Jennifer Gosselin | University of Washington (original) (raw)

Papers by Jennifer Gosselin

Freshwater Science, Jun 1, 2022

Decision triggers, used in adaptive management frameworks to decide when a specific management ac... more Decision triggers, used in adaptive management frameworks to decide when a specific management action will be implemented, are often informed by monitoring data. The identification and application of decision triggers is highly relevant to endangered fishes migrating through regulated rivers, as examined in the current study. The main goal was to determine whether seasonal patterns of behavioral, physical, and physiological indices of juveniles were related to subsequent smolt-to-adult return (SAR) survival and, if so, to determine whether these indices could be used to guide decisions related to the mitigation strategy of the juvenile fish transportation program in the Federal Columbia River Power System (Pacific Northwest, USA). Hatchery yearling Chinook Salmon (Oncorhynchus tshawytscha Walbaum in Artedi, 1792) were collected over the migration season at 3 dams in the hydrosystem and measured for fork length, wet mass, Fulton’s K (or condition factor), Na+/K+-ATPase (NKA) activity (or smoltification index), and % dry mass (or index of energetic reserves and smoltification). We estimated SAR survival from passive integrated transponder-tagged fish representative of our field samples and assessed its relationship to our fish indices, as well as indices of transported vs run-of-river passage and distance of sampling site to ocean. SAR survival was associated to interaction effects between juvenile fish transportation and % dry mass or NKA activity. Transported hatchery Chinook Salmon with dry mass <23% of whole fish wet mass and NKA activity >7 µmol ADP mg protein−1 h−1 showed greater SAR survival than their run-of-river counterparts. Fish with the highest predicted SAR survival had been transported and had fish indices consistent with smolts that were more developed (i.e., lower % dry mass and higher NKA activity). Furthermore, our results on % dry mass provided support for the hypothesis that greater lipid content increases fish buoyancy leading to greater susceptibility to predation. The buoyancy effect is expected to be greatest in hatchery fish. Overall, this study shows that decision triggers based on biological indices of migrating fish are potentially useful tools for in-season management.

Ecological Indicators, Feb 1, 2021

The common practice of incorporating environmental indices into population models has greatly adv... more The common practice of incorporating environmental indices into population models has greatly advanced our understanding of ecological systems. Unfortunately, we are increasingly seeing published correlations between population indicators and environmental indices breaking down when tested with new data. Examining how the correlations among indices change over time could help explain underlying causal mechanisms, which ultimately strengthen the basis for prediction of population indicators. For migratory animals such as anadromous salmon (Oncorhynchus spp.), the habitat conditions they experience can affect their lifetime fitness and population viability. We analyzed 43 freshwater, marine, and climate indices associated with 72 river sites and five coastal ecoregions inhabited by Chinook and coho salmon (O. tshawytscha and O. kisutch) in the western USA. Utilizing long time series (ranging from 32 to 124 years), we examined spatial and temporal patterns in correlations through hierarchical clustering across sites and non-stationarity across time. Individual river sites clustered into two Northwest and one Southwest groups. Northwest sites generally showed stronger correlations between freshwater and climate indices, while Southwest sites showed stronger correlations within freshwater or within marine/climate indices. For a closer examination at shorter periods, we parsed the time series into 10-year windows and showed how pairwise correlations changed over time with spring-summer Pacific Decadal Oscillation index in the Northwest and with spring flow in the Southwest. Stronger correlations across multiple indices tended to occur when large-scale climatic events (e.g., Oceanic Niño and Pacific Decadal Oscillation indices) were in-phase, and phase transitions (e.g., from positive to negative) occurred in the same 10-year window. In a third analysis, we assessed how well indices provided unique vs. confounding/complex information and had consistent vs. varying relationships based on the mean and variance of 10-year correlations. Across index types, the variance in correlations tended to be lowest in marine vs. climate indices, higher among freshwater indices, and highest for freshwater vs. marine/climate indices. Yet, the mean strength of correlations for freshwater vs. marine/climate indices was still comparable to those among freshwater ones. Overall, identifying time periods when correlations tend to change will help interpret historical and projected population indicators. Spatial trends in the strength of correlations also indicate that the level of confounding effects among indices can differ regionally. We emphasize the importance of knowing the strength and variability of correlations among indices, and their representativeness of ecological processes in the context of combined phases of multiple climatic indices.

Geophysical Research Letters, Aug 19, 2020

 This novel climate had a surprising ecosystem impact, indicated by a change in sign of PDO-salm... more  This novel climate had a surprising ecosystem impact, indicated by a change in sign of PDO-salmon correlations  Tracking changing relationships between primary climate variables and climate indices may be broadly useful for measuring climate novelty

Technical report, Nov 29, 2021

PLOS ONE, May 29, 2020

While survivorship curves typically exhibit smooth declines over time, step-patterned curves can ... more While survivorship curves typically exhibit smooth declines over time, step-patterned curves can occur with multiple stressors within a life stage. To explore this process, we examined the effects of heat (24˚C) and food restriction on juvenile rainbow trout (Oncorhynchus mykiss Walbaum) in challenge experiments. We observed step-patterned survivorship curves determined by mortality and loss of equilibrium (LOE) endpoints. To examine the cause of heterogeneity in the stress responses from early to late mortality and LOE, we measured indices of energetic reserves. The step transition in the survivorship curves, the peak mortality rates, and start of when individuals reached a critical energetic threshold (14% dry mass; 4.0 kJ�g-1 energy) all occurred at around days 10-15 of the challenge. The coherence in these temporal patterns suggest heterogeneity in the cohort stress responses, in which an early subgroup died from heat stress and a late subgroup died from starvation. Thus, their endpoint sensitivities resulted in step-patterned survivorship curves. We discuss the implications of the study for understanding effects of multiple stressors on population heterogeneity and note the possible significance of stress response selection under climate change in which heat stress and food limitations occur in concert.

