This family, the requiem or ground sharks, contains more than 50 species of large sharks found world-wide in tropical to warm-temperate waters. There is only 1 species in Iranian fresh waters. A second species is reported from an Iranian river under special circumstances and is not regarded as a resident (see Marine List). They are distinguished from other sharks by a complex of characters including having an anal fin; 5 gill slits; 2 dorsal fins; no fin spines; nictitating eyelids; and a scroll intestinal valve. The first dorsal fin base is in front of the pelvic bases; there is a wavy dorsal tail fin margin; well-developed, knife-like teeth with cutting edges; usually no spiracles; and precaudal pits.

This is one of the largest and most economically important shark families. Most members are voracious predators as their common names suggest and they are frequently dangerous to man. Some of these species enter rivers and remain there for long periods causing human fatalities. These sharks are usually viviparous. Food includes a variety of fishes, sharks, rays, squids, crustaceans, marine reptiles, birds and mammals, and carrion and garbage.

Shark flesh can be eaten and is religiously permissible in Iran.

Genus Carcharhinus
Blainville, 1816

There are about 31 species of gray sharks found world-wide but only one regularly enters fresh water in Iran. A detailed definition of the genus is given by Compagno (1988).

Carcharhinus leucas
(Valenciennes in Müller and Henle, 1839)

Upper and lower tooth

BM(NH)1924.10.1:1, Tigris River at Al Karradah near Baghdad

BM(NH) 1874.4.28:9, Tigris River near Baghdad

Common names

kooseh, kuseh, kooseh-kuli, sag mahi (= dog fish).

[kosetch or kossage, jarjur in Arabic; bull shark].

Systematics

Carcharhinus leucas was originally described from the Antilles.

A number of shark species have been reported as entering rivers of the Tigris-Euphrates basin including Iranian tributaries (Günther, 1874; Day, 1875-1878; Sykes, 1902; Kennedy, 1937; Hunt, 1951; Khalaf, 1961; Mahdi, 1962; Zorzi, 1995; and others). The species appeared under such names as Carcharhinus gangeticus (Müller and Henle, 1839), Eulamia (= Carcharhinus) lamia (Blainville, 1820), and Carcharhinus menisorrah (Valenciennes in Müller and Henle, 1839). A recent revision of carcharhinid sharks by Garrick (1982) cites only Carcharhinus leucas from fresh waters of the Tigris-Euphrates basin and Compagno (1984) concurs. Coad and Papahn (1988) also list specimens which confirm this species to be present.

Key characters

This is the only shark species commonly encountered in Iranian fresh waters and can be recognised by the 5 gill slits, upper caudal fin lobe larger than lower, and the arched mouth armed with teeth on the underside of the head. Distinction from other sharks is given in Compagno (1984).

Morphology

The snout is very short, rounded and ends bluntly. Its length is less than the distance between the nostrils and much less than the mouth width. There are 12-14, usually 13, teeth on each side of a median tooth in the upper jaw and 12-13, usually 12, teeth on each side of a median tooth in the lower jaw. Teeth are heavy, broad, almost triangular, erect near the jaw symphysis but becoming slightly oblique and more concave or notched nearer the mouth corners. The teeth are strongly serrated, more so near the base, and upper teeth more so than lower teeth.

The first dorsal fin lies over or just behind the level of the axil of the pectoral fin. The apex of the first dorsal fin is pointed to somewhat rounded. The second dorsal fin is high, has a short posterior lobe and lies just over the level of the anal fin origin. Pectoral fins are broad and their tips are narrow and pointed. There is no interdorsal ridge (the back is smooth between the dorsal fins). The upper precaudal pit is well-developed while the lower pit is weak.

Sexual dimorphism

Males bear claspers. The pelvic fins are partially modified into grooved, rod-like structures which are held together to form a tube and are used in mating. They are not used to clasp the female but as an intromittent organ. Females are larger than males.

Colour

Fin tips are dusky to black, particularly in young. There is no other obvious colour pattern although the back is darker than the belly, being bluish, grey or brown. Fins are similar in colour to the neighbouring body.

Size

Attains 3.24 m (Garrick, 1982) or 3.40 m (Carpenter et al. 1997). Fish in Iranian fresh waters have been estimated as up to 2 m in length but naturally circumstances were not always favourable for an objective and detached size judgment.

Distribution

Sharks have long been known to enter fresh waters in the Tigris-Euphrates basin. Zorzi (1995) records a book by Pausanias, "Guide to Greece", written in the late second century which refers to sharks in "the Euphrates...., which fatten monsters as man-eating as any in existence".

One of the earliest distributional records is found in the Arabic work "Wonders of Creation" by Zakariya al-Qazwini published in 1263 A.D. and later translated into Persian. The sharks were found at Basrah on the Tigris River in what is now Iraq and were cited as formidable because of their voracity and teeth like the points of spears. Shark attacks still occur at Basrah (Coad and Al-Hassan, 1989).

