Pilot study to access the role of Ceratomyxa shasta infection in mortality of fall-run Chinook smolts migrating through the lower Klamath River in 2008.

Apparent survival and migration rate of radio-tagged hatchery subyearling Chinook salmon released at Iron Gate Hatchery was monitored in the Klamath River to see if the timing of mortality coincided with observations of ceratomyxosis in re-captured coded wire tag cohorts. Despite rapid emigration, these relatively large (mean fork length 92 mm) smolts had a cumulative apparent survival to the estuary of 0.074 (SE 0.024) and standardized rates of survival per 100 km tended to decrease linearly with distance from the hatchery. The last fish detection occurred 26 days after release but median travel time between Iron Gate Hatchery (rkm 309) and the last receiver near the Klamath estuary (Blake’s Riffle rkm 13) was about 10 days. The majority of apparent mortality (8-10 d post-release) occurred before disease from Ceratomyxa shasta
infection is expected after exposure to infectious waters. Despite numerous observations of ceratomyxosis in the Klamath R. during June, an obvious link between disease and apparent survival was not present in this study. Future studies should examine the acute (e.g., predator types and densities) and chronic (e.g., swimming performance impairment due to disease) mortality factors for juvenile Chinook salmon smolts in the Klamath River.