© 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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Bigscale Rubyfish / Rubyfish

Family Name:	Emmelichthyidae
Scientific Name:	Plagiogeneion macrolepis McCulloch, 1914
Recommended Status in S.A:	Data Deficient
Rationale:  The species is included here because (i) the Big-scale Rubyfish apparently has a relatively small geographic distribution; (ii) there is little information on the biology, population dynamics and habitat of this species, but a closely related species of Plagiogeneion is known to be long lived and slow growing, with delayed age at maturity and low reproductive output; (iii) the species schools in lower continental shelf and upper slope waters, and is vulnerable to capture in trawl fisheries; and (iv) Rubyfish is part of the bycatch (mainly discarded) in a number of trawl fisheries in southern Australia, with no assessment of the sustainability, or potential population impacts.

Page Contents

Current Conservation Status

No listings are known for P. macrolepis. It is noted that in New Zealand, for an ecological assessment of commercial fisheries, the related species P. rubiginosum was ranked as being at high risk of impact (category “E”), and therefore is a species that fish consumers should avoid (Weeber and Szabo, 2005).

Distribution

Southern Australia

The Bigscale Rubyfish is endemic to Australia’s south coast, mainly between western S.A. and south-western W.A. (Australian Museum, 2005k). Kuiter, (in Gomon et al., 1994) included Victoria in the distribution, and there are several museum records form Victoria, reported to be this species.
The species is mostly known from the Great Australian Bight (which is the type locality, where Bigscale Rubyfish is taken as trawl bycatch).

South Australia

Examples of locations in South Australia where Bigscale Rubyfish has been recorded include deeper waters across the entire span of the Great Australian Bight (from where the majority of survey records have come); deeper waters south of the tip of Eyre Peninsula and west of Kangaroo Island; deeper waters east of Dudley Peninsula region of Kangaroo Island; and the deeper continental shelf and upper slope waters of the lower South-East of S.A., including sites off Beachport, and sites near the Victorian border (Brown and Knuckey, 2002; CSIRO Marine Research survey records, cited in CSIRO, 2007; Australian Museum records, Museum of Victoria records, cited in OZCAM database, 2007).  
Many thousands of specimens were caught by research fishing vessels in the Great Australian Bight during the 1960s and 1970s (CSIRO Marine Research data, cited in CSIRO, 2007). 
The type locality for this species is the Great Australian Bight, west of Eucla (33°20’S, 126°-127°E) in South Australia, where the first specimens were caught at 70-120 fathoms (128m – 219m) (Eschmeyer, 2001).

Habitat

P. macrolepis is a schooling species that occurs close to the bottom, on the continental shelf and slope. The usual upper depth limit is about 130m (Kuiter, in Gomon et al., 1994; CSIRO Marine Research et al., 2001), and the lower depth limit may be as deep as 413m, according to CSIRO Marine Research specimen records (CSIRO Marine Research et al., 2001). Most published records are from the outer continental shelf and upper slope, about 100m – 250m (CSIRO Marine Research records, cited in CSIRO, 2007).   
It is noted that the related species in south-eastern Australia and New Zealand (Plagiogeneion rubiginosum) has a much broader depth range (50m to 800m, most abundant between 200m and 400m), and has been recorded over sea mounts in part of the range (Ivanin et al., 1996; Clark and O’Driscoll, 2003). It is supposed that P. macrolepis might also be associated with benthic rises (e.g. where food might concentrate) in some parts of its narrower geographic and depth range.

Notes on the Biology

Age and Growth

There is no recent information available on maximum size. The species may grow to somewhere between 32cm (Kuiter, in Gomon et al., 1994) and 47cm (May and Maxwell, 1986, cited in Froese and Pauly, 2007).
Two methods of determining the age of a related species of Rubyfish (P. rubiginosum) in New Zealand have shown that the species is long-lived. Otolith ring counts previously produced a maximum age estimate of at least 45 years, and more recent (presently being validated) age studies using bomb radiocarbon (C¹⁴) have aged the species to at least 70, and possibly more than 90, years of age (Paul et al., 2000 and 2003, cited by New Zealand Ministry of Fisheries, 2003; NIWA, 2004b).

