Research showing that the species is endangered in other geographical areas would be the type of research that is most likely to result in a law that restricts hunting of that particular species. Endangered status typically prompts legal protections to help preserve the population and its habitat, and it often leads to stricter regulations on hunting and other activities that may threaten the species' survival.
While research showing an increase in the population might suggest that hunting could be permitted, research indicating the species is harmful might lead to different management strategies rather than restrictions. Additionally, research showing a decrease in the popularity of hunting could influence policy but wouldn't directly relate to the need for species protection.