© Baker, J.L. (2009) Marine Species of Conservation Concern in South Australia Full citation Baker, J.L. (2009) Marine Species of Conservation Concern in South Australia: Volume 1 - Bony and Cartilaginous Fishes. Report for the South Australian Working Group for Marine Species of Conservation Concern. J. Baker (consultant); Science and Conservation Division, and Coast and Marine Conservation branches of S.A. Department for Environment and Heritage (DEH); Marine and Coastal Community Network of S.A. (MCCN), and Threatened Species Network (TSN). Web version published by Reef Watch, South Australia.

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Gemfish / Common Gemfish (Western Stock) / Hake

Family Name:	Gempylidae
Scientific Name:	Rexea solandri (Cuvier, 1832)
Recommended Status:	Southern Australia (Commonwealth): Near Threatened South Australia (State): Least Concern
Rationale:  Although the western stock of Gemfish has a broad geographic distribution across southern Australia, and is an abundant species, it is included here because (i) it is a schooling species that is valued as a food fish, highly susceptible to capture, targeted by Commonwealth-managed commercial fisheries across the range, and reported to have a low resilience to exploitation, and very high vulnerability to fishing-induced population decline; (ii) year class strength may be highly variable, and environmentally-driven; (iii) the permitted catches are not conservative, nor inclusive: e.g. catches from the Great Australian Bight have not traditionally been part of the Commonwealth quota allocation, yet increasingly large numbers are being caught; (iv) a significant amount of discarding of juvenile gemfish occurs (in both South East and GAB fisheries) in some years of strong recruitment (e.g. 71t in 2004, in the GAB). An abundance of small Gemfish that result from periodic good years of recruitment, helps to contribute to population sustainability, and therefore bycatch mortality of small Gemfish is a threatening process, because those fish do not have an opportunity to grow and mature, and thus contribute to the spawning stock; (v) for the time period that western stock of Gemfish has been commercially fished, there has been no knowledge of biomass; no formal quantitative stock assessments, and no co-operative management between the main fisheries (which reportedly target the same stock); yet permissible catches in the Great Australian Bight have continued to rise; also, catch rates in the south-east fishery have shown a declining trend in recent years, and it is still not known if catches are sustainable in the south-east, or in the GAB; (vi) in risk assessments for species in the Commonwealth-managed South East trawl fishery and the GAB trawl fishery this species has been ranked as being at medium to high risk of fishing-induced population impacts; and (vii) there is inadequate knowledge of the biology and population dynamics of the western stock, including habitat preferences of adults and juveniles; reliable measures of relative abundance and spawning stock biomass over space and time, spawning location and dynamics, recruitment strength over space and time (and determinants of that), larval movement, and distribution and connectivity between populations across the range. The status of the western stock is considered to be of Least Concern in waters under South Australian State jurisdiction, because the main threatening processes occur in Commonwealth-managed waters of south-eastern and southern Australia.

Page Contents

Current Conservation Status

Pogonoski et al. (2002) recommended Data Deficient status for the western stock of Gemfish.

Australian Society of Fish Biology 2001 list recommendation: Data Deficient status for the western stock of Gemfish.

From 1992 to 1997, western stock of Gemfish was classified as “fully fished”, but in 1998, the status was changed to “uncertain” (Caton and McLoughlin, 2000; Caton, 2002) and remained that way for the following decade. In 2008 and 2009, the status of the western stock of Gemfish was still described as “over-fished status and over-fishing status uncertain” (Larcombe and Begg, 2008; Wilson et al., 2009).

Distribution

General

Gemfish occur off southern, south-western and south-eastern Australia, and are also found in Tasmania and New Zealand (Kailola et al., 1993; Nakamura and Parin, 1993; Gomon et al., 1994). There are four known stocks, two in Australia and two in New Zealand, as described below.

