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• 691. [Article] Stream habitat classification and restoration in the Blue Mountians of northeast Oregon

  The restoration of rivers and streams should be based on a strong conceptual framework. Streams are developing systems. As such, streams exhibit temporal behaviors that change with changing stream environments. ...

  Citation × Citation Citation Abstract Copy Title: Stream habitat classification and restoration in the Blue Mountians of northeast Oregon Author: Ebersole, Joseph Lamar The restoration of rivers and streams should be based on a strong conceptual framework. Streams are developing systems. As such, streams exhibit temporal behaviors that change with changing stream environments. Underlying the dynamic development of streams is potential capacity. Streams express this capacity as an array of habitats over time and across the landscape. Human land uses in the western United States have rapidly altered aquatic habitats as well as the processes that shape habitat. As a result, the diversity of native fishes and their habitats has been suppressed. Restoration is fundamentally about allowing stream systems to re-express their capacities. Four steps are provided to guide stream restoration activities. Key tasks include: identification of the historic patterns of habitat development; protection of the developmental diversity that remains; local application of specific knowledge about suppressive factors; classification of sensitive, critical or refugium habitats; release of anthropogenic suppression; and monitoring of biotic response to habitat change. Applying these concepts, I describe potential habitat refugia for aquatic organisms in the Joseph Creek basin in the Blue Mountains of northeast Oregon. Five valley segment classes, differing in valley corridor landforms, are described. Of these, low-gradient wide alluvial valleys have been most altered by human land use. Riparian vegetation has been extensively removed or altered in alluvial valleys. Currently, stream habitats are structurally depauperate, and warm to temperatures well above thermal tolerances of native salmonids. Potential refugia for native coldwater fishes in these valleys include patches of complex habitat within stream reaches. Reaches fenced to exclude domestic livestock exhibit narrower channels, more pools, and higher frequencies of stable vegetated banks than nearby unfenced reaches. During summer low flow periods, cold groundwater seeping into and accumulating in stream channels forms "cold pools". Cold pools provide potential seasonal refuge for coldwater fish at microhabitat scales. Cold pools are associated with channel complexity, and are more frequent in reaches with vigorous riparian vegetation. Seven classes of cold pools are described. Cold pool classes differ in minimum temperature, maximum depth and volume. Distributions of cold pool classes between valley segment classes suggest that valley geomorphology in addition to local channel form may influence development of certain cold pool types. Although refugia at the microhabitat to reach scales are important, the context within which remnant or refugium habitats and associated relict populations are maintained may ultimately determine the persistence of those species and habitats. In managed landscapes, protection and restoration of habitats at many scales may be necessary if we are to best insure the persistence of native species. Title: Stream habitat classification and restoration in the Blue Mountians of northeast Oregon Author: Ebersole, Joseph Lamar The restoration of rivers and streams should be based on a strong conceptual framework. Streams are developing systems. As such, streams exhibit temporal behaviors that change with changing stream environments. Underlying the dynamic development of streams is potential capacity. Streams express this capacity as an array of habitats over time and across the landscape. Human land uses in the western United States have rapidly altered aquatic habitats as well as the processes that shape habitat. As a result, the diversity of native fishes and their habitats has been suppressed. Restoration is fundamentally about allowing stream systems to re-express their capacities. Four steps are provided to guide stream restoration activities. Key tasks include: identification of the historic patterns of habitat development; protection of the developmental diversity that remains; local application of specific knowledge about suppressive factors; classification of sensitive, critical or refugium habitats; release of anthropogenic suppression; and monitoring of biotic response to habitat change. Applying these concepts, I describe potential habitat refugia for aquatic organisms in the Joseph Creek basin in the Blue Mountains of northeast Oregon. Five valley segment classes, differing in valley corridor landforms, are described. Of these, low-gradient wide alluvial valleys have been most altered by human land use. Riparian vegetation has been extensively removed or altered in alluvial valleys. Currently, stream habitats are structurally depauperate, and warm to temperatures well above thermal tolerances of native salmonids. Potential refugia for native coldwater fishes in these valleys include patches of complex habitat within stream reaches. Reaches fenced to exclude domestic livestock exhibit narrower channels, more pools, and higher frequencies of stable vegetated banks than nearby unfenced reaches. During summer low flow periods, cold groundwater seeping into and accumulating in stream channels forms "cold pools". Cold pools provide potential seasonal refuge for coldwater fish at microhabitat scales. Cold pools are associated with channel complexity, and are more frequent in reaches with vigorous riparian vegetation. Seven classes of cold pools are described. Cold pool classes differ in minimum temperature, maximum depth and volume. Distributions of cold pool classes between valley segment classes suggest that valley geomorphology in addition to local channel form may influence development of certain cold pool types. Although refugia at the microhabitat to reach scales are important, the context within which remnant or refugium habitats and associated relict populations are maintained may ultimately determine the persistence of those species and habitats. In managed landscapes, protection and restoration of habitats at many scales may be necessary if we are to best insure the persistence of native species. Close

• 692. [Article] Ecology of aquatic habitats associated with stream margins

  The morphology and ecological importance of habitats associated with the margin of third-order stream channels in the Oregon Cascades were studied in streams in three different riparian types: 450-year-old ...

