You are here:
THE EFFECT OF VARYING ELECTROFISHING DESIGNS AND DISTANCES ON METRIC SCORES IN LARGE RIVERS
Citation:
Flotemersch, J E. AND K A. Blocksom. THE EFFECT OF VARYING ELECTROFISHING DESIGNS AND DISTANCES ON METRIC SCORES IN LARGE RIVERS. Presented at Mid-Atlantic Water Pollution Biology Workshop, Berkeley Springs, WV, March 28-29, 2002.
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:
To study the effects of electrofishing design and distance on metric scores, we electrofished almost 180 km across four rivers of the Ohio River basin and collected data on more than 28,000 fish. We compared three electrofishing designs using four fish assemblage composition metrics, three richness metrics, and catch-per-unit-effort (CPUE). Sites were first separated into deep (> 4 m) and shallow (< 4 m) groups based on principle component analysis of physical habitat data. None of the percentage metrics varied significantly among the designs. However, values for most richness metrics were significantly higher for designs sampling a larger distance. To better understand these changes, we plotted the percent change in each metric with electrofishing distances. A sharp decline and leveling off of richness values occurred after electrofishing along a single bank at approximately 1000 m in shallow sites. At deep sites, metric values leveled off at approximately 1200 m but were erratic; this was likely the result of the diel movements of fish. We used the same eight metrics to compare a 1000-m single-bank design with a 500-m paired-bank design. CPUE was statistically higher for the paired-bank design for both depth groups. At shallow sites, the difference in number of taxa was marginally significant, with the single-bank design collecting one additional species. We concluded that a 500-m paired-bank design is effective and efficient for characterizing fish assemblages at the shallow sites. At deep sites, night electrofishing may be required to produce satisfactory data. If night electrofishing is not feasible, we suggest increasing the electrofishing distance at these sites to a 1000-m paired-banks design or a 2000-m single-bank design and the cautious use of metrics based on fish prone to diel movements. These results apply for these size rivers in this region, but could likely be applied elsewhere in the absence of similar research.