Assessment Methodology

Subwatershed Scale

The EBTJV initial assessment provides information on the status of brook trout populations in 17 states in the Appalachian region, an area that represents 70% of the native range of brook trout in the United States, and 25% of the brook trout's range across North America.  The assessment is based on the status of wild brook trout that occupy historical habitat in streams and rivers by subwatershed, and separately in lakes and ponds by subwatershed.  On average, a subwatershed has an area of approximately 20,000 acres, and they typically contain 25 to 75 miles of streams.  This report also identifies the principal threats identified by regional experts to the continued viability of brook trout populations on a state-by-state basis.

Population Status & Subwatershed Classification System

The assessment team collected existing electronic data on brook trout populations from state and federal agencies in 17 states.  The team then traveled to each state and met personally with fisheries biologists to review and classify each individual subwatershed.  The team used a consistent classification method based on the percentage of historically occupied habitat still maintaining self-reproducing populations of brook trout.  The historical range of brook trout in the Eastern United states was based on research published in 1969 by H.R. MacCrimmon and J.S. Campbell in the Journal f the Fisheries Research Board of Canada 26: 1699-1725.

In total, the assessment team evaluated 11,400 subwatersheds to determine the strength of brook trout populations.  Approximately half (5,563) of those subwatersheds historically supported brook trout.

Each subwatershed was classified as one of the following:

Threats Assessment

Fisheries biologists then used their expert knowledge to list the greatest local threats to wild, self-reproducing brook trout and their habitat.  Threats were categorized as high, medium or low.   A high threat signified the loss of one life cycle component for wild brook trout in that subwatershed, typically elimination of spawning or survival of juveniles.  A medium threat signified a population reduction but not elimination of a life cycle component.  A low threat signified an impact of concern but not currently at a threshold to eliminate a life cycle component or reduce the brook trout population.  Experts also classified threats as historical but no longer currently an impact where appropriate.  Zero, one or multiple threats may have occurred in each subwatershed.