K Holsman - Academia.edu (original) (raw)
Papers by K Holsman
In recent Alaska Fisheries Science Center surveys, we have conducted Stomach Content ANalysis at ... more In recent Alaska Fisheries Science Center surveys, we have conducted Stomach Content ANalysis at sea (SCAN) and analysis in the laboratory for several groundfish species. This provided us with the opportunity to compare our ability to identify key prey types between the two methods. Preliminary analyses indicate that identification of jelly-prey (Cnidaria and Ctenophora) and salp-prey (pelagic Tunicata and Larvacea) differs between the two methods for some zooplanktivores. SCAN more frequently identified jelly-prey in the diets of Dark rockfish, Dusky rockfish, Prowfish, Sablefish. Dissolution of jelly-prey tissues during the preservation process is likely the main factor in the differences observed. Salp-prey was more frequently identified in the laboratory for Sablefish and Walleye pollock. Tissue consistency and size of salp-prey may make them more easily detected in the laboratory. Preliminary analyses also indicate that the identification of fish-prey to species was higher in S...
Late summer and early fall water temperatures on the Klamath River can reach levels that are phys... more Late summer and early fall water temperatures on the Klamath River can reach levels that are physiologically stressful to endangered and threatened salmonids. At the limits of their thermal tolerance, salmonids may behaviorally thermoregulate by moving to localized patches of colder water, or thermal refugia. The presence of these refugia may be key to salmonid survival, especially during periods of elevated mainstem temperatures when refugia may be the only usable habitat available. However, the dynamics and importance of thermal refugia are not thoroughly understood. While fish obtain thermal benefits by using refugia, potential trade-offs include lower food availability, decreased growth rates, and increased risk of disease due to high fish densities. The interplay between these factors influences how much time a fish chooses to spend in the mainstem river versus the refugia. My research focuses on defining the mechanisms driving steelhead thermal refugia use at both landscape an...
As climate change and land-use impacts drive increases in river temperatures, thermal refugia cre... more As climate change and land-use impacts drive increases in river temperatures, thermal refugia created by coolwater tributary inputs are becoming increasingly important habitat for coldwater fish species. Summer mainstem temperatures on the Klamath River in northern California often reach physiologically stressful levels (~22-26°C) for native salmonid populations, driving juvenile salmonids into thermal refugia. These refugia are dynamic environments, and habitat quality may fluctuate in the refuge as well as in the surrounding sub-optimal mainstem habitat. The goal of this study was to determine which environmental factors are driving juvenile steelhead use of thermal refugia, and the timescale at which fish are shifting between thermal environments, in order to gain a better understanding of when these areas become critical habitat and how to effectively manage and restore thermal refugia on warming rivers. I used an innovative approach, taking advantage of relatively new radio tag...
Variability in walleye pollock (Gadus chalcogrammus) growth and survival is structured in part by... more Variability in walleye pollock (Gadus chalcogrammus) growth and survival is structured in part by climate-driven bottom-up control of zooplankton composition. We used two modeling approaches to understand the roles of prey quality, prey composition, and water temperature on juvenile walleye pollock growth: (1) a bioenergetics model that included local predator and prey energy densities, and (2) an individual-based model that included a mechanistic feeding component, local prey densities and size, and physical oceanographic conditions. Prey composition in late-summer shifted from predominantly smaller copepod species in the warmer 2005 season to larger species in the cooler 2010 season, reflecting differences in zooplankton composition between years. Spatial patterns in prey composition and water temperature lead to areas of enhanced growth, or growth ‘hot spots’, for juvenile walleye pollock and survival may be enhanced when fish overlap with these areas. This study provides evidenc...
We fit simple production models with and without covariates for several functionally analogous sp... more We fit simple production models with and without covariates for several functionally analogous species using data for 11 large marine ecosystems. The most complete evaluation of the impacts of covariates on estimates of production were for cod (Gadus morhua) and herring (Clupea harengus). Functionally analogous species included Greenland cod (Gadus ogac) and Pacific cod (Gadus macrocephalus), and Pacific herring (Clupea pallasii). Biological covariates included the abundance of prey (herring for cod and an index of primary production for herring). Physical covariates included common physical forcing functions such as AMO and PDO as well as water temperature. For both functional species, we fit a hierarchy of nested models that included a full model with physical and biological covariates. Models were compared using an information-theoretic framework. The numerical impacts of covariates differed among systems. However, the trends among the different ecosystems were similar. The inclu...
We define extended single-species production models (ESSPMs) as single species production models ... more We define extended single-species production models (ESSPMs) as single species production models that incorporate time series of principal prey and/or predator species as biological covariates. One advantage to ESSPMs over single species production models without biological covariates is that these models can be used to test the existence and direction of (one-way) species interactions. However, estimates of actual interaction strengths are confounded with scaling of the covariates (i.e., catchability). In addition, biological reference points (BRPs; e.g. maximum sustainable yield, MSY) that can be calculated in ESSPMs may be of limited value compared to those estimates that more directly incorporate species interactions, because of a lack of feedback between prey and predator species in ESSPMs. We thus developed a full multispecies production model (MSPM) to estimate biological interaction strengths and examine tradeoffs in multispecies MSY. As a preliminary demonstration, we fit t...
