Myliobatis hamlyni

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES RAJIFORMES MYLIOBATIDAE

Scientific Name: Myliobatis hamlyni
Species Authority: Ogilby, 1911
Common Name(s):
English Purple Eagle Ray
Taxonomic Notes: There has been confusion in the past with other tropical Myliobatis spp. which has not been clearly elucidated. Due to the lack of available material sexual and ontogenetic dimorphism has not been clearly defined in the literature.

A similar but distinct species (from M. hamlyni) exists off Western Australia, with known records from southwest of Shark Bay (26°47?S, 112°35?E) and from off Forestier Island (20°35?S, 117°46?E). This was referred to as M. hamlyni in Last and Stevens (1994) but these specimens are not conspecific with this species.

Assessment Information [top]

Red List Category & Criteria: Endangered B1ab(v); C2a(i) ver 3.1
Year Published: 2006
Date Assessed: 2006-01-31
Assessor(s): Kyne, P.M. & Last, P.R.
Reviewer(s): Compagno, L.J.V. & Fowler, S.L. (Shark Red List Authority)
Justification:
A highly distinctive, poorly recorded eagle ray known from only a handful of specimens off the eastern Australian coast. Recorded from depths of 117-330 m, this species appears unique amongst Myliobatis spp., which are generally inshore species whereas M. hamlyni is a deeper shelf and upper slope species. It also appears to be individually dispersed and not aggregating like some other Myliobatis spp. The biology of the species is completely unknown, but it is likely to share life history characteristics with other myliobatids including relatively low fecundity. Demersal trawl fisheries operate off southern Queensland and New South Wales (NSW) where the species has been recorded. Fishing pressure is high across most of the NSW outer shelf and upper slope and myliobatid rays are highly susceptible to trawl gear. In contrast, fishing pressure in the area where the Coral Sea specimen was taken is low, but this area has been reasonably surveyed and only the single specimen has been recorded. In fact, despite extensive survey work and consistent fishing activities along the east coast of Australia this species is rarely encountered. Subsequently, it appears to be an extremely rare species and as a precautionary measure (even though comprehensive population data do not exist) the species is assessed as Endangered given its inferred very low population size, fragmented distribution, limited available habitat (habitat at depth range is not broad) and ongoing fishing pressure in the southern part of its range where most specimens have been recorded.

Geographic Range [top]

Range Description:Restricted to eastern Australia. References to the species off Western Australia represent a separate species. Available habitat may be small, as its presently known area of occurrence on the outer shelf and upper slope is not a broad area.
Countries:
Native:
Australia (Queensland)
FAO Marine Fishing Areas:
Native:
Pacific – southwest; Pacific – western central
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population: Known from only a handful of specimens (15 individuals). Population sizes unknown but this species appears to be extremely rare. If it was more common it would certainly have been taken more regularly as much of its area or occurrence is heavily fished. Given the high levels of fishing on the NSW outer shelf and upper slope and off southern Queensland it is possible that this species was affected early on by fishing activities and now we are seeing only a depleted population. This is however, speculation but in any instance this is a naturally rare species. Of 13 specimens taken by the NSW Fisheries research vessel Kapala, nine were collected at the beginning of surveying (1976 to 79) while four were collected in the later years of surveying (up until 1997) (K. Graham pers. comm).

Myliobatis australis (and other congeners) are aggregating species, where multiple individuals are taken in single trawls. This is not the case with M. hamlyni, so it appears that it is individually dispersed and not an aggregating species.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Benthopelagic on the outer continental shelf and upper slope, recorded from depths of 117 to 330 m (museum records and K. Graham, pers. comm.). Attains at least 48 cm DW (Last and Stevens 1994). Swains Reef specimen is 44 cm DW and was taken at a depth of 210 to 220 m (Kyne et al. 2005). Nothing known of its biology, however, it is suspected to have low fecundity as with other myliobatids, for example Aetobatus narinari and Aetomylaeus nichofii, which bear litters of up to four (Last and Stevens 1994, Compagno and Last 1999).

Life history parameters
Age at maturity (years): Unknown.
Size at maturity (total length cm): Unknown.
Longevity (years): Unknown.
Maximum size (disc width): At least 48 cm DW.
Size at birth (cm): Unknown.
Average reproductive age (years): Unknown.
Gestation time (months): Unknown.
Reproductive periodicity: Unknown.
Average annual fecundity or litter size: Unknown.
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
Systems: Marine

Threats [top]

Major Threat(s): Appears to be an extremely rare species. Area off Cape Moreton where holotype found receives relatively significant levels of trawling for eastern king prawn by the Queensland East Coast Trawl Fishery (ECTF). Second Queensland specimen (Swains Reef, Coral Sea) collected from champagne lobster trawl bycatch. This area is subject to only very low fishing pressure. Area of occurrence off NSW is subject to heavy trawling activity and has been for a considerable number of years.

Despite many decades of survey work along the east coast of Australia, M. hamlyni has rarely been observed. This suggests a low population size and that the species is naturally rare or that it is somewhat avoiding fishing gear. Given experience from inshore congeneric species, Myliobatis species are susceptible to trawling and so it can be inferred that the first option is likely.

Conservation Actions [top]

Conservation Actions: Any captures of this rare species need to be documented. In the first instance State fisheries authorities and fishers need to be made aware of this species and its precarious situation. Education for safe release of the species after recording of basic information (location, depth, size, sex, maturity) is a priority.

The use of Turtle Exclusion Devices in the Queensland ECTF may assist in limiting catches in that part of the species? range.

The effective implementation of the Australian National Plan of Action for the Conservation and Management of Sharks (Shark Advisory Group and Lack 2004) (under the FAO International Plan of Action for the Conservation and Management of Sharks: IPOA?Sharks) will help to facilitate the conservation and sustainable management of all chondrichthyan species in Australia.

Bibliography [top]

Compagno, L.J.V. and Last, P.R. 1999. Myliobatidae. Eagle rays. In: K.E. Carpenter and V.H. Niem (eds) FAO Species Identification Guide for Fishery Purposes. The Living Marine Resources of the Western Central Pacific. Volume 3. Batoid Fishes, Chimaeras and Bony Fishes Part 1 (Elopidae to Linophrynidae). pp. 1511-1519. Food and Agriculture Organization of the United Nations, Rome.

IUCN. 2006. 2006 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 04 May 2006.

IUCN SSC Shark Specialist Group. Specialist Group website. Available at: http://www.iucnssg.org/.

Kyne, P.M., Johnson, J.W., Courtney, A.J. and Bennett, M.B. 2005. New biogeographical information on Queensland chondrichthyans. Memoirs of the Queensland Museum 50(2):321–327.

Last, P.R. and Stevens, J.D. 1994. Sharks and Rays of Australia. CSIRO, Australia.

Shark Advisory Group and Lack, M. 2004. National Plan of Action for the Conservation and Management of Sharks (Shark-plan). Australian Government Department of Agriculture, Fisheries and Forestry, Canberra.


Citation: Kyne, P.M. & Last, P.R. 2006. Myliobatis hamlyni. In: The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 01 October 2014.
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