Gun shots slow down and lose power almost immediately after they enter water - and the shark would need to have been on or very near the surface for hits to have been fatal, according to experts.
William Cleverdon, owner of Will's Fishing and Firearms on the North Shore, said: "It all depends on the type of gun, the angle he was shooting at and how deep the shark was in the water. If it was shot at near the surface, then it would've been hit.
"Bullets do change direction and the velocity is significantly slower when they hit the water, but they do keep going," he said.
Mr Cleverdon said there was a better chance of striking the shark if the officer had been firing directly downwards.
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"If he was shooting at a 45 degree angle, then it would've been harder to hit as the deflection would have been too great."
A test conducted on the Discovery Channel series, Mythbusters, found that ammunition fired from a high-powered assault rifle travels only a few centimetres through water before losing its deadly force.
The experiment was conducted to test the opening scenes of the film, Saving Private Ryan, where soldiers were shot dead while under water.
Watch the test online: