Aquatic Ecology Laboratory Publications

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    Use of a Quadrat Rotenone Technique and Bioenergetics Modeling to Evaluate Prey Availability to Stocked Piscivores
    (1988) Johnson, Brett M.; Stein, Roy A.; Carline, Robert F.
    Young-of-year gizzard shad Dorosoma cepedianum, the primary prey for piscivores in Ohio impoundments, are difficult to sample by conventional techniques. We developed a technique for sampling littoral zone quadrats with rotenone and compared this method to other gear. To sample, we isolated 0.15-hectare shoreline areas (N = 28 quadrats) with a plastic barrier, which confined the rotenone and even small fish, and applied rotenone at concentrations of 2-3 mg/L. To quantify densities of dead fish that sank, about 18% of the bottom within quadrats was covered with netting. These nets eliminated the need for species-specific recovery rates, which typically are highly variable. Tucker trawls and seines provided lower density and size estimates of gizzard shad than did our quadrat method. Despite difficulties associated with the quadrat rotenone technique such as site selection, variability, and personnel requirements, this method provided the best estimate of size structure and density of gizzard shad populations. To determine if prey size or density influenced stocking success of age-0 piscivores, we used our estimates of gizzard shad biomass and growth to calculate total production of prey (71.3 kg/hectare) during its first growing season. Five taxa of piscivorous fish were stocked and their growth and survival were monitored in conjunction with regular estimates of gizzard shad. Total consumption of prey by all predators, calculated from observed growth by bioenergetics models, was 14.5 kg/hectare, or only about 20% of total young-of-year gizzard shad production. Apparently, factors other than summer prey production, such as spatial and temporal overlap of predators and prey, the gizzard shad: predator size ratio at time of stocking, or availability of gizzard shad in winter, limited first-year growth and survival of stocked predators.
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    Linking Bluegill and Gizzard Shad Prey Assemblages to Growth of Age-0 Largemouth Bass in Reservoirs
    (1998) Garvey, James E.; Stein, Roy A.
    Either gizzard shad Dorosoma cepedianum or bluegills Lepomis macrochirus dominate prey assemblages in many small (<100 ha) Ohio reservoirs. Because gizzard shad spawn early in the spring and their offspring grow rapidly, age-0 gizzard shad may be invulnerable to age-0 largemouth bass Micropterus salmoides, thereby compromising this piscivore's growth and, potentially, recruitment. To test this hypothesis, we quantified growth, abundance, and diets of age-0 largemouth bass in reservoirs dominated by age-0 bluegills (one reservoir) or age-0 gizzard shad (two reservoirs) during June through early October 1992-1994. In the bluegill-dominated reservoir, age-0 largemouth bass grew slowly (about 0.04 g/d) during June through mid-August. Though age-0 bluegills became abundant after mid-August, contributing to rapid growth (about 0.2 g/d) of age-0 largemouth bass, these age-0 largemouth bass only reached small to moderate sizes by fall (range of mean wet weights, 3-7 g). In the reservoirs dominated by gizzard shad, summer growth and fall sizes of largemouth bass varied among systems and years. During one summer in one shad-dominated reservoir, an early rise in temperature plus small age-0 gizzard shad probably contributed to rapid growth (~0.12 g/d) and large fall size (mean wet weight, 10.8 g) of age-0 largemouth bass. More commonly, age-0 largemouth bass grew slowly or moderately (~0.06 g/d). However, fall sizes of largemouth bass always were equivalent to or exceeded those in the bluegill dominated reservoir (range of mean wet weights, 3-11 g). Our results suggest that growth of age-0 largemouth bass should vary more in systems dominated by gizzard shad than in bluegill dominated ones. Management efforts that increase gizzard shad vulnerability during early summer may reduce this variability, thereby enhancing first-summer growth and, potentially, recruitment success of largemouth bass.
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    Direct and Indirect Effects of Fish Predation on the Replacement of a Native Crayfish by an Invading Congener
    (1993) Mather, Martha E.; Stein, Roy A.
