© 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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Large-tooth Flounder

Family Name:	Paralichthyidae
Scientific Name:	Pseudorhombus arsius (Hamilton-Buchanan, 1822)
Recommended Status in S.A:	Data Deficient
Rationale:  The species is included here because P. arsius (i) occurs in coastal areas such as shallow sandy and muddy bays and estuaries, and may thus be vulnerable to coastal impacts; (ii) is taken by commercial and recreational fishers across the range, with little information about numbers taken, and no indication of sustainability of catches over space or time; (iii) in some areas of southern Australia, it is vulnerable to capture by prawn and fish trawling operations, due to its bottom-dwelling habit, poor swimming ability, and presence in trawl grounds; and (iv) there is little information on the population dynamics of this species over space and time, particularly in areas where it is susceptible to capture.

Page Contents

Current Conservation Status

Classified as Least Concern in the Northern Territory (Dept Natural Resources, Environment and the Arts, 2006), but there are no other listings.
 

Distribution

General

Large-tooth Flounder, identified as Pseudorhombus arsius, have been recorded from Australian waters, and also from various other countries in the Western Pacific, and Indian Ocean (Gomon, in Gomon et al., 1994). At a global scale, there is some doubt about the single species classification of fishes currently known as P. arsius (Gomon, in Gomon et al., 1994).
Amaoka and Hensley (2001) considered the species to occur from the east coast of Africa, to Australia, and in tropical and subtropical areas of the western Central Pacific.
 

Southern Australia

The species occurs across Australia, except Victoria and Tasmania (Hutchins and Swainston, 1986; Kuiter, 1993, 1996b; Gomon, in Gomon et al., 1994).
 

South Australia

Examples of locations where P. arsius has been recorded in S.A., include the Outer Harbour area in metropolitan Gulf St Vincent (recorded in low numbers in beam trawl surveys, during the early 2000s – see Tanner, 2004), and other parts of GSV; Spencer Gulf; eastern Great Australian Bight (e.g. Venus Bay / Anxious Bay area) (South Australian Museum records, cited in OZCAM database, 2008).
 

Habitat

Large-tooth Flounder is found in estuaries and bays (Hutchins and Swainston, 1986). Across the range, the species is reported in shallow muddy-sandy or sandy bottoms, from coastal waters to river mouths, with juveniles commonly found in brackish waters (Amaoka and Hensley, 2001).
Pollard (1994) and West and Jones (2001) recorded the species in low numbers in various coastal lakes and estuaries along the south coast of New South Wales.
In a study at Shark Bay in W.A., P. arsius was found almost exclusively over bare sand (Travers and Potter, 2002).  In the Dampier Archipelago, the species has been reported from soft bottom habitats, mangroves, and trawling grounds (Hutchins, 2003). 
In Queensland, the species has been recorded in shallow (less than 1.5m), sandy habitat in estuarine areas (e.g. Baker and Sheaves, 2005; Miller and Skilleter, 2006); in seagrass-lined estuaries (e.g. Noosa – Schlacher et al., 2005); in tropical rivers (e.g. Kroon, 2005); in intertidal and shallow subtidal areas adjacent to ports (Port Curtis – Connolly et al., 2005) and harbours (e.g. Cairns – Coles et al., 1993); also in sub-tropical mangrove Avicennia marina habitat (e.g. in Moreton Bay in Queensland – Morton, 1990), and in saltmarsh mudflats (Melville and Connelly, 2005). The species has also been recorded from an artificial reef (the Brisbane shipwreck) in Queensland (EPA and QPWS, undated). 
Outside of Australia, the maximum depth of the species considered to be P. arsius is reportedly 200m (Sommer et al., 1996), but it is noted that most specimens have been taken by trawl, in the range 15m – 70m (Gomon, in Gomon et al., 1994).
 

Notes on the Biology

Growth and Age

The species is large, growing to about 53cm (Hutchins and Swainston, 1986), but more commonly known to about 30cm, with a maximum standard length of 45cm (Amaoka and Hensley, 2001).  
One of the largest weights recorded in southern Australia is 1.10kg (Hutchins and Swainston, 1986), being a specimen taken at Palm Beach in 1976 (Australian Anglers Association, W.A. Division, 2005). In New South Wales, the maximum size recorded by the N.S.W. Fishing Clubs Association is 0.91kg, being a specimen caught in 1962.
Maximum age appears not to be recorded, but it is noted that studies in Kuwait reported specimens (considered by the authors to be P. arsius) as old as 6 or 7 years, in a fully fished fishery (Bawazeer and Al-Baz, 1990; Mathews and Samuel, 1991)
 

