IN his book Down Under, American author Bill Bryson claims the one animal that instils fear into Australians is the crocodile.
Our estuarine crocodile is a huge aquatic predator that certainly has a fearsome reputation for ‘taking’ humans, even though such ‘attacks’ are actually quite rare. They absolutely have to be respected! Talking to people visiting the region, it seems crocodiles of Cape York are of interest to everyone. Most would like to see some of these iconic reptiles on their trip, while a few just want to stay right away from them.
Being wary of crocodiles is a natural instinct, and certainly nothing to be ashamed of. The reality is visiting crocodile country is much safer than many realise, so long as you follow a few basic but important rules – and have a reasonable understanding of these incredible creatures.
I was involved in some of the first-ever crocodile research and surveys in Queensland, and have continued to be so over the years. The reality is the more we learn about crocodiles, the more we realise what little we know about them. This article is intended to share some authentic and hopefully interesting knowledge about these reptiles.
Crocodiles were around many millions of years before the dinosaurs, and understandably are superbly adapted for hunting and living in the wide range of aquatic habitats they occupy. For example, the scutes on a crocodile’s back are naturally engineered to allow them to move through the water with minimal disturbance.
They also act as solar panels, absorbing the sun’s heat, which in turn heats the blood flowing through them. Every scale, and an even stronger sensory organ in the lower jaw, detects movements by other animals in the water nearby. This of course helps crocodiles locate prey in dark conditions. Crocodiles also feature an extra, transparent eyelid to help them see under water.
Very handy! Lingual glands on the crocodile’s tongue expel salt from the body when they are living in saltwater habitats. The freshwater crocodile is the smaller of the two croc species that occur in Australia, and only inhabits Australia.
As their name suggests, freshies manly inhabit freshwater rivers and billabongs, but they can also occur in brackish water. Easily distinguished by their narrow snout, they grow to about 3m, however 2m is more common for a large male. Male crocodiles always grow longer than females. Freshwater crocodiles are not generally regarded as being dangerous to humans unless interfered with.
They certainly have a head full of sharp, pointy teeth to defend themselves if needed. However, the main purpose of these teeth is for grabbing and securing the fish they mostly feed on. As part of our research, we once flushed out the stomachs of quite a number of freshies to see what they had been eating. The tell-tale crucifix bone of catfish was very commonly found, along with remains of bony bream and archerfish.
A couple of larger crocs had also eaten ‘darters’, a type of waterbird similar to a cormorant, and even Arafura file snakes – an aquatic snake with rough skin like a file. The largest freshwater crocodile we ever caught was 2.5m long. It was living in a turkey nest dam on a cattle station near the Gulf township of Croydon. Amazingly, this croc was feeding only on small fish up to about 15cm long. Freshwater crocodiles are very smart with their breeding habits.
The females lay their eggs (five to 25) in a sandy riverbank in late-July/August, and these usually hatch in November – before the flooding associated with the imminent wet season happens. This strategy eliminates the risk of the developing crocodiles in the eggs from drowning, except when the occasional very early wet season happens. Along with their estuarine crocodile relatives, female freshies assist their young in entering life in quite an unusual way.
Around hatching time, each mum visits her nest each night, and when she eventually finds the young emerging from the nest, she carries them down to the water’s edge in her toothy jaws. This is a very unusual level of parental care for a reptile. The estuarine crocodiles of Cape York, otherwise known as ‘salties’, grow to at least 7m in length and are found in other parts of the Indo-Pacific region as well as Australia.
Neither common name is accurate, as ‘salties’ thrive in fresh water and occur well upriver away from any estuaries, along coastlines and even on islands. They are opportunistic feeders. Anything that can be grabbed or taken down is fair game, though many authorities believe humans are not key prey. Otherwise, they would be pulling people in left, right and centre.
Again, catfish seem to make up a fair part of the diet for crocodiles living in rivers, though all fish may be eaten, including turtles, birds, pigs, dogs and even cattle and horses, depending on the size of the crocodiles. There are plenty of reports of low-flying birds and bats being plucked out of the sky, and flying foxes in particular seem to be a favourite.
Estuarine crocodiles don’t need to feed every day, or even every week, and can actually live for months without eating much at all, though not for prolonged periods. Current research being undertaken by the University of Queensland and Australia Zoo in the Wenlock River on Cape York shows that some large male estuarine crocodiles have distinct home ranges within a river system, while others are more nomadic, nearly always moving about.
Breeding females generally have a smaller home range than the males. Around the start of the wet season, they will leave ‘home’ country to move to a breeding location often tens of kilometres away.
There, they build a nesting mound out of vegetation and soil on a river or swamp bank, and lay about 55 eggs that hatch three months later. The females stay around the nest to defend it from predators during the incubation period, and typically lay in a muddy wallow for much of this time. Big wet seasons will see many nests drowned by floodwaters, especially in Queensland’s low-lying Gulf country.
Crocodiles also have amazing navigating abilities, and relocation of ‘problem’ crocodiles rarely works, as the crocodile can easily find its way back to its original home. The most famous example of this is ‘Weldon’, a 4.2m crocodile captured in the Wenlock River by Steve Irwin and his team back in 2003. Fitted with a satellite tag, Weldon was relocated by chopper to the east coast of Cape York and tracked as part of a research project.
Using ocean currents to help save energy, Weldon unerringly made his way to the tip of Cape York, then swam down the west coast and back into the Wenlock to exactly where he had been caught. The best time to see these remarkable reptiles is during the cooler months when they bask in the sun on riverbanks. At night you can also see their tell-tale ruby red eye shines with a good light (held in front of your eyes).
Some people claim the crocodiles of Cape York ‘eat out’ all the fish. Not so. Wherever you have large populations of crocodiles, you have healthy ecosystems and the best barramundi fishing. The Northern Territory is the classic example of this.
It features the highest populations of estuarine crocodiles in the world, and yes, the best barra fishing! Apex predator crocodiles play a vital role in keeping their aquatic ecosystems balanced, though the way this happens is yet to be fully revealed. The Department of the Environment and Energy has ‘Croc Wise’ safety information readily available on signage, brochures and their website.
In a nutshell, being croc wise is basically about staying out of the water and camping and bank fishing well back from the water’s edge. It is also vital to not discard or leave fish frames or other meat/bones lying around where they will attract scavenging crocodiles – especially at the water’s edge. Crocodiles will even travel some distance from water to find such ‘fast food’.
The attack on beachfront campers at Bathurst Bay in 2004 was triggered by previous campers burying fish frames in the sand, enticing the crocodile up the beach. Otherwise, you can follow the movements of many of the crocodiles tagged by the University of Queensland and Australia Zoo on australiazoo.com.au/conservation/projects/tracking/crocodiles
These interactive tracking maps have been developed by Dr Ross Dwyer and Prof Craig Franklin from UQ and make for super-interesting viewing. They are part of the largest-ever study into estuarine crocodiles.
Until next month! crocodiles cape york