Effects of Chum Salmon Redd Excavation on Benthic Communities in a Stream in the Pacific Northwest

Abstract

We studied effects of redd excavation by wild chum salmon Oncorhynchus keta on insect communities in a stream in the Pacific Northwest. During the salmon redd excavation, the total mean insect densities in the spawning reach decreased to 10.8–14.7% of their predisturbance values. Mean densities of the major taxa, mayflies Baetis spp. and Cinygmula spp., midges Orthocladiinae, stoneflies Paraperla spp., and black flies Simuliidae, in the spawning reach were 0.4–55.1% of the predisturbance values during redd excavation. Densities of these taxa in the spawning reach were 1.1–46.6% of densities in the nonspawning reach during salmon redd excavation. Twenty‐nine days after redd excavation, the densities of Baetis spp., Orthocladiinae, and Simuliidae in the spawning reach exceeded the values of the same taxa in the nonspawning reach. Statistical analyses revealed that the presence or absence of spawning salmon was significantly associated with the distances (or dissimilarities) among stream insect communities (reach × sampling date combination) and the densities of insect taxa (except for Simuliidae); salmon redd excavation reduced insect densities and altered insect community structure.

Disturbance of freshwater habitats by anadromous salmon in Alaska

“…Previous research on introduced populations of salmon has suggested that disturbance by spawning salmon can dramatically reduce benthic invertebrate densities (Hildebrand 1971;Field-Dodgson 1987). Minakawa and Gara (2003) observed substantial decreases in invertebrate populations during native chum salmon (O. keta) spawning. Peterson and Foote (2000) studied native Alaskan populations of sockeye and observed that some taxa decreased after spawning by salmon.…”

Juvenile salmonid (Oncorhynchus spp.) use of constructed and natural side channels in Pacific Northwest rivers

“…While studies from British Columbia indicate that constructed channels may require periodic maintenance to clear spawning gravels of sediment and detritus (but more so in surface water than groundwater channels; Sheng et al 1990;Lister and Finnigan 1997), none of the channels evaluated in this study has shown an appreciable decrease in depth over time, even at sites constructed over a decade ago (C. Detrick, Washington Department of Fish and Wildlife, 600 Capitol Way N., Olympia, WA 98501, personal communication). This could be due in part to frequent disturbance to the channel bed during redd construction by mass spawners such as chum salmon, with further implications for invertebrate production (Minakawa and Gara 2003).…”

Salmonid influences on rivers: A geomorphic fish tail

“…It is not clear which of the two factors dominates with respect to regulating the densities of caddisfly larvae, which ultimately controls the degree of stability imparted to substrates. Benthic macroinvertebrate communities are generally thought to be adapted to the annual disturbance associated with mass salmon spawning, and effects have been found to vary with taxa and the degree to which nutrient enrichment contributes to productivity compared with other factors such as temperature, background water chemistry, and light attenuation (Peterson and Foote, 2000;Minakawa and Gara, 2003;Chaloner et al, 2004;Cak et al, 2008;Janetski et al, 2009;Lessard et al, 2009). In some cases, enrichment and disturbance effects may largely offset each other (Chaloner et al, 2004;Tiegs et al, 2009).…”