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Zearaja maugeana 

Scope: Global
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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Chondrichthyes Rajiformes Rajidae

Scientific Name: Zearaja maugeana
Species Authority: Last & Gledhill, 2007
Common Name(s):
English Maugean Skate, Port Davey Skate
Taxonomic Source(s): Eschmeyer, W.N., Fricke, R. and Van der Laan, R. (eds). 2016. Catalog of Fishes: genera, species, references. Updated 31 March 2016. Available at: http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp. (Accessed: 31 March 2016).

Assessment Information [top]

Red List Category & Criteria: Endangered B1ab(i,ii,iii,iv)+2ab(i,ii,iii,iv) ver 3.1
Year Published: 2016
Date Assessed: 2015-02-20
Assessor(s): Last, P.R., Gledhill, D.C. & Sherman, C.S.
Reviewer(s): Dulvy, N.K. & Kyne, P.M.
Facilitator/Compiler(s): Kyne, P.M., Walls, R.H.L., Simpfendorfer, C. & Chin, A.
Justification:
The Maugean Skate (Zearaja maugeana) is unique among skates in that it is restricted to brackish estuarine waters (occurring almost to freshwater). The Maugean Skate is only recorded from Macquarie and Bathurst Harbours on the west coast of Tasmania in Australia; these may represent two distinct subpopulations. The Maugean Skate is assessed as Endangered due to its small geographic range, presence in only two locations, and a continuing decline in quality of habitat. The extent of occurrence (EOO) is <1,900 km² and the area of occupancy (AOO) is <300 km². One location (Macquarie Harbour) is facing increasing human activity, which is projected to lead to a decrease in EOO, AOO and quality of habitat due to increasing pressures from fish-farming and pollution. Macquarie Harbour currently has anoxic conditions, particularly in the depth range where the eggs are found (20-50 m), and these conditions are continuing. Habitat conditions will need to improve in order for this species not to qualify for a higher threat category in the future. The second subpopulation (Bathurst Harbour) has not been verified in approximately 20 years, despite dedicated surveys, and may be locally extinct.
Previously published Red List assessments:

Geographic Range [top]

Range Description:The Maugean Skate is a temperate Australian species, confined to two large estuary systems in western Tasmania, Bathurst and Macquarie Harbours. The Maugean Skate appears to be mainly in the upper estuary to freshwater sectors of Macquarie Harbour, however, recent studies have shown that they do move quite extensively throughout the harbour (J. Lyle, pers. comm., 01/04/2015). The total available habitat is no more than 200-300 km², therefore, the species' area of occupancy (AOO) is <300 km².
Countries occurrence:
Native:
Australia (Tasmania)
FAO Marine Fishing Areas:
Native:
Indian Ocean – eastern
Additional data:
Estimated area of occupancy (AOO) - km2:200-300Continuing decline in area of occupancy (AOO):Yes
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:1900
Continuing decline in extent of occurrence (EOO):YesExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:2Continuing decline in number of locations:Yes
Extreme fluctuations in the number of locations:No
Lower depth limit (metres):5
Upper depth limit (metres):15
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:The total population size has previously been estimated at <1,000 individuals (P. Last, pers. obs.). A recent tagging study of the Macquarie Harbour subpopulation (unpublished), combined with reports of the species being commonly captured by recreational and commercial gillnetting, suggests this may be a significant underestimate (N. Barrett, pers. comm. 2015).

Concerns for the Macquarie Harbour population remain, in part due to the species primarily utilizing the shallow waters (5-15 m depths) of the harbour (Lyle et al. 2014), where it is most likely to be caught by netting. The harbour is heavily stratified, with water dramatically increasing in salinity between 3 and 10 m, depending on the time of year, whereas the waters below 15 m have low dissolved oxygen (Anon. 2014). These physical parameters likely restrict the species to a narrow depth band within the harbour. Recent reductions in water quality in the harbour between 2009 and 2014, primarily increasingly anoxic conditions below 15 m (Anon. 2014), further restrict the species to this narrow band of ~5-15 m. This time period coincides with a dramatic expansion of salmon aquaculture in the harbour. Declining water quality at depth is of greater concern for breeding success of this species. The Maugean Skate deposits egg cases in the deeper waters of the harbour (Treloar et al. 2013), and the recent reduction in quality of these waters have potential to negatively impact breeding success over coming years.

