Webster Van Winkle

Individual-Based Approach to Fish Population Dynamics: An Overview

Abstract Individual-based simulation modeling tracks the attributes of individual fish through time and aggregates them to generate insights into population function. By seeking to understand how fish of differing phenotypes respond to variations in physicochemical and biological environments, analysts hope to improve predictions of population trends. A review ofeight accompanying papers highlights the promise and current limitations of the individual-based approach. Among the challenges to be faced are accurately representing feeding encounter rates, extending models to account for spatial heterogeneity and transgenerational responses, dealing with practical limits to the amount of data on individuals that can be measured and managed, more fully conceptionalizing natural processes, and acquiring appropriate field data with which to formulate and test the models.

Linking life history theory, environmental setting, and individual-based modeling to compare responses of different fish species to environmental change

Abstract We link life history theory, environmental setting, and individual-based modeling to compare the responses of two fish species to environmental change, Life history theory provides the framework for selecting representative species, and in combination with information on important environmental characteristics, it provides the framework for predicting the results of model simulations. Individual-based modeling offers a promising tool for integrating and extrapolating our mechanistic understanding of reproduction, growth, and mortality at the individual level to population-level responses such as size-frequency distributions and indices of year-class strength. Based on the trade-offs between life history characteristics of striped bass Morone saxatilis and smallmouth bass Micropterus dolomieu and differences in their respective environments, we predicted that young-of-year smallmouth bass are likely to demonstrate a greater compensatory change in growth and mortality than young-of-year striped bas...

A Critical Appraisal of Population Approaches in Assessing Fish Community Health

Abstract The characteristics of a fish population that is healthy from the standpoint of human exploitation include its ability to produce numerous healthy, fecund, and normal-sized adults and to resist or rebound from short-term stresses. These characteristics generally can be expressed in terms of the population staying within a certain range of values in abundance, age structure, length and weight structure, condition factor, and sex ratio. Some of the traditional approaches used in studying fish populations are reviewed and it is shown that, at best, only some of the above population characteristics can be evaluated using these traditional approaches. The individual-based modeling approach is an alternative to traditional models that permits explicit representation of the feedback between the differing physiological states of individual members of the population and their ability to feed, grow, reproduce, and avoid disease and predation. It may be superior for describing and predicting population health. An example of the use of this approach is presented.

Oxyconformers and oxyregulators: A quantitative index

Abstract Five empirical regression models for analysis of data on rate of oxygen uptake against oxygen level are compared. The quadratic polynomial model is the best in terms of providing a good statistical fit, in ease of computation and in providing model parameters of value when comparing and grouping species. Since the intercept parameter ( B 0 ) characterizes only the position of the curve and since there was a strong negative correlation between the linear ( B 1 ) and quadratic ( B 2 ) parameters, the quadratic coefficient ( B 2 ) alone is an informative index of the shape of the curve. B 2 not significantly different from zero implies oxyconformity, while B 2 significantly less than zero implies an appreciable degree of regulation.

Water-Level Fluctuation Effects on Centrarchid Reproductive Success in Reservoirs: A Modeling Analysis

Abstract An individual-based model of nesting smallmouth bass Micropterus dolomieu and white crappie Pomoxis annularis is used to compare reproductive success in a deep reservoir and a shallow reservoir under different amplitudes and periods of water-level fluctuations. The model simulates nest site selection, egg deposition, and the subsequent development and survival of young from eggs through dispersal in a two-dimensional spatial grid of habitat cells representing the reservoir bottom. All simulations are for May through September using a daily time step. Nest site (cell) selection is determined from species-specific habitat suitability indices based on substrate, slope, depth, and structure. The development of the young is temperature dependent. Mortality occurs via attrition, abandonment, and whole-nest catastrophe. Model corroboration was performed with observations of nesting white crappies and smallmouth bass in Brownlee Reservoir, Idaho–Oregon. The predicted egg-to-dispersal survival declined wi...

Regulation of energy acquisition and allocation to respiration, growth and reproduction: simulation model and example using rainbow trout

Recruitment in any fish population is partly dependent on sexual maturity, timing of spawning, and the number and quality of eggs spawned by the reproducing component of the population. Each of these reproductive variables can vary within a population as a function of the size and age of individual fish (Trippel et al., Chapter 2, this volume). Thus, to more fully understand recruitment variation, we require better knowledge of the dynamics of reproduction. This includes trade-offs in energy allocation patterns among respiration, growth and reproduction at the individual level.

