Crocodiles- a conservation success story- Part II
Monday, November 16, 2009 10:45:52 PM
An important factor behind the successful sustainable-use conservation programme was the fact that crocodiles lacked charisma. They weigh hundreds of kilograms, are efficient and deadly carnivores, and have no qualms at all about predating on people. In short, nobody was going out into these river areas and trying to convince people that crocodiles were worth saving because they were so cute. In the end, the argument came down to, save crocodiles because they're worth money.
That meant we had to find ways to make crocodiles worth money to locals. The obvious component of this was leather. Crocodile leather is used to make a variety of luxury products, including very expensive Hermes bags.
But what happened next, nobody predicted. This is what makes this story so fascinating from a conservation perspective. Everybody got it wrong. Critics of this programme in the early 80s said it would lead to over-harvest and poaching. Advocates never predicted that a crocodile meat industry would evolve out of the leather industry. They did not predict that a tourism industry would emerge out of this. And they certainly didn't predict that crocodiles would attain an iconic status in the north, and win much wider acceptance by people.
What the programme was designed to do was mobilise economic forces behind conservation efforts. Unfortunately, the use of economic forces is something that is conspicuously neglected in conservation education programmes. I learned exactly one model that looked at this in my graduate ecology classes. This model was that of optimal extinction. Crudely put, this predicted that if a species population growth rate was less than the interest rate, harvesters would be impelled to wipe out the species and put the money in the bank. This is often the only formal model taught in most graduate conservation classes even today.
Crocodiles were believed to fit this model of optimal extinction well. They took until 25-30 years to reach maturity, and the population grew relatively slowly. So, unleashing any kind of harvest regime on crocodiles again, was predicted to lead to the catastrophic hunting of the 50s and 60s.
In fact, the opposite outcome was achieved. The reason is simply that the model of optimal extinction gets lots of things wrong. It assumes that harvesters are morons. This is done through the logistic population growth equation. The logistic functions takes the birth and mortality rate as fixed. And it takes carrying capacity of the habitat (how much wildlife can be supported) as fixed. In short, the opening assumption is that people are too thick to manage any of these parameters. Farming and ranching of crocodiles has already been ruled out as management option, as this will cause reproductive success to soar. And that can't happen according to this model.
There are a lot of other things wrong with it too. The model assumes your wildlife has no age or sex structure, so there's no point shifting harvests away from adults towards eggs and juveniles. There are some pretty dubious assumptions on the cost side as well.
At a biological level however, it is easy to see why crocodiles could be managed this way. Eggs have an extraordinarily high mortality rate (often by flooding). So removal of eggs has little impact on wild populations. Most would have died anyway. Shifting harvest away from a cohort with low mortality levels to high mortality levels kept harvest within ecological boundaries.
In order to get crocodiles eggs however, you need functioning and growing wild populations. Crocodiles also 'nest' according to female dominance. Dominant females go first. Aborigines already knew this. So, if you increase the area available for nest sites (say by fencing off areas from stock), then you got a fast payoff. The less dominant females would then have room to make their nests. More females would start nesting. Wild population growth rates start to take off.
This is basically what we observed. By making crocodiles valuable, human agents invested in management techniques to raise 'carrying capacity' and 'growth rate' constraints. This was a much stronger effect than the loss of eggs on the population.