© 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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Luderick / Blackfish

Family Name:	Girellidae or Kyphosidae sub-family Girellinae
Scientific Name:	Girella tricuspidata (Quoy and Gaimard, 1824)
Recommended Status in S.A:	Near Threatened
Rationale:  Included here because (i) Luderick is less common in S.A. (which is at the western edge of the geographic range) compared with south-eastern Australia; (ii) the species is intensively fished in some areas of southern Australia, due to its accessibility and ease of capture (in shallow waters) and reputation as a prized food fish, and therefore it is also taken by both commercial and recreational fishers wherever it is found in South Australia; (iii) there are no fishing restrictions on this species in S.A., despite lack of information about populations sizes / abundance in this State (which is likely to be significantly lower than in south-eastern Australia); (v) Luderick is relatively slow growing, site-associated, and periodically aggregates in shallow waters, all of which increases its vulnerability to over-exploitation by fishers; (vi) juveniles that are caught and released by fishers are likely to have a low survival rate; (vii) generally, estuaries are important nursery areas, but the significance of estuaries in S.A. in the life cycle of local Luderick populations is not known;  and (viii) the shallow coastal water habitats (including estuaries) of juveniles and adults, may make populations vulnerable to impacts from nearshore habitat degradation and decline in estuarine water quality and quantity.

Page Contents

Current Conservation Status

No listings known

Distribution

General

The distribution in Australia is from mid-South Australia around the south-east coast (including Tasmania, King I., Flinders I., the Kent Group, Furneaux Group), through to Hervey Bay in Queensland (Edgar, 1984; Prokop, 2000; Edgar et al., 1999; Edgar, 2000; RPDC, 2002). Luderick is mainly an eastern seaboard species, common in New South Wales, and is infrequently / rarely found in South Australia (Hutchins and Swainston, 1986; Fishnet, 2002; Australian Museum, 2002k). The species is also reported to be “commonly encountered” in Victoria (Edmunds and Hart, 2003), and is a “rare vagrant” in Tasmania (Edgar et al., 1999).
The species also occurs in New Zealand (Kuiter, 1993), mainly around the North Island (Francis, 1996; Brook, 2002).

South Australia

South Australia is at the end of the southern Australian range (Kuiter, in Gomon et al., 1994; Kuiter, 1996a). Examples of locations in S.A. where the species occurs include the metropolitan area of Gulf St Vincent (GSV) (e.g. the species has been recorded in deeper waters west of Outer Harbour); southern metropolitan area (e.g. Noarlunga Reef; Port Willunga); south-eastern GSV / Fleurieu Peninsula (e.g. Cape Jervis, and south-east of the Fleurieu, including outer Encounter Bay); northern Kangaroo I. (e.g. Harvey Return, Stokes Bay, Cape Cassini), north-eastern Kangaroo I. (including parts of Eastern Cove, and sites off the Dudley Peninsula, such as Cape Willoughby); off the “heel” of Yorke Peninsula / south-western GSV, and south-western Spencer Gulf (SARDI data, 1995-97; S. Shepherd and K. Brown, unpubl. data, 2002; D. Muirhead, pers. comm., 2005; Edgar et al., 2006; P. Carter, unpubl. data, 2007; J. Baker, unpubl. data, 2007; Australian Museum records, and S.A. Museum records, cited in OZCAM database, 2007).
During surveys of more than 150 reef sites across western and central S.A., Luderick was recorded rarely, in low numbers, and at very few sites (S. Shepherd, unpubl. data, 2002-2006).

