Tuesday, June 5, 2007
536

Completing stream size spectra: a focus on large benthic macroinvertebrates

Jennifer Lento and Antoine Morin. Institute of Biology Ottawa-Carleton, Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, ON K1N 6N5, Canada

Standard techniques for collecting macroinvertebrates may underestimate large individuals because their high mobility reduces capture probability.  We  sampled 11 streams to compare the efficiency of  electrobugging to that of kick samples and cobble collection for estimating abundance of large benthic macroinvertebrates.  At each site, we conducted 3-4 consecutive electrobugging passes followed by 2-3 kick samples (repeating until attrition was observed).  Although more taxa were generally collected by electrobugging than by kick sampling, the overlap of taxa between electrobugging and kick samples was low (12.5% to 60%), indicating that several taxa were only collected by one method.  Electrobugging collected greater numbers of mobile taxa (including Amphipoda, Ephemeroptera, and Plecoptera), while kick sampling was more efficient in high algal densities and collected greater numbers of immobile taxa (including Gastropoda and some case-building Trichoptera).  When compared with cobble collection, electrobugging was found to sample a higher proportion of organisms 5mm in length or longer.  The combination of electrobugging and kick sampling may provide a useful method that could be used in conjunction with other techniques to ensure that stream size spectra are fully represented.

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