there is an interesting article over at swellnet.
http://www.swellnet.com/news/surfpolitik/2015/08/11/north-coast-shark-activity-new-theory I was kinda interested in this myself because I spend a bit of time in northern nsw so started googling some stuff and so now I'm an internet expert...

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I read some interesting stuff and a couple of things jumped out.
there was a study into the east Australian current that found the amount of upwelling off the northern nsw coast is directly related to the position of the East Australian Current. the closer to the coast the more upwelling. The shape of the EAC also has an influence on the water temps. A thin EAC stream tends to leave a pool of colder water along the coast.
There are some studies from WA that say that white shark attacks generally occur in water temps less than 20deg and are more likely when the whales are migrating.
so my leap of faith here is that the position of the EAC and the Upwelling due to wind and EAC position has formed an area of activity along the coast of NSW which the sharks are feeding in. if the area of upwelling was further offshore I'd guess the sharks would be further offshore.
if you look on the BOM sst charts the area along the coast is below 20deg and the area off the coast is above 20 deg.
one thing is for sure that area from Byron to Ballina is the most wildlife packed piece of water I've ever seen.