Congressional direction is federal law.
For planning purposes, a viable population is regarded as one which has the estimated numbers and distribution of reproductive individuals to ensure its continued existence is well distributed in the planning area. In order to insure that viable populations will be maintained, habitat must be provided to support at least a minimum number of reproductive individuals, and that habitat must be well distributed so those individuals can interact with others in the planning area. These species are selected because their populations changes are believed to indicate the effects of management activities. Species with special habitat needs that may be influenced significantly by planned management programs. Species commonly hunted, fished or trapped.