    In Ohio streams, the crayfish Orconectes rusticus is replacing O. sanborni, and herein we test how predators influence this replacement. In a field survey, crayfish were scarce when fish were abundant, suggesting that predators can adversely affect these prey. In laboratory experiments, we examined underlying mechanisms for this inverse relationship; specifically, we tested how crayfish species, adult aggression, and habitat heterogeneity influenced the predator-prey interaction. In a laboratory stream, smallmouth bass (Micropterus dolomieu) ate similar numbers of equal-sized O. rusticus and O. sanborni, but when sizes mimicked those in the field (i.e., O. rusticus 4 mm > O. sanborni), fewer O. rusticus were eaten. Fish also reduced juvenileactivity and behaviors whereas adult aggression increased the frequency of these risky responses. More affected by adult crayfish, O. sanborni should suffer disproportional predation where adults and juveniles interact. Thus, fish predators should increase replacement rates and adult aggression should further accelerate this process. Manifested through crayfish size, both indirect and direct predator effects contribute to the replacement of O. sanborni by O. rusticus
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    A dynamic model of group-size choice in the coral reef fish Dascyllus albisella
    (1999) Martinez, Felix A.; Marschall, Elizabeth A.
    We developed a dynamic programming model of group size choice for settling coral reef fish to help understand variability in observed group sizes. Rather than calculating optimal group size, we modeled optimal choice and calculated the acceptable group sizes that arose from this choice. In the model, settling individuals weigh the fitness value of settling in a group against the expected fitness of searching another day and encountering other groups, choosing the option with the higher value. Model results showed that individuals settling on any given day in the settling season have several acceptable group sizes in which they can settle. The range of acceptable group sizes also changes across the season. Early in the season, when there is still adequate time to grow, large groups (with higher survival) have the highest fitness. Late in the season, when the ability to grow fast becomes more important, small groups, which convey fast growth rates (although riskier), have higher fitness. Thus, according to our model, even when fish all make the same, simple decisions, a variety of outcomes are possible, depending on the specific options encountered and temporally changing ecological pressures. Even when all fish behave optimally, initial variability in group sizes will persist.
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    Juvenile growth and survival of heat-shocked triploid hybrid saugeyes, Stizostedion vitreum × S. canadense
    (2002) Garcia-Abiado, Mary Ann; Lynch, W. E. Jr.; Dabrowski, Konrad; Czesny, Sergiusz; Rinchard, Jacques; Stafford, J.
    Triploid hybrid saugeyes may be a desirable stocking alternative because diploid saugeyes are fertile and can compromise the genetic integrity of parental stocks. Four groups of saugeye eggs were heat-shocked 5 min after fertilization for 15 min at 31°C, which resulted in an 86.7 ± 9.4% triploidy rate and 57.8 ± 24.3% survival to the eyed-stage. Heat shocked and control saugeyes were stocked in two ponds for 40 days at 395 000 ind.ha^-1. Mean length and weight of triploid and heat-shocked diploid saugeyes were greater (P < 0.01) than unshocked diploid saugeyes. Survival of heat-shocked saugeyes (22.4%) was lower than unshocked saugeyes (94.7%). Heat-shocked fish (n = 25 851) harvested from ponds were stocked for 153 days in O'Shaughnessy Reservoir, Ohio, USA. Triploids were 34 mm shorter and weighed 41 g less than heat-shocked diploids (P < 0.01). Mean length and weight of triploids were comparable with unshocked diploids elsewhere in Ohio.
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    Testing for Evidence of Maternal Effects among Individuals and Populations of White Crappie
    (2005) Bunnell, David B.; Scantland, Matthew A.; Stein, Roy A.
