Western Deepwater Trawl Fishery
Chapter 14: Western Deepwater Trawl Fishery
N Mazloumi, J Woodhams and AH Steven
|Biological status||Fishing mortality||Biomass||Fishing mortality||Biomass|
|Deepwater bugs (Ibacus spp.)||Not subject to overfishing||Uncertain||Not subject to overfishing||Uncertain||Fishing mortality levels are unlikely to constitute overfishing. No reliable estimate of biomass.|
|Ruby snapper (Etelis carbunculus, Etelis spp.)||Not subject to overfishing||Uncertain||Not subject to overfishing||Not overfished||Fishing mortality levels are unlikely to constitute overfishing. Biomass above the limit reference point.|
|Economic status||Estimates of NER are unavailable, and gross value of production is confidential because of the low number of active vessels in the fishery. Fishing catch and the number of active vessels have been historically low. An increase in catch and active vessels in the 2017–18 fishing season may indicate economic improvement in the fishery; however, this may have been offset by the increase in fishing effort and fuel prices, which increase costs in the fishery. Therefore, whether NER increased or decreased in the 2017–18 fishing season is uncertain.|
Note: NER Net economic returns.
14.1 Description of the fishery
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). There have been recent changes to the boundary of this fishery to more closely align with the 200 m isobath. Effort in recent years has been localised in the area offshore and slightly south of Shark Bay in Western Australia.
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 isobath, 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. A wide variety of finfish species made up the catch in 2017–18, with deepwater bugs and ruby snapper (Etelis sp.) making up around 50% of the whole catch.
The fishery is managed under the same harvest strategy as the NWSTF (AFMA 2011; see Chapter 6).
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 and deepwater bugs. Total fishing effort was comparatively low between 2005–06 and 2016–17. While only three vessels were active again in 2017–18, trawl-hours increased markedly to just over 1,100 hours (Table 14.2).
Catch in the WDTF has been variable, peaking at around 378 t in 1994–95 and then again at 347 t in 2001–02. The peak in catch in the early to mid 1990s consisted mostly of orange roughy, whereas 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 had been relatively low in recent years, consisting mostly of deepwater bugs, with minimal catch of finfish. However, catches increased substantially in 2017–18, consisting mostly of ruby snapper, deepwater bugs and mixed fish (Table 14.2; Figure 14.2).
|Fishery statistics a||2016–17 fishing season||2017–18 fishing season|
|Stock||TAC (t)||Catch (t)||GVP (2016–16)||TAC (t)||Catch (t)||GVP (2017–18)|
|Effort||11 days, 180.5 trawl-hours||100 days, 1,108.3 trawl-hours|
|Observer coverage||0 days (0%)||6 days (6%)|
|Fishing methods||Demersal trawl|
|Primary landing ports||Carnarvon, Fremantle (Western Australia)|
|Management methods||Input controls: limited entry (11 permits), gear restrictions|
Catch controls: trigger limits for key commercial species
|Primary markets||Domestic: Brisbane, Perth, Sydney—frozen, chilled|
International: Japan, Spain, United States—frozen
|Management plan||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 – 30 June. Value statistics are provided by financial year, which is also 1 July – 30 June.
Notes: GVP Gross value of production. TAC Total allowable catch. – Not applicable.
14.2 Biological status
Deepwater bugs (Ibacus spp.)
Line drawing: FAO
The WDTF targets several species of deepwater bugs. Stock structure of these species is not known, and they are grouped into a multispecies stock for status assessment.
The catch history of deepwater bugs in the WDTF is characterised by relatively low levels of catch in most years, with four years of relatively high catches between 2001–02 and 2004–05, peaking at 160 t in 2002–03 (Figure 14.3). In 2017–18, catch was 22.1 t, up from around 7.6 t in 2016–17 and zero for the two seasons before this period (Figure 14.3).