Habitat

In general, Luderick is a shallow water (0m – 20m) fish, and has been recorded in a variety of different nearshore habitat types, including estuaries, tidal rivers and lakes and pools, mangroves, seagrass beds, rocky foreshores / shallow rocky reefs, macroalgae-dominated reefs (including “kelp forests”), urchin-induced “barrens”, and other nearshore habitats (Russell, 1977; Pollock, 1981; Winstanley, 1985; Morton, 1990; Kuiter, 1996a; Connolly et al., 1999; Edgar, 2000; West and Jones, 2001; Hindell and Jenkins, 2004; Anderson and Millar, 2004; N.S.W. DPI, 2006; DPIW Tasmania, 2006a). The species is also found around piers / jetties (S.A. Museum record 1978; Kuiter, in Gomon et al., 1994; Coleman and Connell, 2001; Fish Victoria, 2002; N.S.W. DPI, 2006), and near structures in estuaries, such as bridge pylons (DPIW Tasmania, 2006a).
The species is reported to “flourish in seagrass areas” (Kailola et al., 1993). In various parts of coastal New South Wales, Bell and Pollard (1989), Ferrell and Bell (1991) and Gray et al. (1996) reported juveniles mainly from Zostera capricorni seagrass beds. More recently, Rotherham and West (2002) and Smith and Sincerchia (2004) reported similar findings: that in central N.S.W. estuaries, G. tricuspidata juveniles recruit during spring and early summer, to Zostera capricorni beds. Similarly, in Victoria, a survey of fish associated with Zostera seagrass in Corner Inlet found that small juvenile G. tricuspidata recruited to the area in December (Jenkins et al., 1997, cited by Plummer et al., 2003). Juvenile Luderick have also been recorded in Heterozostera / Zostera tasmanica seagrass beds in Tasmania (Jordan et al., 1998). In Queensland, juveniles have also been recorded over coastal mudflats adjacent to seagrass beds (Melville and Connolly, 2005).
Adults occur abundantly in estuaries and on shallow coastal reef (usually less than 20m depth), but young juveniles (e.g. 0+) are normally associated with estuarine seagrasses, or mangrove-lined creeks, or macroalgae on rocks (and often in large rock pools), later moving into deeper channels nearby (Kuiter, 1996a; Connolly et al., 1999; Edgar, 2000; Australian Museum, 2002k; Smith and Hindell, 2005). Luderick juveniles are dependent on estuaries as nursery habitat (Edgar et al., 1999). Across the southern part of N.S.W., Luderick have been recorded in many of the estuarine areas (i.e. coastal rivers, lakes and inlets) (e.g. West and Jones, 2001).
G. tricuspidata is sometimes observed in large schools on coastal reefs, moving in and out of estuaries at specific times of the year (Kuiter, 1993).
In New Zealand, G. tricuspidata has been observed in greater numbers on reefs of high relief, compared with flat reefs (Meekan, 1986, cited by Jones, 1988). Juveniles have been observed settling on very shallow sandstone reefs within estuarine areas (e.g. Morrison, 1990).

Notes on Biology and Behaviour

Age and Growth

Luderick grow to around 70cm (N.S.W. DPI, 2006b) or 71 cm (uncited reference, in Caton and McLoughlin, 2000), and a weight or around 4kg (N.S.W. DPI, 2006). The maximum size recorded by the Australian Anglers Association Records Authority is 3.884kg (Australian Anglers Association, 2005). Another of the record weights recorded is 3.5kg, being a specimen reportedly caught in the Snowy River, in 1980 (Australian Anglers Association, Victorian Division, 2003).
Luderick are slow growing, taking up to 5 years to reach 27cm fork length (New South Wales Fisheries, 2001). A study of Luderick in the commercial estuarine fisheries in N.S.W. showed that there is considerable variation in the size at age of Luderick, and fish length is a poor indicator of fish age (Gray et al., 2000). Fish during that survey were aged between 2 and 8 (Gray et al., 2000), and the species may live for longer than 10 or 11 years (uncited reference, in Caton and McLoughlin, 2000; Annalla et al., 2002, 2003; Sullivan et al., 2005).

Diet and Feeding Behaviour

The species is omnivorous (Clements and Choat, 1997; Raubenheimer et al., 2005). Although Luderick eat filamentous red and green macroalgae (including Ulva “cabbage weed”), and also seagrasses (Russell, 1983; Kailola et al., 1993; Anderson, 1987; Moran and Clements, 2002), they also supplement the diet with invertebrates. A study in New Zealand, in which gut contents of field-caught Luderick were analysed, revealed a diet comprising significant proportions both of algal and non-algal (copepods, hydroids, and organic detritus) foods, with the relative proportions of algal and non-algal food items varying from 65% of non-algal foods in winter to 34% in autumn. Preferred algal foods included Enteromorpha intestinalis and Ulva lactuca (Raubenheimer et al., 2005). Molluscs, prawns and polychaetes are reported to be occasionally consumed, more often during winter and spring (uncited reference, in Sea-Ex Australia, 2002).
Luderick feed close to rocks, beneath floating seaweed, and congregate along the lower reaches of estuaries that are open to the sea. The species also congregates at river break walls, sea wall rocks, along rocky coastal shorelines, jetties and bridges. Luderick are mid-water feeders (Fishnet, 2002).
Dolphins feed on large numbers of Luderick, in both in estuaries and areas further offshore (Sea-Ex Australia, 2002). Luderick are eaten by some seabird species. For example, G. tricuspidata is a major component of the diet of the Great Cormorant in some areas (Reside and Coutin, 2001).

Migration and Schooling Behaviour

In New South Wales, Luderick undergo a northerly migration along the coast, prior to spawning (New South Wales Fisheries, 2001).
Along the east coast of Australia, Luderick is often seen in large schools, in the vicinity of rocky outcrops, and in harbours, and under jetties (Kuiter, in Gomon et al., 1994; Australian Museum, 2002k). Large schools of mature Luderick are reported to contain equal numbers of both female and male fish. In about November they make runs from inside the rivers and coastal lakes to sea. They spawn in the surf zone and estuary mouths, from about July to August in southern Queensland, August to December in Central and northern New South Wales and October to February or March in Victoria (Sea-Ex Australia, 2002).

Reproduction

Length at maturity is around 22 - 25cm FL for males, and 26+cm FL for females (Kailola et al., 1993; N.S.W. Fisheries, 2001), which may correspond to an age of about 3 years (uncited reference, in Caton and McLoughlin, 2000).  In New Zealand, the age at maturity is reported to be 4 to 5 years (Annalla et al., 2002, 2003; Sullivan et al., 2005, cited by Weeber and Szabo, 2005).
Luderick is considered to be a marine species that depends on estuaries as nursery areas (Morrison, 1990; Edgar et al., 1999). Maturing Luderick form large aggregations and mature fish undertake spawning 'runs' from inside the rivers and coastal lakes, to the sea. The fish spawn in the surf zone and near estuary mouths, and usually return to estuaries after spawning (Kailola et al., 1993; New South Wales Fisheries, 2001). Along the central and southern coasts of N.S.W., juveniles recruit to estuaries mainly in spring and summer (Worthington et al., 1992; West and Jones, 2001; Rotherham and West, 2002). A study in N.S.W. showed that in a small constructed harbour in Botany Bay, the Zostera capricorni seagrass bed is a “recruitment” sink for new recruits and juveniles of Luderick, with significantly higher numbers (up to 73 times) found in this area than similar habitats at 15 other sites studied in New South Wales (McNeill et al., 1992). Worthington et al. (1992) studied recruitment over a one year period in Botany Bay, and reported that up to seven cohorts of G. tricuspidata occurred in the area between October and February, and most cohorts did not remain in the habitat for more than 2 months. A more recent study in Botany Bay showed that recruitment by G. tricuspidata to Zostera capicorni seagrass beds reflected lunar or tidal cycles, and that juveniles recruited to the seagrass beds in discrete “pulses” (Smith and Sinerchia, 2004). In that study, emigration of G. tricuspidata juveniles out of their seagrass bed “nurseries” appeared to be length-dependent (Smith and Sincerchia, 2004). At a larger scale, there is a latitudinal gradient to the timing of recruitment of Luderick to estuarine habitats in south-eastern Australia (Gray et al., 2000).