  Citation × Citation Citation Abstract Copy Title: Ecology of aquatic habitats associated with stream margins Author: Moore, Kelly M. S. The morphology and ecological importance of habitats associated with the margin of third-order stream channels in the Oregon Cascades were studied in streams in three different riparian types: 450-year-old conifers, 40-year-old alder, and an open, herbaceous-dominated clearcut. Margins, backwaters, and side channels in streams create important habitat for fry of cutthroat trout (Salmo clarki clarki) and support benthic invertebrate assemblages of high denSity and distinctive composition. These lateral habitats are characterized by slow, shallow water, heterogeneous size distribution of substrates, abundant detritus, and by hydraulic and morphologic persistence. In the study reaches, area of lateral habitat was maximum in early summer, averaging 15 percent of total stream area. The amount of lateral habitat decreased with either lower or higher flows. During a 1-yr period lateral habitats in the coniferous site changed the least. The volume and hydraulic characteristics of individual lateral habitats were functions of the morphology of the structures that formed the habitat and the orientation and location of the habitat relative to the central axis of the strea Large woody debris and large boulders created lateral habitats that were larger, had longer hydrologic residence times, and were more persistent when streamflow changed than lateral habitats formed by small boulders and cobble. Stream margins and backwaters were major sites of detritus storage. Average detritus standing crop in backwaters and stream margins was 5 to 15 times greater than standing crops in riffles or pools in the same stream. Detritus at the coniferous reach had higher organic matter content and a greater percentage of lignin than detritus at the deciduous reach. Detritus at the open reach was much lower in organic matter content, but the ratio of cellulose to lignin was greater than in the forested reaches. The activity of microbial assemblages associated with fine detritus was generally highest at the open reach. Average standing crop of chlorophyll a was highest at the open site. The abundance and quality of nutritional resources in lateral habitats were reflected in the associated invertebrate communities. High densities of chironomids, early instar Ephemeroptera and Plecoptera, oligochaetes, and micro-crustacea were found in stream margins and backwaters at each site. Mean invertebrate density in lateral habitats was similar in the coniferous (66,500 individuals/m²) and open (75,000 individuals/m²) reaches, but lower at the deciduous site (24,000 individuals/m²). Collector-gatherer, shredder, and predator functional feeding groups were well represented at each site. Differences in functional roup organization between reaches were primarily related tp increased numbers of herbivorous collector-gatherers at the open site and a greater relative abundance of shredders at the deciduous site. Cutthroat trout fry populations were directly linked to the length of stream edge and the area of lateral habitat. Fry occupy lateral habitats immediately after emergence and may not move from lateral habitats until the end of their first summer. In an experimental manipulation of nine stream reaches, increasing lateral habitat prior to fry emergence resulted in 2.5 times higher fry density than in control reaches and reducing lateral habitat virtually eliminated fry populations. Cutthroat trout in headwater streams continue to use lateral habitats throughout their life cycle as refuge for all age classes during high streamflow and by adult trout as spawning areas. Title: Ecology of aquatic habitats associated with stream margins Author: Moore, Kelly M. S. The morphology and ecological importance of habitats associated with the margin of third-order stream channels in the Oregon Cascades were studied in streams in three different riparian types: 450-year-old conifers, 40-year-old alder, and an open, herbaceous-dominated clearcut. Margins, backwaters, and side channels in streams create important habitat for fry of cutthroat trout (Salmo clarki clarki) and support benthic invertebrate assemblages of high denSity and distinctive composition. These lateral habitats are characterized by slow, shallow water, heterogeneous size distribution of substrates, abundant detritus, and by hydraulic and morphologic persistence. In the study reaches, area of lateral habitat was maximum in early summer, averaging 15 percent of total stream area. The amount of lateral habitat decreased with either lower or higher flows. During a 1-yr period lateral habitats in the coniferous site changed the least. The volume and hydraulic characteristics of individual lateral habitats were functions of the morphology of the structures that formed the habitat and the orientation and location of the habitat relative to the central axis of the strea Large woody debris and large boulders created lateral habitats that were larger, had longer hydrologic residence times, and were more persistent when streamflow changed than lateral habitats formed by small boulders and cobble. Stream margins and backwaters were major sites of detritus storage. Average detritus standing crop in backwaters and stream margins was 5 to 15 times greater than standing crops in riffles or pools in the same stream. Detritus at the coniferous reach had higher organic matter content and a greater percentage of lignin than detritus at the deciduous reach. Detritus at the open reach was much lower in organic matter content, but the ratio of cellulose to lignin was greater than in the forested reaches. The activity of microbial assemblages associated with fine detritus was generally highest at the open reach. Average standing crop of chlorophyll a was highest at the open site. The abundance and quality of nutritional resources in lateral habitats were reflected in the associated invertebrate communities. High densities of chironomids, early instar Ephemeroptera and Plecoptera, oligochaetes, and micro-crustacea were found in stream margins and backwaters at each site. Mean invertebrate density in lateral habitats was similar in the coniferous (66,500 individuals/m²) and open (75,000 individuals/m²) reaches, but lower at the deciduous site (24,000 individuals/m²). Collector-gatherer, shredder, and predator functional feeding groups were well represented at each site. Differences in functional roup organization between reaches were primarily related tp increased numbers of herbivorous collector-gatherers at the open site and a greater relative abundance of shredders at the deciduous site. Cutthroat trout fry populations were directly linked to the length of stream edge and the area of lateral habitat. Fry occupy lateral habitats immediately after emergence and may not move from lateral habitats until the end of their first summer. In an experimental manipulation of nine stream reaches, increasing lateral habitat prior to fry emergence resulted in 2.5 times higher fry density than in control reaches and reducing lateral habitat virtually eliminated fry populations. Cutthroat trout in headwater streams continue to use lateral habitats throughout their life cycle as refuge for all age classes during high streamflow and by adult trout as spawning areas. Close

• 693. [Article] Climate warming effects on the life cycle of the parasite Ceratomyxa shasta in salmon of the Pacific Northwest

  Aquatic ecosystems continue to be increasingly affected by climate warming. For salmonids in the Pacific Northwest of North America, increasing temperatures pose tighter thermal constraints on their habitat ...

