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Somniosus rostratus

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES SQUALIFORMES SOMNIOSIDAE

Scientific Name: Somniosus rostratus
Species Authority: (Risso, 1827)
Common Name(s):
English Little Sleeper Shark
Synonym(s):
Scymnus rostratus Risso, 1827
Taxonomic Notes: Valid species but often confused with other Somniosus species. Yano et al. (2004) resurrected Somnious longus Tanaka, 1912, from the western Pacific; as a result S. rostratus is now restricted to the northeast Atlantic and the Mediterranean Sea. Pacific records of S. rostratus are a result of misidentification (Yano et al. 2004). Somniosus bauchotae (Quéro 1976) was described from a northeast Atlantic specimen but is now considered to be a junior synonym of S. rostratus.

Assessment Information [top]

Red List Category & Criteria: Data Deficient ver 3.1
Year Published: 2009
Date Assessed: 2008-12-01
Assessor(s): Séret, B., Guallart, J., Vacchi, M., Mancusi, C. & McCormack, C.
Reviewer(s): Cavanagh, R.D., Valenti, S.V., Compagno, L.J.V. & Fowler, S.L. (Shark Red List Authority)
Justification:
The Little Sleeper Shark (Somniosus rostratus) is a rare, moderate sized (to 143 cm TL) deepwater shark known from a few records on the outer continental shelf and upper slope in the northeast Atlantic and western Mediterranean Sea, at depths of 180–2,220 m. Also recorded from Israel in the eastern Mediterranean and Cuba in the northwest Atlantic. Occasionally taken as bycatch in deep bottom trawl and bottom longlines fisheries and sometimes landed under the same commercial category as the other sleeper sharks although usually discarded. Very little is known of the popualtion of this species. The scarcity of captures could be related to a natural low-density of the population. It is also possible that the species' bathymetric distribution extends deeper than the depths currently surveyed. The species may occur throughout the deeper reaches of the water column, beyond the depth of many demersal fisheries. The ban on bottom trawling below depths of 1,000 m in the Mediterranean Sea probably affords the species some protection in this region, although it is still vulnerable to capture in the upper half of its depth range there, and by intense deepsea fisheries operating in areas of the northeast Atlantic. The relatively small range of this species, compared to most other sleeper sharks, and rarity in an area which has been subject to very heavy fishing pressure for a long period are cause for concern. Furthermore the species may have limiting life-history characteristics, like other deepwater squaloids, and therefore may not be sufficiently fecund to withstand heavy fishing pressure. Given these concerns and in the absence of any information on trends, this species is assessed as Data Deficient at present. Bycatch levels should be quantified and monitored to provide information to make a full evaluation of this species status.

Geographic Range [top]

Range Description: The distribution of this species is poorly defined because there are few definite records anywhere (L.J.V. Compagno pers. comm. 2007).

Northwest Atlantic:
There are two records of this species from the northwest coast of Cuba (L.J.V. Compagno pers. comm. 2007).

Northeast Atlantic:
Madeira, Canary Islands, Portugal, France and in the Mediterranean Sea from Catalan Sea, Spain, France; Ligurian Sea off northern Italy; Sicily; Israel (L.J.V. Compagno pers. comm. 2007).
Countries:
Native:
Cuba; France; Israel; Italy (Italy (mainland), Sicilia); Portugal (Madeira, Portugal (mainland)); Spain (Canary Is., Spain (mainland))
FAO Marine Fishing Areas:
Native:
Atlantic – northeast; Atlantic – western central; Mediterranean and Black Sea
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: An apparently rare, poorly known species (Compagno in prep, L.J.V. Compagno pers. comm. 2007). No information exists on the relationship between the northeast Atlantic and Mediterranean populations. Mostly known from single records and a few specimens in the scientific literature (L.J.V. Compagno pers. comm. 2007). This species has not been recorded during the MEDITS (at depths of 10–800 m) scientific trawl surveys conducted throughout the Mediterranean Sea.
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: Bathydemersal deep water species reported at depths of 180–2,220 m (Barrull and Mate 2002, Compagno et al. 2005). Found on on or near the sea bottom, over sandy mud substrate on the outer continental shelves and upper slopes (Compagno in prep.). Serena (20005) reports that it appears to prefer bathyal grounds deeper than 1,000 m in the western Mediterranean basin.

Attains a maximum size of about 140 cm total length (TL); size at birth is between 21 and 28 cm TL; males are mature at 71 cm TL and females at 80 cm (Compagno et al. 2005). Reproduction is aplacental viviparous, with 8–17 pups per litter (Tortonese 1956, Barrull and Mate 2002, Compagno in prep.). Reproductive age, periodicity, gestation time, rate of population increase and natural mortality are unknown.

This species feeds on mesobathyal cephalopods such as Histiotheuthis spp. and Todarodes sagittatus (J. Guallart pers. obs. 2007). Although specimens of this species are usually captured with bottom fishing gears, the finding of these highly-mobile cephalopods in the stomach contents may be interpreted as an indicator that S. rostratus moves throughout the deeper reaches of the water column, a propensity that may partially explain the scarcity of captures in deep demersal fisheries.
Systems: Marine

Threats [top]

Major Threat(s): Occasionally taken as by-catch on longlines and with bottom trawls in the eastern Atlantic (Compagno in prep.), but often recorded under the general category “sleeper sharks" or simply “sharks”. In the Mediterranean coast of Spain it is regularly discarded at sea and not landed although post-discard survival is likely very low (J. Guallart pers. obs. 2007). No species-specific catch estimates are available.

Intense deepwater fisheries operate in areas of the northeast Atlantic. For example, a target fishery for deep-water squaloid sharks operated off Portugal at depths of 800–1,400 m since 1992 (DELASS 2003). Catches decreased rapidly and, by 1996, only one longliner was engaged in it at full time. Most of the catch consists of Centrophorus granulosus, though other deep-water species such C. squamosus and C. coelolepis are also caught in small quantities (DELASS 2003).

This species is also a bycatch of the general demersal and black scabbardfish fisheries in the Azores, although species-specific data are not available (DELASS 2003). A recent ban on bottom trawling below 1,000 m in the Mediterranean Sea (see Conservation Measures) may afford this species some protection, particularly if it is mainly distributed at greater depths. However, the species is still vulnerable to capture in fisheries in the upper half of its bathymetric range.

This species may be slow growing and slow to mature, like other deepwater Squaloid sharks, making it vulnerable to population depletion in fisheries. The relatively small range of this species, compared to most other sleeper sharks, and rarity in an area, which has been subject to very heavy fishing pressure for a long period, is of concern (L.J.V. Compagno pers. comm. 2007).

Conservation Actions [top]

Conservation Actions: No species-specific management or conservation measures are currently in place.

The General Fisheries Commission for the Mediterranean (GFCM) banned bottom trawling below depths of 1,000 m in the Mediterranean in February 2005 and this came into force in September 2005. The measure was adopted by consensus by all members of the GFCM, which include: Albania, Algeria, Bulgaria, Croatia, Cyprus, EC, Egypt, France, Greece, Israel, Italy, Japan, Lebanon, Libya, Malta, Morocco, Romania, Slovenia, Serbia and Montenegro, Spain, Syria, Tunisia, and Turkey.

Like many deeper water species more information on biology, ecology and population trends are required to fully assess the status of this species and any future conservation needs.

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: Séret, B., Guallart, J., Vacchi, M., Mancusi, C. & McCormack, C. 2009. Somniosus rostratus. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 20 September 2014.
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