The Newly Formed Ribb Reservoir Could Serve as a Refugia for Conserving Ethiopia's Globally Unique Labeobarbus Species Flock

Abstract

The 17 species of Labeobarbus found in Lake Tana constitute the only extant cyprinid species flock in the world but extensive water development projects are impacting their habitats. Here, we assess if the Labeobarbus spp. are established above the Ribb Dam, constructed in 2017, and if so, the condition of the individuals and if there is evidence of local recruitment. Fish samplings were conducted once a month during the Labeobarbus species' spawning season of July to the end of September 2022, using monofilament and multifilament gillnets at three locations upstream of the Ribb Dam. We collected 10 Labeobarbus spp., with L. intermedius (40.7%) being the most abundant followed by L. brevicephalus (23.0%) and L. nedgia (22.2%). Labeobarbus fork lengths ranged from 7.8 to 43.0 cm and there were no notable gaps across the size ranges. Fulton's condition factors for species where n ≥ 20 were 1.30–1.54 (good), like Lake Tana populations. Our collection included sexually immature and first-time maturing individuals, indicating Labeobarbus are reproducing and recruiting successfully in the watershed above the dam. Our results suggest that the Ribb River watershed above Ribb Dam may serve as a refugia for at least some of the 17 species of the species flock. However, challenges remain before the upper watershed should be viewed as a viable long-term habitat for Labeobarbus, including the need for a fisheries management program, pollution control and mitigation of catchment degradation in the uplands that is leading to the rapid infilling of the reservoir, where current estimates suggest a 30-year reservoir life span.