  Citation × Citation Citation Abstract Copy Title: Climate warming effects on the life cycle of the parasite Ceratomyxa shasta in salmon of the Pacific Northwest Author: Chiaramonte, Luciano V. Aquatic ecosystems continue to be increasingly affected by climate warming. For salmonids in the Pacific Northwest of North America, increasing temperatures pose tighter thermal constraints on their habitat use as well as aspects of their individual performance, such as disease resistance. This thesis examines the effect of temperature on the phenology of the Ceratomyxa shasta life cycle, the effect of thermal refugia on disease risk in juvenile salmonids in the Klamath River, CA, and the spatial and temporal distribution of C. shasta in the Willamette River, OR. We developed a biological model that predicts an acceleration of the C. shasta life cycle development due to climate shifts in the Klamath River, resulting in more generations per year and earlier seasonal parasite occurrence. We showed that in early summer the Beaver Creek-Klamath River confluence provides juvenile Chinook and coho salmon an area of lower parasite doses and cooler temperatures than the main stem, thus lessening disease risk. By accelerating the development of C. shasta in its hosts, increasing temperatures will result in earlier parasite transmission to juvenile salmonids and a longer season of infectivity. These fish may find disease refuge at cold tributary inflows to the main stem of the Klamath River in early summer, further adding to the benefit of these important thermal habitats. To determine if similar disease patterns occur in other rivers with the parasite, we described spatial and temporal occurrence of C. shasta in the Willamette River. By collecting weekly water sampling at four sites over 28 months we characterize seasonal and annual differences of parasite abundance, which varies with weekly temperature. We also collected samples along the length of the main stem and its tributaries and identified spatial differences in C. shasta spore densities. Identification of spatial and temporal variation of C. shasta in the Willamette River provides a foundation for understanding future patterns of disease occurrence in this river where conservation of anadromous fisheries is also of concern. This thesis identifies likely responses of C. shasta to climate warming in the Klamath River, with useful application to other rivers in the Pacific Northwest. Title: Climate warming effects on the life cycle of the parasite Ceratomyxa shasta in salmon of the Pacific Northwest Author: Chiaramonte, Luciano V. Aquatic ecosystems continue to be increasingly affected by climate warming. For salmonids in the Pacific Northwest of North America, increasing temperatures pose tighter thermal constraints on their habitat use as well as aspects of their individual performance, such as disease resistance. This thesis examines the effect of temperature on the phenology of the Ceratomyxa shasta life cycle, the effect of thermal refugia on disease risk in juvenile salmonids in the Klamath River, CA, and the spatial and temporal distribution of C. shasta in the Willamette River, OR. We developed a biological model that predicts an acceleration of the C. shasta life cycle development due to climate shifts in the Klamath River, resulting in more generations per year and earlier seasonal parasite occurrence. We showed that in early summer the Beaver Creek-Klamath River confluence provides juvenile Chinook and coho salmon an area of lower parasite doses and cooler temperatures than the main stem, thus lessening disease risk. By accelerating the development of C. shasta in its hosts, increasing temperatures will result in earlier parasite transmission to juvenile salmonids and a longer season of infectivity. These fish may find disease refuge at cold tributary inflows to the main stem of the Klamath River in early summer, further adding to the benefit of these important thermal habitats. To determine if similar disease patterns occur in other rivers with the parasite, we described spatial and temporal occurrence of C. shasta in the Willamette River. By collecting weekly water sampling at four sites over 28 months we characterize seasonal and annual differences of parasite abundance, which varies with weekly temperature. We also collected samples along the length of the main stem and its tributaries and identified spatial differences in C. shasta spore densities. Identification of spatial and temporal variation of C. shasta in the Willamette River provides a foundation for understanding future patterns of disease occurrence in this river where conservation of anadromous fisheries is also of concern. This thesis identifies likely responses of C. shasta to climate warming in the Klamath River, with useful application to other rivers in the Pacific Northwest. Close

• 694. [Article] Juvenile Rockfish (Sebastes spp.) Community Composition and Habitat use of Yaquina Bay, Oregon

  Estuaries, which provide viable habitat for a plethora of fish and invertebrate species, are being increasingly impacted by anthropogenic and natural forces. Estuaries are important nursery habitat for ...

  Citation × Citation Citation Abstract Copy Title: Juvenile Rockfish (Sebastes spp.) Community Composition and Habitat use of Yaquina Bay, Oregon Author: Lindsley, Amy J. Estuaries, which provide viable habitat for a plethora of fish and invertebrate species, are being increasingly impacted by anthropogenic and natural forces. Estuaries are important nursery habitat for young-of-the-year (YOY) Pacific rockfish (Sebastes spp.). Yaquina Bay, a marine-dominated estuary on the central Oregon Coast, served as a study site for the estuarine use of juvenile rockfishes, and large numbers of juvenile rockfish have been captured in this bay. Nursery habitats must provide rearing habitat, adequate food resources and refuge. A vital but lacking connection in our understanding of estuaries as nursery habitat is how rockfishes use the different microhabitats within an estuarine ecosystem. As habitats structure biotic communities, determining the ecological requirements for juvenile rockfish habitats that minimize mortality, maximize growth and increase population numbers will assist managers and biologists in managing and protecting critical high-quality nursery areas. This study provides insight into Oregon rockfish life history, evaluating the spatial and temporal use of estuarine nursery habitat by juvenile rockfishes. The primary objectives were to (1) determine which species of rockfish utilize Yaquina Bay, (2) determine seasonal variations in abundance, and (3) assess the utilization of natural (eelgrass beds, Zostera marina) versus anthropogenic (piers) estuarine habitat. I conducted a mark-recapture study of juvenile rockfishes to begin to elucidate how these species may be using different habitats in the bay. This study provides evidence for the presence of previously undocumented rockfish species, the overwinter persistence of juvenile rockfish in the estuary, some degree of site fidelity, and apparent minimal movement of juvenile rockfish in the Yaquina Bay estuary during the period of this study, as well as a shift in rockfish community dominance from S. melanops to S. maliger and S. caurinus. The survival and recapture of juveniles in both natural (Z. marina) and anthropogenic (piers) habitat demonstrates rockfishes’ successful use of multiple Yaquina Bay habitat types as nursery grounds year-round. There is seasonal variability in rockfish use of the anthropogenic and natural habitat, with the anthropogenic habitats having an overall higher capture rate and a higher occurrence of larger rockfish. All eight species S. melanops, S. maliger, S. caurinus, S. paucispinis, S. flavidus, S. nebulosus, S. pinniger and S. auriculatus are present in the natural, Z. marina habitat. Sebastes pinniger and S. auriculatus are absent from anthropogenic, pier habitat. The implications of determining habitat parameters, community interactions, seasonal changes of the fish community, and ecosystem mechanisms may be invaluable to support further recreational and commercial fishing and help sustain or increase adult populations. My findings present a significant contribution towards the proper management and conservation of essential habitat for rockfish, a group of species with high commercial value and substantial recreational harvest. Title: Juvenile Rockfish (Sebastes spp.) Community Composition and Habitat use of Yaquina Bay, Oregon Author: Lindsley, Amy J. Estuaries, which provide viable habitat for a plethora of fish and invertebrate species, are being increasingly impacted by anthropogenic and natural forces. Estuaries are important nursery habitat for young-of-the-year (YOY) Pacific rockfish (Sebastes spp.). Yaquina Bay, a marine-dominated estuary on the central Oregon Coast, served as a study site for the estuarine use of juvenile rockfishes, and large numbers of juvenile rockfish have been captured in this bay. Nursery habitats must provide rearing habitat, adequate food resources and refuge. A vital but lacking connection in our understanding of estuaries as nursery habitat is how rockfishes use the different microhabitats within an estuarine ecosystem. As habitats structure biotic communities, determining the ecological requirements for juvenile rockfish habitats that minimize mortality, maximize growth and increase population numbers will assist managers and biologists in managing and protecting critical high-quality nursery areas. This study provides insight into Oregon rockfish life history, evaluating the spatial and temporal use of estuarine nursery habitat by juvenile rockfishes. The primary objectives were to (1) determine which species of rockfish utilize Yaquina Bay, (2) determine seasonal variations in abundance, and (3) assess the utilization of natural (eelgrass beds, Zostera marina) versus anthropogenic (piers) estuarine habitat. I conducted a mark-recapture study of juvenile rockfishes to begin to elucidate how these species may be using different habitats in the bay. This study provides evidence for the presence of previously undocumented rockfish species, the overwinter persistence of juvenile rockfish in the estuary, some degree of site fidelity, and apparent minimal movement of juvenile rockfish in the Yaquina Bay estuary during the period of this study, as well as a shift in rockfish community dominance from S. melanops to S. maliger and S. caurinus. The survival and recapture of juveniles in both natural (Z. marina) and anthropogenic (piers) habitat demonstrates rockfishes’ successful use of multiple Yaquina Bay habitat types as nursery grounds year-round. There is seasonal variability in rockfish use of the anthropogenic and natural habitat, with the anthropogenic habitats having an overall higher capture rate and a higher occurrence of larger rockfish. All eight species S. melanops, S. maliger, S. caurinus, S. paucispinis, S. flavidus, S. nebulosus, S. pinniger and S. auriculatus are present in the natural, Z. marina habitat. Sebastes pinniger and S. auriculatus are absent from anthropogenic, pier habitat. The implications of determining habitat parameters, community interactions, seasonal changes of the fish community, and ecosystem mechanisms may be invaluable to support further recreational and commercial fishing and help sustain or increase adult populations. My findings present a significant contribution towards the proper management and conservation of essential habitat for rockfish, a group of species with high commercial value and substantial recreational harvest. Close

