© 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 Catfish / Cobbler / Southern Cobbler / Estuary Cobbler

Family Name:	Plotosidae
Scientific Name:	Cnidoglanis macrocephalus (Valenciennes, 1840)
Recommended Status:	South Australia: possibly Near Threatened
Rationale:  Although the Estuary Catfish has been recorded across South Australia, from the Great Australian Bight through to the South-East, it is included here because (i) the species occurs in estuaries and shallow marine waters over a narrow depth range (to 30m); (ii) there are few estuarine habitats in South Australia to support part of the life stage of this species, and Estuary Catfish appear to be much less common in S.A. than in some other parts of the range (e.g. W.A.); (iii) the species has a number of characteristics that increase its vulnerability to over-exploitation and decline, including strong habitat association (and the forming of semi-resident populations); little mixing between populations from different regions, even within one State; relatively long life and late age at maturity; low fecundity; aggregative behaviour during breeding period; and site-specific investment in producing and rearing of the young (e.g. pair mating, benthic nesting, and brooding of young); (iv) there is little information on the relative abundance or full distribution of this species in South Australia, and information on habitat requirements of Estuary Catfish in each part of the S.A. is sparse; (v) the estuarine association of this species makes populations susceptible to impacts that reduce estuarine water quality; (vi) Estuary Catfish is highly sought as an eating fish in W.A., and long-term depletion has been recorded, largely due to over-fishing estuarine populations; (vii) although the species is found and caught commercially in much lower numbers in SA (mainly bycatch, in at least  5 commercial fisheries), and also with various recreational fishing gear (including spears), there are no commercial or recreational fishing restrictions on the capture of this species in South Australia, despite the vulnerable characteristics of Estuary Catfish populations, and inadequate knowledge of distribution, relative abundance and habitat requirements of populations in this State.

Page Contents

Current Conservation Status

No listings known

Distribution

Southern Australia

The species has a disjunct distribution, in the shallow coastal waters of southern Australia. In the east, it is found mainly from the Queensland / New South Wales border (e.g. from Kirra in southern Queensland to Jervis Bay in New South Wales), and in the west, from Kingston in South Australia through to the Houtman Abrolhos islands in Western Australia (Kailola et al., 1993; Gomon, in Gomon et al., 1994).
In W.A., Estuary Catfish are found in most estuarine systems and inshore waters below the Houtman Abrolhos Islands, and around the southern coast (W.A. Department of Fisheries, 2001c).
The Estuary Catfish is reported to occur in northern Tasmania (Hutchins and Swainston, 1986, 2001), but is apparently absent from most of that State, and from most of Victoria (Gomon, in Gomon et al., 1994).

South Australia

In South Australia, the species is known from many locations across the State, including the far western Eyre Peninsula / eastern Great Australian Bight (e.g. Ceduna area, Wittelbee Point); southern Eyre Peninsula (e.g. Lake Wangary); north-western Spencer Gulf (e.g. Port Pirie / Davis Creek area); mid-eastern Spencer Gulf (e.g. Cape Elizabeth, and Tiparra / Port Hughes area, and off Wardang I.), south-eastern Spencer Gulf (e.g. Hardwicke Bay; Point Turton); south-western Spencer Gulf (e.g. Port Lincoln area, Thorny Passage islands, and Sir Joseph Banks group islands); southern Yorke Peninsula (e.g. Edithburgh Jetty); Investigator Strait; north-eastern and eastern Kangaroo Island; northern and eastern Gulf St Vincent (including Port River - Barker Inlet estuary, West Lakes, Outer Harbour, Semaphore, North Haven, artificial reefs / wrecks in the Glenelg area, Marino, Seacliff, and Port Noarlunga Reef / Onkaparinga estuary); Fleurieu Peninsula (e.g. Normanville / Carrickalinga area; Rapid Bay); Kangaroo I. (e.g. Pelican Lagoon; Point Tinline); Encounter Bay (e.g. The Bluff; Granite I.); the Murray Mouth, and the upper South-East area, such as Kingston (Glover, 1979; Johnson, 1985b; Jones et al., 1996; Jackson and Jones, 1999; MLSSA, 1999; J. Baker, pers. obs., 1999 and 2008; S.A. commercial fishing records 1995-97; S. Reynolds, unpubl. data 2001; Reynolds, 2002; K. Smith, unpubl. data, 2002-2003; Fairhead et al., 2002; Tanner et al., 2003; K. Smith, pers. comm., 2005; S. Shepherd, SARDI, pers. comm., 2007; South Australian Museum records, Australian Museum records, Museum of Victoria records, cited in OZCAM database, 2008; Gillanders et al., 2008; photo by P. Macdonald, 2008).

Habitat

The Estuary Catfish is an inshore species that occurs in estuaries, shallow bays and sandy inlets near river mouths (Scott et al., 1974; Potter et al., 1983; Loneragan et al., 1987; Gomon, in Gomon et al., 1994; Harrison, 2001).  Generally, the species is found over sand, rocks, seagrass and/or macroalgae, in clear to turbid waters. In some areas, adults are found in holes, and on (or under) ledges in banks, where individuals often conceals themselves during daylight hours (Kailola et al., 1993; Gomon, in Gomon et al., 1994). Juveniles are often found in macroalgae and seagrass beach wrack off sandy beaches (e.g.  Lenanton et al., 1982; Hyndes et al., 1999; Crawley et al., 2006). In south-western Australia, during a study of the relation between fish and beach wrack volume in the surf zone at 2 sandy beaches, Cnidoglanis macrocephalus was one of the two  dominant fish species, and was most abundant in medium and high volumes of beach wrack (Crawley et al., 2006).
In S.A., the Estuary Catfish has been recorded in a variety of habitats, including estuaries, benthic sand, seagrass and artificial reef habitats (Glover, 1979; Johnson, 1985b; Jones et al., 1996; J. Baker, pers. obs., 1999, 2007, 2008; MLSSA, 1999; Jackson and Jones, 1999).
There is a record of the species from “intertidal rock pools, granite bottom covered with Hormosira” (South Australian Museum record, cited in OZCAM database, 2004). The species has also been recorded in rock pools in other areas (e.g. N.S.W. – see Griffiths et al., 2004). 
The species prefers areas where the bottom is sandy, and marine vegetation provides some cover for the nesting burrows (W.A. Department of Fisheries, 2001c). In W.A., the species has been recorded in both dense and sparse seagrass beds inshore (in highly sheltered and moderately sheltered locations), and also on sand bottom in moderately wave-exposed areas, and in dense seagrass beds further offshore (N.B. recorded in the latter habitat during autumn) (Valesini et al., 2004).
The Estuary Catfish has also been recorded in mangrove areas, and is considered to be common in the mangroves around Sydney (Australian Museum, 2004b).
The reported depth range, based on museum records, is from the intertidal to around 30m deep (Paxton et al., 1989, cited in Froese and Pauly, 2007; Anonymous, 2001a).

Notes on Biology and Behaviour

Size and Age

The Estuary Catfish grows to over 70cm. The maximum recorded size is 91cm SL (Neira, 1998). In the Swan River in W.A., the maximum size recorded during survey was 71cm (Nel et al., 1985), and in the Wilson Inlet, 78.75cm (Laurenson et al., 1993).
The maximum weight published is 2.625kg, being a specimen taken by spearfishing (Hutchins and Swainston, 1986, 2001).
The maximum age recorded is 13 years, based on otolith readings (Kailola et al., 1993).

Migration and/or Aggregation

Juvenile Estuary Catfish aggregate at night in drift macrophytes (such as fine red macroalgae, and dead seagrass) in the surf zone, as a means of escaping predation, and also to feed on the small crustacea in the macrophytes (Lenanton et al., 1982; Lenanton and Caputi, 1989).
In W.A., Lenanton et al. (1982) and Hyndes et al. (1999) showed that Cnidoglanis macrocephalus makes seasonal migrations, to areas where detached macrophytes accumulate in winter.
Despite localised migrations to areas where macrophytes accumulate, genetic studies suggest that Estuary Catfish populations do not move far from their home estuary, and that there is little interbreeding between estuarine populations (Ayvazian et al., 1994; W.A. Department of Fisheries, 2001c).

Diet and Feeding Behaviour

Estuary Catfish are opportunistic feeders, and feed primarily at night. Food of adults consists of bivalves (including mussels) and other molluscs, detritus in the sediment, crustaceans (small prawns and amphipods), polychaete worms, algae and organic debris (Thompson, 1957; Lenanton et al., 1982; Lenanton and Caputi, 1989; Platell and Hall, 2006). A study in Wilson Inlet in south-western Australia (Platell et al., 2006), showed that Estuary Catfish consume substantial amounts of coarse organic material, as well as mytilids (mainly Xenostrobus spp.) and other bivalves (especially Tellina deltoidalis and Irus crenata).
Juveniles eat more crustacea - often consuming amphipods from among drifting macrophytes (Lenanton et al., 1982; Lenanton and Caputi, 1989). A study in south-western Australia showed that the amphipod Allorchestes compressa, found in beach wrack, is a major prey item for juvenile C. macrocephalus (Crawley et al, 2006).

