A shortage of great white sharks in Gansbaai has left shark-cage diving operators out of pocket. Not a single shark has been spotted in the bay in more than a week.Gansbaai marine biologist for the Dyer Island Conservation Trust Alison Towner said the absence of sharks could be attributed to:A drop in sea temperature;A great white that was hit by a speed boat in Gansbaai in December - research shows it is common;Whale carcasses in other areas of the coast that could have attracted them;Migrating Orca pods in the area that could have scared them off."We have seen a consistently warm period but as soon as the strong southeasterly winds came in the temperatures dropped by 10 degrees," said Towner.She said sharks were sensitive to water temperature. They may still be around further off-shore.But with 80 000 tourists a year coming to South Africa to dive with the apex predators their absence is not going unnoticed."People aren't taking people out and they have signs on their boats saying, 'no diving, no sharks'," said Towner.Brenda du Toit from Marine Dynamics Shark Tours in Gansbaai said they had periods where sharks are scarce but there had never been a time when they haven't seen a single shark for such an extended period.But it's not the first time the sharks have been scarce.Chris Fallows, a shark cage diving operator from Simon's Town with 25 years' experience with great whites said they had a very "weird" season last year."We had a period of 57 days of seeing no sharks. The last time we experienced it was when there was a research project when a lot of sharks were hooked. The other sharks disappeared as a survival mechanism," he said."They are most certainly caught as by-catch off our coastline. There is a legal shark long-line fishery where six boats go out and kill over a thousand sharks per boat per trip," says Fallows.He said there was also illegal shark fishing along the coastline...