For three decades, Phil Mather has harvested olives from feral trees around South Australia. Mather, a landscape gardener, began hand-picking the fruit and pressing it into oil in his early 20s.
It’s a seasonal pastime that has turned into a business in the past eight years. “This year I have produced over 1,500 litres, which entails nearly nine tonnes of wild fruit and [olives from] relinquished groves,” he says. Now 51, he sells most of his oil locally, at the Willunga farmers’ market and through retailers in Adelaide.
“Priority one is to make a high-end oil. The second is to stop the spread of the olives throughout the environment. They’re the two major things that really drive me to keep going, because it’s a very labour-intensive endeavour.
“Usually a wild tree produces a lower percentage of oil per kilo.”
He gets about 70 litres of oil from one tonne of picked wild olives – less than a third of the oil that fruit from a cultivated olive tree might yield.
Many of the feral olives around Adelaide originate from trees planted in the mid-19th century. Drought-tolerant and well adapted to the local climate, European olives grow well in Australia, where there is a thriving commercial industry. But birds and other animals that disperse their seeds have contributed to uncontrolled spread, and wild-growing European olive trees are considered a major plant pest and a significant bushfire hazard.
Mather’s Wild Harvest Olive Oil is one of a growing number of businesses that have turned invasive species into commercial products. In Melbourne, Edible Weeds runs foraging walks and cooking events for introduced weeds including mallow, clover and wild radish.
Wild boar – feral pigs, as they are less palatably known – have been culled and exported for many years, but are now also a staple of some local restaurants, served braised or in lasagne. Uni Boom Boom, a restaurant in Melbourne’s south-east, specialises in sea urchin. Although the spiny sea urchin is native to Australian waters, it has become a marine pest, causing extensive destruction to kelp forests.
These enterprises serve up some food for thought: one way to manage invasive species could be to eat the problem.
Invasivorism: environmentally friendly diet or feel-good distraction?
The idea of eating invasive species – invasivorism – as a means of controlling pests has become popular in the past decade. The rationale is that in the same way humans eat certain native animal species to extinction, perhaps they could do the same for pests.
Dr Jennifer Atchison, a senior lecturer at the University of Wollongong’s school of geography and sustainable communities, says: “The move to enterprise-based thinking about invasive species is part of a recognition that management of invasive species involves killing, and therefore that killing has both moral and ethical dilemmas.
“Part of the rationale behind using invasive species in some way, either as food or for other kinds of things like fertiliser, acknowledges that people reject this idea of ‘kill to waste’.”
But Atchison says that despite good intentions, commercialising invasive species may also distract from broader issues such as land clearing or lack funding for environmental programs.
“These [invasive] species are far too numerous and far too widespread for any kinds of enterprises to have significant environmental benefits over the landscape,” she says. “If there are any benefits … for the environment they’re likely to be quite localised.”
Australia’s pest animal strategy recognises that pest management requires a variety of control techniques, “including commercial use where appropriate”. Some animals, such as rabbits and foxes, are so well established there is virtually “no prospect of eradication”.
Ken Lang of Yarra Valley Game Meats, who has been farming deer for 35 years, increasingly sources wild-shot venison and other game meats including rabbit, camel and wild boar.
“The animals shouldn’t be here [in Australia] for a start – they never should have been released,” he says.
The venison comes from processing facilities in South Australia and Victoria, where shooters can bring feral deer carcasses to be processed according to regulated standards.
Business has been steady even throughout the Covid-19 pandemic, but even so Lang concedes the demand for invasive animal meats for human consumption “is nowhere near” enough to reduce their populations.
Tim Low, co-founder of the Invasive Species Council, says one risk of edible pests is that they can create economic incentives for the survival of invasive species.
In the US, for example, bounty programs that reward people for killing feral pigs have not helped eradicate the animals: one study even found that wild pig populations increased while a bounty was in place.
“You don’t want a situation where a company becomes reliant on a supply of feral animals,” Low says.
“Once you kill [some of that] group of animals, the rest of them are sneakier, they’re harder to get, so it’s economically less appealing. You get a less of return on your efforts going after them.”
I don’t have to look after the carp – the Murray-Darling basin looks after the carp all by itself
Dr Ben Hoffmann, an invasive species ecologist at the CSIRO, says: “The science has shown that we don’t embark on ventures like this in the anticipation that you’re going to reduce the species.
“Getting rid of invasive species from the environment takes really targeted strategic actions … if that’s even possible at all.” But that doesn’t necessarily make edible pests problematic, he says.
Carp mince: ‘I’ve got converts all the time’
Tracy Hill and her husband own Coorong Wild Seafood in Meningie, South Australia, and turned to fishing common carp when populations of other fish, such as golden perch and yellow-eye mullet, became more difficult to catch.
They produce carp mince and fillets, the texture of which Hill describes as “between soft chicken thigh and tofu”.
“The mince itself behaves like chicken meat – you can brown it,” Hill says. “People … equate invasive or pest species with bad-tasting. I’ve got converts all the time who come and taste it and then they start buying it on a regular basis.”
The company operates at a scale of several tonnes of carp a month, supplying a few South Australian restaurants, and hopes to double or triple the volume.
“There’s no reason why we couldn’t have carp being sold in Woolworths as fillets,” says Hoffmann.
“Do we want to see a sustainable carp industry? No, we want to get rid of them. [But] we’ve never heard of carp being fished to extinction in the Murray River – it’s just not going to happen.”
Hanging over Hill’s business is the controversial plan to release a herpes virus to kill carp in the Murray-Darling.
“No one wants to look at [carp] harvesting as an option because of a perceived possibility that the fishermen may look after them,” she says.
Financially that argument doesn’t hold water, because native fish species are far more commercially profitable.
“I don’t have to look after the carp – the Murray-Darling basin looks after the carp all by itself,” she says. “We’re just offering a potential part solution to the problem.”