© 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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Thetis Fish

Family Name:	Neosebastidae
Scientific Name:	Neosebastes thetidis (Waite, 1899)
Recommended Status in S.A:	Data Deficient in South Australia Possibly Near Threatened or Vulnerable A2(d) in Commonwealth managed waters of south-eastern and southern Australia
Rationale:  Although the Thetis Fish is found throughout southern Australia, and has a broad depth range on the continental shelf and upper slope, it is included here because (i) like other members of the Neosebastidae, it is a benthic, site-associated reef fish of limited mobility, and these characteristics increase the species’ vulnerability to site-specific impacts; (ii) the species is part of the bycatch in various Commonwealth-managed trawl and non-trawl fisheries (where it is recorded in large numbers, and is classified in the SETF and GABTF as being at “high risk” of population impacts), various State-managed fisheries (but no data for S.A.), and it is also taken by some recreational fishers, but there are few requirements to try to minimise bycatch of benthic, site-associated fish species; (iv) given the strong site association and limited dispersal ability of gurnard perches, dredging and other physical damage to shallow, soft bottom habitats may adversely affect populations in the shallow part of the range, but there are no specific data, and (v) there is no knowledge of population sizes or population dynamics, and, apart from dietary studies, little information on the biology (particularly fecundity, annual recruitment strength, and longevity). Data are insufficient for an assessment of conservation status in S.A. waters. However, given the seemingly large, unregulated bycatch in Commonwealth-managed waters ( despite no information on abundance of the population and sustainability of fishing it), the species may qualify for classification as Near Threatened or Vulnerable in Commonwealth-managed waters of southern and south-eastern Australia. It is possible that the population in south-eastern Australia may have been significantly depleted, following almost 100 years of fishing with no regulations over the capture of Thetis Fish, and the species continues to be vulnerable to depletion in the Commonwealth-managed fisheries in south-eastern and southern Australia.

Page Contents

Current Conservation Status

no listings known

Distribution

Southern Australia

The Thetis Fish ranges from N.S.W. through to southern Western Australia (Hutchins and Swainston, 1986; Poss, in Gomon et al., 1994; Australian Museum, 2006l).
The Thetis Fish is considered to be relatively common, and has the largest distributional range of any Neosebastes species (Australian Museum, 2006l).

South Australia

Examples of locations in which the Thetis Fish has been recorded in S.A. include mid-continental shelf waters in the western, central and eastern parts of the Great Australian Bight; metropolitan Gulf St Vincent (e.g. Glenelg) and the Fleurieu Peninsula (e.g. Rapid Bay), and Encounter Bay area (e.g. Victor Harbor) (Hutchins and Swainston, 1986; Museum of Victoria records, South Australian Museum records, cited in OZCAM database, 2007).
There are hundreds of published records of this species from the Great Australian Bight (e.g. CSIRO Marine Research data, 1960s and 1970s, cited in CSIRO, 2007).

Habitat

Thetis Fish is a demersal, reef-dwelling species on the continental shelf (May and Maxwell, 1986; cited in Froese and Pauly, 2007). However, in Tasmania, N. thetidis (particularly juveniles) have been reported from Heterozostera and Posidonia seagrass, sand and mud habitats (Jordan et al., 1998; DPIWE Tasmania, 2004i).
To date, Thetis Fish has been found between 5m (Australian Museum, 2006l) and 288m (Motomura , 2003, cited in Froese and Pauly, 2007) , but it is mainly recorded in deeper offshore waters of the continental shelf, below 100m (Poss, in Gomon et al., 1994). It is noted that CSIRO et al. (2001) reported the depth range to be 18m to 329m, with the species more common recorded in the range 100m – 200m. Many of the records from the Great Australian Bight were collected within the range 40m – 250m (CSIRO Marine Research data, cited in CSIRO, 2007).

Notes on the Biology

Growth

Previously, the published maximum length was 35cm (Poss, in Gomon et al., 1994), but it is noted that during a recreational fishing study in Tasmania, some specimens in the range 35 to 37cm were recorded (Lyle et al., 2000). One of the record weights recorded is 0.790kg (Hutchins and Swainston, 2001).

Diet

No species-specific information on the diet could be found for this report, but it is noted that related species of gurnard perch in southern Australia eat small fish, squid, crabs and other small crustaceans, and marine worms (Bulman et al., 2001; DPIWE Tasmania, 2004i).