    For an increasing number of species, maternal characteristics have been correlated with the characteristics of their eggs or larvae at the individual level. Documenting these maternal effects at the population level, however, is uncommon. For white crappies Pomoxis annularis, we evaluated whether individual maternal effects on eggs existed and then explored whether incorporating maternal effects explained additional variation in recruitment, a population-level response. Individual egg quality (measured as ovary energy density) increased with maternal length among individuals from seven Ohio reservoirs in 1999 and three in 2000. Among these same individuals, egg quality increased with maternal condition factor (measured as residual wet mass for a given length) in 1999 but not in 2000. In 2000 we estimated somatic energy density, an improved measure of condition; egg quality increased with somatic energy density, but somatic energy density was also strongly correlated with maternal length. Hence, we could not determine whether maternal length or condition was the primary factor influencing white crappie egg quality. Across seven populations, the relative population fecundity (i.e., stock size) of the 1999 year-class was unable to explain the variation in recruitment to age 2 (Ricker model r^2 = 0.04 and Beverton and Holt model r^2 = 0.02). Mean ovary energy density (i.e., egg quality), however, was unable to explain additional recruitment variability in either model. Hence, we documented evidence of maternal effects on individual ovaries but not on population-level recruitment. Nonetheless, we recommend that future studies seeking to understand white crappie recruitment continue to consider maternal effects as a potential factor, especially those studies that may have greater sample sizes at the population level and, in turn, a greater probability of documenting a population-level effect.
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    The impact of introduced round gobies (Neogobius me/anostomus) on phosphorus cycling in central Lake Erie
    (2005) Bunnell, David B.; Johnson, Timothy B.; Knight, Carey T.
    We used an individual-based bioenergetic model to simulate the phosphorus flux of the round goby (Neogobius melanostomus) population in central Lake Erie during 1995-2002. Estimates of round goby diet composition, growth rates, and population abundance were derived from field sampling. As an abundant introduced fish, we predicted that round gobies would influence phosphorus cycling both directly, through excretion, and indirectly, through consumption of dreissenid mussels, whose high mass-specific phosphorus excretion enhances recycling. In 1999, when age-1+ round gobies reached peak abundance near 350 million (2.4 kg.ha^-1), annual phosphorus excretion was estimated at 7 t (1.4 X 10^-3 mg P.m^-2·day^-l). From an ecosystem perspective, however, round gobies excreted only 0.4% of the phosphorus needed by the benthic community for primary production. Indirectly, round gobies consumed <0.2% of dreissenid population biomass, indicating that round gobies did not reduce nutrient availability by consuming dreissenids, Compared with previous studies that have revealed introduced species to influence phosphorus cycling, round gobies likely did not attain a sufficiently high biomass density to influence phosphorus cycling in Lake Erie.
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    Food Consumption and Growth of Three Esocids: Field Tests of a Bioenergetic Model
    (1991) Wahl, David H.; Stein, Roy A.
    We quantified diet and compared field estimates of growth and daily ration with predictions from a bioenergetic model for young-of-year muskellunge Esox masquinongy, northern pike E. lucius. and tiger muskellunge E. masquinongy x E. lucius introduced into five Ohio reservoirs. Gizzard shad Dorosoma cepedianum dominated esocid diets (77-97% by weight) through autumn but were absent by spring. Diets in late autumn and spring included sunfishes Lepomis spp. and brook silversides Labidesthes sicculus. Northern pike and tiger muskellunge grew faster than muskellunge through the first year. Food consumption was highest for tiger muskellunge, followed by northern pike, then muskellunge. Growth rates and rations were highest immediately after stocking, declining through autumn to their lowest levels in December and spring. A bioenergetic model underestimated final mass by a factor of two to three for all esocids; predictions for food consumption were better than those for growth but still overestimated observed values by 39-52%. Neither behavioral thermoregulation nor incorporation of seasonal energetic content of prey altered predictions (maximum of 2% increase). In contrast, adjustments in metabolic rates to account for differences in season and temperature substantially improved model predictions. Size-selective mortality did not account for the inaccuracies in model predictions. Conversion efficiencies (39-63%) exceeded those previously measured for esocids fed maximum rations, suggesting that model variables should be determined for a range of ration levels. Though used extensively, the predictions of bioenergetic models should not be accepted until the models have been subjected to additional field verification.
