James E. Breck

Evaluating the constraints of temperature, activity and consumption on growth of largemouth bass

SynopsisWe present a bioenergetics model for largemouth bass (Micropterus salmoides) which simulates growth as a function of body size, temperature, activity and consumption level. We apply the model to investigate seasonal changes in condition factor exhibited by bass in Par Pond, South Carolina, a reservoir receiving heated effluent. Previous authors have suggested that these changes occur due to bioenergetic constraints, primarily the effects of heated effluent on metabolic rate. Model simulations were used to evaluate the hypotheses that seasonal changes in condition factor were caused by the heated effluent, seasonally variable activity, seasonally variable consumption, or reproductive costs.Results indicate that temperature is not directly responsible for the seasonal changes in condition factor. Bass moderate the influence of the heated effluent via behavioral thermoregulation. Activity is not a major factor, and spawning weight-loss can account for only a small portion of the observed variation. However, the pattern of seasonal changes in body condition may be adequately explained by seasonal variations in consumption. The patterns of consumption rate and/or prey availability suggested by model simulations represent testable hypotheses.

Foraging Theory and Piscivorous Fish: Are Forage Fish Just Big Zooplankton?

Abstract Insights into the dynamics of fish growth can be gained by using foraging theory to link bioenergetics models of fish and their prey. These links are critical for modeling fish daily ration and growth, prey mortality, selection among prey, and competition among predators. However, the foraging theory that is relatively well developed for planktivores does not always apply to piscivores without important modifications. Visual encounter is often limited by visual acuity for most planktivores, but probably limited by prey contrast for piscivores, so that piscivore reactive distance is much less dependent on prey size. Whereas handling time per prey may limit the capture rate for some planktivores, it is irrelevant for most piscivores, which eat relatively small numbers of large prey and are more likely to have daily ration limited by rates of digestion or prey encounter. Time for gastric evacuation or digestion should not be a part of handling time, because search can occur simultaneously with diges...

Cumulative stress-induced mortality of gizzard shad in a southeastern U.S. reservoir

SynopsisStarvation was apparently responsible for a large die-off of gizzard shad, Dorosoma cepedianum, in several east Tennessee reservoirs during the spring of 1983. Condition indices, calorific equivalents, lipids, and blood parameters of electrofished (control) shad from Watts Bar Reservoir were significantly higher than these parameters for recently dead shad and for stressed shad, indicating that the stressed and dead fish were at similar levels of physiological condition. We hypothesize that mortality due to starvation resulted from a year-long series of unusual environmental conditions beginning with an abnormally warm spring in 1982 which delayed spawning for some shad, a mild winter in 1982–1983 which increased metabolic demands, and an unusually cool spring in 1983 which delayed food availability. These events may have acted in a cumulative fashion, with each inducing additional increments of stress until lipid stores were depleted to a nonrecovery level, which appears to be about 4% of dry body weight. At least 10% of the adult gizzard shad died of starvation. Most predators were probably not adversely affected by the die-off because of the high availability of shad smaller than 16 cm (total length) and the vulnerability of stressed shad to predation.

Effects of Simulated Angling Regulations on Stunting in Bluegill Populations

Abstract Stunting in populations of bluegill Lepomis macrochirus is a major management problem in the upper midwestern United States, Traditionally, stunting has been attributed to a lack of food resources. An alternative theory suggests that stunting may result from harvest of the large parental males that inhibit spawning by smaller males, allowing small males to direct energy to reproduction instead of to growth. We used a population model to simulate restrictions on harvest of large males under various conditions of vulnerability to angling, growth rate, and angler effort. Regulations tested were a daily bag of 5 fish and seasonal bags of 50 fish or 50 fish but only 1 trophy specimen (>180 mm total length); a limit of only 1 trophy fish during the spawning season; and a spawning season closure. Growth and angler effort had the greatest effects on size structure in simulated bluegill populations; high growth and low effort led to notable increases in mean fish length. Tested regulations and male vulner...

Hurry Up and Wait: Growth of Young Bluegills in Ponds and in Simulations with an Individual-Based Model

Abstract The growth of young-of-the-year bluegills Lepomis macrochirus was measured in six experimental ponds and simulated with an individual-based model. In the ponds the young bluegills grew at a rate of about 0.6 mm/d for 3–4 weeks. An abrupt reduction in growth rate to about 0.2 mm/d occurred when total zooplankton density (exclusive of rotifers) decreased below about 50 organisms/L, and growth rate decreased to nearly zero by September. The model included daily foraging for several sizes of open-water or benthic prey and a revised set of bioenergetics parameters for bluegill. The simulations suggest that the initially rapid growth rate was near the limit set by maximum daily ration; the fish may have obtained full rations even with suboptimal foraging during this phase, Over a wide range of fry densities, the time of growth reduction and the average final fish size at the end of the growing season were strongly density dependent, both in the simulations and in the ponds. Two natal cohorts started 10...

