Multi-scale connectivity dynamics and Pacific salmonids: Opportunities for ecological rehabilitation

In North America, wild Pacific salmonid populations face perhaps the greatest crisis they have known. The importance of many of these species as prized commercial, cultural, and ecological resources has drawn a great deal of attention to their predicament as well as efforts towards their conservation and recovery. The three studies presented here were designed, executed, and juxtaposed to inform (1) our understanding of salmonid ecology and (2) opportunities for recovery of salmonid populations and the habitats and ecosystems that support them through restoration of connectivity dynamics at multiple scales. In Chapter 1 we compared growth and methylmercury accumulation in juvenile Chinook salmon (Oncorhynchus tshawytscha) reared in the Sacramento River and its floodplain the Yolo Bypass during a winter flood event in 2005. In the second Chapter we used data from Chapter 1 on growth and methylmercury accumulation as inputs to a coupled mercury mass balance model and bioenergetics model first presented in Trudel and others (2000). This coupled modeling exercise compared the roles of activity, consumption rate and prey contamination as drivers for growth and mercury accumulation in juvenile Chinook salmon from river and floodplain habitats. Together, these first two studies attempted to provide a cost-benefit analysis of river-floodplain connectivity restoration for juvenile salmon. Specifically, they explored the environmental and bioenergetic implications of improved habitat and increased growth opportunities available on the floodplain in relation to the potential for increased mercury uptake during floodplain rearing. In the third Chapter we addressed the potential for salmonid conservation and improved aquaculture through restoration of connectivity at the food-web level. For this study we reared juvenile rainbow trout (Oncorhynchus mykiss) in benthic and pelagic enclosures for seven weeks in sub-alpine Castle Lake, California to examine the role of dietary fatty acids in benthic versus pelagic energy pathways, food quality, and fish growth. Specifically, we compared growth and liver fatty acid contents in fish reared in benthic and pelagic habitats and examined the relationship between fatty acid content in benthic and pelagic fish and in benthic and pelagic invertebrate prey taxa.