• 695. [Article] Relationship between plant and butterfly community composition on upland prairies of the Willamette Valley, Oregon

  Small remnants of 'natural' habitats exist today throughout much of the world. Upland prairies in the Willamette Valley, Oregon have been nearly eliminated by conversion to agriculture and other uses. ...

  Citation × Citation Citation Abstract Copy Title: Relationship between plant and butterfly community composition on upland prairies of the Willamette Valley, Oregon Author: York, Melissa M. Small remnants of 'natural' habitats exist today throughout much of the world. Upland prairies in the Willamette Valley, Oregon have been nearly eliminated by conversion to agriculture and other uses. As a result, very few prairies remain and at least four butterfly species that require this habitat appear to be locally uncommon. To better understand requirements for conservation and management of upland prairies and the species that depend on them, I investigated plant abundance and species richness, butterfly abundance and species richness, and prairie integrity on 17 prairie remnants. To evaluate the relationship between prairie integrity and butterfly community composition, integrity was defined by abundance and species richness of native, prairie plant species. Because little is known about the habitat requirements of prairie-dwelling organisms, I also investigated juvenile and adult food resource use and spatial patterns associated with resource use by four locally uncommon butterfly species: common checkered-skipper, Fender's blue, Anise swallowtail, and field crescent. Plant species used and not used for nectaring and oviposition and spatial relationships between the two were explored for each butterfly species. My study provides evidence that remnants, including small, degraded sites, serve as refuges for locally uncommon butterfly species. The greatest mean number of butterfly species was detected on sites of high integrity, but total butterfly abundance at all but one unique site was similar to that of low and medium integrity sites. Butterfly species richness appeared to be positively associated with remnant integrity while factors other than remnant integrity as defined here may be influential on butterfly abundance. Furthermore, I suggest that the locally uncommon butterflies studied here have specific habitat requirements and this likely contributed to their sparse distribution. Although host plant abundance did not appear to limit butterfly distributions within either site, I lacked sufficient sample sizes necessary to make strong inferences. Factors other than, or in combination, with host plant occurrence, such as presence of Composite nectar species and native plant abundance, may be important in determining their distribution within a site. Lack of large areas of habitat and incidence of uncommon species on remnants makes it imperative that we conserve biodiversity by the maintenance, improvement, and protection of some very small areas. Title: Relationship between plant and butterfly community composition on upland prairies of the Willamette Valley, Oregon Author: York, Melissa M. Small remnants of 'natural' habitats exist today throughout much of the world. Upland prairies in the Willamette Valley, Oregon have been nearly eliminated by conversion to agriculture and other uses. As a result, very few prairies remain and at least four butterfly species that require this habitat appear to be locally uncommon. To better understand requirements for conservation and management of upland prairies and the species that depend on them, I investigated plant abundance and species richness, butterfly abundance and species richness, and prairie integrity on 17 prairie remnants. To evaluate the relationship between prairie integrity and butterfly community composition, integrity was defined by abundance and species richness of native, prairie plant species. Because little is known about the habitat requirements of prairie-dwelling organisms, I also investigated juvenile and adult food resource use and spatial patterns associated with resource use by four locally uncommon butterfly species: common checkered-skipper, Fender's blue, Anise swallowtail, and field crescent. Plant species used and not used for nectaring and oviposition and spatial relationships between the two were explored for each butterfly species. My study provides evidence that remnants, including small, degraded sites, serve as refuges for locally uncommon butterfly species. The greatest mean number of butterfly species was detected on sites of high integrity, but total butterfly abundance at all but one unique site was similar to that of low and medium integrity sites. Butterfly species richness appeared to be positively associated with remnant integrity while factors other than remnant integrity as defined here may be influential on butterfly abundance. Furthermore, I suggest that the locally uncommon butterflies studied here have specific habitat requirements and this likely contributed to their sparse distribution. Although host plant abundance did not appear to limit butterfly distributions within either site, I lacked sufficient sample sizes necessary to make strong inferences. Factors other than, or in combination, with host plant occurrence, such as presence of Composite nectar species and native plant abundance, may be important in determining their distribution within a site. Lack of large areas of habitat and incidence of uncommon species on remnants makes it imperative that we conserve biodiversity by the maintenance, improvement, and protection of some very small areas. Close

• 696. [Article] Early self-sorting behavior in Chinook salmon is correlated with variation in growth, behavior and morphology later in life.

  Juvenile Chinook salmon (Oncorhynchus tshawytscha) exhibit an array of life history tactics in Oregon's Willamette River Basin, yet we do not know to what extent it is driven by phenotypic plasticity or ...

