Kakadu’s Estuarine Crocodiles

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Kakadu’s Estuarine Crocodiles

March 12th, 2012 by Anja

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!

Estuarine Crocodile (Crocodylus porosus)

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.

“Saltie” in Freshwater Billabong

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.

Painting by Thommo Nganjmirra

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!

Cahills Crossing – Spot the Croc!

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.

Sunbaking

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.

Lurking

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.

Be Crocwise!

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

Bobo!
Anja

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Jim Jim Falls with a Twist

June 10th, 2011 by Anja

The news came through only minutes ago:
Jim Jim Falls will open to the public tomorrow morning,
Saturday, 11 June 2011!

Garnamarr campground will open for business tonight, the gate at the start of the 4WD track will be unlocked at 06:30 tomorrow morning. Yay!

These are the good news – but there is a little twist to the story…

Twin Falls will remain closed for a little while longer as will the Jim Jim day use area and our beautiful morning tea spot at Budjmi lookout.
Work is still continuing to fix the washouts along the way to Twin Falls.

We have also been advised that there won’t be any swimming below
Jim Jim Falls until further notice as rangers have spotted a 2m crocodile in the plunge pool. Park staff have spent the last few days and nights in the gorge on the lookout for crocodiles, conducting their final surveys.

At this point we haven’t been given a great deal of information but our guess is that the crocodile they spotted in the deep pool right under the waterfall is one of the resident (and generally harmless) Freshwater crocodiles – otherwise they wouldn’t grant us access to the gorge at all).

Freshies usually hang out in the creek and the beach pool where there are lots of places to hide from people. However, this one made it into the plunge pool, where, if disturbed or even cornered, it may become aggressive in a bid to defend itself.
Rangers are monitoring the situation as they are concerned about the potential risk to swimmers if the crocodile stays put.

While there’s no opportunity for a swim at the bottom of the falls, there will be on top of the escarpment. Yay!

Barrk Malam Walk

The Barrk Malam walk will definitely be an experience you won’t forget in a hurry, featuring shady monsoonal rainforests, rugged sandstone formations, endemic flora and fauna, awesome views from the edge of the Arnhemland Plateau — and much more.

However, it s not a leisurely stroll in the park, it is actually quite strenuous! This 6km return walk is rated difficult and the initial ascend will get your heart rate started. Once on top of the plateau you’ll have time to catch your breath again.

To tackle this walk you definitely need to be fit and willing to get a bit sweaty. As sitting it out at the bottom of the falls is really not an option, please only book this tour if this sounds like you!

As an alternative, we will continue to offer our Kakadu’s Early Dry for another week or two. Until we’re able to access Budjmi and Twin Falls, we will also be available for touring the southern part of Kakadu. Gunlom’s looking great and so are Motor Car Falls and Ikoymarrwa!

Watch this space for further updates…

Bobo!
Anja

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Volunteering at Yellow Water

May 29th, 2011 by Anja

You know it’s Yegge (cool weather time) when the locals complain about the cold, get their flannelette shirts out and start rummaging for the moisturiser to treat their cracked heels.
You know it’s the dry season when the NT News runs a story titled
“Rare hypothermia case in NT cold snap” after a Darwin woman took herself to Royal Darwin Hospital to be diagnosed with cold feet…

Overnight temperatures have been dropping below 20 degrees lately.
The nights are starry, clear and pleasant – before it gets chilly, not unexpectedly but rather rapidly, just before sunrise. Anyway, it really is worth getting up early to watch the mist rise over Kakadu’s billabongs and floodplains as the sun warms up the country once again.

And to avoid hypothermia I can thoroughly recommend physical work!
We certainly weren’t feeling the cold last week when we were out and about with the Jim Jim district rangers (although our motivation for getting up early and heading down to the ranger station was a different one).

It’s a very busy time of year for park rangers. With flood waters receding and the country slowly drying up they can finally access those destinations that visitors are coming to see here in Kakadu National Park.

Yellow Water in the Wet Season

District staff are doing what they can to prepare visitor sites for public access. Among a lot of other ongoing tasks they’re currently cleaning campgrounds and day use areas, re-installing infrastructure, clearing 4WD and walking tracks, conducting crocodile surveys, patch burning to ‘clean the country’ and protect facilities from hot fires later in the year.

This year, for the first time, we have been given the opportunity to do our bit and help out. Traditional Owners and park managers have extended their invitation to tourism operators and guides to volunteer and help park staff with some of the enormous tasks they’re facing.

Last week Jeanne, John and I helped Jim Jim district rangers Anthony, Jason and Dennis with their clean up at Yellow Water.
In the wet season the whole area, including the car park, the boardwalk and viewing platform and a walking track to Home Billabong get flooded. The other day we found the boardwalk completely overgrown by a green mess of native Hymenachne grass.

