sharks

The Diverse Sharks of Australia

This is a guest post by Melissa Marquez. 

With summer inching closer every day, one way to find relief from the Australian heat is to take a dip at one of Australia’s famous beaches or rivers. What you probably aren’t thinking about is that you’re sharing the water with one of the world’s oldest animals: the shark.

Worldwide, there are about 500 species of sharks. Of these, about 180 species live in Australian waters. Well-known species include the great white shark (Carcharodon carcharias), the grey nurse shark (Carcharias taurus) and the bronze whaler (Carcharhinus brachyurus), but the greater public often forget that sharks aren’t uniformly grey, robust, or in possession of sharp teeth. These less famous sharks are often overlooked, both by the community and by scientists. 

One can be seen if you find yourself on the western coast of Australia and stop by Ningaloo Coast. If you're lucky, you might spot a well-known gentle giant: a whale shark (Rhincodon typus), more than seven metres long, discernible by its unique arrangement of light and dark patterning. As the world’s largest living fish, they are highly migratory and often appear in large filter feeding groups. If you manage to snap a picture of an individual, you can send it over to Wildbook for Whale Sharks, where it will become part of a database of whale shark records that dates back to 1995.

The gentle giant that is the whale shark can be spotted off Ningaloo Coast in WA. 

The gentle giant that is the whale shark can be spotted off Ningaloo Coast in WA. 

Some sharks don’t make such a grand entrance as the massive whale shark; they instead hide in plain sight through camouflage. Sharing the waters are the elusive tasselled wobbegong sharks (Eucrossorhinus dasypogon), which can reach up to four metres in length. What sets these sharks apart is that they’re flattened and ornately patterned to blend in with the seafloor. The word ‘wobbegong’ is thought to come from an Aboriginal word meaning ‘shaggy beard,’ pointing to the growths around their mouth that act as sensory barbs. This bottom-dweller takes advantage of its camouflage by ambushing unsuspecting fish and invertebrates.

Another funky-looking water resident is the green sawfish (Pristis zijsron), a ray with a shark-like body and an elongated snout that bears pairs of teeth that resemble a chainsaw. They are greenish brown in colour and can reach up to four metres in length. Sawfish are most commonly found along the coast of Queensland, the Northern Territory and Western Australia. Little is known about their populations and they are listed as Vulnerable by the International Union for Conservation of Nature and Natural Resources (IUCN).

Think you can escape sharks by skipping the ocean and opting for a river dip instead? Think again! Some sharks, like the speartooth shark (Glyphis glyphis), inhabit freshwater. These sharks tend to look like your ‘typical shark,’ and are grey in colour with a white underbelly, reaching up to two metres in length. Speartooth sharks have only been found in a few locations along the Northern Territory and Queensland, and very little is known about them.

The zebra shark is named for the juveniles' distinctive black and white stripes. 

The zebra shark is named for the juveniles' distinctive black and white stripes. 

If you can catch a flight to Sydney, sneak a peek into the waters and you’ll possibly see a Port Jackson shark (Heterodontus portusjacksoni), affectionately known as the PJ shark. Measuring up to one and a half metres long, it has a distinctive harness-like pattern across its shoulders, ridges above its eyes, and a pig-like snout, and lay spiralled eggs that sometimes wash ashore once the shark pups are born. This species can also be found in Victorian waters and many other areas off the Australian coast. 

While in Sydney, you may also spot a brilliantly spotted shark known as the zebra shark (Stegostoma fasciatum), named for their black and white stripes on juveniles which morph into spots as they mature. These reef inhabitants can reach up to two and a half metres in length and are usually seen resting on the seafloor.

Speaking of stripes, the tiger shark (Galeocerdo cuvier) is also an Australian resident. This shark can reach up to six metres in length and can be seen from shallow reefs to the open ocean. Known as the ‘garbage cans of the sea,’ this scavenger has had some pretty weird stuff found in its stomach: TNT, chicken wire, a suit of armour, and a porcupine, to name a few!