Other Information

A study in New South Wales (Gray et al., 2000) showed that there were spatial, temporal and gear-related patterns in the sex, size and age composition of Luderick catches in the commercial fishery, across several estuaries. The relative abundance of young fish also varied greatly among sites within an estuary, as well as between estuaries (Gray et al., 2000). Curley and Gillings (2006) showed genetic differences between G. tricuspidata samples taken from different reefs in New South Wales.
Luderick are eaten by a variety of predators, such as Spotted Wobbegong Orectolobus maculatus (Compagno, 2005), the Short-beaked Common Dolphin (Delphinus delphis) (Neumann and Orams, 2003) and Bottlenose Dolphin (Tursiops) (Constantine and Baker, 1997), and sea birds such as Osprey (Pandion haliaetus) (Clancy, 2005).

Fisheries Information

Southern Australia – Commercial

Luderick are intensively fished by commercial fishers (Edgar, 2000), particularly in eastern Australian states (N.S.W., Victoria) (Kuiter, 1996a), although the species is also taken commercially in Queensland and Tasmania (Cappo et al., 1998), and in small numbers in South Australia. The commercial name is “Luderick” (Seafood Services Australia, 2003). Commercial Luderick catches are greatest where seagrass is most abundant. Commercial fishing for Luderick occurs all year round in estuaries, and along coastal shores and lakes.  The species is mostly fished for at night.  The methods of capture include tunnel nets, beach seine, haul and pound nets. The entire catch of Luderick is sold on the domestic market in Australia (Sea-Ex Australia, 2002).
Total catches of Luderick in Australian waters during the 1980s and 1990s are listed below, according to statistics from Bureau of Rural Science. The Luderick catch comprises components from NSW, Victoria and Queensland (and a minor catch component form Tasmania) with the annual catches from NSW being an order of magnitude greater than those from Victoria and Queensland (BRS, 1991, 2004a). South Australian catch statistics (see section below) are not included in the BRS databases (Figure 1).

Figure 1 Luderick: Total Reported Catch in Australian Waters.

Note: Catch data are missing from (i) NSW for the period 1984 - 1987; (ii) Victoria, 1972-78, and 1985-90, and (iii) Queensland, 1981 – 1988.  (from BRS, 1991, 2004a)

