| The effects of salmon spawning activities on aquatic insect communities were poorly understood. Effects of redd excavation and salmon carcasses (Oncorhynchus kisutch and O. keta) on insect communities were studied in two salmon streams of Pacific Northwest. This study describes the dynamics of aquatic insect communities associated with salmon spawning.;Redd excavation by salmon reduced epilithon and aquatic insect numbers and biomass, and the effects of salmon spawning remained after redd excavation. During spawning, densities and biomass of major taxa were reduced to 0-30% of pre-disturbance levels. Total insect densities decreased to 2-11% of their pre-disturbance levels and total biomass to 2-3%. Redd excavation also reduced taxonomic richness to 32-63% of the pre-disturbance levels. Ameletus, Baetis, Sweltsa, Simuliidae, Orthocladiinae and Tanytarsini, as well as total insect densities, reestablished their densities in riffles within 42 days after disturbance. Recoveries of insect biomass and taxonomic richness were slower than densities. Chironomids were common within the salmon spawning reaches throughout the year, while hydropsychid caddisflies were scarce in the salmon spawning reaches most of year.;In field studies, salmon flesh was shown to attract immature aquatic insects. In riffles, substrate-filled containers with salmon flesh had significantly greater densities and biomass of mayflies (Ameletus and Baetis), stoneflies (Sweltsa) and midges (Orthocladiinae) than substrate containers without flesh. Blackfly larvae also accumulated below carcasses in riffles. Near stream edges and in backwater, containers with salmon flesh had significantly greater densities and biomass of caddisfly larvae (mainly Limnephilidae) and midges (Orthocladiinae and Tanytarsini). Salmon carcasses were shown to produce a two-fold or greater increase in total insect densities and biomass.;Most studied carcasses (83-95%) remained within the salmon spawning reach, and 51-73% of the salmon carcasses remained in stream edges and backwaters. Carcasses near stream edges and backwaters became potential and nutritive food sources for aquatic insects. In particular, insect shredders, 10 caddisfly genera and two stonefly genera, directly fed on salmon flesh. Caddisfly larvae grew significantly faster when associated with salmon flesh. |
