Crocodiles, Spiders and Leeches

By Bradshaw @conservbytes

I just wrote a fun little piece for a new section in the journal Frontiers in Ecology and the Environment that they’re calling Trails and Tribulations. The basic idea is that the author recounts a particularly interesting field-related experience through which an ecological concept is woven.

Editor-in-Chief Sue Silver said that I could reproduce my article here as long as I acknowledged Frontiers and the Ecological Society of America. It was fun to write, and I hope you enjoy it too [the PDF of the article is available free of charge here].

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“So does each team get a hand gun?”

“No, you get an oar”

“What good is an oar?”

“Listen, mate. When a 3-metre croc jumps out of the swamp at you, there is nothing more natural in the world than to thump him with a big stick. It’s an autonomous response. With a gun, IF you manage to keep it dry, and IF you manage to get it out in time before the croc bites off your head, chances are you’ll just shoot the bloke in front of you anyway. So you get an oar.”

“Fair enough”.

That is an approximate, paraphrased reproduction of the initial conversation I had with renowned Australian crocodile biologist, Grahame Webb, just prior to my first (and as it turns out, only) trip to collect crocodile eggs for his Darwin wildlife park and crocodile farm. I volunteered to take part in the collection because I had recently begun working with Grahame and his team tracking the world’s largest crocodile species – the saltwater or estuarine crocodile Crocodylus porosus – and modelling aspects of its populations (Bradshaw et al. 2006). Having already been out on several occasions to harpoon and satellite-tag animals (some measuring > 4 m) on the Mary River, and cage-trap others in Kakadu National Park, I thought a little egg collection would be a proverbial walk in the park. Little did I know that it would end up being one of my more memorable experiences.

Let me walk you through the process. First, you wait until the height of the wet season and drive out as far as you can toward the breeding swamp of interest (in this case, Melacca Swamp in the Adelaide River flood plain, about one hour’s drive from Darwin). Then you and two other loonies pile into a small helicopter equipped with landing pontoons which ferries you to one of many previously identified crocodile nests. Because there is usually too much vegetation around the nest itself, the helicopter must land about 100-300 m away. Clothed only in long pants, a long-sleeved shirt and cotton gloves to protect your skin from the slicing blade grass, you jump off the helicopter’s pontoons into impenetrably murky, chest-deep water. One of the team drags an esky (chiller box into which eggs will be placed) and another carries an oar. As the noise of the departing helicopter becomes a faint buzz, you suddenly realise via the rapid expansion of your terminal sphincter that you are in the middle of a crocodile-filled swamp – and you are holding an oar.

It gets better. After the initial wave of paralysing terror has passed, you must proceed toward your goal. And it is here one appreciates the second vital role of the oar – checking every prospective footfall for submerged surprises in the form of large, biting reptiles (remember, you cannot see the bottom). As I am sure the reader appreciates, this and the wading ensure slow progress toward the nest. The cutting blade grass quickly fades to irrelevance as finger-long leeches visibly slither just below the surface of the water toward your line of perambulating human flesh. The procession is only occasionally interrupted by the voice of the person behind you saying “hang on, mate”, and then the gentle brush of a hand across your back as a palm-sized spider is swept off you and into the adjacent vegetation. You continue to hone that once-vague feeling that humans were not meant to be in this place.

As you approach your prize – a circle of mounded vegetation 3 metres in diameter and surrounded by a carefully prepared moat – your progression slows and your vigilance rises. On more than one occasion the prodding oar head disturbs something large just ahead of you, and something unseen, but decidedly crocodilian, races ahead under the water’s surface leaving a trembling wake in its stead. Parting that final veil of blade grass reveals the nest, which I am told, often supports an angry, 3-meter, green mum just waiting for a bit of a dust-up. Thankfully during my outing, all visited nests had been recently vacated.

As one team member carefully uncovers the vegetation to locate the 70 or so glassy, white eggs, you assist by standing guard over the nest thief, oar in hand, ready for an attack launched from the surrounding moat (which you had just checked thoroughly before). Each egg is marked with a pencil to indicate its orientation, and then carefully placed in the esky on a matt of nest vegetation. It is a delicate process because misplaced eggs can rotate and cause the embryo to detach from the shell and die. After the eggs are retrieved, you make the long progression back to the helicopter drop-off site from where you are whisked off to the next nest. And then the next – all day long. On one particular occasion, the wade back to the pick-up site revealed the track of a large crocodile (much bigger than most females) that had followed us into the nest. We never did see him, and I think I am happier for it.

Having vicariously shared this experience with you, I turn now to explaining why my brief moment of ‘fun’ has some fairly serious implications. Any seasoned biologist will likely have analogous tales of danger, excitement and intrigue associated with the pursuit of precious and elusive data. This particular story differs only in that it was not specifically related to data collection per se; rather, it is a normal part of the commercial venture that is modern crocodile farming in Australia. Some might baulk at the concept, but such farming is most likely the reason that Crocodylus porosus persists today.

Like many large animals, Australian saltwater crocodiles were hunted to near extinction in the latter half of the 20th Century. Valued for their skins, intensive commercial hunting began in 1945 and quickly depleted populations throughout  northern Australia, until 1972 when an export ban was imposed and full legal protection established (Messel and Vorlicek 1986). Fortunately, C. porosus was recognised under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and listed in its Appendix II (Webb and Manolis 1993b). By 1979, the species was transferred to Appendix I (comprising the most endangered among CITES-listed species). Some subsequent recovery of north Australian populations was used successfully to argue for moving the species back to Appendix II (Webb et al. 1984, Webb et al. 1987). It is this listing, and the data collected to support it (see Webb and Manolis 1993a), that effectively removed the economic incentive to hunt wild crocodiles. A market saturated with skins of known and legal origin made any other form of harvest irrelevant (Webb 2001).

As a conservation ecologist, I find it intriguing that ways to slow biodiversity loss are sometimes, at least superficially, counter-intuitive. It also reminds us that our response to the biodiversity crisis must span more than the purely biological fields – economics, political science, energy technology, sociology, anthropology, psychology, geography and philosophy also play massively important roles (Sodhi and Ehrlich 2010). While I doubt that I will have another opportunity or desire to stress myself quite to that extent again merely out of academic interest, I consider myself fortunate to have had the opportunity to get up close and personal with the world’s largest reptile [addendum: and not in the way that a certain celebrity yob did].

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