Diet

The species feeds on bottom-dwelling invertebrates (Amaoka and Hensley, 2001).
.In Qatar (Arabian Peninsula) a feeding study reported that the diet of specimens in that area (considered by the authors to be P. arsius) comprised bivalves (44%), shrimps (44%) and amphipods (12%) (Nasir, 2001). Another study by the same author, in Kuwait, reported that the diet of specimens in that area, considered to be P. arsius, comprised 94% bony fishes, and 4% shrimps and other crustaceans (Nasir, 2000, cited in Froese and Pauly, 2008). It is likely that size and age of specimens accounts for differences in the diet reported during those two studies. Baker and Sheaves (2005), reported that in Queensland, the diet of P. arsius shows an ontogenetic shift from preying primarily on gammarid amphipods at small sizes, to preying on fish at larger sizes. Crabs, penaeid prawns and shrimps also form a significant component of the diet (Baker and Sheaves, 2005).  
 

Reproduction

Flounders live on the sea floor, but are pelagic spawners (Nelson, 2006). A number of studies have investigated the early life history of this species (e.g. Uyeda and Sasaki, 2002), including spawning (Boer et al., 2003), and size at settlement (e.g. Liew et al., 1988). A study in India reported that female specimens (considered by the authors to be P. arsius) are mature by 16-17cm (Ramanathan and Natarajan, 1979, cited in Froese and Pauly, 2007). 
 

Fisheries Information

Commercial

Little species-specific commercial fishing data are available. However, it is noted that flounder species (unspecified) are taken in minor quantities by commercial fishers in southern Australian States (see section above, on Commercial Fishing for flounders as a group). P. arsius is a commercial species in south-eastern Australia, with the marketing name “Flounder” (Seafood Services Australia, 2003).
P. arsius is usually taken by trawls, at depths of 15m – 70m (Gomon, in Gomon et al., 1994).
In New South Wales, commercial catches of “flounder” include species such as P. arsius, P. jenynsii and various species in Ammotretis. Due to difficulty in identifying individual species, all catches are reported as “flounder”. Since the early 1990s, landings of flounder by NSW ocean prawn trawl fishers (all areas) and ocean fish trawl fishers (ocean zones 4-6, State waters) have ranged between 20 to 30t per annum (N.S.W. Department of Primary Industries, 2004).
Large-tooth Flounder is part of both the retained and discarded bycatch in estuarine fish and prawn hauling fisheries in New South Wales. Pseudorhombus species are caught in areas such as Botany Bay, Lake Macquarie, St Georges Basin, and the Richmond, Manning, Wallamba, Shoalhaven, Clarence and Hawkesbury rivers (Gray et al., 1990; Liggins et al., 1996; Gray and Kennelly, 2001; Macbeth et al., 2004). During bycatch sampling in the St Georges Basin from February 1998 to January 1999, an estimated total of ~350 individuals (= 53kg) of P. arsius were discarded, and 38 individuals (~ 8kg) were retained (Gray and Kennelly, 2001). During the early 2000s, the number of locations in which the P. arsius could be taken as a by-product of the Estuary Prawn trawl fishery was regulated, to include Botany Bay, Port Jackson and Hawkesbury River (New South Wales Fisheries, 2002; New South Wales, Government Gazette, Friday, 21st February 2003).   
P. arsius is a minor component of the bycatch in the prawn trawl fishery in Spencer Gulf, South Australia. For example, 4 Large-tooth Flounder were recorded from 32 trawl tows, in sampling program during the mid 1990s (Carrick, 1997). There are no data available on the bycatch of this species in the prawn fisheries in other parts of South Australia.  
When caught in the bycatch of the South Australian Rock Lobster fishery, flounders are permitted to be retained for sale (Sloan, 20003a).
In Queensland, the species is reported to be taken incidentally for aquaria (Coles et al., 1993), and is a bycatch of the Northern Prawn Fishery (Stobutski et al., 2001). The species is also reported to be part of the bycatch in Queensland’s shallow water eastern king prawn (Penaeus plebejus) trawl fishery (Courtney et al., 2006). It is a bycatch species in the Torres Strait Prawn Fishery (TSPMAC, 2007).
 

