Electrofishing Effort Required to Estimate Biotic Condition in Southern Idaho Rivers

Abstract

An important issue surrounding biomonitoring in large rivers is the minimum sampling effort required to collect an adequate number of fish for accurate and precise determinations of biotic condition. During the summer of 2002, we sampled 15 randomly selected large‐river sites in southern Idaho to evaluate the effects of sampling effort on an index of biotic integrity (IBI). Boat electrofishing was used to collect sample populations of fish in river reaches representing 40 and 100 times the mean channel width (MCW; wetted channel) at base flow. Minimum sampling effort was assessed by comparing the relation between reach length sampled and change in IBI score. Thirty‐two species of fish in the families Catostomidae, Centrarchidae, Cottidae, Cyprinidae, Ictaluridae, Percidae, and Salmonidae were collected. Of these, 12 alien species were collected at 80% (12 of 15) of the sample sites; alien species represented about 38% of all species (N = 32) collected during the study. A total of 60% (9 of 15) of the sample sites had poor IBI scores. A minimum reach length of about 36 times MCW was determined to be sufficient for collecting an adequate number of fish for estimating biotic condition based on an IBI score. For most sites, this equates to collecting 275 fish at a site. Results may be applicable to other semiarid, fifth‐order through seventh‐order rivers sampled during summer low‐flow conditions.

Site length for biological assessment of boatable rivers

“…Site-scale sampling design includes specifying the spatial scale over which the sample(s) will be collected (site length), the amount and types of habitats that will be sampled within that site, the field sampling methods to be used, the estimated number of person-hours (Reynolds et al, 2003;Flotemersch et al, 2006a;Hughes and Peck, 2008), and, sometimes, a minimum number of fish to be caught (Dußling et al, 2004;Hughes and Herlihy, 2007;Maret et al, 2007;USEPA, 2007).…”

“…With exceptions (e.g. Lyons et al, 2001;Cao et al, 2001;Hughes et al, 2002;Reynolds et al, 2003 and references cited therein;Flotemersch and Blocksom, 2005;Hughes and Herlihy, 2007;Maret et al, 2007;LaVigne et al, 2008aLaVigne et al, , 2008b, site length designations have been based on judgment, tradition, untested assumptions or the need to match some other aspect of sampling or management activities. The purpose of this paper is not intended to be an exhaustive review of the topic; rather, it is to provide an overview of different approaches that have been used for site length determination, and to help provide a technical foundation for improving future studies of sampling effort.…”

“…Opponents argue that using a fixed distance results in unequal sampling extents relative to river size, and typically results in greater variability regarding reference condition and relative level of effort (Hughes and Herlihy, 2007;Maret et al, 2007). If true, this would contribute to an increase in the variability attributable to the study design, thus, reducing the overall accuracy and precision of the data, and ultimately the usefulness of the data for detecting differences in condition.…”

“…Gammon, 1976;Penczak and Mann, 1993;Yoder and Smith, 1999;Cao et al, 2001;Lyons et al, 2001;Hughes et al, 2002;Dußling et al, 2004;Flotemersch and Blocksom, 2005;Hughes and Herlihy, 2007;Maret et al, 2007). Site lengths found suitable for sampling fish in rivers vary in length and approach (i.e.…”

Reliable sample sizes for estimating similarity among macroinvertebrate assemblages in tropical streams

“…On the other hand, smaller sample sizes are sufficient to estimate diversity using diversity or biotic indices (Lloyd et al, 1968;Magurran, 2004). For instance, Hughes and Herlihy (2007) and Maret et al (2007) found that the estimation of adequate scores for indices of biotic integrity (IBI) required less sampling effort than estimates of fish species richness.…”