© 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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Estuary Perch

Family Name:	Percichthyidae
Scientific Name:	Macquaria colonorum (Günther, 1863)
Recommended Status in S.A:	Endangered B1 ab(i,iii,v), possibly also C2a(ii)
Rationale:  Estuary Perch is included here because (i) it has a restricted range in S.A., at the edge of the geographic range, and there is very little suitable habitat (such as rivers and estuaries) in most parts of the State, to support the habitat requirements and life history characteristics of this species. In estuarine areas that do exist, freshwater input is also low and inconsistent; (ii) there are no recent records from the Murray Mouth, the largest estuarine area in S.A., which is subject to numerous impacts that affect the utility of the area for estuarine fishes, and long term changes to volume and flow rate (and habitat quality) are likely to directly affect the life cycle of this species, with long term implications for the population in that area; (iii) due to the migration of Estuary Perch between estuarine and fresher waters, structures such as dams and weirs would interfere with the life history, and may act as a barrier to migration; (iv) seasonal closure by sand bars of some estuaries, which prevents tidal inflows, may have marked effects on breeding success of the species; (v) the species is relatively long lived (to at least 30 years), hence habitat impacts have the potential to adversely affect one generation of fish for long (decadal) periods; (vi) the species is reported to have a very low resilience to exploitation, but there are inadequate data on previous commercial and current recreational catches in S.A.; and (vii) generally, across the southern Australian range, estuarine fishes such as M. colonorum may be adversely affected by habitat degradation (due to various forms of water pollution, catchment development and agriculture- related activities), changes to flow regimes, barriers to fish passage, introduced alien and translocated native fish species, and, possibly in some areas, fishing (the latter not likely to be a threat in S.A., due to the scarcity of the species in this State, and the lack of targeting by fishers). The recommendation of the National Parks and Wildlife Council and DEH (in 2003, which sought to list this species as Endangered in South Australia), is supported here.

Page Contents

Current Conservation Status

In New South Wales, the species is protected from commercial fishing, under Section 20 of the Fisheries Management Act (New South Wales DPI, 2004).
Although the species is not formally listed under conservation schedules, it is considered to be of conservation concern in S.A. (Hammer, 2002; Hammer et al., 2007). National Parks and Wildlife Council and DEH (2003) and Hammer et al. (2007) recommended that the species be listed as Endangered, under National Parks and Wildlife Act. Listing criteria in 2003 were B1ab(i,iii): Extent of occurrence estimated to be < 5000 km², and estimates indicating that population is severely fragmented or known to exist at no more than 5 locations; and a continuing decline (observed, inferred or projected) in extent of occurrence, and area, extent and/or quality of habitat. C2a(ii): Population size estimated to number fewer than 2500 mature individuals, and there is a continuing decline (observed, projected, or inferred) in numbers of mature individuals; and at least 95% of mature individuals in one subpopulation . Listing criteria in 2007 were B1ab(iii,v): Extent of occurrence estimated to be < 5000 km2, and estimates indicating that population is severely fragmented or known to exist at no more than 5 locations; and a continuing decline (observed, inferred or projected) in area, extent and/or quality of habitat, and number of mature individuals .

Distribution

Southern Australian States

The species occurs in coastal rivers and lakes of south-eastern Australia, from the Richmond River in N.S.W., throughout Victoria (Koehn and O’Connor, 2002), to the mouth of the Murray River in S.A. (but see below). Macquaria colonorum is considered to be widely distributed throughout Victoria's estuaries (Kirwin, 2000), and has been classified as “common” in that State (DPI Victoria, 2003).
Although Estuary Perch are widely distributed in coastal rivers and estuaries throughout Victoria (78% of waters), they are most abundant, grow fastest and live longest in deep-channeled rivers such as the Glenelg, Hopkins and Curdies in western Victoria, and in the Tambo, Mueller, Bemm, Genoa and Wallagaraugh Rivers in Gippsland (Tunbridge and Rogan, 2006). Significant populations exist in Mallacoota Inlet, Brodribb River, Little River (Mallacoota), Snowy River, Bemm River, Wingan Inlet, Swan Lake, Tamboon Inlet, Cann River, Betka River and Mueller River (Tunbridge and Rogan, 2006).
In Tasmania, the species reportedly occurs in the Arthur River (western Tasmania) and Ansons River (Allen et al., 2002; DPIWE website, 2002), with anecdotal evidence that the species may be more widespread in Tasmania (DPIWE website, 2002).