Oecologia, Aug 3, 2013

Determining when resource competition increases survivorship can reveal processes underlying popu... more Determining when resource competition increases survivorship can reveal processes underlying population dynamics and reinforce the importance of heterogeneity among individuals in conservation. We ran an experiment mimicking the effects of competition in a growing season on survivorship during a selection event (e.g., overwinter starvation, drought). Using a model fish species (Poecilia reticulata), we studied how food availability and competition affect mass in a treatment stage, and subsequently survivorship in a challenge stage of increased temperature and starvation. The post-treatment mean mass was strongly related to the mean time to mortality and mass at mortality at all levels of competition. However, competition increased variance in mass and extended the right tail of the survivorship curve, resulting in a greater number of individuals alive beyond a critical temporal threshold ([Formula: see text]) than without competition. To realize the benefits from previously experienced competition, the duration of the challenge ([Formula: see text]) following the competition must exceed the critical threshold [Formula: see text] (i.e., competition increases survivorship when [Formula: see text]). Furthermore, this benefit was equivalent to increasing food availability by 20 % in a group without competition in our experiment. The relationship of [Formula: see text] to treatment and challenge conditions was modeled by characterizing mortality through mass loss in terms of the stochastic rate of loss of vitality (individual's survival capacity). In essence, when the duration of a selection event exceeds [Formula: see text], competition-induced heterogeneity buffers against mortality through overcompensation processes among individuals of a cohort. Overall, our study demonstrates an approach to quantify how early life stage heterogeneity affects survivorship.

This release contains all data and code to reproduce the results in the submitted manuscript.

Ecosphere, 2020

Ecology is often governed by nonlinear dynamics. Nonlinear ecological relationships can include t... more Ecology is often governed by nonlinear dynamics. Nonlinear ecological relationships can include thresholds—incremental changes in drivers that provoke disproportionately large ecological responses. Among the species that experience nonlinear and threshold dynamics are Pacific salmon (Oncorhynchus spp.). These culturally, ecologically, and economically significant fishes are in many places declining and management focal points. Often, managers can influence or react to ecological conditions that salmon experience, suggesting that nonlinearities, especially thresholds, may provide opportunities to inform decisions. However, nonlinear dynamics are not always invoked in management decisions involving salmon. Here, we review reported nonlinearities and thresholds in salmon ecology, describe potential applications that scientists and managers could develop to leverage nonlinear dynamics, and offer a path toward decisions that account for ecological nonlinearities and thresholds to improve...

PLOS ONE, 2020

While survivorship curves typically exhibit smooth declines over time, step-patterned curves can ... more While survivorship curves typically exhibit smooth declines over time, step-patterned curves can occur with multiple stressors within a life stage. To explore this process, we examined the effects of heat (24˚C) and food restriction on juvenile rainbow trout (Oncorhynchus mykiss Walbaum) in challenge experiments. We observed step-patterned survivorship curves determined by mortality and loss of equilibrium (LOE) endpoints. To examine the cause of heterogeneity in the stress responses from early to late mortality and LOE, we measured indices of energetic reserves. The step transition in the survivorship curves, the peak mortality rates, and start of when individuals reached a critical energetic threshold (14% dry mass; 4.0 kJ�g-1 energy) all occurred at around days 10-15 of the challenge. The coherence in these temporal patterns suggest heterogeneity in the cohort stress responses, in which an early subgroup died from heat stress and a late subgroup died from starvation. Thus, their endpoint sensitivities resulted in step-patterned survivorship curves. We discuss the implications of the study for understanding effects of multiple stressors on population heterogeneity and note the possible significance of stress response selection under climate change in which heat stress and food limitations occur in concert.

ICES Journal of Marine Science, 2019

Preseason abundance forecasts drive management of US West Coast salmon fisheries, yet little is k... more Preseason abundance forecasts drive management of US West Coast salmon fisheries, yet little is known about how environmental variability influences forecast performance. We compared forecasts of Chinook salmon (Oncorhynchus tshawytscha) against returns for (i) key California-Oregon ocean fishery stocks and (ii) high priority prey stocks for endangered Southern Resident Killer Whales (Orcinus orca) in Puget Sound, Washington. We explored how well environmental indices (at multiple locations and time lags) explained performance of forecasts based on different methods (i.e. sibling-based, production-based, environment-based, or recent averages), testing for nonlinear threshold dynamics. For the California stocks, no index tested explained >50% of the variation in forecast performance, but spring Pacific Decadal Oscillation and winter North Pacific Index during the year of return explained >40% of the variation for the sibling-based Sacramento Fall Chinook forecast, with nonlinea...

