Australian Blacktip Shark - Biology and Ecology

Biology and Ecology

The Australian blacktip shark is known to form large groups, segregated by size and sex. It preys mainly on teleost fishes, including ponyfishes, grunters, tunas, and herring. Cephalopods are a secondary food source, which are particularly important around April. This species also occasionally consumes smaller sharks, including snaggletooth sharks (Hemipristis pristis), spottail sharks (C. sorrah), and sharpnose sharks (Rhizoprionodon). Their diets shift with age: smaller individuals feed on proportionately more bottom-dwelling fish, while larger individuals feed on proportionately more midwater fish and cephalopods. A documented parasite of this shark is a species of tapeworm in the genus Platybothrium.

Like other requiem sharks, the Australian blacktip shark is viviparous: once the embryos exhaust their yolk supply, the depleted yolk sac develops into a placental connection through which the mother provides sustenance. Females bear litters of one to six pups (average three) every year. Mating takes place in February and March, with the females storing the sperm until ovulation in March and April. After a gestation period of 10 months, the young are born around January of the following year. Near-term females move into shallow, coastal nurseries, such as Cleveland Bay in northern Queensland, to give birth. Such nursery areas appear to be widespread, as newborns have been recorded throughout the range of the species. The newborns are relatively large, measuring about 60 cm (24 in) long. They grow rapidly in their first year, increasing in length by an average of 17 cm (6.7 in). The growth rate subsequently slows, averaging 8–10 cm (3.1–3.9 in) per year by age five. Both sexes attain sexual maturity at three to four years of age, at lengths of roughly 1.1 and 1.2 m (3.6 and 3.9 ft) for males and females, respectively. The maximum lifespan is estimated to be 20 years.