Work by Parin and Paxton (1990) and Colgan and Paxton (1997) identified the two Australian stocks of Gemfish (eastern stock and southern / western stock), based on electrophoresis of protein enzymes and DNA analysis, with very little gene flow or mixing between the stocks. Ward and Elliot (2001), also reported “striking population differentiation” of gemfish, based on a summary of allozyme, mitochondrial DNA and micro-satellite data. The stock boundary is at the western end of Bass Strait, with few specimens from western Tasmania showing limited mixing (Parin and Paxton, 1990; Colgan and Paxton, 1997, cited by Paxton, 2003). In Australia, the complete range of the two stocks combined, is from Cape Moreton in southern Queensland, around southern Australia, through to the continental slope off the central Western Australian coast (Parin and Paxton, 1990, Kailola et al., 1993; Daley et al., 1998). In New Zealand, two separate gemfish stocks have been identified, based on patterns of year class strengths, trends in commercial landings and likely spawning areas. One stock occurs off the east and north of the North Island, and the other off the west and south of the South Island (Horn and Hurst, 1999).

Western Stock

A genetic study (Colgan and Paxton, 1997, also cited by Caton and McLoughlin, 2005) showed that western gemfish is a single stock distributed from western Bass Strait across the Great Australian Bight to about Geraldton, Western Australia. There is limited mixing of the western and eastern stocks off western Tasmania. Examination of parasite loads has indicated that the western stock may really comprise two stocks (Sewell and Lester, 1995).

The western stock is found mainly in the Great Australian Bight and in Western Australian waters (Australian Government Department of the Environment and Heritage, 2003c).

There are numerous records from the eastern, central and western Great Australian Bight (CSIRO Marine Research data; Museum of Victoria data), where this species is caught commercially, and was also caught in research surveys during the 1960s and 1970s (CSIRO Marine Research data, cited in CSIRO, 2009).

In South Australia, the western stock of this species also occurs south of Kangaroo Island (CSIRO Marine Research data; Australian Museum records), and in the South-East (e.g. off Beachport, and off Port MacDonnell) (Australian Museum records; Museum of Victoria records, cited in OZCAM, 2009).

The western stock also occurs in western Victoria (e.g. off Portland) (Australian Museum records; Museum of Victoria records, cited in OZCAM, 2009).

Habitat

The western stock of Gemfish occurs in schools on the continental shelf and slope, in waters from about 130m to 600m deep (occasionally deeper), and are caught mainly in waters of about 250m to 500m depth (Tilzey and Chesson, 1998; Tilzey, 2000a; Caton and McLoughlin, 2005). In the Great Australian Bight, the species is commonly recorded along the outer shelf and upper slope (Daley et al., 1998; Paxton, 2003; CSIRO Marine Research data, cited in CSIRO, 2009).

There is a record from 900m deep, off Kangaroo Island (South Australian Museum record F06402, cited in OZCAM database, 2009).

Gemfish are normally found close to the sea bed but move into mid-water at times (Kailola et al., 1993; Rowling, 1994b), and can also occur near the surface (e.g. off Tasmania and New Zealand). In situ observations with underwater camera in trawl grounds off south-eastern Australia indicate that Gemfish are found close to the sea bed (within 2m of the sea floor) (Piasente et al., 2004).

In the Great Australian Bight, this species is known to concentrate around the upper part of canyons, and around reef features (CSIRO data).

Juveniles are pelagic (May and Maxwell, 1986), and occur in shallower water than do the adults.

Notes on the Biology

Age and Growth

Maximum size is approximately 120 - 135cm TL (Rowling, 1997; Gomon, in Gomon et al., 1994; Daley et al., 1998). In 2004, an Integrated Scientific Monitoring Program (ISMP) for the trawl fishery in the Great Australian Bight indicated that individuals in a sample of 955 Gemfish from the eastern GAB ranged between 36 and 78cm (majority 49cm – 65cm), with a broader size range in the central and western area (i.e. approximate range 32cm to 110cm, in a sample of 92 fish) (Talman et al., 2005). In south-eastern Australia, Withell and Wankowski (1989) estimated a maximum size of 112.3cm, and Rowling and Reid (1992) estimated a maximum size of 97.5cm for males, and 109.4cm for females.

In south-eastern Australia (eastern stock), maximum weight recorded is around 16kg (Withell and Wankowski, 1989; Rowling, 1995a), although the species is commonly seen at less than 4kg (Daley et al., 1998). Similar weights may be expected for the western stock.

