Loge, Frank et al. "Impact of Environmental Stressors on the Dynamics of Disease Transmission." Environmental Science & Technology 39.18 (2005): 7329-7336. (reviewed by Allyson Goldstein)
Summary:
Loge et. al. examined the effects of both chemical (pollution) and in-river (dams, water temperature etc.) stressors on the disease susceptibility of juvenile Chinook salmon. Using a mathematical model, they examined how both chemical and non-chemical stressors affect disease induced mortality in young salmon. While many studies have examined the immediate physical effects of dams upon salmon, few have examined the delayed effects of environmental stressors on salmon. Environmental stressors weaken salmon, which makes them more susceptible to disease. Therefore reducing environmental stressors could reduce the decline of endangered salmon species by decreasing their susceptibility to diseases.
Using existing data from other studies, Loge et. al. modeled different scenarios including the effects of chemical stressors in rivers, non-chemical stressors in rivers, chemical stressors in estuaries, and non-chemical stressors in estuaries.
Loge et. al found that chemical stressors (both in the river and in the estuary) increased the per fish acquisition rate of infection by a factor of 2.2, and non-chemical stressors by a factor of 1.6. In other words, that higher stress levels in salmon do in fact lead to higher disease mortality, even if the number of pathogens remains the same. The study shows that one of the most important ways to protect a population from disease is to limit its susceptibility to that disease, rather than just reducing the pathogens themselves.
Critique:
This very informative article makes important point about methods of reducing pathogen-induced mortality in salmon. However, it contains a lot of scientific jargon. For instance, one of the last sentences says, "the present approach allows parameterization of the state change kinetic rates on dose of ambient stressor that is accumulated as individuals undergo transport in a spatially heterogeneous environment." It is also difficult for the non-mathematician to wade through the authors' calculations in the methods sections. That being said, the introduction and the conclusion explain an often-overlooked problem for juvenile salmon; disease.
The article also contains numerous charts and graphs, and even a helpful map of all of the dams along the Columbia River. The authors are also very thorough in terms of the data they used with the model, and explain possible sources of error. Though the study looked at Chinook salmon specifically, it applies to all fish and even terrestrial mammals as well.
Robert D. Clark Honors College, University of Oregon
HC 441: Science Colloquium, Columbia River Ecology
Fall term, 2005
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