Poaching rhino horn escalated in the 21st century, with 949 rhinos killed in Kruger in the first 12 years, and more than 520 in 2013 alone. A memorandum of agreement is seen as a necessary milestone in stemming the tide between South Africa and Vietnam, in addition to the one with China, while negotiations have not yet started with Thailand. The amount of rhino horn held in storage is not publicly known. Since 2009, some Kruger rhinos have been fitted with invisible tracing devices in their bodies and horns which enable officials to locate their carcasses and to track the smuggled horns by satellite. South Africa's 22,000 white and black rhinos represent some 93% of these species' world population, 12,000 of which are found in Kruger.