Science, Uncategorized

Sharks of Australia

In Australia, sharks are a very common occurrence all year long. A recent study from CSIRO has for the first time accurately estimated the number of adult Great White Sharks as 2210, from along the Western coast of Australia to Ningaloo reef on the North Eastern coast. This study used groundbreaking genetic data through a method called close-kin mark-recapture. Simply put, they take a small tissue sample from the shark, compared it to other sharks, and determined how related all their samples were. This was taken from juvenile sharks, for many reasons, but mainly they’re easier to control and sample. juveniles have genetic markings for their parents, so once the juveniles siblings were found, an estimate could be made for the adult population.

The findings of the study made me think; White Shark populations have remained stable over the past few years, so why does it seem like shark attacks are becoming more frequent?

While shark attacks are rarely fatal in Australia (2.3% of attacks are), they seem to occur more frequently here than elsewhere. This can be the result of many factors; hotter summers, good surf in sharky areas or the cooler waters down south. We also love being by the sea (and who can blame us), with 85% being with 50km of the ocean, and 90% of us putting it as our top 3 most valuable resource. But one thing that is 100% contributing to these attacks, is that Australia is home to the 22 out of the 26 species of sharks that have been document to unprovokingly attack humans, this includes the “Big 3” of shark species: Great Whites, Tiger Sharks and Bull Sharks.

But what makes these sharks so deadly? All sharks have chemoreceptors through their lateral line, and electroreceptors, specially named Ampullae of Lorenzini around their snout. But these three sharks have other special features that make them more deadly than others. Another unique feature of sharks is their rows of teeth. Each tooth in the three rows is serrated making them razor sharp. Once these teeth become too blunt, then it falls out and is replaced by the tooth from the next row! Their scales are also unique to the shark and ray families. Unlike other fish, their scales are forked and overlapping, so in the direction from head to tail, it is smooth, but in the opposite direction is is rough. This specific type of scale is called placoid scales, and makes for some really tough skin. It is also useful for other fish by removing parasites from their skin if they rub against the shark.

Great White Sharks (Carcharodon carcharias)

White Sharks have an amazing sensory system, including their chemoreceptors and electroreceptors, they also have sharp eye sight, being able to see contrasts very well. They are ambush predators, meaning they generally attack from below at speeds of 60km per hour. Because of this high speed, they end up leaping out of the water in an act called “breaching”. This relates to their name, because their belly is white, so when they breach all you can see is their white underside, hence “Great Whites”. This is then accompanied by their extremely powerful bit force, with produces 4000 psi of force (that is a lot, enough to bit through a brick!). Seals are the main source of food for White Sharks, but often, especially in Western Australia and Ballina on the central coast. But often humans are mistaken for seals because of their silhouette.

Tiger Sharks (Galeocerdo cuvier)

These beautiful sharks are named tiger sharks because of the stripy patterning on their body. Contrary to popular belief, these stripes are only really clear in juveniles, and they fade as the shark matures. These sharks have a reputation for being the garbage trucks of the sea by literally eating anything! Some of the various animals that have been found in their stomachs include stingrays, sea snakes, squids and even weird, non-food like things like old tyres and licence plates! Tiger sharks can often be quite unpredictable in their behaviour, making them a little more dangerous than Great White Sharks.

Bull Sharks (Carcharhinus leucas)

Distinguishable by their lighter grey colour and small distance between their eye and snout, they are the third most dangerous shark in Australian waters. Their snout is short because they live in water with low visibility, meaning they can’t see far ahead so they need their snout to be close to their eye for precision when hunting. They are known to be quite an aggressive shark, often being very territorial and have low tolerance for being provoked. What makes Bull Sharks so amazing, is their ability to tolerate a wide range of salinity levels. They generally hang around river mouths, waiting for the low tide to draw out all of the fish from the river. Bull sharks are a common occurrence in the Brisbane River, and have been known to swim as far inland as Mount Crosby (which is roughly 35km from the mouth of the Brisbane River).

So these are three of the most deadly sharks in Australia! But not all sharks are as scary as these three, such as the Black Tip Reef Shark seen in the feature image. These sharks are extremely chill with humans, and will rarely attack if they are unprovoked. This shark was pictured at Heron Island on the Great Barrier Reef by me when I was there on an excursion for uni. They were always around at low tide, waiting for all the fish to spill over into the harbour from the reef. Sharks are some of the smartest animals on the planet and are highly evolved to be top predators, but there is no need to be scared of them!

If you are smart about the times you swim and how you act around them, you will be amazed at how much they don’t care about you. Human-shark interactions are extremely rare, but let me know if you would like another blog post about how to avoid shark attacks, and what you should do if you find yourself in a situation with a shark, or if you would like to know more abut their behaviour and physiology!

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