South Australia

Estuary Perch has previously been recorded in the small section of the Glenelg River that occurs in South Australia (S.A. Museum records, cited in Hammer, 2002, and OZCAM database, 2007), and Hammer (2002) reported that the species is still likely to occur there, either occasionally or permanently, based on capture of specimens upstream (by the late J. Stehbens, in 2002) and occasional records from anglers (unpubl. data, cited by Hammer et al., 2007). Hammer (2002) also reported that the species might occur in other parts of the south-east, such as Robe Lakes.
Paxton et al. (1989) recorded the South Australian gulfs as part of the distribution. Hammer (2006a) reported that the species may have previously occurred in the Onkaparinga Estuary in Gulf St Vincent, and may occasionally still migrate to the area.
The species is listed as having previously occurred in the S.A. portion of the Murray River (Hammer and Walker, 2004, cited by Smith and Hammer, 2006). Highman et al. (2002) and MDBC (2006) reported that the species is present in the Murray Mouth area, and it is noted that there are previous records from that area (e.g. S.A. Museum record F07343, cited in OZCAM database, 2007). However, during the 1990s, there were no recent records from the Murray Mouth (Gomon, in Gomon et al., 1994). The species has apparently not been recorded in estuarine surveys of that area during the past decade (e.g. Pierce, 1995; Geddes, 2005; Stuart et al., 2005, Higham et al., 2005; Smith, 2006). Hammer et al. (2007) reported its presence at the Mundoo Channel (SAM record, 1990) and Nildotte near Swan Reach (River Murray).

Habitat

The preferred habitat is coastal rivers / estuaries under tidal influence (Williams, 1970; Sanders, 1973; Llewellyn and MacDonald, 1980, cited by Koehn and O’Connor 2002; Barton and Sherwood, 2004) and brackish water (McCarraher, 1979), often in upper estuarine reaches (van der Wal, 1983). Estuary Perch often enter fresh water (Paxton et al., 1989; Tunbridge and Rogan, 2006), including rivers and lakes with salinities less than 1-2 ppt (Allen, 1989).
Estuary Perch is found in habitats ranging from deep channelled and highly brackish areas, to shallow, mud-bottomed and slightly brackish; in waters under tidal influence (McCarraher and McKenzie, 1986, cited by Koehn and O’Connor, 2002). Estuary Perch is often associated with submerged objects, such as logs, stumps, snags, bushes, tree roots, rock piles, reefs and holes along the banks of streams (Sanders, 1973; McCarraher, 1986; both cited by Koehn and O’Connor, 2002; Game Fishing Association of Australia website, December 2003l; Hindell and Jenkins, 2004).
A survey found post larvae and fingerlings only in backwater habitats (McCarraher and McKenzie, 1986, cited by Koehn and O’Connor, 2002). Fishers have found immature fish in large numbers at entrances to tidal lakes (FishNet, 2006). Adults usually live in low salinity waters in the upper reaches of estuaries but move into higher saline water (19,000EC) during July to December to spawn (Tunbridge and Rogan, 2006).
In Victoria, during a study in Western Port Bay and Corner Inlet, Estuary Perch were recorded in higher numbers in mangrove habitats that in unvegetated mud habitat. During that study, only adult Estuary Perch were present in the unvegetated habitat (Hindell and Jenkins, 2004).

Notes on Biology and Behaviour

In general, little is known of the species biology of Estuary Perch, when compared with other recreationally important fish species (Kirwin, 2000).

Age and Growth

The species grows to 70 - 75cm and a weight of 10kg, although it is more commonly recorded at 40 - 54cm, and up to 4kg (Allen, 1989; Harris and Rowland, 1996; Allen et al., 2002, cited by Trnski and Hay, 2005). Although specimens to 54cm - 60cm and 4kg - 5kg are found in parts of Victoria (Native Fish Australia, 2003e; NFA - East Gippsland, undated), DPI Victoria (2005) reported that Estuary Perch above 2kg are considered to be “trophy size”.
A study of age and growth, using otoliths from 805 Estuary Perch collected in the Bemm River system (eastern Victoria) over a 7 year period, reported that the growth of estuary perch was slower, and the natural life span longer, than that previously estimated (Kirwin, 2000).
Kirwin (2000) reported that Estuary Perch live to at least 31 years (validated age), and the maximum age recorded in that study was 36 years. In Victoria, Estuary Perch of 8-9 years old are reported to be about 45cm in length and up to 1.8kg in weight (Tunbridge and Rogan, 2006).
Growth rate may differ between males and females (Kirwin, 2000).

