Many moons ago I blogged on crocodile management in Kakadu National Park and I also gave a brief description of the two different species of crocodiles native to the Top End.
Back then I closed with the words “A lot more is to be said about Kakadu’s crocs, so watch this space!” Many thanks to those who persevered and kept watching, you well and truly deserve to find out more about Crocodylus porosus, the Estuarine (Saltwater) Crocodile.
So, let’s meet these locals – from a safe distance!
Now, every time an incident (like this one) occurs that involves the world’s largest reptile – and Australia’s largest estuarine and freshwater predator respectively – there are calls for the culling of ”salties”. And the quarrels erupting in the wake of an incident make me cringe every time! If people stopped doing silly stuff, putting their own lives and that of others at risk and made an effort to understand this species in its natural habitat a bit better, we could move away from the croc cull debate and just pay these animals the respect they deserve.
Many of those who are in favour of croc culling remember the “olden days” in the Top End, when crocodiles were on the brink of extinction as they had been hunted extensively for their skins – and for fun. Back then swimming was considered safe in places like Twin Falls Gorge. Steve even remembers jumping off the Mary River Bridge on the Arnhem Highway and swimming in Yellow Water Billabong as a teenager! Those were the days when the few surviving crocs generally shied away from people – their only predators.
At the top of the food chain crocodiles play a key role in maintaining a natural balance in our wetlands and river systems, they have done so for many thousands of years. Crocodiles are important predators and help control the population of species such as wallabies, fish, waterbirds as well as feral pests like pigs.
But back in the 1960s and 70s, as a result of human intervention, the balances in the wetland ecosystems were thoroughly out of whack. The introduction of buffaloes and pigs some 120 years earlier and decades of extensive crocodile hunting had disastrous effects on the Top End’s wetland habitats.
Since 1971, when estuarine crocodiles were awarded full protection under the Territory Parks and Wildlife Conservation Act, their numbers have increased to what ecologists and park rangers call a healthy level – back to normal! Populations are now levelling out in most rivers in Kakadu National Park, with exception of the East Alligator River in which the number of estuarine crocodiles is still increasing. Garry Lindner, Field Supervisor, Crocodile Management and Coastal Surveillance Officer with Kakadu National Park, reckons there may be as many as 10.000 estuarine crocodiles in Kakadu these days.
Kakadu surely is crocodile country – just about any body of water near sea level may be the natural habitat of a “saltwater” crocodile!
Bininj/Mungguy are familiar with the crocodiles on their land and know not to be complacent. They have a lot of respect for “Ginga” and many of their stories remind us to always be on the lookout for cheeky crocs.
The best way to safely observe crocodiles is by joining one of the commercial boat cruises. Generally, the late dry season is the best time of the year to see crocodiles in large numbers, when the floodplains dry up and the billabongs shrink.
Another good spot to see crocodiles is the viewing platform at Cahills Crossing. But please observe all warning signs and do not enter the water. Do not become a croc’s dinner!
Estuarine crocodiles are amazing creatures, it’s worth having a closer look at some of their features:
- Crocodylus porosus is a large amphibious and carnivorous reptile inhabiting tropical and subtropical freshwater rivers, coastal and open seas, tidal rivers and billabongs from the Kimberley to the central east coast of Australia – and may be found as far as 300km inland.
- They feed mostly on fish, but may take turtles, birds and large land animals (wallabies, dogs, pigs, horses, cattle, buffalo) as well.
- The saltie shows a distinct sexual dimorphism, meaning the males grow larger and often at a faster rate than females. An average size male reaches 5m, larger specimen may grow over 6m long, weighing over 1,000kg.
- The snout is broad and rounded. The teeth of crocodiles are set in an irregular row and more conspicuous than those of alligators when the mouth is closed. Teeth are replaced continuously with new ones growing from below in the same socket. In older animals this process slows down until it eventually stops.
- A palatal flap closes the entrance to the throat to prevent drowning. When feeding in the water, they have to keep their head above the water which is achieved by lifting the tail out of the water to counterbalance.
- A saltie’s nostrils are prominent on the tip of the snout. Stalking crocodiles are very inconspicuous when drifting only their noses, eyes and the distinct cranial platform behind the eyes may be visible above the water.
- The croc’s skin is covered with scales, or scutes. Many of these scutes, particularly the ones on the back, are reinforced with so-called osteoderms, bony plates that are vascularised (supplied with blood via small capillaries) and act as heat absorbers or radiators, to help control the body temperature.
- Salties are excellent swimmers, under water or at the surface. When chasing prey or fleeing from other individuals (during territorial fights in the breeding season), they can plane along the water surface at high speed by help of their thrashing tail. Crocs also use their muscular tail to propel the body out of the water to lunge at prey in a surprise attack, which these ‘sit-and-wait’ predators are feared for.
- Estuarine crocodiles have a complex social hierarchy. Large males are dominant and territorial (aggressively defending their territory against other male invaders) and are thought to mate with most of the females in their territory.
- Crocodylus porosus breeds in the wet season. After courtship at the end of the dry season (from September onwards the crocs become more aggressive and activity levels increase with the higher ambient temperatures), mount nests made of tall grasses and other compostable materials are built at the onset of the wet season. The breeding season ends around March, depending on weather conditions. The female lays on average between 45 and 55 eggs and at normal field temperatures incubation takes about 80 to 90 days.
- The sex of crocodile hatchlings is determined by the temperature in the nest, rather than genetically. As a guide, crocodile eggs incubated at temperatures below 31˚C produce females and a mixture of sexes is produced between 31˚C and 32˚C. Embryos incubated between 32˚C and 33˚C hatch as males.
- Females aggressively guard the nest, with varying success, from predators such as goannas or snakes. When the hatchlings are ready to emerge from the nest, they call with a characteristic and a rather hard to describe rasping “tshirp”. The mother so encouraged digs up the nest and collects the emerging hatchlings in her snout. She may undertake several trips until she’s helped the entire clutch to the water.
- Even if the nest escapes wet season flooding, only a small percentage of hatchlings reach maturity (only about 1% of the hatchlings make it to a length of 2m). Many small crocodiles fall prey to fish, birds, goannas, snakes – and other crocodiles.
The ones that do reach maturity and even become dominant “boss crocs” may live up to 70 years or longer.
Read on here if you want to find out more:
Gordon Grigg & Carl Gans: 40. Morphology & Physiology of the Crocodylia. Fauna of Australia: http://www.environment.gov.au/biodiversity/abrs/publications/fauna-of-australia/pubs/volume2a/40-fauna-2a-crocodylia-morphology.pdf
Kakadu National Park, Park Note, Crocodiles: http://www.environment.gov.au/parks/publications/kakadu/pubs/crocodile.pdf
NRETAS, Be CROCWISE, Living with Crocodiles: http://www.nretas.nt.gov.au/plants-and-animals/becrocwise/info
If you’re thinking about putting a boat in the water you definitely need to check out the following link as well:
Kakadu National Parl, Park Note, Fishing & Boating: http://environment.gov.au/parks/publications/kakadu/pubs/fishing.pdf