It was introduced in September 2006, after an incident involving Crocodile Hunter Steve Irwin and a stingray, as a blanket ban preventing all sea life from hunting any Australians. It was later narrowed down to just surfers. Sharks were also originally included, but their lawyers got them off on a technicality after a further refinement limited it to cover just mammal.
While it has been successful in averting the extinction of surfers due to overhunting, recent instances of whales 'happy slapping' surfers are the subject of intense debate. Pro-surfer hunting species, notably southern right whale, wish to lift the ban. They say that stocks have recovered sufficiently to sustain limited hunting. They also claim they are involved only on a purely scientific-research basis.
Thanks to Lindy Moore.