Luderick is one of the main species taken in the N.S.W. commercial estuarine finfish fishery. There are two components to the fishery: a specific fishery for flathead and a general fishery (Gray et al., 2003), the latter of which is a multi-species fishery in which many fishers use a variety of methods (Gray et al., 2000), such as gill-nets and hauling nets, mainly in autumn and winter (New South Wales Fisheries, 2001). Examples of estuarine waters in N.S.W. in which Luderick is taken commercially include the Tuggerah Lakes, Clarence, Richmond, Hawkesbury and Shoalhaven rivers, Botany Bay, Lake Macquarie, and St Georges Basin (West and Gordon, 1994; Crosser, 1997; Gray and Kennelly, 2001; IEP on Environmental Flows and NSW Fisheries, 2003). Historically, catch numbers have fluctuated over time. For example, in the Tuggerah Lakes system, commercial catch of Luderick has fluctuated from 10 tonnes caught in 1956 to 140 tonnes in 1966, and back to 10 tonnes in 1980 (Henry and  Virgona, 1980; Virgona and Henry 1987, cited by Crosser, 1997). Collectively in N.S.W. estuaries, the species is taken in large numbers. For example, during the 1990s, a study by Pease showed that the average annual commercial catch of Luderick from 53 estuaries in N.S.W. during the period 1991 to 1995, was 383 tonnes (SE = 47 tonnes). In the Estuarine Commercial Gillnet Fishery, Luderick is one of the 4 main finfish species in the bycatch (FRDC, 2004a). A study by Gray et al. (2000) reported that in the estuarine fishery during the late 1990s, commercial landings of Luderick were of even sex ratios, but there was considerable variation in the size composition of catches, not related to gear type or location. During that period, several year classes contributed to commercial landings (e.g. in the Clarence River in 1997, age of landed Luderick ranged from 2 – 8 year old fish) (Gray et al., 2000). In the estuarine commercial gillnet fishery, the rate of discarding is reported to be low (Gray et al., 2005). During a bycatch study in 2001 (comprising 265 fishing trips), Girella tricuspidata (along with Sea Mullet Mugil cephalus) accounted for 85% by number of total observed catches. G. tricuspidata was one of three species below the minimum legal length which collectively accounted for 69% by number and 49% by weight of all discards observed (Gray et al., 2003). Discarding was greatest in the smallest mesh sizes and during winter, when nets can be set overnight (Gray et al., 2005). Similarly in the estuarine gillnet fishery for flathead Platycephalus fuscus (in which the flathead comprise only ~ 50% of the catch) Luderick was shown to be one of the 5 major bycatch species, which collectively accounted for 82% of total bycatch by number and 71% by weight (Gray et al., 2003, 2004).
Luderick is also one of the 6 main fish species taken in the N.S.W. Ocean Hauling Fishery, in which commercial hauling and purse seine nets operate from sea beaches and in ocean waters within 3 nautical miles of the N.S.W. coast (N.S.W. Fisheries, 2004b). There is a minimum legal size of 25cm for Luderick taken in the Ocean Hauling Fishery. The average catch of Luderick in 1997/98 and 1998/99 by all ocean hauling methods within that fishery was 77.1 tonnes (for all zones of the fishery combined) (New South Wales Fisheries, 2004b, Table B2). In 1998/99 and 1999/2000, it is estimated that the quantities of Luderick taken in N.S.W., by all fisheries combined, were 470t and 489.6t respectively (New South Wales Fisheries, 2004b).
The species is part of the bycatch in the N.S.W. prawn trawl fisheries, in rivers such as the Manning, Wallamba, Shoalhaven, and Clarence (Gray and Kennelly, 2001), and Lake Illawara (Gray et al., 2006). For example, Gray and Kennelly (2001) reported that between September 1998 and August 1999 (and excluding the June to August closure period for the Manning and Shoalhaven Rivers), the prawn haul fleet caught the following numbers of Luderick: Manning River = 81 fish (SE = 52); Wallamba River = 119 fish (SE = 35); and Shoalhaven River = 640 fish (SE = 292). Juvenile Luderick were amongst the 4 scalefish species that dominated the discarded catch (Gray and Kennelly, 2001).
Luderick are often used as bait in the rock lobster fishery in N.S.W., and these fish are supplied by the N.S.W. Ocean Hauling Fishery and the Estuary General fishery (New South Wales Fisheries, 2004b).
In Victoria, the commercial catch (in tonnes live weight) of Luderick in recent years is shown in the table below. The species is taken at locations such as the Gippsland Lakes and Lake Tyers, where the catch per annum has ranged between 9t and 49t per annum between 1978 and 2006, with catches of between 10t and 20t per annum during the past decade (Table 4, DNRE Victoria, 2004; DPI Victoria, 2007).

Table 4 Commercial Catch of Luderick in Victorian Waters 1997/98 – 2005/06
Year	Catch (t)
1997/98	52
1998/99	48
1999/00	28
2000/01	26
2001/02	45
2002/03	25
2003/04	20
2004/05	16
2005/06	21
(DNRE Victoria, 2002, 2003, 2004; DPI Victoria, 2007)

Luderick is reported to be one of the species commonly caught in the bycatch of the commercial eel fishery in Victoria (DPI Victoria, 2003); however data are not available for this report.
Luderick is a minor commercial species in Tasmania (Smith and Heran, 2001), and is sometimes taken when fishers are targeting other species, such as Banded Morwong (Murphy and Lyle, 1999). From the late 1970s to mid 1980s, the reported catches in Tasmania were less than 1 tonne per annum. Catches rose to between 3t and almost 6t per annum during the late 1980s, then reverted back to less than 2 tonnes per annum for most years during the 1990s (Lyle and Jordan, 1999; Smith and Heran, 2001).