Enhancing Bioenergetics Models to Account for Dynamic Changes in Fish Body Composition and Energy Density

Abstract Fish proximate composition and energy density can influence growth, survival, and reproduction, so it is important to develop models to understand the patterns and predict dynamic changes. This paper presents three such models. Model 1 describes the general pattern of changes in lipid, protein, ash, and energy density that occur with changes in water content. The key assumption this model is that there is a fixed amount of water associated with each gram of protein and a much smaller fixed amount of water associated with each gram of lipid. In combination with a mass balance constraint, this explains the commonly observed linear relationship between the fraction lipid and the fraction water. Because energy density varies in direct proportion to the fractions lipid and protein, the linear relationship between body composition and fraction water makes energy density also a linear function of the fraction water. The model is fitted to data for lake trout Salvelinus namaycush and coho salmon Oncorhyn...

Field Test of Two Energetic Models for Yellow Perch

Abstract Field data from a population of yellow perch Perca flavescens in Saginaw Bay, Lake Huron, were used to evaluate the ability of two energetic models to predict consumption by yellow perch. Field estimates of daily ration for age-1–4 fish during May through October 1987 and 1988 were compared with independent predictions made by the Wisconsin energetic model and an energetic model developed by Karas and Thoresson. Predictions of daily ration using the Wisconsin model were lower than daily rations estimated from field data for all ages, primarily due to poor model–field agreement at temperatures above 22°C. This caused estimates of cumulative consumption from the Wisconsin model to be 25–50% lower than field estimates. Predictions of daily ration by the Karas–Thoresson model agreed with field estimates over a temperature range of 10–26°C for age-1–3 yellow perch but not for older fish. Despite improvement, model predictions of cumulative consumption were 2–35% lower than field estimates. Although th...

Developing a Standardized Sampling Program

Abstract In 1995, the Fisheries Division of the Michigan Department of Natural Resources formed a Resource Inventory Planning Committee to develop a statewide sampling program for inland waters. The goal of this sampling program was to provide information needed for the management and conservation of Michigans aquatic resources. Because sampling provides information to a variety of users for multiple purposes, the sampling plan we designed included several subprograms, some of which are under local control and some of which are centrally administered with a broad statistical design. Centrally administered subprograms included designs to (1) evaluate stocking success using angler surveys, (2) evaluate the characteristics of lake fish communities across the state, and (3) evaluate the characteristics of stream fish communities across the state. Two of the major topics addressed by the committee were standardization of sampling gear and choice of sampling sites (i.e., particular lakes or stream segments). A...

A Landscape-Based Classification of Fish Assemblages in Sampled and Unsampled Lakes

Abstract We related fish species patterns and landscape-scale environmental data from 216 Michigan lakes to identify repeatable types of fish assemblages, identify environmental factors related to assemblage types, and classify fish assemblages in unsampled lakes. Multivariate regression tree modeling of fish species abundances identified six assemblage types that were explained by degree-days during the ice-free period, lake surface area, and mean lake surface temperature. Warmwater species dominated southern lakes, while coolwater and coldwater species had higher abundances in northern lakes. Coolwater species were present in large southern lakes, whereas warmwater species were excluded from northern lakes that had low mean surface temperatures or low degree-days. These results suggest that patterns of lake fish assemblages are shaped by differences in climate as well as lake-specific differences in surface temperature regimes and in vertical availability of coldwater and coolwater habitats. Because we ...

Potential importance of spatial and temporal heterogeneity in pH, Al, and Ca in allowing survival of a fish population: A model demonstration

Abstract Discrepancies usually exist between the results of bioassay studies and the status of natural fish populations. One cause of such discrepancies is the spatial and temporal heterogeneity in the stressing factors or contaminant concentrations in natural systems. To provide a means of relating laboratory and field bioassay results to natural populations, we have modified an existing Monte Carlo mathematical model to track the movement and survival of fish in a body of water, represented by a two-dimensional grid, subject to acidification stress. We assumed that the fish (adults or the less mobile and generally more sensitive early life stages) are able to sense realistic gradients of pH, aluminium (Al), and calcium (Ca) (or alkalinity) and to move to reduce the chemical stress. We have also considered the effects of food availability and habitat preference on fish movement. Each fish takes one spatial ‘step’ at a time, the direction being randomly selected but also biased by the above factors. A function for accumulation and repair of damage is implemented within the model to relate mortality to the variable exposure history the fish accumulate by moving in the chemically heterogeneous environment. Using the model, we evaluated the influence of the strength and sensitivity of fish avoidance behavior, the presence or absence of the refuge, and the timing of multiple pulses on fish survival. The results highlight the potential importance of a chemically heterogeneous natural environment in allowing a population to survive under average water-quality conditions that laboratory bioassays suggest should prohibit survival. Laboratory and field behavior experiments, including characterization of water chemistry on a microscale in the field, are suggested to explore this phenomenon further.