Josh Korman

Ecosystem Modeling for Evaluation of Adaptive Management Policies in the Grand Canyon

Introduction Approach to Modeling Multiscale Policy and Ecosystem Dynamics Key Submodels and Comparisons of Model Predictions to Data Physical Submodel Hydrology Sediment budget Camping beaches Temperature Aquatic primary production Aquatic insect production Riparian plant communities and production of allochthonous detritus and insect inputs to the river Vertebrate indicator species Socioeconomic performance indicators Policy Predictions and Uncertainties Sustainability of policies for beach/habitat rebuilding Risks in assuming that physical habitat restoration will result in ecosystem restoration for native fishes Importance of backwater habitats Inability to evaluate experimental outcomes for native fishes with existing monitoring programs Conflicting objectives and trade-offs: uncertain costs and benefits of restoration Conclusion: Experimental Management Options for the Grand Canyon Responses to this Article Acknowledgments Literature Cited Appendix 1 Appendix 2 Appendix 3 Appendix 4 Appendix 5 Appendix 6 Appendix 7 Appendix 8 Appendix 9 Appendix 10 Appendix 11 Appendix 12 Appendix 13 Appendix 14 Appendix 15 Appendix 16 Erratum (added 3 April 2003) Conservation Ecology: Ecosystem Modeling for Evaluation of Adaptive ... http://www.ecologyandsociety.org/vol4/iss2/art1/ 1 of 42 4/20/2009 9:25 AM

Linking recruitment to trophic factors: revisiting the Beverton-Holt recruitment model from a life history and multispecies perspective

The Beverton--Holt recruitment model can be derived from arguments about evolution of life history traits related to foraging and predation risk, along with spatially localized and temporarily competitive relationships in the habitats where juvenile fish forage and face predation risk while foraging. This derivation explicitly represents two key biotic factors, food supply (I) and predator abundance (R), which appear as a risk ratio (R/I) that facilitates modelling of changes in trophic circumstances and analysis of historical data. The same general recruitment relationship is expected whether the juvenile life history is simple or involves a complex sequence of stanzas; in the complex case, the Beverton--Holt parameters represent weighted averages or integrals of risk ratios over the stanzas. The relationship should also apply in settings where there is complex, mesoscale variation in habitat and predation risk, provided that animals sense this variation and move about so as to achieve similar survival at all mesoscale rearing sites. The model predicts that changes in food and predation risk can be amplified violently in settings where juvenile survival rate is low, producing large changes in recruitment rates over time.

Effects of Hydropeaking on Nearshore Habitat Use and Growth of Age-0 Rainbow Trout in a Large Regulated River

Abstract We evaluated the effects of hourly variation in flow caused by power load following at Glen Canyon Dam (“hydropeaking”) on the nearshore habitat use and growth of age-0 rainbow trout Oncorhynchus mykiss downstream from the dam in the Colorado River, Arizona. Reduction in the extent of hydropeaking is a common element of restoration efforts in regulated rivers, but empirical support for such a practice is limited. Our assessment was based on a comparison of abundance in shoreline areas determined by electrofishing at different flows as well as analysis of otolith microstructure. The catch rates of age-0 rainbow trout in nearshore areas were at least two- to fourfold higher at the daily minimum flow than at the daily maximum, indicating that most age-0 rainbow trout do not maintain their position within immediate shoreline areas when flows are high. A striping pattern, identified by the presence of atypical daily increments formed every 7 d, was evident in over 50% of the 259 otoliths examined in 2...

Trout Piscivory in the Colorado River, Grand Canyon: Effects of Turbidity, Temperature, and Fish Prey Availability

Abstract Introductions of nonnative salmonids, such as rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta, have affected native fishes worldwide in unforeseen and undesirable ways. Predation and other interactions with nonnative rainbow trout and brown trout have been hypothesized as contributing to the decline of native fishes (including the endangered humpback chub Gila cypha) in the Colorado River, Grand Canyon. A multiyear study was conducted to remove nonnative fish from a 15-km segment of the Colorado River near the Little Colorado River confluence. We evaluated how sediment, temperature, fish prey availability, and predator abundance influenced the incidence of piscivory (IP) by nonnative salmonids. Study objectives were addressed through spatial (upstream and downstream of the Little Colorado River confluence) and temporal (seasonal and annual) comparisons of prey availability and predator abundance. Data were then evaluated by modeling the quantity of fish prey ingested by trout durin...

