

2005–06 to 2008–09 discards (tonnes)

Goldband snappers (Pristipomoides multidens, P. typus) None 49 1.3

Redspot emperor (Lethrinus lentjan) None 31 0

Saddletail snapper (Lutjanus malabaricus) None 15 0

Mixed fish None 14 21

Squids (Teuthoidea) None 3 0

Bigeye seabream (Gymnocranius grandoculis) None 6 0

Red emperor (Lutjanus sebae) None 4 0.3

Crimson snapper (Lutjanus erythropterus) None 4 0

Painted sweetlip (Haemulidae, except Pomadasys spp.) None 3 0

Pearl perch (Glaucosoma spp.) None 2 0

Mangrove jack (Lutjanus argentimaculatus) None 2 0

Spangled emperor (Lethrinus nebulosus) None 2 0

Sweetlips (Plectorhinchus spp.) None 1 0

c h a p t e r 6 North West Slope Trawl Fishery 125

ta B l e 6 . 5 Biology of deepwater prawns

Parameter Description

General Deepwater prawn species vary in their life history traits, but all are found on sandy and/or muddy bottoms, making them susceptible to trawling. They have a low productivity compared with related inshore species.

Range Species: Coastal waters worldwide. In Australia, they are distributed along the north-west, west and east coasts.Stock: A basket stock of six species, with red prawn (Aristaeomorpha foliacea) dominating historical catches.

Depth 250–800 m

Longevity ~5 years

Maturity (50%) age: ~1 yearSize: 20–36 mm CL (for female Aristaeomorpha foliacea)

Spawning season Royal red prawn is known to spawn biannually off New South Wales in February–April and July–August.

Size Maximum: 55 mm CL (Aristeus virilis), 60 mm CL (Aristaeomorpha foliacea), 40 mm CL (Heterocarpus sibogae), 35 mm CL (Heterocarpus woodmasoni), 45 mm CL (Haliporoides sibogae), 80 mm CL (Aristaeopsis edwardsiana)Recruitment into the fishery: 1–4 years; size 20 mm CL (Heterocarpus woodmasoni, H. sibogae, Haliporoides sibogae), 30 mm CL (Aristaeomorpha foliacea, Aristeus virilis;), 40 mm CL (A. edwardsiana)

CL = carapace length

SOURCES: Wadley (1992a, b); Baelde (1994)

1988−89 1992−93 1996−97 2000−01 2004−05 2008−090.0

0.2

0.4

0.6

0.8

1.0

Figure 6.2 Catch: deepwater prawns, NWS

Cat

ch (

tho

usa

nd

to

nn

es)

F i g u r e 6 . 2 Deepwater prawn catch history, 1985–86 to 2008–09

6 . 4 B i o l o g i c a l s tat u s

deePWater PraWnS(multiple species)

LINE DRAWINGS: FAO

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ScamPi(Metanephrops australiensis, M. boschmai, M. velutinus)

LINE DRAWING: FAO

ta B l e 6 . 6 Biology of scampi

Parameter Description

General Scampi aggregate along muddy bottoms of continental slopes and build extensive burrows. They are relatively slow growing and long lived, with moderately low fecundity.

Range Species: In Australia, scampi occur on the north-west slope in Western Australia up into the Timor Sea, along continental slopes.Stock: The stock comprises three species, and most fishing effort is centred on suitable grounds north-east of the Rowley Shoals. A single stock is assumed for management and assessment purposes.

Depth 250–500 m

Longevity 10–12 years (for M. australiensis)

Maturity (50%) age: 3–5 years (for M. australiensis)Size: ~40 mm CL (for M. boschmai and M. velutinus), 45 mm CL (for M. australiensis)

Spawning season Timing of spawning unknown, though likely to spawn annually

Size Maximum: ~50 mm CL (for M. boschmai), 60 mm CL (for M. velutinus), 70 mm CL (for M. australiensis)Recruitment into the fishery: >3 years; ~45 mm CL (for M. australiensis)

CL = carapace length

SOURCES: Davis & Ward (1984); Rainer (1992).

