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Empirical Relationships Between Watershed Characteristics and Coho Salmon (Oncorhynchus kisutch) Smolt Abundance in 14 Western Washington Streams

Jun 21, 2001


We assembled data on Coho Salmon (Oncorhynchus kisutch) from 14 streams in western Washington, including annual smolt counts and annual escapement, either as absolute counts or as an index. We also compiled data on large woody debris (number*km-1 of stream), road densities in the watersheds (km road*km-2), gradient of the streams (%), valley slope adjacent to the stream (%), drainage area in the watershed (km2), and pool, pond, and lake areas (m2*km-1). We explored the relationships between habitat variables and two measures of Coho production, the maximum production of smolts in the stream (capacity) and the maximum smolts/spawner (productivity). Using the 11 streams with pool and pond counts, we found that pool and pond densities served as good predictors of smolt density (r 2 = 0.85 for pools and 0.68 for ponds, independently). Pools produced 0.39 smolts*m-2 and ponds produced 0.07 smolts*m-2 in the multiple regression fit, accounting for 92% of the residual error. We also found that lower valley slopes, lower road densities, and lower stream gradients were correlated with higher smolt density.


Rishi Sharma and Ray Hilborn


Sharma, R., and R. Hilborn. 2001. Empirical relationships between watershed characteristics and Coho Salmon (Oncorhynchus kisutch) smolt abundance in 14 Western Washington streams. Canadian Journal of Fisheries and Aquatic Sciences 58(7):1453-1463. Online at



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Journal Article