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Long-snout Flounder / Long-snouted Flounder
| Family Name: | Pleuronectidae |
| Scientific Name: | Ammotretis rostratus Günther, 1862 |
| Recommended Status in S.A: | Data Deficient |
| Rationale: The species is included here because A. rostratus (i) may be less common in South Australia than in other parts of the range; (ii) is associated with estuaries (in addition to sandy bays and offshore areas); estuarine habitat for this species is geographically limited in South Australia, and a number of major estuarine habitats in S.A. are significantly polluted, but there are no specific data on potential impacts on flounder populations; (iii) is taken by commercial and recreational fishers (but likely in low numbers in S.A. compared with other parts of the range), with no indication of sustainability of catches; (iv) is considered, in other parts of the range, to be at risk from bycatch in trawl fisheries, but there is no information for S.A. waters, where it is recorded in apparently low numbers in prawn trawlers; (v) there is little existing information about the relative abundance in S.A., or of the population dynamics of this species across its range. | |
Page Contents
Current Conservation Status
(No listings known)Distribution
Southern Australia
The species is reported to range from the central N.S.W. coast through to south-western Australia, and the distribution includes Tasmania (Gomon, in Gomon et al., 1994).A. rostratus is the most common species in the genus Ammotretis (Gomon, in Gomon et al., 1994). It is noted that there are dozens of museum specimens from Victoria (Museum of Victoria records, cited in OZCAM database, 2008). The species is also common in south-eastern Tasmania (Jordan et al., 1998).
South Australia
Examples of locations in S.A. where A. rostratus is reported to have been recorded include Anxious Bay and Point Weyland in the eastern Great Australian Bight; Port Lincoln area in south-western Spencer Gulf; metropolitan Gulf St Vincent (GSV) (e.g. . Port River / Barker Inlet estuary; Outer Harbour, and Marino Rocks); Onkaparinga Estuary in the southern metropolitan area of GSV; other parts of GSV (including central waters), and northern (Middle River; Western River) and north-eastern (e.g. Cygnet River) Kangaroo Island (fishing record from 1986, cited by Australian Anglers Association, 2005; Fairhead et al., 2002b; Tanner et al., 2003; Flinders University data, cited by Hammer, 2006a; Gillanders et al., 2008; Australian Museum records, South Australian Museum records, cited in OZCAM database, 2008).Habitat
The Long-snout Flounder is found in estuaries, sandy bays, and offshore areas, at depths of about 1m to 80m (Gomon, in Gomon et al., 1994; DPI Victoria, 1998e).Juveniles are often associated with un-vegetated sand habitats (Jenkins et al., 1997, cited by Connolly et al., 1999). The species is more abundant on coarse- and medium-grain sand associated with the mouths of estuaries, than it is on fine-grain bottom, such as mud (Crawford, 1984, cited by Morton et al., 2005).
In many parts of Tasmania, the species has been recorded in estuaries (Edgar et al., 1999) and off beaches, in sand and mud habitats, and also in seagrasses e.g. Heterozostera nigricaulis (previously calledH. tasmanica), and, less commonly, in Amphibolis antarctica (Jordan et al., 1998).
In New South Wales, the species has been recorded in numerous sandy bays and estuaries (e.g. examples of the latter include Pollard, 1994, and Gray and Kennelly, 2001). It has also been recorded in intermittently closed coastal lagoons (e.g. Pollard, 1994).
In Victoria, the species is found throughout coastal waters, mainly in estuarine and nearshore habitats over sandy or muddy substrates (e.g. Edgar and Shaw, 1995a), occasionally in fresh water just upstream of estuaries (DPI Victoria, 1998e). Adults are abundant towards the entrance of Port Phillip Bay (Anonymous, 1973, cited by EPA Victoria, 2001). Juveniles are common in shallow bays and estuaries, and sometimes enter fresh water (DPI Victoria, 1998e)
Although Long-snout Flounder is more commonly associated with sandy estuaries, it has also been recorded in low abundance in mangroves and associated mud habitats in Victoria (Hindell and Jenkins, 2004; Smith and Hindell, 2005).