stock status determinationIt is believed that deepwater prawns have not been targeted in the NWSTF since 1993 (Fig. 6.2) as the stock was in a highly depleted state (AFMA pers. comm.). The recovery of the prawn stock was modelled by the ABARE–BRS under the RUSS project, using delay difference models incorporating known biological parameters (Table 6.5). Given the maximum observed annual catch, and the fact that the stock was assumed to be in a highly depleted state at the end of 1993, a conservative estimate of the unfished stock biomass of 872 t was used. Given the potential levels of unreported discards the deepwater prawn stock would be expected to recover to a biomass similar to that prior to fishing within five or six years. Based primarily on the results of the delay difference modelling, the stock is assessed as not overfished. The negligible reported catch of deepwater prawns, even assuming discards, in recent years indicates that the stock is not subject to overfishing (Table 6.1).

reliability of the assessment/sBecause a full quantitative stock assessment has not been conducted, the current deepwater prawn biomass as a proportion of the unfished biomass is not precisely known. However, the minimal targeting of prawns, the fact that most of the fishing effort is not on prawn grounds, the relatively low effort in the fishery for more than 15 years, and the productivity of prawns means that the status of the stock as not overfished and not subject to overfishing can be regarded with confidence.

previous stock assessment/sNot previously assessed.

Future assessment needsShould targeted fishing of deepwater prawns recommence, biological information for each prawn species would need to be collected before the stocks could be assessed. All existing data collected by AFMA observers detailing prawn bycatch should be compiled and examined. Reliable catch data would need to be collected, and deepwater prawn bycatch and discards needs to be recorded in logbooks. Understanding the targeting practice of operators (for prawns rather than scampi) and a summary of changes in fishing gear used over time would assist in interpreting catch and effort data from the fishery.

c h a p t e r 6 North West Slope Trawl Fishery 127

decreased quickly after fishing began in the mid-1980s, before a steady recovery from 1991 to 1996. The model was tested for sensitivity to different assumed stock structures, as well as annual increases in fishing power of 1% and 2%. Both Schaefer and Fox forms of surplus production models were tested. The assessed status of the scampi stock was robust to all sensitivities tested, and general agreement between all models was good, suggesting that the assessment is likely to be reliable.

previous assessment/sA 2005 assessment (Lynch & Garvey 2005) examined trends in CPUE in a number of ways and also considered the length–frequency distribution of the scampi data. Although declines in CPUE were observed between 1985 and 2003, in general, the magnitudes of the declines did not raise concerns. No substantial change in size range of scampi was observed. This contrasts with anecdotal evidence from industry suggesting that the size of scampi catch had decreased. The 2005 assessment was not considered sufficiently robust to provide a reliable assessment of stock status.

Future assessment needsFuture assessments would benefit from improved data on biological parameters. A stock assessment of scampi was identified as a priority for the NWSTF by the Western Trawl Fisheries Management Advisory Committee (WestMAC) in 2007–08. The ABARE–BRS assessment referenced in this report should be submitted to the newly formed consultative panel for comment.

6 . 5 e c o n o m i c s tat u s

economic performanceNo economic surveys of the fishery have been conducted. Catch is confidential for 2007–08 and 2008–09, and the only readily available indicator of economic performance is the level of latent effort.

1988−89 1992−93 1996−97 2000−01 2004−05 2008−090.00

0.05

0.10

0.15

0.20

Figure 6.3 Catch: scampi, NWS

Cat

ch (

tho

usa

nd

to

nn

es)

F i g u r e 6 . 3 Scampi catch history, 1985–86 to 2008–09

stock status determination

An assessment of the scampi stock was conducted under the RUSS project using non-equilibrium surplus production models (ABARE–BRS unpublished). Fox and Schaefer surplus production models (see Polacheck et al. 1993) were fitted to catch and effort data with a stock production model using covariates (ASPIC) (Prager 1994). The analyses suggested that the combined scampi biomass in 2008 was between 1.7 BMSY and 2.2 BMSY, equivalent to 65–85% of the unfished biomass. It is estimated that catch levels in recent years (Fig. 6.3) have been well within sustainable limits. Therefore, the scampi stock has been assessed as not overfished and not subject to overfishing (Table 6.1).

