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• 1. [Article] Thermal controls of Yellowstone cutthroat trout and invasive fishes under climate change

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. The published article is copyrighted by Wiley-Blackwell and can be found at: http:...

  Citation × Citation Citation Abstract Copy Title: Thermal controls of Yellowstone cutthroat trout and invasive fishes under climate change Author: Hostetler, Steven, Gresswell, Robert, Alder, Jay R., Shepard, Bradley, Al-Chokhachy, Robert To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. The published article is copyrighted by Wiley-Blackwell and can be found at: http://onlinelibrary.wiley.com/. Title: Thermal controls of Yellowstone cutthroat trout and invasive fishes under climate change Author: Hostetler, Steven, Gresswell, Robert, Alder, Jay R., Shepard, Bradley, Al-Chokhachy, Robert To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. The published article is copyrighted by Wiley-Blackwell and can be found at: http://onlinelibrary.wiley.com/. Close

• 2. [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

• 3. [Article] Responses of a threatened cutthroat trout to an introduced, invading salmonid : ecological implications for growth, stress, and behavior

  Recent studies suggest that competition from brook trout (Salvelinus fontinalis; EBT) may have negative effects (e.g. displacement) on Lahontan cutthroat trout (Oncorhynchus clarki henshawi; LCT). Results ...

  Citation × Citation Citation Abstract Copy Title: Responses of a threatened cutthroat trout to an introduced, invading salmonid : ecological implications for growth, stress, and behavior Author: Osborne-Gowey, Jeremiah D. Recent studies suggest that competition from brook trout (Salvelinus fontinalis; EBT) may have negative effects (e.g. displacement) on Lahontan cutthroat trout (Oncorhynchus clarki henshawi; LCT). Results from these studies have failed to elucidate the responsible mechanisms and have not examined if changing environmental conditions result in competitive/subordinate role reversals. The primary objectives of this study were to 1) determine if LCT and EBT compete for resources in a stream in which they co-occur, 2) determine the mechanisms responsible for the apparent competition and 3) determine if the results from competitive interactions change under variable environmental conditions. A field study examined how LCT and EBT interacted in a colonization situation typical of many LCT reintroductions, and provided insights into how LCT responded, under natural conditions, to EBT under various habitat conditions. A laboratory experiment, informed largely from the field study, was designed to force competitive interactions and measure the responses of LCT under varying habitat and environmental conditions. Results from the field manipulation revealed that EBT re-colonized a section of stream farther and faster than LCT and that about 25% of the individuals of both species stayed in the relocation pool. When in sympatry, LCT lost five times as much weight as EBT during the three week trial (2.5g to 0.5g, respectively). Lahontan cutthroat trout almost always had empty stomachs whereas EBT usually had at least some food present in their stomachs. Under laboratory conditions where density, species proportions, and temperature were manipulated, LCT typically lost weight and exhibited elevated blood plasma cortisol levels, an indicator of stress, during the 9 day trials (-8% and ~60 ng/mL, respectively) whereas EBT typically gained weight and exhibited lower cortisol levels (+1% and ~23 ng/mL). When the water temperature remained at 13°C, EBT gained an average of 5% of their body weight and had low plasma cortisol levels (~16 ng/mL) whereas LCT lost an average of 6% of their body weight and had elevated plasma cortisol levels (~40 