© 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.

---

Latchet / Sharp-beaked Gurnard

Family Name:	Triglidae
Scientific Name:	Pterygotrigla polyommata (Richardson, 1839)
Recommended Status:	Data Deficient in S.A. State waters Near Threatened in Commonwealth–managed waters
Rationale:  Although it has a broad distribution across southern Australia, Latchet is included here because (i) it is a site-associated benthic species from soft bottom habitats in continental shelf waters, and may be vulnerable to site-specific impacts in some areas; (ii) juveniles are associated with estuarine waters, and may be vulnerable to impacts due to estuarine habitat degradation; (iii) it is caught in a number of fisheries across the range (including fish trawls, prawn trawls, fish and shark gillnets, and other gear) with the trawl catch in some Commonwealth-managed fisheries (such as the GABTF and the SETF) apparently being large, and unregulated; (iv) risk assessments in trawl fisheries indicate that populations are considered to be at medium to high risk of impact from capture; trawl fishing is likely to be the major threatening process and the major impact, and there is some evidence of serial depletion of Latchet in SE Australia; (v) in S.A. State waters, there is inadequate information about the bycatch of this species; (vi) across southern Australia, commercial (particularly trawl) fishing regulations are inadequate, particularly given the large catches in some commercial fisheries, and the lack of stock assessments; and (vii) there are inadequate data on: biology (particularly longevity and reproduction, including annual recruitment strength); stock structure (particularly in southern Australia); population dynamics, and ecology; and (viii) it is possible that, like the related species Red Gurnard, annual recruitment strength of Latchet may fluctuate significantly, and may be strongly associated with environmental variables (which could increase the vulnerability of this exploited species to population impacts), and this requires investigation.

Page Contents

Current Conservation Status

no listings known

Distribution

Southern Australia and New Zealand

The Latchet ranges across southern Australia (including Tasmania), from the central coast of N.S.W. through to the south-western coast of W.A., and also occurs in New Zealand (May and Maxwell, 1986; Paulin et al, 1989; Gomon, in Gomon et al., 1994; Australian Museum, 2004p).
Port Arthur in Tasmania is the type locality (Richardson, 1839).
Williams et al. (2001) characterised P. polyommata as one of the indicator species in “a southern community of the well-defined (continental) shelf break community” in south-western Australia, which contains a number of Flindersian (warm temperate south Australian) species that occur mainly between 200m and 400m depth, and extend northwards to about 28° S latitude.

South Australia

The Latchet is found throughout South Australia, in sandy and muddy habitats of the continental shelf. Previously, during the early decades of the 20^th century, a number of records came from parts of both gulfs (e.g. South Australian Museum records), but many of the more recent records are from mid and outer continental shelf waters of the Great Australian Bight (GAB) (e.g. Museum of Victoria records, cited in OZCAM database, 2007).
Examples of locations where Latchet have been recorded include the W.A/ S.A. border; head of the GAB; Streaky Bay; Point Weyland, Venus Bay and Anxious Bay area (eastern GAB / western Eyre Peninsula); Port Hughes in eastern Spencer Gulf (SG); Franklin Harbour area in western SG; Hardwicke Bay in south-eastern SG; Port Lincoln area in south-western SG; the “heel” of Yorke Peninsula (e.g. Edithburgh, and other locations); south-central Gulf St Vincent (GSV) (between the Fleurieu Peninsula and heel of Yorke Peninsula); eastern GSV (e.g. Black Point, Pine Point); northern GSV (e.g. Port Wakefield, St Kilda); metropolitan GSV (e.g. Semaphore, Glenelg, Marino, and other locations); southern Fleurieu Peninsula; Encounter Bay; northern Kangaroo I. / Investigator Strait (e.g. North Cape; Cape Marsden); north-eastern Kangaroo I. (e.g. Kingscote, American River) (SARDI data, 2002, cited by R. Foster, S.A. Museum, pers. comm., 2006; South Australian Museum records, Museum of Victoria records, cited in OZCAM database, 2007).
In South Australia, the species appears to be commonly recorded across the Great Australian Bight (GAB). There are hundreds of research trawl records from outer continental shelf waters in this area, many collected during the 1960s and 1970s (CSIRO Marine Research data, cited in CSIRO, 2007). A CSIRO Marine Research cruise to the GAB in April – May 1980, recorded P. polyommata in every trawl shot (CSIRO Division of Fisheries and Oceanography, 1980). More recently, bycatch sampling in the GAB during 2001-2002, showed that Latchet, which is not a target species, is nevertheless one of the most commonly recorded species in the GAB Trawl Fishery, and large quantities are discarded as part of the bycatch (Brown and Knuckey, 2002).