In W.A., the species has been recorded in estuaries (e.g. Potter et al., 1993; Potter and Hyndes, 1994), and nearshore marine waters.
Notes on the Biology
Growth
The species grows to between 30cm (Gomon, in Gomon et al., 1994), and 34cm (Last et al., 1983, cited by Morton et al., 2005; DPI Victoria, 2003).One of the maximum sizes recorded was 0.994kg, a specimen taken from Portsea Pier in Victoria in 1999 (Australian Underwater Federation Inc., 2003).
Diet
Generally, most flounders are predatory carnivores, feeding on bottom fauna, such as crustaceans, gastropods, and small fish (DPI Victoria, 1998e). Ammotretis rostratus consumes mainly benthic prey such as crustaceans, polychaete worms and molluscs (Crawford, 1984, cited by Morton et al., 2005; Edgar and Shaw 1995b, cited by Valesini et al., 2004).Juveniles are daytime feeders, and consume mainly amphipods and polychaete worms (Crawford, 1984, cited by Morton et al., 2005).
Migration
There is some evidence of seasonal migration. For example, in Port Phillip Bay in Victoria, throughout the period summer to autumn, A. rostratus is most abundant in shallow regions, whereas there is a greater abundance in deeper regions in winter/spring, suggesting that the species migrates seasonally between these regions (Parry et al. 1995, cited by EPA Victoria, 2001).Reproduction
Flounders live on the sea floor, but are pelagic spawners (Nelson, 2006). It is thought that in order to spawn, adult A. rostratus move into deeper waters (including movement out of estuaries) (Crawford, 1984, cited by Morton et al., 2005; Parry et al. 1995, cited by EPA Victoria, 2001).Long-snouted flounder are prolonged serial spawners, which continually produce eggs over a season; however most spawning takes place from May or June to October (Crawford, 1984, cited by Morton et al., 2005; Jenkins, 1986). Total fecundity appears to be high, with estimates of over 437,000 eggs in a 25cm A. rostratus (Jordan, 1994b, cited by Morton et al., 2005). Flounder larvae are considered to be weak swimmers, and rely on water currents or wind-induced surface water movements to drift inshore to settle (Crawford, 1984, cited by Morton et al., 2005).
During late winter to early summer newly-metamorphosed A. rostratus settle on shallow, sheltered, estuarine sand flats. Substrate type and salinity preferences appear to be the major determinants of their distribution (Burchmore, 1982, cited by Morton et al., 2005).
During the 1980s, larvae were reported to be common in Port Phillip Bay during the winter-spring period (Jenkins, 1986).
The early life history of A. rostratus was discussed in Westlake (1997).
Fisheries Information
Commercial
Ammotretis species are taken commercially in southern Australia. The marketing name for Ammotretis species (including A. rostratus) is “Bay Flounder” (Seafood Services Australia, 2003).The species is listed as part of the bycatch in the Commonwealth-managed Southern and Eastern Scalefish and Shark Fisheries (SESSF) (AFMA, 2002a). Given the distribution of the species, catches in Commonwealth waters are likely to be very minor. For example, in the otter trawl sub-fishery of the SETF, an Integrated Scientific Monitoring Program (ISMP) in 2000/01 reported that in 1 trawl shot, 1kg of A. rostratus specimens were discarded (Wayte et al., 2004).
A. rostratus is a commercial species in southern Australian States, such as W.A. (Cappo et al., 1998), Victoria (Jenkins et al., 1997, cited by Connolly et al., 1999; Coutin, 2000) and Tasmania (Jordan et al., 1998). In Victoria and W.A., the common name for Ammotretis rostratus is reported to be “sole”.