Reproduction

Estuary Catfish usually mature from between 2 to 4 years of age, depending on locality (e.g. Nel et al., 1985; Laurenson et al., 1993; Harrison, 2001; W.A. Department of Fisheries (2001c), but in general, the spawning age is normally 3+ years. Estimates of size at maturity vary; e.g. 38cm to 42.5cm, and the species can form breeding aggregations (Nel et al., 1985; Laurenson et al., 1993; (Harrison, 2001; W.A. Department of Fisheries, 2001c).
Estuary Catfish mate in pairs, and make burrows under seagrass beds and rocks to rear their young. Vegetated areas are preferred, which provides some cover for the nesting burrows (W.A. Department of Fisheries, 2001c). Nest-building and mating take place in spring, between August and December depending on location and environmental conditions (W.A. Department of Fisheries, 2001c). In the Swan River in W.A., Estuary Catfish spawn between October and December (Harrison, 2001), and in the Wilson Inlet, between October and January (Laurenson et al., 1993). Differences in spawning time may be related to water temperature (Laurenson et al., 1993). In general, September to November is the peak spawning and nesting period for Estuary Catfish in Western Australia (W.A. Department of Fisheries, 2001c).
The species spawns once per year, and a commonly cited fecundity estimate for this species is 500-3,500 eggs (Nel et al., 1985; W.A. Department of Fisheries, 2001c). It is noted that Harrison (2001, uncited reference) reported that the species produces up to 5,550 eggs, with an average of 2,078. A study by Laurenson et al (1993) showed that, in comparison with the larvae of three other plotosid genera, the larvae of C. macrocephalus are far larger in size and more developed at hatching and take a shorter time to transform into juveniles.
Male C. macrocephalus brood and protect eggs in burrows, in inshore waters and estuaries (Nel et al., 1985; W.A. Department of Fisheries, 2001c). The male Estuary Catfish constructs a nest, among seagrass beds and rocks. The male in the nest guards the eggs between its pelvic fins (Laurenson et al., 1993). The drift weeds found in inshore marine waters, protected inshore marine environments and estuaries, act as nursery areas. Estuary Catfish enter these areas during their first year of life, and often remain there for long periods (Lenanton and Potter, 1987; Lenanton and Caputi, 1989; Kailola et al., 1993).

Other Information

In W.A., a study using enzyme electrophoresis of Estuary Catfish samples from 1500km of coastline (including various estuaries), indicated genetic divergence between west coast and south coast populations. There was also high genetic divergence between populations from different estuaries within each of the southern and western regions, with higher genetic divergence between samples from different estuaries, compared with samples from marine waters (Ayvazian et al., 1994). The authors concluded that there is population sub-division between marine and estuarine environments, and possible also between Estuarine Catfish in different estuaries over the range studied.
C. macrocephalus have venomous glands associated with the sharp spines of the dorsal and pectoral fins, and can inflict painful wounds (Scott et al., 1974; Gomon, in Gomon et al., 1994).
Birds such as cormorants and pelicans prey upon Estuary Catfish (Lenanton and Caputi, 1989; Humphries et al., 1992).

Fisheries Information

General

The species is considered to have flesh “of an excellent quality” (Gomon, in Gomon et al., 1994), and is described as a “high value” fish for eating (Harrison, 2001). It is taken both commercially and recreationally, as discussed in the sections below.
The National Recreational and Indigenous Fishing Survey (Henry and Lyle, 2003) reported that 17,871 Estuary Catfish were caught and kept by recreational fishers in southern Australian states during the survey time period (May 2000 to April 2001), comprising 9,242 specimens in N.S.W.; 482 in Queensland; and 8,147 in Western Australia. Recreational catch statistics were not provided for South Australia.

