If it attacks and kills sentient beings, it's basically a declaration of war and should be treated equally.
At Omicron Theta at least, the beast appeared to eat the whole planet - the few colonists might have been an irrelevant and essentially unnoticed smidgen of biomass. The same appears to go for the planet where Riker lost his sweetheart. We don't know the full story of the other targets Marr speaks about, but we do know that at least one target was a spacecraft whose only biomass was that of her crew. Nothing about that should indicate the CE knows about the concept of sapience, though. Biomass is biomass.
Doesn't mean we couldn't declare war on the CE species. We declare wars on wolves and sharks, after all. Although we still prevaricate on whether to declare one on mosquitoes.
In practice, though, combat shields protect humanoid sapience. So "feeding 'em antelopes" could be achieved by letting whole planets die around the humanoid colonies. Living planets are a dime in a dozen in Star Trek, after all, and the CE species hasn't endangered the supply yet. But ecological management would call for at least some data, regardless of whether it takes the form of declaring war or dishing out Danegeld.
Timo Saloniemi