Space matters: incorporating mechanistically determined spatial patterns into projected impacts of climate change on stream temperature

River temperatures are increasing as a results of climate change, and combined with decreased summertime flows, coldwater species are becoming increasingly stressed. In order to conserve sensitive species, managers need an estimate of how the availability of summertime thermal refuges in rivers will change in the future. Here, we applied the DHSVM-RBM, an existing process-based water temperature model that has been shown to accurately represent temporal variance in water temperature over hours to years. We calibrated this model to empirical data for two case study watersheds (Siletz River, Oregon and Snoqualmie River, Washington) to also ensure representation of observed spatial heterogeneity during summer. We used the model to predict future spatiotemporal patterns in water temperature that may arise as a result of climate change and to assess Pacific salmon vulnerability. We then compared our predictions to those made by statistical models to assess the unique benefits and constraints of a process-based approach. We found that a substantial decrease of snowmelt, and subsequently summer flow, will drive increases in water temperature and spatial variability in future summers. Our vulnerability analysis suggested that for salmon and steelhead exposed to warm August temperatures, conditions are already stressful in lower portions of the case study watersheds, and unlikely to become better in the future. All models predicted generally similar spatial patterns of water temperature in the future; across models, future cool patches will be reduced in number and located farther upstream. However, projected increases in water temperature were strikingly different among models, ranging from about +5 oC in the Snoqualmie River as predicted by DHSVM-RBM, to a negligible change in both watersheds as predicted by statistical methods. This information can be used to identify locations where protection and restoration of coolwater habitats may be most important into the future

Overwinter Growth and Survival of Largemouth Bass: Interactions among Size, Food, Origin, and Winter Severity

Winter severity (temperature, duration, and photocycle), geographic origin, food availability, and initial body size likely influence growth, survival, and, therefore, recruitment of age-0 largemouth bass Micropterus salmoides. We collected age-0 largemouth bass (70–160 mm total length) from low (33N), intermediate (40N), and high (45N) latitudes throughout their natural range (origin), and we subjected all three groups of fish to three experimental winters that mimicked these latitudes (N = 9 largemouth bass per treatment). Within each winter and origin, one-half of the largemouth bass were fed fish prey, whereas the remaining one-half were starved. Winter strongly influenced survival; overall survival rates in the high-, intermediate-, and low-latitude winters were 34.9, 59.4, and 61.1%, respectively (x2 test, P < 0.05). Largemouth bass from 33N suffered high mortality in the high-latitude winter. Across all winters, more fed fish (64.5%) survived than did starved fish (38.1%) (x2 test, P =100 mm) size classes revealed that more small fish died than did large fish in the low- and high-latitude winters, but this was not the case in the middle-latitude winter. Wet weights (g) of fed largemouth bass increased, remained constant, and declined in the low-, intermediate-, and high-latitude winters, respectively. Wet weights and total energy content (kJ) of fed individuals were consistently higher than those of their starved counterparts in all winters. However, energy density (kJ/g) of fed individuals often declined to levels similar to those of starved largemouth bass. Winter temperature combined with duration likely dictate the northern limit of largemouth bass by reducing growth, even when food is abundant. Because survival of individuals from the low latitude was poor in higher latitude winters, stocking southern largemouth bass in northern systems may translate to high mortality and perhaps to degradation of physiological tolerances of local populations through hybridization.This research was funded by National Science Foundation grant DEB 9407859 and associated Research Experiences for Undergraduates supplement to A. H. Fullerton and by Federal Aid in Sport Fish Restoration project F-69-P, administered jointly by the U.S. Fish and Wildlife Service and the Ohio Division of Wildlife. A Presidential Fellowship from The Ohio State University supported J. E. Garvey

Predicting How Winter Affects Energetics of Age-0 Largemouth Bass: How Do Current Models Fare?

