TRAVERSE CITY, Mich. — For visitors to Isle Royale National Park, nothing beats the spine-tingling thrill of a wolf’s howl piercing an otherwise silent night — or a glimpse of the wily beast slipping across a forest path. But such experiences are becoming increasingly rare, and before long may disappear forever.

The gray wolf population has dropped steadily in recent years at Isle Royale, a rocky, heavily wooded archipelago in Lake Superior that is among the least visited national parks because of its remote location — a six-hour ferryboat ride from the Michigan mainland.