Diet

The Estuary Perch is a predatory species that feeds close to the bottom, on crustaceans (prawns and shrimps), worms, bivalve molluscs, and small fishes (Allen, 1989; Gomon, in Gomon et al., 1994; Native Fish Australia, 2003e). During a study of the diet of Estuary Perch in Victoria (Department of Primary Industries data, 1975 and 1980, cited by Tunbridge and Rogan, 2006), fish remains formed 50% of the contents of Estuary Perch stomachs examined, with identified remains including 52% yellow-eye mullet and 22% gudgeon, with the remainder being Tupong, Pygmy Perch, Common Galaxias, Brown Trout and Short-finned Eel. Other food items were prawns and shrimps, which were found in 41% of all stomachs. The study concluded that estuary perch are mainly surface and mid-water feeders during winter and bottom feeders during summer (Tunbridge and Rogan, 2006).
During a study in Westernport Bay and Corner Inlet in Victoria, small mullet found in the mangrove forests were eaten by larger Estuary Perch (research by J. Hindell, cited in Anonymous, 2002d).
There are spatial, temporal and size class variations in the diet (Howell et al., 2004). For example, during a study in the Hopkins river in Victoria, Estuary Perch caught from estuarine locations consumed primarily the fresh water shrimp Paratya australiensis (40% IRI) while Estuary Perch in fresh water consumed mostly caddisfly (Tricoptera) larvae (63.5% IRI). In both fresh water and estuarine locations, the relative importance of P. australiensis decreased with increasing length of fish. Diet changed seasonally, indicating opportunistic changes in prey. The Estuary Perch selected particular prey items (P. australiensis, and the fresh water crab Amarinus lacustris) relative to environmental availability (Howell et al., 2004).
Larval Estuary Perch feed on zooplankton, and have been recorded over an extended period, rather than a seasonal peak (e.g. Newton, 1996).
Estuary Perch are primarily surface and mid-water feeders during winter, and bottom feeders during summer (McCarraher and McKenzie, 1986, cited by Koehn and O’Connor, 2002).

Behaviour

Young-of-the-year exhibit schooling behaviour (McCarraher and McKenzie, 1986). Larvae and juveniles may move further upstream as they grow, to less saline reaches (MDBC, undated).
Fishers have noted that Estuary Perch in waters above tidal influence tend to reside in shelter, closer to stream bank edges during daylight hours, and those perch in the middle of streams tend to be in deeper waters, away from the surface light, until dusk, when they move closer to the surface to feed (Fish Net, 2006).