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    Changes in Prey Fish Populations in Western Lake Erie, 1969-88, as Related to Walleye, Stizostedion vitreum, Predation
    (1993) Knight, Roger L.; Vondracek, Bruce
    Relative abundance of the total prey fish community in the western basin of Lake Erie varied little from 1969 to 1988, but species composition changed significantly. Soft-rayed fishes such as emerald shiner, Notropis atherinoides, spottail shiner, N. hudsonius, and alewife, Alosa pseudoharengus, declined significantly after 1977 whereas only one spiny-rayed species, white bass, Morone chrysops, declined over the same period. Trout-perch, Percopsis omiscomaycus, a relatively abundant species rarely eaten by piscivores in this system, experienced only minor shifts in abundance between 1969 and 1988. Although several factors could be responsible for the shift in species composition, predation by increasingly abundant walleye, Stizostedion vitreum, played a major role. Walleye prefer to eat soft-rayed fishes; thus, observed shifts in the community match expectations of selection noted in the diet. We suggest that management goals focusing primarily on walleye affected not only the targeted species but the entire fish community of western Lake Erie.
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    Scale-Dependent Associations Among Fish Predation, Littoral Habitat, and Distributions of Crayfish Species
    (2003) Garvey, James E.; Rettig, Jessica E.; Stein, Roy A.; Lodge, David M.; Klosiewski, Steven P.
    To predict how species establish and disperse within novel communities, the spatial scale at which competition, predation, and habitat interact must be understood. We explored how these factors affect the distribution and abundance of the exotic crayfishes Orconectes rusticus and O. propinquus and the native O. virilis at both the site-specific and whole-lake scales in northern Wisconsin lakes. During summer 1990, we quantified crayfish, fish predators, and fish diets in cobble and macrophyte sites in Trout Lake, comparing resulting patterns to those in 21 lakes surveyed during summer 1987. Within and across lakes, fish abundance was unrelated to habitat. Within Trout Lake, O. rusticus and O. propinquus were common in both cobble and macrophyte. Orconectes virilis was restricted to macrophyte, probably due to strong displacement by the invaders in cobble. Across lakes, O. rusticus increased where habitat was more than 16.7% cobble, O. propinquus was generally rare, and O. virilis abundance was unrelated to cobble. Crayfish were generally small in cobble and large in macrophyte, perhaps because of habitat-specific, size-selective fish predation or because large crayfish leave cobble when it no longer provides refuge. Orconectes virilis, the largest of three congeners, may have a size refuge in macrophyte but not in cobble. Across lakes, O. rusticus was only abundant when fish biomass was low; O. virilis abundance varied positively with fish. Effects of fish predation and habitat on the ability of invaders Orconectes rusticus and O. propinquus to establish and replace O. virilis appear to be scale dependent. At local (site-specific) scales, cobble likely interacts with selective predation for O. virilis to allow the invaders to establish and replace the native. At the lake-wide scale, high cobble facilitates invaders but predation may curb their successful dispersal and establishment at new sites. Models of community assembly and invasions need to incorporate scale dependencies in habitat availability and biotic interactions to effectively assess the invasion potential of novel species.
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    Feeding Preferences of Omnivorous Gizzard Shad as Influenced by Fish Size and Zooplankton Density
    (1996) Yako, Lisa A.; Dettmers, John M.; Stein, Roy A.
