EFFICIENCY OF SORTING CHIRONOMIDAE SURFACE FLOATING PUPAL EXUVIAE SAMPLES FROM URBAN TROUT STREAMS IN NORTHEAST MINNESOTA

Collections of Chironomidae surface-floating pupal exuviae (SFPE) provide an effective means of assessing water quality in streams. Although not widely used in the US, the technique is not new and has been shown to be more costefficient than traditional dip-net sampling techniques in organically enriched streams. The intent of this research was to document the efficiency of sorting SFPE samples relative to dip-net samples in trout streams with catchments varying in amount of impervious surface. Samples of SFPE were collected from 17 trout streams in Duluth, MN; dip-net samples of the entire macroinvertebrate community were also collected from these streams. We quantified time needed to sort subsamples of 100 macroinvertebrates and SFPE; time to subsample up to 300 SFPE was also recorded. The average time to sort subsamples of 100 specimens was 22.5 minutes for SFPE samples, compared to 32.7 minutes for 100 macroinvertebrates in dip-net samples. Average time to sort up to 300 SFPE was 37.7 minutes. These results indicate that sorting SFPE samples is more time-efficient than traditional dip-net techniques in trout streams with varying catchment characteristics.