Fisheries Information

Commercial – Commonwealth Fisheries

Thetis Fish has been marketed as “Coral Perch”, as have other Neosebastes species (Seafood Services Australia, 2003). When taken outside of 3 nautical miles (NM) from the coast, catches are managed by the Commonwealth, and when taken inside 3 NM, are managed by States (AFMA, 2002a). In the scalefish hook, shark hook, and gillnet sectors of the Commonwealth-managed Gillnet, Hook and Trap Fishery (GHAT), N. thetidis may be caught in waters outside 3 NM but not in coastal waters inside 3NM with a concession that allows methods other than trawl (AFMA, 2004e). Catch data from the GHAT are not available for this report.
In Commonwealth-managed fisheries, the species is a bycatch species in the SESSF (AFMA, 2002a); is occasionally taken by trawlers in the Commonwealth-managed South East Fishery, and is also taken by anglers who work in deeper waters. In the South East Trawl Fishery, an Integrated Scientific Monitoring Program during the early 2000s reported that in 468 trawl shots, about 4.486 tonnes of Thetis Fish were discarded (Wayte et al., 2004), which is an average of 9.5kg per trawl shot. In the Danish seine sub-fishery, the species was recorded in 14 shots during the monitoring program, with none retained, and 103kg discarded (Wayte et al., 2004).
In the Great Australian Bight Trawl Fishery, during a bycatch sampling program in 2001, Thetis Fish was recorded in 31 of 209 trawl shots; none was retained, and an average of 9.1kg per trawl shot was discarded (Brown and Knuckey, 2002). During the survey period, AFMA (2002a) reported that 618kg of Thetis Fish were recorded, and all were discarded.

Commercial – State Fisheries

Previously, Thetis Fish was one of the top 12 bony fish species taken by trawlers off the coast of New South Wales. For example, between 1915 and 1916, almost two and a half million pounds of fish were taken, and Thetis Fish was 10^th in terms of weight (Klaer, 2002). In contrast, during 1921, approximately 445kg of Thetis Fish were recorded (Klaer, 2002), but the accuracy of this estimate is not known for this report.
The species is a minor part of the bycatch in the N.S.W. Ocean Trawl Fishery (N.S.W. Department of Primary Industries, 2004). In N.S.W., fishery-independent surveys to assess bycatch composition in the Ocean Trawl Fishery have been undertaken, using ocean fish trawl and prawn trawl gear. Results showed that the percentage frequency of occurrence of across all trawls was 1% in the ocean fish trawl - shelf sector (N.S.W. Department of Primary Industries, 2004).

Recreational

The Thetis Fish is occasionally taken by anglers (Hutchins and Swainston, 1986), but usually occurs in deeper waters than those fished recreationally.
It is noted that in the National Recreational and Indigenous Fishing Survey (Henry and Lyle, 2003, and associated data), results for all species in the Neosebastidae were aggregated, hence it is difficult to determine species-specific catches. Aggregated catches of gurnard perches are listed above, in the synopsis for Neosebastes bougainvillii.
Species in the Neosebastes genus are taken by spear fishers (e.g. Australian Underwater Federation Inc., 2003), and although no records of this species could be found for this report, it is likely that N. thetidis would be targeted, as it is one of the larger, edible gurnard perches. More recently, gurnards (unspecified, with specimens over 0.4kg) were listed as target species in the 54^th Australian Spearfishing Titles 2006, held on northern Kangaroo Island (Australian Underwater Federation Inc., 2006).

Vulnerable Characteristics of the Species and Threatening Processes

Like other members of the Scorpaenidae, Thetis Fish is a benthic, site-associated reef fish of limited mobility, and these characteristics increase the species’ vulnerability to site-specific impacts, and to capture by a number of fishing methods.
Fishing may be a threatening process to N. thetidis populations. In a draft ecological risk assessment of the South East Trawl and Danish Seine Fishery (Wayte et al., 2004), 3 “productivity attributes” and 6 “attributes of susceptibility” for the N. thetidis were used to categorise it as a “high risk” species; i.e. susceptible to population impacts from trawling.
In 2006, an Ecological Risk Assessment (ERA) for species in the Great Australian Bight Trawl Fishery (Daley et al., 2006), ranked N. thetidis as a “high risk” species, in terms of population impacts from capture in the GAB Trawl Fishery, with the proviso that some of the data required for accurate assessment do not exist. Apart from trawl fishing, populations may be at risk from fishing impacts due to shark hooks and gillnets, in south-eastern Australia, but there are insufficient data.

Research Requirements

More information is required on the distribution and abundance within the range, and the biology and population dynamics of this species (particularly fecundity, annual recruitment strength, and longevity).
Data are required on the numbers taken by commercial and recreational fishers across the range, in relation to required studies of abundance.

Management Requirements

Where possible, measures are required to reduce the bycatch of benthic fishes (such as those in Neosebastidae and Scorpaenidae) in Commonwealth- and State-managed trawl fisheries.
In States other than Tasmania (where regulations already exist), recreational fishing regulations (e.g. size limits and bag limits) are recommended to regulate the capture of benthic, site-associated fishes such as members of the Scorpaenidae and Neosebastidae.

Other Information

Thetis Fish is venomous (Smith and Wheeler, 2006)