Interactions among Introduced and Native Species in Lake Tahoe: Implications for the Restoration of the Lahontan Cutthroat Trout and Current Fishery Management Sudeep Chandra, Jake Vander Zanden, Brant Allen, John Reuter, and Charles R. Goldman Tahoe Research Group, Department of Environmental Science and Policy, UC Davis Cener for Limnology, University of Wisconson, Madison      Species introductions are emerging as perhaps the leading threat to aquatic ecosystem sustainability (McCann, 2000; Moyle et al., 1986). Often accompanied by dramatic changes in food web structure and ecosystem function, these introductions are likely to have major consequences for lake management. In Lake Tahoe, understanding and predicting impacts of species introductions will greatly benefit efforts to: manage the lake in a sustainable manner, and restore the native Lahontan cutthroat trout into the system.      Past species introductions into the lake have already greatly impacted water quality and biodiversity (Goldman et al., 1979; Cordone, 1986). These introductions may also effect the sustainability of the current lake trout fishery and the potential success of cutthroat restoration efforts. Furthermore, the impending establishment of bass species recently introduced into Lake Tahoe (Lehr, 1999) could substantially disrupt the current fishery and inhibit efforts to restore the native cutthroat trout (e.g. further reducing forage fish populations, a potentially important food source for the trout). This proposed study addresss how 1) previous food web changes and 2) establishment of bass species in Lake Tahoe will effect the reintroduction of native cutthroat populations. Specifically, the objectives are to: provide resource managers with information on the original feeding behavior of the Lahontan cutthroat trout, determine the impact of subsequent alterations to the food web which may impede current restoration efforts, and determine the impact of the newly introduced bass species on the restoration of the Lahontan cutthroat trout and TahoeÕs native fishes. Often, unsuccessful species introductions could be avoided if the proper studies are conducted beforehand. The goal of this research is to provide Lake Tahoe resource managers with appropriate information on which to base cutthroat trout restoration efforts.      This past year we have gained further information on the first two of our project objectives by determining Lake TahoeÕs food web structure from four distinct time periods (1880, 1910, 1960, 2000). In order to determine the impact of the newly introduced bass species on the contemporary food web, we thoroughly researched existing literature on the important abiotic and biotic parameters involved in the establishment of these species in aquatic systems. We also placed temperature probes and conducted late summer surveys during 2000 in 8 marinas and embayments to determine whether bass have established in the surrounding waters of the lake.