African elephants were listed as Vulnerable species by the International Union for Conservation of Nature (IUCN) in 2008, with no independent assessment of the conservation status of the two forms. In 1979, Africa had an estimated minimum population of 1.3 million elephants, with a possible upper limit of 3.0 million. By 1989, the population was estimated to be 609,000; with 277,000 in Central Africa, 110,000 in East Africa, 204,000 in southern Africa, and 19,000 in West Africa. About 214,000 elephants were estimated to live in the rainforests, fewer than had previously been thought. From 1977 to 1989, elephant populations declined by 74% in East Africa. After 1987, losses in elephant numbers accelerated, and savannah populations from Cameroon to Somalia experienced a decline of 80%. African forest elephants had a total loss of 43%. Population trends in southern Africa were mixed, with anecdotal reports of losses in Zambia, Mozambique and Angola while populations grew in Botswana and Zimbabwe and were stable in South Africa. Conversely, studies in 2005 and 2007 found populations in eastern and southern Africa were increasing by an average annual rate of 4.0%. Due to the vast areas involved, assessing the total African elephant population remains difficult and involves an element of guesswork. The IUCN estimates a total of around 440,000 individuals for 2012.
Question: How many years was the time span where elephant populations declined by 74% in East Africa?
Answer: 12