PS 60-21
Drought decisions in a large Mediterranean-climate river: Using umbrella species to inform water management
Virtually all large California rivers have been altered by damming and regulation to provide power, water, and flood protection to the world’s eighth largest economy. This has created conflict between perceived economic needs and the protection of key ecological processes and production. This past year, the worst drought in recorded California history pushed this issue to the forefront of scientific and political discussion. Reservoir storage in the American River, a key California water artery, was at an all-time low with a relatively large native Chinook salmon cohort incubating in the gravel of the lower river. Resource agencies, along with local stakeholders, developed a decision–tree management process to identify and implement impact mitigation for key ecological processes using Chinook salmon as an umbrella species. Chinook salmon lifecycle models, including fry emergence and migration timing, were developed. Processes and environmental conditions needed to support key lifestages such as intergravel temperature and dissolved oxygen and migration corridors and triggers were distinguished, collaborative monitoring was implemented, and several suggestions for flow manipulation were identified and suggested to water managers.
Results/Conclusions
It was estimated that up to 12% of the 2013-14 Chinook salmon brood-year was stranded in dewatered or disconnected incubation (fry) or rearing (juvenile) habitat within the lower river and that temperatures and dissolved oxygen were reaching unhealthy levels. Observations suggest stressful conditions for both life stages up to the March 5-7 pulse and emerged fry, stranded in off-channel pools, demonstrated stressed behavior including aggression and very low condition factors. Considering critically low water storage availability, a two-day pulse flow was identified as the most feasible management action to mimic a spring freshet, reconnect migration corridors for stranded fry within the gravel and juveniles in off channel habitats, and ameliorate unhealthy water quality parameters.
During the pulse, stranded fry emerged from redds and entered the water column and over 63% of stranded juveniles emigrated from disconnected side channels with a portion identified in migration traps downstream. Water quality also demonstrated significant improvements related to the managed pulse. Results from this exercise provide a framework for coping with future water management decisions as human demands increase and climate continues to trend toward greater precipitation extremes within the Mediterranean climate of California.