© 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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Southern Sea Carp / Marblefish

Family Name:	Aplodactylidae
Scientific Name:	Aplodactylus arctidens Richardson, 1839
Recommended Status in S.A:	Least Concern (in S.A.)
Rationale:  Although the Southern Sea Carp has a broad geographic range across southern Australia (and within South Australia), it is included here because (i) it is a sedentary, site-associated reef fish that relies upon macroalgae-covered reefs for feeding, shelter and presumably other aspects of the life cycle, and these characteristics may render populations vulnerable to direct impacts (fishing mortality) or indirect impacts (due to habitat loss). However, the suggested status is Least Concern for South Australia, because there is little evidence of habitat degradation in many of the areas in S.A. where this species has been recorded, and other threats, such as fishing mortality, are assumed to be minor. Over the geographic range, it is likely that the species is most frequently caught in Tasmania, where it is taken commercially and recreationally. There is some evidence that fully protected marine reserves can benefit populations of fish species with strong habitat association, such as Southern Sea Carp.

Page Contents

Current Conservation Status

No listings known

Distribution

Southern Australia and New Zealand

A. arctidens is found throughout northern and southern New Zealand (but more common south of Cook Strait), and in south-eastern and southern Australia (Victoria, Tasmania and South Australia) (Paulin and Roberts, 1992; Francis, 1996; Edgar, 2000; Russell, 2000). The species is more numerous in Tasmania and Victoria (including Bass Strait) than in S.A. (Hutchins and Swainston, 1986; Kuiter, 1993, 2000).
The species is considered to have a cool temperate distribution, and A. arctidens is an indicator species for the Tasmanian Province, a biogeographical province which extends from the north-eastern tip of Tasmania at Cape Naturaliste, and encircling the west, south and east coasts up to Cape Grim at its north-western extremity (IMCRA Technical Group, 1996).
In Victoria, A. arctidens is one of the common species that characterise the Maugean (southern) elements of the Central Victorian and Flinders Bioregions (Edmunds et al., 2000).

South Australia

Examples of locations in S.A. where A. arctidens has been recorded include west of Coffin Bay off southern Eyre Peninsula; eastern Spencer Gulf; parts of southern Yorke Peninsula (e.g. West Cape, and Howling Cave Bay I.); Newland Head, Parsons Beach, Waitpinga, Cape Jervis, Fishery Beach, Second Valley and Rapid Head (all lower Fleurieu Peninsula); Port Noarlunga Reef (lower metropolitan coast); Harvey Return, Snug Cove, King George Beach, and Stokes Bay (northern Kangaroo I.); Cape Cassini, Hog Point / Penneshaw area, Snapper Point and Kangaroo Head (north-eastern Kangaroo I.); Cape Coutts, Moncrieff Bay and Cape Willoughby (eastern Kangaroo I.), Encounter Bay; and Beachport, in south-eastern S.A. (photograph by D. Cook, 1999, cited in Froese and Pauly, 2007; S. Shepherd, K. Brown, A. Brown, J. Brook, J. Mather and D. Ashcroft, unpubl. data, 2002; S. Shepherd and J. Baker, unpubl. data, 2003; S. Shepherd, unpubl. data, 2002, 2004; South Australian Museum data, 2002, cited by T. Bertozzi, SAM, pers. comm., 2005; Australian Anglers Association, 2005; D. Muirhead, unpubl. data, 2006; Edgar et al., 2006; J. Baker, unpubl. data, 2007; Australian Museum record, South Australian Museum records, cited in OZCAM database, 2007).
During recent surveys of nearshore reef fishes in the Gulf St Vincent, Investigator Strait and southern Yorke Peninsula regions, Southern Sea Carp was recorded as being most numerous at sites along north-western Kangaroo I., with an abundance of 6.7 (SD = 9.3) fish per 2000m² (data by S. Shepherd, K. Brown, A. Brown, J. Brook, J. Mather and D. Ashcroft, 2002, cited in Shepherd and Baker, 2008).

Habitat

Marblefish occurs on shallow, wave- and surge-exposed, coastal rocky reefs (Hutchins and Swainston, 1986) with abundant macroalgae, particularly kelp (Edgar, 2000). The habitat has also been described as “weedy reef slopes” (Kuiter, 1993, 2000). In south-eastern Australia, Southern Sea Carp is found in large numbers among kelp plants on shallow coastal reefs (Edgar, 2000). Similarly in New Zealand, the species is known from kelp “forests”, and from “shallow broken rock” reefs (Cole, 2001).
The published depth range is 0m to about 40m (Paulin and Roberts, 1992; Kuiter, 2000; Edgar, 2000); however it is noted that the South Australian Museum has a specimen (F 09287) reported from 65m deep. Within the depth range, the species is found mostly in waters less than 15m deep (Kuiter, 2000). In northern Tasmania, A. arctidens is a common species on shallow subtidal (e.g. 0m – 5m) reefs (Barrett and Wilcox, 2001).
In Victoria, although A. arctidens is mainly found on shallow reefs, it is noted that the species has also been recorded on deeper reefs of about 25m – 30m, such as those in the Port Phillip Heads area (Elias et al., 2004).

