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16 BIOLOGICAL REPoRT 19 Table 6. Proposed Index of Biotic Integrity metrics to describe the fish communities in the Minnesota River basin. Total number of native species. Number of darter species. Number of sunfish species. Number of sucker species (excluding white sucker) or number of minnow species (excluding common carp, creek chub, and fathead minnow) at sites <250 lan2 drainage area. Number of intolerant species. Proportion of individuals that are tolerant (white sucker, carp, fathead minnow, creek chub, and black bullhead). Proportion of individuals that are omnivores. Proportion of individuals that are specialized insectivores. Proportion of individuals that are top carnivores or number of top carnivore species at sites <500 lan2 drainage area. Catch per unit effort (time) by gear type. Proportion of individuals that are simple lithophils. Proportion of individuals with cleformities, eroded fins, lesions, and anomalies. Metric 1 Metric 2 Metric 3 Metric 4 Metric 5 Metric 6 Metric 7 Metric 8 Metric 9 Metric 10 Metric 11 Metric 12 conditions in the Minnesota River watershed (Ta- ble 6). Whenever changes were made, the original intent of Karr's metric was adhered to as much as possible. Metrics 6, 8, and 11 were modified for all stream sizes. Metrics 4 and 9 were changed for streams with small (<260 km2 and <520 km2, respectively) drainage areas because KalT's condi- tions did not exist in those streams. Development of Minnesota River mI scores re- quired compilation of a reference database indicat- ing the highest attainable fish community charac- teristics for the watershed. The reference database was compiled in a two-part process. The first part involved eXAmining historical information from 650 site collections conducted by Minnesota De- partment of Natural Resources, J. Underhill (Uni- versity of Minnesota), and K. Schmidt (private collector). The second part was composed of collec- tions made in 1990 at 45 sites considered to be least affected. For each site collection in the historical data- base, the number of individuals of each species collected, sampling gear used, drainage area of the watershed above the sampling site, and location of the sampling site were considered in determining if the site collection should be used for calculating mI metric expected values. Sites were excluded from the database if they were within 5 km of a much larger river or lake or were influenced by a dam or other obstruction. Because fish migrate from larger habitats into adjacent smaller habi- tats, sites close to a confluence may have fish community characteristics more representative of the larger stream or lake and would tend to elevate the maximum species richness line. Reference sites sampled in 1990 were selected based on available information and field recon- naissance. Land use, riparian cover, pool-riffle presence, avoidance of point source pollution dis- charge, and overall similarity with other streams in the area were considered in selecting sites. The 45 sites were distributed throughout the basin and covered a diversity of stream habitats, from small headwater streams to the mainstem of the Minne- sota River. These sites were considered to be some of the least-degraded stream segments in the wa- tershed. However, all sites had been modified from their natural conditions by extensive human ac- tivities. Fish were sampled using backpack, stream, or boom electrofishing equipment (Reynolds 1983), depending on stream size. All electrofishing equip- ment used adjustable, square-wave, pulsed DC cUITent. Pulse width, frequency, voltage, and am- perage were modified at each site to maximize efficiency for individual stream conditions. Flow, conductivity, dissolved oxygen, temperature, and QHEI measurements were made at each site. All captured fish were identified to species and exam- ined for external anomalies. Voucher specimens and fish of uncertain identity were preserved in 10010 formalin and submitted to the University of Minnesota.