IUCN threat status:

Vulnerable (VU)

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Biology

Relatively little is known about the biology of the smalleye hammerhead. What is known is that this is a viviparous species; embryos develop inside the mother, receiving nutrition via a yolk-sac placenta (2). After ten months of pregnancy, the mother gives birth to a litter of 5 to 12 pups, each measuring about 30 centimetres (3). Birthing takes place in shallow waters from late May to June (3). It is believed that females mate and are fertilised again shortly after giving birth, and thus they can reproduce annually (3). The difference in colour between adults and juveniles is thought to be due to differences in diets; juveniles feed primarily on shrimp, whilst the majority of the adult's diet consists of small bony fishes and catfish eggs (3). This reportedly timid shark also feeds on swimming crabs, squid, and even preys on the newborn of the closely related scalloped hammerheads (2) (7). The evolutionary purpose of the unique cephalofoil structure, formed from the front of the expanded skull, is not entirely clear, but several functions have been suggested. It may act to increase swimming efficiency, by adding lift; or it may allow the hammerhead to get a better appreciation of distance due to the widely spaced eyes. As the head swings from side to side in the water whilst swimming, the nostrils sample a greater volume of water than they would do otherwise, which may allow more opportunity to use its sense of smell. Its purpose could be to provide an increased surface area for the electrosensitive ampullae of Lorenzini, enhancing the shark's ability to detect prey, or it could be a useful tool to pin slippery prey against the seabed (5) (6).

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Source: ARKive

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