JOHANNESBURG – Africa’s elephant population is decreasing dramatically due to poaching, plunging by more than 140,000 between 2007 and 2014, according to a study published Wednesday.

The Great Elephant Census carried out by scientists and conservationists, which was published in the journal PeerJ, is the widest such survey so far.

It estimated the population of savannah elephants in 18 countries at 352,271.

Africa may have held more than 20 million elephants prior to European colonization, and 1 million as recently as the 1970s, according to the survey.

Elephant populations have decreased due to habitat loss and fragmentation, conflict with humans, and isolation of populations, but the main reason currently is poaching.

A renewed outbreak of poaching beginning in 2005 has led to the deaths of an estimated 30,000 elephants a year, according to figures quoted by the survey.

African elephant populations are currently shrinking by 8 percent annually.

The largest population among the countries surveyed was in Botswana, which held 37 percent of the overall total. Zimbabwe accounted for 23 percent and Tanzania 12 percent.

Carcass ratios, which indicate a declining population, were the highest in Cameroon, Mozambique, Angola and Tanzania.

The primary sources for ivory were Mozambique, Tanzania and Congo.

Poaching could lead to the extinction of elephants in countries with small and isolated populations, such as Mali, Chad and Cameroon, according to the survey.