Search

Search Results

• 31. [Article] Distribution and movement patterns of gray whales off central Oregon: Shore-based observations from Yaquina Head during the 2007/2008 migration: Report submitted to the Oregon Wave Energy Trust

  The objective of the study is to generate accurate, current data on distribution (distance to shore, travel path) and behavior (travel speed, migration timing) of gray whales migrating along the central ...

  Citation × Citation Citation Abstract Copy Title: Distribution and movement patterns of gray whales off central Oregon: Shore-based observations from Yaquina Head during the 2007/2008 migration: Report submitted to the Oregon Wave Energy Trust Author: Mate, Bruce R., Ortega-Ortiz, Jose G. The objective of the study is to generate accurate, current data on distribution (distance to shore, travel path) and behavior (travel speed, migration timing) of gray whales migrating along the central Oregon coast (Pacific Ocean). Migration paths of tracked whales seem to follow a constant depth rather than following the shoreline. Speed estimates were within range of values reported by others. As expected, migration paths of some gray whales cross through areas of proposed wave energy development. This baseline information combined with further observations to monitor gray whale behavior after wave energy facilities are installed can be used to determine potential effects and to evaluate the need for and effectiveness of mitigation measures. Title: Distribution and movement patterns of gray whales off central Oregon: Shore-based observations from Yaquina Head during the 2007/2008 migration: Report submitted to the Oregon Wave Energy Trust Author: Mate, Bruce R., Ortega-Ortiz, Jose G. The objective of the study is to generate accurate, current data on distribution (distance to shore, travel path) and behavior (travel speed, migration timing) of gray whales migrating along the central Oregon coast (Pacific Ocean). Migration paths of tracked whales seem to follow a constant depth rather than following the shoreline. Speed estimates were within range of values reported by others. As expected, migration paths of some gray whales cross through areas of proposed wave energy development. This baseline information combined with further observations to monitor gray whale behavior after wave energy facilities are installed can be used to determine potential effects and to evaluate the need for and effectiveness of mitigation measures. Close

• 32. [Article] Northwest forest plan effects on county net migration and employment growth : causality of policy variables, timing of response, relevant time periods, rural vs. metro policy effects and effects on industry employment

  County-level net migration and employment growth rates associated with the Northwest Forest Plan (NWFP) are examined. The NWFP area encompasses federal land in 53 Oregon, Washington and California counties; ...