During the first winter of life, loss of energy reserves as a function of low feeding activity and scarce prey may contribute to high mortality of age-0 largemouth bass Micropterus salmoides. To explore how two current bioenergetics models predict winter energy depletion, we quantified growth and consumption by age-0 largemouth bass from Alabama, Ohio, and Wisconsin fed maintenance rations in 55-L aquaria in three simulated winters mimicking temperatures and photoperiods at low temperate latitudes (Alabama; 33N), middle latitudes (Ohio; 40N), and high temperate latitudes (Wisconsin; 46N).We compared observed growth in aquaria with that predicted by putting observed consumption into both models. During winter 1995–1996, we validated one of the models with a separate pool experiment (5,800-L) in which age-0 largemouth bass were fed either at 0.5 X or 1.5 X maintenance ration. In aquaria, energy density of the largemouth bass declined in the high- and middle- but not in the low-latitude winter. Though error was slight in the low- and middle-latitude winters for one of the models, both models underestimated growth in the high-latitude winter. To fit the model to the data, the function that estimates weight-specific resting metabolism had to be reduced by about 16%. In pools, where we predicted consumption from observed growth, the model adequately predicted consumption by largemouth bass fed 1.5 X maintenance, but overestimated consumption by 0.5 X maintenance individuals. Current bioenergetics models perform poorly at the cold temperatures (<6C), photoperiods, and low prey abundances typical of high-latitude lakes, likely because metabolic costs are overestimated.This research was funded by National Science Foundation grant DEB 9407859 to R.A.S. and Federal Aid in Sport Fish Restoration Project F-69-P, administered jointly by the U.S. Fish and Wildlife Service and the Ohio Division of Wildlife. A University PostDoctoral Fellowship and a Presidential Fellowship from The Ohio State University supported R.A.W. and J.E.G., respectively, during part of this work

Providing modeling tools on extreme events of climate change to Puget Sound managers

As climate change becomes a reality for the management of Puget Sound, water resource and fisheries managers should consider incorporating predictions and outcomes of future climate drivers into their long-range plans and daily operations. Modeling tools that focus on climate impacts and predictions show that extreme events are more often responsible for large impacts than the long-term press of climate change. Working with water resource and fisheries managers in the Dungeness and Skagit watersheds, this project uses outputs of existing climate and estuarine models to define thresholds and metrics associated with extreme climate-driven events that are of importance to the resource managers. Managers from the Dungeness and Skagit basins were brought together to assist with defining information needs for sustainable fish habitat and human water uses. The resource managers participating in the project include municipal waste water treatment operators and planners, fisheries managers, agricultural practitioners and conservation district staff, flood control specialists, and others. The information needs identified by the planners, based on the climate model outputs, include better predictions for low stream flows, stream temperature, extent of salinity intrusion into tidal rivers, and timing of extreme events that fall outside the historical norm. The project is developing a decision-support system to meet these needs. The metrics used to drive the decision-support system are derived from model outputs, driven by resource management needs. The information needs, metrics derived from existing models, and the draft decision-support system will be presented. The research team also seeks to use the project to define improved communication pathways between the scientific community and local managers

Modeling timing and size of juvenile Chinook salmon out-migrants at three Elwha River rotary screw traps: a window into early life history post dam removal

Chinook salmon (Oncorhynchus tshawytscha) populations express diverse early life history pathways that increase habitat utilization and demographic resiliency. Extensive anthropogenic alterations to freshwater habitats along with hatchery and harvest impacts have led to marked reductions in early life history diversity across much of the species’ range. The recent removal of two Elwha River dams between 2011 and 2014 restored access to over 90% of the available habitat that had been inaccessible to Chinook salmon since the early 1900s. This provided an opportunity to investigate how renewed access to this habitat might affect life history diversity. As exotherms, egg-to-fry development, juvenile growth, and movement are influenced by water temperatures. We used spatially and temporally explicit Elwha River water temperature and Chinook salmon spawning location data, in conjunction with spawn timing, emergence, growth, and movement models, to predict observed timing and sizes of juvenile Chinook salmon captured in three rotary screw traps in the mainstem and two tributaries during four trap years. This effort allowed us to test hypotheses regarding Elwha River Chinook salmon early life history, identify potential problems with the data, and predict how emergence and growth would change with increased spawning in the upper watershed. Predicted Chinook salmon emergence timing and predicted dates that juveniles reached 65 mm differed by as much as 2 months for different river locations due to large differences in thermal regimes longitudinally in the mainstem and between tributaries. For 10 out of the 12 trap–year combinations, the model was able to replicate important characteristics of the out-migrant timing and length data collected at the three traps. However, in most cases, there were many plausible parameter combinations that performed well, and in some cases, the model predictions and observations differed. Potential problems with the data and model assumptions were identified as partial explanations for differences and provide avenues for future work. We show that juvenile out-migrant data combined with mechanistic models can improve our understanding of how differences in temperature, spawning extent, and spawn timing affect the emergence, growth, and movement of juvenile fish across diverse riverine habitats

Closing the gap between science and management of cold-water refuges in rivers and streams