Habitat

Adults are found mainly on the outer continental shelf, and juvenile latchets are known to enter bays and estuaries, particularly in autumn (May and Maxwell, 1986; Sea-Ex Australia, 2004). Latchets are sometimes found in shallow estuaries in Tasmania (Gomon, in Gomon et al., 1994).
Latchets mostly occur in areas with sandy or muddy bottom (Gomon, in Gomon et al., 1994; Australian Museum, 2004p).
Various published depth ranges (in order of increasing depth) include 35m -  200m (Gomon, in Gomon et al., 1994; Australian Museum, 2004p); 20m – 220m (Sea-Ex Australia, 2004); 35m – 400m (May and Maxwell, 1986; Paulin et al., 1989), or 10m – 600m, but mostly within the depth range 50m – 400m (CSIRO et al., 2001; N.S.W. Department of Primary Industries, 2004).
In a survey of nearshore fishes in south-western Australia, Latchet was recorded rarely in soft-bottom habitat worked by trawls / dredge (Hutchins, 2005). Williams et al. (2001) characterised Latchet as one of the indicator species in “a southern community of the well-defined (continental) shelf break community” in south-western Australia, indicating that the species is more common on the outer continental shelf and upper slope than at other depths.

Notes on the Biology

Growth

P. polyommata grows to around 57cm (Gomon, in Gomon et al., 1994; Australian Museum, 2004p) or 62cm fork length (May and Maxwell, 1986, cited in Froese and Pauly, 2007; Sea-Ex Australia, 2004). During a bycatch survey in 2001-02, most specimens caught in the Great Australian Bight ranged between 23 – 33cm (Brown and Knuckey, 2002).
Latchet is reported to grow to about 2.6kg (Sea-Ex Australia, 2004), but it is noted that one of the maximum sizes recorded is 1.8kg (Hutchins and Swainston, 2001).

Diet

Latchet eat small fish (Coleman and Mobley, 1984; Bulman et al., 2001). It is likely that Latchet feed mostly at night, based on trawl survey results in the Great Australian Bight, which showed that 87% of Latchet caught in the post-dawn trawl had food in their stomachs, compared with 25-30% at other times of the day (CSIRO Division of Fisheries and Oceanography, 1980).

Reproduction

Latchet first spawn when they are about 45cm long (Sea-Ex Australia, 2004).
Spawning occurs in July and August in New South Wales waters (Sea-Ex Australia, 2004).

Behaviour

Like other gurnards, this species can “walk” along the sea floor using the feelers in front of the enlarged pectoral fins (Hutchins and Swainston, 1986).

Other Information

Latchet is a minor part of the diet of Australian Fur Seal, Arctocephalus pusillus doriferus (Page et al., 2005).

Fisheries and Trade Information

Southern Australia - Commercial

Latchet is often sold in fish markets (Gomon, in Gomon et al., 1994; AFMA, 2002a), using its correct common name, “Latchet” (Seafood Services Australia, 2003). Latchet is available all year round, and is sold whole and chilled on domestic markets across southern Australia (Sea-Ex Australia, 2004), including South Australia. According to AFFA (2004d), Latchet is also imported into Australia.
When taken outside of 3 nautical miles (NM) from the coast, catches of Latchet are managed by the Commonwealth, and when taken inside 3 NM, are managed by the States (AFMA, 2002a). For Commonwealth licence holders with Scalefish Hook, Shark Hook, Gillnet Sectors and Coastal Waters permits, Latchet may be caught in Commonwealth waters (outside 3 NM) but not in coastal waters (inside 3NM), with a concession that allows methods other than trawl, and there are no catch restrictions (AFMA, 2004e).
According to FAO (2003c), the following tonnages of Latchet have been taken in Australian waters since 1970 (Table 12). The figures are reported to be the combined total of catches from both the “Pacific – South-West” and “Indian Ocean – Eastern” statistical areas within Australia. For the period from the early 1970s to the late 1980s, the FAO figures closely match those provided by Bureau of Rural Resources (1991). According to BRR (1991), the majority of the Latchet catch since 1964 has come from N.S.W., with a lesser contribution from Victoria (maximum 25t in 1981/82, usually less than 10t per annum during the 1970s and 1980s), and Tasmania (average several tonnes per annum); occasional catches are also recorded from Western Australia (e.g. 3t in 91985/86). The species is also taken in deeper waters of the Great Australian Bight (both W.A. and S.A.), as discussed below.
 