The aim of this project was to conduct a formal Management Strategy Evaluation (MSE) in which the... more The aim of this project was to conduct a formal Management Strategy Evaluation (MSE) in which the FEAST model acts as an "operating model" and currently developed methods (stock assessments, MSMt, and Ecosim) act as "assessment" models. The project planned to test assessment models from the range currently available for the Bering Sea, including: single species-assessments w/ correlative recruitment indices; multi-species models; and whole ecosystem models. In addition, testing of autocorrelative biomass dynamics/network models and nonlinear correlative models would provide results for "null" models for determining the added value of the more mechanistic approaches. The metrics for evaluating the success of the "assessment" models was to be the accuracy (lack of bias) and precision (lack of variance) of key model outputs (such as recruitment and biomass, both in the past and as forecast under given management regimes) when they are fit to data generated (with observation error) from the operating (Forage/Euphausiid Abundance in Space and Time, FEAST) model. The aim of the project was to provide information about the skill of each model in determining past and current states (hindcast/nowcast) as well as the success of each model when predicting future states from current states. When combined with management decision rules, success was to be defined as the ability to keep fish populations and yields above a "best performance" reference point determined from the operating model and the ability to achieve high economic returns. However, the MSE project as planned became untenable as the project deadline approached and a FEAST hindcast with the required level of performance remained unavailable. Nevertheless, the work conducted under this project shows that it is feasible to develop a Management Strategy Evaluation system which could be based on an operating model of the complexity of FEAST. The specifications and code developed during the project could be used in any follow-up modeling work. The project conducted a stakeholder workshop which led to analyses which showed that it is feasible to develop harvest control rules which are both consistent with US federal fisheries law and can be applied using the outputs from multispecies and ecosystem models. Furthermore, the project did conduct MSE forecasts using MSM as an operating model and developed an approach for blending results from multiple models so that model projections reflect estimation error, uncertainty about future recruitment success and well as model error. The key conclusions of this study pertain primarily to the lessons learnt conducting a modeling project of this magnitude as the challenges of including and charactering uncertainty when conducting forecasts of fish systems.
Risk assessments quantify the probability of undesirable events along with their consequences. Th... more Risk assessments quantify the probability of undesirable events along with their consequences. They are used to prioritize management interventions and assess tradeoffs, serving as an essential component of ecosystem-based management (EBM). A central objective of most risk assessments for conservation and management is to characterize uncertainty and impacts associated with one or more pressures of interest. Risk assessments have been used in marine resource management to help evaluate the risk of environmental, ecological, and anthropogenic pressures on species or habitats including for data-poor fisheries management (e.g., toxicity, probability of extinction, habitat alteration impacts). Traditionally, marine risk assessments focused on singular pressure-response relationships, but recent advancements have included use of risk assessments in an EBM context, providing a method for evaluating the cumulative impacts of multiple pressures on multiple ecosystem components. Here, we describe a conceptual framework for ecosystem risk assessment (ERA), highlighting its role in operationalizing EBM, with specific attention to ocean management considerations. This framework builds on the ecotoxicological and conservation literature on risk assessment and includes recent advances that focus on risks posed by fishing to marine ecosystems. We review how examples of ERAs from the United States fit into this framework, explore the variety of analytical approaches that have been used to conduct ERAs, and assess the challenges and data gaps that remain. This review discusses future prospects for ERAs as EBM decision-support tools, their expanded role in integrated ecosystem assessments, and the development of next-generation risk assessments for coupled natural–human systems.
Modelling spatially dependent predation mortality of eastern Bering Sea walleye pollock, and its ... more Modelling spatially dependent predation mortality of eastern Bering Sea walleye pollock, and its implications for stock dynamics under future climate scenarios. Arrowtooth flounder (Atheresthes stomias) are an important predator of juvenile walleye pollock (Gadus chalcogramus) in the eastern Bering Sea (EBS) shelf and have increased 3-fold in biomass from 1977 to 2014. Arrowtooth flounder avoid the summer " cold pool " (bottom water ≤28C) and variability in cold pool size and location has affected their spatial overlap with juvenile walleye pollock. Developing a method to account for the relationship between climate change and pollock mortality can highlight ecosystem dynamics and contribute to better assessments for fisheries management. Consequently, spatially resolved predation mortality rates were estimated within an age-structured walleye pollock stock assessment population model (based on spatial information on diet and abundance from trawl surveys), along with the effect of sea surface temperature (SST) on pollock recruitment. Projections of SST and cold pool area to 2050 were obtained (or statistically downscaled) from nine global climate models and used within an age-structure population model to project pollock abundance given estimated relationships between environmental variables and predator and prey spatial distributions, pollock recruitment, and maximum rate of arrowtooth flounder consumption. The climate projections show a wide range of variability but an overall trend of increasing SST and decreasing cold pool area. Projected pollock biomass decreased largely due to the negative effect of increased SST on pollock recruitment. A sensitivity analysis indicated that the decline in projected pollock biomass would be exacerbated if arrowtooth flounder increased their relative distribution in the EBS northwest middle shelf (an area of relatively high density of juvenile pollock) in warm years.
Ecosystem-based fisheries management (EBFM) approaches allow a broader and more extensive conside... more Ecosystem-based fisheries management (EBFM) approaches allow a broader and more extensive consideration of objectives than is typically possible with conventional single-species approaches. Ecosystem linkages may include trophic interactions and climate change effects on productivity for the relevant species within the system. Presently, models are evolving to include a comprehensive set of fishery and ecosystem information to address these broader management considerations. The increased scope of EBFM approaches is accompanied with a greater number of plausible models to describe the systems. This can lead to harvest recommendations and biological reference points that differ considerably among models. Model selection for projections (and specific catch recommendations) often occurs through a process that tends to adopt familiar, often simpler, models without considering those that incorporate more complex ecosystem information. Multi-model inference provides a framework that resolves this dilemma by providing a means of including information from alternative, often divergent models to inform biological reference points and possible catch consequences. We apply an example of this approach to data for three species of groundfish in the Bering Sea: walleye pollock, Pacific cod, and arrowtooth flounder using three models: 1) an age-structured “conventional” single-species model, 2) an age-structured single-species model with temperature-specific weight at age, and 3) a temperature-specific multi-species stock assessment model. The latter two approaches also include consideration of alternative future climate scenarios, adding another dimension to evaluate model projection uncertainty. We show how Bayesian model-averaging methods can be used to incorporate such trophic and climate information to broaden single-species stock assessments by using an EBFM approach that may better characterize uncertainty.
