Murphy, C.A., Pollock, A.M., Johnson, S.L., and Arismendi, I. (accepted) Linked foraging and bioenergetics modeling may inform fish parasite infection dynamics. Environmental Biology of Fishes
The parasitic copepod Salmincola californiensis infects Pacific salmon and trout (Oncorhynchus spp.) and often reaches high prevalence and intensity in reservoirs compared to stream systems. Recent research has indicated an important role of temperature in copepod development and fish susceptibility. Here, we examine the role of temperature on relative infection risk for juvenile Chinook Salmon in multiple reservoirs of the upper Willamette River Basin, Oregon. We used and expanded the GrowChinook model (a linked foraging and bioenergetics model) to estimate juvenile salmon infection risk. Based on salmon vertical migration patterns, we added estimates of copepod generations produced and thermal strata metrics for the infectious copepodid lifestage that appear associated with copepodid aggregations and increased infection risk. Our model predicted that Chinook Salmon in Lookout Point Reservoir consistently presented the greatest infection hours and estimated copepod generations, especially compared to Cougar Reservoir. This relative modelled risk is consistent with recent models of infection driven mortality and the severe damage caused by the infectious copepodid, a lifestage that is not readily visible in the field and thus has not been included in traditional infection prevalence and intensity counts. We discuss model limitations, potential for future research, and the potential for application of the copepod expansion equations to existing linked foraging and bioenergetics models or observed behaviors of salmonids in other lentic systems. We demonstrate that using a temperature sensitive model framework to test our existing knowledge and assumptions about copepod infection dynamics is useful in interpreting other lines of evidence, such as mortality estimates. Collectively, this work provides a testable framework for future comparisons of infection potential by this parasite infecting Pacific salmon and trout species.