By Yoshiyasu Shida and Deborah M. Todd TOKYO/SAN FRANCISCO (Reuters) – Yahoo Japan, the country's biggest online auction site, is rebuffing calls to end online ivory trading despite Yahoo Inc CEO Marissa Mayer's misgivings over facilitating a business blamed for the illegal slaughter of African elephants. Yahoo Japan doesn't accept that ivory sold on its platform – supposedly imported into Japan before a 1989 ban on international shipments – is a factor behind the sharp rise in poaching on the African savannah in recent years. Dismissing animal rights campaigners' concerns, even though the ivory business contributes a fraction of its sales, Yahoo Japan also argues that so long as no laws are broken people should be able to trade whatever they like on the internet.