  Citation × Citation Citation Abstract Copy Title: Northwest forest plan effects on county net migration and employment growth : causality of policy variables, timing of response, relevant time periods, rural vs. metro policy effects and effects on industry employment Author: Eichman, Henry N. County-level net migration and employment growth rates associated with the Northwest Forest Plan (NWFP) are examined. The NWFP area encompasses federal land in 53 Oregon, Washington and California counties; 20 counties adjacent to NWFP counties are also included in the sample. The NWFP was enacted in December of 1993, however, this analysis examines the 24 year time period from 1980 through 2003. Net migration (the change in population due to in-migration and out-migration) and employment growth are represented by a simultaneous equation model (SEM) that is corrected for spatial autocorrelation. While the NWFP land allocations are expected to influence net migration and employment growth, they are potentially determined by similar processes as the endogenous economic indicators. Logistic regression analysis shows the probability that NWFP lands were allocated to biodiversity purposes or to land uses subject to timber harvest depends on natural, political and economic variables. The SEM is run on a yearly basis to explore changes in net migration and employment growth due to policy enactment, future expectations about land allocations, and market fluctuations. These results suggest the time period was characterized by many changes the endogenous variables from the effects of land management. In addition, the yearly analysis suggests that variation in yearly employment growth and net migration may not be sufficient for precise estimation of the effects of the exogenous variables. Pooling the yearly data over policy-relevant time periods is thus appropriate and provides insight into the NWFP effects on the economic indicators. Counties with more land reserved for biodiversity purposes had higher net migration and employment growth. In contrast, counties with more land allocated to extractive uses experienced low net migration. During the period following NWFP enactment, from 1994 to 2003, the classification of land according to NWFP management yields no significant relationship, suggesting adjustment to the NWFP had occurred. The effects of land management variables for rural and metropolitan counties are distinguished in another SEM. Contrary to the popular notion that employment effects were felt in large part by rural counties, this analysis shows changes in employment growth due to policy effects were felt primarily in metropolitan counties within the NWFP region. In addition, higher net migration occurred in rural and metropolitan counties containing land reserved for biodiversity purposes. These counties also experienced a simultaneous increase in employment growth as a result of allocation of these lands. Analysis of employment growth changes in specific industry sectors indicates manufacturing jobs were lost, however, service industry growth was encouraged as a result of NWFP land allocations. In addition, land allocated solely for the purpose of biodiversity services was not associated with changes in the manufacturing employment while potentially promoting growth in service sector employment. Title: Northwest forest plan effects on county net migration and employment growth : causality of policy variables, timing of response, relevant time periods, rural vs. metro policy effects and effects on industry employment Author: Eichman, Henry N. County-level net migration and employment growth rates associated with the Northwest Forest Plan (NWFP) are examined. The NWFP area encompasses federal land in 53 Oregon, Washington and California counties; 20 counties adjacent to NWFP counties are also included in the sample. The NWFP was enacted in December of 1993, however, this analysis examines the 24 year time period from 1980 through 2003. Net migration (the change in population due to in-migration and out-migration) and employment growth are represented by a simultaneous equation model (SEM) that is corrected for spatial autocorrelation. While the NWFP land allocations are expected to influence net migration and employment growth, they are potentially determined by similar processes as the endogenous economic indicators. Logistic regression analysis shows the probability that NWFP lands were allocated to biodiversity purposes or to land uses subject to timber harvest depends on natural, political and economic variables. The SEM is run on a yearly basis to explore changes in net migration and employment growth due to policy enactment, future expectations about land allocations, and market fluctuations. These results suggest the time period was characterized by many changes the endogenous variables from the effects of land management. In addition, the yearly analysis suggests that variation in yearly employment growth and net migration may not be sufficient for precise estimation of the effects of the exogenous variables. Pooling the yearly data over policy-relevant time periods is thus appropriate and provides insight into the NWFP effects on the economic indicators. Counties with more land reserved for biodiversity purposes had higher net migration and employment growth. In contrast, counties with more land allocated to extractive uses experienced low net migration. During the period following NWFP enactment, from 1994 to 2003, the classification of land according to NWFP management yields no significant relationship, suggesting adjustment to the NWFP had occurred. The effects of land management variables for rural and metropolitan counties are distinguished in another SEM. Contrary to the popular notion that employment effects were felt in large part by rural counties, this analysis shows changes in employment growth due to policy effects were felt primarily in metropolitan counties within the NWFP region. In addition, higher net migration occurred in rural and metropolitan counties containing land reserved for biodiversity purposes. These counties also experienced a simultaneous increase in employment growth as a result of allocation of these lands. Analysis of employment growth changes in specific industry sectors indicates manufacturing jobs were lost, however, service industry growth was encouraged as a result of NWFP land allocations. In addition, land allocated solely for the purpose of biodiversity services was not associated with changes in the manufacturing employment while potentially promoting growth in service sector employment. Close

• 33. [Article] Nocturnal light and lunar cycle effects on diel migration of micronekton

  The roles of nocturnal light and lunar phase in the diel migration of micronekton from a nearshore scattering layer were examined. Migration patterns were measured over six complete lunar cycles using ...

