2013 and 2015 data is taken from statistics from major production regions.
2011 and 2012 data is also not representative of total production due to the limitation of commercial shipments due to contamination from the Fukushima Nuclear Power Plant meltdown.
Data taken from Ministry of Agriculture, Forestry, and Fisheries report: http://www.maff.go.jp/j/tokei/sokuhou/syukaku_tya_syusan_15_2/