Reproduction

Age at maturity is around 3 years for females, and 2 years for males (McCarraher and McKenzie, 1986, cited by Koehn and O’Connor, 2002). Size at maturity is around 28cm – 30cm for females, and 22cm for males (McCarraher, 1979, Llewellyn and MacDonald 1980, cited by Koehn and O’Connor, 2002).
Summary of spawning, mainly from Koehn and O’Connor (2002): Spawning occurs in either winter, spring or summer (Sanders, 1973; McCarraher, 1979; Llewellyn and MacDonald, 1980), depending upon the location, and seasonal conditions (McCarraher, 1986). Breeding may commence as early as July to August in New South Wales, but usually occurs much later, into October, November or December, in Victorian waters (Allen, 1989; Barton and Sherwood, 2004), especially in the western regions (Native Fish Australia – East Gippsland, undated), although eggs have been collected from June to November (Newton, 1996, cited by Trnski et al., 2005). Spawning is likely to occur in spring and summer in Tasmania (Nelson, 2000). Spawning occurs earlier in eastern drainages, and progressively later in more western drainages. For example, in Victoria, spawning starts in Gippsland in July, but not until mid October to early November in western Victoria (Tunbridge and Rogan, 2006). Spawning can be delayed by factors such as flooding (McCarraher and McKenzie, 1986), or by unseasonably cold water temperatures (McCarraher, 1986). Duration of spawning season depends upon the availability of water of required salinities, water temperature and preferred spawning habitat (McCarraher and McKenzie, 1986, cited by Koehn and O’Connor, 2002). Generally, Estuary Perch require salinities between 10 and 24 ppt for breeding (Cadwallader and Backhouse, 1983, cited by Barton and Sherwood, 2004). Adult Estuary Perch can tolerate a wide range of salinities, but can experience spawning failure if oxygenated waters of correct salinity are not in present in the estuary during spawning period (Tunbridge and Glenane, 1988, cited by Barton and Sherwood, 2004).
Spawning usually occurs in the lower sections (including mouths) of estuaries, in waters of intermediate salinity, and when water temperatures are about 14 – 19^oC. During this period, the semi-buoyant eggs are dispersed in areas with submerged aquatic vegetation, or submerged rocks / reef or both habitat types (Sanders, 1973; Llewellyn and MacDonald, 1980; McCarraher and McKenzie, 1986, cited by Koehn and O’Connor, 2002). These sites are considered to be important 'nursery areas' and carry an abundance of fingerling estuary perch (Tunbridge and Rogan, 2006).
During spawning season, ripe fish move downstream from non-tidal to estuarine water, prior to spawning. One study showed that fish can travel more than 10km (29km was recorded in one instance) during spawning season (McCarraher, 1979, cited by Koehn and O’Connor, 2002).
Spawning may be episodic rather than a regular occurrence. A study in Victoria (Kirwin, 2000) reported that a single year class (spawned in 1986) dominated the Estuary Perch community in the Bemm River, and also, significant bias was encountered in the ratio of male and female fish.
Spawning can occur nearer to the sea in wetter years (G. Searle, pers. comm., cited by Trnski et al., 2005), and adult Estuary Perch have occasionally been found in marine waters (McCarraher and McKenzie, 1986, cited by Trnski et al., 2005). There is some evidence that larvae can occur in nearshore marine waters (prior to entering estuaries on flood tides), and therefore the possibility of dispersal of larvae between estuaries (Trnski et al., 2005).
Eggs hatch several days after they are spawned (Allen, 1989). After spawning season, mature fish move from lower reaches of estuaries to less saline conditions upstream; occasionally spawning populations move out to sea, and stocks also move along the coastline and periodically enter open estuaries (McCarraher and McKenzie, 1986, cited by Koehn and O’Connor, 2002).
Estuary Perch hybridizes with Australian Bass (Macquaria novemaculeata) and produces viable offspring (Jerry et al., 1999).

Fisheries Information

General

M. colonorum is a commercial food fish in Victoria, considered to be of excellent eating quality, and is also an important species for anglers (Gomon, in Gomon et al., 1994).
The species has been described as “a highly rated sportsfish with tough, sometimes spectacular, fighting ability” (FishNet, 2006). Fishers often target the species at creek mouths entering estuarine rivers. Catch and release is recommended by recreational fishing experts for larger (female) fish. Specimens taken by anglers are often in the range 100g to 4kg (FishNet , 2006).
The Australian National Sportsfishing Association includes Estuary Perch in rule-based fishing competitions, and the Game Fishing Association of Australia also includes Estuary Perch as an eligible species. The International Game Fish Association also includes M. colonorum in its line class records.
Estuary Perch are also taken by spear fishers in some areas of southern Australia (e.g. see Australian Underwater Federation Inc., 2003).

Victoria

The commercial catch (in tonnes live weight) of Estuary Perch in Victorian waters, in recent years, is as follows (Table 34).

Table 34 Commercial catch of Estuary Perch in Victorian waters 1997 – 2005
Year	Catch (t)
1997/98	2
1998/99	5
1999/00	2
2000/01	3
2001/02	3
2002/03	0
2003/04	2
2004/05	1
(From DNRE Victoria, 2002, 2003, 2004, 2005)