Transactions of the American Fisheries Society, 2017

Supplemental Figure S.1. Correlation coefficients between environmental covariates that were exam... more Supplemental Figure S.1. Correlation coefficients between environmental covariates that were examined for their effects on freshwater survival of Chinook Salmon: (a) daily observations and (b) 7-d averaged observations of temperature (theta ), flow, and spill at Lower Granite Dam (LGR), Lower Monumental Dam (LMN), and Bonneville Dam (BON) on a given day of the year (DOY).

Oecologia, 2013

Determining when resource competition increases survivorship can reveal processes underlying popu... more Determining when resource competition increases survivorship can reveal processes underlying population dynamics and reinforce the importance of heterogeneity among individuals in conservation. We ran an experiment mimicking the effects of competition in a growing season on survivorship during a selection event (e.g., overwinter starvation, drought). Using a model fish species (Poecilia reticulata), we studied how food availability and competition affect mass in a treatment stage, and subsequently survivorship in a challenge stage of increased temperature and starvation. The post-treatment mean mass was strongly related to the mean time to mortality and mass at mortality at all levels of competition. However, competition increased variance in mass and extended the right tail of the survivorship curve, resulting in a greater number of individuals alive beyond a critical temporal threshold ([Formula: see text]) than without competition. To realize the benefits from previously experienced competition, the duration of the challenge ([Formula: see text]) following the competition must exceed the critical threshold [Formula: see text] (i.e., competition increases survivorship when [Formula: see text]). Furthermore, this benefit was equivalent to increasing food availability by 20 % in a group without competition in our experiment. The relationship of [Formula: see text] to treatment and challenge conditions was modeled by characterizing mortality through mass loss in terms of the stochastic rate of loss of vitality (individual's survival capacity). In essence, when the duration of a selection event exceeds [Formula: see text], competition-induced heterogeneity buffers against mortality through overcompensation processes among individuals of a cohort. Overall, our study demonstrates an approach to quantify how early life stage heterogeneity affects survivorship.

Proceedings of the National Academy of Sciences, 2020

Climate change is likely to change the relationships between commonly used climate indices and un... more Climate change is likely to change the relationships between commonly used climate indices and underlying patterns of climate variability, but this complexity is rarely considered in studies using climate indices. Here, we show that the physical and ecological conditions mapping onto the Pacific Decadal Oscillation (PDO) index and North Pacific Gyre Oscillation (NPGO) index have changed over multidecadal timescales. These changes apparently began around a 1988/1989 North Pacific climate shift that was marked by abrupt northeast Pacific warming, declining temporal variance in the Aleutian Low (a leading atmospheric driver of the PDO), and increasing correlation between the PDO and NPGO patterns. Sea level pressure and surface temperature patterns associated with each climate index changed after 1988/1989, indicating that identical index values reflect different states of basin-scale climate over time. The PDO and NPGO also show time-dependent skill as indices of regional northeast Pa...

Ecological Indicators, 2021

The common practice of incorporating environmental indices into population models has greatly adv... more The common practice of incorporating environmental indices into population models has greatly advanced our understanding of ecological systems. Unfortunately, we are increasingly seeing published correlations between population indicators and environmental indices breaking down when tested with new data. Examining how the correlations among indices change over time could help explain underlying causal mechanisms, which ultimately strengthen the basis for prediction of population indicators. For migratory animals such as anadromous salmon (Oncorhynchus spp.), the habitat conditions they experience can affect their lifetime fitness and population viability. We analyzed 43 freshwater, marine, and climate indices associated with 72 river sites and five coastal ecoregions inhabited by Chinook and coho salmon (O. tshawytscha and O. kisutch) in the western USA. Utilizing long time series (ranging from 32 to 124 years), we examined spatial and temporal patterns in correlations through hierarchical clustering across sites and non-stationarity across time. Individual river sites clustered into two Northwest and one Southwest groups. Northwest sites generally showed stronger correlations between freshwater and climate indices, while Southwest sites showed stronger correlations within freshwater or within marine/climate indices. For a closer examination at shorter periods, we parsed the time series into 10-year windows and showed how pairwise correlations changed over time with spring-summer Pacific Decadal Oscillation index in the Northwest and with spring flow in the Southwest. Stronger correlations across multiple indices tended to occur when large-scale climatic events (e.g., Oceanic Niño and Pacific Decadal Oscillation indices) were in-phase, and phase transitions (e.g., from positive to negative) occurred in the same 10-year window. In a third analysis, we assessed how well indices provided unique vs. confounding/complex information and had consistent vs. varying relationships based on the mean and variance of 10-year correlations. Across index types, the variance in correlations tended to be lowest in marine vs. climate indices, higher among freshwater indices, and highest for freshwater vs. marine/climate indices. Yet, the mean strength of correlations for freshwater vs. marine/climate indices was still comparable to those among freshwater ones. Overall, identifying time periods when correlations tend to change will help interpret historical and projected population indicators. Spatial trends in the strength of correlations also indicate that the level of confounding effects among indices can differ regionally. We emphasize the importance of knowing the strength and variability of correlations among indices, and their representativeness of ecological processes in the context of combined phases of multiple climatic indices.

