Humans are reshuffling the global distribution of organisms through introductions, climate-induced range shifts, and extirpations from native ranges. These processes lead to novel assemblages of species often with losses of ecosystem goods and services. Sacramento pikeminnow (Ptychocheilus. grandis) were introduced to the Eel River in 1979, and spread throughout most the basin in under a decade. These large predatory cyprinids consume many of the native fishes including culturally and economically important salmonids. We use a combination of snorkel surveys and temperature monitoring to track cues and consequences of seasonal movements of these large introduced predators.
Results/Conclusions
Pikeminnow in the South Fork Eel expand their range seasonally. Pikeminnow overwinter near the mouth of the mainstem Eel and move up towards headwaters over the course of the summer. As water temperatures warm in the summer, fish invade previously unoccupied upstream areas. The timing of this range expansion varies interannually, and appears to be influenced by antecedent flow conditions and river temperature. In a drier warmer year (e.g. 2015), upstream movement occured about four weeks earlier than in 2016, a wetter cooler year. Early upstream migration could increase pikeminnows’ negative impact on rearing salmonids and other native prey, by reducing the time predator-free refugia are available. These findings suggest that this invasive species’ impact will increase with the predicted warming and longer periods of drought in the future, and could be exacerbated by spring or summer water diversions.