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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...

A method was developed for assessing coastwide effects of power plant impingement and entrainment on managed fish stocks. The method imbeds an assessment of anthropogenic effects that occur during the first year of life of fish (the period when most entrainment and impingement occur) into a standard age-structured stock assessment that addresses age-1 and older fish. The method thereby provides a straightforward means for comparing the effects of entrainment and impingement mortality to other forms of anthropogenic mortality affecting coastwide fish stocks. The method uses standard equations from fishery science that represent the relationships among independent competing forces of mortality, stock abundance, and landings. Power plant mortality is treated like fishing mortality, and power plant losses are treated like fishery landings. The total age-0 natural mortality rate is allocated to the individual age-0 life stages based on a power function relating daily natural mortality rates to age-spe...

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.

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.

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...

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.

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.

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.

This analysis presents a correction of that presented in Van Winkle et al. (1981; Can. J. Fish. Aquat. Sci. 38: 627–632). An exact solution is obtained based on the noncentral t-distribution to replace the incorrect solution based on the central t-distribution used in our earlier analysis. Our new results, although less pessimistic than before, still are not encouraging. They indicate that variability in baseline data is so great that data from 10 additional years are not adequate for detecting even substantial (> 50%) reductions in mean year-class strength, and that at least 20 years of data collection would be required to detect an actual 50% reduction in mean year-class strength, given a Type II error of 50%.Key words: fractional reduction, impingement, power plant, statistical power, Type I and Type II errors, white perch, year-class strength

Atlantic Coast striped bass (Morone saxatilis) commercial fisheries data are examined for periodicities in the appearance of dominant year-classes using autocorrelation and spectral-analysis techniques. Results obtained using maximum entropy and classical Fourier spectral-analysis methods are compared. Statistically significant periodicities of approximately 20 yr and of 6–8 yr are common to the time series for most states and regions. Since the periodicities are neither very pronounced nor simple, it is difficult to isolate the causative factors, which are more likely to be density-independent environmental factors enhancing survival of the young than intrinsic characteristics of the life cycle of striped bass. The spectra for Maryland landings and Maryland landings per unit gear are nearly identical, suggesting that at least for Maryland the landings and landings-per-unit-gear data are approximately equally reliable as indices of stock size. The structure of the North Carolina time series is unique, which supports the opinion that this stock does not mix appreciably with Chesapeake and Hudson stocks. Impact assessments and monitoring programs should not be predicted on the expectation of pronounced or simple periodicities of 6 years or any other time interval in the appearance of dominant year-classes in Atlantic Coast striped bass populations. Key words: autocorrelation analysis, commercial fisheries data, Fourier spectral analysis, maximum entropy spectral analysis, periodicities, striped bass

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.

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.

Nutrient cycling in streams involves some downstream transport before the cycle is completed. Thus, the path traveled by a nutrient atom in passing through the cycle can be visualized as a spiral. As an index of the spiralling process, we introduce spiralling length, defined as the average distance associated with one complete cycle of a nutrient atom. This index provides a measure of the utilization of nutrients relative to the available supply from upstream. Using 32P as a tracer, we estimated a spiralling length of 193 m for phosphorus in a small woodland stream.Key words: downstream transport, nutrient cycling, phosphorus, spiralling, stream

1. 1. Oxygen consumption of gill tissue from Crassostrea virginica, Mercenaria mercenaria, Modiolis demissus and Mytilus edulis was measured at salinities of 5, 10, 15, 20, 25 and 30 ppt and at temperatures of 10, 18 and 26°C during winter and summer. 2. 2. The seasonal differences were variable, i.e. winter values greater than, the same as and less than the corresponding summer values were observed. 3. 3. Oxygen consumption was greater at higher temperatures. Summer as compared to winter Q 10 values tended to be higher from 10–18°C and lower from 18–26°C. 4. 4. Season and experimental temperature modified only slightly the effects of experimental salinity. 5. 5. Oxygen consumption was relatively constant from 5–30 ppt for Crassostrea and Mytilus , but was greater at low salinities for Mercenaria and Modiolus . The effect of salinity on oxygen consumption of isolated gill does not appear to be correlated with the lower salinity boundaries of the whole animals.

Several models for the analysis of data relating the rate of oxygen uptake to environmental oxygen level have been evaluated. We conclude that the quadratic (or second-degree) polynomial, though hardly perfect, is the best. Data from 31 species of aquatic invertebrates are described by constants of the quadratic (or second-degree) polynomial equation. The results suggest a phylogenetic trend of increasing regulation of aerobic metabolism in response to declining environmental levels as animals acquire structures that effectively insulate their respiring tissue from the habitat. Many of these species apparently cease withdrawing oxygen from their external environment long before they have exhausted its supply. Presumably, those species with long lasting internal oxygen reservoirs, such as gas bubbles or pools of high oxygen affinity hemoglobin, continue to operate aerobic pathways, but those without substantial oxygen storage devices must switch over to anaerobic pathways, despite the availability of small residual volumes of external oxygen.

A probability model and associated statistical techniques are presented which are specifically designed to analyze the home range of animals inhibiting nonhomogeneous habitats with the special characteristics of an ecotone. The utilization distribution of an individual animal is approximated with a continuous bivariate probability distribution having unimodal and independent X and Y distributions with axes parallel and at right angles to the ecotone. Statistical techniques based on this model are used to analyze a set of capture points for bullfrogs (Rana catesbeiana) inhabiting the shoreline of a pond. The approach used is applicable to other animals inhabiting other ecotones, but not to animals inhibating homogeneous habitats. See full-text article at JSTOR

1. l. Ciliary activity of gill tissue from low and high salinity acclimated Crassostrea virginica, Mercenaria mercenaria, Modiolus demissus and Mytilusedulis was measured at various salinities. 2. 2. For each species there is an initial inhibition of activity at experimental salinities differing appreciably from the acclimation salinity. If the difference between experimental and acclimation salinities is not too great, inhibition is followed by recovery. 3. 3. Recovery time-experimental salinity response surfaces are shifted towards lower salinities for low salinity acclimated Crassostrea, Modiolus and Mytilus (but not Mercenaria) relative to the high salinity acclimated groups. 4. 4. A positive correlation exists between lower salinity boundaries for ciliary activity of isolated gill tissue and whole animal activity. 5. 5. The effects of salinity on ciliary activity and rate of oxygen consumption are compared. At low as compared to high salinities, ciliary activity decreases whereas oxygen consumption increases or remains approximately constant.

1. 1. Data and a line of reasoning are presented to indicate the problems in establishing the relationship between pumping rate and oxygen consumption rate in the hard clam, Mercenaria mercenaria, on the basis of pumping-rate measurements and external, oxygen-concentration measurements alone. 2. 2. An analysis is presented illustrating the two extreme possibilities for gill tissue VdotO2 relative to total VdotO2 following an increase in total VdotO2 from an average rate where gill tissue accounts for 20 per cent of the total.

Two questions are addressed: ''To what extent can we presently assess the population-level effects of power plant exploitation'' and ''What can we do to improve these assessments.'' Each of these questions is addressed from the point of view of an optimist, a pessimist, and a realist. The realist adopts a flexible blend of the optimist's and the pessimist's positions. He envisions a continuum of possible assessment situations. At one extreme, population-level assessments are not feasible because of the dominating influence of the pessimist's unavoidable limitations. At the other extreme, population-level assessments are both necessary and possible using the tools proposed by the optimist.