Multi-species models can improve our understanding of the effects of fishing so that it is possib... more Multi-species models can improve our understanding of the effects of fishing so that it is possible to make informed and transparent decisions regarding fishery impacts. Broad application of multi-species assessment models to support ecosystem-based fisheries management (EBFM) requires the development and testing of multi-species biological reference points (MBRPs) for use in harvest control rules. We outline and contrast several possible MBRPs that range from those that can be readily used in current frameworks to those belonging to a broader EBFM context. We demonstrate each of the possible MBRPs using a simple two species model, motivated by walleye pollock (Gadus chalcogrammus) and Pacific cod (Gadus macrocephalus) in the eastern Bering Sea, to illustrate differences among methods. The MBRPs we outline each differ in how they approach the multiple, potentially conflicting management objectives and trade-offs of EBFM. These options for MBRPs allow multi-species models to be readily adapted for EBFM across a diversity of management mandates and approaches.
Multi-species statistical catch at age models (MSCAA) can quantify interacting effects of climate... more Multi-species statistical catch at age models (MSCAA) can quantify interacting effects of climate and fisheries harvest on species populations, and evaluate management trade-offs for fisheries that target several species in a food web. We modified an existing MSCAA model to include temperature-specific growth and predation rates and applied the modified model to three fish species, walleye pollock (Gadus chalcogrammus), Pacific cod (Gadus macrocephalus) and arrowtooth flounder (Atheresthes stomias), from the eastern Bering Sea (USA). We fit the model to data from 1979 through 2012, with and without trophic interactions and temperature effects and use projections to derive single- and multi-species biological reference points (BRP and MBRP, respectively) for fisheries management. The multi-species model achieved a higher over-all goodness of fit to the data (i.e., lower negative log-likelihood) for pollock and Pacific cod. Variability from water temperature typically resulted in 5-15% changes in spawning, survey, and total biomasses, but did not strongly impact recruitment estimates or mortality. Despite this, inclusion of temperature in projections did have a strong effect on BRPs, including recommended yield, which were higher in single species models for Pacific cod and arrowtooth flounder that included temperature compared to the same models without temperature effects. While the temperature-driven multi-species model resulted in higher yield MBPRs for arrowtooth flounder than the same model without temperature, we did not observe the same patterns in multi-species models for pollock and Pacific cod, where variability between harvest scenarios and predation greatly exceed temperature-driven variability in yield MBRPs. Annual predation on juvenile pollock (primarily cannibalism) in the multi-species model was 2-5 times the annual harvest of adult fish in the system, thus predators represent a strong control on population dynamics that exceeds temperature-driven changes to growth and is attenuated through harvest-driven reductions in predator populations. Additionally, although we observed differences in spawning biomasses at the accepted biological catch (ABC) proxy between harvest scenarios and single- and multi-species models, discrepancies in spawning stock biomass estimates did not translate to large differences in yield. We found that multi-species models produced higher estimates of combined yield for aggregate maximum sustainable yield (MSY) targets than single species models, but were more conservative than single-species models when individual MSY targets were used, with the exception of scenarios where minimum biomass thresholds were imposed. Collectively our results suggest that climate and trophic drivers can interact to affect MBRPs, but for prey species with high predation rates, trophic- and management-driven changes may exceed direct effects of temperature on growth and predation. Additionally, MBRPs are not inherently more conservative than single-species BRPs. This framework provides a basis for the application of MSCAA models for tactical ecosystem-based fisheries management decisions under changing climate conditions.
The “Wisconsin” bioenergetics model is widely used to evaluate the effects of environmental condi... more The “Wisconsin” bioenergetics model is widely used to evaluate the effects of environmental conditions, trophic interactions, and human-mediated alterations to physical and trophodynamic processes on the growth and survival of individual fish species. In particular, bioenergetics models are increasingly applied to evaluate conditions that vary on subdaily time-steps, such as vertical migrations that influence thermal experience or fluvial alterations that increase diurnal temperature variability. However, because the algorithms that describe the relationship between temperature and physiological rates are often non-linear, using inputs of daily mean temperatures can result in under- or overestimates of growth and energetic demand. Using simulations of daily and subdaily Chinook Salmon Oncorhynchus tshawytscha models as an example, we demonstrate that the non-linear temperature-dependent algorithms for consumption and respiration induce large differences in growth between constant and fluctuating temperature conditions (despite the same mean daily temperature), which increase with high diurnal variability and as temperatures approach the thermal optimum for the species. To correct for model bias in growth, we propose an integrated temperature-scaling algorithm that allows the daily model to be applied to systems where daily temperatures exhibit considerable subdaily variation. This approach can also be used for any bioenergetics model that includes non-linear temperature-dependent algorithms, and should be considered when modeled temperatures approach inflection points in non-linear relationships.
