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Characteristics, distribution and ecology
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Author: (Rüppell, 1837)

Field Marks:
In its area the only requiem shark with long upper and lower labial furrows, the first dorsal origin well behind the anal origin, and long preanal ridges. Key to species and diagnostic features give characters separating this from other, similar species in its genus.

Diagnostic Features:
Prenarial snout 4 to 5.4% of total length; upper labial furrows long, 1.4 to 2% of total length; total count of enlarged hyomandibular pores on both sides of head just behind mouth angle usually over 16; teeth serrated in adults; teeth not well-differentiated between sexes; total tooth rows usually 25/24. First dorsal origin usually over or slightly in front of pectoral free rear tips; second dorsal origin ranges from above last third of anal base to over its insertion; pectoral anterior margin usually equal to or shorter than first dorsal length from origin to free rear tip. Posterior monospondylous precaudal centra greatly enlarged; precaudal centra usually less numerous than caudals (rarely the two are equal), precaudals 55 to 79, total centra 121 to 162. Size moderate, males maturing over 60 cm total length. Colour grey, grey-brown or purplish brown above, pale below, pectoral fins with a light margin.

Geographical Distribution:
Eastern Atlantic: Madeira and Mauritania to Angola. Indo-West Pacific: South Africa and Red Sea to Pakistan, India, Malaysia, Indonesia, Thailand, China (including Taiwan Province), Japan, The Philippines, Australia (Queensland).

Habitat and Biology:
An abundant inshore and offshore shark of continental shelves, at depths of a metre or less down to about 200 m. It often occurs off sandy beaches, in midwater or near the bottom, and sometimes in estuaries, but it does not tolerate very low salinities and does not range into fresh water. Off Natal, South Africa, numbers fluctuate throughout the year, with greatest abundance in summer.

A viviparous shark, with a yolk-sac placenta; number of young 1 to 8 per litter, usually 2 to 5. Off South Africa mating occurs in summer, young are born in summer after a gestation period of about a year, and maturation occurs at about two years of age; maximum age is at least 8 years. Inthe eastern Atlantic, young are also born in summer, but in winter off Bombay, India.

The milk shark feeds primarily on bony fishes but also takes cephalopods and other invertebrates. Its diet includes lizard fish, wrasses, goatfishes, sardines and herring, threadfins, hairtails, croakers, mojarras, tonguesoles, squid, octopi, cuttlefish, crabs, shrimp and sea snails.

This species is harmless to people. It is often preyed upon by larger sharks, but off Natal, South Africa, the use of gillnets to reduce the numbers of large, dangerous sharks off beaches has resulted in an increase in numbers of milk sharks through reduced predation by larger sharks.

Size:
Maximum exceptionally to 178 cm, but most adults smaller, less than 1.1 m; males maturing at about 68 to 72 cm, and reaching 178 cm; females maturing at about 70 to 81 cm and reaching 165 cm; size at birth between 25 and 39 cm.

Interest to Fisheries:
This is one of the most abundant sharks if not the most abundant shark in the inshore waters where it occurs, and is a ready object of artisanal and smallscale commercial fisheries as well as offshore fishing fleets. It is caught on longlines, hook-and-line, in bottom trawls, and probably other gear and utilized fresh and possibly dried salted for food and for fishmeal.

Remarks:
The name 'milk shark' refers to the use of its flesh in India to promote lactation in women.

Type material:
Lectotype: Naturmuseums Senckenberg, SMF 2783, 440 mm stuffed specimen, designated by Klausewitz (1960:292). Type Locality: Djedda, Red Sea.

Milk shark (Rhizoprionodon acutus)