A formal stock assessment for deepwater bugs has not been done, and little information is available with which to assess stock status. Relatively low levels of fishing effort, low levels of catch and sporadic targeting of key commercial species make it difficult to quantitatively assess stock status.
Stock status determination
Catch of bugs in the WDTF in 2017–18 was the highest since the historical peak in 2001–02 to 2004–05. There is no current or reliable indication of what sustainable catch might be for this stock. However, catch of bugs in the WDTF over the preceeding decade was relatively low, averaging less than 10 t. This level of catch is substantially below the levels of bug catch taken on the east coast of Australia, where stocks are considered to be sustainable (Stewardson et al. 2018) (Figure 14.3). Given that recent catches have been relatively low and localised, and catches of the same complex of species in another fishery are substantially higher and considered to be sustainable, the level of catch in the WDTF is be unlikely to drive the stock into an overfished state. As a result, deepwater bugs are classified as not subject to overfishing. While catches remain relatively low, it is unlikely that the stock would be considered as being subject to overfishing. However, given the absence of reliable information on sustainable catch levels, if catches continue to increase, additional information may be required that confirms these levels of catch are sustainable in the long term to avoid an uncertain fishing mortality status classification. Few empirical data inform the biomass status for this stock. As a result, the level of biomass of the stock is uncertain.
Ruby snapper (Etelis carbunculus and Etelis spp.)
Line drawing: FAO
Four species of Etelis are captured in the WDTF, although ruby snapper (Etelis sp.) is the most commonly captured. A recent taxonomic revision of ruby snapper revealed two morphologically similar species that are now recognised as Etelis sp. (ruby snapper) and Etelis carbunculus (pygmy ruby snapper) (Andrews et al. 2016; Wakefield et al. 2014; Williams et al. 2017). However, catches for these two species are currently reported as a single species. The stock structure of ruby snapper caught in the WDTF is uncertain. In the absence of clear information on biological stock structure, this stock is assessed at the fishery level.
Catches of ruby snapper in the WDTF peaked in 2000–01 (around 70 t), with a smaller peak in 2008–09 (around 24 t). Catches were relatively small between 2010–11 and 2016–17, but increased in 2017–18 to 28 t (Figure 14.4).
The only stock assessment for ruby snapper in the WDTF was published in 2002 (Hunter, Dichmont & Venables 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 slow growth rate and aggregates in restricted continental-shelf habitats. Hunter, Dichmont & Venables (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/hr in January 1997, peaked at 900 kg/hr in September 1997 and declined to less than 200 kg/hr towards the end of the study period in mid 2001. Although Hunter, Dichmont and Venables (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.
The WDTF overlaps with Western Australian state-managed demersal fisheries that also target ruby snapper. Therefore, it is highly likely that these fisheries are exploiting the same stock of ruby snapper. Catch-curve and spawner-per-recruit analyses using direct age data from 1997 and 2011 were used to assess the status of ruby snapper in Western Australian fisheries (Wakefield et al. forthcoming). Results indicated that the stock was at approximately 60% of the unfished biomass level in 1997 and 2011. Fishing mortality rates were relatively low for 1997 (0.04) and 2011 (0.05) compared with the estimated natural mortality rate of 0.11 per year, which suggests that the stock was not subject to overfishing during those periods.
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 and the assessments undertaken for Western Australian state-managed fisheries (summarised above), were used to determine stock status.
Although catch in 2017–18 was the third largest on record for the fishery, and substantially above that of previous years, catches of ruby snapper in the WDTF over the past decade have been relatively low (average around 11 t). There is no current or reliable indication of what the sustainable catch might be for this stock. However, the assessment of the ruby snapper stock from the Western Australian state-managed fisheries indicates that the biomass of the stock was well above the Commonwealth’s limit reference point of 0.2B0 in 1997 and 2011. Catches from 2011 to 2016–17 were substantially lower than in previous years, and likely well below levels that would drive the stock into an overfished state. It is also unlikely that the catch increase to 28 t for a single year (2017–18) would be sufficient to drive the stock into an overfished state. As a result, ruby snapper is classified as not overfished and not subject to overfishing.