  Citation × Citation Citation Abstract Copy Title: Nocturnal light and lunar cycle effects on diel migration of micronekton Author: Au, Whitlow W. L., Wisdom, Daniel W., Benoit-Bird, Kelly J. The roles of nocturnal light and lunar phase in the diel migration of micronekton from a nearshore scattering layer were examined. Migration patterns were measured over six complete lunar cycles using moored upwardlooking echosounders while nocturnal surface irradiance was recorded. We hypothesized that animals would remain at a constant isolume at night despite changes in nocturnal illumination between nights. The scattering layer migrated closer to the surface during dark nights than during well-lit ones. However, this movement was not enough to compensate for observed changes in light, and at night animals often remained at light levels higher than they experience at depth during the day. Light and lunar cycle were not completely coupled, allowing separation of the light and lunar phases. Contrary to the initial hypothesis, lunar phase accounted for substantially more of the variability in layer migration than surface irradiance, showing strong effects on the scattering layer’s depth and animal density within the layer. Changes in layer depth and animal density were amplified a small amount by variations in light level but were minimized by the seafloor in shallow areas. The horizontal component of the scattering layer’s migration was also affected by lunar phase, with animals remaining further offshore in deeper waters during nights near and during the full moon, even when these were not the nights with the highest light levels. These results suggest that moonlight may be a cue for an endogenous lunar rhythm in the process of diel migration rather than a direct cause. Title: Nocturnal light and lunar cycle effects on diel migration of micronekton Author: Au, Whitlow W. L., Wisdom, Daniel W., Benoit-Bird, Kelly J. The roles of nocturnal light and lunar phase in the diel migration of micronekton from a nearshore scattering layer were examined. Migration patterns were measured over six complete lunar cycles using moored upwardlooking echosounders while nocturnal surface irradiance was recorded. We hypothesized that animals would remain at a constant isolume at night despite changes in nocturnal illumination between nights. The scattering layer migrated closer to the surface during dark nights than during well-lit ones. However, this movement was not enough to compensate for observed changes in light, and at night animals often remained at light levels higher than they experience at depth during the day. Light and lunar cycle were not completely coupled, allowing separation of the light and lunar phases. Contrary to the initial hypothesis, lunar phase accounted for substantially more of the variability in layer migration than surface irradiance, showing strong effects on the scattering layer’s depth and animal density within the layer. Changes in layer depth and animal density were amplified a small amount by variations in light level but were minimized by the seafloor in shallow areas. The horizontal component of the scattering layer’s migration was also affected by lunar phase, with animals remaining further offshore in deeper waters during nights near and during the full moon, even when these were not the nights with the highest light levels. These results suggest that moonlight may be a cue for an endogenous lunar rhythm in the process of diel migration rather than a direct cause. Close

• 34. [Article] Innate and adaptive immune responses in migrating spring-run adult chinook salmon, Oncorhynchus tshawytscha

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by Elsevier ...

  Citation × Citation Citation Abstract Copy Title: Innate and adaptive immune responses in migrating spring-run adult chinook salmon, Oncorhynchus tshawytscha Author: Schreck, Carl B., Kent, Michael L., Dolan, Brian P., Colvin, Michael E., Fisher, Kathleen M., Benda, Susan E., Peterson, James T. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/fish-and-shellfish-immunology/ Title: Innate and adaptive immune responses in migrating spring-run adult chinook salmon, Oncorhynchus tshawytscha Author: Schreck, Carl B., Kent, Michael L., Dolan, Brian P., Colvin, Michael E., Fisher, Kathleen M., Benda, Susan E., Peterson, James T. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/fish-and-shellfish-immunology/ Close

• 35. [Article] Neural gene expression profiling in chinook salmon (Oncorhynchus tshawytscha) of alternate run times

  Chinook salmon (Oncorhynchus tshawytscha) display the greatest variability of return times to freshwater of all Pacific salmon. Differential return times to freshwater have segregated populations of ...

  Citation × Citation Citation Abstract Copy Title: Neural gene expression profiling in chinook salmon (Oncorhynchus tshawytscha) of alternate run times Author: Bernier, Jeremiah C. Chinook salmon (Oncorhynchus tshawytscha) display the greatest variability of return times to freshwater of all Pacific salmon. Differential return times to freshwater have segregated populations of Chinook into two broad types or runs, fall and spring, named for the time of year in which they migrate to freshwater. Migration time in Chinook has a strong genetic component, and historically, fall and spring runs were spatially and temporally isolated in watersheds. Using a population of Chinook from California’s Central Valley, I sought to examine gene regulation that results in differential run-timing. Functional genomics has proven to be powerful in distinguishing genes differentially expressed between alternate behaviors in other systems and I used the technique LongSAGE to examine genes differentially regulated between fall and spring run Chinook during freshwater migration. I constructed three LongSAGE libraries from the brains of a spring, fall and ocean sample and observed 221 differentially expressed tags. Using expressed sequence tag (EST) libraries from Atlantic salmon (Salmo salar) and rainbow trout (O. mykiss), I was able to assign putative functions to 59% of differentially expressed tags. Additionally, I tested the expression levels of seven genes in the brains of 8 additional individuals from both runs and found none significantly differentially expressed between fall and spring runs. This study is the first to apply LongSAGE to salmon and provides a framework for conducting future gene expression research into reproduction and migration times, as well as physiology of migrating salmon. Title: Neural gene expression profiling in chinook salmon (Oncorhynchus tshawytscha) of alternate run times Author: Bernier, Jeremiah C. Chinook salmon (Oncorhynchus tshawytscha) display the greatest variability of return times to freshwater of all Pacific salmon. Differential return times to freshwater have segregated populations of Chinook into two broad types or runs, fall and spring, named for the time of year in which they migrate to freshwater. Migration time in Chinook has a strong genetic component, and historically, fall and spring runs were spatially and temporally isolated in watersheds. Using a population of Chinook from California’s Central Valley, I sought to examine gene regulation that results in differential run-timing. Functional genomics has proven to be powerful in distinguishing genes differentially expressed between alternate behaviors in other systems and I used the technique LongSAGE to examine genes differentially regulated between fall and spring run Chinook during freshwater migration. I constructed three LongSAGE libraries from the brains of a spring, fall and ocean sample and observed 221 differentially expressed tags. Using expressed sequence tag (EST) libraries from Atlantic salmon (Salmo salar) and rainbow trout (O. mykiss), I was able to assign putative functions to 59% of differentially expressed tags. Additionally, I tested the expression levels of seven genes in the brains of 8 additional individuals from both runs and found none significantly differentially expressed between fall and spring runs. This study is the first to apply LongSAGE to salmon and provides a framework for conducting future gene expression research into reproduction and migration times, as well as physiology of migrating salmon. Close

• 36. [Article] Geographic variation in timing of fry emergence and smolt migration of coho salmon (Oncorhynchus kisutch)

  The timing of two events in the early life history of coho salmon--emergence from the gravel and entry into the ocean--is presumed to have evolved to ensure maximum survival during these transition periods. ...

