Integrating Hydrodynamic and Statistical Models to Predict Distribution of the Invertebrate Host of Myxosporean Parasites That Plague Klamath River Salmon

Manayunkia speciosa, a freshwater polychaete, is the invertebrate host of myxosporean parasites that impact salmonid populations in the Pacific Northwest. The more lethal of these parasites, Ceratonova shasta, causes enteronecrosis in its fish host, leading to high mortality of outmigrating juvenile salmonids in the Klamath River, CA. Factors driving the distribution of M. speciosa are not well understood. We described the distribution of M. speciosa at three sites on the Klamath River using two-dimensional hydraulic models (2DHMs) and a statistical predictive model. We assessed the presence-absence of M. speciosa at 372 locations in July 2012 and built statistical models to characterize relationships between the distribution of M. speciosa and (1) substrate size, (2) observed hydraulic conditions at summer base flow discharge, and (3) 2DHM-predicted hydraulic conditions at the water year’s peak discharge. The best-fitting statistical models demonstrated that summer M. speciosa distributions were associated with substrate and depth-velocity (both observed during summer and predicted at peak discharge). Additionally, our model performed well in predicting locations with and without polychaetes when tested in the following year.