    In Ohio reservoirs, larval gizzard shad Dorosoma cepedianum less than 30 mm total length consume only zooplankton but frequently switch to detritus as they grow longer than 30 mm. However, in laboratory studies without detritus, gizzard shad longer than 30 mm consume crustacean zooplankton. To explore the composition of diets of omnivorous 30-100-mm gizzard shad, we completed 1-h laboratory feeding trials with different amounts of zooplankton and detritus and quantified the diets of gizzard shad in reservoirs. In both laboratory and field, gizzard shad ate primarily detritus but also ate zooplankton, consuming more as more became available, which demonstrates that this species is a facultative detritivore. In the field, zooplankton consumption declined as gizzard shad body size increased. We believe gizzard shad maximize growth by supplementing their low-protein detritus diet with more zooplankton as more becomes available. With this strategy, omnivorous gizzard shad may compromise the potential for food web manipulations based on the trophic cascade hypothesis in Ohio reservoirs.
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    Food Consumption by Larval Gizzard Shad: Zooplankton Effects and Implications for Reservoir Communities
    (1992) Dettmers, John M.; Stein, Roy A.
    Because peak abundance of larval gizzard shad Dorosoma cepedianum occurs simultaneously with the midsummer decline of macrozooplankton in Ohio reservoirs, we hypothesized that zooplanktivory by larval gizzard shad caused this decline. To test this hypothesis, we compared larval food consumption with zooplankton productivity in two reservoirs. Larval gizzard shad began to influence zooplankton production in a reservoir with high zooplankton productivity (exceeding 125 mg.m^3.d^-1) only after peak zooplankton biomass occurred, even at high larval densities (38 shad.m^-3). However, consumption by early juvenile (25-30-mm) gizzard shad severely reduced zooplankton in this reservoir. Conversely, relatively low densities of larval gizzard shad (3-7 shad.m^-3) had variable effects on zooplankton in a reservoir with low zooplankton productivity (at most 4 mg.m^-3.d^-1). Depending on larval gizzard shad density and zooplankton production, larval gizzard shad alone or in conjunction with early juveniles may control zooplankton assemblages, increasing competition for limited resources at a time when zooplankton are critical to sport-fish recruitment
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    Androgenesis and Homozygous Gynogenesis in Muskellunge (Esox masquinongy): Evaluation Using Flow Cytometry
    (1998) Lin, Feng; Dabrowski, Konrad
    The purpose of this work was to study the effects of ultraviolet (UV) irradiation on denucleation of eggs and investigate the heat-shock conditions for diploidization for induction of androgenesis in muskellunge, Esox masquinongy. Several egg incubation media, including saline, Ringer’s solution, and Ringer’s solution supplemented with bovine serum albumin (BSA), were found suitable to maintain the egg fertility as high as in muskellunge ovarian fluid. The optimal doses of UV radiation were 660-1320 J/m^2, at which 100% haploid larvae were produced at a hatching rate of 22.5 ± 2.8%. UV irradiation at low doses (165-330 J/m^2) generated abnormal larvae, which were morphologically identical to haploids. Using a flow cytometry method, it was found that cellular DNA content of these larvae was close to that of diploids but significantly lower in value and had a wider distribution (expressed as coefficient of variation) than that of control fish. This suggested that a low dose of UV irradiation might cause gene mutations, alteration of chromosomal conformation and fragmentation, but did not prevent maternal DNA from participating in mitotic division. Interference of maternal DNA residues could be another reason for the poor viability of androgenetic fish. A high dose of UV radiation (1980 J/m^2) caused development of severely deformed embryos, indicating that UV radiation also damaged molecules in the eggs other than the denucleation. Our results suggest that classic color and allozyme markers might not be sufficient to prove a complete androgenesis. In order to optimize time and duration of shock for induced diploidization, we investigated the heat-shock conditions for inhibiting the first mitotic cleavage through induction of homozygous gynogenesis. We found that heat-shock treatment at 31 °C for 9 min starting at 1.4 τ0 (a dimensionless factor describing progress in embryo development) after fertilization produced the highest percentage of diploids at hatching.
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    Foraging in a patchy environment: prey-encounter rate and residence time distributions
    (1989) Marschall, Elizabeth A.; Chesson, Peter L.; Stein, Roy A.
