|Scientific Name:||Pseudotriakis microdon|
|Species Authority:||de Brito Capello, 1868|
Pseudotriakis acrales Jordan & Snyder, 1904
|Taxonomic Notes:||Yano and Musick (1992) showed that morphometric characters used to separate Pacific Pseudotriakis acrales Jordan & Snyder, 1904 from Atlantic P. microdon Capello, 1868 did not differ significantly, and these authors confirmed P. acrales as a junior synonm of P. microdon. Pseudotriakis is thus a mono-specific genus.|
|Red List Category & Criteria:||Data Deficient ver 3.1|
|Assessor(s):||Kyne, P.M., Kazunari Yano & White, W.T. (SSG Deepsea Chondrichthyan Workshop, November 2003)|
|Reviewer(s):||Cavanagh, R.D. & Fowler, S.L. (Shark Red List Authority)|
A wide-ranging but sporadically captured, large, deepwater shark with most records from the Northern Hemisphere (it appears rarer in the Southern Hemisphere). May be cosmopolitan, but as yet has not been recorded from the South Atlantic or Eastern Pacific. Primarily inhabits the continental and insular slopes at depths of 200 to 1,890 m, but also occasionally occurs on the continental shelf. Pseudotriakis microdon reaches a maximum size of 296 cm total length (TL). This species displays a modified form of oophagy, the first confirmed oophagous species outside the Lamniformes. Fecundity is low (typically two embryos per litter), and this, combined with an estimated long gestation period and presumed slow growth rate may place populations at risk of localised depletion if the species becomes more regularly caught. At present the species is of no interest to fisheries but is taken sporadically as bycatch in deepwater longline and trawl fisheries. Deepwater fisheries are generally expanding globally, and given the biology of this species, bycatch of this rare fish may be of concern for any localised populations in areas where fishing may be concentrated, such as deepwater reefs or seamounts. However, since there is no available information on population trends, and because of the overall lack on information concerning biology (particularly age, growth rates and gestation) the species is assessed as Data Deficient.
|Range Description:||Extent of occurrence uncertain as records are sporadic. Records from the Southern Hemisphere are scarce and the species most likely occurs at more locations than presently recorded.
Northwest Atlantic (Canada (Gilhen and Coad 1999), New York to New Jersey (Compagno (in prep. b)); Northeast and Eastern Central Atlantic (Atlantic Slope off Iceland, France, Portugal, Madeira, Azores, Canary Islands, Senegal and Cape Verde Is.); Western Indian Ocean (Aldabra Island group) and locations in the Southwest Indian (Alastair Graham, pers. comm.); Northwest Pacific (Japan (southern Honshu and Okinawa) and Taiwan); Eastern Indian Ocean (Australia (Cape Leeuwin, Western Australia) (Allen and Cowan 1995)); Western Central Pacific (Coral Sea, off Mackay, Queensland (Johnson and Kyne in press)); Southwest Pacific (New Zealand (Three Kings Ridge and Hikurangi Trough, east of Mahia Peninsula) (Stewart and Clark 1988, Yano 1992, Yano and Musick 1992, Stewart 2000)); and Central Pacific (Hawaiian Islands).
Native:Australia (Queensland, Western Australia); Canada; Cape Verde; France; Iceland; Japan (Honshu); New Zealand; Portugal (Azores, Madeira); Senegal; Seychelles (Aldabra); Spain (Canary Is.); Taiwan, Province of China; United States (Hawaiian Is., New Jersey, New York)
|FAO Marine Fishing Areas:||
Atlantic – eastern central; Atlantic – northeast; Atlantic – northwest; Indian Ocean – western; Pacific – eastern central; Pacific – southwest; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Seemingly uncommon or rare wherever it occurs in its deepwater habitat.|
|Habitat and Ecology:||
A large deepwater benthic shark recorded from depths of 200 to 1,890 m on the continental and insular slopes, including around seamounts, troughs and deepwater reefs. This species is occasionally recorded on the continental shelves including in shallow water. This may be abnormal behaviour or where submarine canyons extend close to shore (Compagno in prep. b). The anatomy of this shark (large body cavity, soft fins, musculature and skin) suggests an inactive and sluggish lifestyle (Compagno in prep. b).
Maximum size 296 cm total length (TL) (female), 295 cm TL (male) (Yano 1992); mature individuals 200 to 269 cm TL (males), 212 to 295 cm TL (females) (Compagno in prep. b). Taniuchi et al. (1984) observed near-term embryos of 112 and 113 cm TL, and Yano (1992) at 116 to 120 cm TL. A 156 cm TL immature female had an umbilical scar (Yano 1992). Size at birth 120 to 150 cm TL (Yano, unpubl. data).
Forster et al. (1970) suggested that P. microdon was oophagous based on the large number of ova (estimated at 20,000) of 9 mm mean diameter observed in the ovary of a 280 cm TL female. Taniuchi et al. (1984) reported mid-term and near-term embryos with stomachs full of yolk. Yano (1992) confirmed the existence of oophagy in this species showing that embryos ingest and utilise yolk material from ovulated ova. Yolk material was observed in the uteri of gravid females and the stomachs of two embryos contained yolk material and egg capsules. Yano (1992) reported that the reproductive mode in this species is a modified form of oophagy in which embryos appear to transfer yolk from ingested egg fragments to their external yolk sac, replenishing external yolk sac reserves and using them in the last stages of gestation. Reported litter size of this species is two (Taniuchi et al. 1984, Yano 1992, Stewart 2000) but may be four according to Compagno (in prep. b). Gestation period is unknown, but is presumed to be > 1 year and possibly more than two or three years (Yano unpublished data).
Yano and Musick (1992) found that this species feeds predominantly on teleost fishes (52.8% frequency of occurrence in North Pacific specimens, 80% in South Pacific specimens). Other prey items included etmopterid sharks, squid and octopi. Its very large mouth may allow prey items of considerable size to be ingested (Compagno in prep. b). False catsharks have been photographed in the Indian Ocean (feeding on teleosts used as bait on the camera) and from a submersible off the Hawaiian Islands (feeding on heterocarpid prawns at the entrance to a trap) (Compagno in prep. b).
Localised populations of this large shark could be rapidly depleted if it began to be captured more regularly, however, at present it is of little interest to fisheries and is only taken as sporadic bycatch.
Most specimens of this species have been taken on deep-set longlines or in deepwater bottom trawls (Compagno in prep. b). Among the specimens reported in the literature as taken from commercial fishing operations, individuals have been captured as bycatch of trawls for Atlantic halibut Hippoglossus hippoglossus in the North Atlantic (Gilhen and Coad 1999) and orange roughy Hoplostethus atlanticus in the southern Indian (Allen and Cowan 1995), and developmental fishing surveys for bottom longline fisheries in the North Pacific (Yano 1992). The Queensland, Australia specimen was taken by exploratory deepwater dropline fishing targeting deepwater reef fishes, particularly flame and ruby snapper (Etelis spp.) and bar cod (Epinephelus spp.) (J. Johnson, pers. comm.).
Utilization not reported.
|Conservation Actions:||None in place. Deep-sea marine protected areas would be important in preserving habitat of this and other deepwater species.|
|Citation:||Kyne, P.M., Kazunari Yano & White, W.T. (SSG Deepsea Chondrichthyan Workshop, November 2003) 2004. Pseudotriakis microdon. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 03 July 2015.|