Predation on Fishes in the Sacramento–San Joaquin Delta: Current Knowledge and Future Directions

The Delta is a diverse, highly modified aquatic system. This paper reviews relevant predator–prey theory, describes data on predator–prey relationships of Delta fishes, ranks predator consumption rates, and presents hypotheses for the effects of predation on native and invasive species. Thiry-two different predator categories and 41 different prey categories are identified.

The analysis yielded few generalizations regarding predator–prey interactions for Delta fishes. The only evidence for predator specialization occurred in Prickly Sculpin which, when it consumed fishes, ate mostly native species. Data for reptilian, avian, and mammalian predators were sparse; however, these predators may be significant fish predators in altered habitats or when hatchery salmonids are released. The database for predators and their fish prey was not strong, and long-term dietary studies combined with prey availability and behavioral and experimental studies are needed. The behavioral effects of contaminants on prey species also warrant further examination. Although it has been suggested that a reduction in the Striped Bass population be implemented to reduce predation mortality of Chinook Salmon, the large number of salmon predators in the Delta make it unlikely that this effort will significantly affect salmon mortality.