Conservationists at an international wildlife meeting in South Africa say poaching syndicates moved large shipments of elephant ivory in 2015, despite increasing calls to dismantle trafficking networks that often collude with government officials.

A document released by conference organizers on Saturday says the illegal ivory trade "has remained fairly constant at unacceptably high levels" since 2010.

Tom Milliken, a report co-author, estimates that there are about 50 ivory seizures of more than half a ton, and sometimes as many as four tons, every year. Milliken says such big shipments are a sign that organized crime groups are involved in poaching.

The meeting of member nations of the Convention on International Trade in Endangered Species of Wild Fauna and Flora, or CITES, started Saturday.