Quantifying Consumption of Native Fishes by Nonnative Channel Catfish in a Desert River

The establishment of nonnative predators can have devastating consequences for native fish communities, but predation rates are often difficult to quantify due to spatial and temporal variation in predator foraging behavior. Predation by Channel Catfish Ictalurus punctatus throughout the Colorado River basin potentially threatens the recovery of native fishes. Because Channel Catfish are highly opportunistic feeders, an understanding of how piscivory by this species impacts prey populations should help to guide management in invaded systems. We used laboratory observations to model temperature-dependent stomach evacuation rates and combined those estimates with field-collected diet data to derive annual consumption across a 152-km reach of the San Juan River (New Mexico, Colorado, and Utah). In the field, stomach fullness increased with water temperature while the probability of observing fish prey in the diet increased with TL of Channel Catfish and water turbidity. Based on estimates of daily ration, diet composition, and Channel Catfish population demographics, we estimated the San Juan River population's fish consumption to be 4.9 kg center dot ha(-1)center dot year(-1) (95% CI = 4.0-6.1 kg center dot ha(-1)center dot year(-1)) in 2018 and 2.3 kg center dot ha(-1)center dot year(-1) (95% CI = 1.8-2.8 kg center dot ha(-1)center dot year(-1)) in 2019. Native fishes accounted for 54% of the fish biomass consumed, which included two incidents of endangered Colorado Pikeminnow Ptychocheilus lucius consumption. Although these estimates should help managers to assess the predatory threat of Channel Catfish, additional information, such as the efficacy of nonnative control and prey population compensatory responses, will likely be necessary to develop robust management strategies aimed at reducing the predatory impacts of this nonnative species on native fish assemblages.

Automated summary

The establishment of nonnative predators, such as Channel Catfish, poses a threat to native fish communities in the Colorado River basin. Research on the San Juan River revealed that the feeding behavior of Channel Catfish is influenced by water temperature, turbidity, and fish prey size. The estimated fish consumption of Channel Catfish in the river indicates a significant consumption of native fish, including endangered species like the Colorado Pikeminnow. Additional research on control strategies and prey population responses is needed to develop effective management strategies to mitigate the predatory impacts of nonnative species on native fish populations.