There have been no confirmed sightings of the species at the second location, Bathurst Harbour, in the past 20 years, despite dedicated survey efforts (Treloar et al. 2013). This is of great concern, especially given the increasing human impacts within Macquarie Harbour.

The two subpopulations (Bathurst Harbour and Macquarie Harbour) are separated by ocean and, to date, no individuals have been captured in the marine environment. Due to the physical segregation of these populations, the two subpopulations may be genetically distinct.
Current Population Trend:Decreasing
Additional data:
Extreme fluctuations:No
No. of subpopulations:2Continuing decline in subpopulations:No
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:No

Habitat and Ecology [top]

Habitat and Ecology:The Maugean Skate is a medium-sized skate (to ~84 cm total length (TL)) and is unique among skates in that it is found only in brackish water (Last and Stevens 2009). The estuarine systems in which it lives are high in tannin content, with low light penetration and silty bottoms, resulting in the encroachment of several deepwater invertebrate species into relatively shallow depths. The morphology of this skate resembles that of Dipturus species found on the continental slope (Last and Stevens 1994). Males mature at ~65 cm TL (Last and Stevens 2009) but little else is known of the biological or ecological requirements of this species. Specimens have been caught in a broad range of brackish salinities to almost freshwater (P. Last, pers. obs.). Eggs are deposited at depths of 20-50 m (N. Barrett, pers. comm. 2015).
Systems:Marine
Continuing decline in area, extent and/or quality of habitat:Yes

Use and Trade [top]

Use and Trade: This species is protected under Australian law and is not utilized or traded.

Threats [top]

Major Threat(s): Both subpopulations of this skate are in scenic and important recreational areas facing increasing pressure from ecotourism (Edgar et al. 2010). They are also regularly caught by recreational and commercial gillnetting in Macquarie Harbour (Lyle et al. 2014).

Macquarie Harbour is an estuary heavily polluted by prolonged mining operations. A recently rapid expansion of fish-farming has also coincided with considerable reduction in water quality, including extreme hypoxic conditions beyond 15 m depth (Anon. 2014), the habitat used by the skate for egg deposition. Persistent water quality issues could drastically reduce breeding success over coming years and could be catastrophic for this population. It is estimated that due to the hypoxic conditions at least one full year class has been lost, with others expected (N. Barrett, pers. comm. 2015).

The isolation of Bathurst Harbour in the Tasmanian Wilderness World Heritage Area affords some habitat protection for this species. Unfortunately, there are rising anthropogenic stressors including boating, fishing, dive tourism, introduced species, global climate change, nutrient enrichment, and onshore development (Edgar et al. 2010). Of great concern is the lack of sightings of this species in Bathurst Harbour in the last twenty years, despite dedicated survey efforts, indicating that the population may be locally extinct there (Treloar et al. 2013).

Conservation Actions [top]

Conservation Actions: The species is listed as Endangered on the Commonwealth Environment Protection and Biodiversity Conservation Act and the Tasmania Threatened Species Protection Act, and is therefore protected by Australian and Tasmanian law. Bathurst Harbour is part of the Tasmanian Wilderness World Heritage Area, which provides some protection for Maugean Skate habitat, however, dedicated scientific surveys have failed to find the species there in the past 20 years. There are ongoing research projects being conducted by the University of Tasmania's Institute for Marine and Antarctic Studies (IMAS) in Macquarie Harbour aiming to better identify the preferred habitat and distribution of this skate within the estuary (J. Lyle, pers. comms., 01/04/2015). Urgent study is needed into egg deposition and likely impacts of rapidly declining water quality on egg viability and juvenile survival.

Citation: Last, P.R., Gledhill, D.C. & Sherman, C.S. 2016. Zearaja maugeana. The IUCN Red List of Threatened Species 2016: e.T64442A68650404. . Downloaded on 24 August 2016.
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