Mackerel Sharks Pt 1: “Der-dum… der-dum… der-dum-der-dum…”

Smile, you're on camera!

Smile, you're on camera!

Sharks have everything a scientist dreams of. They're beautiful―God, how beautiful they are! They're like an impossibly perfect piece of machinery. They're as graceful as any bird. They're as mysterious as any animal on earth.

Peter Benchley, author of Jaws.

The mackerel sharks (Family: Lamindae) are among the most awe-inspiring, charismatic and powerful sharks in Australia’s waters. Found at sizes of up to 6 metres long, with torpedo-shaped bodies, powerful tails and jaws to match, these species are the kings of their domain; perfectly built for speed, power and agility. Mackerels also have the amazing ability of keeping their body temperature above that of the surrounding water using a special heat-exchange circulatory system, allowing them to remain active and occupy both temperate and tropical waters. This article is the first of three, highlighting the members of this family: the Great White, the Mako and the Porbeagle.

 

Known by many names (White Death, White Pointer and White Shark), the Great White Shark, orCarcharodon carcharias, is named after its distinctive two-toned colouration and is considered the most famous of all sharks. The largest of the mackerels, the dimensions of these majestic beasts range from 4 to 6 metres (13 to 20 ft) long, approximately 1.8 metres (6 ft) wide and over 2000 kg. Pace this out and you will truly appreciate their size - they are essentially as big as a minibus!

Reproductive rates in Great Whites are extremely slow, males maturing at approximately 7 years, and females between 12 and 17 years. Gestation lasts up to 18 months with reproductive cycles estimated at every 3 years. When pregnant, a female can hold 2 to 17 embryos, which are oophagous, meaning that they get their nutrition from eating the unfertilised eggs produced by their mother. At birth, offspring can measure a little over 1 metre long and weigh approximately 35 kg. Tracking studies have shown that White Sharks frequently travel through the Bass Straight ‘corridor’, and it is believed that our very own Victorian waters may be where they give birth.

 

Smaller Great Whites (under 3 metres long) tend to feed on fish and smaller sharks, whereas larger Great Whites tend to feed on marine mammals such as seals. Hunting animals like seals is no easy task, as they’re fast and incredibly agile. To counter this, Great Whites show enormous cognitive ability and rely on hunting skills learnt through experience, utilising a variety of ways to attack seals efficiently and effectively. The design of their teeth is specialised for tearing through the relatively tough skin of seals, as well as sickly or dead whales. The bottom teeth often make surgeon-like incisions, puncturing and holding prey firmly in place, while the serrated top teeth act like a giant saw as the head shakes side-to-side to tear flesh.

The one that got away! 

The one that got away! 

 

 

Great Whites are also capable of traveling extraordinary distances. Not only do they travel back and forth along the coasts of Australia, but one shark was found to have traveled from South Africa to Australia (and back!) - a distance of more than 15,000 km, in less than 9 months! What is even more incredible is that they’re probably not the eating machines people think they are. On long migrations, Great Whites (as well as other species) may be able to make use of energy stores in their enlarged livers and therefore not eat for months when food is scarce.

'Nicole', the first trans-oceanic Great White recorded. 

'Nicole', the first trans-oceanic Great White recorded. 

Although considered solitary animals, several observations have shown Great Whites to travel in pairs and sometimes swim around in loose groups. In light of this, recent research into their behaviour has shown them to be somewhat social. When in groups or coming across another’s path, their body language changes to communicate their intent and purpose. Tail slaps at the water’s surface may indicate aggression, warning other sharks to steer clear; parallel swimming alongside another may be a way of sizing each other up and establishing superiority; when approaching each other, a carefully timed ‘turn-away’ may be a way of displaying their personal space. Analysing shark social behaviour is at its very infancy, but is still shedding light on the complex, beautiful and amazing nature of these creatures.

 

Unfortunately, White Sharks are a victim of us more than we are of them. Our imagination is enthralled with these majestic animals, but our fear has unfortunately taken the place of rational thought. Public media often paints these creatures as merciless, indiscriminate killers and, as a result, heavy persecution and hunting of Great Whites in the 1960s through to the 1980s saw many disappear from the waters around the seal colonies at Phillip Island. Many people are in fact unaware that Great Whites are perhaps more curious of us than we are of them. Sharks can often be seen testing or inspecting items, like boats or cages, by a relatively gentle bite. Unfortunately, this ‘testing’ bite for most humans is quite damaging and often results in the loss of limbs or life. What we must remember is that many attacks are not a result of ‘hunger’, but more probably curiosity, and most fatalities are in fact from blood loss and not from being eaten. Great Whites are undeniably dangerous and should be respected as such. However, their slaughter simply out of our fear for them is unwarranted for an animal that is simply going about its business in its own domain.

 

Great Whites are listed as ‘Threatened’ in Victoria and have been a protected species in Australia since 1999.

Not such a mindless human-hunter after all... 

Not such a mindless human-hunter after all...