In south-eastern Australia and New Zealand, maximum age is reported to be 16 or 17 years (females) (Kailola et al., 1993; Rowling, 1994b; New Zealand Ministry of Fisheries, 2009a), although few fish survive beyond 12 years of age. In south-eastern Australia (eastern stock), females live longer (up to 17 years) and attain a greater length (116cm Fork Length, FL) than males (longevity up to 13 years and maximum length 106cm FL) (Tilzey and Chesson, 1998; Tilzey, 2000a, cited by Pogonoski et al., 2002).

Diet and Feeding Behaviour

Gemfish feed near the sea floor, on bentho-pelagic fish (Bulman et al., 2001). Examples of dietary items include bony fish such as whiptails (Macrouridae) and deepwater cardinalfish Apogonops anomalus, as well as squid (Ommastrephidae), cuttlefish, and shrimps / prawns (including royal red prawns Haliporoides sibogae) (Kailola et al., 1993).

For the related stock (eastern Gemfish) in eastern Australia, fishers have described a seasonal cycle of species in the mid-water, which culminates in increased Gemfish abundance. During autumn and winter each year, “feed layers” of gelatinous zooplankton develop, and as the season progresses, there is an increasing amount of crustacea, followed by small fish (such as Myctophid lantern fish and Macrourid whiptails), then followed by jack mackerel Trachurus declivis, and eventually larger piscivorous fish such as Gemfish (Prince, 2001).

Reproduction

In New Zealand, age at maturity is reported to be 5 to 8 years (New Zealand Ministry of Fisheries, 2009a). Studies in southern Australian waters have shown that male Gemfish reach maturity at 50cm – 60cm (= 4 years old) and females mature at 60cm – 70cm ( = 5 years old) (Kailola et al., 1993; Rowling, 1987, 1990, 1994b, cited in Froese and Pauly, 2009). Bruce et al. (2001, citing Smith and Wayte, 2001) reported that reproductive age in the western stock of Gemfish was 3 – 6 years of age.

Larvae are caught in inshore waters which may indicate that gemfish move onto the shelf to spawn, or currents carry larvae in from offshore spawning grounds (Nakamura and Parin, 1993; Rowling, 1994b, cited in Froese and Pauly, 2009).

The biology of western Gemfish appears to be similar to that of eastern Gemfish, except they are thought to spawn in summer (in western Great Australian Bight) rather than winter; however, further biological work is required to test this hypothesis (Tilzey and Chesson, 1998, cited by Pogonoski et al., 2002; Smith and Wayte, 2001).

The western stock of Gemfish spawns in waters west of Bass Strait, and there might be a spawning migration to Great Australian Bight waters (Caton and McLoughlin, 2005).

The western stock of Gemfish does not appear to aggregate to spawn (or at least the aggregations have not been found) (Pogonoski et al., 2002). It has been suggested that if a spawning migration occurs, it may be in Great Australian Bight waters that are not accessible to fishers (Caton and McLoughlin, 2005). Generation length for the species, i.e. the average age of mature breeding parents of the current cohort, is accepted to be nine years (Anonymous, 2009).

Recruitment appears to be inter-annually variable, but the causes have not been ascertained (Bruce et al., 2002). Smith and Wayte (2003) reported significant levels of recruitment to the fishery every few years, based on an indirect measure (time series of length distribution data). Length frequency distributions are variable from year to year, which may be indicative of variable recruitment strength. In 1997 and 2000 there was evidence of a strong cohort of fish entering the fishery in southern Australia (Smith and Wayte, 2005). In New Zealand, recruitment variability in some areas has been correlated with wind and sea surface temperature patterns during the winter spawning season (Renwick et al., 1998), with spawning success apparently being reduced when local sea surface temperatures are lower than normal, and when there is a higher than normal frequency of south-westerly flow patterns over New Zealand. Similarly, in south-eastern Australia, it has been suggested that a relationship might exist between recruitment, and the strength of westerly winds (Shelf Resource Assessment Group, in AFMA, 2008g). This is based upon the observation that peaks in recruitment appear to match periods of strong zonal westerly winds off Tasmania, and the relationship is being investigated by researchers. Modelling work on the eastern stock in south-eastern Australia indicates that there may be long periods of poor recruitment (e.g. decadal time scale) (Shelf Resource Assessment Group, in AFMA, 2008g).