Freshwater Science, 2022

Decision triggers, used in adaptive management frameworks to decide when a specific management ac... more Decision triggers, used in adaptive management frameworks to decide when a specific management action will be implemented, are often informed by monitoring data. The identification and application of decision triggers is highly relevant to endangered fishes migrating through regulated rivers, as examined in the current study. The main goal was to determine whether seasonal patterns of behavioral, physical, and physiological indices of juveniles were related to subsequent smolt-to-adult return (SAR) survival and, if so, to determine whether these indices could be used to guide decisions related to the mitigation strategy of the juvenile fish transportation program in the Federal Columbia River Power System (Pacific Northwest, USA). Hatchery yearling Chinook Salmon (Oncorhynchus tshawytscha Walbaum in Artedi, 1792) were collected over the migration season at 3 dams in the hydrosystem and measured for fork length, wet mass, Fulton’s K (or condition factor), Na+/K+-ATPase (NKA) activity (or smoltification index), and % dry mass (or index of energetic reserves and smoltification). We estimated SAR survival from passive integrated transponder-tagged fish representative of our field samples and assessed its relationship to our fish indices, as well as indices of transported vs run-of-river passage and distance of sampling site to ocean. SAR survival was associated to interaction effects between juvenile fish transportation and % dry mass or NKA activity. Transported hatchery Chinook Salmon with dry mass <23% of whole fish wet mass and NKA activity >7 µmol ADP mg protein−1 h−1 showed greater SAR survival than their run-of-river counterparts. Fish with the highest predicted SAR survival had been transported and had fish indices consistent with smolts that were more developed (i.e., lower % dry mass and higher NKA activity). Furthermore, our results on % dry mass provided support for the hypothesis that greater lipid content increases fish buoyancy leading to greater susceptibility to predation. The buoyancy effect is expected to be greatest in hatchery fish. Overall, this study shows that decision triggers based on biological indices of migrating fish are potentially useful tools for in-season management.

Ecosphere, 2021

Determining which factors are most effective for mitigative strategies in conservation management... more Determining which factors are most effective for mitigative strategies in conservation management can be difficult for species with complex life cycles. Salmon (Oncorhynchus spp.) migrating through a hydroelectric power system experience conditions that can affect their survival directly within a life stage and indirectly in subsequent life stages through carryover effects. We quantified the association of covariates with survival across life stages of Chinook salmon (O. tshawytscha): juveniles migrating downstream, juveniles in the estuary, subadults in the ocean, and adults migrating upstream. We applied a hierarchical Bayesian mark-recapture model to~400,000 wild Snake River Chinook salmon (Pacific Northwest, USA). Modeled covariates of survival included migration timing, river temperature, flow, percent of water spilled over dams, snow water equivalent, juvenile fish transportation, juvenile fish length, dam powerhouse passage, sea surface temperature, and the North Pacific Gyre Oscillation. By analyzing these covariates in a unified model, we evaluated their relationships to survival within and across life stages in a common currency. Among direct effects, the negative relationship of sea surface temperature to ocean survival had the largest marginal effect size. Carryover effects also had substantial marginal effect sizes. Ocean survival was associated positively with juvenile length and snow water equivalent and negatively with river temperature. In comparison, direct effects on juvenile and adult survival generally showed smaller marginal effect sizes. Both juvenile and adult survival were negatively associated with river temperature. Juvenile survival increased with fish length, while adult survival was positively related to flow and negatively to percent water spilled at dams. The greatest variability in survival, however, was in the ocean stage. Thus, as the ocean continues to warm and as the human population exerts more pressure on the ecosystem, carryover effects will be increasingly important for recovering salmon and other migratory species.

Ecosphere, 2020

Ecology is often governed by nonlinear dynamics. Nonlinear ecological relationships can include t... more Ecology is often governed by nonlinear dynamics. Nonlinear ecological relationships can include thresholds-incremental changes in drivers that provoke disproportionately large ecological responses. Among the species that experience nonlinear and threshold dynamics are Pacific salmon (Oncor-hynchus spp.). These culturally, ecologically, and economically significant fishes are in many places declining and management focal points. Often, managers can influence or react to ecological conditions that salmon experience, suggesting that nonlinearities, especially thresholds, may provide opportunities to inform decisions. However, nonlinear dynamics are not always invoked in management decisions involving salmon. Here, we review reported nonlinearities and thresholds in salmon ecology, describe potential applications that scientists and managers could develop to leverage nonlinear dynamics, and offer a path toward decisions that account for ecological nonlinearities and thresholds to improve salmon outcomes. It appears that nonlinear dynamics are not uncommon in salmon ecology and that many management arenas may potentially leverage them to enable more effective or efficient decisions. Indeed, decisions guided by nonlinearities and thresholds may be particularly desirable considering salmon management arenas are often characterized by limited resources and mounting ecological stressors, practical constraints, and conservation challenges. More broadly, many salmon systems are data-rich and there are an extensive range of ecological contexts in which salmon are sensitive to anthropogenic decisions. Approaches developed to leverage nonlinearities in salmon ecology may serve as examples that may inform analogous approaches in other systems and taxa.