Diet

The closely related Rubyfish species P. rubiginosum feeds on larger zooplankton / mid-water crustaceans (Heemstra, 1984, cited in Froese and Pauly, 2006), salps and myctophid fishes (New Zealand Ministry of Fisheries, 2005d). Given the similarity of habit (i.e. a schooling species that occurs close to the bottom), the diet of P. macrolepis is presumed to be similar. 

Reproduction

The related species of Rubyfish P. rubiginosum is reported to mature at around 24cm standard length, and spawn during winter-spring (e.g. in the southern Indian Ocean) (Mel’nikov and Ivanin, 1995, cited by Welsford and Lyle, 2003). Age at maturity might be around 7 years for that species (Annala et al., 2003, cited by Weeber and Szabo, 2005).

Fisheries Information

P. macrolepis is a bycatch of trawl fisheries in coastal waters of southern Australia (Kuiter, in Gomon et al., 1994). “Rubyfish” is a seafood marketing name for P. macrolepis (Seafood Services Australia, 2003), which indicates that some proportion of the catch is marketed.
Rubyfish form a part of the bycatch in the Commonwealth-managed Southern and Eastern Scalefish and Shark Fisheries (SESSF), including the South East Trawl Fishery (SETF) (AFMA, 2002a). Plagiogeneion species are both by-product (i.e. retained and sold) and discarded in the otter trawl sub-fishery of the South East Trawl Fishery (Wayte et al., 2004). A scientific monitoring program in 2001 recorded 437kg in the bycatch of the SETF (all of which was discarded), and 270kg was recorded in fishers’ logbook as bycatch during the 2000/01 period (AFMA, 2002a).
The amount of Rubyfish recorded annually as bycatch in the Great Australian Bight Trawl Fishery (GABTF) appears to be inconsistent over time. For example, during the period 1987 to 1998, AFMA (2001c) reported that the quantity of Rubyfish discarded in the GABTF ranged between 0kg per annum and 1.3t per annum, with an average of 191kg per annum discarded during that period. In the GABTF, bycatch sampling reported by Brown and Knuckey (2002) showed that Rubyfish were caught during the sampling periods in 2001 and 2002, and all of those caught were discarded. During that period, Plagiogeneion macrolepis was observed in 18 of the 209 trawl shots; the average quantity discarded was 120kg per trawl shot (Brown and Knuckey, 2002). During a pilot bycatch monitoring project in 2000-01, about 1.6 tonnes were recorded in the bycatch, 90% of which was discarded (AFMA, 2002a). It is noted that Bromhead and Bolton (2005) reported P. macrolepis to be a retained by-product in the GABTF.
Rubyfish (Plagiogeneion sp.) is a minor bycatch in some years, in the Western Deepwater Trawl Fishery in W.A. (AFMA, 2004f).  
There are museum records, reportedly this species, of specimens taken by commercial fishing in the Port Phillip Bay / Bass Strait area (Anonymous, 2002b), presumably as bycatch.

Vulnerable Characteristics of the Species

The Bigscale Rubyfish may have a relatively small geographic distribution, known mostly from outer continental shelf waters of the Great Australian Bight.
There is very little biological information for this species, but a closely related species (P. rubiginosum) is known to be long-lived (45+ years, possibly 70 years or more), slow-growing, with a delayed age at maturity (possibly greater than 7 years), and a low reproductive output (Weeber and Szabo, 2004, citing Annala et al., 2003). In New Zealand, P. rubiginosum has been ranked as an “E” species, meaning that the species is unlikely to sustain exploitation beyond a very low level, due to characteristics such as late onset of sexual maturity, few young, and/or limited habitat/range (Weeber and Szabo, 2004).
The closely related species P. rubiginosum is associated with sea mounts (Ivanin et al., 1996), and it is possible that P. macrolepis might also utilise underwater rises (where food might concentrate) in some part of its depth range. Rubyfish that are site-associated with sea mounts are reported to be vulnerable to over-fishing by trawlers (Ivanin et al., 1996; Weeber and Szabo, 2005).

