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Sharks, Crocodiles and Jellyfish

Great White Shark (Carcharodon carcharias)

Great White Shark - Photo by Terry GrossGreat White Shark
(Photo: Terry Gross)
Well known from the novel and movie "Jaws", this shark is one of the most powerful predators of the ocean. It can reach a length of more than 6 metres and a weight of well over 2,000 kg. Unlike the image of a man-eater painted in the novel / movie, great white sharks do not typically attack humans and certainly humans are not a typical prey. But sharks do have the habit of talking a test-bite on objects they don't know like buoys, floatsam or in some cases surfboards and humans.

Another reason that is frequently attributed to shark attacks on humans is mistaken identity. From below - especially in waters with low visibility - a human's shape (especially when lying on a surfboard with only arms and feet in the water) can be mistaken for a seal which is the natural prey of great white sharks.

While there is no denying that sharks can be dangerous and pose a threat to swimmers, I believe it is important to put things into proportion. Between 1990 and 2011 a total of 139 unprovoked great white shark attacks occured wordwide and only 29 of those were fatal.

Saltwater Crocodile (Crocodilus porosus)

Photo of large estuarine crocodileLarge estuarine crocodile
(Source: Wikipedia)
Saltwater Crocodiles are also known as Estuarine crocodiles and are among the most fearsome predators on earth. Adult males reach a length of typically 4.1 to 5.5 metres but sizes of more than 6 metres have been reported.  Weight is around 400 to 1,000 kg for male crocodiles but can be over 1,000 kg for a particulary large specimen. Females are much smaller averaging 2.3 to 3.5 metres but can reach a size of more than 4 metres and have a weight of 80-150 kg. The power of their jaws exceeds that of any other animal by far and can even crush the skull of a water buffalo.

Crocodiles are opportunistic and adaptable predator, lying in wait, hidden and almost invisible in the water only waiting for their prey to come close enough. If the prey is not killed immediately, crushed between the powerful jaws, it is pulled into the water and almost inevitably drowns. That way crocodiles can kill prey more than twice their own size or weight.

Don't be fooled by the name, saltwater crocodiles live as well in fresh water rivers and lakes as they do in saltwater environments and take as prey everything they can overpower - which given their size and strength is about every other animal be it on land or in the water. Unlike sharks, crocodiles are not picky about their prey and will take on humans just like any other food. Fish is a large part of their diet and that is, where the problem starts.

Example of two different crocodile warning signsExample of two different crocodile warning signsCrocodiles and humans share the same habitat. Where rivers meet the ocean, lots of fish can be found and those places are therefore as popular with crocodiles as they are with humans for fishing. Trowing the entrails back into the water only worsenes the problem as it attracts the crocodiles. The same of course applies to rivers and lakes in northern Australia. Never assume a place is safe, even if no warning signs (see right for two examples) are posted. When you make camp, leave at least 50, better 100 metres between your camp and the water's edge. If you absolutely have to get close to the water, never turn your back to it, be watchful and never form a routine (i. e. getting your water from the same spot every day), because one day a crocodile will lay in wait.

Each year only one or two saltwater crocodile attackes are reported in Australia. The outcome is almost always fatal.

Australian Box Jellyfish (Chironex Fleckeri)

Image of a box jellyfishBox Jellyfish
(Photo: Guido Gautsch)
The bell of these jellyfish is cube shaped, having 4 distinct sides which each edge accomodating about 15 tentacles. Fully grown, the bell can reach 30 centimetres in diameter and the tentacles can be as long as 3 metres having hundreds of thousands of nemocystes, the stinging cells which release the venom on contact.

They inhabit the tropical oceans all around northern Australia and hang around river mouths, estuaries and creeks, especially after rain when small fish - their prey -  are washed into the sea. With rising tide they move towards more shallow waters. For reasons unknown they don't seem to like deep waters, coral reefs, large sea grass areas or rough seas.