Unfortunately, these magnificent animals often get a bad rap, and whilst some are dangerous, it is important not to ignite hysteria when it comes to sharing the waters with our shark neighbours. Smart drum lines, nets to protect beaches and other warning systems are all being used to manage sharks and their interactions with humans. However, these interventions may cause problems for other marine life.

Instead, an increase in shark-spotting initiatives and other non-lethal ways to alert beachgoers when sharks are in the area could be used to help raise awareness and appreciation of these mysterious marine creatures. Perhaps by educating the public about these diverse sharks, we can better share and protect their habitats into the future. 


Melissa Marquez is a marine biologist studying sharks, skates, rays and chimaeras in Wellington, New Zealand. You can follow her research on Twitter (@mcmsharksxx) and outreach efforts at www.finsunited.co.nz.

Monster or Marvel: The Truth About Sharks

In only the past five years, Australia has witnessed 15 fatal shark attacks, giving us the infamous reputation of ‘shark attack capital of the world’. It would seem our waters are infested with eating machines just waiting for another human morsel. But are sharks really the monsters that we fear?

When sharks make the news, the media generally take a sensationalist approach - a good monster story is a great money-maker. In a recent study, it was found that in 300 news items on sharks across 20 major publications in the U.S.A. and Australia spanning 10 years, over half of the publications were negative in content and focused on attacks. Only 11% of content was related to the conservation and ecological significance of these creatures.

Sharks are arguably the most misunderstood creatures in the world. Unfortunately, their importance to the overall health of the ocean and the dire need for increased conservation efforts is often overshadowed by our misguided fear and lack of knowledge.

WHY DO SHARKS BITE US?

Sharks are intelligent, curious animals capable of exhibiting complex behaviours that we’re only beginning to scratch the surface of. Why sharks bite people is not an easy question to answer, but there are some theories as to why this might occur.

Sharks are curious and just want to see what you are. With no natural predators (other than larger sharks), sharks tend to investigate objects with little fear. Since they lack hands or paws, they ‘test’ objects with a bite. Needless to say, these bites are capable of inflicting serious injury or death. Sharks have been known to bite surfboards, boat motors and even plastic bags.

Sharks may have made a mistake and thought you were something else. Sharks use their vision in the final stages of an attack and may mistake the shape of a paddling surfer or scuba diver for a turtle or seal silhouetted against the sun.

Note the similarities in the silhouettes. Image courtesy of @nakawe_project.

Note the similarities in the silhouettes. Image courtesy of @nakawe_project.

Sharks can be social and ‘moody’. Using specific body postures and swimming patterns, sharks are believed to communicate their social dominance to defend their personal space and food. Sharks may therefore sense that a human (who may not even know a shark is nearby) is encroaching on its space or fear that said human may even be after the same food!

ARE SHARKS STARTING TO ‘LIKE’ HUMANS?           

It is true, shark attacks have been on the increase. However, this has been shown to match very well with the increased numbers of people living near the coast and using the water. Considering our ever increasing population and, in particular, how summer temperatures can from vary year to year, it is more accurate to average the number of shark attacks per decade rather than annually.

In Western Australia, there have been eight fatal shark attacks since 2010, three of which were between September and October in 2013. At face value, such quick successions in attacks made the waters seem ‘unswimmable’ because of the idea that sharks were ‘on the hunt’ for humans. Nevertheless, if you place these incidents in the context of decadal averages, the rate of fatalities has remained constant at about 1.1 per year. It is important to note though that despite these statistics, we should by no means ever detract from the necessity to deal with such events with appropriate sensitivity towards victims’ friends and family.

HOW CAN WE LIVE WITH SHARKS?