Freshwater Science, Jun 1, 2022

Decision triggers, used in adaptive management frameworks to decide when a specific management ac... more Decision triggers, used in adaptive management frameworks to decide when a specific management action will be implemented, are often informed by monitoring data. The identification and application of decision triggers is highly relevant to endangered fishes migrating through regulated rivers, as examined in the current study. The main goal was to determine whether seasonal patterns of behavioral, physical, and physiological indices of juveniles were related to subsequent smolt-to-adult return (SAR) survival and, if so, to determine whether these indices could be used to guide decisions related to the mitigation strategy of the juvenile fish transportation program in the Federal Columbia River Power System (Pacific Northwest, USA). Hatchery yearling Chinook Salmon (Oncorhynchus tshawytscha Walbaum in Artedi, 1792) were collected over the migration season at 3 dams in the hydrosystem and measured for fork length, wet mass, Fulton’s K (or condition factor), Na+/K+-ATPase (NKA) activity (or smoltification index), and % dry mass (or index of energetic reserves and smoltification). We estimated SAR survival from passive integrated transponder-tagged fish representative of our field samples and assessed its relationship to our fish indices, as well as indices of transported vs run-of-river passage and distance of sampling site to ocean. SAR survival was associated to interaction effects between juvenile fish transportation and % dry mass or NKA activity. Transported hatchery Chinook Salmon with dry mass &lt;23% of whole fish wet mass and NKA activity &gt;7 µmol ADP mg protein−1 h−1 showed greater SAR survival than their run-of-river counterparts. Fish with the highest predicted SAR survival had been transported and had fish indices consistent with smolts that were more developed (i.e., lower % dry mass and higher NKA activity). Furthermore, our results on % dry mass provided support for the hypothesis that greater lipid content increases fish buoyancy leading to greater susceptibility to predation. The buoyancy effect is expected to be greatest in hatchery fish. Overall, this study shows that decision triggers based on biological indices of migrating fish are potentially useful tools for in-season management.

Ecological Indicators, Feb 1, 2021

The common practice of incorporating environmental indices into population models has greatly adv... more The common practice of incorporating environmental indices into population models has greatly advanced our understanding of ecological systems. Unfortunately, we are increasingly seeing published correlations between population indicators and environmental indices breaking down when tested with new data. Examining how the correlations among indices change over time could help explain underlying causal mechanisms, which ultimately strengthen the basis for prediction of population indicators. For migratory animals such as anadromous salmon (Oncorhynchus spp.), the habitat conditions they experience can affect their lifetime fitness and population viability. We analyzed 43 freshwater, marine, and climate indices associated with 72 river sites and five coastal ecoregions inhabited by Chinook and coho salmon (O. tshawytscha and O. kisutch) in the western USA. Utilizing long time series (ranging from 32 to 124 years), we examined spatial and temporal patterns in correlations through hierarchical clustering across sites and non-stationarity across time. Individual river sites clustered into two Northwest and one Southwest groups. Northwest sites generally showed stronger correlations between freshwater and climate indices, while Southwest sites showed stronger correlations within freshwater or within marine/climate indices. For a closer examination at shorter periods, we parsed the time series into 10-year windows and showed how pairwise correlations changed over time with spring-summer Pacific Decadal Oscillation index in the Northwest and with spring flow in the Southwest. Stronger correlations across multiple indices tended to occur when large-scale climatic events (e.g., Oceanic Niño and Pacific Decadal Oscillation indices) were in-phase, and phase transitions (e.g., from positive to negative) occurred in the same 10-year window. In a third analysis, we assessed how well indices provided unique vs. confounding/complex information and had consistent vs. varying relationships based on the mean and variance of 10-year correlations. Across index types, the variance in correlations tended to be lowest in marine vs. climate indices, higher among freshwater indices, and highest for freshwater vs. marine/climate indices. Yet, the mean strength of correlations for freshwater vs. marine/climate indices was still comparable to those among freshwater ones. Overall, identifying time periods when correlations tend to change will help interpret historical and projected population indicators. Spatial trends in the strength of correlations also indicate that the level of confounding effects among indices can differ regionally. We emphasize the importance of knowing the strength and variability of correlations among indices, and their representativeness of ecological processes in the context of combined phases of multiple climatic indices.

Geophysical Research Letters, Aug 19, 2020

 This novel climate had a surprising ecosystem impact, indicated by a change in sign of PDO-salm... more  This novel climate had a surprising ecosystem impact, indicated by a change in sign of PDO-salmon correlations  Tracking changing relationships between primary climate variables and climate indices may be broadly useful for measuring climate novelty

Technical report, Nov 29, 2021

PLOS ONE, May 29, 2020

While survivorship curves typically exhibit smooth declines over time, step-patterned curves can ... more While survivorship curves typically exhibit smooth declines over time, step-patterned curves can occur with multiple stressors within a life stage. To explore this process, we examined the effects of heat (24˚C) and food restriction on juvenile rainbow trout (Oncorhynchus mykiss Walbaum) in challenge experiments. We observed step-patterned survivorship curves determined by mortality and loss of equilibrium (LOE) endpoints. To examine the cause of heterogeneity in the stress responses from early to late mortality and LOE, we measured indices of energetic reserves. The step transition in the survivorship curves, the peak mortality rates, and start of when individuals reached a critical energetic threshold (14% dry mass; 4.0 kJ�g-1 energy) all occurred at around days 10-15 of the challenge. The coherence in these temporal patterns suggest heterogeneity in the cohort stress responses, in which an early subgroup died from heat stress and a late subgroup died from starvation. Thus, their endpoint sensitivities resulted in step-patterned survivorship curves. We discuss the implications of the study for understanding effects of multiple stressors on population heterogeneity and note the possible significance of stress response selection under climate change in which heat stress and food limitations occur in concert.