Other Information on the Biology

According to Bulman and Blaber (1986, cited in Froese and Pauly, 2009), Blue Grenadier Macruronus novaezelandiae prey upon Gemfish, and Gemfish are also eaten by Blue-eye Trevalla Hyperoglyphe antarctica (who prey on juveniles) and Pink Ling (Kailola et al., 1993, cited by Webb et al., 2004).

Western stock of Gemfish is a significant dietary item of New Zealand Fur Seal Arctocephalus forsteri (e.g. Page et al., 2005), and Gemfish are also part of the diet of Australian Fur Seals Arctocephalus pusillus doriferus (e.g. Littnan et al., 2007).

Sharks such as Sharpnose Sevengill Heptranchias perlo and Broadnose Sevengill Notorynchus cepedianus also consume Gemfish, a part of a mixed diet (e.g. Braccini, 2008).

Fisheries Information

(N.B. The southern / western stock of Gemfish in Australia is discussed here. The eastern Australian stock, which is over-fished, does not occur in South Australian waters).

The Western stock of Gemfish is one of the 8 major seafood products sold by one of Australia’s largest seafood supply companies, based in South Australia. The Western stock is taken mostly by the trawl sector, from Portland in Victoria to Shark Bay in W.A. (SIV, 2004). The Western stock of Gemfish is taken under quota in the Commonwealth-managed Southern and Eastern Scalefish and Shark Fisheries (SESSF), including the south-eastern trawl and non-trawl sectors (under quota), and the Great Australian Bight trawl fishery (no quota). The fishery for Gemfish is divided into zones. The western zone is also the management zone for “western Gemfish”, with gemfish caught outside this zone being deemed “eastern Gemfish”.

The western stock of Gemfish is caught throughout the year, but catch rates tend to be highest during spring (Smith and Wayte, 2003). Throughout the 1990s, the annual Total Allowable Catch (TAC) in the Commonwealth-managed fisheries of south-eastern Australia was about 300 tonnes. Prior to that, catches in the south-east fisheries declined from 1986 to 1992. An increase in fishing effort west of Bass Strait resulted in increased landings of western Gemfish during the 1990s. However, annual catches from 1992 to 1995 never exceeded 50% of the 300t TAC allocated annually. Catches and catch rates improved in 1996 and again in 1997 when 227t were landed. In 1998, 185t were landed (Tilzey, 2000a, cited by Pogonoski et al., 2002; Caton and McLoughlin, 2000). The actual catch exceeded the TAC (336t) in 2000. Landings in 2002 fell sharply, reportedly partly due to extended periods of unfavourable weather which restricted fishing effort. Less than 60% of the TAC was caught in 2003. During the mid to late 2000s, the TAC was reduced to 167t, and landings in 2007 were 99t (Larcombe and Begg, 2008). The table below shows the TACs and actual reported catches of the western stock of Gemfish in recent years, in the Commonwealth-managed South East trawl and non-trawl (scalefish hook) fisheries (from AFMA, 2003j; AFFA, 2004a; Larcombe and Begg, 2008). The western stock of Gemfish in the South East trawl and scalefish hook sectors are taken from the eastern extent of the stock that also occurs in the GAB. According to the Commonwealth assessments, the fishery has not targeted spawning aggregations (unlike the case for eastern Gemfish). The trawl sector takes the majority of the catch, although non-trawl sector catches have increased in recent years. Discarding is low in most years, and ranged between 3% and 7% from 2000 to 2003 (Smith and Wayte, 2005). Associated species in the gemfish catches include Blue Grenadier, Ling, Mirror Dory and Spotted Warehou, and the majority of the catch is taken between 200m and 500m deep (Smith and Wayte, 2002, 2005). In age composition studies, during the early 2000s, the majority of the fish in the sampled catch were estimated to be aged less than 7 years, and prior to that, during the early – mid 1990s, the majority of fish sampled were reported to be less than 5 years old (Smith and Wayte, 2005). Size composition of the retained and discarded catch varies with year. For example, in 1997 and 2000, a large number of the discards were fish under 40cm. In 2003, a year in which larger fish were being caught, many of those between 40cm and 60cm were discarded, and fishes larger than 60cm were retained (Smith and Wayte, 2005).
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Western Gemfish Catches in the Commonwealth trawl and scalefish hook fisheries
	Total Allowable Catch (Global TAC)	Actual Catch
2000	Agreed combined TAC: 300t Actual combined TAC: 336t	349t trawl 0t non-trawl
2001	Agreed combined TAC: 330t Actual combined TAC: 307t (= 306t trawl; 1t non-trawl)	254t trawl <1t non-trawl 9t discards
2002	Agreed combined TAC: 330t Actual combined TAC: 360t (= 359t trawl, 1t non-trawl)	138t trawl <1t non-trawl
2003	Agreed combined TAC: 300t (= 299.4t trawl; 0.6t non-trawl) Actual combined TAC: 335t (= 330t trawl; 5t non-trawl)	174t trawl 4t non-trawl 13t discards
2004	Agreed combined TAC: 300t (= 299.4t trawl; 0.6t non-trawl) Actual combined TAC: 322t or 323t (= approx. 317t or 322t trawl; 1t or 5t non-trawl)	146t trawl 4t non-trawl 9t discards
2005	Agreed combined TAC: 300t Actual combined TAC: 327t
2006	Agreed combined TAC: 167t Actual combined TAC: 190t	136t trawl 24t non-trawl <1t discards
2007	Agreed combined TAC: 167t Actual combined TAC: 173t	90t trawl 9t non-trawl
2008	Agreed combined TAC: 167t	76 trawl 11 non-trawl
(Caton 2002, 2003; Caton & McLoughlin, 2005, 2006; Larcombe & Begg, 2008; Wilson et al., 2009)