ng/mL). As temperatures increased to 23°C, both species lost weight and exhibited elevated cortisol levels but LCT lost more weight than EBT (11% vs. 5%). As the proportion of EBT increased relative to LCT in experimental trials, LCT lost more weight and generally exhibited higher cortisol levels. Additionally, feeding observations in tanks that contained both species indicated that EBT were the first feed greater than 90% of the time, while LCT almost never fed and remained inactive when in the presence of EBT. In tanks that did not contain EBT, LCT were active and readily fed. Collectively, these results suggest that EBT are the dominant competitor and that the mechanisms for competitive dominance may, in part, be both physiological and behavioral in nature. Title: Responses of a threatened cutthroat trout to an introduced, invading salmonid : ecological implications for growth, stress, and behavior Author: Osborne-Gowey, Jeremiah D. Recent studies suggest that competition from brook trout (Salvelinus fontinalis; EBT) may have negative effects (e.g. displacement) on Lahontan cutthroat trout (Oncorhynchus clarki henshawi; LCT). Results from these studies have failed to elucidate the responsible mechanisms and have not examined if changing environmental conditions result in competitive/subordinate role reversals. The primary objectives of this study were to 1) determine if LCT and EBT compete for resources in a stream in which they co-occur, 2) determine the mechanisms responsible for the apparent competition and 3) determine if the results from competitive interactions change under variable environmental conditions. A field study examined how LCT and EBT interacted in a colonization situation typical of many LCT reintroductions, and provided insights into how LCT responded, under natural conditions, to EBT under various habitat conditions. A laboratory experiment, informed largely from the field study, was designed to force competitive interactions and measure the responses of LCT under varying habitat and environmental conditions. Results from the field manipulation revealed that EBT re-colonized a section of stream farther and faster than LCT and that about 25% of the individuals of both species stayed in the relocation pool. When in sympatry, LCT lost five times as much weight as EBT during the three week trial (2.5g to 0.5g, respectively). Lahontan cutthroat trout almost always had empty stomachs whereas EBT usually had at least some food present in their stomachs. Under laboratory conditions where density, species proportions, and temperature were manipulated, LCT typically lost weight and exhibited elevated blood plasma cortisol levels, an indicator of stress, during the 9 day trials (-8% and ~60 ng/mL, respectively) whereas EBT typically gained weight and exhibited lower cortisol levels (+1% and ~23 ng/mL). When the water temperature remained at 13°C, EBT gained an average of 5% of their body weight and had low plasma cortisol levels (~16 ng/mL) whereas LCT lost an average of 6% of their body weight and had elevated plasma cortisol levels (~40 ng/mL). As temperatures increased to 23°C, both species lost weight and exhibited elevated cortisol levels but LCT lost more weight than EBT (11% vs. 5%). As the proportion of EBT increased relative to LCT in experimental trials, LCT lost more weight and generally exhibited higher cortisol levels. Additionally, feeding observations in tanks that contained both species indicated that EBT were the first feed greater than 90% of the time, while LCT almost never fed and remained inactive when in the presence of EBT. In tanks that did not contain EBT, LCT were active and readily fed. Collectively, these results suggest that EBT are the dominant competitor and that the mechanisms for competitive dominance may, in part, be both physiological and behavioral in nature. Close