Oecologia, Aug 3, 2013

Determining when resource competition increases survivorship can reveal processes underlying popu... more Determining when resource competition increases survivorship can reveal processes underlying population dynamics and reinforce the importance of heterogeneity among individuals in conservation. We ran an experiment mimicking the effects of competition in a growing season on survivorship during a selection event (e.g., overwinter starvation, drought). Using a model fish species (Poecilia reticulata), we studied how food availability and competition affect mass in a treatment stage, and subsequently survivorship in a challenge stage of increased temperature and starvation. The post-treatment mean mass was strongly related to the mean time to mortality and mass at mortality at all levels of competition. However, competition increased variance in mass and extended the right tail of the survivorship curve, resulting in a greater number of individuals alive beyond a critical temporal threshold ([Formula: see text]) than without competition. To realize the benefits from previously experienced competition, the duration of the challenge ([Formula: see text]) following the competition must exceed the critical threshold [Formula: see text] (i.e., competition increases survivorship when [Formula: see text]). Furthermore, this benefit was equivalent to increasing food availability by 20 % in a group without competition in our experiment. The relationship of [Formula: see text] to treatment and challenge conditions was modeled by characterizing mortality through mass loss in terms of the stochastic rate of loss of vitality (individual&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s survival capacity). In essence, when the duration of a selection event exceeds [Formula: see text], competition-induced heterogeneity buffers against mortality through overcompensation processes among individuals of a cohort. Overall, our study demonstrates an approach to quantify how early life stage heterogeneity affects survivorship.

This release contains all data and code to reproduce the results in the submitted manuscript.

Ecosphere, 2020

Ecology is often governed by nonlinear dynamics. Nonlinear ecological relationships can include t... more Ecology is often governed by nonlinear dynamics. Nonlinear ecological relationships can include thresholds—incremental changes in drivers that provoke disproportionately large ecological responses. Among the species that experience nonlinear and threshold dynamics are Pacific salmon (Oncorhynchus spp.). These culturally, ecologically, and economically significant fishes are in many places declining and management focal points. Often, managers can influence or react to ecological conditions that salmon experience, suggesting that nonlinearities, especially thresholds, may provide opportunities to inform decisions. However, nonlinear dynamics are not always invoked in management decisions involving salmon. Here, we review reported nonlinearities and thresholds in salmon ecology, describe potential applications that scientists and managers could develop to leverage nonlinear dynamics, and offer a path toward decisions that account for ecological nonlinearities and thresholds to improve...

PLOS ONE, 2020

While survivorship curves typically exhibit smooth declines over time, step-patterned curves can ... more While survivorship curves typically exhibit smooth declines over time, step-patterned curves can occur with multiple stressors within a life stage. To explore this process, we examined the effects of heat (24˚C) and food restriction on juvenile rainbow trout (Oncorhynchus mykiss Walbaum) in challenge experiments. We observed step-patterned survivorship curves determined by mortality and loss of equilibrium (LOE) endpoints. To examine the cause of heterogeneity in the stress responses from early to late mortality and LOE, we measured indices of energetic reserves. The step transition in the survivorship curves, the peak mortality rates, and start of when individuals reached a critical energetic threshold (14% dry mass; 4.0 kJ�g-1 energy) all occurred at around days 10-15 of the challenge. The coherence in these temporal patterns suggest heterogeneity in the cohort stress responses, in which an early subgroup died from heat stress and a late subgroup died from starvation. Thus, their endpoint sensitivities resulted in step-patterned survivorship curves. We discuss the implications of the study for understanding effects of multiple stressors on population heterogeneity and note the possible significance of stress response selection under climate change in which heat stress and food limitations occur in concert.

ICES Journal of Marine Science, 2019

Preseason abundance forecasts drive management of US West Coast salmon fisheries, yet little is k... more Preseason abundance forecasts drive management of US West Coast salmon fisheries, yet little is known about how environmental variability influences forecast performance. We compared forecasts of Chinook salmon (Oncorhynchus tshawytscha) against returns for (i) key California-Oregon ocean fishery stocks and (ii) high priority prey stocks for endangered Southern Resident Killer Whales (Orcinus orca) in Puget Sound, Washington. We explored how well environmental indices (at multiple locations and time lags) explained performance of forecasts based on different methods (i.e. sibling-based, production-based, environment-based, or recent averages), testing for nonlinear threshold dynamics. For the California stocks, no index tested explained >50% of the variation in forecast performance, but spring Pacific Decadal Oscillation and winter North Pacific Index during the year of return explained >40% of the variation for the sibling-based Sacramento Fall Chinook forecast, with nonlinea...