    Small bluegill sunfish, Lepomis macrochirus, foraging among patches in the laboratory did not search systematically within a patch; their intercapture intervals did not differ from a model of random prey encounter within a patch. Patch-residence time, number of prey eaten, and giving-up time (time between last prey capture and leaving the patch) were measured for bluegills foraging in two different three-patch 'environments' (a constant environment, in which each patch began with the same number of prey and a variable environment, in which two patches began with low prey density and one patch with high prey density). When compared with three decision rules a forager may use to determine when to leave a patch, the data most closely agreed with predictions from a 'constant residence time' rule. Bluegills responded to changes in the distribution of prey among patches, but not by using different decision rules. There was qualitative, but not quantitative, agreement with a model of random residence times. The total number of prey eaten by a bluegill during a foraging bout was similar to the number predicted from a model of random search and random residence times.
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    Prey Selection by Larval Fishes as Influenced by Available Zooplankton and Gape Limitation
    (1998) DeVries, Dennis R.; Bremigan, Mary T.; Stein, Roy A.
    Feeding success during the first weeks of life is critical to determining survival and ultimate year-class strength of fishes. To compare the relative influence of gape limitation and available zooplankton on prey size selection among the larvae of three species of freshwater fishes, we gathered data on fish gape size, prey size, and size-specific prey selection in lakes and reservoirs. These variables were compared among black crappies Pomoxis nigromaculatus from a lake that contained large zooplankton as prey and white crappies P. annularis and gizzard shad Dorosoma cepedianum (a potential competitor of white crappie) from reservoirs that contained small zooplankton. In three Ohio reservoirs (i.e., small-zooplankton systems), available zooplankton and larval stages of white crappies and gizzard shad were collected once per week during April through September 1987 and 1988. Although mean prey size of white crappies continued to increase with fish size, mean prey size of smaller-gaped gizzard shad did not. However, as documented for black crappies in north-temperate lakes, white crappies in reservoirs continued to consume prey that were smaller than other available prey, even when they were no longer gape limited. Thus, although the potential for gape limitation differed between large- and small-zooplankton assemblages, prey selection did not differ as expected. Given between-species prey size selection, gizzard shad (that prefer small zooplankton) should be relatively more successful in reservoirs with small zooplankton, whereas white and black crappies (that prefer large zooplankton) should have better success in lakes with large zooplankton.
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    Use of Erythrocyte Measurements to Identify Triploid Saugeyes
    (1999) Garcia-Abiado, Mary Ann; Dabrowski, Konrad; Christensen, James E.; Czesny, Sergiusz; Bajer, Przemyslaw
    The use of erythrocyte size measurements as a possible alternative to flow cytometry for identifying triploid saugeyes (female walleye Stizostedion vitreum X male sauger S. canadense) was evaluated. Blood smear preparations were made from 32 heat-shocked saugeyes (1.0-42.7 g; 52-185 mm total length), which consisted of 12 diploids and 20 triploids, as determined by flow cytometry after blood cells were stained with propidium iodide. The length, width, surface area, and volume of the cell and nucleus of 100 erythrocytes were determined for each fish. The cell and nuclear dimensions were measured at 1,000X magnification with a calibrated ocular micrometer. Discriminant analysis was used to distinguish diploids and triploids based on their score profiles. Results showed that triploid saugeyes had significantly larger erythrocyte cell and nucleus measurements than their diploid counterparts (N = 32; P < 0.0001). Erythrocyte measurements correctly distinguished 93.8% of fish samples as diploids or triploids, but measurements require about 1 h/fish. The potential applications of this technique for fisheries management and aquaculture are discussed.
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    Complex predator-prey interactions and predator intimidation among crayfish, piscivorous fish, and small benthic fish
    (1988) Rahel, Frank J.; Stein, Roy A.
