Scientists unlock secrets of the Great Australian Bight

Others are planning to boost recruiting in racially diverse areas. But in states that have already banned affirmative action, similar efforts at selective colleges have largely failed to maintain diversity gains.

It will be the first river-barrier in the state's history, but the Bicton and Melville City councils agreed that it was the best thing to do after the latest attack, according to Fisheries Minister Don Punch.

The three-metre shark was sighted just off the shore near Barrack Street Jetty in Perth and reported by a keen-eyed member of the public, as locals remain vigilant after the death of 16-year old Stella Berry in February.

'There is complexity putting barriers into the river, we have to take into account the environment of the river, and also the fact there's a lot of traffic on the river, and a river flow,' Mr Punch said.