Notes on the Biology

Growth

Marblefish is reported to grow to 60cm (Hutchins and Swainston, 1986; Edgar, 2000) or 65cm (Kuiter, 1993, 2000), but they are rarely recorded at these large sizes. Most fish seen on reefs in southern Australia less than 40cm, commonly around 30cm.
One of the maximum-recorded weights is 2.43 kg, being a specimen from West Cape in S.A., caught in 1971 (Hutchins and Swainston, 1986; Australian Anglers Association, 2005). In New Zealand, a 51cm individual weighed about 2.38kg (Russell, 1977).

Diet and Feeding Behaviour

Marblefish spend most of the time resting on the bottom, and usually they swim only to grab food (Kuiter, 2000).
Studies in New Zealand (Russell, 1983; Choat and Clements, 1992) showed that Southern Sea Carp eats a variety of brown and red macroalgae, the latter in particular. Russell’s study recorded in the diet: Champia sp., Corallina officinalis, Gigartina macrocarpa, Laurencia botryoides, Plocamium sp., Pterocladia lucida, Rhodymenia leptophylla, Vidalia colensoi, Glossophora kunthii, Scytothamnus australis, Zonaria angustata, Codium adhaerens, and Gelidium caulacantheum. Choat and Clements (1992) described A. arctidens as a facultative herbivore, with the diet dominated by understorey and epiphytic red algae. Choat and Clements showed that the diet of Southern Sea Carp in Goat Bay New Zealand comprises about 98% - 99% plant material, with an example being: 54% thallose red algae, 21% filamentous red algae, 20% sheet-like red algae, 2% Ecklonia kelp, 1.3% Carpophyllum, 0.5% calcareous red algae, 0.6% mixed benthic invertebrates, 0.2% Xiphophora chondrophylla, 0.3% benthic crustaceans.

Reproduction

In New Zealand, the Marblefish has been recorded spawning in late autumn – early spring.

Other Information

Southern Sea Carp A. arctidens does not have a swim bladder (Tomonaga et al., 1996), and fish in the family have been described as “sloppy swimmers” (Kuiter, 2000).
This species has a low energy diet, which accounts for its low level of activity (S. Shepherd, SARDI, pers. comm., 2006).

Fisheries Information

Commercial - Australia

Generally, the species is not targeted commercially because the flesh has an unpleasant smell.
Work in the Southern Shark Fishery in southern Australia showed that Marblefish is vulnerable to capture in 4-inch and 5-inch gillnets. During a survey of Southern Shark Fishery bycatch in 1973-1976, 7 and 19 Marblefish were caught per 1000 km hours, using the 4-inch and 5-inch gillnets respectively (Walker et al., 2003). A. arctidens was also recorded as a very minor part of the bycatch of 6-inch gillnets. However, the there are no quantitative data on the current bycatch of this species in commercial shark fisheries in southern Australia.
There is a small commercial catch of Southern Sea Carp exported from Tasmania to Sydney markets (Edgar, 2000). In Tasmania, the species is a bycatch in the commercial gillnet fishery for Banded Morwong (Murphy and Lyle, 1999). During the 1980s, the annual catch from Tasmania was less than 1t. During the 1990s, the Tasmanian catch ranged between 0.2t (in 1990/91) and almost 6t (in 1996/97), with higher annual catches in the second half of that decade compared with the first (Lyle and Jordan, 1999; Lyle and Hodgson, 2002; BRS, 2004). During the late 1990s and early 2000s, the annual catch was about 4t (Lyle and Hodgson, 2002).
There are records of the species being taken by commercial fishing in Port Phillip Bay and Bass Strait in Victoria (Anonymous, 2002b). The Victorian catch is likely to be lower than that from Tasmania. Bureau of Rural Sciences Victorian catch statistics for the 1990s (BRS, 2004), reported 1t per annum taken in 1995/96 and in 1997/98, and none in other years of that decade.

Commercial – New Zealand

In New Zealand, the species has a commercial fishing code (“GTR”), but catch statistics are not available for this report. In New Zealand, A. arctidens is often called Granite Trout or Marblefish.
Experiments in New Zealand have shown that A. arctidens is vulnerable to capture in 5.5-inch commercial gillnets, and, to a lesser extent, in 4.5-inch gillnets (Hickford et al., 1997). In 15 sets of the 5.5-inch gillnets, 21 specimens of A. arctidens were caught (Hickford et al., 1997).

