Milk shark

Photo: Pedro Niny Duarte

​Milk sharks (Rhizoprionodon acutus) are ground sharks in the Rhizoprionodon genus that can be found worldwide from West Africa to the southern parts of Japan. These sharks with a long, narrow snout and big eyes are grey-brown in colour that gives way to a creamy underbelly. Their caudal (tail) fin usually has a dark margin and white margins around their pectoral (side) fins. They prefer shallow water and feed on small pelagic and benthic bony fishes, cephalopods and other invertebrates in this area. While it provides some good noms, but with them straying no deeper than 200 metres, it does make them vulnerable to fisheries.

Milk sharks are viviparous. Females tend to give birth between two to eights pups after a gestation period of about 12 months. When born, the pups can measure at about 25 to 39 cm in length, maturing when they reach between 70 to 80 cm long. They average about 175 cm in length, and the maximum reported age of these sharks is eight years old.

Despite its widespread occurrence in fisheries, there is limited data available about how the fisheries impact their population. "In northern Australia, they are the most commonly taken in shark species in fish and prawn trawls. They also represent the 2% of the catch in gill nets and 6% of catch on longlines. Despite these catches, the Australian population does not appear to be affected," stated the IUCN website. Still, the IUCN has listed milk sharks as Least Concern (LC) because they are found worldwide. 

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GLOSSARY

• Artisanal fishery: There is, as yet, no universally-accepted definition; the term is used interchangeably with ‘small scale fishery.’ In general, artisanal fishing will be family-based, employing small or no boats and simple and/or traditional methods.
• Benthic zone: The bottom of an ocean or lake.
• Bycatch: The part of a fishery’s catch that is made up of non-target species.  
• Cephalopods: The most intelligent, mobile, and largest of all molluscs. These include: squid, octopuses, cuttlefish, the chambered nautilus, and their relatives.
• Commercial fishery: The activity of catching fish and other seafood for profit.
• Invertebrates: Animals with no backbone (i.e. crustaceans, jellyfish, corals, sea anemones).
• IUCN: International Union for Conservation of Nature.​
• Viviparous with yolk-sac: Also known as aplacental viviparous and previously known as ovoviviparous/ovoviviparity; it is the production of eggs that are fertilised and hatch inside the female shark but the embryos lack a placental connection to the oviduct or uterus and so do not feed off the mother.

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