Abstract
Large areas of California’s historic floodplain have been separated from adjacent river channels by levee construction, allowing the development of an extensive agricultural industry. Based on successful partnerships between agriculture and conservation groups to support migrating waterfowl, we examined whether seasonally flooded rice fields could be modified to provide off-channel rearing habitat for juvenile Chinook Salmon Oncorhynchus tshawytscha. During winter and spring of 2012-2017, we conducted a series of experiments in Yolo Bypass and other regions of California’s Central Valley using hatchery Chinook Salmon as a surrogate for wild Chinook Salmon, the management target for our project. Overall, we found that seasonally flooded fields are highly productive, resulting in significantly higher levels of zooplankton and high Chinook Salmon growth rates as compared to the adjacent Sacramento River. We found similar results for multiple geographical areas in the Central Valley, and in different cover types, such as non-rice crops and fallow areas. Although field substrate type did not detectably affect fish growth and survival, connectivity with upstream and downstream areas appeared to drive fish occupancy, because rearing young salmon were generally attracted to inflow in the fields, and not all of the fish successfully emigrated off the fields without efficient drainage. In general, we faced numerous logistic and environmental challenges to complete our research. For example, periodic unmanaged floods in the Yolo Bypass made it difficult to schedule and complete experiments. During severe drought conditions, we found that managed agricultural habitats produced low and variable salmon survival results, likely because of periodically high temperatures and concentrated avian predation. In addition, our project required substantial landowner time and effort to install and maintain experimental fields. Recent and future infrastructure improvements in Yolo Bypass could substantially improve options for experimental work and broaden efforts to enhance salmon habitat.
Highlights
Worldwide, the loss of floodplain habitat has resulted in considerable reduction in the productivity and diversity of large river ecosystems (Winemiller et al 2016)
We found that management of agricultural floodplain habitat was challenging
Based on over 2 decades of research, California has some of the best-studied temperate floodplains in the world
Summary
The loss of floodplain habitat has resulted in considerable reduction in the productivity and diversity of large river ecosystems (Winemiller et al 2016). A case in point is the Central Valley Joint Venture Partnership, which promotes the use of flooded rice fields as a means to increase available wetlands to support shorebirds and waterfowl migrating, overwintering, and breeding along the Pacific Flyway (Shuford and Dybala 2017). Conservation biologists working in partnership with local farmers have developed a system by which fields are reflooded after rice harvest to create seasonal wetland habitat for water birds during fall and winter. These temporary agricultural wetlands are relatively productive habitats (Dybala et al 2017), helping California meet some of its shorebird and waterfowl conservation objectives (Gardali et al 2017; Strum et al 2017)
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