This species is caught commercially in the Great Australian Bight Trawl fishery. A survey of the GAB Trawl Fishery in 2000 and 2001 showed that in the continental shelf / upper slope part of the fishery, Western Gemfish is one of 7 main fish and shark species that are retained as by-product (Brown and Knuckey, 2002). Trawl catches during the 1980s to 2000s were not covered by a TAC, and non-trawl catches taken in the GAB are under the quota for the South East fishery (see above) (Smith and Wayte, 2005). An Integrated Scientific Monitoring Program (ISMP) during the early – mid 2000s recorded an average annual catch of about 62 tonnes. In the ISMP program of 2000/01, western Gemfish was recorded in 63 shots, with an average quantity of 109kg per shot retained, and 4kg per shot discarded (Brown and Knuckey, 2002). Approximately 60t of Western Gemfish was landed in the GAB Trawl Fishery in 2002 (AFFA, 2004b), but catches increased during the mid to late 2000s. Western Gemfish is usually retained when caught, and previously, the recorded quantity discarded in the GABTF was low (i.e. 0.47t in 1988; 1t in 1990, and 3t in 1997, according to logbook data submitted to AFMA) (see AFMA, 2001c). However, higher discard rates have occurred in some years (e.g. 71 tonnes in 2004, representing 24% of the Gemfish catch for that year, according to Talman et al., 2005). During the mid 2000s, both catch and effort increased. For example, effort has increased on the upper slope with a catch of 268t in one year (AFMA Logbook data, cited by Daley et al., 2006). Although the western stock of Gemfish has been designated as a by-product species, its depth range does not overlap with those of the major ‘target species’ and may have been targeted or caught during exploratory fishing (Smith and Wayte, 2003; Daley et al., 2006). A summary of western Gemfish catches in the GAB Trawl fishery component of the SESSF is shown in the table below.

Catch of Western Gemfish in the GAB Trawl Fishery, 1995 – 2007
Year	Catch (t)
1995	23^
1996	20^
1997	62^
1998	85^
1999	147^
2000	32^
2001	91 or 124#
2002	60+
2003	87+
2004	384+
2005	281*
2006	326*
2007	380*
2008	106*
^ = Lynch & Garvey, 2003; # = AFFA, 2004c; + = Caton & McLoughlin, 2005, 2006; * = Larcombe & Begg, 2008 & Wilson et al., 2009);

In the Western Deepwater Trawl Fishery off southern W.A., Rexea solandri is reported to be an important component of the catch at depths between 300m to 600m, and generally south of 25°S (AFMA, 2007d). “Catch volumes” recorded by fishers have been highly variable, and included 2,369 in 1993/94; 52 in 1994/95; 24,062 in 1995/96; 510 in 1997/98 and 8,128 in 2001/02 (AFMA, 2004f).

