Spatial and temporal dynamics of fish assemblages in a desert reservoir over 38 years

Abstract

Processes associated with reservoir aging threaten the capacity of systems to continue providing productive fisheries, and declining productivity might be exacerbated by decreasing water level associated with climate change and water abstraction. Despite their prevalence in riverscapes, we know little about long-term fish dynamics in reservoirs. Using a 38-year dataset from Lake Powell, USA, we tested for changes in assemblage structure and changes in fish condition for the most abundant species. The assemblage has undergone re-ordering of species relative abundance, but the same core species captured in 1981 were still present in 2018. Five species increased in relative abundance, while two declined, and seven remained unchanged. Walleye Sander vitreus and Smallmouth Bass Micropterus dolomieu were among those increasing over time, while Channel Catfish Ictalurus punctatus and Common Carp Cyprinus carpio declined. We were not able to attribute changes in fish assemblages with a suite of abiotic and biotic variables. Condition was low and declined over time for four of the six species. Although water level declined over time, we did not observe obvious declines in basal food resources. Declining water level has reduced availability of littoral habitat and likely contributed to declines in some species associated with this zone.