bluuebunny/crossref_metadata_2025 huggingface dataset:
Global Gene Expression as a Function of the Iron Status of the Bacterial Cell: Influence of Differentially Expressed Genes in the Virulence of the Human Pathogen
Vibrio vulnificus
Authors: Alice Alejandro F. , Naka Hiroaki , Crosa Jorge H.
Published: June 2008

Vibrio vulnificus
multiplies rapidly in host tissues under iron-overloaded conditions. To understand the effects of iron in the physiology of this pathogen, we performed a genome-wide transcriptional analysis of
V. vulnificus
growing at three different iron concentrations, i.e., iron-limiting [Trypticase soy broth with 1.5% NaCl (TSBS) plus ethylenediamine-di-(
o
-hydroxyphenylacetic) acid (EDDA)], low-iron (1 μg Fe/ml; TSBS), and iron-rich (38 μg Fe/ml; TSBS plus ferric ammonium citrate) concentrations. A few genes were upregulated under the last two conditions, while several genes were expressed differentially under only one of them. A gene upregulated under both conditions encodes the outer membrane porin, OmpH, while others are related to the biosynthesis of amino sugars. An
ompH
mutant showed sensitivity to sodium dodecyl sulfate (SDS) and polymyxin B and also had a reduced competitive index compared with the wild type in the iron-overloaded mice. Under iron-limiting conditions, two of the TonB systems involved in vulnibactin transport were induced. These genes were essential for virulence in the iron-overloaded mice inoculated subcutaneously, underscoring the importance of active iron transport in infection, even under the high-iron conditions of this animal model. Furthermore, we demonstrated that a RyhB homologue is also essential for virulence in the iron-overloaded mouse. This novel information on the role of genes induced under iron limitation in the iron-overloaded mouse model and the finding of new genes with putative roles in virulence that are expressed only under iron-rich conditions shed light on the many strategies used by this pathogen to multiply rapidly in the susceptible host.
Comparison of the Susceptibilities of C57BL/6 and A/J Mouse Strains toStreptococcus suisSerotype 2 Infection
Authors: Domínguez-Punaro María de la Cruz , Segura Mariela , Radzioch Danuta , Rivest Serge , Gottschalk Marcelo
Published: June 2008

Streptococcus suisis an important swine and human pathogen. Assessment of susceptibility toS. suisusing animal models has been limited to monitoring mortality rates. We recently developed a hematogenous model ofS. suisinfection in adult CD1 outbred mice to study the in vivo development of an early septic shock-like syndrome that leads to death and a late phase that clearly induces central nervous system damage, including meningitis. In the present study, we compared the severities of septic shock-like syndrome caused byS. suisbetween adult C57BL/6J (B6) and A/J inbred mice. Clinical parameters, proinflammatory mediators, and bacterial clearance were measured to dissect potential immune factors associated with genetic susceptibility toS. suisinfection. Results showed that A/J mice were significantly more susceptible than B6 mice toS. suisinfection, especially during the acute septic phase of infection (100% of A/J and 16% of B6 mice died before 24 h postinfection). The greater susceptibility of A/J mice was associated with an exaggerated inflammatory response, as indicated by their higher production of tumor necrosis factor alpha, interleukin-12p40/p70 (IL-12p40/p70), gamma interferon, and IL-1β, but not with different bacterial loads in the blood. In addition, IL-10 was shown to be responsible, at least in part, for the higher survival in B6 mice. Our findings demonstrate that A/J mice are very susceptible toS. suisinfection and provide evidence that the balance between pro- and anti-inflammatory mediators is crucial for host survival during the septic phase.
Essential Role of the Response Regulator Rrp2 in the Infectious Cycle of
Borrelia burgdorferi
Authors: Boardman Bethany K. , He Ming , Ouyang Zhiming , Xu Haijun , Pang Xiujuan , Yang X. Frank
Published: June 2008

