|Scientific Name:||Hydrolagus lemures|
|Species Authority:||(Whitley, 1939)|
|Taxonomic Notes:||Hydrolagus lemurs is very similar to Hydrolagus ogilbyi, in fact the two species are nearly indistinguishable. Juveniles and subadults are particularly difficult to distinguish and H. lemurs is likely often misidentified as H. ogilbyi. This species may exhibit color variation throughout its range, making it even more challenging to distinguish this species from the very similar H. ogilbyi. It is possible H. lemurs is in fact a synonym of H. ogilbyi; however, according to Last and Stevens (1994) H. lemurs appears to be more widespread and occurring in deeper water than H. ogilbyi. Research on taxonomic distinction between these two species is ongoing and until conclusive evidence is presented to the contrary, H. lemurs and H. ogilbyi are valid as separate species.|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Dagit, D.D. & Kyne, P.M.|
|Reviewer(s):||Fowler, S.L. & Compagno, L.J.V. (Shark Red List Authority)|
Hydrolagus lemurs is a small-bodied holocephalan species, very similar and sometimes nearly indistinguishable from H. ogilbyi, with which its range overlaps. It is endemic to Australia and widespread throughout its range, which is nearly continuous from North Queensland to Western Australia. It is also reported off Darwin, but not known from Bass Strait or Tasmania. A shelf and upper slope dweller, this species is reported from depths of 190 to 825 m but is most common at 200 to 510 m. The species is apparently relatively abundant in parts of its range, but in the first instance confirmation of taxonomic distinction between H. lemurs and H. ogilbyi is needed to better define distribution. Fishery-independent surveys on the NSW upper slope have documented significant declines (of 96.4% overall and >99% in some regions) in the catch rate of "silver ghostsharks" (documented as mostly H. ogilbyi, these surveys were likely to have taken some H. lemurs, however the bulk of catches appeared to be H. ogilbyi) over a 20 year period as a result of intensive trawl fishing on the narrow NSW continental slope. This area represents only a proportion of the range of this species and while other trawl fisheries operate in the range of H. lemurs, effort is low in the western part of its range and in the Great Australian Bight while there is no fishing in the vast majority of the species' range off Queensland. Therefore, the species is assessed as Least Concern, although catch levels should continue to be monitored as localised depletions are possible where trawl fishing pressure is high in southeastern Australia.
|Range Description:||Widespread on the Australian continental slope, with nearly continuous distribution from Queensland, New South Wales, Victoria, South Australia and Western Australia, but excluding Tasmania and Bass Strait. Not known from off the northern coasts of Australia, but reported from off Darwin.|
Native:Australia (New South Wales, Queensland, Victoria, Western Australia)
|FAO Marine Fishing Areas:||
Indian Ocean – eastern; Pacific – southwest; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Apparently relatively common throughout its range. Nothing is known of population size or structure, but this species is likely represented by a single population from Australia.|
|Habitat and Ecology:||
Continental shelf and upper slope dweller, occurring at or near the bottom. Reported from depths of 190 to 825 m, but apparently most common at 200_510 m. Little else is known of biology and habits, although probably shares similar biology and life history traits with other smaller-bodied shelf and upper slope dwellers such as Hydrolagus colliei.
Life history parameters
Age at maturity (years): Unknown.
Size at maturity (total/body length): Female: ~55 to 60 cm TL (~30 to 35 cm BDL); Male: ~50 cm TL (~30 to 35 cm BDL).
Longevity (years): Unknown.
Maximum size (total/body length): ~90 to 100 cm TL (~40 cm BDL) with filament; 58 cm TL without filament.
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.
A number of demersal fisheries operate in this species' area of occurrence and this species is likely taken as bycatch in these fisheries, however little information is available on bycatch levels. Within the Southern and Eastern Scalefish and Shark Fishery (SESSF), Hydrolagus lemurs is considered to have a high catch susceptibility to otter trawl, a medium catch susceptibility to auto hook gear and a low susceptibility to shark gillnet, shark hook and trap/pot gear (Walker 2004) (catch susceptibility is defined as "availability" x "encounterability" x "selectivity" x "post-capture mortality"; Walker 2004). Both the Western Deepwater Trawl Fishery (WDWTF) and the Great Australian Bight Trawl Sector (GABTS) of the SESSF have relatively low effort. The WDWTF is managed by limited entry with only 11 fishing permits issued on a five yearly basis. Bycatch "is composed of small volumes of a diverse range of species" (AFMA 2003) and it is likely that H. lemurs forms a negligible bycatch in this fishery. The GABTS operates over a large geographical area and is also managed by limited entry with 10 fishing concessions and while overall effort is low, there is a trend of increasing effort (Lynch and Garvey 2003). Holocephalans are not reported in the top 40 species/species groups recorded in the fishery (Lynch and Garvey 2003), but are likely to form negligible bycatch. Observer and Fisheries-Independent surveys have shown the species to be a very rare discarded bycatch in the Queensland East Coast Trawl Fishery (deepwater component of the eastern king prawn sector). This fishery does not operate beyond 200 m depth and so is at the upper limit of the depth range of H. lemurs (P. Kyne, unpublished data). There is very little fishing pressure over the species' geographical and bathymetrical depth range off Queensland.
Significant declines in the catch of "silver ghostsharks" from 1976-77 to 1996-97 from the upper slope trawl fishery off NSW have been documented by fishery-independent surveys (Graham et al. 2001). Graham et al. (2001) stated that "silver ghostsharks" were identified as H. ogilbyi. Sampling for this study occurred in 200?605 m and so it is likely both H. ogilbyi (which occurs at 40-524 m) and H. lemurs (which occurs at 190-825 m) were captured, however the bulk of catches did appear to be H. ogilbyi (K. Graham pers. comm.). The aggregated data does not allow species-specific declines to be elucidated, however, overall "silver ghostshark" declined from a mean catch rate of 8.3 kg/hour to 0.3 kg/hour in the twenty year period, equating to a decline of 96.4%. Reductions are even more striking when data are broken down into region, with the mean catch rate off Eden-Gabo Island (northern NSW/southern Victoria) declining from 17.4 kg/hour in 1976-77 to <0.1 kg/hour in 1996-97, equating to a decline of greater than 99.4%. Even if these catches are mostly H. ogilbyi, these data do indicate the vulnerability of Hydrolagus species, including H. lemurs, to trawl operations, showing that large declines from heavy fishing pressure are possible. The relatively narrow continental slope off northern/central NSW, including most of the depth range of H. lemurs, is intensively fished and there would be continued pressure on Hydrolagus species in this area.
A continued effort should be made to gain bycatch information in fisheries within the range of this species.
None are known. More data are required to determine levels of bycatch of this species. Additional data on life history and biology are also needed. Reevaluation of this species is recommended pending outcome of ongoing taxonomic study.
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:||Dagit, D.D. & Kyne, P.M. 2006. Hydrolagus lemures. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 05 July 2015.|
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