• 4. [Article] Effects of wildfire on growth and demographics of coastal cutthroat trout in headwater streams

  Wildfire is a largely terrestrial perturbation broadly recognized as an agent of disturbance and ecological change in forested biomes. Effects of post-fire conditions on biotic components of aquatic systems ...

  Citation × Citation Citation Abstract Copy Title: Effects of wildfire on growth and demographics of coastal cutthroat trout in headwater streams Author: Heck, Michael P. Wildfire is a largely terrestrial perturbation broadly recognized as an agent of disturbance and ecological change in forested biomes. Effects of post-fire conditions on biotic components of aquatic systems have been less well-documented, although hypothetically, the two are strongly connected. In fact, the influence of wildfire may be most profound in headwater streams because of the tight linkage between aquatic and terrestrial ecosystems. We sought to understand the influence of post-fire conditions on fish in headwater streams by observing growth and demographics of coastal cutthroat trout (Oncorhynchus clarkii clarkii) following wildfire. During the summer of 2002, wildfire burned portions of three headwater watersheds in the North Umpqua basin of western Oregon. Burn severities ranged from moderate to severe. A reference stream was selected from a nearby fourth watershed. All fish-bearing portions of the stream network in the four watersheds were surveyed for 3 years following the wildfire, and 1,295 scale samples were collected from coastal cutthroat trout for age and growth analysis. Stream temperatures in the burned watersheds changed significantly following the wildfire (p < 0.016), with increases of up to 23% in the most severely burned watershed. During summer electrofishing surveys in the burned watersheds, both young-of-the-year and fish ≥ age 1 were captured; in the unburned watershed, the vast majority of fish captured were ≥ age 1. Age-frequency analyses revealed that fish in older age classes (age ≥ 3) were more prevalent in the unburned watershed than in the burned watersheds. Relative growth rates and length at last annulus formation of coastal cutthroat trout were positively related to the number of degree days during the growing season, and Pearson correlation coefficients ranged from 0.60 (p < 0.07) to 0.90 (p < 0.01). Growth rates and size of fish were not significantly correlated with relative density of fish (p ≥ 0.14). Contrary to the commonly held assumption that wildfire is detrimental to biota in aquatic systems, these results suggest that in the short term (≤ 3 years), fish in the study streams adjusted to environmental change caused by wildfire. Title: Effects of wildfire on growth and demographics of coastal cutthroat trout in headwater streams Author: Heck, Michael P. Wildfire is a largely terrestrial perturbation broadly recognized as an agent of disturbance and ecological change in forested biomes. Effects of post-fire conditions on biotic components of aquatic systems have been less well-documented, although hypothetically, the two are strongly connected. In fact, the influence of wildfire may be most profound in headwater streams because of the tight linkage between aquatic and terrestrial ecosystems. We sought to understand the influence of post-fire conditions on fish in headwater streams by observing growth and demographics of coastal cutthroat trout (Oncorhynchus clarkii clarkii) following wildfire. During the summer of 2002, wildfire burned portions of three headwater watersheds in the North Umpqua basin of western Oregon. Burn severities ranged from moderate to severe. A reference stream was selected from a nearby fourth watershed. All fish-bearing portions of the stream network in the four watersheds were surveyed for 3 years following the wildfire, and 1,295 scale samples were collected from coastal cutthroat trout for age and growth analysis. Stream temperatures in the burned watersheds changed significantly following the wildfire (p < 0.016), with increases of up to 23% in the most severely burned watershed. During summer electrofishing surveys in the burned watersheds, both young-of-the-year and fish ≥ age 1 were captured; in the unburned watershed, the vast majority of fish captured were ≥ age 1. Age-frequency analyses revealed that fish in older age classes (age ≥ 3) were more prevalent in the unburned watershed than in the burned watersheds. Relative growth rates and length at last annulus formation of coastal cutthroat trout were positively related to the number of degree days during the growing season, and Pearson correlation coefficients ranged from 0.60 (p < 0.07) to 0.90 (p < 0.01). Growth rates and size of fish were not significantly correlated with relative density of fish (p ≥ 0.14). Contrary to the commonly held assumption that wildfire is detrimental to biota in aquatic systems, these results suggest that in the short term (≤ 3 years), fish in the study streams adjusted to environmental change caused by wildfire. Close

