Shark proof cage
A shark proof cage is an extremely strong, metal cage used by a scuba diver to safely examine dangerous types of sharks up close. This can include various species of shark, but the most commonly observed within the confines of a cage are the great white shark and the bull shark, which are both known to be aggressive at times. Shark proof cages are built to withstand being rammed at high velocities, and be able to protect the user from massive force from attacks. Cages can provide a visual and tactile deterrent to sharks. Cage-diving allows people to closely monitor sharks, and sometimes interact with them.
On September 4, 1979, US patent number 4166462 was issued for a self-propelled shark proof cage; being designed to allow abalone divers to collect abalone without becoming vulnerable to attack. Thanks to the propulsion system, abalone divers would exert themselves less and, therefore, be able to collect their prey for longer periods of time. The patent abstract details a self-propelled cage with at least one access opening and a propeller mounting frame that carries both an air motor and a propeller. Buoyant objects are attached to the frame so that the cage may be made approximately the same density as saltwater. This patent expired on September 4, 1996.
Shark cage accidents
In 2005, a British tourist, Mark Currie, was nearly killed when a 6-metre (20 ft) great white shark bit through the bars of a shark cage being used during a recreational shark dive off the coast of South Africa. The shark circled several times before charging the cage; biting through a portion of the cage. The shark then severed it from the cable connecting it to a boat on the surface. Currie realized that his cage was sinking as the shark mounted what would have been its final attack. Currie quickly swam out of the top of the cage and was pulled to safety by the boat's captain, who fended off the shark with blows to its head.
In 2007, a commercial shark cage was destroyed off the coast of Guadalupe Island after a 4.6-metre (15 ft) great white shark became entangled in it and tore the cage apart in a frantic effort to free itself.Tourists captured video of the incident,[dead link] which quickly spread throughout the Internet.
Shark baiting controversy
Opponents of the cage-diving industry, such as shark-attack survivor Craig Bovim, believe that the constant shark-baiting used to lure sharks to tourists' cages may alter sharks' behaviour. Bovim's opponents, such as marine environmentalist Wilfred Chivell, contend that there is no correlation between shark-baiting and shark attacks against humans. However, there is evidence that the baiting of sharks for tourism does alter the patterns of movement of Great White Sharks 
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