Dynamics of a Northern Squawfish Population and the Potential to Reduce Predation on Juvenile Salmonids in a Columbia River Reservoir

Northern squawfish Ptychocheilus oregonensis prey on salmonid smolts ( Oncorhynchus spp.) in Columbia River reservoirs. We used simulation models to determine the potential influence of exploitation of northern squawfish on that predation. We also used correlation analysis to examine factors that may influence predation through predator recruitment. We based our simulations on estimates of mortality, relative year‐class strength, and growth made from a 4‐year study of resident fish predators in John Day Reservoir. Simulated predation declined with exploitation of fish longer than 275 mm (fork length) such that sustained exploitation of 10–20% annually reduced predation by 50% or more. The magnitude of change was related to the type of reproductive compensation. Recruitment was not obviously related to any environmental variable we examined, although year‐class strength was negatively correlated with concurrent year‐class strength of walleye Stizostedion vitreum . We believe that limited, but sustained, exploitation of northern squawfish provides an alternative to more radical control measures. We are uncertain about the potential recovery rate of exploited northern squawfish populations, however, and there is some risk that unsustained exploitation could aggravate predation. Any control program should evaluate density‐dependent responses of predators.