  Citation × Citation Citation Abstract Copy Title: Geographic variation in timing of fry emergence and smolt migration of coho salmon (Oncorhynchus kisutch) Author: Spence, Brian C. The timing of two events in the early life history of coho salmon--emergence from the gravel and entry into the ocean--is presumed to have evolved to ensure maximum survival during these transition periods. Anthropogenic disturbances may disrupt the timing of these events to the detriment of salmon populations. Multivariate analyses were used to examine regional patterns in downstream migration in relation to environmental variation for 50 smolt populations located between central California and southern Alaska. Significant latitudinal gradients were observed in the timing of the peak of migration, duration of migration, and degree of interannual variation in the peak of migration. Smolt migrations of northern populations generally occurred later in the spring, were shorter in duration, and exhibited lower interannual variability in their timing than did those of southern populations. Some variability in these patterns was associated with watershed characteristics (e.g., elevation, distance from ocean); however, latitudinal patterns transcended this variability and may reflect adaptation to differences in temporal "windows of opportunity" in the ocean environments into which smolts enter. Logistic regression models were used to model within- and between-year variation in probability of smolts migrating during 2-d intervals from four streams in Alaska, British Columbia, and Oregon as a function of time interval, lunar periodicity, temperature (absolute, change, cumulative degree days), and streamflow (absolute, change). Migration probability was positively associated with time, temperature, and change in flow, and negatively associated with absolute flow for at least four of the five data sets examined (P <0.05). Significant, but contradictory, relationships between lunar phase and migration probability were also found. Temperature-based models of embryo and alevin development were coupled with information on stream temperatures to examine regional differences in sensitivity of these life stages to climate warming. Modest stream warming (0.5 to 2.0°C) would substantially accelerate embryo and alevin development, reducing the time between spawning and emergence by two months or more. Changes in development time were predicted to be greatest at higher latitudes and elevations (e.g., Alaska and interior British Columbia), where average incubation temperatures are presently the coldest. Title: Geographic variation in timing of fry emergence and smolt migration of coho salmon (Oncorhynchus kisutch) Author: Spence, Brian C. The timing of two events in the early life history of coho salmon--emergence from the gravel and entry into the ocean--is presumed to have evolved to ensure maximum survival during these transition periods. Anthropogenic disturbances may disrupt the timing of these events to the detriment of salmon populations. Multivariate analyses were used to examine regional patterns in downstream migration in relation to environmental variation for 50 smolt populations located between central California and southern Alaska. Significant latitudinal gradients were observed in the timing of the peak of migration, duration of migration, and degree of interannual variation in the peak of migration. Smolt migrations of northern populations generally occurred later in the spring, were shorter in duration, and exhibited lower interannual variability in their timing than did those of southern populations. Some variability in these patterns was associated with watershed characteristics (e.g., elevation, distance from ocean); however, latitudinal patterns transcended this variability and may reflect adaptation to differences in temporal "windows of opportunity" in the ocean environments into which smolts enter. Logistic regression models were used to model within- and between-year variation in probability of smolts migrating during 2-d intervals from four streams in Alaska, British Columbia, and Oregon as a function of time interval, lunar periodicity, temperature (absolute, change, cumulative degree days), and streamflow (absolute, change). Migration probability was positively associated with time, temperature, and change in flow, and negatively associated with absolute flow for at least four of the five data sets examined (P <0.05). Significant, but contradictory, relationships between lunar phase and migration probability were also found. Temperature-based models of embryo and alevin development were coupled with information on stream temperatures to examine regional differences in sensitivity of these life stages to climate warming. Modest stream warming (0.5 to 2.0°C) would substantially accelerate embryo and alevin development, reducing the time between spawning and emergence by two months or more. Changes in development time were predicted to be greatest at higher latitudes and elevations (e.g., Alaska and interior British Columbia), where average incubation temperatures are presently the coldest. Close

