Evaluating Fish–Habitat Relationships for Refining Regional Indexes of Biotic Integrity: Development of a Tolerance Index of Habitat Degradation for Maryland Stream Fishes

Abstract

I present tolerance values of stream fishes to specific characteristics of habitat quality in an effort to refine mid-Atlantic regional indices of biotic integrity. Species presence and abundance data were examined within ranges of habitat quality variables to reveal normalized habitat tolerance characteristics for 54 species found in nontidal streams of Maryland. Development of a fish habitat tolerance index (FHTI) provided information on the overall susceptibility of individual species to habitat degradation. Designations of intolerant, moderately intolerant, and tolerant were assigned to all species individually and compared across three regional strata (Coastal Plain, Eastern Piedmont, Highlands). Family Cyprinidae (minnows) contributed the five most intolerant species. Omnivores and invertivores contributed the top 10% of species, showing general intolerance to declining habitat quality. Candidate fish habitat metrics derived from FHTI values were evaluated and compared with selected core metrics to assess the utility of the index for inclusion in the Maryland fish index of biotic integrity (IBI). Classification efficiency (CE) testing of approximately 12 candidate metrics revealed significant discrimination between IBI reference (minimally affected) and degraded stream site locations. Highest CEs among candidate fish habitat metrics were equivalent or higher than CEs obtained for metrics used in the current version of the Maryland fish IBI. Metric performance suggested that physical habitat tolerance indices have significant potential to improve accuracy and effectiveness of existing regional fish IBIs in the mid-Atlantic region.