I recently saw Riley Elliot, the shark scientist, speak at a conference.

He backed up his gnarly stories about being up close and personal with great whites by giving the crowd an explanation of what happens when you take out apex predators - such as sharks - from the ecosystem.

Essentially, when you mess with nature it disrupts the food chain and can have a negative impact on other species. The phenomenon is called a 'trophic cascade'.

Perhaps you have noticed while out snorkelling this summer, that there are a great deal of barren rocks around that are covered in sea urchins. This is because snapper - perhaps our most popular table fish, whose natural stocks have plummeted due to its fame - feed on kina.

Take the snapper out and the spiky eggs thrive, which in turn eat the seaweed and cause disruption for other fish stocks that feed on or live amongst the aquatic plants.

When diving at a marine reserve or a remote and healthy ecosystem, this is not the case as the nature is balanced.

Trophic cascades can easily cause havoc on nature, including disrupting the nutrient cycle and natural processes that maintain the quality of air water and soil. It usually happens when humans hunt big predator animals without realising the unintended consequences that their actions have.

But what I have found fascinating is that when you re-introduce animals, they can have a remarkable remediation effect. Check out the following video (which is great for kids to watch too), where the wolves that were brought back to the Yellowstone Park actually changed the course of the river by altering the numbers and behaviour of the deer.

We can even replicate the effects that animals have on ecosystems as a way of regenerating natural areas. I heard Bill Reed speak about a regeneration project in Santa Fe, New Mexico in the USA. He said that in white human settlers history, no water had ever been present on the site. By replicating the activites of beavers in building dams where the geology showed rich soil where water must have once been, they managed to permanently renew a running stream, which no doubt would have greatly increase the value of the land.

There is no doubt that introduced pests cause major problems for the land in New Zealand. But the last thing we want to do is introduce carnivores from overseas to bring down the deer, pig, possum and other populations. So perhaps we should employ the services of the ultimate predators on earth: humans.

My mate in Ruatoria on the East Cape tells me that the stories of his Ngati Porou ancestors hold that the rivers used to be very different. It is without doubt that introduced fauna would have contributed to this.

Perhaps we should be employing some of the people who might otherwise be on the dole in places like this, to replicate the actions of the Yellowstone wolves, control the pest population and feed people who are struggling?

I certainly think that for people who don't easily fit into normal employment that encouraging gangs of food hunters removing pest is better than young people joining criminal gangs. What do you think? Do you have any examples of trophic cascades you have witnessed or potential solutions? Please leave a comment below or email me.