It is possible to live with sharks and mitigate against attacks. Beach nets and drumlines (floating drums with a hanging baited hook) are a popular method to protect people, but unfortunately these may be doing more harm than good by killing whales, dolphins and sea turtles. It is even possible that captured animals (including other sharks) may act as bait, actually attracting more sharks to the area.   

Non-lethal and more cost-effective options are currently being explored, with many having added benefits such as public education and offering positive interaction with sharks themselves. Tracking technology, for example, allows scientists to monitor where sharks travel in real-time by equipping them with satellite tags and thus warning beach-goers of certain areas. Scientists have even provided sharks with a ‘voice’ by giving them their very own Twitter accounts with live map updates - you can therefore follow the adventures of your favourite shark!  

Follow Lydia and Mary Lee now @ https://twitter.com/rockstarlydia and https://twitter.com/maryleeshark.

A great white shark photographed in False Bay, Cape Town, South Africa. Photographed by Leonardo Guida.

A great white shark photographed in False Bay, Cape Town, South Africa. Photographed by Leonardo Guida.

Observation towers already exist at popular beaches primarily to prevent drowning, a phenomenon killing an average of 93 Australians at beaches per year in the past 10 years. With the addition of more observers and/or observational methods (e.g. helicopter patrol), more eyes on the water could not only mean fewer drownings, but also a larger likelihood of warning beach-goers about sharks in the immediate vicinity and along nearby stretches of coastline.

Research into repellent technology still has significant obstacles to overcome, but in principle it is working towards exploiting shark behaviour and biology to reduce incidents. Electronic deterrents exploit the shark’s ability to detect bio-electrical signals from other animals and ideally discourage the shark from coming nearby. Another repellent involves wetsuit design. Certain patterns and colours help break up your ‘outline’ so that you would essentially be invisible in the water or look like an unappetising, poisonous fish. Research is very much preliminary, although it is great to see scientists exploring options that minimize harm to both human and shark.

Wetsuits designed to deter sharks. On the left, a wetsuit designed to appear unappetising like a poisonous fish. On the right, a wetsuit designed to make you appear ‘invisible’ in the water. Image courtesy of www.dailymail.co.uk

Wetsuits designed to deter sharks. On the left, a wetsuit designed to appear unappetising like a poisonous fish. On the right, a wetsuit designed to make you appear ‘invisible’ in the water. Image courtesy of www.dailymail.co.uk

CHANGING OUR PERCEPTION OF SHARKS

Attitudes towards sharks haven’t always been negative and indeed vary across cultures. For example, some island cultures have traditionally had an intimate relationship with the ocean for sustenance and long ago recognised the importance of sharks in the ocean, some even worshipping them as gods. Both Fijian and Hawaiian mythologies, as examples, included sharks as significant aspects of their belief systems. In contrast, Western cultures have often viewed sharks as demons of the ocean; you only need to view some 17th and 18th Century paintings of sailors in trouble at sea to understand this perception. Arguably, Western society has had less reliance on and interaction with the shark compared to more island-based cultures and, as such, the everyday significance of shark species has been vastly different.

'Watson and the Shark' by John Singleton Copley,    1778.

'Watson and the Shark' by John Singleton Copley,  1778.

Fortunately, we are all reconnecting with and understanding the shark. Reputable aquariums and ecotourism have not only provided positive interaction and education, but have shown that sharks are worth more alive than dead. When the controversial Western Australian shark cull policy was announced, there was unprecedented support across all of Australia to protect the shark with rallies, protests and social media publications involving thousands of people.

Ironically, shark attack survivors are some of the greatest defenders of sharks and advocates for their conservation. Despite experiencing a traumatic event, the power of survivors to use this experience in a positive manner adds a unique and powerful aspect to communicating the importance of shark conservation. To quote shark attack survivor Paul De Gelder, “They're not our sharks to kill... It's a natural predator, an apex predator, it's essential to the ecosystem of the ocean.”

