EXPERT REACTION: Second shark attack in the Whitsundays in 24 hours

Two attacks in the same general area within 24 hours sounds like the danger from sharks is now very high.

But unlikely random events can occur close together fairly easily - times between such events can often be within short intervals, and less frequently at longer and longer intervals. While diving on the Great Barrier Reef, I saw 18 large sharks in two days, then saw one large shark in the next year.

Two events are not enough to draw any firm conclusions, and the chance of another attack may well be extremely low. The last attack in this area was many years ago.

Another point is that large sharks can move a long way in a short time. This may be the same shark. Perhaps this is a starved or damaged shark that cannot catch its normal types of food. And by tomorrow it may be many miles away.

So setting drum lines to catch sharks in this area may do little more than create an illusion that the shark attack risk has been reduced.

Worse, it may kill many innocent sharks that do not attack people. And sharks have an important role in the reef ecosystem.

Shark encounters still remain rare. Environmental factors have been shown to influence shark occurrence and behaviours, predominately ocean temperatures, depth, rain and eddy formations.

Temperatures create a barrier for sharks depending on their thermal preferences (eg. white sharks are cold water species) and often changes in boundary currents (eg. East Australian Current) change temperatures and ocean currents affecting not only sharks but also their prey species. This can lead to sharks coming closer to shallow waters or moving away from home ranges.

Sharks cannot see in dirty water thus may often lead to investigative 'test bites', as they use their mouths to investigate objects, this is seen in sharks bumping random objects (eg. drift wood) in the ocean.

Opportunistic generalist species tend to investigate objects often, but also display territorial behaviors when they feel threatened. Sharks are also seasonal, coming close to shore when laying pups (eg. bull sharks) and have a wider area of occupation when their season starts: Summer for most species and heavy rain for bull sharks.

Sharks also display two movement behaviours, in transit and residency. Most species also have aggregation sites along the coast and tend to be near shore (eg. white sharks).