There are museum records of specimens that were caught by commercial fishing in the Port Phillip Bay / Bass Strait region (Anon., 2002b, in Froese and Pauly, 2006).
In Victoria, the species is reported to have been common in commercial and recreational fishing catches from Corner Inlet (Gunthorpe et al., 2000, cited by Plummer et al., 2003). (n.b. There is now a Marine National Park in Corner Inlet – see Parks Victoria, 2003).
Estuary Perch is one of the species caught in the bycatch of the commercial eel fishery in Victoria (DPI Victoria, 2003), but data are not available for this report. Eel fishing is reportedly not permitted in waters where Estuary Perch (an “indicator species”) is known to exist, and one example is the closure of the Hopkins River (Hopkins Basin) to commercial eel fishing due to the presence of significant populations of Estuary Perch (DPI Victoria, 2003).
Native Fish Australia – East Gippsland (undated) reported that although the species is usually overlooked as an angling target, it is a “good fighting fish” and is readily taken on artificial lures and baits such as sand worms, prawns and yabbies. Fishing for this species occurs during tidal “runs” up and down the lower parts of river streams, and Estuary Perch can be abundant during such periods. Estuary Perch is listed among the top 3 species / groups that are susceptible to catch-and-release mortality by line fishing in Victoria (McLeay et al., 2002).
Estuary Perch is widely promoted in information materials from Department of Primary Industries Victoria and Department of Sustainability and Environment, and also on signage, as a fish for anglers to catch in the Victorian rivers. A Guide to the Inland Angling Waters of Victoria (Tunbridge and Rogan, 2006) reported that few anglers are adept at fishing for (and catching) Estuary Perch, and the guide reported that “stocks are greatly under-exploited and provide opportunities for a very rewarding fishing experience”, with “good numbers of large fish”. Examples of rivers in which the catching of Estuary Perch is promoted include the Hopkins (near Warrnambool), Betka River estuary and upstream; Genoa and Wallagaraugh rivers; “The Back Water”; Tamboon Inlet; Bemm River and Sydenham Inlet; Marlo ramp / jetty; inlet and adjacent estuaries of the Snowy River; Yeerung River estuary; Nicholson River entrance and upstream; McLennan Strait leading to Lake Wellington; the Tarwin, Bass, and Angelsea rivers; Painkalac Creek; lower reaches of the Erskine River; Barham River; and the Glenelg River Estuary (DSE Victoria, 2005). Curdies Inlet and Glenelg River rank highly as fishing areas because they contain populations of large Estuary Perch (McCarraher and McKenzie, 1986, cited by Barton and Sherwood, 2004). Specimens taken in Victoria are usually in the range 400g to 2kg (Tunbridge and Rogan, 2006).
According to the Guide to the Inland Angling Waters of Victoria (Tunbridge and Rogan, 2006), Estuary Perch is a “good sporting and eating fish, [but] it is not heavily exploited in some parts of its range (eastern Victoria) because of difficulty of access to streams and estuaries, and a general lack of knowledge of the abundance and distribution of the species and its sport fish qualities”.
The National Recreational and Indigenous Fishing Survey (Henry and Lyle, 2003) reported that 2,064 Estuary Perch were caught and kept by recreational fishers in Victoria during the survey time period (May 2000 to April 2001). Some recreational fishing clubs and associations keep records of the maximum sizes caught (e.g. Australian Anglers Association, Victorian Division, 2003).
In Victoria, the minimum legal size for Estuary Perch taken by licensed recreational fishers is 25cm, and there is a bag / possession limit of 10 fish. Because of the confusion between Australian Bass and Estuary Perch in areas where both species can be caught, there is a combined bag limit of 10 fish which can include a maximum of 2 Australian Bass (Victorian Recreational Fishing Guide, 2003-2004; Tunbridge and Rogan, 2006).

New South Wales

There is no commercial fishing for Estuary Perch in New South Wales, but it may be an incidental bycatch of prawn trawling in some estuarine areas, such as the Shoalhaven River (e.g. Gray and Kennelly, 2001). The species may also be incidentally captured in the Estuary General fishery (N.S.W. Fisheries, 2003).
The species is promoted for estuary fishing in N.S.W., including recreational fishing in the Recreational Fishing Havens (N.S.W. Fisheries web site, 2003). Estuary Perch is considered to be a “prized species” for angling.  In N.S.W., Estuary Perch are commonly caught up to 3kg and 50cm in length (Hawkesbury Nepean Bass Anglers Association, 2005). Increasing numbers of anglers are now targeting the species due to advances in lure technology and fishing techniques. In particular, there is a growing fishery for estuary perch based on artificial lures and flies, with many fish being released following capture (Hawkesbury Nepean Bass Anglers Association, 2005).
For recreational fishers, there is a size and catch limit of 1 Estuary Perch longer than 35cm, and the bag limit is 4 Estuary Perch and/or Australian Bass (maximum 2 fish per day) (N.S.W. Fisheries website, December, 2003).
The species is targeted by indigenous recreational fishers in all regions of New South Wales (Department of Primary Industries, 2004).

