Comparability of a regional and state survey: effects on fish IBI assessment for West Virginia,U.S.A.

Probability-based survey designs are now being investigated to allow condition to be assessed for a discrete population of watershed management units and to infer probability of impairment to other unsampled watersheds. Results can be used to focus further monitoring and restoration efforts. Fish community data and index of biotic integrity (IBI) development were compared between the 1993 and 1998 Environmental Monitoring and Assessment Program Mid-Atlantic Integrated Assessment (EMAP-MAIA) survey and a West Virginia Regional EMAP (WV REMAP) survey conducted in 2001–2002. Both designs were based on probability surveys, but the EMAP design treated streams as a continuous linear network comprising an infinite population of points, while the REMAP design used a discrete set of watershed outlets as defined by 12-digit Hydrologic Cataloging Units (HUC12) as the sample population. The comparability of the watershed-based WV REMAP survey design results with the linear network-based EMAP-MAIA survey results for West Virginia was affected by the different size range of watershed areas included in each target population. Once similar watershed area ranges were considered by narrowing the size range included in the West Virginia EMAP-MAIA data set, virtually identical cumulative distribution functions for fish IBI scores were obtained. The reduced variability in reference conditions obtained by applying a restricted range of watershed areas allowed us to detect and correct for ecoregional differences in fish IBI metrics and scores, after excluding the biogeographically distinct Potomac River drainage basin located in the Central Appalachian Ridge and Valley Ecoregion. Handling editor: K. Martens