Somniosus longus 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Chondrichthyes Squaliformes Somniosidae

Scientific Name: Somniosus longus (Tanaka, 1912)
Common Name(s):
English Frog Shark
Heteroscymnus longus Tanaka, 1912
Taxonomic Source(s): Compagno, L.J.V. 1984. FAO species catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark species known to date. FAO Fisheries Synopsis No. 125, Volume 4, Part 1.
Taxonomic Notes: Somniosus longus from the Pacific Ocean has long been considered a synonym of S. rostratus from the Atlantic Ocean and Mediterranean Sea (Compagno 1984, Francis et al. 1988, Compagno 1999). A recent study (Yano et al. 2004) resurrected S. longus on the basis of several morphological and meristic characters. However their sample sizes of S. longus and S. rostratus were too small to properly define the range of variation in these characters, so their conclusion needs verification using larger sample sizes and preferably DNA analyses. Nevertheless, S. longus has been considered valid by recent authors (Compagno et al. 2005).

Assessment Information [top]

Red List Category & Criteria: Data Deficient ver 3.1
Year Published: 2009
Date Assessed: 2008-12-01
Assessor(s): Francis, M. & Tanaka, S.
Reviewer(s): Valenti, S.V., Gibson, C.G. & Fowler, S.L. (Shark Red List Authority)
This moderate sized (to at least 143 cm total length, but probably larger) and apparently rare deepwater shark is known from fewer than a dozen specimens, collected from widely dispersed localities in the Pacific Ocean. The Frogshark (Somniosus longus) has been recorded off Japan, New Zealand, and possibly the Sala Y Gómez - Nazca ridges, from as shallow as 120-150 m to as deep as 1,116 m. It has been reportedly caught by trawl, longline and crab pot. Parts of the species' known range have been subject to heavy fishing pressure in the past but no information is available on population trends and at present it cannot be assessed beyond Data Deficient.

Geographic Range [top]

Range Description:Known from only the northwest Pacific, southwest Pacific and possibly the southeast Pacific, but probably much more widespread.

Northwest Pacific: central to southern Japan (including Okinawa Island) (about ten specimens or reports (Tanaka 1912, Higashi et al. 1954, Kuroda 1956, Shimma and Shimma 1969, Yano and Kugai 1993, Tanaka 1998, Yano et al. 2004, S. Tanaka unpubl. data).

Southwest Pacific: three specimens from New Zealand (Francis et al. 1988; Yano et al. 2004). Two other unpublished records of this species from New Zealand trawl surveys are unconfirmed (the 500 kg weight of one was too large to be S. longus).

Southeast Pacific: A specimen from the Sala Y Gómez to the Nazca ridges in Chile was reported as S. rostratus but no details were given (Parin et al. 1997); the Pacific Ocean locality suggests that this specimen was S. longus, but its presence in the Southeast Pacific requires confirmation.
Countries occurrence:
Chile (Easter Is., Tarapacá); Japan (Honshu, Kyushu, Nansei-shoto, Shikoku); New Zealand
FAO Marine Fishing Areas:
Pacific – northwest; Pacific – southeast; Pacific – southwest
Additional data:
Lower depth limit (metres):1116
Upper depth limit (metres):120
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Apparently very rare.
Current Population Trend:Unknown
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:This species occurs on the upper to middle continental slope. The few known specimens have come from depths at least as shallow as 120-150 m (S. Tanaka unpub. data) to as deep as 1,116 m (Yano and Kugai 1993, A. Stewart pers. comm. 2006). Several specimens have been caught in midwater, which may explain the rarity of this species in fishery and survey catches (A. Stewart pers. comm. 2006). Maximum length likely to be 150 cm or greater. Greatest reported length was 143 cm (Francis et al. 1988), but this specimen had shrunk following preservation; furthermore few specimens have been examined. Males are probably smaller than females (males of 98-110 cm TL were mature (Yano et al. 2004, S. Tanaka unpub. data). Reproductive mode is unknown but is probably aplacental viviparity as in the closely related S. rostratus. A Japanese female of 128 cm TL was reported as "having eggs" (Shimma and Shimma 1969), and was presumably mature, as was another female of 130 cm (Yano et al. 2004). Size at birth is unknown, but may be similar to the 21-28 cm reported for S. rostratus (Compagno 1984). Litter size is also unknown, but probably low (six to nine embryos reported for S. rostratus, Compagno 1984). Nothing else is known about the biology or ecology of this species.

Threats [top]

Major Threat(s): This species been occasionally reported in catches by trawl, longline and crab pot fisheries (M. Francis pers. obs.). It may be slow growing and slow to mature, like other deepwater Squaloid sharks, making it vulnerable to population depletion in fisheries.

Conservation Actions [top]

Conservation Actions: No species-specific management or conservation efforts are currently in place. Like many deeper water species more information on biology, ecology and importance in fisheries are required to further assess status and any future conservation needs. Further surveys would benefit the collection of data on the wider range of this species. Where taken, catches require monitoring, particularly as deepwater fisheries expand worldwide.

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 management of all chondrichthyan species in the region.

Citation: Francis, M. & Tanaka, S. 2009. Somniosus longus. The IUCN Red List of Threatened Species 2009: e.T161552A5449863. . Downloaded on 23 September 2018.
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