Long-term acoustic telemetry reveals limited movement of fish in an unregulated, perennial river

Anthropogenic changes to river flows can alter hydrological connectivity and cues necessary for the movement of fish to complete their life cycles. Quantifying flow-related movement ecology of fish and understanding how this varies between species and river systems is important for effective environmental flow management. This study aimed to determine hydroecological factors that influence fish movements in an unregulated, perennial river and to compare these findings to fish from regulated river systems. Broad-scale movements of the endangered Maccullochella ikei and Tandanus tandanus were recorded over 3 years in the unregulated, perennial Nymboida River, Australia. The limited movements both species exhibited were infrequent and over short distances. Although M. ikei movements appeared mostly unrelated to environmental changes, T. tandanus moved on flow pulse peaks and were more likely to move during the breeding season. These findings contrast with previous studies of the same or similar species in differing flow regimes, suggesting that fish in perennial, highly connected rivers may not need to move as frequently as those in more regulated or intermittent systems. Should these disparate behaviours be present in other species occurring among contrasting flow regimes, it will be challenging to define generalisable environmental flow rules to inform river management.