Development and Testing of a Fish-based IBI to Quantify the Health of Grassland Streams in Alberta, 2006


Cameron Stevens, Garry Scrimgeour, William Tonn, Cynthia Paszkowski, Michael Sullivan and Scott Millar


We developed a fish-based index of biological integrity (IBI) to aid resource managers with assessing the health of grassland streams in Alberta. The IBI consisted of five metrics reflecting structural and functional attributes of a fish assemblage comprising only five species. With the aid of a simple spreadsheet, formulas provided within this report, and information on stream size, land managers and researchers in east-central Alberta can quickly calculate stream IBI scores using data collected on their fish assemblages. The IBI may be a valuable tool for resource management when it is used to compare biotic integrity among sites, and for making regional assessments of stream health. In our study, scores approaching a perfect score of 50 would suggest highquality conditions appropriate for maintaining biological integrity. High-quality sites (i.e., IBI scores > 30) include a relatively high proportion of older fish, high numbers of ≥1 yr fathead minnow, the presence of white sucker but low numbers of young-of-year, and a relatively low proportion of fish with disease and deformities. Below a disturbance threshold however, the environmental conditions and streamside activities are no longer capable of supporting systems displaying biological integrity. For example, low-quality sites (i.e., IBI scores < 20) in streams may be linked to human disturbance, particularly activities contributing to phosphorus inputs. However, we acknowledge uncertainty in correctly identifying healthy versus unhealthy conditions for sites with mid-range IBI scores (i.e., 20-30), and recommend that resource managers, whenever possible, incorporate data on other biota and the physical and chemical attributes of a site.

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