Recreational

Recreational survey catch statistics (e.g. Henry and Lyle, 2003) group recreational catches of flounders with soles and other flatfish, and summary statistics, as well as other State-level data, are provided in the section on Recreational Fishing, at the beginning of this chapter.
In N.S.W., larger flounder species are caught by recreational fishers and the total recreational catch of flounder (species combined) in NSW is estimated to be about 5t per annum (N.S.W. Department of Primary Industries, 2004). In a survey of daytime recreational fishing at Lake Macquarie from March 1999 to February 2000, Steffe and Chapman (2003) reported that the total catch of P. arsius from that area was about 10,310 (± 2,624) specimens, equivalent to about 2.1 tonnes. At Lake Macquarie, the recreational catch of Pseudorhombus flounders (i.e. P. jenynsii and P. arsius combined) is about 10 times that of the commercial catch (Steffe and Chapman, 2003).   
In W.A., during a 12-month survey of recreational fishing in the Swan-Canning estuary basin in 1998-99 (Malseed and Sumner, 2001a), 775 (SE = 136) flounders in the genus Pseudorhombus were kept, and 765 (SE = 123) were released, by boat-based fishers. Small numbers were caught by shore-based fishers (Malseed and Sumner, 2001).  The proportion of the catch that was P. arsius (compared with P. jenynsii) is not known. During a 12-month survey of recreational fishing in the Peel-Harvey estuary basin in 1998-99 (Malseed and Sumner, 2001b), 86 (SE = 17) flounders in the genus Pseudorhombus were kept, and none were released, by boat-based fishers. Small numbers were caught by shore-based fishers (Malseed and Sumner, 2001b). The proportion of the catch that was P. arsius (compared with P. jenynsii) is not known.  Small quantities of Pseudorhombus flounders are also caught by fishers in the Leschenault Estuary (Malseed et al., 2000).   In W.A., there is a legal minimum size of 25cm for all flounder species, and a combined daily bag limit of 8 flathead and flounder (all species) in the West Coast, Gascoyne and South Coast regions (Department of Fisheries, 2007c, 2008a, 2008b).
For recreational fishers in South Australia, there is a daily bag limit of 20 flounder (all species) and a boat limit of 60, but there is no legal minimum size (PIRSA, 2008a, 2008b). 
 

Vulnerable Characteristics of the Species, and Threatening Processes

Benthic fishes in general have limited mobility, more localised reproduction than most pelagic species, and limited opportunity for population dispersal, all of which can increase the vulnerability of populations to decline.
Large-tooth Flounder occurs in coastal areas such as estuaries and shallow sandy bays, and populations may thus be vulnerable to decline in coastal areas where impacts degrade the habitat. There are few pristine or near pristine estuaries remaining in South Australia, and most are subject to numerous impacts (see Bucher and Saenger, 1989; Lewis et al., 1998; Barnett, 2001; GeoScience Australia, 2001; Baker, 2004; Gillanders et al., 2008). A summary of many of the impacts in shallow coastal bays in S.A. is provided in Baker (2004).
Other than for R. tapiria (see synopsis), there are few specific studies on the impacts of pollutants on flounders in Australia, but it is noted that in the northern hemisphere, sub-lethal effects of sediment contamination (from municipal sources such as  sewage; also industrial pollutants, and other contaminants such as tri-butyl tin from ship and boat anti-foulants) have been recorded. Impacts upon flounders from contaminants include changes in body chemistry, hepatic and other lesions, and reproductive impairment (e.g. Johnson et al., 1993; Myers et al., 1998; CSTEE, 1999; WWF, 1999; Rice et al., 2000). Flounders such as P. arsius can uptake and concentrate metal contaminants (such as zinc) that have entered estuaries and bays (e.g. Jones et al., 2000), but the impacts of this uptake on populations are insufficiently studied
The species is found in the prawn trawling grounds in S.A. (e.g. GSV / Investigator Strait, Spencer Gulf, and off the Anxious Bay area on the west cost). Prawn trawling may be a threatening process to some populations of this species; however there are few species-specific data, other than a bycatch study in Spencer Gulf during the mid 1990s.
Tanner (2003 and 2005) discussed impacts of prawn trawling on habitats and benthos in Gulf St Vincent and Investigator Strait.
Flounder species in general are defined as “Category 2” fish in Western Australia, with a “medium risk” of over-exploitation. Category 2 fish species generally mature at two to three years old, are of moderate abundance, are highly targeted, and/or often utilise estuarine and inshore habitats extensively (Department of Fisheries, 2004).
The combined effects of commercial and recreational fishing, in areas where these are high (e.g. N.S.W.), may be a threatening process.
 