Western Australia

Estuary Catfish is generally prized for its soft and delicate flesh, and is one of the most popular recreational fishing species in the South West region of Western Australia. The species is known as “Cobbler” in W.A., and that is the marketing name in Australia (Seafood Services Australia, 2003). The species was once a staple in the fish and chips shops of W.A., but the price of Estuary Catfish fillets has risen sharply in recent years (due to declining abundance), and now the species is not always available (W.A. Department of Fisheries, 2001c).
In W.A., most fishing for this species occurs in the Swan-Canning, Peel-Harvey and Leschenault estuaries with small catches from Hardy Inlet (W.A. Department of Fisheries, 2001c, 2005c). Cobbler is one of the top 8 species taken in the estuarine and nearshore marine fisheries in W.A. (Lenanton and Potter, 1987). In the South Coast bioregion, Cobbler is one of the species targeted by the estuarine and beach seine fisheries. In 2001, approximately 77t of Cobbler were taken from the south coast estuaries (Fisheries Research Division, W.A. Department of Fisheries, 2003).
Notes from Kailola et al. (1993): In Western Australia, Estuary Catfish have been exploited commercially since the inception of the inshore, estuarine fishery in that State, but targeted only since the 1970s. The commercial fishery for Estuary Catfish is concentrated in southern waters between Perth and Albany. The Swan-Avon and Peel-Harvey estuaries have been the traditional centres of the fishery; however, Wilson Inlet has been the major contributor to the overall catch in more recent years. The fishery is mainly located in the lower and middle sections of estuaries (Loneragan et al., 1989), with a few fish caught in marine embayments around Albany. Fishing occurs all year, although the catch per unit effort (CPUE) varies markedly with the season. The annual catch and CPUE also fluctuate widely between years (Nel et al., 1985; Lenanton et al., 1984; Loneragan et al., 1989, cited by Kailola et al., 1993). Generally, Estuary Catfish, together with sea mullet (Mugil cephalus) and yellow-eye mullet (Aldrichetta forsteri) comprise between 70% and 90% of the annual commercial catch from the south-west estuaries in Western Australia. Estuary Catfish are caught at night, with bottom set gillnets and haul nets, bunting and funnel traps. The fish are sold fresh, and consumed locally, mostly in Perth.
Apart from target fishing, the species is also caught in low numbers as part of the bycatch in the W.A. temperate Demersal Gillnet and Demersal Long-line Fishery (McAuley and Simpfendorfer, 2003).
BRR (1991) reported that annual catches of Estuary Catfish (called Cobbler, in W.A.) ranged between 70t and ~115t during the mid to late 1960s;  173t – 364t during the 1970s; and 92t – 258t during the 1980s. For the 1990s and early 2000s, the combined annual catch of Estuary Catfish from all commercial fisheries in W.A. is provided below, according to fishers’ statutory monthly returns. Most of the catch comes from the South Coast estuaries (W.A. Department of Fisheries, 2005c). The figures presented below may slightly underestimate the total catch, because additional data from research logbooks and processors are not included (W.A. State of the Fisheries report, 2002-2003). For example, in 2000/01, the total reported commercial catch of Estuary Catfish from the South Coast estuaries, was 77.1t (Fisheries Research Division, W.A. Fisheries, 2002), yet the figure collated using statutory monthly returns was 58.6t, for the whole State (Table 1).

Table 1 Reported catches of Estuary Catfish (Cobbler) from W.A. waters, 1994-95 to 2004-05
Year	Live weight (kg)	Landed weight (kg)
1994/95	121,110	86,272
1995/96	69,500	48,702
1996/97	69,993	49,515
1997/98	78,294	56,399
1998/99	77,324	55,102
1999/00	73,980	52,613
2000/01	58,572	41,856
2001/02	103,664	73,529
2002/03	104,519	74,279
2003/04	68,051	48,266
2004/05	41,773	30,234

(W.A. Fisheries Research Services Division statistics 1994-2001, extracted from W.A. Fisheries website, 2003, and W.A. State of the Fisheries reports, 2000/2001 - 2005/2006)

In W.A., Estuary Catfish has long been a popular species for recreational fishers (Kailola et al., 1993), and is still considered to be one of several key species for angling / sports fishing (Harrison, 2001). On the west coast, hand-lining is popular, especially in the Swan-Avon and Peel-Harvey estuaries, and from the ocean around Hillary's Beach near Perth (Kailola et al., 1993). They are usually caught by line in the Swan River, where recreational netting is banned. In the Peel-Harvey estuary, a recreational survey in 1998-999 shoed that the species was caught in small numbers by boat-based fishers (Malseed and Sumner, 2001). Cobbler are also caught with hand spears at night (Kailola et al., 1993). Previously, setting unbaited traps in Estuary Catfish breeding areas was a popular fishing method, but the use of fish traps is now banned in Western Australia (W.A. Department of Fisheries, 2001c). In estuaries further south, C. macrocephalus are also taken by recreational gill-netters (W.A. Department of Fisheries, 2001c). The legal minimum size is 43cm. Previously, the daily bag limit was 8 Estuary Catfish per fisher in all fishing regions of W.A. (Harrison, 2001). The bag limit has been reduced in recent years to 4 per fisher in the West Coast region, although the previous bag limit of 8 fish still applies in the South Coast fishing region of W.A. (W.A. Department of Fisheries, 2003b, 2004a, 2005).

