Sampling Emerging Chironomidae (Diptera) with Submerged Funnel Traps in a New Northern Canadian Reservoir, Southern Indian Lake, Manitoba

Abstract

We examined sampling characteristics of submerged funnel traps which were used to study emergence of Chironomidae in a large boreal riverine reservoir. Clay, bedrock, and marsh shorelines were sampled at 1.0-, 2.0-, 3.5-, and 4.5-m depths with four replicate traps at each depth. Numbers∙m−2 emerging from the three shorelines were similar but differences among depths were significant. The most common species emerging offshore (3.5 and 4.5 m) differed from those emerging inshore (1.0 and 2.0 m). Species emerging from all three shorelines were similar offshore. Inshore, clay and bedrock shorelines were similar but differed from the marsh shoreline. Twelve traps for each depth and 16 traps for each shoreline usually gave a ± 30% precision of the mean no.∙m−2 emerging. Single traps collected [Formula: see text] the number of species collected by 16 traps. All of the more abundant (≥ 1% of the total numbers caught) species in Southern Indian Lake were caught in two to four traps. A minimum of four traps was required to interpret emergence patterns of the most common species with one emergence peak; 16 for the most common species with two emergence peaks. Discontinuous trapping (48 h∙wk−1) gave similar results to continuous trapping (168 h∙wk−1). Our studies in Southern Indian Lake suggest that an optimal sampling strategy for mesotrophic lakes would be to trap discontinuously and use high numbers of traps.Key words: Chironomidae, sampling (biological), submerged funnel traps, reservoirs (water), trapping time, shorelines, depths, replicates, precision