A Comparison of Visual Measurement-Based Techniques for Quantifying Cobble Embeddedness and Fine Sediment Levels in Salmonid-Bearing Steams
Document Type
Article
Journal/Book Title/Conference
North American Journal of Fisheries Management
Volume
25
Publication Date
2005
Keywords
Comparison, Visual, Measurement, Techniques, Quantifying, Cobble, Fine Sediment, Levels, Salmonid-Bearing, Streams
First Page
1208
Last Page
1214
Abstract
Excess fine-sediment loading can strongly affect the performance of salmonids rearing in fluvial habitats. Consequently, there are multiple techniques for quantifying the biologically relevant aspects of streambed material quality. While similar methods should provide similar measurements for a given attribute, little information is available that validates this assumption. Nevertheless, there are ongoing efforts toward assembling and analyzing large-scale habitat databases using existing information collected via multiple techniques. For these reasons, we used regression to compare visual and measurement-based approaches for two commonly assessed substrate variables (cobble embeddedness and percent surface fines). For both embeddedness and percent fines, we found moderate to strong linear relationships (R 2 = 0.46–0.83) between estimates obtained by visual and measurement-based approaches. However, the fitted line differed significantly from a null 1:1 expectation for the percent fines and embeddedness analyses, indicating that there is a differential bias between visual and measurement-based techniques relative to the true, but unknown, value. The observed deviation between embeddedness methods, which is primarily due to differences in measurement strategy, is probably of considerable practical significance. Conversely, the difference between techniques for percent fines appears to be negligible considering published information on observer variability for this attribute. In summary, our study provides a means for understanding and accounting for differences in substrate methods of direct relevance to large-scale habitat assessment efforts.
Recommended Citation
McHugh, P., and P. Budy. 2005. A comparison of visual measurement-‐based techniques for quantifying cobble embeddedness and fine sediment levels in salmonid-‐bearing streams. North American Journal of Fisheries Management 25:1208-‐1214.