Human activities and climate change threaten coldwater organisms in freshwater eco-systems by causing rivers and streams to warm, increasing the intensity and frequency of warm temperature events, and reducing thermal heterogeneity. Cold-water refuges are discrete patches of relatively cool water that are used by coldwater organisms for thermal relief and short-term survival. Globally, cohesive management approaches are needed that consider interlinked physical, biological, and social factors of cold-water refuges. We review current understanding of cold-water refuges, identify gaps between science and management, and evaluate policies aimed at protecting thermally sensitive species. Existing policies include designating cold-water habitats, restricting fishing during warm periods, and implementing threshold temperature standards or guidelines. However, these policies are rare and uncoordinated across spatial scales and often do not consider input from Indigenous peoples. We propose that cold-water refuges be managed as dis-tinct operational landscape units, which provide a social and ecological context that is relevant at the watershed scale. These operational landscape units provide the founda-tion for an integrated framework that links science and management by (1) mapping and characterizing cold-water refuges to prioritize management and conservation actions, (2) leveraging existing and new policies, (3) improving coordination across jurisdictions, and (4) implementing adaptive management practices across scales. Our findings show that while there are many opportunities for scientific advancement, the current state of the sciences is sufficient to inform policy and management. Our proposed framework pro-vides a path forward for managing and protecting cold-water refuges using existing and new policies to protect coldwater organisms in the face of global change. behavioral thermoregulation, climate change adaptation, lotic ecosystem management, refugia, salmonids, temperature, thermal heterogeneity, thermal refugespublishedVersio

Closing the gap between science and management of cold‐water refuges in rivers and streams

Human activities and climate change threaten coldwater organisms in freshwater ecosystems by causing rivers and streams to warm, increasing the intensity and frequency of warm temperature events, and reducing thermal heterogeneity. Cold-water refuges are discrete patches of relatively cool water that are used by coldwater organisms for thermal relief and short-term survival. Globally, cohesive management approaches are needed that consider interlinked physical, biological, and social factors of cold-water refuges. We review current understanding of cold-water refuges, identify gaps between science and management, and evaluate policies aimed at protecting thermally sensitive species. Existing policies include designating cold-water habitats, restricting fishing during warm periods, and implementing threshold temperature standards or guidelines. However, these policies are rare and uncoordinated across spatial scales and often do not consider input from Indigenous peoples. We propose that cold-water refuges be managed as distinct operational landscape units, which provide a social and ecological context that is relevant at the watershed scale. These operational landscape units provide the foundation for an integrated framework that links science and management by (1) mapping and characterizing cold-water refuges to prioritize management and conservation actions, (2) leveraging existing and new policies, (3) improving coordination across jurisdictions, and (4) implementing adaptive management practices across scales. Our findings show that while there are many opportunities for scientific advancement, the current state of the sciences is sufficient to inform policy and management. Our proposed framework provides a path forward for managing and protecting cold-water refuges using existing and new policies to protect coldwater organisms in the face of global change

Conservation of freshwater thermal habitats for Pacific salmon in a changing climate

Thesis (Ph.D.)--University of Washington, 2016-06Climate adaptation strategies for freshwater biota have focused on how water temperature and hydrology will change over time, but understanding spatial patterns in water temperature will also be essential for evaluating vulnerability of biota to future climate and for identifying and protecting diverse thermal habitats. I used high-resolution remotely sensed water temperature data for over 16,000 km of 2nd to 7th-order rivers throughout the Pacific Northwest and California to evaluate spatial patterns of summertime water temperature at multiple spatial scales. I found a diverse and geographically distributed suite of whole-river patterns. About half of rivers warmed asymptotically in a downstream direction, as expected, whereas the rest exhibited complex and unique spatial patterns. Patterns were associated with both broad-scale hydroclimatic variables as well as characteristics unique to each basin. Within-river thermal heterogeneity patterns were highly river-specific, but median size and spacing of cool patches <15 °C were both around 250 m. Patches of this size are large enough for juvenile rearing and for resting during migration, and the distance between patches is well within the movement capabilities of both juvenile and adult salmon. The density, size, and spacing of patches were nonlinearly related to the resolution of water temperature; there was a lot of heterogeneity at very fine scales that may be important to fish that would be missed if data were analyzed at coarser scales. Climate change will cause warmer temperatures overall, but thermal heterogeneity patterns may remain similar in the future for many rivers. Maintaining this diverse portfolio of habitats will promote resiliency of salmon to natural and anthropogenic disturbance. I also developed an individual-based model to evaluate whether influences of climate change on growth and phenology of juvenile salmon could be mediated by the shape of stream networks. I used three network shapes of increasing spatial complexity: long, typical, and compact. Growth and movement of fish were based on water temperature and conspecific density. Under current-day climate conditions, salmon grew best and were large enough to smolt earliest in the long network. However, salmon grew best and outmigrated earliest in the compact network under future climate scenarios, suggesting that areas of high productivity may shift in the future. Increases in summer maximum temperature had a greater effect on fish responses than did increases in the rate of spring warming or day-to-day variability. Results from my research can be used to inform restoration and conservation strategies that minimize vulnerability of Pacific salmon to climate change and other stressors