Rexea solandri has also been listed as one of the bycatch species in the Southern Bluefin Tuna Fishery (Ward et al., 2003); however catch figures are not available for this report. It is also a minor bycatch of Japanese long-liners in the Southern and Western Tuna and Billfish fishery, with an observer program from 1992 to 1997 indicating very low (i.e. trivial) numbers in the discarded catch (AFMA, 2003l).

Vulnerable Characteristics of the Species and Threatening Processes

Gemfish is reported to have a low resilience to exploitation, in terms of minimum population doubling time (based on the following parameters: K=0.15-0.21; tm=3-6; tmax=16; Fec= 500,000) (Froese and Pauly, 2009). Gemfish is also reported to be highly to very highly vulnerable to fishing-induced population decline (Cheung et al., 2005, cited in Froese and Pauly, 2009).

The western stock of Gemfish does not appear to aggregate to spawn (or at least the aggregations have not been found), and fishers reportedly do not target aggregations of western Gemfish (Pogonoski et al., 2002; Smith and Wayte, 2003, 2005). Therefore, the western stock should not be as vulnerable to exploitation as the eastern stock. However, given the over-fishing of the eastern Australian stock that has occurred, it is important that the total catch allocation for the western stock be inclusive and conservative. Currently, that is not the case, because (i) not all catches are included in the TAC (e.g. GAB catches have not been part of the Commonwealth quota allocation, yet increasingly large numbers are being caught), and (ii) a significant amount of discarding of juvenile gemfish occurs (in both south-east and GAB fisheries) in some years of strong recruitment.

For the time period that the western stock of Gemfish has been commercially fished, there have been no biomass estimates. During the 1990s, it was unknown if the catches were sustainable (Pogonoski et al., 2002), and during the late 2000s, it is still unknown. During the early to mid 1990s to late 2000s, when there was no quantitative assessment of the stock in combined Commonwealth-managed fisheries, catch rates in the south-east sector were at times (e.g. 1995 and 2002) well below Australian Fisheries Management Authority’s reference point for management action, and it was not clear whether the declines related to a drop in overall abundance (AFFA, 2004a). Despite assessment results of standardised catch rates differing from unstandardised (e.g. Smith and Wayte, 2005), catch rates have declined since 2001. The decline in landings and catch rate in 2002 has been partly attributed to extended periods of lower fishing effort due to unfavourable weather (Larbombe and Begg, 2008). It is noted that the 2004 catch rate was reportedly the lowest on record. There was a slight improvement in 2005; however, given the distribution of western Gemfish, and the location of the main fisheries, it is uncertain whether catch rates are a good indicator of stock abundance (Smith and Wayte, 2003; Larcombe and Begg, 2008).

No formal quantitative assessments of the western stock of Gemfish have been made, and there are no yield estimates (Larcombe and Begg, 2008). Despite this limitation, from 1992 to 1997, the western stock of Gemfish was classified as “fully fished”, but in 1998, the status was changed to “uncertain” (Caton and McLoughlin, 2000; Caton, 2002) and remained that way for the following decade. In 2008 and 2009, the status of the western stock of Gemfish was still described as “over-fished status and over-fishing status uncertain” (Larcombe and Begg, 2008; Wilson et al., 2009), because assessment based on catch rates only gives no indication as to whether the stock is being over-fished. It is noted here that there has been a gradual and continuing downward trend in catch per unit effort (CPUE) for the combined Commonwealth fisheries since at least 1994, despite short-term increases (such as mid-2000s) (see Smith and Wayte, 2005; Larcombe and Begg, 2008, p. 131; Wilson et al., 2009, p. 134). There is inadequate knowledge of biomass, or biomass trends for the western stock of gemfish (e.g. Smith and Wayte, 2005; Larcombe and Begg, 2008; Wilson et al., 2009), and it is not known whether current catches are sustainable.