Effects of Fish Size, Habitat, Flow, and Density on Capture Probabilities of Age-0 Rainbow Trout Estimated from Electrofishing at Discrete Sites in a Large River

We estimated size-specific capture probabilities of age-0 rainbow trout Oncorhynchus mykiss in the Lees Ferry Reach of the Colorado River, Arizona, by backpack and boat electrofishing at discrete shoreline sites using both depletion and mark-recapture experiments. Our objectives were to evaluate the feasibility of estimating capture probability for juvenile fish in larger rivers; to determine how it is influenced by fish size, habitat, flow, density, and recovery period; and to test population closure assumptions. There was no mortality among the 351 rainbow trout that were captured by electrofishing, marked, and held for 24 h. Of a total of 2,966 fish that were marked and released, only 0.61% were captured outside of mark-recapture sites, and total emigration from mark-recapture sites was 2.2-2.6%. These data strongly suggest that populations within discrete sites can be treated as effectively closed for the 24-h period between marking and recapture. Eighty percent of capture probability estimates from 66 depletion experiments and 42 mark-recapture experiments ranged from 0.28 to 0.75 and from 0.17 to 0.45, respectively, and the average coefficient of variation of estimates was 0.26. There was strong support for a fish size-capture probability relationship that accounted for the differences in vulnerability across habitat types. Smaller fish were less vulnerable in high- angle shorelines that were sampled by boat electrofishing. There was little support for capture probability models that accounted for within-day and across-month variation in flow. The effects of fish density on capture probability were challenging to discern, variable among habitat types and estimation methodologies, and confounded with the effect of fish size. As capture probability estimates were generally precise and the closure assumption was met, our results demonstrate that electrofishing-based mark-recapture experiments at discrete sites can be used to estimate the abundance of juvenile fish in large rivers.

Effects of Fluctuating Flows and a Controlled Flood on Incubation Success and Early Survival Rates and Growth of Age‐0 Rainbow Trout in a Large Regulated River

Abstract Hourly fluctuations in flow from Glen Canyon Dam were increased in an attempt to limit the population of nonnative rainbow trout Oncorhynchus mykiss in the Colorado River, Arizona, due to concerns about negative effects of nonnative trout on endangered native fishes. Controlled floods have also been conducted to enhance native fish habitat. We estimated that rainbow trout incubation mortality rates resulting from greater fluctuations in flow were 23–49% (2003 and 2004) compared with 5–11% under normal flow fluctuations (2006–2010). Effects of this mortality were apparent in redd excavations but were not seen in hatch date distributions or in the abundance of the age-0 population. Multiple lines of evidence indicated that a controlled flood in March 2008, which was intended to enhance native fish habitat, resulted in a large increase in early survival rates of age-0 rainbow trout. Age-0 abundance in July 2008 was over fourfold higher than expected given the number of viable eggs that produced thes...

A quantitative life history of endangered humpback chub that spawn in the Little Colorado River: variation in movement, growth, and survival.