PLoS ONE, 2013
Understanding mechanisms behind variability in early life survival of marine fishes through model... more Understanding mechanisms behind variability in early life survival of marine fishes through modeling efforts can improve predictive capabilities for recruitment success under changing climate conditions. Walleye pollock (Theragra chalcogramma) support the largest single-species commercial fishery in the United States and represent an ecologically important component of the Bering Sea ecosystem. Variability in walleye pollock growth and survival is structured in part by climatedriven bottom-up control of zooplankton composition. We used two modeling approaches, informed by observations, to understand the roles of prey quality, prey composition, and water temperature on juvenile walleye pollock growth: (1) a bioenergetics model that included local predator and prey energy densities, and an individual-based model that included a mechanistic feeding component dependent on larval development and behavior, local prey densities and size, and physical oceanographic conditions. Prey composition in late-summer shifted from predominantly smaller copepod species in the warmer 2005 season to larger species in the cooler 2010 season, reflecting differences in zooplankton composition between years. In 2010, the main prey of juvenile walleye pollock were more abundant, had greater biomass, and higher mean energy density, resulting in better growth conditions. Moreover, spatial patterns in prey composition and water temperature lead to areas of enhanced growth, or growth 'hot spots', for juvenile walleye pollock and survival may be enhanced when fish overlap with these areas. This study provides evidence that a spatial mismatch between juvenile walleye pollock and growth 'hot spots' in 2005 contributed to poor recruitment while a higher degree of overlap in 2010 resulted in improved recruitment. Our results indicate that climate-driven changes in prey quality and composition can impact growth of juvenile walleye pollock, potentially severely affecting recruitment variability.
Climate change is expected to strongly impact Alaskan (USA) marine ecosystems, particularly those... more Climate change is expected to strongly impact Alaskan (USA) marine ecosystems, particularly those of the northern Bering Sea. To understand how climate change may alter predator demand for prey resources, we quantified the relationship between temperature and allometric rates of prey consumption for 3 major groundfish predators: walleye pollock (Gadus chalcogrammus), Pacific cod (Gadus macrocephalus), and arrowtooth flounder (Atheresthes stomias). We contrasted regional patterns in foraging rates of more than 120 thousand fish collected annually from 1981-2011 from eastern Bering Sea (EBS), Gulf of Alaska (GOA), and Aleutian Islands (AI). From field observations, we estimate that juveniles and adults of each species eat 1.15–3.94 and 0.84 -3.13 times their body weight (BW) per year, respectively (i.e., 0.2%-1.2% BW d-1) with arrowtooth from in all 3 regions and adult EBS Pacific cod exhibiting the highest rates. If historical patterns signify future conditions, we estimate that a 2 oC projected increase in water temperature would cause 26% and 14% increases in daily rations of adult EBS pollock and Pacific cod, respectively, whereas we predict a 37% decline in the daily rations of EBS arrowtooth. Similarly, we predict that GOA pollock, Pacific cod and arrowtooth rations would increase markedly (70%, 34%, and 65%, respectively). Although daily ration of AI arrowtooth may increase 31%, our models predict 41% and 3% declines in AI pollock and Pacific cod rations, respectively. These results portend (sometimes counterintuitive) region- and species-specific shifts in Alaska groundfish predator foraging rates and trophodynamic interactions concomitant with climate change.
Understanding mechanisms behind variability in early life survival of marine fishes through model... more Understanding mechanisms behind variability in early life survival of marine fishes through modeling efforts can improve predictive capabilities for recruitment success under changing climate conditions. Walleye pollock (Theragra chalcogramma) support the largest single-species commercial fishery in the United States and represent an ecologically important component of the Bering Sea ecosystem. Variability in walleye pollock growth and survival is structured in part by climatedriven bottom-up control of zooplankton composition. We used two modeling approaches, informed by observations, to understand the roles of prey quality, prey composition, and water temperature on juvenile walleye pollock growth: (1) a bioenergetics model that included local predator and prey energy densities, and (2) an individual-based model that included a mechanistic feeding component dependent on larval development and behavior, local prey densities and size, and physical oceanographic conditions. Prey composition in late-summer shifted from predominantly smaller copepod species in the warmer 2005 season to larger species in the cooler 2010 season, reflecting differences in zooplankton composition between years. In 2010, the main prey of juvenile walleye pollock were more abundant, had greater biomass, and higher mean energy density, resulting in better growth conditions. Moreover, spatial patterns in prey composition and water temperature lead to areas of enhanced growth, or growth ‘hot spots’, for juvenile walleye pollock and survival may be enhanced when fish overlap with these areas. This study provides evidence that a spatial mismatch between juvenile walleye pollock and growth ‘hot spots’ in 2005 contributed to poor recruitment while a higher degree of overlap in 2010 resulted in improved recruitment. Our results indicate that climate-driven changes in prey quality and composition can impact growth of juvenile walleye pollock, potentially severely affecting recruitment variability.
In recent Alaska Fisheries Science Center surveys, we have conducted Stomach Content ANalysis at ... more In recent Alaska Fisheries Science Center surveys, we have conducted Stomach Content ANalysis at sea (SCAN) and analysis in the laboratory for several groundfish species. This provided us with the opportunity to compare our ability to identify key prey types between the two methods. Preliminary analyses indicate that identification of jelly-prey (Cnidaria and Ctenophora) and salp-prey (pelagic Tunicata and Larvacea) differs between the two methods for some zooplanktivores. SCAN more frequently identified jelly-prey in the diets of Dark rockfish, Dusky rockfish, Prowfish, Sablefish. Dissolution of jelly-prey tissues during the preservation process is likely the main factor in the differences observed. Salp-prey was more frequently identified in the laboratory for Sablefish and Walleye pollock. Tissue consistency and size of salp-prey may make them more easily detected in the laboratory. Preliminary analyses also indicate that the identification of fish-prey to species was higher in S...