South Australia

In South Australia, both commercial and recreational fishers take this species (Jones et al., 1996, Table 2).
Estuary Catfish forms a very small component of the marine scalefish fishery in South Australia. It is sometimes taken, but not targeted. In past years, Estuary Catfish has been recorded as bycatch by fishers targeting species such as mullet. During the 1980s, the highest recorded catch per annum was 72kg (BRR, 1991). Records of capture during the past 15 years include small quantities (e.g. less than 50kg per trip) taken by gillnets and hauling nets, from areas such as south-western Spencer Gulf; south-eastern Spencer Gulf / Hardwicke Bay area; mid-western Spencer Gulf (e.g. Franklin Harbour and Arno Bay); Investigator Strait; far northern Gulf St Vincent, and the Murray Mouth region.
Small numbers of Estuary Catfish are taken as a bycatch of the commercial haul net fishery, mainly in southern Spencer Gulf (Kailola et al., 1993, cited by Froese and Pauly, 2004).
Bycatch sampling during the early and mid 1990s showed that the species is a very minor component of the bycatch in the Spencer Gulf prawn trawl fishery (see Carrick, 1997).
The species is a minor component of the bycatch in the Blue Crab Fishery. During a bycatch sampling program from 2002 - 2005, no specimens were recorded from 2002-2004; however in 2005, 4 Estuary Catfish were recorded in 880 pot lifts, in Gulf St Vincent (Currie and Hooper, 2006).
In southern Spencer Gulf, Estuary Catfish are taken occasionally by recreational fishers (Kailola et al., 1993, cited by Froese and Pauly, 2006).
In South Australia, the species is recorded as having been taken in shore-based and boat-based spearfishing competitions (e.g. see Johnson, 1985a, 1985b). Estuary Catfish was one of the species included in the list of fish taken in spearfishing competitions during the 1980s (e.g. 32nd Australian Skindiving Convention) (Johnson, 1985b). More recently, Estuary Catfish (specimens over 0.4kg) was listed as one of the targets in the 54th Australian Spearfishing Titles 2006, held on northern Kangaroo Island (Australian Underwater Federation Inc., 2006). 
The National Recreational and Indigenous Fishing Survey (Henry and Lyle, 2003) recorded no catches of Estuary Catfish from South Australia during the survey time period (May 2000 to April 2001), although the catches of this species were provided for other states (see section above).

New South Wales

C. macrocephalus is a significant bycatch species in the New South Wales estuarine prawn hauling fishery. A sampling program between September 1998 and August 1999 reported that about 23,000 Estuarine Catfish were caught in the Richmond, Manning and Wallamba rivers during that period (Gray and Kennelly, 2001).
The species is also a minor component of the bycatch in the N.S.W. Lobster Fishery (New South Wales Fisheries (2004c), and in the shelf sector of the Ocean Prawn Trawl Fishery (e.g. frequency of occurrence of less than 2% across all trawls) (New South Wales Department of Primary Industries, 2004).

Victoria

Although the species is not usually recorded in Victorian waters, there are more than a dozen museum records of Estuary Catfish specimens that were caught by commercial fishing in Port Phillip Bay (Anonymous, 2002b, in Froese and Pauly, 2007).