  Citation × Citation Citation Abstract Copy Title: Early self-sorting behavior in Chinook salmon is correlated with variation in growth, behavior and morphology later in life. Author: Unrein, Julia R. Juvenile Chinook salmon (Oncorhynchus tshawytscha) exhibit an array of life history tactics in Oregon's Willamette River Basin, yet we do not know to what extent it is driven by phenotypic plasticity or whether it is predetermined and how conditions in the early rearing environment may affect phenotype expression. We have found hatchery-origin fry sort themselves into distinct surface and bottom oriented phenotypes within days of first feeding and this orientation persists after separation. Surface and bottom phenotypes demonstrated differences in head and body morphology at 2 months post-swim up across three brood years (BY). The surface phenotype exhibits a shorter head and deeper body compared to bottom phenotype. The BY 2012 surface phenotype spent 3 times longer, on average, interacting with their mirror image in an open arena than the bottom phenotype. Tests conducted with BY 2013 fish indicated that bottom-oriented fish engaged in swimming-against-mirror behavior 5 times more than the surface phenotype when the mirror was near gravel refuge. After 8 months of rearing, the BY 2012 surface phenotype was 10% larger than bottom fish and morphometric differences persisted. Surface and bottom phenotypes from BY 2013, were reared under two temperatures and as either separate or combined phenotype groups. The two phenotypes grew at the same rate at 12°C, irrespective of separate or combined rearing, but at 7°C surface fish were significantly larger than bottom fish after three months until temperatures increased after which the two phenotypes converged. While equal in size, the morphologies of the BY 2013 orientation phenotypes were consistent with previous findings. These differences seen in body shape between the surface and bottom oriented groups are similar to differences exhibited between wild subyearling and yearling life history types in the basin. Such phenotypic differences may offer potential for predicting juvenile life history trajectory early in life. Title: Early self-sorting behavior in Chinook salmon is correlated with variation in growth, behavior and morphology later in life. Author: Unrein, Julia R. Juvenile Chinook salmon (Oncorhynchus tshawytscha) exhibit an array of life history tactics in Oregon's Willamette River Basin, yet we do not know to what extent it is driven by phenotypic plasticity or whether it is predetermined and how conditions in the early rearing environment may affect phenotype expression. We have found hatchery-origin fry sort themselves into distinct surface and bottom oriented phenotypes within days of first feeding and this orientation persists after separation. Surface and bottom phenotypes demonstrated differences in head and body morphology at 2 months post-swim up across three brood years (BY). The surface phenotype exhibits a shorter head and deeper body compared to bottom phenotype. The BY 2012 surface phenotype spent 3 times longer, on average, interacting with their mirror image in an open arena than the bottom phenotype. Tests conducted with BY 2013 fish indicated that bottom-oriented fish engaged in swimming-against-mirror behavior 5 times more than the surface phenotype when the mirror was near gravel refuge. After 8 months of rearing, the BY 2012 surface phenotype was 10% larger than bottom fish and morphometric differences persisted. Surface and bottom phenotypes from BY 2013, were reared under two temperatures and as either separate or combined phenotype groups. The two phenotypes grew at the same rate at 12°C, irrespective of separate or combined rearing, but at 7°C surface fish were significantly larger than bottom fish after three months until temperatures increased after which the two phenotypes converged. While equal in size, the morphologies of the BY 2013 orientation phenotypes were consistent with previous findings. These differences seen in body shape between the surface and bottom oriented groups are similar to differences exhibited between wild subyearling and yearling life history types in the basin. Such phenotypic differences may offer potential for predicting juvenile life history trajectory early in life. Close

• 697. [Article] Emergence, survival and reproduction of three species of forbs important to sage grouse nutrition in response to fire, microsite and method of establishment

  Since settlement of the Intermountain West, sage grouse abundance and productivity has declined and their range has decreased. The decline of sage grouse populations is primarily due to permanent loss ...

  Citation × Citation Citation Abstract Copy Title: Emergence, survival and reproduction of three species of forbs important to sage grouse nutrition in response to fire, microsite and method of establishment Author: Wirth, Troy A. Since settlement of the Intermountain West, sage grouse abundance and productivity has declined and their range has decreased. The decline of sage grouse populations is primarily due to permanent loss and degradation of sagebrush-grassland habitat. Recently, several studies have shown that sage grouse productivity may be limited by the availability of certain preferred, highly nutritious forb species that have also declined within sagebrush ecosystems of the Intermountain West. During the spring and summer, forbs are extremely important in maintaining the nutritional status and productivity of pre-laying hens and growth and survival of rapidly growing chicks. Researchers studying sage grouse have suggested several methods for restoring forbs in depleted sage grouse habitat. Among the methods proposed are prescribed fires that produce small mosaics of burned and unburned patches on the landscape. For this to occur, an adequate pre-burn forb community must exist in the location of the fire. In areas without adequate pre-burn forb communites, forbs must reseed naturally or be revegetated. The purpose of this study was to determine the suitability of three species of forbs for revegetation projects where improving sage grouse habitat is a goal. Species suitability was determined by evaluating the emergence, survival and reproduction of Crepis modocensis Greene, Crepis occidentalis Nutt. and Astragalus purshii in response to method of establishment (seeding or transplanting), pre-establishment treatment (burned or unburned), and microsite (mound or interspace). Four prescription burns of sagebrush grassland were set at the United States Fish and Wildlife Service Hart Mountain National Antelope Refuge, Oregon. After burning, one experimental plot was randomly located within each burned and unburned site. Of the seeds planted in 1997, A. purshil had the lowest emergence (8%) of all three species. Both Crepis species had similar overall emergence (38%). Significantly more Crepis seedlings emerged from shrub mounds in unburned areas (50%) than in any other fire by microsite treatment (33 to 36%). Significantly more A. purshuii emerged in the burned interspace (10.9) compared to the burned mounds (3.5). Nearly twice as many emerging Crepis seedlings survived in the burned areas as opposed to unburned areas (P<0.01). This resulted in more plant establishment in burned mounds despite higher emergence in unburned mounds. Microsite also significantly affected survival of Crepis seedlings (P<0.01). Approximately 10% more Crepis seedlings survived in mounds compared to interspaces. A. purshuii seedlings also survived better in burned areas (P=0.06), but had no differential response to microsite. Fire enhanced survival of both Crepis and A. purshii transplants (P=0.08 and P=0.001), although, transplanting did not enhance plant establishment over seedings. Therefore, I conclude that revegetation of sage grouse habitat with Crepis species is a viable option given its high germinability, favorable response to fire and wide distribution. Title: Emergence, survival and reproduction of three species of forbs important to sage grouse nutrition in response to fire, microsite and method of establishment Author: Wirth, Troy A. Since settlement of the Intermountain West, sage grouse abundance and productivity has declined and their range has decreased. The decline of sage grouse populations is primarily due to permanent loss and degradation of sagebrush-grassland habitat. Recently, several studies have shown that sage grouse productivity may be limited by the availability of certain preferred, highly nutritious forb species that have also declined within sagebrush ecosystems of the Intermountain West. During the spring and summer, forbs are extremely important in maintaining the nutritional status and productivity of pre-laying hens and growth and survival of rapidly growing chicks. Researchers studying sage grouse have suggested several methods for restoring forbs in depleted sage grouse habitat. Among the methods proposed are prescribed fires that produce small mosaics of burned and unburned patches on the landscape. For this to occur, an adequate pre-burn forb community must exist in the location of the fire. In areas without adequate pre-burn forb communites, forbs must reseed naturally or be revegetated. The purpose of this study was to determine the suitability of three species of forbs for revegetation projects where improving sage grouse habitat is a goal. Species suitability was determined by evaluating the emergence, survival and reproduction of Crepis modocensis Greene, Crepis occidentalis Nutt. and Astragalus purshii in response to method of establishment (seeding or transplanting), pre-establishment treatment (burned or unburned), and microsite (mound or interspace). Four prescription burns of sagebrush grassland were set at the United States Fish and Wildlife Service Hart Mountain National Antelope Refuge, Oregon. After burning, one experimental plot was randomly located within each burned and unburned site. Of the seeds planted in 1997, A. purshil had the lowest emergence (8%) of all three species. Both Crepis species had similar overall emergence (38%). Significantly more Crepis seedlings emerged from shrub mounds in unburned areas (50%) than in any other fire by microsite treatment (33 to 36%). Significantly more A. purshuii emerged in the burned interspace (10.9) compared to the burned mounds (3.5). Nearly twice as many emerging Crepis seedlings survived in the burned areas as opposed to unburned areas (P<0.01). This resulted in more plant establishment in burned mounds despite higher emergence in unburned mounds. Microsite also significantly affected survival of Crepis seedlings (P<0.01). Approximately 10% more Crepis seedlings survived in mounds compared to interspaces. A. purshuii seedlings also survived better in burned areas (P=0.06), but had no differential response to microsite. Fire enhanced survival of both Crepis and A. purshii transplants (P=0.08 and P=0.001), although, transplanting did not enhance plant establishment over seedings. Therefore, I conclude that revegetation of sage grouse habitat with Crepis species is a viable option given its high germinability, favorable response to fire and wide distribution. Close