Late summer and early fall water temperatures on the Klamath River can reach levels that are phys... more Late summer and early fall water temperatures on the Klamath River can reach levels that are physiologically stressful to endangered and threatened salmonids. At the limits of their thermal tolerance, salmonids may behaviorally thermoregulate by moving to localized patches of colder water, or thermal refugia. The presence of these refugia may be key to salmonid survival, especially during periods of elevated mainstem temperatures when refugia may be the only usable habitat available. However, the dynamics and importance of thermal refugia are not thoroughly understood. While fish obtain thermal benefits by using refugia, potential trade-offs include lower food availability, decreased growth rates, and increased risk of disease due to high fish densities. The interplay between these factors influences how much time a fish chooses to spend in the mainstem river versus the refugia. My research focuses on defining the mechanisms driving steelhead thermal refugia use at both landscape an...
As climate change and land-use impacts drive increases in river temperatures, thermal refugia cre... more As climate change and land-use impacts drive increases in river temperatures, thermal refugia created by coolwater tributary inputs are becoming increasingly important habitat for coldwater fish species. Summer mainstem temperatures on the Klamath River in northern California often reach physiologically stressful levels (~22-26°C) for native salmonid populations, driving juvenile salmonids into thermal refugia. These refugia are dynamic environments, and habitat quality may fluctuate in the refuge as well as in the surrounding sub-optimal mainstem habitat. The goal of this study was to determine which environmental factors are driving juvenile steelhead use of thermal refugia, and the timescale at which fish are shifting between thermal environments, in order to gain a better understanding of when these areas become critical habitat and how to effectively manage and restore thermal refugia on warming rivers. I used an innovative approach, taking advantage of relatively new radio tag...
Variability in walleye pollock (Gadus chalcogrammus) growth and survival is structured in part by... more Variability in walleye pollock (Gadus chalcogrammus) growth and survival is structured in part by climate-driven bottom-up control of zooplankton composition. We used two modeling approaches to understand the roles of prey quality, prey composition, and water temperature on juvenile walleye pollock growth: (1) a bioenergetics model that included local predator and prey energy densities, and (2) an individual-based model that included a mechanistic feeding component, local prey densities and size, and physical oceanographic conditions. Prey composition in late-summer shifted from predominantly smaller copepod species in the warmer 2005 season to larger species in the cooler 2010 season, reflecting differences in zooplankton composition between years. Spatial patterns in prey composition and water temperature lead to areas of enhanced growth, or growth ‘hot spots’, for juvenile walleye pollock and survival may be enhanced when fish overlap with these areas. This study provides evidenc...
We fit simple production models with and without covariates for several functionally analogous sp... more We fit simple production models with and without covariates for several functionally analogous species using data for 11 large marine ecosystems. The most complete evaluation of the impacts of covariates on estimates of production were for cod (Gadus morhua) and herring (Clupea harengus). Functionally analogous species included Greenland cod (Gadus ogac) and Pacific cod (Gadus macrocephalus), and Pacific herring (Clupea pallasii). Biological covariates included the abundance of prey (herring for cod and an index of primary production for herring). Physical covariates included common physical forcing functions such as AMO and PDO as well as water temperature. For both functional species, we fit a hierarchy of nested models that included a full model with physical and biological covariates. Models were compared using an information-theoretic framework. The numerical impacts of covariates differed among systems. However, the trends among the different ecosystems were similar. The inclu...
We define extended single-species production models (ESSPMs) as single species production models ... more We define extended single-species production models (ESSPMs) as single species production models that incorporate time series of principal prey and/or predator species as biological covariates. One advantage to ESSPMs over single species production models without biological covariates is that these models can be used to test the existence and direction of (one-way) species interactions. However, estimates of actual interaction strengths are confounded with scaling of the covariates (i.e., catchability). In addition, biological reference points (BRPs; e.g. maximum sustainable yield, MSY) that can be calculated in ESSPMs may be of limited value compared to those estimates that more directly incorporate species interactions, because of a lack of feedback between prey and predator species in ESSPMs. We thus developed a full multispecies production model (MSPM) to estimate biological interaction strengths and examine tradeoffs in multispecies MSY. As a preliminary demonstration, we fit t...
The aim of this project was to conduct a formal Management Strategy Evaluation (MSE) in which the... more The aim of this project was to conduct a formal Management Strategy Evaluation (MSE) in which the FEAST model acts as an "operating model" and currently developed methods (stock assessments, MSMt, and Ecosim) act as "assessment" models. The project planned to test assessment models from the range currently available for the Bering Sea, including: single species-assessments w/ correlative recruitment indices; multi-species models; and whole ecosystem models. In addition, testing of autocorrelative biomass dynamics/network models and nonlinear correlative models would provide results for "null" models for determining the added value of the more mechanistic approaches. The metrics for evaluating the success of the "assessment" models was to be the accuracy (lack of bias) and precision (lack of variance) of key model outputs (such as recruitment and biomass, both in the past and as forecast under given management regimes) when they are fit to data generated (with observation error) from the operating (Forage/Euphausiid Abundance in Space and Time, FEAST) model. The aim of the project was to provide information about the skill of each model in determining past and current states (hindcast/nowcast) as well as the success of each model when predicting future states from current states. When combined with management decision rules, success was to be defined as the ability to keep fish populations and yields above a "best performance" reference point determined from the operating model and the ability to achieve high economic returns. However, the MSE project as planned became untenable as the project deadline approached and a FEAST hindcast with the required level of performance remained unavailable. Nevertheless, the work conducted under this project shows that it is feasible to develop a Management Strategy Evaluation system which could be based on an operating model of the complexity of FEAST. The specifications and code developed during the project could be used in any follow-up modeling work. The project conducted a stakeholder workshop which led to analyses which showed that it is feasible to develop harvest control rules which are both consistent with US federal fisheries law and can be applied using the outputs from multispecies and ecosystem models. Furthermore, the project did conduct MSE forecasts using MSM as an operating model and developed an approach for blending results from multiple models so that model projections reflect estimation error, uncertainty about future recruitment success and well as model error. The key conclusions of this study pertain primarily to the lessons learnt conducting a modeling project of this magnitude as the challenges of including and charactering uncertainty when conducting forecasts of fish systems.