In some years, in the GAB trawl fishery, there is a significant catch of undersized Gemfish (e.g. 71t in 2004, according to Talman et al., 2005), and these are discarded. An abundance of small Gemfish resulting from periodic good years of recruitment, helps to contribute to population sustainability, and therefore bycatch mortality of small Gemfish is a threatening process, because those fish do not have an opportunity to grow and mature, and thus contribute to the spawning stock. In the south-east fishery for the western stock of Gemfish, length frequency distributions are variable from year to year. In both 1997 and 2000 there was evidence of a strong cohort of fish entering the fishery, but the fish were of a size that is mostly discarded. During 2001, there was less discarding of the year 2000 pulse of recruits as they reached larger sizes and also, more quota was available (Smith and Wayte, 2003) However, progression of these “cohorts” in subsequent years is not clear (Smith and Wayte, 2005), perhaps because a significant proportion of the increased numbers of juvenile fish (from periodic strong recruitments) do not progress through the fishery, because they are caught, discarded, and therefore die.

In 2004, a draft Ecological Risk Assessment (ERA) for species in the South East Trawl and Danish seine fishery listed Gemfish (both eastern and western stocks are caught in the fishery) as a “high risk” species, in terms of population impacts from capture in the fishery (Wayte et al., 2004). During the mid 2000s, the Commonwealth’s Shelf Resource Assessment Group (ShelfRAG) considered the western stock of gemfish to be a “medium risk” species, in keeping with a proposal from the South East Trawl Management Advisory Committee (SETMAC) (Smith and Wayte, 2003).

In 2006, a draft Ecological Risk Assessment (ERA) for species in the Great Australian Bight Trawl Fishery (Daley et al., 2006), ranked western stock of Gemfish as a “high risk” species, in terms of population impacts from capture in the GAB Trawl Fishery. In a Residual Risk Assessment of the Level 2 Ecological Risk Assessment, this species was considered at “low risk” i.e. lower than when initially assessed. Similarly, in a “rapid quantitative Level 3 assessment, or Sustainability Assessment of Fishing Effects (SAFE) assessment” undertaken by AFMA, a supplement to the ecological risk assessment (by CSIRO) for the GABTF, this species was ranked as “low risk” of impact from operation of the fishery. According to AFMA (2008c), the Level 3 assessment process considers the mitigating effects of management arrangements that were not explicitly included in the ERAs, or introduced after the process commenced. It is noted that the level 3 assessment is made proportional to the spatial area in which the fishery operates, compared with the spatial area of distribution of the species, but this does not account for aggregation, assuming an even distribution throughout space (which is unrealistic for reef-associated species in a heterogeneous benthic environment).

Research Notes

In recent years, there have been some attempts to increase monitoring of catches landed in Beachport from the South East fishery, and the Great Australian Bight trawl fishery (Smith and Wayte, 2003).

Trends in standardised catch rates have been used in fishery reporting for Gemfish, as an indirect indicator (Smith and Wayte, 2005).

There is a time series of length distribution data, which are used as an indirect measure of recruitment strength (Smith and Wayte, 2003).

Research Recommendations

Little is known about the habitat of western Gemfish at most life history stages (Pogonoski et al., 2002).

For the western stock, there is little information about spawning location, spawning dynamics and spawning migrations (Bruce et al., 2002), and recruitment dynamics over space and time are largely unknown. Very little is known about environmental conditions required for successful spawning and juvenile survival (Pogonoski et al., 2002). In particular, the influence of the Leeuwin Current should be investigated, because this has been suggested as a possible “environmental driver” of the stock (Smith and Wayte, 2005).

There is inadequate information for determining status of the stock, and sustainability of the fishery. Assessment currently relies mainly upon catch per unit effort data, with limited length and age composition data (see Smith and Wayte, 2005; Larcombe and Begg, 2008; Wilson et al., 2009). This is in contrast with the eastern stock of Gemfish, for which some data required for stock assessment exist, including: a long time series of length-composition data; age structure data; biomass estimates over time; and an index of recruitment strength (the latter determined mostly during the 1990s, because there are no recent surveys) (e.g. see Blackburn, 1978; Rowling, 1994c; Punt and Smith, 1999; Little et al., 2008).

There is a need to collect basic biological information on western Gemfish and to continue to monitor the size and age composition (Smith and Wayte, 2003, 2005; Wilson et al., 2009). Stock size is unknown (particularly spawning stock biomass), size and age composition over space and time is inadequately known, and very few biological parameters have been determined.

In summary, there is inadequate knowledge of the biology and population dynamics of the western stock, including habitat preferences of adults and juveniles; reliable measures of relative abundance and spawning stock biomass over space and time, spawning location and dynamics, recruitment strength over space and time (and determinants of that), larval movement, and distribution and connectivity between populations across the range.