Southern Australia – Recreational

The species is popular for anglers, and intensively fished (Edgar, 2000) particularly in Queensland and N.S.W. (Kuiter, in Gomon et al., 1994). Luderick has been described as “a great sport fish which is hard to hook and offers a good fight to land” (Fishnet, 2002). Specimens caught recreationally are often in the range 500g - 2kg, and the Australian record is reported to be 3.884kg (Fishnet, 2002).  Most recreational fishing is reported to take place in winter.  Fish are caught with hand lines and long rods with light lines, from boats, jetties and shore (e.g. rock walls and rocky headlands) (Sea-Ex Australia, 2002).
Luderick is considered to have “a huge angling following” in Victoria (Fish Victoria, 2002). Examples of coastal locations in Victoria in which the fishing of Luderick is promoted, include Hopkins River and Moyne River estuaries; the bridge linking Ocean Grove to Barwon Heads; Fishermen’s Jetty and Ozone Jetty on the Bellarine Peninsula; Mallacoota boat ramp and Captains Point; waters near entrance to Sydenham Inlet; Snowy River inlet; Devils Hole and Florence Bay in the Lake Tyers region; various locations in the Gippsland area (Entrance Channel, Bullock Island, Reeve Channel off Flannagan Island, Jemmy’s Point and the jetty at Kalimna); Tambo River and entrance to Nicholson River; and McLennan Strait (leading to Lake Wellington) (DSE Victoria, 2005).  In Victoria, the legal minimum size is 22cm, and there is a daily bag limit and possession limit of 10 Luderick (DPI Victoria web site, 2004).
Luderick is also a popular angling species in N.S.W. (Australian Museum, 2002k), where it is described as having a “cult-like” following amongst anglers, and is mostly caught in winter (N.S.W. DPI, 2006). Both shore fishers and boat fishers target the species, in coastal lakes, rivers (e.g. Richmond, Clarence, and others), inlets and other estuarine areas, as well as open coastal waters. The recreational catch in some coastal waters of N.S.W. is significantly larger than the commercial catch (e.g. Steffe and Chapman, 2003), and recreational catches are seemingly large in some areas. For example, Steffe and Chapman (2003) estimated a total catch of 66,771 (± 10,998) Luderick from Lake Macquarie alone, during a one year period (1999-2000). In the Richmond River, Walsh et al. (2003) estimated that the daytime recreational catch of Luderick during the period July to December 2001 was 13,680 fish, equivalent to 7.3 tonnes of Luderick (from only one river, in a six month period). Additionally, an estimated 5,560 Luderick were discarded during that period (Walsh et al., 2003). In N.S.W., the species is reported to have high susceptibility to catch and release mortality (McLeay et al., 2002). In N.S.W., there is a size limit of 25cmTL, and a bag limit of 20 Luderick per day (N.S.W. Fisheries web site, October, 2006).
In Tasmania, the species is taken by recreational fishers using gillnets, graball nets and lines (Lyle and Campbell, 1999; Murphy and Lyle, 1999; Smith and Heran, 2001), sometimes when fishers are targeting Blue Warehou (Lyle and Campbell, 1999). The total recreational catch is unknown (Smith and Heran, 2001). There is a daily bag limit of 30 and a possession limit of 45 Luderick. Fishing for this species is promoted in various locations in northern and eastern Tasmania (e.g. DPIW Tasmania, 2006a, 2006b), although it is reported than not many fishers in Tasmania target Luderick (DPIW Tasmania, 2006b). The commercial fishery for Luderick in Tasmanian waters has licence restrictions, and the fishery is considered to be very small. The commercial catch in 1999 was 0.6 tonnes (Smith and Heran, 2001), and the status of the stock in Tasmania is unknown.
National recreational fishing associations and their State divisions keep records of the maximum sizes caught (e.g. Australian National Sportsfishing Association).
The recent National Recreational and Indigenous Fishing Survey (Henry and Lyle, 2003) reported that 702,530 Luderick were caught and kept by recreational fishers during the survey time period (May 2000 to April 2001), comprising the following state catches (number of fish): NSW: 660,531; VIC: 33,096; QLD: 2,575; SA: 3,742; TAS: 2,587.
In Australia, Luderick is promoted as a species for spear fishers to catch in south-eastern and southern waters (Smith, 2000; International Freediving and Spearfishing News, undated). In 2006, the species was listed as one of the targets in the 54th Australian Spearfishing Titles 2006, held on northern Kangaroo Island (Australian Underwater Federation, 2006). The maximum size of Luderick taken by spearfishing is reported to be a specimen of 2.863kg, taken from North Head in N.S.W., in 1971 (Australian Underwater Federation Inc., 2003).