Risk assessments quantify the probability of undesirable events along with their consequences. Th... more Risk assessments quantify the probability of undesirable events along with their consequences. They are used to prioritize management interventions and assess tradeoffs, serving as an essential component of ecosystem-based management (EBM). A central objective of most risk assessments for conservation and management is to characterize uncertainty and impacts associated with one or more pressures of interest. Risk assessments have been used in marine resource management to help evaluate the risk of environmental, ecological, and anthropogenic pressures on species or habitats including for data-poor fisheries management (e.g., toxicity, probability of extinction, habitat alteration impacts). Traditionally, marine risk assessments focused on singular pressure-response relationships, but recent advancements have included use of risk assessments in an EBM context, providing a method for evaluating the cumulative impacts of multiple pressures on multiple ecosystem components. Here, we describe a conceptual framework for ecosystem risk assessment (ERA), highlighting its role in operationalizing EBM, with specific attention to ocean management considerations. This framework builds on the ecotoxicological and conservation literature on risk assessment and includes recent advances that focus on risks posed by fishing to marine ecosystems. We review how examples of ERAs from the United States fit into this framework, explore the variety of analytical approaches that have been used to conduct ERAs, and assess the challenges and data gaps that remain. This review discusses future prospects for ERAs as EBM decision-support tools, their expanded role in integrated ecosystem assessments, and the development of next-generation risk assessments for coupled natural–human systems.
Modelling spatially dependent predation mortality of eastern Bering Sea walleye pollock, and its ... more Modelling spatially dependent predation mortality of eastern Bering Sea walleye pollock, and its implications for stock dynamics under future climate scenarios. Arrowtooth flounder (Atheresthes stomias) are an important predator of juvenile walleye pollock (Gadus chalcogramus) in the eastern Bering Sea (EBS) shelf and have increased 3-fold in biomass from 1977 to 2014. Arrowtooth flounder avoid the summer " cold pool " (bottom water ≤28C) and variability in cold pool size and location has affected their spatial overlap with juvenile walleye pollock. Developing a method to account for the relationship between climate change and pollock mortality can highlight ecosystem dynamics and contribute to better assessments for fisheries management. Consequently, spatially resolved predation mortality rates were estimated within an age-structured walleye pollock stock assessment population model (based on spatial information on diet and abundance from trawl surveys), along with the effect of sea surface temperature (SST) on pollock recruitment. Projections of SST and cold pool area to 2050 were obtained (or statistically downscaled) from nine global climate models and used within an age-structure population model to project pollock abundance given estimated relationships between environmental variables and predator and prey spatial distributions, pollock recruitment, and maximum rate of arrowtooth flounder consumption. The climate projections show a wide range of variability but an overall trend of increasing SST and decreasing cold pool area. Projected pollock biomass decreased largely due to the negative effect of increased SST on pollock recruitment. A sensitivity analysis indicated that the decline in projected pollock biomass would be exacerbated if arrowtooth flounder increased their relative distribution in the EBS northwest middle shelf (an area of relatively high density of juvenile pollock) in warm years.
Ecosystem-based fisheries management (EBFM) approaches allow a broader and more extensive conside... more Ecosystem-based fisheries management (EBFM) approaches allow a broader and more extensive consideration of objectives than is typically possible with conventional single-species approaches. Ecosystem linkages may include trophic interactions and climate change effects on productivity for the relevant species within the system. Presently, models are evolving to include a comprehensive set of fishery and ecosystem information to address these broader management considerations. The increased scope of EBFM approaches is accompanied with a greater number of plausible models to describe the systems. This can lead to harvest recommendations and biological reference points that differ considerably among models. Model selection for projections (and specific catch recommendations) often occurs through a process that tends to adopt familiar, often simpler, models without considering those that incorporate more complex ecosystem information. Multi-model inference provides a framework that resolves this dilemma by providing a means of including information from alternative, often divergent models to inform biological reference points and possible catch consequences. We apply an example of this approach to data for three species of groundfish in the Bering Sea: walleye pollock, Pacific cod, and arrowtooth flounder using three models: 1) an age-structured “conventional” single-species model, 2) an age-structured single-species model with temperature-specific weight at age, and 3) a temperature-specific multi-species stock assessment model. The latter two approaches also include consideration of alternative future climate scenarios, adding another dimension to evaluate model projection uncertainty. We show how Bayesian model-averaging methods can be used to incorporate such trophic and climate information to broaden single-species stock assessments by using an EBFM approach that may better characterize uncertainty.
Multi-species models can improve our understanding of the effects of fishing so that it is possib... more Multi-species models can improve our understanding of the effects of fishing so that it is possible to make informed and transparent decisions regarding fishery impacts. Broad application of multi-species assessment models to support ecosystem-based fisheries management (EBFM) requires the development and testing of multi-species biological reference points (MBRPs) for use in harvest control rules. We outline and contrast several possible MBRPs that range from those that can be readily used in current frameworks to those belonging to a broader EBFM context. We demonstrate each of the possible MBRPs using a simple two species model, motivated by walleye pollock (Gadus chalcogrammus) and Pacific cod (Gadus macrocephalus) in the eastern Bering Sea, to illustrate differences among methods. The MBRPs we outline each differ in how they approach the multiple, potentially conflicting management objectives and trade-offs of EBFM. These options for MBRPs allow multi-species models to be readily adapted for EBFM across a diversity of management mandates and approaches.