Image Courtesy Kakadu National Park

Armed with buckets, rags and scourers we got stuck into it, always keeping an eye out for Estuarine crocodiles and prepared for other wildlife encounters as well. After a full day’s work only about one third of the boardwalk was freed of the buffalo grass.
But let me tell you, we felt immensely proud of our achievement!

Image Courtesy Kakadu National Park

A few days earlier Jeanne and John had already put a few hours in at Garnamarr campground and also on the 4WD track into the Jim Jim Falls and Twin Falls area, where the rangers have since placed the crocodile traps and commenced their crocodile surveys. They will have to remove at least three rather large Estuarine crocodiles from the precinct before it will be safe for us to visit.

A big ‘Thank You’ goes to Jessie Alderson and Jeffrey Lee for allowing us to help looking after their country. We would also like to thank Kathy Wilson and all her staff at Jim Jim Ranger Station for making us feel so welcome.

Giving us the chance to gain an insight into the work of park rangers, getting to know the guys we share our workplace with and to experience this stunning environment from a different perspective is much appreciated!

We’ll definitely be back for more in the coming weeks!

Bobo!
Anja

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Crocodile Management in Kakadu National Park

March 27th, 2009 by Anja

Kakadu National Park is home to both species of Australian crocodile.

There is the relatively small and rather timid Freshwater Crocodile (Crocodylus johnstoni) which is generally considered harmless to humans. “Freshies” thrive on a diet of insects, frogs, fish, crustaceans, generally small stuff they can get down their narrow throat, and are usually found in the upper regions of tidal rivers, billabongs and creeks, right up into the stone country.
Attacks on humans are rare and usually only occur when these shy animals are provoked by those rather inconsiderate individuals who feel the need to crowd or annoy them.

The other crocodilian calling Australia home is the infamous Estuarine or Saltwater Crocodile (Crocodylus porosus).
While you would expect “Salties” to inhabit the coastlines, mangrove mud-flats and tidal sections of rivers of tropical Australia, as their name suggests, they can also be found in freshwater billabongs and wetlands and all the way up in the headwaters of our freshwater streams — and sometimes even in the plunge pools under Kakadu’s waterfalls.

Make no mistake!

Estuarine Crocodile

Expect to come across this cunning stalker in any body of water connected with the tidal rivers of Australia’s tropical north, whether permanently or only temporarily during wet season flooding. And only because you can’t see them while you’re fishing — with the water of the East Alligator River up to your knees at Cahill’s Crossing — doesn’t mean there aren’t any!

Right now you’re probably wondering why we’re asking you to bring your bathers on tour — and I’ve probably got some explaining to do…
Rest assured, if there was only the slightest risk of a hungry saltie lurking in the shallows, we wouldn’t be allowed anywhere near the water!

One of the reasons why we can’t predict in March when Top End Explorer Tours will actually be able to visit Gunlom and Maguk in the early dry season and Jim Jim Falls and Twin Falls hopefully following soon after is that we have to wait for the completion of the mandatory crocodile surveys in the dedicated crocodile management zones.

Kakadu National Park staff involved in crocdile management take their job very seriously. And it’s a good thing they’re taking their time with it!

Crocodile management in Kakadu serves two purposes. While it is aimed at minimising the risk of crocodile attacks on humans, it is also supposed to ensure the protection of crocodile populations at the same time.

Crocodile Warning

To start with, rangers might visit the sites by helicopter, even before they have road access after a wet season that usually leaves the 4WD tracks with bad washouts and in need of repair. Crocodiles can easily be spotted in the clear water of the creeks and plunge pools from the air. It gives the rangers an idea of how many Estuarine crocodiles (or “Ginga”, as they’re called in the local Aboriginal languages) have made the journey up the swollen rivers during the wet season and how many Freshwater crocodiles have remained in their habitat.

Once the roads have been fixed, large baited traps will be brought in and positioned. The bait, usually a pigs leg, is attached to the trap door via a rope. When a croc swims in and takes the bait — bingo!
It will then be removed and taken either to a crocodile farm in Darwin or to one of the local communities as a food source.

Rangers use large spotlights during night time surveys to detect the reflective pairs of eyes of crocs that have been avoiding the traps.
They also regularly check the banks for slide marks and fresh tracks, they’re on the lookout for floating carcasses and they also use their noses:
Salties sport a very fishy, pungent smell from a gland on the back their necks — a dead giveaway!

These checks usually take several weeks and only when the final surveys return no indication at all of Ginga in the area, travellers will be allowed to visit Kakadu’s beautiful waterfalls.

Don’t expect to see any official stamps of approval reading “guaranteed crocodile free swimming spot”! There are reasons why these days we’re not permitted to swim up Twin Falls gorge anymore and we stay away from the water’s edge at the Jim Jim Creek crossing.
But salties aren’t any good at rock climbing and therefore we know quite a few swimming spots they won’t conquer!

A lot more is to be said about Kakadu’s crocs, so watch this space!
In the meantime, we’d love to read your comments!

Bobo!
Anja

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