• 37. [Article] Nearshore sandbar migration predicted by an eddy-diffusive boundary layer model

  copyrighted by American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Nearshore sandbar migration predicted by an eddy-diffusive boundary layer model Author: Henderson, Stephen M., Newberger, P. A., Allen, John S. copyrighted by American Geophysical Union Title: Nearshore sandbar migration predicted by an eddy-diffusive boundary layer model Author: Henderson, Stephen M., Newberger, P. A., Allen, John S. copyrighted by American Geophysical Union Close

• 38. [Article] The economic incentives facing illegal Mexican aliens in the U.S. : a case study at Hood River, Oregon

  Illegal Mexican migration to the U.S. appears to have increased substantially over the past fifteen years. Most illegal Mexican aliens migrate with the aim of obtaining better employment opportunities ...

  Citation × Citation Citation Abstract Copy Title: The economic incentives facing illegal Mexican aliens in the U.S. : a case study at Hood River, Oregon Author: Cuthbert, Richard W. Illegal Mexican migration to the U.S. appears to have increased substantially over the past fifteen years. Most illegal Mexican aliens migrate with the aim of obtaining better employment opportunities and higher earnings in the U.S. than are available in Mexico. The potential impacts of this migration on various U.S. interests, however, are not agreed upon by scholars in the field. In fact, little empirical data on illegal Mexican aliens in the U.S. have been collected, especially with regard to the economic incentives for their migration. This study is an attempt to obtain empirical data on illegal Mexican aliens who are employed in the U.S. The principle aim of this research is to describe a random sample of illegal Mexican aliens surveyed at Hood River, Oregon, where they were employed in agricultural harvest activities. Specific attention is placed on the earnings differential for illegal Mexican aliens in the U.S. and foregone earnings in Mexico as a measure of the economic incentive for illegal migration. The study finds that illegal Mexican aliens interviewed at Hood River generally conform to the demographic profile described in previous studies. but that the data on their earnings and expenditures are considerably different. Both wage earnings and living costs in the U.S. appear to be considerably higher for most illegal Mexican aliens than indicated by previous studies, and their differential between potential U.S. and Mexican earnings is substantial. Illegal Mexican aliens at Hood River had gross earnings of approximately six-times their foregone Mexican earnings by working in the U.S. for roughly the same period of time. By accounting for expenses that the illegal aliens face in the U.S., this amount is reduced to four-times their foregone earnings. The study concludes that considerable illegal Mexican migration will likely continue in the near future and that further research on other aspects of the phenomenon and in other geographic regions would be useful. Several specific suggestions for future research are also outlined. Title: The economic incentives facing illegal Mexican aliens in the U.S. : a case study at Hood River, Oregon Author: Cuthbert, Richard W. Illegal Mexican migration to the U.S. appears to have increased substantially over the past fifteen years. Most illegal Mexican aliens migrate with the aim of obtaining better employment opportunities and higher earnings in the U.S. than are available in Mexico. The potential impacts of this migration on various U.S. interests, however, are not agreed upon by scholars in the field. In fact, little empirical data on illegal Mexican aliens in the U.S. have been collected, especially with regard to the economic incentives for their migration. This study is an attempt to obtain empirical data on illegal Mexican aliens who are employed in the U.S. The principle aim of this research is to describe a random sample of illegal Mexican aliens surveyed at Hood River, Oregon, where they were employed in agricultural harvest activities. Specific attention is placed on the earnings differential for illegal Mexican aliens in the U.S. and foregone earnings in Mexico as a measure of the economic incentive for illegal migration. The study finds that illegal Mexican aliens interviewed at Hood River generally conform to the demographic profile described in previous studies. but that the data on their earnings and expenditures are considerably different. Both wage earnings and living costs in the U.S. appear to be considerably higher for most illegal Mexican aliens than indicated by previous studies, and their differential between potential U.S. and Mexican earnings is substantial. Illegal Mexican aliens at Hood River had gross earnings of approximately six-times their foregone Mexican earnings by working in the U.S. for roughly the same period of time. By accounting for expenses that the illegal aliens face in the U.S., this amount is reduced to four-times their foregone earnings. The study concludes that considerable illegal Mexican migration will likely continue in the near future and that further research on other aspects of the phenomenon and in other geographic regions would be useful. Several specific suggestions for future research are also outlined. Close

• 39. [Article] Bioenergetic evaluation of diel vertical migration by bull trout

  I evaluated hypotheses related to growth as a driver of depth use and diel vertical migration by bull trout (Salvelinus confluentus) in a thermally stratified reservoir. I applied a bioenergetic model ...

  Citation × Citation Citation Abstract Copy Title: Bioenergetic evaluation of diel vertical migration by bull trout Author: Eckmann, Madeleine I evaluated hypotheses related to growth as a driver of depth use and diel vertical migration by bull trout (Salvelinus confluentus) in a thermally stratified reservoir. I applied a bioenergetic model to evaluate growth of bull trout in relation to potential patterns of diel depth use by bull trout in Ross Lake, Washington. Modeled patterns of growth were derived from observed vertical distributions of temperature and prey availability. I also observed bull trout depth (and corresponding temperature) use patterns to determine if observed behaviors corresponded with those predicted to maximize growth. Results of this work suggest that bull trout migrations beyond 25 m deep in Ross Lake cannot be explained exclusively by growth and survival alone, two common explanations for diel vertical migration. These deeper excursions may be explained by a third driver that has not been previously emphasized: the importance of colder water for gametogenesis. Further evaluation of this hypothesis as a means of explaining diel vertical migration for bull trout and other fish species in similar environments is warranted. Title: Bioenergetic evaluation of diel vertical migration by bull trout Author: Eckmann, Madeleine I evaluated hypotheses related to growth as a driver of depth use and diel vertical migration by bull trout (Salvelinus confluentus) in a thermally stratified reservoir. I applied a bioenergetic model to evaluate growth of bull trout in relation to potential patterns of diel depth use by bull trout in Ross Lake, Washington. Modeled patterns of growth were derived from observed vertical distributions of temperature and prey availability. I also observed bull trout depth (and corresponding temperature) use patterns to determine if observed behaviors corresponded with those predicted to maximize growth. Results of this work suggest that bull trout migrations beyond 25 m deep in Ross Lake cannot be explained exclusively by growth and survival alone, two common explanations for diel vertical migration. These deeper excursions may be explained by a third driver that has not been previously emphasized: the importance of colder water for gametogenesis. Further evaluation of this hypothesis as a means of explaining diel vertical migration for bull trout and other fish species in similar environments is warranted. Close

• 40. [Article] Factors influencing spawning migration of bull trout (Salvelinus confluentus) in the North Fork Skokomish River, Olympic National Park, Washington

  Distribution and life history characteristics of lacustrine-adfluvial bull trout (Salvelinus confluentus) were described in the North Fork Skokomish River Basin (including Lake Cushman, a reservoir) from ...

