Coalition for a Sustainable Delta

Capitol Public Radio on predation

QUEST on KQED Public Media.

PREDATION

Few issues in the Delta are as clear cut as predation. Larger predator species eat smaller fish. Nonnative species pose a particularly significant predation threat in the estuary. Many of these predators were planted in the Delta for sport and recreational fishing purposes with little concern for the native species they now endanger, such as salmon, delta smelt and steelhead. Exacerbating the problem, it has also long been the State’s misguided policy to protect and maintain the populations of these predators through the use of size and bag limits. Fish stocking programs have also been utilized in the past to increase the adult populations of these voracious feeders. Many species that are nonnative to the Delta have direct or indirect impacts on native threatened species such as the delta smelt and salmon by predation, which greatly reduces survival of native fishes.

Striped bass represent a direct predatory threat to the delta smelt and salmon and yet are protected by an ongoing California Department of Fish and Game program that regulates fishing and maintains the population at artificially high levels to the detriment of native species. Until recently, the Department restocked striped bass as part of an active population management program.

Nine-out-of-ten juvenile salmon are being killed by predators before ever reaching the Delta.
The National Marine Fisheries Service has stated that predation by striped bass on winter-run salmon is a “major stressor.”
The California Department of Fish and Game’s own experts have estimated that striped bass may consume upwards of 25-50 percent of winter- and spring-run Chinook salmon.
The National Marine Fisheries Service recently requested the California Fish and Game Commission "begin the process to consider proposed regulations directed at reducing, to the extent practicable, the effects of non-native predators in federally listed anadromous species in California, especially in the Central Valley."
2009 research by highly regarded fishery biologist Dr. Charles Hanson estimated that striped bass consumed 21 to 42 percent of endangered winter- and spring-run juvenile salmon, respectively. By comparison, other studies show the state and federal water projects took less than 3 percent.