Applying the mean free-path length model to juvenile Chinook salmon migrating in the Sacramento River, California
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Applying the mean free-path length model to juvenile Chinook salmon migrating in the Sacramento River, California Anna E. Steel & James J. Anderson & Brian Mulvey & David L. Smith
Received: 9 August 2019 / Accepted: 3 November 2020 / Published online: 20 November 2020 # Springer Nature B.V. 2020
Abstract Population vital rates, such as stage-specific survival, are influenced by individual behavior and movement patterns. Yet few methods exist to incorporate behavior into predator-prey models, omitting a potentially important source of variability in population dynamics. Here were combine results from an acoustic telemetry study of juvenile Chinook salmon (Oncorhynchus tshawytscha) with an existing predator prey model, called the mean free-path length model, originally presented in Anderson et al. (2005). The model describes the probability of predator-prey encounters as a function of the predator density and the movement patterns of predators and prey. Greater predator densities and greater variation in movement vectors should result in higher predator-prey encounter rates, and lower survival for the prey. Fitting this model to data provides insight into mechanisms of mortality for migrating fishes. Here we estimate model parameters for A. E. Steel (*) Department of Wildlife, Fish and Conservation Biology, University of California Davis, Davis, CA 95616, USA e-mail: [email protected] J. J. Anderson School of Fisheries, University of Washington, Seattle, WA 98195, USA B. Mulvey Sacramento District, U.S. Army Corps of Engineers, Sacramento, CA 95814, USA D. L. Smith Environmental Laboratory, U.S. Army Engineer Research and Development Center, Vicksburg, MS 39180, USA
two flow conditions in the Sacramento River, California, examining the importance of natural environmental variation in shaping encounters and prey survival. Survival estimates were similar between the high and low flow conditions, yet travel time was slower at lower flows. The model estimates of mean free-path length were lower when compared to those estimated in the Snake River system, corresponding with lower survival. We discuss the value of model parameters estimated from telemetry data in providing a tool for forecasting population-level responses to structural or hydrodynamic modifications in large river systems, and we explore how the XT model can provide insight into nonlinear and threshold-like responses of migratory fish survival to flow. Keywords Predator-prey . XT model . Acoustic telemetry . Ideal gas law
Introduction Population vital rates, such as stage-specific survival, are central to many ecological processes. These rates determine the persistence or extinction of a population and can be influenced by human-alterations to ecosystems, making this a central issue for many topics in natural resource management. There is a long history of modeling survival rate as a result of predator-prey interactions (Leslie 1948; Holling 1959; Arditi and Ginzburg 1989). Classical models continue to be modified and improved, providing new insight into
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