|Scientific Name:||Trygonoptera imitata Yearsley, Last & Gomon, 2008|
Trygonoptera sp. [Last & Stevens, 1994] ssp. B
|Taxonomic Notes:||Related to, but distinct from, Trygonoptera mucosa.
Local synonymy = Urolophus testaceus (Scott et al. 1980) (misidentification).
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Assessor(s):||Last, P.R., Marshall, L.J. & Trinnie, F.I.|
|Reviewer(s):||Kyne, P.M., Fowler, S.L. & Compagno, L.J.V. (Shark Red List Authority)|
An undescribed species endemic to southeastern Australia, with its primary distribution off Victoria. Common in Port Phillip Bay and Western Port Bay but patchy in more exposed areas throughout its range. Litter size ranges from one to five, but little is currently known of its biology. Caught frequently as bycatch in inshore Danish seine and trawl fisheries but typically discarded. The eastern extent of the species' range historically has been, and presently is, intensively fished. As it is usually caught in shallow water in small catches it is relatively robust after discard, however in some locations where heavy trawl gear is used and catches are more substantial, mechanical damage can be problematic. A further concern is the high rate of abortion amongst trawl caught urolophids. As the species is patchily distributed, its true area of occupancy is uncertain. Partial protection is offered in the inshore extremities of embayments and in small marine reserves where commercial fishing activities are not permitted. However, a steady decline has been reported in Port Phillip Bay over a 10 year period. A lack of trawling in Bass Strait provides reasonable protection for the species across a large portion of its range. Given the species' endemism together with a reported population decline and heavy fishing pressure in some areas careful monitoring will be required in the future. The species is assessed as Near Threatened until such monitoring can show that the overall population is stable.
|Range Description:||Endemic to the Bass Strait Province and adjacent transition zones of southeastern Australia: from Beachport (SA) through Victoria to Bermagui (NSW), excluding Tasmania. Primary distribution off Victoria.|
Native:Australia (New South Wales, South Australia, Victoria)
|FAO Marine Fishing Areas:|
Indian Ocean – eastern; Pacific – southwest
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Common in Port Phillip Bay and Western Port Bay, Victoria. Patchy in more exposed areas throughout its range. Aggregates in some locations.|
|Current Population Trend:||Unknown|
|Habitat and Ecology:||Trygonoptera sp. B is an inshore demersal species of sheltered coastal areas over soft substrates but is also recorded to depths of at least 120 m (Last and Stevens 1994). Females reach a larger maximum size than males. Ageing studies using whole and sectioned vertebrae indicate that females and males reach at least 12 years and 10 years, respectively (Trinnie 2003). The species exhibits aplacental viviparity but demonstrates extreme atrophy of the left ovary, with embryos developing from both internal and external yolk sacs. Litter size varies 1 to 5, though abortion of pups can occur at all sizes of pregnant animals when handled or caught in fishing gear. Size at which 50% are mature was ~46.1 cm TL for females and ~49.1 cm TL for males. The maximum size of in utero embryos was 25.0 cm TL for males and 24.0 cm TL for females. Their diet mainly consists of polycheate worms. Life history information from Trinnie (2003) unless otherwise stated.
Life history parameters
Age at maturity (years): ~ 4.5 years at 50% maturity (female); ~ 5.0 years at 50% maturity (male).
Size at maturity (total length cm): ~ 50% mature at 46.1 cm TL based on ovarian development (female); ~ 50% mature at 49.1 cm TL based on seminal vesicle development (male).
Longevity (years): 12+ years (females); 10+ years (males) based on sectioned vertebrae ageing technique.
Maximum size (total length cm): 80 cm TL (Last and Stevens 1994).
Size at birth (cm): Largest in utero embryo 25.0 cm TL (male).
Average reproductive age (years): Unknown.
Gestation time (months): Unknown.
Reproductive periodicity: Unknown maternity pattern.
Average annual fecundity or litter size: 1 to 5 pups per litter.
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
Main threats are inshore commercial fishing, specifically beach and Danish seine and inshore trawl, particularly in the Southern and Eastern Scalefish and Shark Fishery (SESSF), which operates off southeastern Australia. Taken as bycatch and usually discarded. Reasonably robust after discard as usually caught in shallow water in small catches. Mechanical damage problematic in some locations using heavy trawl gear where catches become more substantial. Partial protection offered in the inshore extremities of embayments where fishing activities are not permitted. Rapid assessment of the species' "catch susceptability" defined from "availability", "selectivity", "encounterability" and "post-capture mortality", rates this species as low to all fishing methods in the SESSF (Walker 2004). However, both its "availability" and "encounterability" to otter trawl gear are high. Of animals caught and released, the high rate of abortion in pregnant urolophids when caught and handled is of concern.
In Port Phillip Bay, Victoria, long-term assessments of the abundance of Trygonoptera sp. B indicate that there has been a steady decline over a 10 year period (Hobday and Parry 1999). The species is possibly subject to environmental degradation in areas of main human habitation and the increasing level of recreational water use and development in shallow embayments around southern Australia may represent a threat to the suitable habitat of this species.
A substantial number of introduced marine organisms are well established in many estuaries in southern Australia (for example, Port Phillip Bay in Victoria) and these are altering the natural structure of these ecosystems. The exact impact upon benthic predators (through habitat alteration and changes to prey abundance and distribution) is not well documented.
Victoria has a recently declared system of small Marine Protected Areas and these together with commercial fishing restrictions on the inshore environment will provide the species with a level of protection. A lack of trawling in Bass Strait provides reasonable protection for the species across a large portion of its range.
Further information is required on habitat requirements given the patchy nature of the species' occurrence. The level of catches by recreational fishers also needs to be determined.
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.
|Citation:||Last, P.R., Marshall, L.J. & Trinnie, F.I. 2006. Trygonoptera imitata. The IUCN Red List of Threatened Species 2006: e.T60081A12231496.Downloaded on 21 April 2018.|