While the ecology and evolution of partial migratory systems (defined broadly to include skip spawning) have been well studied, we are only beginning to understand how partial migratory populations are responding to ongoing environmental change. Environmental change can lead to differences in the fitness of residents and migrants, which could eventually lead to changes in the frequency of the strategies in the overall population. Here, we address questions concerning the life history of the endangered Gila cypha (humpback chub) in the regulated Colorado River and the unregulated tributary and primary spawning area, the Little Colorado River. We develop eight multistate models for the population based on three movement hypotheses, in which states are defined in terms of fish size classes and river locations. We fit these models to mark–recapture data collected in 2009–2012. We compare survival and growth estimates between the Colorado River and Little Colorado River and calculate abundances for all size classes. The best model supports the hypotheses that larger adults spawn more frequently than smaller adults, that there are residents in the spawning grounds, and that juveniles move out of the Little Colorado River in large numbers during the monsoon season (July–September). Monthly survival rates for G. cypha in the Colorado River are higher than in the Little Colorado River in all size classes; however, growth is slower. While the hypothetical life histories of life-long residents in the Little Colorado River and partial migrants spending most of its time in the Colorado River are very different, they lead to roughly similar fitness expectations when we used expected number of spawns as a proxy. However, more research is needed because our study period covers a period of years when conditions in the Colorado River for G. cypha are likely to have been better than has been typical over the last few decades.

Cross-Scale Modeling of Riparian Ecosystem Responses to Hydrologic Management

ABSTRACT There is much demand for quantitative models to aid in comparison of policy options and design of adaptive management policies for riparian ecosystems. Such models must represent a wide variety of physical and biological factors that can vary on space–time scales from meters-seconds to basin-decades. It is not possible in practice to develop a complete model for all variation. Incomplete but still useful models can be developed by using state variable identification methods that focus scientific attention on causal pathways of most direct policy concern, and by using various analytical methods to provide cross-scale analytical predictions about effects of microscale variation. The main value of such models has not been to provide detailed quantitative prescriptions, but to help identify robust, qualitative arguments about efficacy of various policy choices. However, they have not been successful at representing some important dynamic effects in riparian systems, where small physical changes (such as overtopping dikes) and infrequent extreme physical events can cause habitat changes at large spatial scales and ecological impacts that last for decadal or even longer time scales.

Surprise and Opportunity for Learning in Grand Canyon: the Glen Canyon Dam Adaptive Management Program

With a focus on resources of the Colorado River ecosystem below Glen Canyon Dam, the Glen Canyon Dam Adaptive Management Program has included a variety of experimental policy tests, ranging from manipulation of water releases from the dam to removal of non-native fish within Grand Canyon National Park. None of these field-scale experiments has yet produced unambiguous results in terms of management prescriptions. But there has been adaptive learning, mostly from unanticipated or surprising resource responses relative to predictions from ecosystem modeling. Surprise learning opportunities may often be viewed with dismay by some stakeholders who might not be clear about the purpose of science and modeling in adaptive management. However, the experimental results from the Glen Canyon Dam program actually represent scientific successes in terms of revealing new opportunities for developing better river management policies. A new long-term experimental management planning process for Glen Canyon Dam operations, started in 2011 by the U.S. Department of the Interior, provides an opportunity to refocus management objectives, identify and evaluate key uncertainties about the influence of dam releases, and refine monitoring for learning over the next several decades. Adaptive learning since 1995 is critical input to this long-term planning effort. Embracing uncertainty and surprise outcomes revealed by monitoring and ecosystem modeling will likely continue the advancement of resource objectives below the dam, and may also promote efficient learning in other complex programs.

Estimating Riverwide Abundance of Juvenile Fish Populations: How Much Sampling is Enough?

AbstractEstimating riverwide abundance of juvenile fish populations is challenging because detection probability is typically low and juveniles can be patchily distributed over large areas. We used a hierarchical Bayesian model to estimate the abundance of juvenile steelhead Oncorhynchus mykiss in two rivers in British Columbia over 3 years based on a multigear, two-phase sampling design. These estimates were used to drive a simulation model to evaluate how the precision of abundance estimates varied with the number of single-pass index and mark–recapture sites that were sampled, the proportion of shoreline sampled, and the mean and variation of detection probability and fish density across sites. The extent of variation in fish densities across index sites was the most important factor influencing the precision of river-wide abundance estimates, and increasing the number of index sites was the best approach to reduce variability in abundance estimates. River size, which controls the proportion of habitat...