Management Recommendations

Increased monitoring of catches in the Great Australian Bight (and in the South East fishery) is required (Smith and Wayte, 2005).

Catches in the Great Australian Bight Trawl Fishery have continued to increase, and were an order of magnitude higher in the mid 2000s (Larcombe and Begg, 2008) compared with the mid 1990s. The South-East trawl and non-trawl fisheries target the same stock as is taken in the Great Australian Bight trawl sector. According to Larcombe and Begg (2008): Separate management controls for the two fisheries increase the risk that total catches will not be limited to desirable levels for the stock as a whole. The TAC for the south-eastern fisheries should include catches from the Great Australian Bight in a global quota of western Gemfish for all Commonwealth-managed fisheries (Smith and Wayte, 2003; Caton and McLoughlin, 2005, 2006; Larcombe and Begg, 2008). This recommendation has been made since the early 2000s.

Despite the significant increases in catch in the Great Australian Bight, no formal stock assessments of western Gemfish have been made, and there are no biomass estimates (Caton and McLoughlin, 2006; Larcombe and Begg, 2008; Wilson et al., 2009). Catches of western Gemfish (total 991t for 2004 to 2006, and 985t for 2005 to 2007) have come close to the levels that require formal stock assessments to be undertaken (Wilson et al., 2009). Given the uncertainty of the sustainability of current catch levels, this should be a priority area for research and management.

Future assessments should incorporate all relevant data from both the south-east fishery and the GAB trawl fishery (Smith and Wayte, 2005).

Although the level of discarding of the western stock of Gemfish is often less than 10% (Smith and Wayte, 2003, 2005), this increases with the entry of smaller recruits into the fishery, following irregular periods of strong recruitment. In 2000, for example, the catch of the western stock of Gemfish exceeded the quota, and there was increased discarding of small gemfish. In 2003, the discard level was 7% of the catch (Smith and Wayte, 2005. In 2004, the recorded discard quantity was as high as 71t (Talman et al., 2005). As is the case for the eastern stock of Gemfish, the capture of juvenile western Gemfish (i.e. less than 55cm) should be discouraged or prevented, to increase the number of fish entering the mature population in coming years (K. Rowling, pers. comm., cited by Pogonoski et al., 2002 and Smith and Wayte, 2005). It would be imprudent to increase quota on the strength of irregular periods of favourable recruitment, and a more sustainable management action would be to alter gear selectivity to reduce capture of small western stock Gemfish (as recommended by the Shelf Resource Advisory group, during the early and mid 2000s: Smith and Wayte, 2003, 2005). Reducing or eliminating the capture of juvenile Gemfish might be possible by increasing the mesh sizes of nets used. This may also reduce the catches of other species, by allowing the smaller fish to escape, but may be necessary to reduce the Gemfish catch (Pogonoski et al., 2002). As all gemfish that are brought to the surface do not survive release, changes in the gear selectivity and/or seasonal closure of grounds to fishing are measures that may reduce the catch of undersized Gemfish.

The case with the eastern stock of Gemfish (see Pogonoski et al., 2002 and Larcombe and Begg, 2008, for overview) has indicated that even with a much larger population than exists at present (i.e. pre-1970s), periods of poor recruitment can occur. The combination of previous high levels of fishing of “spawning run” aggregations of eastern Gemfish, coupled with periodic poor recruitment, and continued fishing of a very depleted stock, have all reduced the chance of the significantly over-fished stock of eastern Gemfish from recovering. The more restrictive management that is now in place for the eastern stock of Gemfish has not resulted in any significant recovery; the spawning stock is still very low, and the stock is still legally fished, despite its depleted state. Given that the western stock of Gemfish may exhibit similar population dynamics to the eastern stock (with perhaps the exception of a distinct spawning run, which has not been observed in the western stock), management actions and allowable catches should be precautionary, so that the western stock is not depleted in future, in the same manner as the eastern stock.

Management Notes

In the Great Australian Bight trawl fishery, the western stock of Gemfish is one of 6 fish species that are listed as being a priority for a formal “harvest strategy” to be developed, and there are trigger limits in place (i.e. maximum catch levels that trigger management action) (AFMA, 2008d).