• 698. [Article] Hult Reservoir (Siuslaw Basin) Fish Species Composition Size and Relative Abundance_Final2018

  Abstract -- Seven species of fish were encountered in Hult Reservoir in 2017: largemouth bass (Micropterus salmoides), cutthroat trout (Oncorhynchus clarkii), tainbow trout/winter steelhead (Oncorhynchus ...

  Citation × Citation Citation Abstract Copy Title: Hult Reservoir (Siuslaw Basin) Fish Species Composition Size and Relative Abundance_Final2018 Abstract -- Seven species of fish were encountered in Hult Reservoir in 2017: largemouth bass (Micropterus salmoides), cutthroat trout (Oncorhynchus clarkii), tainbow trout/winter steelhead (Oncorhynchus mykiss), bluegill (Lepomis macrochirus), reticulate sculpin (Cottus perplexus), brown bullhead (Ameiurus nebulosus) and western brook lamprey (Lampetra richardsoni). The most abundant fish observed were largemouth bass and bluegill in the summer and fall, and cutthroat in the winter. Cutthroat trout were much more prevalent in the fall and winter sampling than in the summer. Presumably, most cutthroat trout moved up into the tributaries to seek thermal refuge during the summer months and returned to the reservoir once the temperatures were more conducive to growth and survival. However, some of them likely moved downstream, were preyed upon, or perished from the high summer temperatures and low dissolved oxygen conditions in the reservoir in summer. Under current conditions, high surface temperature (>20?), bass predation, and hypoxic dissolved oxygen levels below four meters of depth show that reservoir conditions are inhospitable for juvenile salmonids in the summer. Currently there are well established fisheries for both cutthroat trout (spring, fall, winter) and largemouth bass (summer) in the reservoir, and we talked to several anglers who target each of these species. Habitat segregation in the summer between the salmonids who move out of the reservoir and the warm-water fish that remain and spawn in the reservoir results in a diversified year-round angling opportunity. There were no coho salmon (juvenile or adult) observed in Hult Reservoir in 2017, but adult coho salmon were observed spawning just downstream of the dam. This observation verifies that a proportion of the adult coho attempting to ascend the ladder at Lake Creek Falls are successful and continue migration upstream to the vicinity of Hult Reservoir. It may be possible to keep the current fishery in Hult Reservoir as it stands and still increase coho production in the system by improving adult passage at Lake Creek Falls, and possibly at Hult Dam. Title: Hult Reservoir (Siuslaw Basin) Fish Species Composition Size and Relative Abundance_Final2018 Abstract -- Seven species of fish were encountered in Hult Reservoir in 2017: largemouth bass (Micropterus salmoides), cutthroat trout (Oncorhynchus clarkii), tainbow trout/winter steelhead (Oncorhynchus mykiss), bluegill (Lepomis macrochirus), reticulate sculpin (Cottus perplexus), brown bullhead (Ameiurus nebulosus) and western brook lamprey (Lampetra richardsoni). The most abundant fish observed were largemouth bass and bluegill in the summer and fall, and cutthroat in the winter. Cutthroat trout were much more prevalent in the fall and winter sampling than in the summer. Presumably, most cutthroat trout moved up into the tributaries to seek thermal refuge during the summer months and returned to the reservoir once the temperatures were more conducive to growth and survival. However, some of them likely moved downstream, were preyed upon, or perished from the high summer temperatures and low dissolved oxygen conditions in the reservoir in summer. Under current conditions, high surface temperature (>20?), bass predation, and hypoxic dissolved oxygen levels below four meters of depth show that reservoir conditions are inhospitable for juvenile salmonids in the summer. Currently there are well established fisheries for both cutthroat trout (spring, fall, winter) and largemouth bass (summer) in the reservoir, and we talked to several anglers who target each of these species. Habitat segregation in the summer between the salmonids who move out of the reservoir and the warm-water fish that remain and spawn in the reservoir results in a diversified year-round angling opportunity. There were no coho salmon (juvenile or adult) observed in Hult Reservoir in 2017, but adult coho salmon were observed spawning just downstream of the dam. This observation verifies that a proportion of the adult coho attempting to ascend the ladder at Lake Creek Falls are successful and continue migration upstream to the vicinity of Hult Reservoir. It may be possible to keep the current fishery in Hult Reservoir as it stands and still increase coho production in the system by improving adult passage at Lake Creek Falls, and possibly at Hult Dam. Close

• 699. [Article] Patterns of interactive segregation in three species of sculpins (Cottus) in western Oregon

  Species interactions and their effect on the use of habitat by benthic fishes were examined in a guild composed of Cottus perplexus, C. rhotheus, and C. beldingi in the Marys River above Philomath, Oregon, ...