Tasmania

There is no commercial fishery for M. colonorum in Tasmania (DPIWE website, 2002).
M. colonorum is taken by anglers in Tasmania and the total recreational catch in that State is unknown (Smith and Heran, 2001). Only certain stocks occur in Arthur River (Tasmanian west coast), but anecdotal evidence suggests that the species may be more widespread (Smith and Heran, 2001). DPIWE considers that there is potential for development of the recreational fishery for M. colonorum in Tasmania waters. There is a daily bag limit of 30, and a possession limit of 45 fish (DPIWE Tasmania web site, 2002).
The National Recreational and Indigenous Fishing Survey (Henry and Lyle, 2003) reported that 34 Estuary Perch were caught and kept by recreational fishers in Tasmania during the survey time period (May 2000 to April 2001).

Vulnerable Population Characteristics, and Threatening Processes

Generally, the main threats facing estuarine fishes such as M. colonorum include habitat degradation (due to various forms of water pollution, catchment development and agriculture- related activities), changes to flow regimes, barriers to fish passage, introduced alien and translocated native fish species, and fishing pressure (Pollard and Morris, 2002).
Specifically, Estuary Perch has a restricted range in S.A.(Hammer, 2002), which is at the edge of the geographic range, and there is very little suitable habitat (such as rivers and estuaries) in most parts of the State, that could support the habitat requirements and life history characteristics of this species. In estuarine areas that do exist, the freshwater input is also low and inconsistent.
The largest estuarine area in S.A., the Murray Mouth, is subject to numerous impacts that affect the utility of the area for estuarine fish species (e.g. see Edyvane et al., 1996; Higham et al., 2002). Periodic closure of the Murray Mouth, in addition to the long term changes to volume and flow rate that have occurred in the area, is likely to directly affect the life cycle of this species, with long term implications for the population in that area (Higham et al., 2002). Due to the migration of Estuary Perch between estuarine and fresher waters, structures such as dams and weirs would interfere with the life history, and may act as a barrier to migration. Reduction in flow rate and volume in estuarine areas such as the Murray Mouth, and decline in water quality, all have the potential to impact on this species. The extensive modifications that have occurred in the drainages of the south-east of S.A. are also likely to have reduced available habitat for Estuary Perch.
The species is relatively long lived (to at least 30 years), hence habitat impacts have the potential to adversely affect one generation of fish for long (decadal) periods.
In parts of south-eastern Australia, dam construction, flow diversion and regulation are likely to have inhibited upstream movement of Estuary Perch populations (e.g. in the Hawkesbury-Nepean – Gehrke et al., 1999, and the Shoalhaven River – Gehrke et al., 2001, 2002). The effects of flow alteration in the system are confounded by geomorphic and climatic variation and other disturbances within the catchments (Gehrke et al., 1999).
 In Victoria, the distribution and abundance of Estuary Perch appears to have been affected by in-stream structures, flood mitigation work and pollution. The seasonal closure by sand bars of some estuaries, which prevents tidal inflows, may have marked effects on breeding success of the species (Tunbridge and Rogan, 2006).
Snags and other woody debris are important for the habitat of Estuary Perch (Sanders 1973; McCarraher, 1986), and their removal from coastal water bodies may reduce habitat quality for this species.
Reduction in available mangrove habitat (e.g. through flood mitigation works) may adversely affect populations in some parts of southern Australia (e.g. Pollard and Hannan, 1994).
Fishing may be a threatening process, but there appears to be no information available on commercial or recreational catches of this species in South Australia. McLeay et al. (2002) reported Estuary Perch to be one of the top 3 fish species in Victoria that is susceptible to catch and release mortality. Allen et al. (2002) reported that numbers have declined in recent years, probably due to over-fishing.
The species is reported to have a very low resilience to exploitation, in terms of minimum population doubling time (Froese and Pauly, 2007). There are inadequate data on previous commercial and current recreational catches in South Australia, but fishing as a current threat is likely to be low in this State (due to scarcity of the species, and the lack of targeting).

