A PRELIMINARY INDEX OF BIOLOGICAL INTEGRITY FOR FISH ASSEMBLAGES OF SMALL COLDWATER STREAMS IN VERMONT

An existing index of biotic integrity (IBI) for Vermont streams performed poorly in assessing coldwater streams with fewer than five species. A coldwater IBI (CWIBI) for these small streams was subsequently devised that effectively measures the integrity of fish assemblages containing two to four species. Fourteen candidate metrics were tested on eighteen least-disturbed stream sites and eleven degraded sites. Impacts to streams that were assessed included mostly physical habitat degradation with some experiencing acid mine drainage. Metrics were evaluated for sensitivity to impact and redundancy. Six were selected for final inclusion into the CWIBI. In composite, the metrics clearly reflected the widely observed shift from brook trout and slimy sculpin-dominated assemblages in least-degraded streams, to minnow-sucker based assemblages with increasing degradation.