South Australia

Luderick (species no. 565) is listed as one that is caught in the commercial Marine Scalefish Fishery in South Australia, but no catch and effort data are available for this report.
Under the Commonwealth’s Fisheries Management Amendment Regulations 2000 (No. 6) 2000 No. 339 - Schedule 1, there are restrictions to the number of Luderick that may be taken by Commonwealth fishers who have permits to fish in South Australian state waters.
Luderick have been fished by spear fishers in some parts of South Australia (e.g. South Australian Museum record, 1969; Johnson, 1985a and 1985b). More recently, Luderick (with specimens over 0.4kg) was listed as one of the targets in the 54^th Australian Spearfishing Titles 2006, held on northern Kangaroo Island (Australian Underwater Federation Inc., 2006).
The recent National Recreational and Indigenous Fishing Survey (Henry and Lyle, 2003) reported that 3,742 Luderick were caught and kept by recreational fishers in South Australia during the survey time period (May 2000 to April 2001); however it is not known whether this figure refers entirely to individuals of G. tricuspidata, or whether some misidentifications (e.g. G. zebra) are included in the number.

Other

In N.S.W., Luderick are taken in all coastal regions by indigenous fishers (Schnierer and Faulker, 2002).

Vulnerable Characteristics of the Species and Threatening Processes

Luderick (i) are found in shallow, nearshore, easily accessible areas; (ii) aggregate at times (e.g. during spawning periods); (iii) are easily caught, using a variety of methods, and (iii) are a prized food fish, and all of these factors may increase the vulnerability of populations to over-exploitation.
In N.S.W., the species is reported to have high susceptibility to catch and release mortality (McLeay et al., 2002), hence juveniles that are caught and released are likely to have a low survival rate.
The shallow coastal habitats (including estuaries and shallow seagrass beds) in which both juvenile and adult Luderick are found, are susceptible to habitat degradation, which may threaten some populations. The strong linkages of the life stages of Luderick with estuarine seagrass beds may increase the susceptibility of populations from impacts. For example, Connolly et al. (1999, citing Ramm, 1986, and MacDonald, 1992) reported that in Victoria, Luderick catches declined from 70-80t per annum. Historically low catches coincide with a period of seagrass dieback over several decades. In N.S.W., estuarine fishes such as Luderick, exploited by both commercial and recreational fishers, are subject to significant additional pressure from habitat degradation (Gray et al., 2000). Populations are also susceptible to impacts that reduce estuarine water quality. Examples include periodic “fish kills” from flood-induced de-oxygenation of estuarine waters, in which significant number of Luderick may be killed, and take longer to re-colonise such estuaries compared with some other fish species (e.g. Kennelly and McVea, 2002; Walsh et al., 2003). Estuarine fish kills can occur when extremely low dissolved oxygen levels occur in coastal rivers, due to a combination of factors such as acid sulphate soil-derived drainage sediments, and rapid flooding of contaminated pasture-land drainage into rivers (Walsh et al., 2003).
Compared with south-eastern Australia, there are few estuaries in South Australia to support the life cycle of this species, and some of the major estuarine areas, such as the Murray Mouth / Coorong) are subject to significant impacts (e.g. see Edyvane et al., 1996; Murray Darling Basin Commission and Department of Water, Land and Biodiversity, 2002; Baker, 2004).
Luderick are uncommon in South Australia, which is the western edge of the geographic range.

