JOHANNESBURG (AP) — Hippos, malaria and capsized canoes were among the hazards for National Geographic researchers paddling along an Angolan river that had been barely studied. On a separate survey in Angola, a conservationist drove on remote tracks where wrecked tanks and other remnants of decades of civil war are still visible.

"The ghosts of war are still there in the landscape," Seamus Maclennan, a member of the New York-based Panthera group, wrote in an email. "Tanks and shrapnel from 30 years ago are still strewn across marambas (wide river valleys) in some places. Gutted buildings pockm...