Abstract
Author(s): Stompe, Dylan K.; Roberts, Jason D.; Estrada, Carlos A.; Keller, David M.; Balfour, Nicholas M.; Banet, Amanda I. | Abstract: This study examined diets of two predatory fish species, the native Sacramento Pikeminnow (Ptychocheilus grandis) and the introduced Striped Bass (Morone saxatilis), in the Sacramento River, California, USA. Both species have been implicated in native species declines through predation, eliciting our investigation of their diets in the Sacramento River. Sampling occurred between March and November 2017, and was conducted via hook and line on a 35-km reach near Chico, California. Habitat types sampled include engineered structures (water diversions and beam bridges), rip-rapped channel edges, and natural riverbank. Stomach contents were collected via gastric lavage and later processed using visual, gravimetric, and genetic techniques. Diets of Sacramento Pikeminnow and Striped Bass were highly similar as determined through index of relative importance and PERMANOVA modeling. Water temperature was the only variable that significantly affected diet composition. Results reflect similar dietary niches for both species in the Sacramento River.
Highlights
Because predation is a challenge with which most organisms must contend, it is often considered in the management of vulnerable populations of fishes (Zimmerman and Ward 1999; Link 2002)
Of the four Chinook Salmon runs native to the Sacramento River, winter-run are listed as endangered, spring-run are listed as threatened, and both Central Valley fallrun and late fall-run have been identified as California species of special concern (Moyle et al 2015; NOAA Fisheries 2018)
We were unable to identify prey from several of the individuals that contained stomach contents, which reduced the sample size of Sacramento Pikeminnow and Striped Bass included in dietary analysis to n = 30 and n = 47, respectively
Summary
Because predation is a challenge with which most organisms must contend, it is often considered in the management of vulnerable populations of fishes (Zimmerman and Ward 1999; Link 2002). In the Sacramento River, California, this challenge may be amplified for populations of juvenile Chinook Salmon by climate change, a complex water diversion system, hatchery domestication effects, lack of juvenile rearing habitat, and non-native predatory fish species (Brown and Moyle 1981; NOAA Fisheries 2018). Green Sturgeon (Acipenser medirostris) and Steelhead (Oncorhynchus mykiss), both species native to the Sacramento River, are listed as threatened under the federal Endangered Species Act. Prior studies have investigated the potential for population-scale effects of predation by nonnative species on prey populations, including listed Chinook Salmon, through population modeling (Lindley and Mohr 2003), bioenergetic modeling (Loboschefsky et al 2012), and telemetry survival studies (Cavallo et al 2013) within the Sacramento River and adjacent watersheds. While these studies identify predation as a tangible “top-down” control of prey populations, populationscale effects are often difficult to quantify in the highly dynamic and heterogeneous Sacramento River system
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