Transactions of the American Fisheries Society, 2017

Supplemental Figure S.1. Correlation coefficients between environmental covariates that were exam... more Supplemental Figure S.1. Correlation coefficients between environmental covariates that were examined for their effects on freshwater survival of Chinook Salmon: (a) daily observations and (b) 7-d averaged observations of temperature (theta ), flow, and spill at Lower Granite Dam (LGR), Lower Monumental Dam (LMN), and Bonneville Dam (BON) on a given day of the year (DOY).

Oecologia, 2013

Determining when resource competition increases survivorship can reveal processes underlying popu... more Determining when resource competition increases survivorship can reveal processes underlying population dynamics and reinforce the importance of heterogeneity among individuals in conservation. We ran an experiment mimicking the effects of competition in a growing season on survivorship during a selection event (e.g., overwinter starvation, drought). Using a model fish species (Poecilia reticulata), we studied how food availability and competition affect mass in a treatment stage, and subsequently survivorship in a challenge stage of increased temperature and starvation. The post-treatment mean mass was strongly related to the mean time to mortality and mass at mortality at all levels of competition. However, competition increased variance in mass and extended the right tail of the survivorship curve, resulting in a greater number of individuals alive beyond a critical temporal threshold ([Formula: see text]) than without competition. To realize the benefits from previously experienced competition, the duration of the challenge ([Formula: see text]) following the competition must exceed the critical threshold [Formula: see text] (i.e., competition increases survivorship when [Formula: see text]). Furthermore, this benefit was equivalent to increasing food availability by 20 % in a group without competition in our experiment. The relationship of [Formula: see text] to treatment and challenge conditions was modeled by characterizing mortality through mass loss in terms of the stochastic rate of loss of vitality (individual&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s survival capacity). In essence, when the duration of a selection event exceeds [Formula: see text], competition-induced heterogeneity buffers against mortality through overcompensation processes among individuals of a cohort. Overall, our study demonstrates an approach to quantify how early life stage heterogeneity affects survivorship.

Proceedings of the National Academy of Sciences, 2020

Climate change is likely to change the relationships between commonly used climate indices and un... more Climate change is likely to change the relationships between commonly used climate indices and underlying patterns of climate variability, but this complexity is rarely considered in studies using climate indices. Here, we show that the physical and ecological conditions mapping onto the Pacific Decadal Oscillation (PDO) index and North Pacific Gyre Oscillation (NPGO) index have changed over multidecadal timescales. These changes apparently began around a 1988/1989 North Pacific climate shift that was marked by abrupt northeast Pacific warming, declining temporal variance in the Aleutian Low (a leading atmospheric driver of the PDO), and increasing correlation between the PDO and NPGO patterns. Sea level pressure and surface temperature patterns associated with each climate index changed after 1988/1989, indicating that identical index values reflect different states of basin-scale climate over time. The PDO and NPGO also show time-dependent skill as indices of regional northeast Pa...

Ecological Indicators, 2021

The common practice of incorporating environmental indices into population models has greatly adv... more The common practice of incorporating environmental indices into population models has greatly advanced our understanding of ecological systems. Unfortunately, we are increasingly seeing published correlations between population indicators and environmental indices breaking down when tested with new data. Examining how the correlations among indices change over time could help explain underlying causal mechanisms, which ultimately strengthen the basis for prediction of population indicators. For migratory animals such as anadromous salmon (Oncorhynchus spp.), the habitat conditions they experience can affect their lifetime fitness and population viability. We analyzed 43 freshwater, marine, and climate indices associated with 72 river sites and five coastal ecoregions inhabited by Chinook and coho salmon (O. tshawytscha and O. kisutch) in the western USA. Utilizing long time series (ranging from 32 to 124 years), we examined spatial and temporal patterns in correlations through hierarchical clustering across sites and non-stationarity across time. Individual river sites clustered into two Northwest and one Southwest groups. Northwest sites generally showed stronger correlations between freshwater and climate indices, while Southwest sites showed stronger correlations within freshwater or within marine/climate indices. For a closer examination at shorter periods, we parsed the time series into 10-year windows and showed how pairwise correlations changed over time with spring-summer Pacific Decadal Oscillation index in the Northwest and with spring flow in the Southwest. Stronger correlations across multiple indices tended to occur when large-scale climatic events (e.g., Oceanic Niño and Pacific Decadal Oscillation indices) were in-phase, and phase transitions (e.g., from positive to negative) occurred in the same 10-year window. In a third analysis, we assessed how well indices provided unique vs. confounding/complex information and had consistent vs. varying relationships based on the mean and variance of 10-year correlations. Across index types, the variance in correlations tended to be lowest in marine vs. climate indices, higher among freshwater indices, and highest for freshwater vs. marine/climate indices. Yet, the mean strength of correlations for freshwater vs. marine/climate indices was still comparable to those among freshwater ones. Overall, identifying time periods when correlations tend to change will help interpret historical and projected population indicators. Spatial trends in the strength of correlations also indicate that the level of confounding effects among indices can differ regionally. We emphasize the importance of knowing the strength and variability of correlations among indices, and their representativeness of ecological processes in the context of combined phases of multiple climatic indices.

