Smoothtooth blacktip shark
|Smoothtooth blacktip shark|
|Range of the smoothtooth blacktip shark|
The smoothtooth blacktip shark (Carcharhinus leiodon) is a species of requiem shark, in the family Carcharhinidae. It is known only from the type specimen caught from the Gulf of Aden, off eastern Yemen, and a handful of additional specimens caught from the Persian Gulf, off Kuwait. Reaching 1.2 m (3.9 ft) in length, this species has a stocky greenish-colored body, a short snout, and black-tipped fins. It can be distinguished from similar species by its teeth, which are narrow, erect, and smooth-edged.
Little is known of the smoothtooth blacktip shark's natural history; it likely inhabits shallow waters and feeds on small bony fishes. It is presumably viviparous like other members of its family. The International Union for Conservation of Nature (IUCN) last assessed this species as Vulnerable, when only the sole type specimen was known. Although more specimens have since been discovered, the conservation status of this species remains precarious due to heavy fishing and habitat degradation within its range.
Taxonomy and phylogeny
The first known specimen of the smoothtooth blacktip shark was a 75 cm (30 in) long immature male caught by Wilhelm Hein in 1902 and deposited at the Naturhistorisches Museum in Vienna. The location was recorded as the Gulf of Aden near "Gischin", which likely refers to the town of Qishn in eastern Yemen. In 1985, the shark was examined and described as a new species by New Zealand ichthyologist Jack Garrick in a National Oceanic and Atmospheric Administration (NOAA) Technical Report. He gave it the specific epithet leiodon, from the Greek leios meaning "smooth", and odon meaning "tooth". This species was known only by the single specimen until 2008, when fishery surveys in Kuwait uncovered several more specimens.
Based on morphology, Leonard Compagno in 1988 tentatively grouped the smoothtooth blacktip shark with the spinner shark (C. brevipinna), the blacktip shark (C. limbatus), the graceful shark (C. amblyrhynchoides), and the finetooth shark (C. isodon). Using molecular phylogenetic techniques on mitochondrial DNA sequences, Alec Moore and colleagues reported in 2011 that this species is closely related to the graceful shark, the blacktip shark, and the Australian blacktip shark (C. tilstoni).
Superficially, the smoothtooth blacktip shark resembles the blacktip reef shark (C. melanopterus). It is rather robust in build, with a short and blunt snout. The large nostrils are preceded by well-developed, triangular flaps of skin. The small, circular eyes are equipped with nictitating membranes. The mouth forms a wide arch and has very short furrows at the corners. There are 16 upper and 14–15 lower tooth rows on either side, along with two to three small teeth at the symphysis (center) of either jaw. The teeth are distinctive in shape, having narrow, upright cusps without serrations; finetooth sharks and juvenile spinner sharks are the only other members of Carcharhinus with similar teeth. The five pairs of gill slits are long.
The fairly long and pointed pectoral fins are slightly falcate (sickle-shaped) and originate between the fourth and fifth gill slits. The first dorsal fin is medium-sized and triangular with a pointed apex, and originates over the rear of the pectoral fin bases. The second dorsal fin is small and positioned opposite the anal fin. There is no ridge between the dorsal fins. The pelvic fins are triangular and larger than the anal fin, which has a deep notch in the trailing margin. A crescent-shaped notch is present on the caudal peduncle at the upper caudal fin origin. The caudal fin is asymmetrical, with a well-developed lower lobe and a longer upper lobe with a ventral notch near the tip. The dermal denticles are slightly overlapping and bear three prominent horizontal ridges leading to three or five marginal teeth. This species is greenish yellow to greenish gray above, sometimes with a scattering of tiny dark dots. The underside is white, which extends in a pale band onto the flanks. All the fins have sharply defined black tips, and there is a broad, dark midline stripe running from the second dorsal fin base to the tip of the upper caudal fin lobe. The largest recorded specimen is 1.2 m (3.9 ft) long.
Distribution and habitat
The smoothtooth blacktip shark has only been recorded from eastern Yemen and Kuwait, some 3,000 km (1,900 mi) apart. These two locations differ markedly: the Gulf of Aden near Yemen is over 2.5 km (1.6 mi) deep with a narrow continental shelf and no permanent riverine inputs, while the Persian Gulf near Kuwait is entirely shallower than 40 m (130 ft) and receives abundant freshwater from the Tigris-Euphrates-Karun river system. The Kuwait specimens were obtained from fish markets; given the practices of Kuwaiti speedboat fishers, this shark can be supposed to inhabit shallow, coastal waters. Still, these waters encompass a range of habitats from estuaries to coral reefs, and thus the habitat requirements of the smoothtooth blacktip shark remain largely unknown.
Biology and ecology
Considering its resemblance to the blacktip reef shark, the smoothtooth blacktip shark may play an equivalent shallow-water ecological role within its range. It is known to feed on marine catfish, and its diet probably also includes other small bony fishes. This species is presumably viviparous like all other Carcharhinus species, with the developing young sustained to term by a placental connection to the mother. Judging from the available specimens, males reach sexual maturity at some point between 0.9 and 1.2 m (3.0 and 3.9 ft) long.
Prior to the finding of additional specimens in Kuwait, the International Union for Conservation of Nature (IUCN) assessed the smoothtooth blacktip shark as Vulnerable based on its presumed small range and population. Despite the discovery of a second subpopulation off Kuwait, this species likely still warrants a Vulnerable assessment (or higher) because the waters around the Arabian Peninsula are subject to heavy fishing pressure and habitat degradation. Gillnet and other fisheries off Kuwait are known to take the smoothtooth blacktip shark as bycatch, while intensive Yemeni and Somalian shark fisheries operate in the Gulf of Aden. The status of the Yemen subpopulation is uncertain because no further specimens have been recorded since the original over a century ago.
- Compagno, L.J.V. (2005). "Carcharhinus leiodon". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature.
- Moore, A.B.M.; White, W.T.; Ward, R.D.; Naylor, G.J.P.; Peirce, R. (2011). "Rediscovery and redescription of the smoothtooth blacktip shark, Carcharhinus leiodon (Carcharhinidae), from Kuwait, with notes on its possible conservation status". Marine and Freshwater Research. 62: 528–539. doi:10.1071/MF10159.
- Garrick, J.A.F. (November 1985). Additions to a revision of the shark genus Carcharhinus: Synonymy of Aprionodon and Hypoprion, and description of a new species of Carcharhinus (Carcharhinidae). NOAA Technical Report NMFS-34: 1–26.
- Compagno, L.J.V. (1988). Sharks of the Order Carcharhiniformes. Princeton University Press. pp. 319–320. ISBN 0-691-08453-X.
- Voigt, M.; Weber, D. (2011). Field Guide for Sharks of the Genus Carcharhinus. Verlag Dr. Friedrich Pfeil. pp. 70–71. ISBN 978-3-89937-132-1.