Table 12 Reported Catches of Latchet from Australia, 1970 – 2001
Year	Catch (t)	Year	Catch (t)
1970	100	1986	156
1971	100	1987	199
1972	200	1988	208
1972	300	1989	173
1974	206	1990	220
1975	77	1991	220
1976	155	1992	142
1977	59	1993	176
1978	150	1994	153
1979	128	1995	121
1980	188	1996	58
1981	180	1997	136
1982	172	1998	92
1983	126	1999	94
1984	108	2000	120
1985	111	2001	149
(from FAO, 2003c)

Latchet is a retained by-product (and in some cases, discarded bycatch) in numerous Commonwealth-managed fisheries across southern Australia, including Gillnet, Hook and Trap Fishery (a retained by-product, according to Bromhead and Bolton, 2005), South East Trawl Fishery (retained), Great Australian Bight Trawl Fishery, and Western Deepwater Trawl Fishery (retained), as well as the High Seas Trawl Fishery (Bromhead and Bolton, 2005). Much of the catch is from commercial trawling in the South East Trawl Fishery (SETF) and the Great Australian Bight Trawl fishery. In the SETF, the species is part of the saleable by-product of both otter trawls and Danish seines (Wayte et al., 2004).
According to Barratt et al. (2001), historic trawl records of Latchet catches in the Commonwealth-managed South East Trawl Fishery showed that the species was (unofficially) considered a target species by fishers, even though Latchet has always officially been classified as a bycatch species. In the South East Trawl Fishery, the species is taken in large quantities. For example, about 89.5t was recorded as bycatch in fishers’ logbook data during the 2000/01 period (AFMA, 2002a). In contrast, a scientific monitoring program in 2001 recorded 6.7t in the bycatch (almost all of which was retained), in the same fishery (AFMA, 2002a).
A large quantity of P. polyommata that is trawled in southern Australia is discarded. During the period 1995 – 2002, one estimate of the average catch of Latchet in the Great Australian Bight Trawl fishery was 30t per annum (Lynch and Garvey, 2003). According to AFMA (2001c), the tonnage of Latchet discarded in the Great Australian Bight Trawl fishery during the period 1987 to 1998 ranged between 1.8 tonnes (in 1987) and 145 tonnes (in 1990), with an average of 42 tonnes per annum. Bycatch sampling in the GABTF (during 2001 and 2002) showed that Pterygotrigla polyommata was observed in 162 of the 209 trawl shots over that period; the average quantity discarded was 253kg per trawl shot, and the average quantity retained was 2kg per trawl shot (Brown and Knuckey, 2002). Latchet is taken mostly in the Central and Western Zones of the GAB Trawl fishery, and the quantity discarded is particularly high in the central zone, with more than 600kg of Latchet per shot recorded in the discards during a bycatch survey in 2001-02 (Brown and Knuckey, 2002). During that survey, the quantity of Latchet discarded per trawl shot in the GAB Trawl fishery was greater than that of any other species taken as bycatch in that fishery (see Brown and Knuckey, 2002, Table 4). The average catch reported in fishers’ logbooks over the period 2001- 2004, was 50 tonnes per annum (Daley et al., 2006). AFFA (2004b) reported that (i) up to 40% of the entire catch of all fish and shark species from shelf waters is discarded in the GABTF; and (ii) Latchet forms one of the major components of that discarded catch, despite the potential commercial value of the species. Industry is attempting to find markets for the large quantity of latchet caught in this fishery (AFMA data, cited by Commonwealth of Australia and Government of South Australia, 2004).
The species is a minor bycatch in the Southern Shark Fishery. A study of bycatch from 1998 to 2001 recorded only 23 specimens of Latchet in the catch of 6-inch gillnets in Bass Strait, and 5 specimens in the catch of 6.5-inch gillnets off S.A., during that period (Walker et al., 2003).
Latchet is one of approximately 20 main scalefish species taken in the New South Wales Ocean Trawl fishery (New South Wales Department of Primary Industries, 2004), and is described as a “key secondary species”. In the Ocean Trawl Fishery, landings of Chelidonichthys kumu (Red Gurnard), Pterygotrigla polyommata (Latchet) and Pterygotrigla andertoni (Painted Latchet) are combined. Total annual reported landings (not including discards) between 1984 and 2001 usually ranged between 20t and 30t, apart from a peak of 40t in 1992/93 (New South Wales Department of Primary Industries, 2004). Latchet is also a very minor component in the bycatch of the Estuary General Fishery in N.S.W., and has been recorded as part of both the retained and discarded bycatch in areas such as St Georges Basin (Gray and Kennelly, 2001; New South Wales Fisheries, 2001).
Latchet is a minor part of the discarded bycatch in the Bass Strait Scallop Fishery. During a bycatch survey in 2002, 24 Latchet specimens were recorded in 59 random tows (Haddon and Semmens, 2002), and 6 were recorded in 36 tows, in 2004 (Haddon et al., 2004).
The species is caught commercially in Tasmania (Lyle and Jordan, 1999), and more than half the catch of gurnard species is taken by line fishers (McLeay et al., 2002). Between 1990 and 2000, the reported catch of Latchet has ranged between 1.3t (in 1998/99) and 13.9t (in 1990/91), with a catch of less than 5t per annum between 1996 and 2000 (Lyle and Hodgson, 2001).
The species is also part of the bycatch in the Western Deepwater Trawl Fishery (WDWTF) in W.A. (AFMA, 2004f). In the WDTF, fishery logbook data recorded variable numbers per annum in the bycatch during the 1990s and early 2000s, including 486 individuals of P. polyommata in 1993-94, 991 in 1996-97, 10 in 1997-98, and 283 during part of the 2002-03 season to March 2003 (AFMA, 2004f). It is not known for this report whether the data from logbooks accurately reflect the total catch, or are underestimated.
The species occurs in habitat types and at depths worked by prawn trawl fisheries in South Australia. It is noted that Latchet was not recorded as part of the bycatch in Spencer Gulf, during bycatch surveys in the 1990s (Carrick, 1997), but other members of the family were (e.g. L. papilio, in large numbers).  P. polyommata has been recorded in the prawn trawl fishery of GSV / Investigator Strait (e.g. Museum of Victoria data, 1985, cited in OZCAM database, 2006).
It is possible that the use of Latchet as a food species may increase during the 2000s. For example, P. polyommata is now one of the 8 main seafood products sold by one of Australia’s largest seafood supply companies, based in South Australia.

