Eradication of an invasive cyprinid (Gila bicolor) to achieve water quality goals in Diamond Lake, Oregon (USA)

Abstract

We used a case study of whole-lake fish removal to demonstrate the importance of the fish community to nutrient cycling in Diamond Lake, Oregon, USA, to meet regulated water quality standards for pH, dissolved oxygen and nuisance algae. The cyprinid tui chub (Gila bicolor) was removed through a process beginning with netting and ending with a whole-lake and tributary rotenone treatment in September 2006. The lake was stocked with rainbow trout in spring 2007. Between 2007 and 2009, lake transparency increased 250%, accompanied by decreases in epilimnetic pH, total nitrogen, and total organic carbon. Mean concentrations of total phosphorus and ortho-phosphorus remained unchanged in epilimnetic waters. Chlorophyll a, phytoplankton biovolume, Anabaena biovolume, and Anabaena cell density declined. Daphnia pulicaria, a large herbivorous cladoceran virtually absent for 10 years, returned in abundance, and benthic biomass increased more than 12-fold. The project successfully demonstrated that water quality and fishery goals can be met through eradication of the invasive cyprinid. Fish populations need to be considered in some lakes to achieve water quality standards.