|Scientific Name:||Hemitrygon akajei (Müller & Henle, 1841)|
Dasyatis akajei (Müller & Henle, 1841)
Dasyatis gigantea (Lindberg, 1930)
Trygon akajei Müller & Henle, 1841
|Taxonomic Source(s):||Last, P.R., Naylor, G.J.P. and Manjaji-Matsumoto, B.M. 2016. A revised classification of the family Dasyatidae (Chondrichthyes: Myliobatiformes) based on new morphological and molecular insights. Zootaxa 4139(3): 345-368. http://doi.org/10.11646/zootaxa.4139.3.2.|
|Taxonomic Notes:||The genus Hemitrygon formerly was a junior synonym of Dasyatis; it was resurrected by Last et al. (2016) in their revision of the family Dasyatidae.
Further taxonomic research is required in order to determine the relationship of nominal Western Central Pacific (including the Philippines; Compagno et al. 2005) forms to the Northwest Pacific D. akajei (P.R. Last and L.J.V. Compagno, pers. comm).
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Assessor(s):||Huveneers, C. & Ishihara, H.|
|Reviewer(s):||Kyne, P.M. & Fowler, S.L.|
This is an amended version of the 2006 assessment to accommodate the recent change in genus name from Dasyatis to Hemitrygon.
A probably Northwest Pacific endemic known from Japan, Taiwan and China (other forms from the Western Central Pacific need to be critically compared). Hemitrygon akajei plays an important role as an apex predator in the demersal food network of coastal regions across its range. However, very little is known of its life-history traits. The species is subject to high fishing effort and caught in commercial quantities in the coastal waters of Japan and even in brackish waters. It is taken as bycatch in the bottom trawl fishery, gillnet, set net and hook and line fishery targeting demersal bottom fishes such as flounders. This bycatch is utilized and landings are reported to be declining. Fecundity is very low with one pup per litter reported. Due to the current high level of bycatch and strong fishing pressure in its area of occurrence, which will have depleted the population, this species should be classified as Near Threatened. Data need to be collected in order to accurately assess the population status, which may show that the species falls into a higher threat category.
|Previously published Red List assessments:|
|Range Description:||Probable Northwest Pacific endemic. In Japan, commonly distributed in shallow coastal waters and bays from Hokkaido to Okinawa (Taniuchi and Shimizu 1993).|
Native:China; Japan; Taiwan, Province of China
|FAO Marine Fishing Areas:|
Present - origin uncertain:
Pacific – western central; Pacific – northwest
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Declines have reported to have occurred where the species is fished.|
|Current Population Trend:||Unknown|
|Habitat and Ecology:||Hemitrygon akajei plays an important role as an apex predator in the demersal food network of coastal areas (Taniuchi and Shimizu 1993). However, very little is known of its life-history traits. It is found in coastal areas and on the continental shelf.|
Males attain maturity at ~35 cm disc width (DW) and almost all the males become mature at >40 cm DW. Females attain first maturity between 50 and 55 cm DW and most females >60 cm DW may be mature (Taniuchi and Shimizu 1993).
Hemitrygon akajei feeds predominantly on crustaceans and osteichthyes. Annelida was also reported in their stomachs whilst Bivalvia and Cephalopoda were seldom found (Taniuchi and Shimizu 1993).
Dasyatidae are mostly demersal in inshore waters, although several species range offshore and a few large species occur along the upper continental slopes as deep as 480 m. Several species are euryhaline while some others are confined to freshwater. All are aplacental viviparous. Litter varies between two to six young with gestation periods, which may take as long as 12 months (Last and Compagno 1999). Hemitrygon akajei appears to have a lower fecundity with gravid females bearing one pup/litter (H. Ishihara, unpublished data).
Life history parameters
Age at maturity (years): Unknown.
Size at maturity (disc width): 50-55 cm DW (Taniuchi and Shimizu 1993) (female); 35-40 cm DW (Taniuchi and Shimizu 1993) (male).
Longevity (years): Unknown.
Maximum size (disc width): At least 66 cm DW (Last and Compagno 1999).
Size at birth (cm): Unknown.
Average reproductive age (years): Unknown.
Gestation time (months): Unknown.
Reproductive periodicity: Unknown.
Average annual fecundity or litter size: 1 pup/litter (H. Ishihara, unpublished data).
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
|Major Threat(s):||Hemitrygon akajei is caught in commercial quantities in coastal and even brackish waters. It is taken as bycatch in the bottom trawl fishery, gillnet, set net and hook and line fishery targeting demersal bottom fishes such as flounders, and this bycatch is utilized. Landings are reported to be declining. Population is therefore strongly affected by present level of fishing.|
Data need to be collected in order to accurately assess the population status and to document catch levels.
The development and implementation of management plans (national and/or regional e.g., under the FAO International Plan of Action for the Conservation and Management of Sharks: IPOA-Sharks) are required to facilitate the conservation and sustainable management of all chondrichthyan species in the region. See Anon. (2004) for an update of progress made by nations in the range of H. akajei.
|Citation:||Huveneers, C. & Ishihara, H. 2016. Hemitrygon akajei. The IUCN Red List of Threatened Species 2016: e.T60148A104113240.Downloaded on 19 October 2017.|
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