New Zealand – Commercial

No information on the catch of P. polyommata in New Zealand could be found for this report.
Latchet from New Zealand is reported to be used commercially in the aquarium trade (Paulin et al., 1989, cited in Froese and Pauly, 2006), but no other information is available for this report.

Southern Australia - Recreational

Gurnards in general are taken by some recreational fishers in southern Australia, including South Australia (see statistics from Henry and Lyle, 2003, cited above in section on Triglidae); however species-specific information is not available. Latchet is taken by recreational fishers in Tasmania (Lyle and Campbell, 1999).
Latchet is also taken by charter boat fishers, and other recreational fishers who fish deeper waters. For example, the species is taken by charter boat fishers as part of the mixed fish catch from deeper continental shelf waters off Robe in South Australia (Mensforth, 2002). As another example, Latchet is promoted as one of the species that can be taken when fishing the offshore waters in north-eastern Tasmania (e.g. see Stevens, 2004).
Some recreational fishing clubs and associations keep records of the maximum sizes caught (e.g. Australian Anglers Association, WA Division Inc., 2002a; New South Wales Fishing Clubs Association, 2003). The record size of Latchet taken by an angler is reported to be 1.8kg, being a specimen taken from Batemans Bay in 1987 (New South Wales Fishing Clubs Association, 2003)
Latchets are also taken by spear fishers in some areas. There is an Australian spearfishing record of a 1.46kg specimen taken from Victoria in 1972 (Australian Underwater Federation, Inc., 2003).

