Sources of Nonnative Centrarchids in the Upper Colorado River Revealed by Stable Isotope and Microchemical Analyses of Otoliths

Nonnative fishes represent a significant impediment to the recovery of imperiled fishes, including those endemic to the Colorado River in the southwestern United States. Efforts to control nonindigenous fish abundance in the upper Colorado River basin have been unsuccessful owing in part to lack of knowledge regarding nonnative fish recruitment sources. We determined the source habitat (floodplain pond versus riverine habitats) for nonnative centrarchid fishes (largemouth bass Micropterus salmoides, green sunfish Lepomis cyanellus, bluegill L. macrochirus, and black crappie Pomoxis nigromaculatus) in the upper Colorado River using stable hydrogen isotopic composition (δD) and strontium:calcium (Sr:Ca) ratios in fish otoliths as natural markers of environmental history. Stable hydrogen isotope analysis revealed that 59% of centrarchids exhibited the otolith core signatures expected for riverine-origin fish, while 22% had emigrated from floodplain ponds and 19% were of uncertain origin. Strontium:calcium ratio data were consistent with the δD assays and indicated that relatively few fish immigrated to the river from high-salinity habitats. Black crappie was the only species that originated primarily from floodplain ponds. Efforts to control the abundance of most of the fishes included in this study should be concentrated in riverine habitats given the hydrologic conditions (below-average river discharge) present during our study. However, the proportion of pond-origin fish increased with fish age, which, coupled with historical river discharge data, suggested that floodplain pond contributions to riverine nonnative fish populations fluctuate with the interannual variations in flow regime and river–pond connectivity. Our results are the first to demonstrate the utility of δD as a natural marker of fish environmental history that will probably provide valuable insights into the management of fish in other environments

School’s Back: Scaffolding Reminiscence in Social Virtual Reality with Older Adults

Social virtual reality (social VR) is an emerging technology that has the potential to support unique social experiences for groups of older adults. In this paper we explore the use of social VR to support group reminiscence, an activity that has been shown to have a positive impact on the lives of older adults. We developed School Days, a bespoke social VR application that enables groups of geographically dispersed older adults to meet in a virtual environment to reminisce about their school experiences. We conducted a user study over the course of 5 months with 16 participants aged 70--81 to evaluate how School Days supported reminiscence. In this paper, we focus on how the use of reminiscence scaffolding features in School Days impacted on the older adults' ability to participate more fully in the reminiscence activities. Our results illustrate the value of social VR for connecting older adults over distance, and contribute new knowledge of how virtual environments can be designed to scaffold reminiscence; how techniques such as 3D conversation starters and individual artefacts can be used to scaffold reminiscence; and how pre-recorded holographic stories (Avacasts) can be used to introduce new perspectives and prompt self-reflection. We contribute five design reflections aimed at guiding the design of future reminiscence tools in social VR