Research Notes

In New South Wales, a project is being undertaken to determine the biology and population structure of Luderick (N.S.W. Fisheries, 2006a). The research aims to collate and synthesize all existing information on Luderick, and to obtain basic biological information, and compare some of the data with those collected during the 1990s. Parameters under study include growth rates, age/length composition, mortality rates, size and age at sexual maturity, fecundity and other aspects of reproductive biology, timing and locations of spawning, and recruitment rates). Other aspects of the research include assessing the results of previous tagging studies on Luderick, and developing a ‘recreational fisher-based’ tagging program for this species in N.S.W. (N.S.W. Fisheries, 2006a). The review of all relevant existing information, plus new data from the research program, will be used assess the current state of knowledge of Luderick in N.S.W., and to recommend areas for future research and management.

Management Notes

Fisheries management strategy documents have been prepared for the major fisheries in N.S.W. in which Luderick are taken (N.S.W. Fisheries, 2006b). Given the serious decline in Luderick catches in some parts of south-eastern Australia, time series data have been analysed in N.S.W. to determine trigger points that indicate potential recruitment failure, and survival failure (e.g. Scanlon and Forrest, 2001).
In the general (multi-species) component of the Estuarine Gillnet Fishery in N.S.W., Gray et al. (2005) recommended that increasing the minimum permitted mesh size, as well as reducing the maximum soak time of nets set in winter would reduce the level of discarding in that fishery, including undersized Luderick (Gray et al., 2003, 2005). Gray et al. (2005) reported a method to reduce the bycatch of Luderick in the component of the Estuarine Gillnet Fishery in which the flathead Platycephalus fuscus and the crab Portunus pelagicus are the only species permitted to be retained. Lowering the fishing height of the float-line significantly reduced total by-catch (of all species) by up to 46% and the individuals of key by-catch species (one of which is Girella tricuspidata) by 60% - 85%, with no effect on catches of targeted species (Gray et al., 2005).
In Queensland, a study has shown Luderick to be one of a suite of useful indicator species in estuaries contaminated with nutrient-rich wastewater (including sewage). In estuaries with both large and small loads of wastewater nitrogen, the increased nitrogen from wastewater sources was measurable in the fish muscle, and distinguishable from natural sources (and levels) of nitrogen in unpolluted conditions (Schlacher et al., 2005).

Research Requirements

The importance of estuarine areas to the life cycle of Luderick in South Australia should be investigated.
There is inadequate information on the potential impacts of reduced estuarine flow (quantity and rate), and degradation of estuarine habitats, on juvenile Luderick.
In parts of the range (including N.S.W., where the species is comparatively well-studied), there is little information about age, growth, migration, reproduction (size/age at maturity, spawning times/locations, fecundity, etc), and variation in these parameters between populations associated with different estuaries across the range (New South Wales Fisheries, 2006a).

Management Requirements (S.A.)

Given the uncommonness of Luderick in S.A. compared with south-eastern Australia, commercial and recreational fishing regulations (including minimum sizes, and catch limits) are required in South Australia.

Other Information

G. tricuspidata occurs in a number of Marine National Parks and Sanctuaries in Victoria (e.g. Wilsons Promontory; Corner Inlet; Bunurong; Gabo Island; Phillip I., Port Phillip Heads) (Norman and Marshall survey data, University of Melbourne, 2000; Ferns and Hough, 2002; Plummer et al., 2003; Edmunds et al., 2003).
The species is also found in a number of protected areas in New Zealand, such as Cape Rodney – Okakari Point (Leigh) (Taylor et al., 2003), Te Wahanganui A Hei (Taylor et al., 2004); the Poor Knights Islands (Brook, 2002; Denny et al., 2003), Goat Island (Russell, 1977; Jones, 1988).

Support for S.A. Listing:

Barry Hutchins (ex-W.A. Museum)