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Most attacks on Humans have occurred with sick sharks or in brown murky waters where the shark picks up on the vibrations in the water. Of course there have been unexplainable attacks but these are very minimal. My advice if you are worried check the statistics below, it’s more dangerous walking down the road.  Australian Shark Attack Register
Sharks occur in all the coastal waters and estuarine habitats around the 27,000 km of
Australia’s coast. As the population of the country increases (1900 = 3,765,300; 1950 = 8,307,500; 1990 = 17,046,700; 2004 = 20,204,789) many more people are entering coastal waters for recreational and commercial reasons throughout the year. Although
Australia continues to have a bad reputation concerning the threat of shark attacks to swimmers, the statistics do not support these contentions. In the last 50 years, there have been only 60 human fatalities (1.2 per year) in Australian waters from shark attack. Some years there are none, other years there have been up to three in a year, but the average remains around one per year. Yet each year 100,000s of swimmer-days take place on our beaches, harbors and rivers and the number is increasing with both increasing population and tourism. Sharks (elasmobranchs) comprise about 1% of all living fishes, and share nearly all the major features of their finned relatives. Like all fishes sharks use gills to extract oxygen from the water in which they live. Sharks have five to seven gill openings along each side of the head, through which they breathe. Primarily marine fishes, a few have adapted to fresh water, such as the Northern River Shark and Speartooth Sharks (Glyphis sp A and C respectively) found in the Northern Territory of Australia.About 350 species of sharks occur worldwide. Sharks are primarily oceanic and are widespread in tropical to temperate zones. Sharks vary greatly in size. The largest species, also the largest of all fishes, is the plankton eating giant the Whale Shark (Rhincodon typus). The largest measured specimen was 12.65 m long and weighed 21.5 tonnes, but the Whale Shark probably attains 18 metres. Some of the deepwater shark species attain only about 25cm.FeedingMost sharks are predators. Many sharks species become active after dusk and hunt during the night. The majority of sharks feed on other fishes. Large sharks, such as the Great White Shark (Carcharodon carcharias) and Tiger Shark (Galeocerdo cuvier), prey on large marine mammals such as seals, sea-lions, dolphins as well as large fishes, turtles and even sea birds.Several species of shark are known to be dangerous to humans: the Great White Shark, Tiger Shark, Bull Shark (Carcharhinus leucas) and other whaler sharks (Carcharhinus sp.). No shark is thought to target humans as prey, rather the majority of shark attacks can be attributed to the shark confusing us with its normal prey.While some sharks are probably not very selective feeders, certain sharks eat some foods more than others. For example, hammerhead sharks are known for eating stingrays; bull sharks eat other sharks; and smooth dogfish eat crabs and lobsters. Tiger sharks have been called “garbage cans of the sea” because they feed opportunistically on both live food and carrion. Prey includes bony fishes, other sharks, marine mammals, seabirds, and invertebrates. Many sharks prey most often on the weak, elderly members of a population. They select this because it is easier to catch.Many species of sharks are adapted for bottom feeding. Bottom feeders use the upper jaw to help pick up prey items. One example of a bottom feeder, the Port Jackson shark, has two types of teeth. Front teeth are pointed for grasping and back teeth are flat and molarlike for crushing. Another mechanism some sharks use for collecting food is filter feeding. The basking shark (Cetorhinus maximus) and the megamouth shark (Megachasma pelagios)strain enormous quantities of plankton from the water on gill rakers. Whale sharks also filter feed, but instead of using gill rakers, they strain plankton through a spongy tissue supported by cartilaginous rods between the gill arches. Filter feeders have reduced, nonfunctional teeth.BreedingMating in sharks is facilitated by the clasper organs of males, which are inserted into the female’s cloaca during courtship. Fertilisation is always internal, and reproduction occurs in one of three modes:

1. Laying eggs (oviparous)
2. Live bearing (viviparous)
3. Young hatching from eggs within the mother (ovoviviparous)

Examples of all three reproduction methods are found in sharks living in Australian waters. The Port Jackson Shark (heterodontus portusjacksoni) lays spiral shaped eggs that young hatch from (oviparous), the Smooth Hammerhead Shark (Hphyrna zygaena) gives birth to live young (viviparous) and the Grey Nurse Shark (Carcharias taurus) gives birth to pups after they have hatched from eggs within the uterus (ovoviviparous).AgeLittle is known about the growth and age of Sharks. Many of the conventional methods for aging animals, such as examining teeth, will not work with Sharks. Sharks grow slowly compared to bony fishes, possibly due to sharks’ slow digestive time and feeding rates. There is considerable variation in age and growth rates between species, and even between populations of the same species. Growth rings are periodically deposited on the vertebrae of some sharks. Vertebrae can be stained and examined for these growth rings. Growth rings may, however, stop developing in older sharks. Examining the vertebrae of captive-born sharks after their death enables researchers to compare the number of growth rings with the shark’s known age. In some areas tagged sharks are providing information about growth rates. Once a shark is caught, it is measured, tagged, and released. The shark is measured again when it is recaptured. Researchers correlate the measurements with the number of years since capture and calculate a yearly growth rate.ProtectionIn Australia, species are listed as threatened species under the Environmental Protection and Biodiversity Conservation Act 1999. The listed shark species are:Critically Endangered species

• Grey Nurse Shark (Carcharias taurus) – East Coast population
• Speartooth Shark (Glyphis sp. A)

Endangered species

• Northern River Shark (Glyphis sp. C)

Vulnerable

• Grey Nurse Shark (Carcharias taurus) – West Coast population
• Whale Shark (Rhincodon typhus)
• Great White Shark (Carcharodon carcharias)

Projects aimed at the conservation of these species have been funded under the Natural Heritage Trust’s Marine Species Protection Program.Shark AttackShark attacks occur rarely. Only a few of the 450 or so shark species have been known to attack people. Unfortunately, some attacks are fatal.There are some easy and commonsense precautions to take that can help reduce the risk of a shark attack. This risk minimisation advice is reproduced from the Australian Shark Attack File.

1. Do not swim, dive or surf where dangerous sharks are known to congregate.
2. Always swim, dive or surf with other people.
3. Do not swim in dirty or turbid water.
4. Avoid swimming well offshore, near deep channels, at river mouths or along drop-offs to deeper water.
5. If schooling fish start to behave erratically or congregate in large numbers, leave the water.
6. Do not swim with pets and domestic animals.
7. Look carefully before jumping into the water from a boat or wharf.
8. If possible do not swim a dusk or at night.
9. Do not swim near people fishing or spear fishing.
10. If a shark is sighted in the area leave the water as quickly and calmly as possible.

This information was supplied by the Australian Government and the Department of the Environment and Heritage and The Taronga Zoo
Australia and written by Marty Ware (Surfing Phuket)