reliability of the assessment/s

Surplus production models are relatively simple, incorporating only a time series of annual catch and an index of abundance, which in this case was provided by a standardised CPUE series. Despite their simplicity, surplus production models have been shown to provide more accurate and precise estimates than more complex methods in some situations (Polacheck et al. 1993). Surplus production models are less reliable when the index of abundance used exhibits little contrast or when a continual decline in biomass is suggested. The index of abundance produced for the combined scampi stock suggests that biomass

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latencyEffort is restricted in the NWSTF by a limit on the number of vessel permits. In 2008–09 seven permits existed in the fishery. Given that only two vessels fished in 2008–09 and three in the previous year, some latent effort is present, possibly indicating low net economic returns from fishing.

overall economic statusIn the past, the vessels operating in the NWSTF tended to be NPF trawlers that fished opportunistically while the NPF was closed. However, none of the vessels that have operated in the NWSTF since 2007 have fished in the NPF in the same period. Despite this development, there is significant latency and a low gross value of production (not generally higher than one million dollars per year), indicating that economic returns for the fishery are not likely to be large.

future considerationsThe fishery is currently managed using input controls, primarily in the form of limited entry. After reviewing the potential to implement individual transferable quotas in the fishery in 2006, WestMAC concluded that these quotas do not appear to be a viable option for the fishery at this time and that the fishery should continue to be managed using input controls (WestMAC 2006).

6 . 6 e n v i r o n m e n ta l s tat u s

Commercial fishing is excluded in three marine protected areas in the NWSTF: the Cartier Island Marine Reserve, the Ashmore Reef National Nature Reserve and the Mermaid Reef Marine National Nature Reserve (part of the Rowley Shoals). There have been no reports of illegal fishing in the NWSTF.

ecological risk assessment

AFMA’s ERAs provide an inventory of high-risk species, based on their productivity (life history) and susceptibility to fishing. The ERAs consider target, byproduct, and threatened, endangered or protected (TEP) species. Based on the ERA process one high-risk species, giant scarlet prawn, was identified (AFMA 2010). Following completion of the residual risk assessment, giant scarlet prawn remained in the high-risk category and was incorporated into the HS for the fishery. The ERA results will be reviewed in detail in the next Fishery status reports.

threatened, endangered and protected species (sharks, marine turtles and seabirds)

No interactions with TEP species were reported in the NWSTF during 2008–09.

Pt Samson Harbour berths PHOTO: GAVIN KEWAN, AFMA

Pt Samson Harbour entrance PHOTO: GAVIN KEWAN, AFMA

c h a p t e r 6 North West Slope Trawl Fishery 129

The scampi stock assessment conducted by the ABARE–BRS indicates that an annual scampi catch below the Level 1 trigger of 50 t would be sustainable. However, if annual catches were to regularly exceed 70 t, the stock would need to be carefully reassessed. The limit reference point for scampi of 200 t suggested by the Level 3 trigger is well above the estimated maximum sustainable yield of the stock.

The Western Trawl Fisheries statement of management arrangements (AFMA 2004) stipulates a maximum codend mesh size in the NWSTF of 50 mm to discourage the trawling of demersal finfish. An increase in mesh size would be expected to reduce bycatch of prawns and small fish. As an alternative to the current maximum codend mesh size, the targeting of finfish could be discouraged by mandating the use of bycatch reduction devices, such as square mesh windows or Nordmøre sorting grids (e.g. Hartill et al. 2006). The merits of the current strategy compared with alternatives should be considered.

6 . 8 l i t e r at u r e c i t e d

AFMA (Australian Fisheries Management Authority) 2004, Western Trawl Fisheries statement of management arrangements, AFMA, Canberra.

——2007, Western trawl fisheries harvest strategy—North West Slope Trawl Fishery (NWSTF) and Western Deepwater Trawl Fishery (WDTF), AFMA, Canberra.

——2008, North West Slope Trawl Fishery Bycatch and Discarding Workplan 31 October 2008–1 November 2010, AFMA, Canberra.

——2010, Residual risk assessment of Level 2 Ecological Risk Assessment species results, report for the North West Slope Trawl Fishery, AFMA, Canberra.