During the mid 1990s to early 2000s, between 1.2t and 2.7t of A. rostratus per annum were reported to be taken by commercial fishers in W.A., and the catch in 2003/04 was 853 kg (Department of Fisheries, W.A., 2002, 2004f, 2005c). Additional commercial catches of unspecified flounders in W.A. (which may include A. rostratus) are listed at the beginning of this chapter.
In Victoria, A. rostratus is considered to be of “medium significance” in the commercial fishery of Port Phillip Bay (Coutin, 2000).
A. rostratus is one of two species of flounder in Tasmania that comprises the majority of commercial flounder catches (Morton et al., 2005). Flounders are taken mainly by spear and gillnet. Tasmanian catches comprise mainly Greenback Flounder Rhombosolea tapirina, with a lesser component of A. rostratus, and the two species are not distinguished in catch returns. Combined catches of both species rose in the late 1980s from less than 20 tonnes per annum to over 40 tonnes, but have since declined steadily to about 10t in 2002/03 (Morton et al., 2005). The main capture methods are spear and gillnet, and while spear catch rates have remained relatively stable since the mid 1990s gillnet catch rates have generally declined over this period (Lyle et al., 2004). Although Greenback Flounder Rhombosolea tapirina comprise the majority of the catch, a proportion is A. rostratus. Spear catch rates have remained relatively stable since the mid 1990s, but gillnet catch rates have generally declined over this period (Lyle et al., 2004, cited by Morton et al., 2005).
In New South Wales, A. rostratus is listed as both a retained and discarded species in some parts of the estuarine fish haul fishery (e.g. Botany Bay) (Gray and Kennelly, 2001). It has also been listed as an incidental catch in the Estuary Prawn Trawl Fishery (e.g. in Botany Bay and Port Jackson) (New South Wales Fisheries, 2002).
A. rostratus is a minor component of the bycatch in the prawn trawl fishery in Spencer Gulf, South Australia. For example, 3 Long-snout 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, but it is likely to occur in the trawl grounds of the GSV / Investigator Strait, and also the eastern Great Australian Bight.
When caught in the bycatch of the S.A. Rock Lobster fishery, flounders are permitted to be retained for sale (Sloan, 20003a).
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.A. rostratus is taken by recreational fishers in Tasmania (Jordan et al., 1998; Lyle and Campbell, 1999), mainly by spearing (Morton et al., 2005), but also as bycatch of inshore gill-netting in soft bottom habitats (e.g. Williams and Schaap, 1992; Jordan et al., 1998; Lyle et al., 2000). A. rostratus is one of two species of flounder in Tasmania that comprises the majority of recreational catches (Morton et al., 2005). In Tasmania, there is a minimum legal size of 25cm for all flounder species taken by recreational fishers (Morton et al., 2005) and there is a personal possession limit of 30 (DPIWE Tasmania, 2007). The estimated recreational catch of flounder (all species) in 2000/01 of 21 tonnes was double the size of commercial catch, indicating the importance of the recreational component of this fishery (Henry and Lyle 2003, cited by Lyle et al., 2004).
In Victoria, the species is taken by recreational fishers in areas such as Port Phillip Bay, using hand spears (Department of Primary Industries data, 2003). One of the record sized specimens was taken by spearfishing, off Portsea Pier, in 1999 (Australian Underwater Federation, 2003). In Victoria, the minimum legal size is 23cm, for all flounder species taken by recreational fishers, with a bag limit / possession limit of 20 flounder (DPI Victoria, 2007b). For recreational fishers in South Australia, there is a daily bag limit of 20 flounder (all species) and a boat limit of 60. There is no legal minimum size (PIRSA, 2008a, 2008b).
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 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 Bioregions, and South Coast regions (Department of Fisheries, 2007c, 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 more limited opportunity for population dispersal, all of which can increase the vulnerability of populations to decline.The combined effects of commercial and recreational fishing, in areas where this species is regularly caught (e.g. Tasmania and other parts of south-eastern Australia, and also W.A.), may be a threatening process.
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).
