Chapter 14: Western Deepwater Trawl Fishery
C Harte and R Curtotti
TABLE 14.1 Status of the Western Deepwater Trawl Fishery
| 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||Uncertain||Fishing mortality levels are unlikely to constitute overfishing. No reliable|
estimate of biomass.
|Economic status||Limited fishing activity occurred in the fishery during the 2016–17 fishing season.|
Estimates of NER for previous years are not available, but a low number of active vessels in recent years indicates that NER have been low.
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.
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, although fishing effort (and consequently catch) has decreased substantially in recent years.
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 (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. A single vessel was active in the 2016–17 fishing season.
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, 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 has been relatively low in recent years, consisting mostly of deepwater bugs, with minimal catch of finfish. Catches in 2016–17 remained at low levels following two years of no catch or effort (Table 14.2; Figure 14.2).
TABLE 14.2 Main features and statistics for the WDTF
|Fishery statistics a||2015–16 fishing season||2016–17 fishing season|
(t)||Real value (2015–16)||TAC
(t)||Catch (t)||Real value (2016–17)|
|Effort||0||11 days, 180.5 trawl-hours|
|Observer coverage||0 days (0%)||0 days (0%)|
|Fishing methods||Demersal trawl|
|Primary landing ports||Carnarvon, Fremantle|
|Management methods||Input controls: limited entry (11 permits), gear restrictions|
|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. Real-value statistics are provided by financial year, which is also 1 July – 30 June.
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 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. Catches increased in 2016–17, but were still low compared with historical catch (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. The low fishing effort, low catch levels and sporadic targeting of key commercial species make it difficult to quantitatively assess stock status.
Stock status determination
There was minimal fishing in the WDTF in 2016–17 (Figure 14.3). As a result, deepwater bugs are classified as not subject to overfishing.There are currently few 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.)
Line drawing: FAO
The stock structure of ruby snapper caught in the WDTF is uncertain. In the absence of clear information on biological stock structure, stock is assessed at the fishery level.
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 a single vessel active in the fishery in 2016–17 (Figure 14.4).
The only stock assessment for ruby snapper 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/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, Dichmont & 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.
Status determination for ruby snapper in the WDTF is further complicated because the same stock may also be 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 two distinct species (E. carbunculus and Etelis spp.)that are almost indistinguishable apart from differences in otolith shape (Andrews et al. 2016; 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 2016–17. 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 in the 2015–16 season, which decreased to four in the 2016–17 season. There were no active vessels in the fishery in the 2015–16 season and one active vessel in the 2016–17 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 2016–17, the limited fishing activity and low level of catch indicate that fishers expect limited economic return from operating in the fishery.
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 limited fishing activity during 2015–16 and 2016–17, 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 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 2017.
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.
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.