Eilers JM, Truemper HA, Jackson LS, Eilers BJ, Loomis DW. 2011. Eradication of an invasive cyprinid (Gila bicolor) to achieve water quality goals in Diamond Lake, Oregon (USA). Lake Reserv Manage. 27:194-204. 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.

Biological responses to a formerly fi shless lake in the Cascade Range, Oregon (USA) were assessed through monitoring of recent changes and paleolimnological techniques to assess earlier changes. We used unpublished fi sheries reports, sediment cores, and available published and unpublished water quality data to evaluate changes to the lake. Diamond Lake has undergone four periods of fi sh introductions in the 20 th century. Rainbow trout (Salmo gairdneri) were annually released from 1910-2006, except for 1949 and 1954. Tui chub (Gila bicolor), an omnivorous cyprinid, were introduced in the late 1930s and the late 1980s, presumably as discarded live bait. Diamond Lake was treated with rotenone in 1954 which successfully eradicated the tui chub. The introductions of trout caused relatively modest changes in water quality and lake biota, whereas the introductions of tui chub caused major increases in cyanobacteria, changes in diatom community composition, reduction in transparency, increases in the proportion of rotifers, major reduction in benthic standing crop, and virtual elimination of amphipods, gastropods, and other large-bodied invertebrates. The unintended biomanipulations demonstrate the importance of an omnivorous cyprinid in promoting a series of biological responses throughout the lake food web.

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