Management Requirements

Generally, populations of estuarine fishes like Estuary Perch can be assisted by protection of in-stream cover and riparian vegetation, restoration of natural flow and temperature regimes, removal of barriers to fish passage, management of pest fish species, and better fisheries management (Pollard and Morris, 2002).
A public awareness campaign might help improve recognition, reporting (by fishers) and protection (Hammer et al., 2007).

Research Requirements (S.A.)

Further surveys are required to determine the distribution and abundance of this species in South Australia.
Information is required on the recreational fishing catch of Estuary Perch in S.A.
More information is required on critical habitats for this species in S.A., the current threats to that habitat, and specific measures required to restore estuarine habitats to a level of quality whereby the life history stages of the species can be supported.

Research Notes

During the early 2000s in N.S.W., the Hawkesbury Nepean Bass Anglers Association, in association with the Department of Primary Industries, undertook a study into the biology and fishery for Estuary Perch in coastal catchments of NSW. The study aimed to collect monthly samples to determine basic biological parameters (including age, growth, size and age at maturity, and timing and location of spawning). An associated tag-release program in conjunction with recreational fishers was also used to study the movement and growth of fish throughout estuaries in NSW (Hawkesbury Nepean Bass Anglers Association, 2005). Acoustic transmitters are being used to track estuary perch in real time, to monitor short term movements, and habitat relationships. Fixed listening stations deployed within an estuary are being used to monitor longer term (seasonal) migrations of estuary perch. The study also aims to establish a profile of the recreational fishery (using logbook information), because there is currently very little information on the catch of Estuary Perch by this sector, and its interaction with the commercial sector.  Recreational data collected include quantities and sizes of fish caught, as well as other important catch variables. A series of hook mortality experiments are being used to test the effects of a variety of fishing methods on the post-release survival of these fish (Hawkesbury Nepean Bass Anglers Association, 2005).
During the early 2000s, research was being undertaken (C. Burridge, Deakin University) into the population structure of Macquaria colonorum throughout its natural range.

Management Notes

In Tasmania, there is a State policy devised by a State Technical Panel (including representatives of DPIWE, the Hydro-Electric Corporation and University of Tasmania) to maintain spawning and rearing habitat for estuarine species such as Estuary Perch (e.g. McKenny and Read, 1999; Nelson, 2000).
In Victoria, some water bodies (e.g. Hopkins Basin) are closed to commercial eel fishing, to protect Estuary Perch from becoming fatally enmeshed in the fyke net material (DPI Victoria, 2003a).
In South Australia, and Action Plan for freshwater and estuarine fish has been written, to provide recommendations for better protection (and population recovery) of such species and their habitats.

Research Notes

Genetic markers have been identified that can be used to distinguish between M. colonorum and the congeneric Macquaria novemaculeata (Australian Bass), as well as hybrids between the two species (Schwartz et al., 2005).
During the early 2000s, a PhD project was undertaken to determine the genetics of south-eastern Australian populations of Estuary Perch (research by M. Truong, cited by Barton and Sherwood, 2004).

Other Information

Estuary Perch is found in a number of marine protected areas in Victoria, such as Corner Inlet Marine National Park (Plummer et al., 2003).
Estuary Perch is an aquaculture species in Victoria (NRE, 2002; DPI Victoria, 2004b) and New South Wales. In Victoria, fingerlings are produced using ‘green pond’ methods and the young fish are used to restock waterways (e.g. Lake Hamilton, and others) and farm dams, and for controlled grow-out farming in recirculation systems. The species is offered for sale in the Gippsland area, for stocking farm dams, as an angling species.
In N.S.W., it is one of a range of species that are cultured to supply fingerlings for stock enhancement of public waterways and private dams, and also for grow-out to market size for human consumption (Kennelly and McVea, 2003).
In South Australia, Estuary Perch is an approved species for aquaculture in the South-East region (“Limestone Coast”), but has not been cultured commercially to date (EconSearch et al., 2002).
Estuary Perch has also been translocated in Australia as a biological control agent (Lintermans, 2004).
The species is not permitted to be imported into Western Australia without a permit, under Regulation 176 of the Fish Resources Management Regulations 1995.
The species has been introduced to waters of some Pacific island countries, including Fiji and Papua New Guinea (Glucksman et al., 1976, and Ryan, 1980, cited by Eldridge, 1993, and Humphry, 1995).

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