Baelde, P 1994, ‘Royal red prawn, Haliporoides sibogae’, in RJ Tilzey (ed), The South East Fishery: a scientific review with reference to quota management, Bureau of Resource Sciences, Canberra, pp. 257–64.

benthic habitatsDemersal trawling can have a significant impact on the sea floor by reducing the structural complexity of the environment, and crushing, burying or exposing marine organisms. The recovery potential of benthic assemblages depends on the growth potential of structure-forming organisms and the period of time between disturbances (Watling & Norse 1998). The most susceptible areas tend to be those that do not experience disturbance, such as shelf and slope habitats, and those that rely on slow-growing organisms for habitat complexity (e.g. coral reefs) (Watling & Norse 1998). Most work on characterising benthic assemblages has focused on the shelf habitat, and there is a paucity of information on the slope habitat.

Demersal trawl gear is used in the NWSTF, with fishing for scampi and prawns occurring over soft, muddy sediments or sandy habitats, typically at depths of 350–600 m on the continental slope. In 2006–07 and 2007–08, some targeting of finfish in shallower waters may have resulted in interactions with reef habitat.

6 . 7 h a rv e s t s t r at e g y p e r F o r m a n c e

The HS has been implemented and the reported catch levels of scampi and deepwater prawns have not exceeded the first trigger level, and so the control rules have not been enacted. The reference period used in the HS to set the trigger levels appears to be from the recent past and therefore excludes large catches taken in the late 1980s and early 1990s. The result is that prawn triggers may be lower than necessary. At present, the majority of prawn catch is likely to be unreported discards. If prawn discards were considered, it is possible that HS triggers for the deepwater prawn stock would have been activated. However, annual prawn catch of 100 t is most likely sustainable, and prawn discards in the NWSTF are unlikely to approach this level while fishers target scampi (due to the differences in fishing area).

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Wadley, VA 1992a, ‘Distribution, growth and reproductive development of giant red prawn, Aristaeomorpha foliacea (Risso, 1827), in the North West Slope Trawl Fishery’, in SF Rainer (ed), The fisheries biology of deepwater crustaceans and finfish on the continental slope of Western Australia, final report to the FRDC, FRDC project 1988/74.

——1992b, ‘The Biology of Scampi, Prawns, Carids, Bugs and Crabs Exploited by Deepwater Trawling’, in SF Rainer (ed), The fisheries biology of deepwater crustaceans and finfish on the continental slope of Western Australia, final report to the FRDC, FRDC project 1988/74.

Watling, L & Norse, EA 1998, ‘Disturbance of seabed by mobile fishing gear: a comparison to forest clearcutting’, Conservation Biology, vol. 12, no. 6, pp. 1180–97.

WestMAC (Western Trawl Fisheries Management Advisory Committee) 2009, MAC chair’s summary, Fremantle, 10 June 2009, AFMA, Canberra.

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

Davis, TLO & Ward, TJ 1994, ‘CSIRO finds two new scampi grounds off the North West Shelf’, Australian Fisheries, vol 43, pp. 41–7.

Hartill, BW, Cryer, M & MacDiarmid, AB 2006, ‘Reducing bycatch in New Zealand’s scampi trawl fisheries’, New Zealand Aquatic Environment and Biodiversity Report no. 4, New Zealand. Ministry of Fisheries, Wellington.

Holloway, PE, Humphries, SE, Atkinson, M & Imberger, J 1985, ‘Mechanisms for nutrient supply to the Australian north-west shelf’, Australian Journal of Marine and Freshwater Research, vol. 36, pp. 753–64.

Lynch, AW & Garvey, JR 2005, North West Slope Trawl Fishery scampi stock assessment 2004, AFMA, Canberra.

Newman, SJ & Skepper, C 2007, ‘Northern Demersal Scalefish Managed Fishery status report’, in WJ Fletcher & K Santoro (eds), State of the fisheries report 2006/07, Department of Fisheries, Western Australia, pp. 161–8.

——2009, ‘North Coast Demersal Fisheries status report’, in WJ Fletcher & K Santoro (eds), State of the fisheries report 2008/09, Department of Fisheries, Western Australia, pp. 149–69.

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