During the early medieval age, the population of trolls is declining. These are savage creatures who aren't as cunning as humans, and not only are we part of their diet, humans are in fact their only source of food.
An adult troll is about ten times as large as a mature human but half as agile. They use their sensitive noses to track and swallow humans whole. They usually reside in mountains and are nocturnal animals; when night falls, they are often sighted terrorizing villagers.
However, things change when humans launch a worldwide campaign to exterminate the trolls, and within a period of two decades their numbers have fallen to around a couple hundreds. The reason for their rapid decline is due to stress: humans erect tall fences to keep them at bay, but since the trolls can't eat anything else, they are starved to death. Many people have become concerned about the imbalance their disappearance could place on the ecosystem. They have also begun to wonder if these once terrifying creatures also have the right to live.
How can we preserve this now-endangered species? They are not scavengers, meaning they prefer to chase food.
Acceptable answer should touch on how the remaining trolls can flourish and co-exist with human and yet at the same time their diet stays the same.