Multi-species statistical catch at age models (MSCAA) can quantify interacting effects of climate... more Multi-species statistical catch at age models (MSCAA) can quantify interacting effects of climate and fisheries harvest on species populations, and evaluate management trade-offs for fisheries that target several species in a food web. We modified an existing MSCAA model to include temperature-specific growth and predation rates and applied the modified model to three fish species, walleye pollock (Gadus chalcogrammus), Pacific cod (Gadus macrocephalus) and arrowtooth flounder (Atheresthes stomias), from the eastern Bering Sea (USA). We fit the model to data from 1979 through 2012, with and without trophic interactions and temperature effects and use projections to derive single- and multi-species biological reference points (BRP and MBRP, respectively) for fisheries management. The multi-species model achieved a higher over-all goodness of fit to the data (i.e., lower negative log-likelihood) for pollock and Pacific cod. Variability from water temperature typically resulted in 5-15% changes in spawning, survey, and total biomasses, but did not strongly impact recruitment estimates or mortality. Despite this, inclusion of temperature in projections did have a strong effect on BRPs, including recommended yield, which were higher in single species models for Pacific cod and arrowtooth flounder that included temperature compared to the same models without temperature effects. While the temperature-driven multi-species model resulted in higher yield MBPRs for arrowtooth flounder than the same model without temperature, we did not observe the same patterns in multi-species models for pollock and Pacific cod, where variability between harvest scenarios and predation greatly exceed temperature-driven variability in yield MBRPs. Annual predation on juvenile pollock (primarily cannibalism) in the multi-species model was 2-5 times the annual harvest of adult fish in the system, thus predators represent a strong control on population dynamics that exceeds temperature-driven changes to growth and is attenuated through harvest-driven reductions in predator populations. Additionally, although we observed differences in spawning biomasses at the accepted biological catch (ABC) proxy between harvest scenarios and single- and multi-species models, discrepancies in spawning stock biomass estimates did not translate to large differences in yield. We found that multi-species models produced higher estimates of combined yield for aggregate maximum sustainable yield (MSY) targets than single species models, but were more conservative than single-species models when individual MSY targets were used, with the exception of scenarios where minimum biomass thresholds were imposed. Collectively our results suggest that climate and trophic drivers can interact to affect MBRPs, but for prey species with high predation rates, trophic- and management-driven changes may exceed direct effects of temperature on growth and predation. Additionally, MBRPs are not inherently more conservative than single-species BRPs. This framework provides a basis for the application of MSCAA models for tactical ecosystem-based fisheries management decisions under changing climate conditions.
The “Wisconsin” bioenergetics model is widely used to evaluate the effects of environmental condi... more The “Wisconsin” bioenergetics model is widely used to evaluate the effects of environmental conditions, trophic interactions, and human-mediated alterations to physical and trophodynamic processes on the growth and survival of individual fish species. In particular, bioenergetics models are increasingly applied to evaluate conditions that vary on subdaily time-steps, such as vertical migrations that influence thermal experience or fluvial alterations that increase diurnal temperature variability. However, because the algorithms that describe the relationship between temperature and physiological rates are often non-linear, using inputs of daily mean temperatures can result in under- or overestimates of growth and energetic demand. Using simulations of daily and subdaily Chinook Salmon Oncorhynchus tshawytscha models as an example, we demonstrate that the non-linear temperature-dependent algorithms for consumption and respiration induce large differences in growth between constant and fluctuating temperature conditions (despite the same mean daily temperature), which increase with high diurnal variability and as temperatures approach the thermal optimum for the species. To correct for model bias in growth, we propose an integrated temperature-scaling algorithm that allows the daily model to be applied to systems where daily temperatures exhibit considerable subdaily variation. This approach can also be used for any bioenergetics model that includes non-linear temperature-dependent algorithms, and should be considered when modeled temperatures approach inflection points in non-linear relationships.
PLoS ONE, 2013
Understanding mechanisms behind variability in early life survival of marine fishes through model... more Understanding mechanisms behind variability in early life survival of marine fishes through modeling efforts can improve predictive capabilities for recruitment success under changing climate conditions. Walleye pollock (Theragra chalcogramma) support the largest single-species commercial fishery in the United States and represent an ecologically important component of the Bering Sea ecosystem. Variability in walleye pollock growth and survival is structured in part by climatedriven bottom-up control of zooplankton composition. We used two modeling approaches, informed by observations, to understand the roles of prey quality, prey composition, and water temperature on juvenile walleye pollock growth: (1) a bioenergetics model that included local predator and prey energy densities, and an individual-based model that included a mechanistic feeding component dependent on larval development and behavior, local prey densities and size, and physical oceanographic conditions. Prey composition in late-summer shifted from predominantly smaller copepod species in the warmer 2005 season to larger species in the cooler 2010 season, reflecting differences in zooplankton composition between years. In 2010, the main prey of juvenile walleye pollock were more abundant, had greater biomass, and higher mean energy density, resulting in better growth conditions. Moreover, spatial patterns in prey composition and water temperature lead to areas of enhanced growth, or growth 'hot spots', for juvenile walleye pollock and survival may be enhanced when fish overlap with these areas. This study provides evidence that a spatial mismatch between juvenile walleye pollock and growth 'hot spots' in 2005 contributed to poor recruitment while a higher degree of overlap in 2010 resulted in improved recruitment. Our results indicate that climate-driven changes in prey quality and composition can impact growth of juvenile walleye pollock, potentially severely affecting recruitment variability.
