Regetz, James. “Landscape level constraints on recruitment of Chinook salmon (Oncorhynchus tshawytscha) in the Columbia River Basin, USA.” Aquatic Conserv.: Mar. Freshw. Ecosyst. 13 (2003): 35-49. (Reviewed by Laura Gayton)
Summary:
Although damming and commercial fishing both reduce salmonid populations, another large factor involved in the endangerment of salmon is loss of habitat and loss of quality spawning ground. Previously, it has been postulated that one factor in the endangerment of salmon may be the degradation of spawning grounds. This study examines the relationship between Chinook salmon ( Oncorhynchus tshawytscha ) productivity and landscape characteristics of streams used as spawning grounds. In this study, habitat conditions were measured by means of data on land use, cover, water quality and hydrology.
Productivity was measured by mean and maximum recruitment for 22 different stocks between 1980 and 1990. Correlations between salmon recruitment and three different factors were found to be significant. These three factors included percentage of urban land, proportion of stream length that fails to meet water quality standards and the stream ability to recovery from sediment flow events, as measured by an index. Together, these variables accounted for over half of the variation in mean salmon recruitment (Regetz 35).
An interesting aspect of this study was that two of the factors that these analyses included, river distance and number of dams, were not significant predictors of salmon productivity. This means, perhaps, that dams may have less of an effect, at least at these particular spawning grounds, than land use surrounding the spawning habitat, although this effect was uneven and perhaps just not the same across spawning sites.
As this paper points out, although salmon face huge impediments while moving toward their spawning grounds like dams and commercial fisherman, the habitat awaiting them impacts them as well. This spawning ground quality is determined in many cases by what is occurring on land nearby. Though he admits that there are so many factors at play in fish productivity that habitat restoration alone would not completely recover salmon populations to previous levels, “the results reported here clearly indicate that some landscape-level attributes are related to salmon productivity, and may in fact impose a constraint on potential population recruitment rates” (Regetz 46).
Critique:
This paper is somewhat revolutionary and is different than other studies on salmon productivity because of its landscape-scale view of in-stream habitat variables and life-history aspects of the salmon (Regetz 36). Instead of fine-scale linkages, productivity was measured versus landscape variables. This was done because in addition to small-scale variables, “landscape scale environmental factors can also strongly influence aquatic populations” (Regetz 36). What occurs on the banks of the stream has much to do with what goes on in the stream, especially when talking about specific spawning sites. This different approach is one of the strengths of the paper, because this methodology allows land use to be tied to direct effects on salmon populations. This kind of link must be made before restoration becomes a priority.
One negative aspect of this study is that their “coarse-grain” data, taken from landscape-scale variables, doesn't allow analysis of things such as forest management on productivity. As Regetz writes, “evaluating the impacts of forest management requires finer scale data than we've used here” (46).
Robert D. Clark Honors College, University of Oregon
HC 441: Science Colloquium, Columbia River Ecology
Fall term, 2005
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