Density and distribution of piscivorous fishes in the Sacramento – San Joaquin Delta

Predatory fishes, including numerous introduced species, are common to the Sacramento – San Joaquin Delta, but abundance data for most species is insufficient to determine the Delta-wide distribution and ecological impacts of these species. Predatory fishes (e.g. Striped Bass, Largemouth Bass have long been suspected of contributing to the decline of native species, including salmonids, but data has been insufficient to investigate this hypothesis. In this study, I present a novel method to assess predator fish populations across the southern Delta using DIDSON acoustic cameras and analyze the environmental associations that form the landscape and fine-scale distribution of predatory fishes. I found that a mobile application of DIDSON acoustic cameras can be an effective method to enumerate predator fishes in a non-disruptive manner; however, factors affecting detection including environmental conditions and habitat complexity should be evaluated to refine these methods. Additionally, species differentiation of DIDSON footage would benefit from a larger library of acoustic footage of known predator fish species. I found that predator fish distributions were primarily driven by spatial and structural habitat components with little evidence of temporal trends, though high temporal variation was apparent. Landscape-scale distribution was primarily driven by channel sinuosity, variation in depth, and the number of patches of submerged aquatic vegetation (SAV) within reaches. On a fine scale, predators were generally more likely to be found near shallow, littoral habitats, submerged and emergent vegetation, and human-made structures. These results provide both guidance on how to implement a new survey method to assess the abundance of juvenile salmon predators in the Delta and insight into management actions that could affect predator populations in the Delta