Not all sharks are built equally, but all occupy key positions and roles in marine food webs. As apex predators, they keep populations of other animals in check. For example, tiger sharks help to control populations of turtles and dugongs which graze on seagrass: an important habitat that provides shelter and food for smaller fish and invertebrates to grow and reproduce. Without sharks, we may see more ecosystem collapses that ultimately affect us; in both Japan and America, the overfishing of sharks has caused several shellfish fisheries to collapse because of the increase in rays (which eat shellfish) that would otherwise be eaten by sharks.

 WE ARE THEIR WORST ENEMY AND GREATEST HOPE

We are the shark’s worst enemy and also its greatest hope. Over-fishing is currently estimated to kill an average of 100 million sharks per year. Shark populations are not as resilient as other fish, as they take several years to reach sexual maturity and only give birth to relatively few young. However, our improved knowledge of their role in our oceans has led to finning bans and the creation of sustainable fisheries. We can indeed live with sharks and, by recognising the value of them, we add value to our oceans and in turn add value to our lives.

Two blacktip reef sharks (Carcharhinus limbatus) cruising the rocky reefs of Aliwal Shoal, South Africa. Photographed by Leonardo Guida

Two blacktip reef sharks (Carcharhinus limbatus) cruising the rocky reefs of Aliwal Shoal, South Africa. Photographed by Leonardo Guida

Banner image courtesy of National Geographic

Mackerel Sharks Pt.2: The Makos

“What you lookin’ at?”     http://www.factzoo.com/fish/shortfin-mako-fast-bright-eyed-open-water-shark.html

“What you lookin’ at?”

http://www.factzoo.com/fish/shortfin-mako-fast-bright-eyed-open-water-shark.html

Nature’s purpose-built torpedo is the mako shark. The mako is the fastest of all sharks, capable of powering through the water at speeds of up to 27 to 38 knots – that’s 50 to 70 kilometres per hour! Makos are divided into two species: the short-finned (Isurus oxyrhincus) and the long-finned (Isurus paucus) mako, which look very similar to each other bar the size of their pectoral fin (as their names suggest). Both species are global in their distribution, but in our Victorian waters, you’re more likely to come across the short-finned species.

 

Makos are clearly identified by their slender fusiform body, which is coloured by a brilliant, indigo blue dorsal side and a white underside. They also possess large black eyes and rows of long needle-like teeth that often protrude from the mouth. Like the other mackerel sharks, sexual maturity is relatively late in life, with males and females reaching maturity at approximately 8 and 18 years respectively. The average number of pups born to a female is 12 following a gestation period of up to 18 months in a three-year reproductive cycle.

Although approximately half the size (about 2.8 metres) of their bigger cousin, the great white (Carcharodon carcharias), makos are formidable hunters, chasing down medium to large-sized fish, such as tuna and small cetaceans (whales and dolphins). The mako has a unique arrangement of red muscle (which is fatigue-resistant) in the centre of its body, which is linked to the tail by long tendons. These allow for rapid, powerful and repeated contractions to occur with maximal transfer of energy to the tail. Funnily enough, tuna also have a similar muscle arrangement, illustrating the beauty of evolution - although two very different kinds of fish, they’ve both evolved a similar way to solve the same problem: to eat and to avoid being eaten! Using its speed to chase down prey, the mako is even capable of launching itself six metres into the air if it means securing dinner! If the chase is successful, the mako ensures its prey cannot escape using its perfectly-designed teeth like rows of spears to puncture and hold.

Makos are considered aggressive sharks, readily chasing and attacking baited lines. Despite this, there have only been three fatal attacks globally since 1980. Many non-fatal incidences with makos have occurred when harassing the animal whilst on the fishing line or when it has been landed in the boat. The tenacity of the mako and its prized flesh has made it a very popular target for sport fishers, which has unfortunately placed increased pressures on their already declining populations. The International Union of the Conservation of Nature (IUCN) red list has makos listed as ‘vulnerable’. 

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

Smile, you're on camera! Smile,

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...