Roby, Daniel D. et al. “Quantifying the Effect of Predators on Endangered Species Using a Bioenergetics Approach: Caspian Terns and Juvenile Salmonids in the Columbia River Estuary.” Canadian Journal of Zoology 81.2 (2003) 250-265. (reviewed by Allyson Goldstein)
Summary:
Roby et. al. used a bioenergetics model structure to determine predation on juvenile salmonids and other forage fishes by Caspian terns on Rice Island in the Columbia River estuary. They undertook the study because of concerns that Caspian tern predation might be a substantial source of mortality to out-migrating populations throughout the Columbia River Basin. Many of these species are listed as endangered or threatened, and so it is important for scientists to understand all of the threats to these fish, and not just human induced threats like dams and pollution.
The bioenergetics model used estimates energy needs of the tern population, and what percentage of those energy needs is met by eating juvenile salmon. Using direct measurements of tern colony size, diet composition, and prey energy content, and daily energy expenditure (DEE) the researchers used the model to determine the effects that terns have on salmon population.
They determined that tern predation of juvenile salmonids is substantial, and that 15% of the juvenile salmonids that reach the estuary are eaten by terns. However, based on simple age-structured models of salmonid populations, it is unlikely that management of Caspian tern predation alone would increase salmon populations. As part of a comprehensive effort to stop salmon decline though, management to reduce tern predation could be effective. They also researched the terns' effects on specific types of salmon, and looked at effects on Chinook, Coho, and Steelhead specifically.
The article, which appears in a peer-reviewed journal, contains many charts and graphs to help the reader understand the complicated mathematics involved in the bioenergetics model. It was funded by the Bonneville Power Administration in Conjunction with the U.S. Army Corps of Engineers.
Critique:
This article is very well researched and well cited. The methodology section is particularly useful for scientists because it accounts for a wide variety of possible errors in the study and how those errors were avoided. It addition to offering useful information about the Caspian terns' effects on salmon, it offers information about the tern populations themselves, and about bird energy consumption and expenditure in general.
Although the article itself is quite complicated to read, the graphs and charts make it more accessible to a non-scientific audience, and the abstract which is published in English and in French (because it is in a Canadian journal) clearly summarizes the studies' intents and results. The end of the article has a lengthy acknowledgements section, which lends credibility to the manuscript because so many different scientists were involved with working on it.
Robert D. Clark Honors College, University of Oregon
HC 441: Science Colloquium, Columbia River Ecology
Fall term, 2005
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