This Saturday we were fortunate enough to spot a Zambezi (also known as ‘Bull’ Shark) on Manta! Despite Manta being one of the top ten dive sites in the world, it was awesome to bump into the lone shark among the enormous schools of fish.
Our encounter did not, however, live up to the reputation of this shark. Their name (Bull) refers to the bullish, unpredictable and often aggressive behaviour recorded; but our experience was anything but. He was sitting at 18m until we swam closer, when he cruised away in the opposite direction – but fortunately no faster than our efforts, giving us a wonderful display.
Zambezi’s are unusual in that they are diadromous – able to swim between fresh and salt water. As a result, they are found in most corners of the world; from Massachusetts to Southern Brazil in the Atlantic, Kenya to South Africa in the Indian and Vietnam to Australia in the Pacific. The fish have a preference for shallow, warm waters, tending not to swim deeper than 30m.
It is not just their behaviour that accounts for their name – they are also bullish in appearance. These sharks are identifiable by a broad, flat snout and stocky shape lacking an interdorsal ridge. Like Great Whites, the Zambezi’s are grey on the top and white below. Females are larger than males, averaging 2.4m and 130kg, while the males 2.25m and 96kg. The largest recorded Zambezi was an astonishing 315kg.
The cartilaginous fish feed on a variety of species: turtles, dolphins, terrestrial mammals, birds, stingrays and fellow Zambezi’s are all recorded prey. They tend to hunt solitary, only occasionally teaming up with members of their school. A ‘bump and bite’ technique is deployed: the initial ‘bump’ sufficiently disorientating and/or injuring unsuspecting prey, before the ‘bite’ when prey is eaten. Due to this, murky waters provide the ideal conditions for feeding as the sharks cannot be seen.
In spite of numerous encounters with humans, specific reproductive behaviours such as courtship are only speculated upon. It is thought that males will bite a female on the tail, until the female turns upside down and the male can copulate. The gestation period is interestingly long, 12 months, but the pups are viviparous (born live and free swimming) and immediately independent. A single litter can have between 1-20 pups. They reach sexual maturity at 10 years, and average life expectancy is 16 years.
Fortunately Zambezi’s are not currently listed as threatened or endangered, but it is likely their numbers are shrinking due to demand for their meat, hides and oil.