Dworshak Dam Resident Fish Mitigation

Résumé du livre

The Idaho Department of Fish and Game (IDFG) and the U.S. Army Corps of Engineers (USACE) cooperatively conducted a pilot project to test nutrient restoration as a means to restore declining reservoir productivity and improve the Dworshak Reservoir fishery. Under this agreement, the USACE applied nutrients in the form of ammonium nitrate, IDFG monitored the results using a combination of limnological and fish surveys, and Advanced Eco-Solutions provided the application schedule and limnological analysis. This report summarizes the results of the project from 2007 through 2018. Water quality standards set by the U.S. Environmental Protection Agency and the Idaho Department of Environmental Quality were not violated. We did not observe significant changes in Secchi depth, chlorophyll concentration, or phytoplankton biovolume. However, the biovolume of edible phytoplankton and the proportion of edible phytoplankton were both significantly higher during the restoration period. The proportion of Dolichospermum (formerly Anabaena) was significantly lower during the restoration period. The density of all zooplankton, as well as the density and biomass of consumable Daphnia, were all greater during the restoration period. The abundance and size of kokanee Oncorhynchus nerka was also greater for the restoration period, leading to significant increases in biomass beginning four years from initiating N additions. Except in a single year of record abundance, the observed increases in kokanee length and abundance have likely led to increases in catch rates and angling effort for the kokanee fishery. Furthermore, the increase in kokanee biomass is expected to benefit piscivorous fishes, including Bull Trout and Smallmouth Bass. Dworshak Reservoir has responded positively to nutrient restoration, resulting in a more efficient food web and more productive fisheries.