  Citation × Citation Citation Abstract Copy Title: Patterns of interactive segregation in three species of sculpins (Cottus) in western Oregon Author: Finger, Terry Richard Species interactions and their effect on the use of habitat by benthic fishes were examined in a guild composed of Cottus perplexus, C. rhotheus, and C. beldingi in the Marys River above Philomath, Oregon, and in a constant environment provided by an artificial stream. In the Marys River system, the pattern of longitudinal succession in this guild was one of species additions downstream rather than sequential longitudinal replacement. Cottus perplexus occurred throughout the river system, C. rhotheus was found only in the middle and lower reaches, and C. beldingi was restricted to the lower reaches within the study area. Longitudinal distributions appeared to be most strongly related to substrate characteristics in riffles. Cottus perplexus occurred on all substrates, C. rhotheus was found only where rock was present, and C. beldingi was captured only in riffles dominated by loose, cobble-sized rock with many interstitial spaces. Local use of habitat was strongly related to the breadth of environmental tolerance of each species arid the presence or absence of other cottus species. The species broadly overlapped in their use of different substrates, depths, and distances from shore, but segregated in an orderly manner with respect to current velocity. Where it existed alone, C. perplexus utilized both pools and riffles and was found in greatest densities near cover. Where it coexisted with C. rhotheus, C. perplexus was primarily confined to pools and declined significantly in abundance. The degree to which C. perplexus was excluded from riffles varied in relation to seasons and the size composition of the C. rhotheus population. In areas where there were low densities of large C. rhotheus, the exclusion of C. perplexus was not as pronounced as in areas where there were many large C. rhotheus, and was apparently due mainly to competition. In these areas overlap between the species was also greater in spring, the time of peak food abundance, than in summer or winter. In areas where there were greater numbers of large C. rhotheus, the exclusion of C. perplexus from riffles was more pronounced and did not vary seasonally. In these areas predation was apparently the most important mechanism causing the interactive segregation. Cottus rhotheus was generally confined to riffles, although some large individuals did wander into pools during times of food scarcity. Cottus beldingi was exclusively found in riffles and had a greater maximum current velocity tolerance than C. rhotheus. In summer, all riffle areas in the Marys River flowed slowly enough for C. rhotheus, and C. beldingi apparently was forced, by predation and competition exerted by C. rhotheus, to burrow into the substrate. In winter and spring, C. rhotheus was excluded from areas of some riffles by the faster currents. tn these areas C. beldingi had a refuge from competition and predation and was found atop the substrate to a greater degree. Experiments with the three species in the artificial stream supported the field data and suggested that the competition contributing to the habitat shifts was interference competition for space. Cottus perplexus selected riffle areas when alone, but was displaced partially to pools by C. beldingi through interference competition. The addition of C. rhotheus caused C. perplexus to be more rigidly confined to pools, but C. beldingi was able to coexist in riffles with C. rhotheus apparently by utilizing the interstitial spaces in the substrate. Comparison of these results with those of other studies suggests that segregation in stream fishes should be more commonly based on habitat than on food or time. A model was constructed that could be used to predict patterns of habitat utilization in other guilds of benthic fishes. Species interactions were also suggested as having a major influence on the evolutionary patterns of Cottus in western North America. Large, dominant species will obtain their preferred habitat throughout their geographical range. They will therefore not need to adapt to a wide range of conditions and thus may exhibit low morphological variability. Contrastingly, less dominant species may be forced into many different habitats, depending on which dominant species are also present, and may thus exhibit greater morphological variability. Title: Patterns of interactive segregation in three species of sculpins (Cottus) in western Oregon Author: Finger, Terry Richard Species interactions and their effect on the use of habitat by benthic fishes were examined in a guild composed of Cottus perplexus, C. rhotheus, and C. beldingi in the Marys River above Philomath, Oregon, and in a constant environment provided by an artificial stream. In the Marys River system, the pattern of longitudinal succession in this guild was one of species additions downstream rather than sequential longitudinal replacement. Cottus perplexus occurred throughout the river system, C. rhotheus was found only in the middle and lower reaches, and C. beldingi was restricted to the lower reaches within the study area. Longitudinal distributions appeared to be most strongly related to substrate characteristics in riffles. Cottus perplexus occurred on all substrates, C. rhotheus was found only where rock was present, and C. beldingi was captured only in riffles dominated by loose, cobble-sized rock with many interstitial spaces. Local use of habitat was strongly related to the breadth of environmental tolerance of each species arid the presence or absence of other cottus species. The species broadly overlapped in their use of different substrates, depths, and distances from shore, but segregated in an orderly manner with respect to current velocity. Where it existed alone, C. perplexus utilized both pools and riffles and was found in greatest densities near cover. Where it coexisted with C. rhotheus, C. perplexus was primarily confined to pools and declined significantly in abundance. The degree to which C. perplexus was excluded from riffles varied in relation to seasons and the size composition of the C. rhotheus population. In areas where there were low densities of large C. rhotheus, the exclusion of C. perplexus was not as pronounced as in areas where there were many large C. rhotheus, and was apparently due mainly to competition. In these areas overlap between the species was also greater in spring, the time of peak food abundance, than in summer or winter. In areas where there were greater numbers of large C. rhotheus, the exclusion of C. perplexus from riffles was more pronounced and did not vary seasonally. In these areas predation was apparently the most important mechanism causing the interactive segregation. Cottus rhotheus was generally confined to riffles, although some large individuals did wander into pools during times of food scarcity. Cottus beldingi was exclusively found in riffles and had a greater maximum current velocity tolerance than C. rhotheus. In summer, all riffle areas in the Marys River flowed slowly enough for C. rhotheus, and C. beldingi apparently was forced, by predation and competition exerted by C. rhotheus, to burrow into the substrate. In winter and spring, C. rhotheus was excluded from areas of some riffles by the faster currents. tn these areas C. beldingi had a refuge from competition and predation and was found atop the substrate to a greater degree. Experiments with the three species in the artificial stream supported the field data and suggested that the competition contributing to the habitat shifts was interference competition for space. Cottus perplexus selected riffle areas when alone, but was displaced partially to pools by C. beldingi through interference competition. The addition of C. rhotheus caused C. perplexus to be more rigidly confined to pools, but C. beldingi was able to coexist in riffles with C. rhotheus apparently by utilizing the interstitial spaces in the substrate. Comparison of these results with those of other studies suggests that segregation in stream fishes should be more commonly based on habitat than on food or time. A model was constructed that could be used to predict patterns of habitat utilization in other guilds of benthic fishes. Species interactions were also suggested as having a major influence on the evolutionary patterns of Cottus in western North America. Large, dominant species will obtain their preferred habitat throughout their geographical range. They will therefore not need to adapt to a wide range of conditions and thus may exhibit low morphological variability. Contrastingly, less dominant species may be forced into many different habitats, depending on which dominant species are also present, and may thus exhibit greater morphological variability. Close

• 700. [Article] Passage, migration behavior, and autoecology of adult Pacific lamprey at Winchester Dam and within the North Umpqua River Basin, Oregon, USA

  The extensive reduction in adult Pacific lamprey (Entosphenus tridentatus) counts at many hydroelectric dams in the northwestern USA signals a substantial decline in lamprey numbers across the entire region ...

