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

Abstract

Sampling characteristics of submerged funnel traps which were used to study emergence of Chirononomidae in a large boreal riverine reservoir were examined. Clay, bedrock and marsh shorelines were sampled at 1.0, 2.0, 3.5 and 4.5 m depths with 4 replicate traps at each depth. The numbers of Chironomidae per square meter from the 3 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 3 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. .cntdot. m-2 emerging. Single traps collected < 1/2 the number of species collected by 16 traps. All of the more abundant (.gtoreq. 1% of the total numbers caught) species in Southern Indian Lake were caught in 2 to 4 traps. A minimum of 4 traps was required to interpret emergence patterns of the most common species with 1 emergence peak; 16 for the most common species with 2 emergence peaks. Discontinuous trapping (48 h .cntdot. wk-1) gave similar results to continuous trapping (168 h .cntdot. wk-1). An optimal sampling strategy for mesotrophic lakes would be to trap discontinuously and to use high numbers of traps.