In a draft ecological risk assessment report for the South East Trawl Fishery (Wayte et al. 2004), 3 “productivity attributes” and 6 “susceptibility attributes” were used to classify A. rostratus as being a “medium risk” species in terms of potential population impacts from trawling, but it is noted that bycatch number are likely to be low in commonwealth-managed fisheries, given the depth range of this species. .
Ammotretis rostratus is considered to be one of the key fish species (other than Sardinops pilchards) that is susceptible to viral haemorrhagic septicaemia virus (VHSV) (Commonwealth of Australia, 2003), but the risk of this disease entering Australian native fish populations is considered to be “very low” (Commonwealth of Australia, 2003).
Flounders are vulnerable to capture in prawn trawls, due to their benthic nature, existence in the same habitats as prawns are found, and their poor swimming ability (Carrick, 1997; PIRSA, 2003). Long-snout Flounders are found in the bycatch by prawn trawlers, but the extent to which this practice impacts upon populations is not known for this report (see below, on Research Requirements). Mortality due to trawling may be a threatening process for some of the flounder species of lesser abundance in S.A., but no species-specific data are available. It is noted, however, that one study reported A. rostratus as only a minor component of the prawn trawl bycatch in Spencer Gulf (i.e. Carrick, 1997), hence threat of impact on this species from trawling may be low, at least for that gulf.
Tanner (2003 and 2005) discussed the impacts of prawn trawling on habitats and benthos in Gulf St Vincent and Investigator Strait, and A. rostratus occurs in such trawled habitat.
A. rostratus occurs in relatively shallow waters, including estuarine areas, and may therefore be vulnerable to coastal impacts in some areas, including decline in estuarine habitat and water quality, but there are no species-specific data. Estuaries are often subject to many pollutants, and other impacts that degrade water quality and habitat. Polluted estuarine areas can take a long time to recover, as toxicants accumulate in their sediments (Pogonoski et al., 2002). 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).
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).
Research Requirements
Although well-known in some parts of the range where it is fished commercially, Long-snout Flounder is less known in S.A., and more information is required on the distribution and habitat in this State.More information is required on the relative abundance and population dynamics of this species over the range.
Where possible, flounders in prawn trawling bycatch from Gulf St Vincent, Spencer Gulf and the West Coast of S.A. should be recorded, with data analysed and monitored to determine the presence and relative abundance of this species over time.
Over the range in which this species is fished commercially, catch and effort data should be monitored over space and time where possible, and an assessment of sustainability is required (see below).
Management Requirements
Documentation and quantification of flounder bycatch in fisheries across the geographic range is required.For the ongoing commercial capture of this species in southern Australia, an assessment of sustainability is required (given the vulnerable life history characteristics, and high catchability of flounders in trawls).
As indicated in Research Requirements above, in S.A. a system should be developed for the ongoing collection and monitoring of bycatch data from the Gulf St Vincent 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; Dixon et al., 2005).
Measures (such as improvements in net design) to reduce the bycatch of benthic fish species in all trawl fisheries are recommended (see Management Notes, below). This is particularly required in areas where bycatch is high.
Assessment of the sustainability of catches in commercial fisheries in Tasmania, Victoria and W.A. 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
It is noted that prawn fisheries in southern Australia have made significant efforts during the past decades to reduce the bycatch of finfish species. Examples for Spencer Gulf and Gulf St Vincent 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; South Australian 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 the previously used sorting equipment. However, Australian Government DEH (2004b) reported that further work is required to confirm this assumption.Other Information
A. rostratus has been recorded in a number of in a number of marine protected areas in Victoria the Yaringa Marine National Park (MNP), French Island MNP, Ricketts Point Marine Sanctuary (MS) and Beware Reef MS (Bird and Watson, 1993; Plummer et al., 2003).During the 1980s and 1990s, a number of projects were undertaken n Tasmania, to culture and rear this species as a food fish (e.g. Crawford, 1984; Battaglene and Fielder, 1997).
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