Trachystoma Petardi
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THREATENED SPECIES SCIENTIFIC COMMITTEE Established under the Environment Protection and Biodiversity Conservation Act 1999 The Minister decided that this species was not eligible for listing as threatened on 01/02/2018 Listing Advice Trachystoma petardi pinkeye mullet Taxonomy Conventionally accepted as Trachystoma petardi (Castelnau 1875). Synonym of Myxus petardi (Castelnau 1875). The species has been referred to as both Myxus petardi and Trachystoma petardi (Durand et al., 2012a, 2012b). Analysis of mitochondrial-DNA found that the species Trachystoma petardi (found only on the east coast of Australia) was clearly distinct from mullet in the genus Myxus (Durand et al., 2012a; 2012b). It is the only species in its genus (Durand et al, 2012a). Summary of assessment Conservation status Not eligible. The Committee judges that Trachystoma petardi is not eligible for listing as a threatened species under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). Species can be listed as threatened under state and territory legislation. For information on the listing status of this species under relevant state or territory legislation, see http://www.environment.gov.au/cgi-bin/sprat/public/sprat.pl Reason for conservation assessment by the Threatened Species Scientific Committee This advice follows assessment of information provided by a nomination from the public. Public consultation Notice of the proposed amendment and a consultation document was made available for public comment for 35 business days between 16 June 2017 and 4 August 2017. Any comments received that were relevant to the survival of the species were considered by the Committee as part of the assessment process. Species/sub-species information Description Pinkeye mullet are medium, stout, diadromous fish (migrate between fresh and salt water habitats) which are known to grow to a maximum length of 58.1 cm from NSW DPI Fisheries records of the species (NSW FSC, pers. comm. 2017), but another source reports the species to 80 cm (Thomson 1996). Pinkeye mullet differ from Mugil cephalus (sea mullet), which are common in the estuaries of eastern Australia, by having a smaller, more slender and pointed snout. The species is dark olive-green in colour on the back with a silvery belly (Thomson 1996; Allen et al., 2002). Fins are pale-yellow and the eye is gold to pinkish (Thomson 1996; Allen Trachystoma petardi (pinkeye mullet) Listing Advice Page 1 of 13 et al., 2002). The species exhibits sexual dimorphism in a number of physical characters such as the positioning of dorsal and anal fins along the main body axis (Grant et al., 1977). Distribution Pinkeye mullet inhabit the freshwater and estuarine reaches of eastern draining river systems from Water Park Creek (just north of the Fitzroy River mouth) in Queensland south to the Merimbula Lake catchment in southern New South Wales (Thomson 1996; Allen et al., 2002; Miles 2007; Donaldson et al., 2012; MV 2017; QM 2017; QWD 2017). While the northern limit of the pinkeye mullet distribution was thought to be the Burnett River in Queensland, a survey in 2011 detected the species in Water Park Creek, which is approximately 270 km north of the Burnett River mouth (Donaldson et al., 2012). The southern limit of the pinkeye mullet distribution was thought to be at the Clyde River at Batemans Bay, southern New South Wales (Thomson 1996; Allen et al., 2002). However, 21 individuals were collected in 1999 from Millingandi Creek, within the Merimbula Lake catchment further south in New South Wales (MV 2017). In 2006, an individual was collected by NSW Fisheries from the Brogo River which is part of the Bega River catchment to the north of Merimbula Lake but south of the Clyde River (AM 2017). It has been suggested that pinkeye mullet prefer the deep pools and gently flowing sections of rivers, often occurring in small shoals (Thomson 1996). Recent acoustic telemetry studies have suggested a catadromous life history (Miles et al., 2014; Qld DNRM 2016; NSW DPI pers. comm. 2017). The species is tolerant of water temperatures between 9 and 27°C (Allen et al., 2002). Cultural significance Mullet in the Mary River catchment are regarded as being culturally significant by Indigenous groups. One elder of the Kabi Kabi group has reported that the mullet is a totem of the area around Gympie (Bargo pers. comm., 2012). Relevant biology/ecology Pinkeye mullet have long been assumed to spawn during February (Thomson 1996; Allen et al., 2002). A recent study found that in southern Queensland, the species’ spawning season can extend into April (Qld DNRM 2016). A study on otolith chemistry proposed that the species may have an amphidromous life history (Miles et al., 2009), however recent acoustic telemetry studies indicate that pinkeye mullet migrate to the lower estuary, but remain there for only a short time before migrating back upstream, which is indicative more of a catadromous life history (Miles et al., 2014; Qld DNRM 2016; NSW DPI pers. comm. 2017). NSW DPI Fisheries acoustic telemetry data indicates that spawning occurs at the