Failure to achieve recommended environmental flows coincides with declining fish populations: Long‐term trends in regulated and unregulated rivers

Dams can be operated to mimic components of the natural flow regime to minimise impacts on downstream ecosystems. However, infrastructure, societal needs, water management, and catchment runoff constrain which and when flow regime attributes can be mimicked. We compared fish assemblage responses, in...

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Bibliographic Details
Published in:Freshwater biology 2022-09, Vol.67 (9), p.1631-1643
Main Authors: Pennock, Casey A., Bruckerhoff, Lindsey A., Gido, Keith B., Barkalow, Adam L., Breen, Matthew J., Budy, Phaedra, Macfarlane, William W., Propst, David L.
Format: Article
Language:English
Subjects:
Aridity
Catchment area
Catchments
climate change
drought
Fish
Fish populations
flow–ecology
Indigenous species
long‐term data
native fish conservation
Native organisms
Natural flow
non‐native species
Population decline
River basins
Rivers
Runoff
Strategic management
Water management
Water use
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Summary:Dams can be operated to mimic components of the natural flow regime to minimise impacts on downstream ecosystems. However, infrastructure, societal needs, water management, and catchment runoff constrain which and when flow regime attributes can be mimicked. We compared fish assemblage responses, including native and non‐native species, over 2 decades of managed environmental flows to those in a river retaining a relatively unaltered flow regime. Both of these arid‐land rivers are within the overallocated Colorado River basin and have experienced declines in catchment runoff over the past 20 years. We predicted that fish–flow relationships would be conserved across time and between managed and unmanaged rivers. Declines in flow in both rivers coincided with declines in some native fishes, and more native and non‐native fish species exhibited declines in the managed river than in the unmanaged river. Our ability to detect previously documented native fish–flow relationships diminished in the managed river system because established environmental flow targets were not met due to water management, but we detected these fish–flow relationships in the unmanaged river. Our results suggest declining catchment runoff and increased consumptive water use could reduce the effectiveness of environmental flows that have lower priority in most years.
ISSN:0046-5070
1365-2427
DOI:10.1111/fwb.13966