  Citation × Citation Citation Abstract Copy Title: Passage, migration behavior, and autoecology of adult Pacific lamprey at Winchester Dam and within the North Umpqua River Basin, Oregon, USA Author: Lampman, Ralph Tatsuo The extensive reduction in adult Pacific lamprey (Entosphenus tridentatus) counts at many hydroelectric dams in the northwestern USA signals a substantial decline in lamprey numbers across the entire region in the past 40 to 50 years. Among the many potential causes of this decline, obstruction of migration routes has likely played a substantial role. Within the North Umpqua River basin in southwest Oregon, USA, I focused on the following three research goals: 1) to describe the passage efficiency and migration routes of adult Pacific lamprey at Winchester Dam; 2) to evaluate the seasonal movement patterns of adult Pacific lamprey and their use of holding habitat at Winchester Dam in relation to temperature conditions; and 3) to portray the diversity of upstream migratory behaviors of adult Pacific lamprey and the environmental factors that influence these behaviors. This radio telemetry study was conducted between March 2009 and August 2011 with a combination of fixed stations and manual tracking. Passage efficiency was low in both years (8% and 19%, respectively), and all tagged lamprey that successfully passed the dam used routes other than the fish ladder. Lamprey that migrated early within the run and those with relatively small tags had higher passage rates and traveled further than the other groups of lamprey. Lamprey released above of the dam or those that passed the dam on their own distributed themselves widely in the upstream environment, suggesting that the dam deterred their upstream migration. Using mark-recapture data for the two years, the adult Pacific lamprey population upstream of Winchester Dam was estimated at 960 (95% C.I. [188, 4760]) in 2009 and 556 (95% C.I. [110, 2798]) in 2010, which was considerably lower than historical counts at the dam (between 14,532-46,785 in 1965-1971). Most tagged lamprey that did not pass the dam remained at the base of the dam at the end of the summer migration (63% in 2009 and 67% in 2010). Types of habitat most frequently used by lamprey downstream from the dam included the dam surface (wooden structures with crevices), interface zones between fast and slow water, and highway bridge pilings. The lamprey movement changed considerably between August and September, and the frequency of movements decreased sharply during this period. Tagged lamprey were detected using thermal refuges immediately downstream of the dam that were 0.4 to 2.8 C° colder than the mean river temperature at the dam, and this temperature differential increased as the season progressed. Lamprey may be seeking overwintering habitat associated with hyporheic exchange flows at the dam towards the end of the summer season after their display of heightened activity early in the summer. Ninety-five percent of the overall upstream migration took place during the first spring/summer period, and only small-scale upstream movements were observed during the winter and second spring/summer (4% and 1%, respectively). The rate of upstream migration (median) was the fastest during the initial migration phase and was 1.9 km/day (ranging from 0.3 to 11.0 km/day) for tagged lamprey released above Winchester Dam. During winter, 71% of the lamprey remained in the same location where they initiated holding. Multiple regression analysis indicated that the total upstream distance traveled by individual lamprey was most strongly related to presence/absence of Winchester Dam, relative tag size, and water temperature and photoperiod conditions at release. The presence of Winchester Dam, large relative tag size, and high water temperature / short photoperiod conditions at release significantly reduced upstream migration distance. Title: Passage, migration behavior, and autoecology of adult Pacific lamprey at Winchester Dam and within the North Umpqua River Basin, Oregon, USA Author: Lampman, Ralph Tatsuo The extensive reduction in adult Pacific lamprey (Entosphenus tridentatus) counts at many hydroelectric dams in the northwestern USA signals a substantial decline in lamprey numbers across the entire region in the past 40 to 50 years. Among the many potential causes of this decline, obstruction of migration routes has likely played a substantial role. Within the North Umpqua River basin in southwest Oregon, USA, I focused on the following three research goals: 1) to describe the passage efficiency and migration routes of adult Pacific lamprey at Winchester Dam; 2) to evaluate the seasonal movement patterns of adult Pacific lamprey and their use of holding habitat at Winchester Dam in relation to temperature conditions; and 3) to portray the diversity of upstream migratory behaviors of adult Pacific lamprey and the environmental factors that influence these behaviors. This radio telemetry study was conducted between March 2009 and August 2011 with a combination of fixed stations and manual tracking. Passage efficiency was low in both years (8% and 19%, respectively), and all tagged lamprey that successfully passed the dam used routes other than the fish ladder. Lamprey that migrated early within the run and those with relatively small tags had higher passage rates and traveled further than the other groups of lamprey. Lamprey released above of the dam or those that passed the dam on their own distributed themselves widely in the upstream environment, suggesting that the dam deterred their upstream migration. Using mark-recapture data for the two years, the adult Pacific lamprey population upstream of Winchester Dam was estimated at 960 (95% C.I. [188, 4760]) in 2009 and 556 (95% C.I. [110, 2798]) in 2010, which was considerably lower than historical counts at the dam (between 14,532-46,785 in 1965-1971). Most tagged lamprey that did not pass the dam remained at the base of the dam at the end of the summer migration (63% in 2009 and 67% in 2010). Types of habitat most frequently used by lamprey downstream from the dam included the dam surface (wooden structures with crevices), interface zones between fast and slow water, and highway bridge pilings. The lamprey movement changed considerably between August and September, and the frequency of movements decreased sharply during this period. Tagged lamprey were detected using thermal refuges immediately downstream of the dam that were 0.4 to 2.8 C° colder than the mean river temperature at the dam, and this temperature differential increased as the season progressed. Lamprey may be seeking overwintering habitat associated with hyporheic exchange flows at the dam towards the end of the summer season after their display of heightened activity early in the summer. Ninety-five percent of the overall upstream migration took place during the first spring/summer period, and only small-scale upstream movements were observed during the winter and second spring/summer (4% and 1%, respectively). The rate of upstream migration (median) was the fastest during the initial migration phase and was 1.9 km/day (ranging from 0.3 to 11.0 km/day) for tagged lamprey released above Winchester Dam. During winter, 71% of the lamprey remained in the same location where they initiated holding. Multiple regression analysis indicated that the total upstream distance traveled by individual lamprey was most strongly related to presence/absence of Winchester Dam, relative tag size, and water temperature and photoperiod conditions at release. The presence of Winchester Dam, large relative tag size, and high water temperature / short photoperiod conditions at release significantly reduced upstream migration distance. Close