Predicting establishment and impact of warmwater non-native fishes in a large, sub-alpine, oligotrophic lake

In response to a warming climate, non-native aquatic species establishment is increasing at mid to northerly latitudes, enhancing threats to native species and ecosystem function. This study examines the present and potential distribution and impacts of warmwater non-native fishes in Lake-Tahoe, CA-NV, USA. In chapter 1, current distribution and diet composition of two warmwater non-native fishes was determined. Diet analysis revealed that largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus) are predating and potentially competing with native cyprinids. Electroshocking and snorkel data suggest that when warmwater nonnatives are present, native fishes are absent or reduced in number. During nearshore surveys a parasitic copepod (Salmincola Californiensis) was discovered in the northwest nearshore zone of Lake Tahoe and this observation is documented in Chapter 2. In Chapter 3, distribution and population data from 2006 were used to classify establishment likelihood and potential predation impacts of largemouth bass. The likelihood model suggested that the entire nearshore zone is currently thermally suitable for largemouth bass spawning, and that vegetation is likely limiting current bass establishment. Bioenergetics models for consumption revealed that largemouth bass could consume anywhere from 100 to 2600 native cyprinid species over the growing season. As Lake Tahoe warms, growth and consumption will likely increase, and establishment could become widespread. Establishment likelihood and predation predictions of non-native bass are provided at ∼2 km scale, and can prioritize management efforts aimed at preventing widespread establishment of warmwater non-natives and loss of native species.