'Throw the life-vest, then swim the other way ...'

"C'mon, Aggro. Do your stuff …"

Aggro didn't seem particularly interested in the brace of pork chops dangled in front of his snout. Though he had cared enough to slither out of his comfortable mud on the side of the Adelaide River to join us.

"Remember, keep your hands inside," our skipper and guide, Steve, warned. At that point, with Aggro up very close and personal to the riverboat, we really didn't need the reminder. The crocodile might not be showing big interest in raw chops, but a couple of fingers or a hand might well have tempted him to an appetiser.

"Come on, Aggro," Steve called again, this time almost bouncing the tasty pork on the croc's nostrils. After a further investigation, swishing his tail to stay with us against the current, he made a rather half-hearted jump at the bait, but failed to win as it was whipped beyond him. Then he simply gave up and disappeared under the boat.

"OK, we'll go and see if one of the others is hungry," our guide said, unfazed at Aggro's lack of commitment. "His loss this time."

Later, we were given a number of jumping exhibitions as a couple of other crocodile residents on this stretch of the river proved both that they were interested in a tit-bit, and also that they had the jumping skills to get it. But truth to tell, it was really more interesting to watch the various specimens going about their normal, fairly lazy lives on the slippery banks or cruising on the water. Very quickly the instinctive fear dissipated, and they almost seemed friendly.

Though we all still did keep our hands inboard of the gunwhales ...

Steve knew each of the beasts by name, and pointed out individual characteristics. "That one has lost four inches of his tail, we call him Stumpy." Another had a lower tooth protruding through his upper jaw, having snapped too hard with his five-tonnes closing pressure on something — a pair of teasing pork chops? We came across Mary Jane, who was looking somewhat grumpy about the green praying mantis hitching a ride just back of one of her eyeballs. She sorted that with a quick submergence, then came back and gave Steve some relief by becoming the first to win the porky snacks off this particular tour.

Crocodiles have reputedly been around since before the dinosaurs, and despite having a brain only the size of a walnut they've managed to hang around ever since, seeing off into extinction many other species, including said dinos. But by around the 1970s in northern Australia they were themselves heading for the same fate, a species victim to massive hunting to satisfy a fad for expensive croc skin accessories. Reputedly down to about 3,000, a campaign by a husband and wife team of former hunters turned conservationists helped win them a protected status in 1970. Without any predators, it's now estimated that they number 100,000 plus in the Northern Territory, with maybe another 50,000 in other areas including Queensland.

"But we can't just let them keep multiplying," one woman on the boat suggested, reasonably enough.

"Well, they're protected," was the answer. "But about 80,000 eggs are removed from their nests every year." Since only one out of hundreds of eggs laid ever becomes a croc, that is likely to curtail numbers somewhat.

Still, each one of those new crocs has a fair chance of making their presence felt — they can live for typically in excess of 60-80 years. And they don't need much to keep them going. "About the equivalent of one chicken a week will do it," Steve says. When pressed on the makeup of that diet, he lists local fish like barramundi, small animals that stray to the river banks — dogs are particularly appreciated — and the occasional kite that miscalculates on a dive and lands in the water. "Their feathers aren't waxed, so they can't easily fly off again."

His inevitable addendum joke about 'the occasional tourist and local' adding variety to the crocs' food intake is recognised as just that, since he had told us in his initial briefing that 'more people are killed by sharks in Australia than by crocodiles' … the average is a little over one a year. That said, like sharks, crocodiles have evolved over millions of years to become almost perfect predators.

The same kites buzz the boat with their own performance as Steve throws scraps of pork rind into the air. Their flashing dives are all accurate as they catch the pieces in the air. None of them reach the water.

On the way back downriver there was a sudden thump and judder, and Steve cut the engine. For a few moments we drifted, then the engine restarted and we continued on our way. "A bit of floating log, under the surface …"

But for just those moments, I probably wasn't the only one on board who wondered would we have to take Steve's advice in his briefing, about the life-vests stowed under everyone's seat?

"There's one for everybody," he'd noted. "But crocs are attracted to bright colours, and they're bright red. So, maybe the best thing to do in an emergency would be to throw the life-vest in one direction as a decoy and then swim as hard as you can for the bank in the opposite direction …"

That might even have properly piqued Aggro's interest.