Freshwater Science, 2022

Decision triggers, used in adaptive management frameworks to decide when a specific management ac... more Decision triggers, used in adaptive management frameworks to decide when a specific management action will be implemented, are often informed by monitoring data. The identification and application of decision triggers is highly relevant to endangered fishes migrating through regulated rivers, as examined in the current study. The main goal was to determine whether seasonal patterns of behavioral, physical, and physiological indices of juveniles were related to subsequent smolt-to-adult return (SAR) survival and, if so, to determine whether these indices could be used to guide decisions related to the mitigation strategy of the juvenile fish transportation program in the Federal Columbia River Power System (Pacific Northwest, USA). Hatchery yearling Chinook Salmon (Oncorhynchus tshawytscha Walbaum in Artedi, 1792) were collected over the migration season at 3 dams in the hydrosystem and measured for fork length, wet mass, Fulton’s K (or condition factor), Na+/K+-ATPase (NKA) activity (or smoltification index), and % dry mass (or index of energetic reserves and smoltification). We estimated SAR survival from passive integrated transponder-tagged fish representative of our field samples and assessed its relationship to our fish indices, as well as indices of transported vs run-of-river passage and distance of sampling site to ocean. SAR survival was associated to interaction effects between juvenile fish transportation and % dry mass or NKA activity. Transported hatchery Chinook Salmon with dry mass <23% of whole fish wet mass and NKA activity >7 µmol ADP mg protein−1 h−1 showed greater SAR survival than their run-of-river counterparts. Fish with the highest predicted SAR survival had been transported and had fish indices consistent with smolts that were more developed (i.e., lower % dry mass and higher NKA activity). Furthermore, our results on % dry mass provided support for the hypothesis that greater lipid content increases fish buoyancy leading to greater susceptibility to predation. The buoyancy effect is expected to be greatest in hatchery fish. Overall, this study shows that decision triggers based on biological indices of migrating fish are potentially useful tools for in-season management.

Ecosphere, 2021

Determining which factors are most effective for mitigative strategies in conservation management... more Determining which factors are most effective for mitigative strategies in conservation management can be difficult for species with complex life cycles. Salmon (Oncorhynchus spp.) migrating through a hydroelectric power system experience conditions that can affect their survival directly within a life stage and indirectly in subsequent life stages through carryover effects. We quantified the association of covariates with survival across life stages of Chinook salmon (O. tshawytscha): juveniles migrating downstream, juveniles in the estuary, subadults in the ocean, and adults migrating upstream. We applied a hierarchical Bayesian mark-recapture model to~400,000 wild Snake River Chinook salmon (Pacific Northwest, USA). Modeled covariates of survival included migration timing, river temperature, flow, percent of water spilled over dams, snow water equivalent, juvenile fish transportation, juvenile fish length, dam powerhouse passage, sea surface temperature, and the North Pacific Gyre Oscillation. By analyzing these covariates in a unified model, we evaluated their relationships to survival within and across life stages in a common currency. Among direct effects, the negative relationship of sea surface temperature to ocean survival had the largest marginal effect size. Carryover effects also had substantial marginal effect sizes. Ocean survival was associated positively with juvenile length and snow water equivalent and negatively with river temperature. In comparison, direct effects on juvenile and adult survival generally showed smaller marginal effect sizes. Both juvenile and adult survival were negatively associated with river temperature. Juvenile survival increased with fish length, while adult survival was positively related to flow and negatively to percent water spilled at dams. The greatest variability in survival, however, was in the ocean stage. Thus, as the ocean continues to warm and as the human population exerts more pressure on the ecosystem, carryover effects will be increasingly important for recovering salmon and other migratory species.

Ecosphere, 2020

Ecology is often governed by nonlinear dynamics. Nonlinear ecological relationships can include t... more Ecology is often governed by nonlinear dynamics. Nonlinear ecological relationships can include thresholds-incremental changes in drivers that provoke disproportionately large ecological responses. Among the species that experience nonlinear and threshold dynamics are Pacific salmon (Oncor-hynchus spp.). These culturally, ecologically, and economically significant fishes are in many places declining and management focal points. Often, managers can influence or react to ecological conditions that salmon experience, suggesting that nonlinearities, especially thresholds, may provide opportunities to inform decisions. However, nonlinear dynamics are not always invoked in management decisions involving salmon. Here, we review reported nonlinearities and thresholds in salmon ecology, describe potential applications that scientists and managers could develop to leverage nonlinear dynamics, and offer a path toward decisions that account for ecological nonlinearities and thresholds to improve salmon outcomes. It appears that nonlinear dynamics are not uncommon in salmon ecology and that many management arenas may potentially leverage them to enable more effective or efficient decisions. Indeed, decisions guided by nonlinearities and thresholds may be particularly desirable considering salmon management arenas are often characterized by limited resources and mounting ecological stressors, practical constraints, and conservation challenges. More broadly, many salmon systems are data-rich and there are an extensive range of ecological contexts in which salmon are sensitive to anthropogenic decisions. Approaches developed to leverage nonlinearities in salmon ecology may serve as examples that may inform analogous approaches in other systems and taxa.