Why does the hunter reveal Prof and Luc's location to Monsieur Tatagani in the novel, Threatened?

The hunter sells Prof and Luc the canoe that takes them into the jungle. When Luc, however, discovers that the Hunter has been hunting chimpanzees in the jungle even though it is illegal, he tells Prof, who catches the hunter and scares him off. To get his revenge, the Hunter tells Monsieur Tatagani where Luc and Prof are.