Threatening Processes

The capture of Rubyfish in southern Australian trawl fisheries, without knowledge of the species composition, or of the distribution or relative abundance of stocks, can be considered a threatening process. A draft ecological assessment for the otter trawl sub-fishery of the South East Trawl Fishery (Wayte et al., 2004) excluded Rubyfish from the assessment of potential impacts of trawling, because the exact species is not specified in bycatch data. In a draft ecological impact assessment of the Great Australian Bight Trawl Fishery, Daley et al. (2006) listed P. macrolepis (“bonnetmouth”) as being at high risk of population impacts from trawling in that fishery, and “Plagiogeneion spp.” (“rubyfish”) as being of “medium risk”. The authors noted that there is uncertainty as to which species is being captured in the GABTF, which is considered to increase the risk value for P. macrolepis.
Rubyfish are part of the discarded bycatch in various trawl fisheries in southern Australia (see section above, on Fisheries Information). Although the species is not currently targeted, it might be so in future, given its edibility, coupled with the rise in targeted fishing for closely related rubyfish species (e.g. in New Zealand). Capture in trawl fisheries is likely to be the main threatening process for Rubyfish species, including P. macrolepis. In New Zealand, declines in catches of the closely related species P. rubiginosum, taken by trawling (bycatch, and more recently, targeted trawling) is considered to be a threat to populations (Weeber and Szabo, 2005). For that species, catches are increasing, despite no knowledge of population sizes or sustainability of catching this long-lived, slow-growing species with low reproductive output (Weeber and Szabo, 2005). In that country, Rubyfish are most abundant between 200m and 400+m (New Zealand Ministry of Fisheries, 2005d), and have previously been taken mainly as a by-product of mid-water trawling for Alfonsino Beryx splendens, over shallower seamounts and on the slope edge (Smith, 2001). The species is also caught as bycatch in trawl fisheries for Gemfish, Barracouta, Hoki and Jack Mackerel, and there is also a developing target trawl fishery (Weeber and Szabo, 2005). At least a third of recent annual catches were reported to be from targeted mid-water trawling fished close to the bottom (Weeber and Szabo, 2005). Rubyfish P. rubiginosum is under a quota system in New Zealand, and the N.Z. Ministry of Fisheries (2005d) reported that it is not known whether declines in trawl catch indicate localised or even regional over-fishing, or change in fishing practices. In an ecological assessment of fished species in New Zealand (the “Best Fish Guide”), P. rubiginosum was ranked as “E”, a “fish to avoid”, due to the apparent unsustainable nature of the fishing practices (Weeber and Szabo, 2005). 
There is also concern that mid-water trawls that catch Rubyfish may touch the bottom, which would adversely affect previously untrawled habitat on higher ground (New Zealand Ministry of Fisheries, 2005d).  It is noted that in New Zealand, for the related species of Rubyfish (P. rubiginosum), one study of fishing patterns showed that about 24% of targeted effort and 15% of catch occurs within 10km of a  seamount, and half the catch and effort occurs within 20km of a seamount (Clark and O’Driscoll, 2003).

Research Requirements

The taxonomic identity and stock status of all Rubyfish species in the South East Trawl Fishery and the Great Australian Bight Trawl Fishery should be determined. Fisheries stock assessments cannot be undertaken without such information. Furthermore, lack of specific information on the species taken in each of these fisheries has hindered risk assessments (e.g. Wayte et al., 2004; Daley et al., 2006).
Unlike the related species P.  rubiginosum, there is virtually no information on the biology and population dynamics of P. macrolepis. Information is required on the growth, age structure and longevity, and reproductive potential of this species in southern Australian waters.
More information is required on distribution, relative abundance and habitat requirements of Rubyfish.
Research is required to determine the potential population impacts of trawling.

Management Requirements

Further quantification over space and time of the Rubyfish bycatch in southern Australian trawl fisheries.
Where possible, introduction of measures to reduce trawl bycatch of this species.

Other Information

There has been a study of organo-metallic compounds (of arsenic, tin and selenium) in marine fish, including the Bigscale Rubyfish (Maher and Batley, 1990).