freshwater tidal limit and upper estuary (NSW FSC pers. comm. 2017). This is not inconsistent with a similar study in the Logan River catchment in southeast Queensland, which indicated a downstream spawning migration of pinkeye mullet occurred during large river flows between February and April (Qld DNRM 2016). Pinkeye mullet migrations stopped near the river mouth, where salinity conditions were relatively fresh (0–5 ppt), before quickly returning to upstream habitats (Qld DNRM 2016). It would appear further study needs to focus on the physical and water chemical requirements for spawning and spawning locations for the species within estuaries (Harding pers. comm. 2017). The species appears to reach maturity at four years with fecundity very high, with larger females producing between 1 000 000 – 3 000 000 eggs (Thomson 1996; Allen et al., 2002). Currently, Trachystoma petardi (pinkeye mullet) Listing Advice Page 2 of 13 the oldest known individual to be aged was 21 years at 39.4 cm long (G. Butler and C. Walsh unpub. data., cited in NSW FSC pers. comm. 2017) and given that the species has potential to grow considerably larger, to at least 58.1 cm, maximum life span may be somewhat higher than 21 years (NSW FSC pers. comm. 2017). In the absence of more data, using the known maximum age of 21 years generation length is estimated to be approximately 13.68 years. Pinkeye mullet feed on microscopic algae and other plant material, detritus and benthic invertebrates (Allen et al., 2002). Threats There has been little directed research into the threats impacting upon pinkeye mullet. There are indications that riparian vegetation degradation has “significantly” decreased abundances of the species (Growns et al., 1998). It is uncertain what level other threats are impacting on the species. Table 1 – Threats impacting the pinkeye mullet in approximate order of severity of risk, based on available evidence. Threat factor Threat Evidence base type and status Habitat loss, disturbance and modification Riparian known A study of fish assemblages in two reaches of the vegetation past, Hawkesbury-Nepean river system in New South Wales found degradation current that pinkeye mullet abundances were affected by riparian vegetation degradation (Growns et al., 1998). The mean suspected abundance of the species was higher near vegetated banks future than along degraded banks in both river reaches (Growns et al., 1998). Barriers to suspected Ensuring that pinkeye mullet have access to both freshwater movement past, and estuarine habitats is important (Anon 2014). While current, migration between river systems via nearshore oceanic future habitats is uncommon, there are some NSW DPI Fisheries data indicating that individuals do move between separated catchments via the sea (NSW FSC pers. comm. 2017). However, barriers to movement within river catchments are an important threatening process. An audit identified 3300 barriers to fish movement (weirs, dams, road crossings and floodgates) in coastal New South Wales catchments (Gordos et al., 2007). Following a fishway installation on Tallowa Dam on the Shoalhaven River in southern New South Wales, pinkeye mullet have been recorded in strong numbers below the dam wall indicating desire to migrate further upstream, but have not been detected above the dam wall (Walsh et al., 2014). A tagging study on the species which captured individuals downstream of Tallowa Dam and released them upstream of Trachystoma petardi (pinkeye mullet) Listing Advice Page 3 of 13 the dam, showed that 85% (17 of 20) tagged individuals successfully migrated downstream over the spillway with high rates of survivorship (Walsh et al., 2014). Only one individual made at least one return migration upstream through the fishway (Walsh et al., 2014), possibly indicating that downstream movement over the dam spillway is not adversely impacting the species here, but upstream movement may be inhibited and not adequately supported by the fishway. In the Burnett River in Queensland, the Ben Anderson Barrage is a 4 m high tidal barrier dividing fresh and estuarine waters. At the time of construction in 1974 it had a pool-and-weir fishway installed (SunWater 2010). In 1997, the fishway was upgraded to a “vertical-slot” style (SunWater 2010). However the species remains undetected in the Burnett River system, suggesting no recolonisation has occurred from populations further south (Anon 2014). In the Mary River catchment, anecdotal evidence suggests that pinkeye mullet are now locally extinct in Tinana Creek above the barrier created by Teddington Weir (Hutchison pers. comm. 2012). Anecdotal observations from the Logan River in southeast Queensland indicate that vertical slot fishways appear to be more effective for allowing passage for pinkeye mullet than lock style (fish lift) fishways (Harding pers. comm. 2017). This is consistent with results from a study in the Hawkesbury- Nepean catchment in New South Wales, whereby upstream distribution of pinkeye mullet, along with a range of other species, was dramatically improved following the retrofitting of ten weirs with vertical slot fishways (Duncan et al., 2016).