ALMOST two rhinos a day are being poached in South Africa for their horns, which are worth more than their weight in gold.This surge in rhino killings has coincided with a rise in elephant poaching for ivory across the continent and reignited debate about whether or not the trade in the commodities these animals are being killed for should be opened up.The questions raised are not just ethical or ecological but also economic, and we are not talking small change.Take rhino horn, which now has a street value of $65,000 a kg, making it more valuable than gold, platinum or cocaine.Used to treat a range of ailments in China and southeast Asia, its demand has rocketed in tandem with the region’s blistering economic growth and appetite for other commodities.Trouble is, the sale of rhino horn is strictly banned under the Convention on International Trade in Endangered Species (CITES), the global treaty that governs trade in plants and animals.Almost 450 rhinos were poached in South Africa last year and at current rates, that number could reach 600 or more in 2012.