    Predator-prey interactions were studied among a small prey fish (the johnny darter Etheostoma nigrum) and two predators (crayfish Orconectes rusticus and small-mouth bass Micropterus dolomieui) with complementary foraging behaviors. When only smallmouth bass were present, darters reduced activity to 6% of control rates and spent most of the time hiding under tile shelters. When only crayfish were present, darter activity and shelter-use were similar to controls. When both crayfish and bass were present, an interaction occurred. Darters, normally inactive in the presence of bass, were often forced to move by approaching crayfish and thus activity increased to 19% of control rates. Also, darters were often evicted from shelters by intruding crayfish. Thus, crayfish increased the vulnerability of small fish to bass by evicting them from shelters and causing increased activity. Conversely, bass increased the vulnerability of small fish to crayfish by forcing these fish to seek cover under shelters occupied by crayfish. Intimidation effects of bass on darters last for some time. After a 30-min exposure to bass, darters showed reduced activity and increased shelter use lasting at least 24 h after the bass was removed. Thus predators, through intimidation, can influence prey behavior even though the predators are no longer present.
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    Predicting Crappie Recruitment in Ohio Reservoirs with Spawning Stock Size, Larval Density, and Chlorophyll Concentrations
    (2006) Bunnell, David B.; Hale, R. Scott; Vanni, Michael J.; Stein, Roy A.
    Stock-recruit models typically use only spawning stock size as a predictor of recruitment to a fishery. In this paper, however, we used spawning stock size as well as larval density and key environmental variables to predict recruitment of white crappies Pomoxis annularis and black crappies P. nigromaculatus, a genus notorious for variable recruitment. We sampled adults and recruits from 11 Ohio reservoirs and larvae from 9 reservoirs during 1998-2001. We sampled chlorophyll as an index of reservoir productivity and obtained daily estimates of water elevation to determine the impact of hydrology on recruitment. Akaike's information criterion (AIC) revealed that Ricker and Beverton-Holt stock-recruit models that included chlorophyll best explained the variation in larval density and age-2 recruits. Specifically, spawning stock catch per effort (CPE) and chlorophyll explained 63-64% of the variation in larval density. In turn, larval density and chlorophyll explained 43-49% of the variation in age-2 recruit CPE. Finally, spawning stock CPE and chlorophyll were the best predictors of recruit CPE (i.e., 74-86%). Although larval density and recruitment increased with chlorophyll, neither was related to seasonal water elevation. Also, the AIC generally did not distinguish between Ricker and Beverton-Holt models. From these relationships, we concluded that crappie recruitment can be limited by spawning stock CPE and larval production when spawning stock sizes are low (i.e., CPE , 5 crappies/net-night). At higher levels of spawning stock sizes, spawning stock CPE and recruitment were less clearly related. To predict recruitment in Ohio reservoirs, managers should assess spawning stock CPE with trap nets and estimate chlorophyll concentrations. To increase crappie recruitment in reservoirs where recruitment is consistently poor, managers should use regulations to increase spawning stock size, which, in turn, should increase larval production and recruits to the fishery.
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    Escape tactics used by bluegills and fathead minnows to avoid predation by tiger muskellunge
    (1983) Moody, Robert C.; Helland, John M.; Stein, Roy A.
    To explain why esocids prefer cylindrical, soft-rayed prey over compressed, spiny-rayed prey, we quantified behavioral interaction between tiger muskellunge (F1 hybrid of male northern pike Esox lucius and female muskellunge E. masquinongy) and fathead minnows (Pimephales promelas) and bluegills (Lepomis macrochirus). Tiger muskellunge required four times as many strikes and longer pursuits to capture bluegills than fathead minnows. Tiger muskellunge attacked each prey species differently; fathead minnows were grasped at midbody and bluegills were attacked in the caudal area. Each prey species exhibited different escape tactics. Fathead minnows remained in open water and consistently schooled; bluegills dispersed throughout the tank and sought cover by moving to corners and edges. Due to their antipredatory behavior (dispersing, cover seeking, and remaining motionless) and morphology (deep body and spines), bluegills were less susceptible to capture by tiger muskellunge than were fathead minnows.