A Density-dependent Function for Fishing Mortality Rate and a Method for Determining Elements of a Leslie Matrix with Density-dependent Parameters

Abstract A density-dependent function for the instantaneous fishing mortality rate is presented. It is shown that this function may be readily incorporated into the age-specific probability of survival in a Leslie-matrix population model. A method is presented for indirectly determining the probability of survival for age-class 0 of a fish population using a density-dependent Leslie matrix. The method involves the two constraints that the population be at equilibrium and that the index of absolute population size in the density-dependent function be assigned a value. In addition, given the probability of survival for age-class 0, it is shown that the probability of survival through a selected life stage within age-class 0 can be indirectly determined. Three problems in modeling a fish population using a Leslie model are discussed in light of the difficulties involved in modeling density dependence due to insufficient information and lack of understanding concerning density-dependent phenomena.

Linking laboratory and field responses of fish populations to acidification

To increase understanding of mechanisms by which fish populations respond to water chemistry changes resulting from acidification, it is necessary to link the results of laboratory studies of the effects of pH, Al, and Ca on the survival, growth, and reproduction of individual fish to responses of fish populations in the field. Our framework for achieving this goal is based on the types of data commonly available from both laboratory and field studies. One of the models (PHALCA) in this framework estimates the number of fish surviving as a function of time, given pH, Al, and Ca levels. A second model (FISHEGGS) evaluates the reduction in reproductive potential of a fish population attributable to the effects of pH, Al, and Ca on the survival of young-of-the-year and older fish and on fecundity. Preliminary results from these two models are presented, and the entire framework will be applied and tested over the next year using data for brook trout and lakes in the Adirondacks. The framework and models are a complementary alternative to the statistical analysis of survey data on water chemistry and on presence or absence of a fish species.

Simulating smallmouth bass reproductive success in reservoirs

An individual-based model of nesting smallmouth bass, Micropterus dolomieu, is used to predict the effects of water level fluctuations on reproductive success. The model simulates daily nest site selection, spawning, nest guarding, and development and survival of eggs, embryos, and larvae until dispersal. The model was configured for Brownlee Reservoir, Idaho-Oregon. Each reservoir bank is represented as a rectangular grid of cells, with each cell characterized by an assigned slope, substrate, and elevation, and by a water depth that varied daily. Nest site (cell) selection is determined from a habitat suitability index (HSI) based on substrate, slope, and depth. Development of young is temperature-dependent. Mortality of young occurs via attrition, abandonment by the guarding male, and probabilistic whole-nest catastrophe. Simulations were performed that used observed data for 1991 to 1996. Model predicted nest habitat selection and egg-to-dispersal survival rates were similar to observed values. Additional model simulations showed that: (1) nest habitat selection was best predicted when depth, slope, and substrate were considered together rather than singly, (2) egg-to-dispersal survival was related to the magnitude of water level fluctuations during the peak spawning period, (3) relating mortality to HSI values resulted in lower survival, while relating growth to HSI values resulted in higher survival, and (4) spawning habitat is not limiting in Brownlee Reservoir. Suggestions for future monitoring of reservoir-based smallmouth bass populations are discussed.

A perspective on power generation impacts and compensation in fish populations

Abstract Renewed interest in the topic of compensation in fish populations has been stimulated by new EPA 316(b) regulations relating to entrainment and impingement looming on the horizon. The purpose of this paper is to revisit the topic of population compensation for fish populations in the context of assessing power generation impacts. I define compensation as the net population-level outcome of changes in growth, survival, and reproduction at the individual fish level that offsets decreases or increases in population density. Potential mechanisms of compensation have been well document in laboratory and field experiments. The process underlying all these mechanisms is that changes in population density can change per capita availability of essential resources such as food and space. The state of science in this area is constrained both retrospectively and prospectively by five technical stumbling blocks. Technological advances have improved our ability to bound the phenotypic plasticity of a species and to assess the potential effects of power generation impacts through a combination of monitoring, special studies, and simulation modeling. Four generalizations concerning compensation are mentioned. Progress has been made over the past three decades, but this topic remains scientifically challenging and politically controversial.