Vulnerable Characteristics of the Species and Threatening Processes

Latchet is a site-associated benthic species from various habitats in continental shelf and upper slope waters, and may be vulnerable to site-specific impacts in some areas.
Although the species is vulnerable to capture using a variety of fishing gear, trawl fishing is likely to be the major threatening process, and the major impact. Latchet are highly vulnerable to capture using benthic trawls; the species is a large part of the bycatch in a number of fisheries across south-eastern and southern Australia; and the catch in some fisheries is large, and unregulated. Latchet has been fished since the early 1900s in south-eastern Australia, and serial depletion of stocks may have occurred in some areas. For example, in the Commonwealth’s South East Fishery, examination of 64,371 steam trawler records from the periods 1918-23, 1937-43 and 1952-57, showed that Latchet (Pterygotrigla polyommata), a species that was apparently abundant in the early years of the fishery, virtually disappeared from catches in later years (Klaer, 2001). The fishing fleet moved to more distant fishing grounds and deeper waters as catch rates declined. The authors considered that the disappearance of species such as Latchet from the catch may be due to high fishing pressure alone, or to a combination of fishing pressure, changes in the shelf habitat possibly caused by the trawl gear, and environmental fluctuations (Klaer, 2001). In the aforementioned analysis of per-haul records of Latchet catches by steam trawlers on the south-eastern Australian continental shelf from 1918 to 1957 (Klaer, 2004), catch rates (in weight per haul per species) were standardised to annual indices of abundance using a log-linear model, and the results of the standardised annual index trends showed a strong to severe decline during the period covered by the data (Klaer, 2004).
In a draft ecological risk assessment report for the South East Trawl Fishery (Wayte et al. 2004), 4 “productivity attributes” and 6 “susceptibility attributes” were used to classify Latchet as being a “medium risk” species in terms of potential population impacts from trawling, and it is noted that the calculated risk value was at the upper end of the range for the “medium” category, hence the species almost qualified as being at “high risk”.
The species is taken in relatively large quantities in the Great Australian Bight Trawl Fishery, and most of the catch is discarded (see section above, on Fisheries Information). For example, a recent onboard observer program has shown that a significant proportion (about 44% by weight) of the continental shelf catch of fish and sharks is discarded, with the bulk of discards being latchet, stingarees and small leatherjackets (AFFA, 2004b, 2004c). Daley et al. (2006) identified Latchet as being at “high risk” of population impacts from capture in the GAB Trawl Fishery, in part due to the large quantities taken every year (e.g. during the early 2000s, ~ 50t per annum).
The species has been recorded in prawn trawl bycatch in S.A. (see section above, on Commercial Fishing), but there are inadequate data on Latchet bycatch over space and time in prawn fisheries in South Australia (and no analysis), hence it is not known to what extent prawn trawl fishing is a threatening process.
Juveniles are associated with estuarine waters, and may be vulnerable to impacts due to estuarine habitat degradation, which is the case for many estuaries across southern Australia.
It is possible that, like the related species Red Gurnard (see synopsis for Chelidonichthys kumu, annual recruitment strength of Latchet may fluctuate significantly, and may be strongly associated with environmental variables, and this requires investigation. Environmentally-driven fluctuations in recruitment strength can increase the vulnerability of exploited species to population impacts.

Research and Management Requirements

Considering that Latchet is taken in large quantities in several fisheries across the southern Australian part of the range, there is little information on age, growth, reproduction and annual recruitment strength. Also, the relationship between Latchet populations from south-eastern, southern and south-western Australia should be determined.
In the South East Trawl Fishery and the Great Australian Bight Trawl Fishery, large, unregulated catches (and discarding) of Latchet is a significant issue. Other than risk rankings in 2004 and 2006 (Wayte et al., 2004; Daley et al., 2006), there has been little assessment undertaken of the sustainability of the continued high bycatch of this species (as by-product in some fisheries, and discards in others), and the impact on populations across southern Australia.  The potential impact of trawl fishing on populations of P. polyommata should be assessed, and measures to reduce bycatch should be undertaken where possible. During the period in which stock assessment is being undertaken, measures to reduce Latchet catches and discarding in Commonwealth-managed trawl fisheries are required. Consideration should be given to introducing a quota on catch, with measures to ensure, where possible, that the quota serves to reduce total catch (both retained and discarded), and does not increase the discarding practice.
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). As part of that undertaking, the catch of P. polyommata in South Australian prawn trawl fisheries should be determined. For example, there are records of the species the bycatch of the GSV (incl. Investigator Strait) Prawn Fishery, but bycatch is not quantified over space and time in this fishery, nor in the West Coast Prawn Trawl fishery in the eastern Great Australian Bight. Given that the species also occurs in areas trawled by the Spencer Gulf Prawn Trawl fishery, the bycatch of this species should also be quantified in that fishery.
Numerous measures have been undertaken in the prawn fisheries in southern Australia to reduce the bycatch of benthic fish species (see synopsis above, on Lepidotrigla papilio), and continual improvements (e.g. in net design etc.) should be encouraged, to further reduce the bycatch of benthic fish species in prawn trawl fisheries.
There should be recreational fishing limits for gurnard species in all southern States, including South Australia.

Other Information

P. polyommata is part of a species complex in the sub-genus Pterygotrigla, with members collectively from southern temperate areas off Chile and around Australia and New Zealand. P. polyommata is related to P. andertoni Waite / P. picta (Günther), and P. pauli Hardy (Richards et al., 2003). The complex of related species possibly also includes a few species from the tropical western Pacific, P. acanthoplomate (Fowler) and a yet to be identified species (Richards et al., 2003).