Milk shark

Lore & Background

The German naturalist Eduard Rüppell first described the milk shark as Carcharias acutus in 1837. It has since been placed in several genera before being synonymized with Rhizoprionodon crenidens. In 1960, Wolfgang Klausewitz designated a 44 cm male caught off Jeddah, Saudi Arabia as the lectotype. The common name 'milk shark' comes from an Indian belief that its meat enhances lactation; other names include fish shark, grey dog shark, little blue shark, and white-eye shark. A 1992 phylogenetic analysis by Gavin Naylor found it to be the most basal of four Rhizoprionodon species examined. The extinct R. fischeuri from the Middle Miocene may be the same species.

The milk shark has a slender body with a long, pointed snout, large eyes, and long furrows at the corners of its mouth. It is nondescript gray above and white below. It can be distinguished from similar species by the long furrows and 7 to 15 enlarged pores above them. Juveniles have smooth-edged teeth, while adults have finely serrated, oblique upper teeth. The first dorsal fin originates over the pectoral fin free rear tips, and there is no ridge between the dorsal fins.

Reader's Guide

The milk shark is among the most abundant sharks within its range, feeding primarily on small bony fishes, cephalopods, and crustaceans. It is preyed upon by larger sharks such as the blacktip shark and Australian blacktip shark, and possibly marine mammals. Off KwaZulu-Natal, the decimation of large sharks by gillnets has led to an increase in milk shark numbers. The species is viviparous, with embryos sustained by a placental connection. Females give birth to one to eight young, either during a defined breeding season or year-round depending on location. The reproductive cycle is usually annual, but may be biennial or triennial. Large numbers are caught by artisanal and commercial fisheries for meat, fins, and fishmeal. The International Union for Conservation of Nature has assessed this species as vulnerable.

Did You Know?

• The milk shark has been recorded swimming up rivers in Cambodia, as far upstream as the Tonlé Sap.
• Juveniles are known to inhabit tidal pools and seagrass meadows.
• The specific epithet 'acutus' means 'sharp' in Latin.
• Off KwaZulu-Natal, milk shark numbers have increased after large sharks were reduced by gillnets.