Regional frameworks and candidate metrics for assessing biotic integrity in mid-atlantic highland streams

Regionally stratified biological criteria are being used increasingly to assess stream quality. We used multivariate analysis of variance and canonical analysis to examine the utility of two regional frameworks (basins and ecoregions) and 14 candidate metrics of local fish assemblages for assessing the biotic integrity of streams in the mid-Atlantic highlands (montane areas from Pennsylvania to Virginia). In particular, we determined (1) how metrics varied naturally among basins and ecoregions and (2) which metrics varied most consistently with site quality. We also examined the ability of preliminary multimetric indices (MMIs) to distinguish site quality. Metrics varied meaningfully among both basins and ecoregions, but most metrics differed more among basins. The basin effect was especially strong for taxonomic metrics (e.g., number of species [TOTSP]), which reflected the influence of zoogeography on fish community composition. Few metrics differed strongly among both basins and ecoregions. Collectively, metrics distinguished among high-, medium-, and low-quality sites within most regions, but the discriminative ability of individual metrics differed by region. The number of darter or sculpin species (DOSSP) was the only metric related to site quality both in most basins and most ecoregions. Metric differences among site-quality classes were more consistent with a priori expectations within basins than within ecoregions. In each of five regions, we built an MMI from the most discriminative metrics. Only DOSSP and the proportional abundance of tolerants were included in all five MMIs, All MMIs included taxonomic and reproductive (e.g., proportional abundance of simple lithophils, excluding tolerants) metrics, but not all included trophic metrics (e.g., proportional abundance of invertivores). Multimetric indices distinguished between high- and low-quality sites in each region tested, but they usually did not do so to a greater degree than did taxonomic metrics alone. Among the metrics included in MMIs, TOTSP was most consistently related to site quality. Our findings indicate that both basins and ecoregions provide useful frameworks for regionalizing biotic assessments based on fishes and that metric utility may vary considerably among regions even when regions are environmentally similar. To enhance MMI performance, we encourage an increased reliance on region-specific empirical relations in the development of metrics and scoring criteria.