• 5. [Article] Feeding Ecology and Growth of Juvenile Chinook Salmon (Oncorhynchus tshawytscha) During Early Marine Residence

  The early marine phase following freshwater emigration has been identified as a critical period in salmonid (Oncorhynchus spp.) life history, characterized by high but variable mortality. Consistent with ...

  Citation × Citation Citation Abstract Copy Title: Feeding Ecology and Growth of Juvenile Chinook Salmon (Oncorhynchus tshawytscha) During Early Marine Residence Author: Litz, Marisa Norma Chantal The early marine phase following freshwater emigration has been identified as a critical period in salmonid (Oncorhynchus spp.) life history, characterized by high but variable mortality. Consistent with the “growth-mortality” and “bigger-is-better” hypotheses, at least some of the mortality during the critical period appears to be size-dependent – with smaller or slower growing individuals less likely to survive than larger, faster growing conspecifics. Size and growth are flexible morphological traits that vary with prey availability, yet there is incomplete information on the temporal and spatial match/mismatch between juvenile salmonids and their marine prey in the Northern California Current Ecosystem. This work addressed a gap in the understanding of seasonal variability in prey community composition, abundance, and quality during early marine residence. Three studies were conducted using a population of subyearling (age-0) Chinook salmon (O. tshawytscha) from the upper Columbia River in order to evaluate the effects of prey on salmon growth, biochemistry, and performance. The first was a laboratory study that tested for growth rate and swimming speed differences in salmon reared on three treatment diets followed by three fasting treatments to assess the effects of variability in summer diet quality and winter diet quantity. Significant differences in growth were detected among fasting treatments but not diet treatments. Also, larger salmon with more storage lipids swam faster than smaller leaner fish following fasting, indirectly supporting the notion that growth during the critical period provides a carryover benefit important for overwinter survival. Salmon fatty acids and bulk stable isotopes of carbon and nitrogen were measured throughout the experiment to provide estimates of turnover and incorporation rates. The next study was a longitudinal field study that measured variation in salmon size and prey field community throughout the early ocean period (May – September) over two years of high marine survival (2011 and 2012) to better understand the relationship between prey community composition and salmon growth. Maximum growth rates were associated with high biomass of northern anchovy (Engraulis mordax) which peaked in abundance at different times in each year. The final bioenergetics modeling study combined data from the laboratory and field studies to evaluate the relative importance of prey availability, prey energy density, and temperature on salmon growth. Variation in feeding rate was related most with growth rate variability and least with prey energy density. Throughout their range, subyearlings can grow at high rates in the ocean (>2% body weight per day) by consuming both invertebrate and marine fish prey. However, when marine fish prey are highly abundant they likely provide an energetic advantage over invertebrate prey by reducing overall foraging costs. Quantifying the abundance, size, diet, and distribution of juvenile salmonids relative to their prey field throughout early ocean residence will contribute to a better understanding of seasonal differences in trophic interactions that are associated with differences in annual growth and survival rates. Moreover, an integrated approach that combines sampling of prey with measurements of predator growth, diet, fatty acids, and stable isotopes provides a useful framework for assessing trophic dynamics and evaluating the effects of climate variability and change on predator and prey communities. Title: Feeding Ecology and Growth of Juvenile Chinook Salmon (Oncorhynchus tshawytscha) During Early Marine Residence Author: Litz, Marisa Norma Chantal The early marine phase following freshwater emigration has been identified as a critical period in salmonid (Oncorhynchus spp.) life history, characterized by high but variable mortality. Consistent with the “growth-mortality” and “bigger-is-better” hypotheses, at least some of the mortality during the critical period appears to be size-dependent – with smaller or slower growing individuals less likely to survive than larger, faster growing conspecifics. Size and growth are flexible morphological traits that vary with prey availability, yet there is incomplete information on the temporal and spatial match/mismatch between juvenile salmonids and their marine prey in the Northern California Current Ecosystem. This work addressed a gap in the understanding of seasonal variability in prey community composition, abundance, and quality during early marine residence. Three studies were conducted using a population of subyearling (age-0) Chinook salmon (O. tshawytscha) from the upper Columbia River in order to evaluate the effects of prey on salmon growth, biochemistry, and performance. The first was a laboratory study that tested for growth rate and swimming speed differences in salmon reared on three treatment diets followed by three fasting treatments to assess the effects of variability in summer diet quality and winter diet quantity. Significant differences in growth were detected among fasting treatments but not diet treatments. Also, larger salmon with more storage lipids swam faster than smaller leaner fish following fasting, indirectly supporting the notion that growth during the critical period provides a carryover benefit important for overwinter survival. Salmon fatty acids and bulk stable isotopes of carbon and nitrogen were measured throughout the experiment to provide estimates of turnover and incorporation rates. The next study was a longitudinal field study that measured variation in salmon size and prey field community throughout the early ocean period (May – September) over two years of high marine survival (2011 and 2012) to better understand the relationship between prey community composition and salmon growth. Maximum growth rates were associated with high biomass of northern anchovy (Engraulis mordax) which peaked in abundance at different times in each year. The final bioenergetics modeling study combined data from the laboratory and field studies to evaluate the relative importance of prey availability, prey energy density, and temperature on salmon growth. Variation in feeding rate was related most with growth rate variability and least with prey energy density. Throughout their range, subyearlings can grow at high rates in the ocean (>2% body weight per day) by consuming both invertebrate and marine fish prey. However, when marine fish prey are highly abundant they likely provide an energetic advantage over invertebrate prey by reducing overall foraging costs. Quantifying the abundance, size, diet, and distribution of juvenile salmonids relative to their prey field throughout early ocean residence will contribute to a better understanding of seasonal differences in trophic interactions that are associated with differences in annual growth and survival rates. Moreover, an integrated approach that combines sampling of prey with measurements of predator growth, diet, fatty acids, and stable isotopes provides a useful framework for assessing trophic dynamics and evaluating the effects of climate variability and change on predator and prey communities. Close

• 6. [Article] The effect of landscape topography and in-stream habitat on the distribution, growth, and survival of Lahontan cutthroat trout (Oncorhynchus clarki henshawi) in a high desert watershed

  Lahontan cutthroat trout (LCT) (Oncorhynchus clarki henshawi) are currently limited in their distribution to a patchwork of small isolated populations, the result of habitat degradation and natural variation ...

