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The relationships between fluctuations in oceanographic conditions, forage fishes, predatory fishes, predator food habits, and juvenile salmonid marine survival off the Columbia River

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dc.contributor.advisor Sampson, David, B.
dc.creator Emmett, Robert L.
dc.date.accessioned 2006-04-26T20:25:31Z
dc.date.available 2006-04-26T20:25:31Z
dc.date.copyright 2006-03-21
dc.date.issued 2006-04-26T20:25:31Z
dc.identifier.uri http://hdl.handle.net/1957/1783
dc.description Graduation date: 2006
dc.description.abstract Salmonid run sizes are strongly affected by their early marine stage. Fully understanding the life history of salmonids means understanding how they interact with their marine environment and with other fishes. Changes in the biological and physical environment off the Columbia River region affects the distribution and abundance of predatory fishes and their feeding, forage fishes, and juvenile salmonid marine survival. From 1998-2004, forage fish and predatory fish distribution and abundance off the Columbia River was quantified by surface trawling at night during spring/summer. The effect of predation on salmonids was measured by stomach analysis of predatory fishes. During the study period (1998-2004), forage fishes increased in abundance by orders of magnitude and were strongly related to the abundance of cold-water copepods the previous year. Higher forage fish populations were also linked to cooler ocean conditions and perhaps fewer predatory Pacific hake (Merluccius productus). Most forage fishes were distributed nearshore while predators had a more offshore distribution. Pacific hake was most abundant in 1998, 2003, and 2004; warm ocean years. Jack mackerel (Trachurus symmetricus) was most abundant during 1999-2002; relatively cool ocean years. Deep (50-m) ocean temperatures and the date of the spring transition, when nearshore currents switched from northward to southward, were good predictors of Pacific hake abundance in the study area. Forage fish or salmonid occurrence in a haul was negatively related to the occurrence of predators. Pacific hake and jack mackerel ate primarily euphausiids and small fishes. Salmonids were rarely eaten by either predator. However, because the Pacific hake population can be very large, hake predation can be a significant source of juvenile salmon mortality off the Columbia River during some years. A trophic model showed that marine mortality of Columbia River juvenile salmonids may be related to the abundance of Pacific hake and forage fishes. A multiple regression using the predictions from the trophic model of annual numbers of juvenile salmonids eaten by hake and Columbia River spring flows as independent variables, accounted for much of the variation observed in the annual marine survival of Columbia River coho (Oncorhynchus kisutch) and Chinook salmon (O. tshawytscha), the dependent variable. Future research should identify the physical and biological forces that alter the feeding habits, migration and movements of Pacific hake and jack mackerel off the Northwest, and how Columbia River flows affect trophic interactions. en
dc.format.extent 13469429 bytes
dc.format.mimetype application/pdf
dc.language.iso en_US en
dc.subject Forage fish en
dc.subject Pacific hake en
dc.subject Predatory fishes en
dc.subject Salmonids en
dc.subject Oceanography en
dc.subject Marine survival en
dc.subject.lcsh Salmonidae -- Effect of predation on -- Columbia River en
dc.subject.lcsh Piscivorous fishes -- Ecology -- Columbia River en
dc.subject.lcsh Forage fishes -- Ecology -- Columbia River en
dc.subject.lcsh Pacific hake -- Ecology -- Columbia River en
dc.subject.lcsh Jack mackerel -- Ecology -- Columbia River en
dc.title The relationships between fluctuations in oceanographic conditions, forage fishes, predatory fishes, predator food habits, and juvenile salmonid marine survival off the Columbia River en
dc.type Thesis en
dc.degree.name Doctor of Philosophy (Ph. D.) in Fisheries Science en
dc.degree.level Doctoral en
dc.degree.discipline Fisheries and Wildlife en
dc.degree.grantor Oregon State University en
dc.contributor.committeemember Pearcy, William
dc.contributor.committeemember Peterson, William
dc.contributor.committeemember Markle, Douglas
dc.contributor.committeemember Bolte, John

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