Cooperative Fish and Wildlife Research Units Program: California
Education, Research and Technical Assistance for Managing Our Natural Resources

Abundance data for fish predators is in the Delta is lacking, and has been identified as a primary research need in the Delta. The limited abundance data currently available for predators in the Delta cover relatively few locations and periods during the year, and fishery independent population estimates are unavailable. Both native and non-native species of predator fishes inhabit the South Delta and feed on migrating smolts and there is likely significant annual and seasonal variation in the presence of absence of individual predators. Predators are likely to exhibit positive selectivity for salmonid species because they are highly caloric, are likely naive to invasive predators and have no physical defense structures; therefore are easily eaten and handled. Our ability to make qualitative inferences about the scale and effects of fish predation on the salmonid population are greatly hindered by this lack of information. Through a combination of paired electrofishing sampling and results from acoustic surveys conducted using Dual-frequency identification sonar (DIDSON), we will be able to quantify the abundance of potential predatory fish throughout our study region.