Research Requirements

In southern Australia, there is very little information on the population sizes, biology, and population dynamics of this species.  
Most flounders in southern Australia (but see Hourston et al., 2004) have been little studied, and for most species there is very little known about their biology and life history (N.S.W. Department of Primary Industries, 2004).
Where possible, prawn trawling bycatch data from GSV, Spencer Gulf and the West Coast of S.A. should be analysed and monitored to determine the presence and relative abundance of this species over time (see Management Requirements). 
 

Management Requirements

Documentation and quantification of flounder bycatch in fisheries across the geographic range is required.  For example, status of flounder stocks in N.S.W. is uncertain, because the species composition of the catch needs to be determined. Collection of biological and fishery data for the important commercial species of flounder is considered to be a high priority (N.S.W. DPI, 2004).
As indicated in Research Requirements, in S.A., a system should be developed for the ongoing collection and monitoring of bycatch data from the GSV Prawn Fishery and the West Coast Prawn Fishery (as currently occurs in the Spencer Gulf Prawn Trawl Fishery), sufficient to enable identification of long-term trends in bycatch (Australian Government DEH, 2004b).
Measures (such as further improvements in net design) to reduce the bycatch of benthic fish species in all trawl fisheries should be implemented (see Management Notes). This is particularly required in areas where bycatch is high.
Assessment of the sustainability of catches in the N.S.W. commercial fishery is required.
Further recreational fishing controls (e.g. legal minimum sizes, and possession limits) are required in areas where these do not yet exist, and enforcement is also required.
Generally required is the ongoing management and mitigation of the multiple impacts that have reduced the quality of estuarine habitats in S.A. and other southern States. This includes protection of shallow coastal bays from land-based discharges, and, where possible, from coastal activities (such as dredging, and aquaculture developments) that can reduce benthic habitat quality in such bays.  
 

Management Notes

In New South Wales, a number of projects have investigated methods of reducing bycatch in estuarine and coastal water trawl fisheries for prawns and scalefish. For example, Gray and Kennelly (2001) reported on changes to the regulations concerning gears and practices used in these fisheries, such as mid-stream retrieval of nets (as opposed to riverbank); increase in maximum permitted size of mesh in the bunts and cod-ends of fish haul nets; and amendments to the regulations concerning the use and configurations of haul nets. Macbeth et al. (2004) reported on the utility of square end mesh to reduce bycatch of benthic fishes in prawn trawls in New South Wales. Broadhurst (2005) and Broadhurst et al. (2005) discussed modifications to the body, extension and cod-end in trawls, to reduce bycatch in N.S.W. inshore trawl fisheries for whiting, prawns and cephalopods. Experiments showed a slight smaller catch of P. arsius if a 63mm mesh trawl body was used instead of the conventional 45mm mesh (Broadhurst et al., 2005).
In Queensland, use of bycatch reduction devices (BRD) and turtle exclusion devices (TED) may reduce the bycatch of bony fishes such as flounders (e.g. Courtney et al., 2006). 
It is noted that prawn fisheries in South Australia have made significant efforts during the past decades to reduce the bycatch of finfish species. Examples for Spencer Gulf and GSV include the spatial and temporal organisation and “real time” management of the fishing fleet in some areas (e.g. Spencer Gulf) to minimise capture of undersized prawns and bycatch species, and developments in gear design to reduce bycatch, such as square-mesh cod-ends, bycatch chutes, hopper/conveyor systems, and the fitting of exclusion devices (e.g. MacDonald, 1998; Carrick, 1997; Broadhurst et al., 1999; S.A. Prawn Industry Association web site, 2000; PIRSA, 2003). PIRSA (2003) reported that field studies have indicated that survival of flounders (e.g. the commonly caught species Pseudorhombus jenynsii) is higher with hopper/conveyors systems, compared with previously used sorting equipment. However, Australian Government DEH (2004b) reported that further work is required to confirm this assumption
 

Other Information

During the past two decades, investigations have been undertaken into aquaculture of species such as P. arsius and P. jenynsii (e.g. Treadwell et al., 1992). In W.A., Pseudorhombus species are considered to have future potential for culture in sea cages or land-based tanks / ponds (Kendrick et al., 2002). P. arsius is listed as an aquaculture species of  “secondary importance” with proposed sites of interest for aquaculture including Ningaloo Coast, Shark Bay Coast, Central West Coast, Leeuwin-Naturaliste Coast (Makaira Pty Ltd and Ecologia Environmental Consultants, 1997).