Recreational

The species is taken by some anglers and spearfishers. Some clubs and associations keep records of the maximum sizes caught, such as 2.43kg (a national angling record specimen taken off West Cape in S.A., in 1971), and 1.72kg (the Victorian angling record, being a specimen taken from Kilcunda, in 1981) (Australian Anglers Association – Victorian Division, 2003; Australian Anglers Association, 2005).
Most recreational anglers in Tasmania discard Marblefish, or use it as bait for rock lobster fishing (Lyle et al., 2000).
In Tasmania, Marblefish is vulnerable to capture over reefs by recreational “graball” nets (e.g. 108mm and 114mm mesh gillnets) (Lyle and Campbell, 1999; Lyle et al., 2000) and the smaller “mullet nets” (Lyle and Smith, 1998). The species is an occasional bycatch when recreational gill-netters are targeting Striped Trumpeter or Blue Warehou, and some fishers cannot identify Marblefish in their catches, which they refer to as “grouper” (Lyle and Campbell, 1999). Between December 1996 and April 1998, the recreational catch by licensed fishers in Tasmania was 2,714 Marblefish (2,111 in 1997) (Lyle, 2000).
The National Recreational and Indigenous Fishing Survey (Henry and Lyle, 2003) reported that recreational fishers in Tasmania caught 789 Marblefish specimens during the survey time period (May 2000 to April 2001). Catch statistics for this species were not reported for any other State.

Other Information

The Marblefish is of some significance to Maori in New Zealand, as a traditional food (Waitangi Tribunal, 2006).

Vulnerable Characteristics of the Species, and Threatening Processes

Southern Sea Carp is a benthic, sedentary fish with poor swimming ability, and such characteristics can render populations vulnerable to exploitation.
The species is associated with shallow, macroalgae-covered reefs, particularly kelp. The species relies upon such macroalgae-covered habitats for feeding, shelter and presumably also reproduction. Any processes (e.g. such as nutrient pollution and sedimentation from coastal discharges, physical damage and sedimentation from dredging, channel clearing etc) which reduce the cover of large macroalgae in nearshore areas, may adversely affect populations of this species; however there are no specific data.
Mortality from bycatch in commercial and recreational fishing nets (and also mortality due to angling and possibly spear-fishing) may be a threat to Marblefish populations in some areas, but more data are required. It is noted that in Victoria, periodic surveys on a metropolitan reef over a long period have shown that the average number of A. arctidens recorded in the area decreased from an average of 200 sighted per 6 transects in 1959, to 60 sighted in 1964, and 0 in both 1982 and 2006 (Nevill, 2006). The ease with which this species can be taken by spearfishers in the area was considered to contribute to the decline in Marblefish numbers over time (Nevill, 2006).

Research Requirements

More information is required on the relative abundance of this species in some parts of the geographic range, including most parts of South Australia.
There is little information on reproduction in this species.
Potential impacts of nearshore reef degradation on species such as Sea Carp (that rely upon macroalgae-rich habitats) should be investigated.

Management Requirements

Measures to reduce the bycatch of Southern Sea Carp in Commonwealth- and State-managed fisheries (particularly gill-net fisheries) should be investigated.
Recreational catch restrictions may be required in some parts of southeastern Australia, to discourage use of this species as bait.
Plans for marine protected areas (including South Australia). should give due consideration to site-associated reef fish species such as the Sea Carps. It is noted that, during a netting survey in the Governor Island Marine Reserve in Tasmania (Murphy and Lyle, 1999), the numbers and total weight of Southern Sea Carp caught inside the reserve were more than double those from outside the reserve.

Other Information

The Marblefish occurs in a number of marine reserves in New Zealand, such as Cape Rodney-Okakari Point (Leigh) (Cole, 2001), Goat Island (Cole et al., 1990), Te Angiangi (Department of Conservation, New Zealand, 2003), Poor Knights Islands (Denny et al., 2003), Te Whanganui a Hei (Haggitt and Kelly, 2004), Long Island – Kokomohua (Davidson, 1994; Cole, 2001), and Sugar Loaf Islands (Ngä Motu) (Miller et al., 2005).
In Tasmania, A. arctidens is found in a number of marine reserves (e.g. Murphy and Lyle, 1999; Edgar et al., 2004) and areas proposed as marine reserves (e.g. Barrett and Wilcox, 2001).
In Victoria, the species is found in a number of Marine Parks and Sanctuaries, such as Port Phillip Heads Marine National Park (MNP), and Phillip Island (Edmunds et al., 2000), Bunurong MNP (Edmunds et al., 2003), Discovery Bay MNP (Roob et al., 1999; Plummer et al., 2003), The Arches Marine Sanctuary (Plummer et al., 2003), the Merri Marine Sanctuary (Plummer et al., 2003; Hart et al., 2005), and Marengo Reefs (Tsernjavski, 1995, cited by Plummer et al., 2003).
Southern Sea Carp A. arctidens is one of the species monitored by community divers in the Reef Watch programs in South Australia and Victoria.