Effects of Ceratomyxosis on Population Dynamics of Klamath Fall‐Run Chinook Salmon

Abstract

Animal populations are frequently infected by pathogens, but it is not always easy to determine the importance of pathogens to overall population dynamics. It is especially difficult to detect the effects of disease in population time series data because the effects are often local while overall population dynamics are also affected by larger-scale environmental factors. We overcame this difficulty by applying multivariate time series analysis to extract local effects from spawning abundance data and by comparing the survival rate of juvenile fall-run Chinook salmon Oncorhynchus tshawytscha from two locations in the Klamath River basin of California, one of which is affected by a high concentration of the myxozoan parasite Ceratomyxa shasta. To assess the effect of the disease (ceratomyxosis) caused by C. shasta on the population dynamics, we analyzed spatially structured abundance data for naturally spawning salmon and survival data for hatchery-released salmon for associations with exposure to C. shasta and stream discharge, another important factor with respect to ceratomyxosis in juvenile salmon. The results suggest that ceratomyxosis reduces the survival of the Chinook salmon that migrate through the location where parasite densities are highest and that this effect is also detectable in spawning abundance estimates.

Density of the Waterborne Parasite Ceratomyxa shasta and Its Biological Effects on Salmon

“…In contrast, higher flows may dilute infectious stages and affect transmission efficiency. The survival rate of hatchery-released juvenile fall Chinook that migrated through a C. shasta-infectious region of the KR main stem, between the Shasta River (located between our KB and BC sites) and Seiad Creek confluence (our SV site), correlated significantly with stream discharge in this reach (13). Differences in flow and temperature may explain the strong intersite differences that we observed for C. shasta, and our future studies will incorporate flow measurements.…”

“…For the past decade, ceratomyxosis (enteronecrosis) has been regarded as the major cause of mortality in fall Chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon (10,13). Ceratomyxosis is caused by the myxozoan parasite Ceratomyxa shasta, which is present throughout the Pacific Northwest, but its negative impacts on native salmonids are most thoroughly documented in the KR.…”

“…Ceratomyxosis is caused by the myxozoan parasite Ceratomyxa shasta, which is present throughout the Pacific Northwest, but its negative impacts on native salmonids are most thoroughly documented in the KR. Severe ceratomyxosis in outmigrating juvenile fish contributes to reduced recruitment and adult returns (13,29).…”

Modeling the Effects of Climate Change on Disease Severity: A Case Study of Ceratonova (syn Ceratomyxa) shasta in the Klamath River

“…Disease impacts on fish populations vary widely, from largely unnoticeable to highly significant effects (Ching and Munday 1984;Hallett and Bartholomew 2011). The Klamath River, California, is one of the more heavily affected rivers, and despite an intensive hatchery enrichment program (from Iron Gate Hatchery), salmon populations have continued to decline, in part due to high C. shasta-related mortality (Stocking et al 2006;Fujiwara et al 2011;True et al 2011). Therefore, managing the parasite is a high priority in this river.…”

Klamath River Thermal Refuge Provides Juvenile Salmon Reduced Exposure to the Parasite Ceratonova shasta

“…Salmon in the Klamath River also encounter several pathogens, the myxozoan Ceratonova shasta being one of the most significant (Foott et al 2004;Fujiwara et al 2011). Infections by this parasite cause severe intestinal disease, ceratomyxosis (enteronecrosis), often resulting in death (Noble 1950;Bartholomew 1998).…”