Climate change is expected to strongly impact Alaskan (USA) marine ecosystems, particularly those... more Climate change is expected to strongly impact Alaskan (USA) marine ecosystems, particularly those of the northern Bering Sea. To understand how climate change may alter predator demand for prey resources, we quantified the relationship between temperature and allometric rates of prey consumption for 3 major groundfish predators: walleye pollock (Gadus chalcogrammus), Pacific cod (Gadus macrocephalus), and arrowtooth flounder (Atheresthes stomias). We contrasted regional patterns in foraging rates of more than 120 thousand fish collected annually from 1981-2011 from eastern Bering Sea (EBS), Gulf of Alaska (GOA), and Aleutian Islands (AI). From field observations, we estimate that juveniles and adults of each species eat 1.15–3.94 and 0.84 -3.13 times their body weight (BW) per year, respectively (i.e., 0.2%-1.2% BW d-1) with arrowtooth from in all 3 regions and adult EBS Pacific cod exhibiting the highest rates. If historical patterns signify future conditions, we estimate that a 2 oC projected increase in water temperature would cause 26% and 14% increases in daily rations of adult EBS pollock and Pacific cod, respectively, whereas we predict a 37% decline in the daily rations of EBS arrowtooth. Similarly, we predict that GOA pollock, Pacific cod and arrowtooth rations would increase markedly (70%, 34%, and 65%, respectively). Although daily ration of AI arrowtooth may increase 31%, our models predict 41% and 3% declines in AI pollock and Pacific cod rations, respectively. These results portend (sometimes counterintuitive) region- and species-specific shifts in Alaska groundfish predator foraging rates and trophodynamic interactions concomitant with climate change.
Understanding mechanisms behind variability in early life survival of marine fishes through model... more Understanding mechanisms behind variability in early life survival of marine fishes through modeling efforts can improve predictive capabilities for recruitment success under changing climate conditions. Walleye pollock (Theragra chalcogramma) support the largest single-species commercial fishery in the United States and represent an ecologically important component of the Bering Sea ecosystem. Variability in walleye pollock growth and survival is structured in part by climatedriven bottom-up control of zooplankton composition. We used two modeling approaches, informed by observations, to understand the roles of prey quality, prey composition, and water temperature on juvenile walleye pollock growth: (1) a bioenergetics model that included local predator and prey energy densities, and (2) an individual-based model that included a mechanistic feeding component dependent on larval development and behavior, local prey densities and size, and physical oceanographic conditions. Prey composition in late-summer shifted from predominantly smaller copepod species in the warmer 2005 season to larger species in the cooler 2010 season, reflecting differences in zooplankton composition between years. In 2010, the main prey of juvenile walleye pollock were more abundant, had greater biomass, and higher mean energy density, resulting in better growth conditions. Moreover, spatial patterns in prey composition and water temperature lead to areas of enhanced growth, or growth ‘hot spots’, for juvenile walleye pollock and survival may be enhanced when fish overlap with these areas. This study provides evidence that a spatial mismatch between juvenile walleye pollock and growth ‘hot spots’ in 2005 contributed to poor recruitment while a higher degree of overlap in 2010 resulted in improved recruitment. Our results indicate that climate-driven changes in prey quality and composition can impact growth of juvenile walleye pollock, potentially severely affecting recruitment variability.
The size-at-age (SAA) for Pacific halibut has changed from small SAA in the 1920s, through major ... more The size-at-age (SAA) for Pacific halibut has changed from small SAA in the 1920s, through major increases in the 1970s, followed by major decreases in the 1990s and 2000s. This study examined potential causes of changes in SAA from aging methodology, to ecological and fishery induced changes to growth and mortality. Analyses of otoliths from each decade from the 1920s to the 1980s showed that historical trends of halibut SAA are not biased by changes in ageing methodology over time. Also, we found that otolith size does not reflect sexual dimorphism in somatic length at age and that otolith growth patterns cannot be used to infer somatic growth patterns. Stomach samples from waters off Alaska showed that temporal and spatial patterns in diet composition of key prey species could impact energy available for growth. Bioenergetic analysis of more than 14,000 stomach samples from the eastern Bering Sea and Gulf of Alaska (1985-2015) revealed regional and temporal changes in foraging rates and potential growth that varied with ontology, suggesting that trophic and environmental constraints collectively limit adult growth during years of low productivity or high prey competition in the GOA. Next, we used fishery-independent SAA to explore spatial and temporal patterns in growth and SAA using statistical models of ecological and environmental effects. Results suggest a negative correlation of proportional growth and the biomass of arrowtooth flounder and to a lesser extent with Pacific halibut. Our best fitting model with ecological factors explained only 28% of the observed variability in growth, indicating that other factors (e.g. bioenergetics or size-selective fishing) may be more important contributors to variability in SAA. Finally, we examined relationships with fishing mortality and found that fishing can explain 30 ̶ 100% of the observed declines in SAA since the 1980s depending on sex, age, and region. Unusually large variability in length-at-age for any given cohort renders Pacific halibut vulnerable to the cumulative effects of size-selective fishing. Considered jointly, our results indicate that changes in SAA in the GOA may be the collective outcome of size-selective fishing (which is strongest in the GOA) combined with reduced foraging efficiency, changes in prey availability and quality, and increased metabolic demands that limit growth rates (especially rapid compensatory) of adult fish.