Subsequently reported in the Tigris River above Baghdad about 850 km from the sea (Günther, 1874; Kennedy, 1937) before dams were built. Sykes (1902) saw sharks in the Ab-e Gargar (Karun River in Iran) at Shushtar 420 km from the sea, Wilson (1942) reporting on events in 1908 records sharks from between Shushtar and Ahvaz and near Shushtar, Blegvad and Løppenthin (1944) report then from Khorramshahr, and Hunt (1951) reported them from the Karun River, Khowr-e Bahmanshir and Shatt al Arab (Arvand River). Coad and Papahn (1988) report sharks at Ahvaz on the Karun River about 275 km from the sea as well as further up river at Shushtar and down river in the Khowr-e Bahmanshir.

Zoogeography

This shark is found world-wide in warm temperate to tropical seas and is reported from fresh waters in Africa, Asia, Australia and the Americas.

Habitat

This is a shark of coastal waters such as harbours, bays and estuaries but unusually it will penetrate far up rivers, as far as 4000 km up the Amazon River. It is said to be a sluggish bottom dweller except when attacking prey and in the sea may be found down to at least 150 m although usually at less than 30 m. They are said to invade the Khowr-e Bahmanshir and Karun River of Iran from July to September when freshwater flow is at a minimum and tidal penetration of salt water is at its highest. However they do travel well beyond tidal influence in Iran. Local people along the Bahmanshir River near Tangeh Se in Khuzestan maintain that it is dangerous to swim there because of these sharks. They are occasionally trapped in nets set for Tenualosa ilisha and may be caught on hooks. They are not as common as in the past (N. Najafpour, pers. comm., November 2000).

Age and growth

Maturity in males is attained at 1.60-2.25 m and in females at 1.80-2.30 m. Mature fish are about 6 years old and life span is up to about 14 years.

Food

Food is a wide variety of fishes including tunas, small sharks, and rays, as well as crabs, shrimps, molluscs, cephalopods, sea urchins, turtles, sea birds and mammals. Diet in fresh water has not been investigated in Southwest Asia although Blegvad and Løppenthin (1944) reported that sharks station themselves under the date palms at Khorramshahr to eat the falling dates!

Reproduction

Birth size is about 56-81 cm and takes place in estuaries and river mouths. Females may contain up to 13 embryos and the gestation period is 10-11 months. This species is known to breed in fresh waters, such as Lake Nicaragua in Central America, but there have been no reports of reproduction in the Tigris-Euphrates basin.

Parasites and predators

None are reported for Iran.

Economic importance

This shark has a considerable impact on people using water directly in Khuzestan. A number of severe injuries and fatalities have been reported in fresh waters through shark attacks. The first comprehensive report in modern times was by Hunt (1951) although accounts date back to the thirteenth century (Coad and Papahn, 1988). The latter summarize recorded attacks and add new ones for a total of 34 in the period 1941-1985, of which about half were fatal. Additionally Wilson (1942) reports a woman taken by a shark while drawing water between Shushtar and Ahvaz and a 9 foot (= 2.8 m) near Shushtar which killed two boys and a girl. These Iranian records are a significant proportion of freshwater attacks worldwide, about 28%. A number of soldiers were apparently victims during the Iran-Iraq war but no records have come to light. Men, women and children are attacked as well as horses and sheep, only the massive water buffalo is said to be safe. Many minor attacks and narrow misses are probably not reported. Attacks are said to have declined in recent years since shark oil is no longer used to caulk boats but this is probably a local legend. People were attacked while swimming, paddling, bathing, washing vehicles or fishing. There was no apparent triggering factors for the attacks as victims were dressed in various colours and types of clothing, engaged in various activities and environmental conditions where known varied between attack sites.

Freshwater shark attacks have even appeared in a novel "Harem" by Mossanen (2002).

In other parts of the world, this species has been used for its flesh and fins, as leather, for its liver oil and for fishmeal. Sharks can be eaten by Muslims if "reliable experts confirmed that shark fell into the category of cartilaginous and scaly fish" (http://netiran.com:80/news/IRNA/html/950216IRGG13.html) which appears to be so (netiran.com/news/IranNews/html/95021814INPL.html).

Conservation

This shark appears to still be common in Iranian fresh waters judging from the attacks reported over the past 50 years or more and no conservation measures are needed (or likely to be acceptable to the local population).

Further work

The biology of this species in fresh water is unknown for Iran and Iraq and should be thoroughly investigated as a real hazard to those using rivers of Mesopotamia. Are the sharks permanent residents or seasonal visitors? Detailed records of attacks should be kept and analyzed in an attempt to determine any triggering actions. It may prove possible to make recommendations for use of water resources so as to avoid shark attacks in future.

Sources

Garrick (1982) and Compagno (1984, 1988) for general anatomy and biology.

Comparative material: BM(NH) 1874.4.28:9, 1, ca. 76.8 cm total length, Iraq, Tigris River near Baghdad (ca. 33º21'N, ca. 44º25'E); BM(NH) 1924.10.1:1 1, (head only, recorded length 4 ft 1 inch = 1.25 m), Tigris River at Al Karradah near Baghdad (33º17'N, 44º23'E).

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