What is a threat to 60% of the u. s. wildlife refuges?

The correct answer is too much hunting and fishing and non native species invade the sanctuary of the wild animals.

Wildlife Refuges are considered to be sanctuaries for wild life animals to be away from predation, hunting and competition as well. These sanctuaries are serves as protection to these animals. These sanctuaries may be an island, a forest or a safe place for wildlife to dwell on.

What was the length to begin with?