Vulnerable Characteristics of the Species, and Threatening Processes

The species appears to be much less common in S.A. than in parts of the range where it is a significant commercial species (i.e. W.A.).
In W.A., Estuary Catfish (Cobbler) is defined as a “Category 1” fish species; meaning that it is considered to be “highly vulnerable to over-fishing”. Category 1 species are generally long-lived, slow-growing, and mature at four years-plus; form semi-resident populations; are vulnerable to localised depletion due to their life history, and are of low abundance and/or highly targeted. Category 1 species have low catch rates, and are generally highly regarded for their eating quality. The Category 1 status is reflected in the recreational fishing limits on this species (Harrison, 2001; W.A. Department of Fisheries, 2004a).
The breeding habits of Estuary Catfish have made them vulnerable to over-fishing, as they spawn and nest in burrows, and the males remain nearby to guard eggs and rear the young. Unlike many fish which spawn prolifically several times a year, Estuary Catfish spawn only once per year, and produce a relatively small number of eggs (W.A. Department of Fisheries, 2001c).
Research in W.A. has shown that there may be little mixing between isolated populations, and in areas where the species is commonly recorded in estuaries (e.g. in southern W.A.), each estuarine population may be a genetically unique stock, and therefore the distinct populations need to be protected in their own habitats (W.A. Department of Fisheries, 2001c).
In recent years, commercial catches of Estuary Catfish in W.A. have declined dramatically, and large breeding-size catfish are making rarer appearances in catches (W.A. Department of Fisheries, 2001c; 2005c). For example, the reported catches of Estuary Catfish in the Swan / Canning Estuary have been declining from the late 1980s, and during the early 2000s, catches were negligible (< 100 kg). During the early 2000s, the catch in the Peel/Harvey Estuary was also low (e.g. 1.4t in 2003), and at the lower end of historical catches (W.A. Department of Fisheries, 2005c). Commercial catch statistics are cited above, and have ranged between approximately 70t and 120t per annum between the mid 1990s and the present. Estuary Catfish stocks in W.A. are considered to have declined in recent years, and in the past, many catfish were caught before they had an opportunity to spawn (W.A. Department of Fisheries, 2001c; Harrison, 2001). Since the 1960s, commercial catches in the Swan-Canning, Peel-Harvey and Leschenault Estuaries have fallen from more than 400 tonnes, to less than 10 tonnes a year in 1993 (W.A. Department of Fisheries, 2001c).  By the early 1990s, despite the decline in Estuary Catfish catches from the south-western estuaries in W.A., recreational fishing pressure was increasing in inshore coastal waters. At that time, there were still no estimates of the size of the Estuary Catfish populations (Kailola et al., 1993), despite the fact that the species had been actively fished commercially and recreationally for several decades.
A study of the susceptibility of trawl-caught fishes to population impacts (Stobutski et al., 2001) ranked fish bycatch species according to two overriding characteristics (based upon biological and ecological criteria): (i) the susceptibility to capture and mortality due to prawn trawling, and (ii) the population's capacity to recover after depletion. The rank of each species on these two characteristics determined its relative capacity to sustain trawling, and therefore its priority for research and management. Species that were the least likely to be sustainable included those in the Plotosidae. These species are highly susceptible to capture by trawls, they are benthic or demersal, their primary habitat is soft sediments, and their diet may include prawns. The recovery capacity of these species is also low, with the estimated removal rate by trawling (Stobutski et al., 2001).
A summary of factors considered to contribute to the vulnerability of this species include the isolation of populations; the very low fecundity (W.A. Department of Fisheries, 2001c; Harrison, 2001); the brooding habit of the species; localised reproduction; and aggregative behaviour during breeding period, coupled with the fact that fishing pressure is moderate to high (and increasing), and fisheries occur around key population centres (Harrison, 2001).
The estuarine association of this species makes populations susceptible to impacts that reduce estuarine water quality. Examples include periodic “fish kills” from flood-induced deoxygenation of estuarine waters (e.g. Kennelly and McVea, 2002). Estuary Catfish also accumulate heavy metals (such as arsenic and mercury) from contaminated estuaries and harbours (e.g. Edmonds et al., 1993; Francesconi et al., 1997).

Existing Stock Conservation and Management Measures

In Western Australia, there are numerous management actions to protect populations of this species, including minimum size limits, species and mixed bag limits, gear restrictions, netting controls, and area closures and seasonal closures in estuaries, to protect breeding catfish during the peak spawning and nesting periods (W.A. Department of Fisheries, 2001c; Harrison, 2001).

Research Recommendations (S.A.)

More information is required on the distribution, relative abundance and habitat requirements of Estuary Catfish populations throughout South Australia.
Stock structure of Estuary Catfish in S.A. and W.A. should be elucidated, through population genetic research, which would assist management of the different stocks across the range (M. Hammer, Aquasave, pers. comm., 2007).

Management Recommendations (S.A.)

Commercial and recreational fishing regulations are required, given the vulnerable characteristics of Estuary Catfish populations.