Effect of Flow Manipulation on Dislodgement of a Polychaete Host for Salmonid Pathogens in a Laboratory Flume

The polychaete Manayunkia speciosa is the intermediate host for two myxozoan parasites that have been implicated in significant mortalities for salmonids in the Klamath River Basin, CA-OR, and it has become an organism of interest for fisheries management agencies because of its involvement in the salmon disease cycle.  We studied the effects of varying water velocities on polychaete response to evaluate the potential of using flow manipulation as a tool to reduce the incidence of disease-related salmonid mortalities.  In trials conducted within a laboratory flume, we measured the critical shear stress required to dislodge polychaetes from varying substrate types, evaluated survivorship of dislodged worms, and made observations of behavioral responses of the worms. We used logistic regression modeling to evaluate the probability of worm scour for treatment combinations of velocity and substrate.  Few worms were dislodged at velocities below 60 cm/s on any substrate. Above this velocity, probability of scour was strongly associated with both substrate type and velocity.  Survivorship of dislodged polychaetes was high.  Observations revealed that polychaetes exhibited a variety of behaviors for avoiding increases in current.  Taken together, our findings suggest that the probability of significantly reducing polychaete populations using flow manipulations will be low.