Aquatic Community Responses to Salmon Carcass Analog and Wood Bundle Additions in Restored Floodplain Habitats in an Alaskan Stream

Abstract

Land use activities often directly and indirectly limit the capacity of freshwater habitats to produce fish. Consequently, habitat creation and enhancement actions are often undertaken to increase the quantity and quality of resources available to aquatic communities within these impaired systems, with the intent to increase fish production. The objectives of this study were to (1) determine whether aquatic community colonization and development could be accelerated through additions of woody debris bundles and marine-derived nutrients (via salmon carcass analog pellets) and (2) measure how aquatic communities (biofilm, invertebrates, and fish) respond to these additions after the creation of off-channel (alcove) fish habitat in a stream in south-central Alaska. Biofilm, invertebrates, and juvenile coho salmon Oncorhynchus kisutch were sampled in four treatments (control, wood, analog, and analog plus wood). Biofilm chlorophyll-a concentrations were 4–10 times higher in analog-enriched treatments than in the control and wood treatments. No treatment effects were detected in benthic invertebrate density; however, treatment differences were detected in coho salmon diets, with nearly twice the amount of invertebrate abundance and biomass (primarily various dipteran, ephemeropteran, and plecopteran larvae) in the analog and analog plus wood treatments compared with the control and wood treatments. Juvenile coho salmon density and biomass were significantly higher in the wood treatment than in the analog plus wood treatment, and fish in the control showed possible signs of density-dependent limitation. Further, body condition of juvenile coho salmon was highest in the two analog-enriched treatments at the end of the study; juveniles in these habitats showed nearly two times the condition increase of fish inhabiting the control and wood treatment alcoves. These results demonstrate that the combination of salmon carcass analog and woody debris bundle additions aids in the short-term development of aquatic communities in newly created off-channel habitats, providing a boost in limited resources such as food and shelter.