9304

• UCREFRP Catalog Number: 9304
• Author: Mueller, G., L. Boobar, R. Wydoski and K. Comella.
• Title: Aquatic Survey of the Lower Escalante River, Glen Canyon National Recreation Area, Utah; June 22-26, 1998.
• USFW Year: 1998.
• USFW - Doc Type: \
• Copyright Material: NO

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CHAPTER l--INVERTEBRA TES

By Lewis Boobar (NPS)

METHODS

A total of 16 Surber (30 X 30 cm sample area, 500 um net) samples (Merritt and Cummins 1996)
were collected from riffles along the lower Escalante River. Two of the 16 samples were
collected from each of four riffles (sites), four from the upper and four from the lower reaches
(Map 1). Additionally, 30 minutes were spent at each site collecting macroinvertebrates from
debris and snags. The samples and associated water were mixed with 95% ethyl alcohol to
obtain a concentration (ca. 50% ethyl alcohol) high enough to temporarily preserve the animals.
Later, samples were composited by type and river-section. The resulting two composite Surber
samples and two composite qualitative samples (one of each type from each river-section) were
processed by the Bureau of Land Management and U.S. Forest Service National Aquatic
Monitoring Center at Utah State University, Logan, UT as described by Vinson and Hawkins
(1996). Initially, the entire sample was sorted for large and less-numerous organisms. If the
sample contained more than 250 organisms, it was sub-sampled. They took additional
sub-samples until at least 250 organisms are found. The identified portion of the sample was
placed in 70% ethyl alcohol, cataloged, and archived. The data was entered into a common
computer database at the National Aquatic Monitoring Center. This database currently contains
aquatic macroinvertebrate data and corresponding geographic information for more than 4000
samples.

RESULTS

A total of 475 macroinvertebrates representing 19 taxa were collected, 116 from the upper reach
and 359 from the lower reach (Table 1.1, Appendix A). The dominant families were
Chironomidae, Hydrosychidae, Simuliidae and Tricorythidae (Table 1.2). Diversity was fairly
constant throughout the study area as was the Modified HilsenhoffBiotic Index
(MHBI)(Hilsenhoff 1987, 1988; Bode et al. 1991), which summarizes the overall pollution
tolerances of the taxa collected, and the USGS Community tolerant quotient (Wingett and
Mangum 1979). The taxa richness (Table 1.3) and abundance (Table 1.4) of functional feeding
groups showed collector gatherers and collector filters to be slightly greater in the lower reach,
and scrapers to be slightly greater in the upper reach.

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