Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 525
Title: Summer distribution and growth of juvenile coho salmon during colonization of newly accessible habitat
Author: J. H. Anderson, Peter M. Kiffney, G. R. Pess, T. P. Quinn
Publication Year: 2008
Journal: Transactions of the American Fisheries Society
Volume: 137
Issue: 3
Pages: 772-781
Keywords: salmonids, dispersal, streams, growth, dams

    Pacific salmon Oncorhynchus spp. are capable of exploiting vacant habitat, but most research has focused on straying and colonization by adults.  However, dispersal of juveniles of stream-rearing species, such as coho salmon O. kisutch, may also be an important component of colonization.  Installation of fish passage structures on the Cedar River, Washington, and subsequent adult migration into the newly accessible habitat provided a rare opportunity to investigate colonization as coho salmon regained access to 33 km of habitat from which they had been excluded for more than a century.  In this study, we describe the spatial distribution and growth patterns of the first two generations of juvenile coho salmon produced in the new habitat.  Snorkel surveys in the Cedar River revealed patchy distributions of juvenile coho salmon that largely matched the distribution of adults spawning the previous fall, and higher densities occurred in lower reaches (i.e., those not far upstream from the dam).  However, sequential surveys indicated that juveniles entered and moved upstream within a Cedar River tributary, Rock Creek, where few, if any, adults spawned.  Juveniles captured in the Cedar River were similar in size to those in Rock Creek, but sizes differed between years and larger fish tended to occur farther upriver.  We found no evidence for density–dependent growth; there was no relationship between fish size and local density in either mainstem or tributary habitat.  Abundance estimates suggest that relatively few juvenile coho salmon dispersed long distances into reaches neglected by spawning adults.  We were unable to find any clear evidence that juvenile dispersal would increase the number of adults returning in the next generation, but such movements could accelerate the spatial expansion of the colonizing population in philopatric species like coho salmon.

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