  Citation × Citation Citation Abstract Copy Title: Factors influencing spawning migration of bull trout (Salvelinus confluentus) in the North Fork Skokomish River, Olympic National Park, Washington Author: Brenkman, Samuel J. Distribution and life history characteristics of lacustrine-adfluvial bull trout (Salvelinus confluentus) were described in the North Fork Skokomish River Basin (including Lake Cushman, a reservoir) from 1994 to 1996. Day snorkeling was conducted in the river to determine initiation of the bull trout spawning migration, abundance of spawners, and duration of spawning. Declining photoperiod, increased river discharge, and decreased water temperature appeared to influence timing of migration and spawning. Lacustrine-adfluvial bull trout typically entered the North Fork Skokomish River in October although some fish entered as early as May. Mean lengths of spawners consistently increased from June to December 1996, and early migrating bull trout were shorter than those fish that entered after river discharge increased in October. The presence of two phases of the spawning migration may be indicative of two populations spawning in the river. Bull trout spawned between mid-September and December in the river and tributaries after water temperatures declined. All spawning occurred at temperatures less than 7.5°C. Comparisons with studies of other lacustrine-adfiuvial bull trout populations that inhabit river and reservoir complexes suggested that bull trout exhibit specific migratory strategies related to local environmental conditions. In the North Fork Skokomish River, changes in abundance of bull trout, mountain whitefish (Prosopium wilhamsom), cutthroat trout (Oncorhynchus dark), and rainbow trout (Oncorhynchus mykiss) revealed distinct temporal segregation among these species. Olympic National Park, a designated Biosphere Reserve, contains one of the largest remaining areas of relatively pristine habitat in the range of bull trout. Knowledge of responses of bull trout to changes in river discharge and temperature from relatively undisturbed systems, such as the North Fork Skokomish River, may be useful in understanding patterns observed in degraded environments. Title: Factors influencing spawning migration of bull trout (Salvelinus confluentus) in the North Fork Skokomish River, Olympic National Park, Washington Author: Brenkman, Samuel J. Distribution and life history characteristics of lacustrine-adfluvial bull trout (Salvelinus confluentus) were described in the North Fork Skokomish River Basin (including Lake Cushman, a reservoir) from 1994 to 1996. Day snorkeling was conducted in the river to determine initiation of the bull trout spawning migration, abundance of spawners, and duration of spawning. Declining photoperiod, increased river discharge, and decreased water temperature appeared to influence timing of migration and spawning. Lacustrine-adfluvial bull trout typically entered the North Fork Skokomish River in October although some fish entered as early as May. Mean lengths of spawners consistently increased from June to December 1996, and early migrating bull trout were shorter than those fish that entered after river discharge increased in October. The presence of two phases of the spawning migration may be indicative of two populations spawning in the river. Bull trout spawned between mid-September and December in the river and tributaries after water temperatures declined. All spawning occurred at temperatures less than 7.5°C. Comparisons with studies of other lacustrine-adfiuvial bull trout populations that inhabit river and reservoir complexes suggested that bull trout exhibit specific migratory strategies related to local environmental conditions. In the North Fork Skokomish River, changes in abundance of bull trout, mountain whitefish (Prosopium wilhamsom), cutthroat trout (Oncorhynchus dark), and rainbow trout (Oncorhynchus mykiss) revealed distinct temporal segregation among these species. Olympic National Park, a designated Biosphere Reserve, contains one of the largest remaining areas of relatively pristine habitat in the range of bull trout. Knowledge of responses of bull trout to changes in river discharge and temperature from relatively undisturbed systems, such as the North Fork Skokomish River, may be useful in understanding patterns observed in degraded environments. Close