Milk Shark

The largest member of its genus, off West Africa the milk shark has been reported to reach 1.78 m (5.8 ft) and 22 kg (49 lb) for males, and 1.65 m (5.4 ft) and 17 kg (37 lb) for females, though there is uncertainty regarding the species identity of these specimens. Even if accepted, these figures are considered exceptional and most individuals do not exceed 1.1 m (3.6 ft) in length. Generally, females are heavier and attain a greater maximum size than males. The milk shark has a slender build with a long, pointed snout, large, round eyes with nictitating membranes (protective third eyelids), and no spiracles. On each side of the head behind the corner of the jaw, there are usually seven to 15 enlarged pores. The nostrils are small, as are the adjacent triangular skin flaps. There are long furrows at the corners of the mouth on both the upper and lower jaws. The tooth rows number 24–25 in both jaws. The upper teeth are finely serrated and strongly oblique; the lower teeth have a similar shape, though the serrations are smaller and the tips curve gently upward. The teeth of juveniles are smooth-edged. The broad, triangular pectoral fins originate below the third or fourth gill slits, and are no longer than the front margin of the first dorsal fin. The anal fin is about twice as long as the second dorsal fin and preceded by long ridges. …

The milk shark has the widest distribution of any Rhizoprionodon species. In the eastern Atlantic Ocean, it is found from Mauritania to Angola, as well as around Madeira. Since 1985, there have been four occurrences, temporally and spatially distinct, of the milk shark in the central Mediterranean Sea, with a likely entry via the Strait of Gibraltar. In the Indian Ocean, it occurs from South Africa and Madagascar northward to the Arabian Peninsula, and eastward to South and Southeast Asia. In the Pacific Ocean, this species occurs from China and southern Japan, through the Philippines and Indonesia, to New Guinea and northern Australia. The milk shark likely once had a contiguous distribution by way of the Tethys Sea, until during the Miocene epoch, when eastern Atlantic sharks were isolated from Indo-Pacific sharks by the collision of Asia and Africa. Occurring close to shore from the surf zone to a depth of 200 m (660 ft), the milk shark favors turbid water off sandy beaches and occasionally enters estuaries. In Shark Bay, Western Australia, juvenile milk sharks inhabit seagrass meadows composed of Amphibolis antarctica and Posidonia australis. Although some sources state this species avoids low salinities, it has been reported several times from fresh water in Cambodia, as far upstream as the Tonlé Sap. …

One of the most (if not the most) abundant near-shore sharks within its range, the milk shark feeds mainly on small benthic and bony fishes. Occasionally squid, octopus, cuttlefish, crabs, shrimp, and gastropods are also taken. In Shark Bay, the most important prey are silversides, herring, smelt-whitings, and wrasses; this is also the only local shark species that preys on the Waigeo seaperch (Psammoperca waigiensis), found in seagrass beds avoided by other sharks. In the Gulf of Carpentaria, it feeds mainly on halfbeaks, herring, and mullets, and is also a major predator of penaeid prawns. Smaller sharks eat proportionately more cephalopods and crustaceans, switching to fish as they grow older. Many predators feed on the milk shark, including larger sharks such as the blacktip shark (Carcharhinus limbatus) and Australian blacktip shark (Carcharhinus tilstoni), and possibly also marine mammals. Off KwaZulu-Natal, the decimation of large sharks by the use of gillnets to protect beaches has led to a recent increase in milk shark numbers. A known parasite of this species is the copepod Pseudopandarus australis. There is some evidence that male and female milk sharks segregate from each other.

Life history. …