Mesh-size effects on drift sample composition as determined with a triple net sampler

Abstract

Nested nets of three different mesh apertures were used to study mesh-size effects on drift collected in a small mountain stream. The innermost, middle, and outermost nets had, respectively, 425 pm, 209 pm and 106 pm openings, a design that reduced clogging while partitioning collections into three size groups. The open area of mesh in each net, from largest to smallest mesh opening, was 3.7, 5.7 and 8.0 times the area of the net mouth. Volumes of filtered water were determined with a flowmeter. The results are expressed as (1) drift retained by each net, (2) drift that would have been collected by a single net of given mesh size, and (3) the percentage of total drift (the sum of the catches from all three nets) that passed through the 425 pm and 209 pm nets. During a two day period in August 1986, Chironomidae larvae were dominant numerically in all 209 ,um and 106 pm samples and midday 425 pm samples. Large drifters (Ephemerellidae) occurred only in 425 pm or 209 pm nets, but the general pattern was an increase in abundance and number of taxa with decreasing mesh size. Relatively more individuals occurred in the larger mesh nets at night than during the day. The two larger mesh sizes retained 70% of the total sediment/detritus in the drift collections, and this decreased the rate of clogging of the 106 pm net. If an objective of a sampling program is to compare drift density or drift rate between areas or sampling dates, the same mesh size should be used for all sample collection and processing. The mesh aperture used for drift collection should retain all species and life stages of significance in a study. The nested net design enables an investigator to test the adequacy of drift samples.

The comparability of bioassessments: a review of conceptual and methodological issues

“…Mesh size.-The mesh size used to collect stream invertebrates can influence the size composition of the organisms in a sample (Slack et al 1991, Gage et al 2000. These differences can affect sample comparability because mesh sizes used in invertebrate sampling devices typically range between 250 and 1200 mm (Carter and Resh 2001).…”

Bioassessment of benthic macroinvertebrates in wetlands: a paired comparison of two standardized sampling protocols

“…Even where methodologies to collect benthic macroinvertebrates have many similarities, finer-scale differences in sampling equipment, sample location, and number of samples can confound comparisons of benthic communities characterized by the samples (Carter and Resh 2001). For example, when identical sampling devices with difference mesh sizes are used, smaller meshes can collect higher abundances and richness of invertebrates (Slack et al 1991) and increase the relative abundance of small taxa like microcrustaceans (Carter and Resh 2001). Differences in sampling and laboratory methodologies also have significant implications for the cost of a monitoring program (Haase et al 2004), and within a single sampling protocol, the response variable chosen can significantly impact the interpretation of data collected during monitoring (e.g., Lindig-Cisneros et al 2003).…”

A model for accurate drift estimation in streams

“…The ideal drift net design has been discussed widely as a source of error (Waters, 1969; Elliot, 1970; Slack et al ., 1987). Nets in common use for drift estimation can vary in length, aperture opening, as well as net mesh size (Gale, 1975; Gale & Mohr, 1978; Slack, Tilley & Kennelly, 1991), and can be fixed or designed to trawl the bed (Brown & Langford, 1975). However, there may be other, more significant influences on the quality and value of the resulting data than an inappropriate net design or mesh size.…”

“…Organic debris creates the additional difficulty that, because of the retardant effect exerted by CPOM accumulation on the entry velocity of the sampled flows to the net (Williams, 1985; Slack et al ., 1991), errors can occur in subsequent calculations of filtered water volume. The effect is usually countered by measuring velocity at the net entrance at the end of an experimental run, and calculating the reduced sample volume assuming a linear reduction in velocity because of the clogging effect (i.e.…”