  Citation × Citation Citation Abstract Copy Title: The effect of landscape topography and in-stream habitat on the distribution, growth, and survival of Lahontan cutthroat trout (Oncorhynchus clarki henshawi) in a high desert watershed Author: Boxall, George D. Lahontan cutthroat trout (LCT) (Oncorhynchus clarki henshawi) are currently limited in their distribution to a patchwork of small isolated populations, the result of habitat degradation and natural variation in landscape and in-stream conditions. The objectives of this study were to determine how landscape level topographic features influence LCT distribution patterns. The work was carried out in a sub-basin of the Quinn River system, McDermitt Creek, which drains the sagebrush desert of southeastern Oregon and northern Nevada. Headwater tributaries of this creek consist of alternating canyon-confined and valley bounded reaches and LCT within these systems are challenged by low discharge and high temperatures during the summer, and anchor ice during the winter. Contiguous whole stream surveys were used to look at trout distribution during the summer of 2003 and spring and fall of 2004. Our results showed that topography affected LCT distribution in all reaches. LCT numbers were highest in areas with greater numbers of nick-points (the transition zones between less confined and more confined valley segments) and greater valley confinement. Additionally, in the downstream portion of our headwater reaches, more LCT were found in nick-points than expected based on the availability of this habitat type. Our data suggest that hyporheic inputs may be high in such areas, thus providing LCT with shelter from warm water in the summer, anchor ice in the winter and shallow stream depths during all seasons. Spatial occurrence of these areas of refugia can be taken into consideration when planning land-use activities and restoration efforts. After almost 30 years of conservation effort, Lahontan cutthroat trout (LCT) (Oncorhynchus clarki henshawi) populations remain in peril throughout the Great Basin region of southeastern Oregon and northern Nevada. This is not surprising since very little research has been done on the ecology of LCT, and management has been carried out without essential information on this sub-species. The objectives of our study were to determine whether there are inter-stream or inter-reach differences in LCT habitat selection, and if those differences corresponded to differences in fish survival and growth. We relied upon contiguous whole stream surveys to look at fish distribution and in-stream habitat. The use of half duplex PIT tags allowed us to determine the growth, movement patterns, and survival rates of most adult (>100 mm) LCT within the system. We found greater trout growth (median daily change in biomass 0.46% vs. 0.07%), but lower survival (35% vs. 61% between July and November), in relatively warmer and more open reaches than in cooler reaches. Additionally, undercut banks (predation shelter) were more important to trout in cooler stream reaches than in warmer ones, where habitat choice responded first to cold water input (which was influenced by topography). Our results will be useful in identifying and describing areas of high quality LCT habitat in low order streams throughout the Great Basin, thus allowing informed management decisions to facilitate the recovery of the sub-species. Title: The effect of landscape topography and in-stream habitat on the distribution, growth, and survival of Lahontan cutthroat trout (Oncorhynchus clarki henshawi) in a high desert watershed Author: Boxall, George D. Lahontan cutthroat trout (LCT) (Oncorhynchus clarki henshawi) are currently limited in their distribution to a patchwork of small isolated populations, the result of habitat degradation and natural variation in landscape and in-stream conditions. The objectives of this study were to determine how landscape level topographic features influence LCT distribution patterns. The work was carried out in a sub-basin of the Quinn River system, McDermitt Creek, which drains the sagebrush desert of southeastern Oregon and northern Nevada. Headwater tributaries of this creek consist of alternating canyon-confined and valley bounded reaches and LCT within these systems are challenged by low discharge and high temperatures during the summer, and anchor ice during the winter. Contiguous whole stream surveys were used to look at trout distribution during the summer of 2003 and spring and fall of 2004. Our results showed that topography affected LCT distribution in all reaches. LCT numbers were highest in areas with greater numbers of nick-points (the transition zones between less confined and more confined valley segments) and greater valley confinement. Additionally, in the downstream portion of our headwater reaches, more LCT were found in nick-points than expected based on the availability of this habitat type. Our data suggest that hyporheic inputs may be high in such areas, thus providing LCT with shelter from warm water in the summer, anchor ice in the winter and shallow stream depths during all seasons. Spatial occurrence of these areas of refugia can be taken into consideration when planning land-use activities and restoration efforts. After almost 30 years of conservation effort, Lahontan cutthroat trout (LCT) (Oncorhynchus clarki henshawi) populations remain in peril throughout the Great Basin region of southeastern Oregon and northern Nevada. This is not surprising since very little research has been done on the ecology of LCT, and management has been carried out without essential information on this sub-species. The objectives of our study were to determine whether there are inter-stream or inter-reach differences in LCT habitat selection, and if those differences corresponded to differences in fish survival and growth. We relied upon contiguous whole stream surveys to look at fish distribution and in-stream habitat. The use of half duplex PIT tags allowed us to determine the growth, movement patterns, and survival rates of most adult (>100 mm) LCT within the system. We found greater trout growth (median daily change in biomass 0.46% vs. 0.07%), but lower survival (35% vs. 61% between July and November), in relatively warmer and more open reaches than in cooler reaches. Additionally, undercut banks (predation shelter) were more important to trout in cooler stream reaches than in warmer ones, where habitat choice responded first to cold water input (which was influenced by topography). Our results will be useful in identifying and describing areas of high quality LCT habitat in low order streams throughout the Great Basin, thus allowing informed management decisions to facilitate the recovery of the sub-species. Close