14.3 Economic status
Key economic trends
Net economic returns (NER) are unavailable for the WDTF. The gross value of production (GVP) of the fishery is confidential because of the low number of active vessels. Historically, fishing has been opportunistic in the fishery, and catch levels have been variable.
The number of permits, the number of active vessels and fishing effort all increased in the 2017–18 fishing season, suggesting increased incentive to participate in the fishery. Total catch increased more than 10-fold to around 102 t (the 2017–18 fishing season was the first year since 2003–04 when catch exceeded 100 t), indicating increased fishing income. However, the increases in the number of active boats, fishing effort (hours trawled) and higher fuel prices are likely to have increased the total operating cost for the fishery. Therefore, whether NER increased or decreased in the 2017–18 fishing season is uncertain.
Changes in species catch composition in the fishery can indicate changes in the economic incentives to target different species. Of the target species, bugs represented 91% of the total catch in 2016–17, decreasing to 22% in 2017–18. Ruby snapper value may have increased in the 2017–18 season; it represented 0% of the catch in 2016–17, increasing to 27% in 2017–18. Catch of other species represented 9% in 2016–17 and increased to 51% in 2017–18, also indicating increased economic value of non-target species.
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. Historically, fishing has been opportunistic, with a range of species caught in low volumes, typically generating low overall value. Given these characteristics, low-cost management arrangements are appropriate. However, management structures may require review if catch continues to trend upwards.
14.4 Environmental status
The WDTF is included on the List of Exempt Native Specimens under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and is exempt from export controls until 18 December 2020.
The Western Trawl fisheries (NWSTF and WDTF) have been assessed to level 3 of the Australian Fisheries Management Authority (AFMA) ecological risk assessment (Zhou, Fuller & Smith 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. No interactions with protected species listed under the EPBC Act were reported in the WDTF in 2018.
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.
Andrews, KR, Williams, AJ, Fernandez-Silva, I, Newman, SJ, Copus, JM, Wakefield, CB, Randall, JE & Bowen, BW 2016, ‘Phylogeny of deepwater snappers (genus Etelis) reveals a cryptic species pair in the Indo-Pacific and Pleistocene invasion of the Atlantic’, Molecular Phylogenetics and Evolution, vol. 100, pp. 363–71.
Hunter, C, Dichmont, C & Venables, B 2002, Ruby snapper stock assessment (Western Deepwater Trawl Fishery), CSIRO, Brisbane.
Stewardson, C, Andrews, J, Ashby, C, Haddon, M, Hartmann, K, Hone, P, Horvat, P, Klemke, J, Mayfield, S, Roelofs, A, Sainsbury, K, Saunders, T, Stewart, J, Nicol, N & Wise, B (eds) 2018, Status of Australian fish stocks reports 2018, Fisheries Research and Development Corporation, Canberra.
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.
——, Williams, AJ, Fisher, EA, Hall, NG, Hesp, SA, Halafihi, T, Kaltavara, J, Vouorey, E, Taylor, BM, O’Malley, JO, Nicol, SJ & Newman, SJ forthcoming, ‘Variations in life history characteristic of the deep-water giant ruby snapper (Etelis sp.) between the Indian and Pacific oceans: stock status for north-western Australia’.
Williams, AJ, Wakefield, CB, Newman, SJ, Vourey, E, Crespo, FA, Halafihi, T, Kaltavara, J & Nicol, SJ 2017, ‘Oceanic, latitudinal and sex-specific variation in demography of a tropical deepwater snapper across the Indo-Pacific region’, Frontiers in Marine Science, 4:382, doi: 10.3389/fmars.2017.00382, accessed 22 May 2019.
Zhou, S, Fuller, M & Smith, T 2009, Rapid quantitative risk assessment for fish species in seven Commonwealth fisheries, report to AFMA, Canberra.