Citation:

Flotemersch, J E. AND K A. Blocksom. ELECTROFISHING IN BOATABLE RIVERS: DOES SAMPLING DESIGN AFFECT BIOASSESSMENT METRICS? ENVIRONMENTAL MONITORING AND ASSESSMENT 102(1-3):263-283, (2005).

Impact/Purpose:

The goal of this research is to develop methods and indicators that are useful for evaluating the condition of aquatic communities, for assessing the restoration of aquatic communities in response to mitigation and best management practices, and for determining the exposure of aquatic communities to different classes of stressors (i.e., pesticides, sedimentation, habitat alteration).

Description:

The accurate bioassessment of boatable rivers using fish assemblage data requires that a representative sample of the assemblage be collected. In this study, data were collected using an electrofishing design that permitted comparisons of the effects of designs and distances on fish assemblage metrics. These fish and habitat data were collected from 60 boatable sites distributed among four rivers within the Ohio River Basin. Sites were classified a priori as either Run-of-the-River (ROR) or Restricted Flow (RF). At each site, one bank was electrofished to a distance of 40 times the wetted width, up to a maximum distance of 2000 m, and the opposite bank was electrofished to a distance of 1000 m. Fish were processed at up to 14 points during data collection. Data representing four different design options (i.e., 1000 and 2000 m for both single and paired banks) were extracted from the dataset and analyzed. A principle components analysis on physical habitat variables showed that depth was the most important variable in separating ROR and RF sites. Friedman tests comparing metric values among the four designs detected significant differences for all richness metrics at both types of sites and for catch per unit effort and percent tolerant species at ROR sites. Richness metrics were generally higher for the two 2000-m designs than for the two 1000-m designs. When plotted against cumulative electrofishing distance, the percent change in metrics declined sharply within approximately 1000 m, after which metrics usually varied by less than 10 percent. These data demonstrate that designs electrofishing 1000 m of shoreline are sufficient for bioassessments on boatable rivers similar to those in this study, regardless of whether the shoreline is along a single bank or distributed equally among paired banks. However, at sites with depths > 4 m, it may be advisable to employ nighttime electrofishing or increase day electrofishing designs to 2000 m.

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