While there is a season in so far as the likelihood to encounter a marine stinger is migher between October and May, stings have reported in the northern Territory in all months of the year and in Queensland in all months apart from June and July.

Box jellyfish have one of the most potent venoms known. It has cardiotoxic, neurotoxic (poisonous to the heart and nervous system) and dermatonecrotic (destructive to skin) components. If stung, the victim can go into cardiac arrest within minutes and/or go into shock. If this happens while swimming and there is nobody around to help, death by drowning (if it does not already happened due to cardiac arrest or shock) is the likely end.

Of course in the case of cardiac arrest resuscitation takes precedence over everything else. Luckily not every box jellyfish sting is that bad. If no resuscitationi is necessary, the most important thing to do is to deactivate and remove the remaining stinging cells to prevent further venom to be released. To do this, you need plenty of vinegar (yes, normal vinegar). Pour it generously over the affected skin for at least 30 seconds and then carefully remove the tentacles. Do not use water for this! Do not try to remove the tentacles without first having poured vinegar, they will stick to the skin and release more venom.

If at hand, antihistamins can help to at least reduce the anaphylactic reaction. And ice packs might help to relieve the pain a bit. But unless the case is very mild, seeking immediate medical help is indicated as all hospitals and medical centres in box jellyfish affected areas have antivenom available which often means the difference between life and death.

If you plan to swim or dive in northern Australia, make sure to include a bottle of vinegar in your first aid kit. This simple precaution can save your life. There are also special protective suits available which are made of the same fabric as your normal swimming clothes, only they cover the whole body and therefore greatly reduce the risk of being stung.

Every few years a fatal jellyfish encounter occurs in Australia. In the past 100 years, about 60 fatal cases have been reported.

Irukandji Jellyfish

This is a group of very small Jellyfish with a very powerful venom which cause what is known as Irukandji Syndrome. The name is derived from the indigenous tribe of the Irukandji people which inhabit the area where the syndrome was first described.

The syndrome encompasses severe pains especially in the lower back, headaches, cramps in arms and legs, sweating, vomiting and critically increased heart rate and blood pressure. Especially the later can be fatal for people that have existing medical conditions which make them more vulnerable.

It was not until 1964 when Jack Barnes identified a tiny jellyfish as cause for the syndrome. The scientific name Carukia barnesi given to the jellyfish is in his honour. Since then only one other type of jellyfish has been found to cause this symptome, Malo kingi. However, a victim of Irukandji Syndrome was found that had nematocysts (stinging cells) still attached to his skin which matched neither of the two known species. It is therefore assumed that several more species of jellyfish fall into the group of the Irukandji.

Carukia barnesi has a box shaped bell with a diameter of only 2.5 centimetres but the four tentacles (one from each side of the bell) can reach a length of up to 1 metre. As a unique feature, the bell of the jellyfish has stinging cells as well, not only the tentacles as with other jellyfish. Very little is known about the lifecycle of these tiny and very fragile creatures. It appreas they live in deeper waters but sometimes move closer to the surface where they pose a threat to swimmers.

The actual sting is not more painful than a mosquito bite but 10-45 minutes after the sting, the severe symptoms start and develop into the full Irukandji syndrome.

There are only a handful cases known where Irukandji jellyfish have caused fatalities and in most of these cases the victim had a medical precondition. Those numbers are not listed separately but included in the overall jellyfish fatality numbers as mentioned above in the box jellyfish section.

Want to know more?Books and DVDs I can recommend

Dangerous Creatures of Australia

On almost 100 pages the author gives an introduction to the most dangerous creatures in Australia. Given the limited space this book can only provide a brief overview.

Spiders of Australia: An Introduction to Their Classification, Biology & Distribution

A comprehensive guide to Australian spiders, their identification and classification.

Spectacular Snakes of Australia

The book presents the snakes of Australia and unlike other books has a particular focus on the photographic presentation. Ideal for every friend of snakes and reptiles.

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