Pods of orcas, which eat sharks, is a reason for departure of Great Whites: Reports (Representational)

Great white sharks, which support South Africa's shark-diving industry and have been responsible for a number of fatal attacks off Cape Town, haven't been seen in the region for 18 months.

Between 2010 and 2016 staff at the Shark Spotting Programme, established to warn swimmers when the three-ton predators approached beaches, reported an average of 205 sightings of the fish off the beaches of False Bay. In 2018 that fell to 50 and this year not one has been seen. None have been seen at Seal Island, a one-time feeding ground off the coast.

"Further supporting evidence of the absence of these large apex predators is the lack of any feeding or bite marks on whale carcasses the city has removed from False Bay this year," Cape Town's municipality said in a statement on Wednesday. "We do not know how their absence from False Bay would affect the ecosystem. Neither do we know the causes for their disappearance."

Local media reports have postulated the arrival of pods of orcas, which eat sharks, in the bay as a reason for departure of the Great Whites and over fishing of fish that the predators target as prey.