Alteration of surface lipoprotein profiles is a key strategy that the Lyme disease pathogen,
Borrelia burgdorferi
, has evolved to be maintained within its enzootic cycle between arthropods and mammals. Accumulated evidence indicates that the central regulatory pathway controlling differential gene expression by
B. burgdorferi
is the RpoN-RpoS pathway (the σ
54
-σ
S
sigma factor cascade). It was previously shown that activation of the RpoN-RpoS pathway is controlled by Rrp2, a two-component response regulator and σ
54
-dependent transcriptional activator. The role of Rrp2 in the infectious cycle of
B. burgdorferi
has not been determined heretofore. In this report, we demonstrate that an
rrp2
mutant defective in activating σ
54
-dependent transcription was unable to establish infection in mice, but the
rrp2
mutant was capable of surviving within ticks during and after tick feeding. Because the
rrp2
mutant was defective in the production of OspC, an outer surface lipoprotein essential for mammalian host infection, we further examined whether the loss of infectivity of the
rrp2
mutant was solely due to the inability to produce OspC. While transformation with a shuttle vector carrying
ospC
under the control of a constitutive
flaB
promoter restored infection to an
ospC
mutant in immunodeficient SCID mice, it could not rescue the avirulent phenotype of the
rrp2
mutant. These data indicate that, in addition to controlling OspC, Rrp2 controls another factor(s) essential for
B. burgdorferi
to establish infection in mammals. Furthermore, microarray analyses revealed that 125 and 19 genes were positively and negatively regulated, respectively, by Rrp2, which provides a foundation for future identification of additional Rrp2-dependent virulence determinants in
B. burgdorferi
.
The Resistance of BALB/cJ Mice toYersinia pestisMaps to the Major Histocompatibility Complex of Chromosome 17
Authors: Turner Joshua K. , McAllister Milton M. , Xu John L. , Tapping Richard I.
Published: June 2008

Yersinia pestis, the causative agent of plague, has been well studied at the molecular and genetic levels, but little is known about the role that host genes play in combating this highly lethal pathogen. We challenged several inbred strains of mice withY. pestisand found that BALB/cJ mice are highly resistant compared to susceptible strains such as C57BL/6J. This resistance was observed only in BALB/cJ mice and not in other BALB/c substrains. Compared to C57BL/6J mice, the BALB/cJ strain exhibited reduced bacterial burden in the spleen and liver early after infection as well as lower levels of serum interleukin-6. These differences were evident 24 h postinfection and became more pronounced with time. Although a significant influx of neutrophils in the spleen and liver was exhibited in both strains, occlusive fibrinous thrombi resulting in necrosis of the surrounding tissue was observed only in C57BL/6J mice. In an effort to identify the gene(s) responsible for resistance, we measured total splenic bacteria in 95 F2mice 48 h postinfection and performed quantitative trait locus mapping using 58 microsatellite markers spaced throughout the genome. This analysis revealed a single nonrecessive plague resistance locus, designatedprl1(plagueresistancelocus1), which coincides with the major histocompatibility complex of chromosome 17. A second screen of 95 backcrossed mice verified that this locus confers resistance toY. pestisearly in infection. Finally, eighth generation backcrossed mice harboringprl1were found to maintain resistance in the susceptible C57BL/6J background. These results identify a novel genetic locus in BALB/cJ mice that confers resistance toY. pestis.
Diverse Myeloid and Lymphoid Cell Subpopulations Produce Gamma Interferon during Early Innate Immune Responses toFrancisella tularensisLive Vaccine Strain
Authors: De Pascalis Roberto , Taylor Betsy C. , Elkins Karen L.
Published: June 2008

Francisella tularensis, a small gram-negative intracellular bacterium responsible for causing tularemia, is highly pathogenic and classified as a category A agent of bioterrorism. As for other intracellular pathogens, successful protective immune responses toFrancisella tularensisrequire rapid and efficient induction of gamma interferon (IFN-γ) production. Studies using intracellular bacteria such asListeria monocytogenesas well asFrancisellasuggest that natural killer (NK) and T cells are important sources of IFN-γ. However, comprehensive characterization of specific sources of IFN-γ produced duringFrancisellainfection in vivo remains incomplete, and depletion of NK cells before infection of mice with theF. tularensislive vaccine strain (LVS) has little impact on the course or outcome of infection. In this study, we determined the cell subpopulations that respond quickly to intradermalF. tularensisLVS infection of mice by producing IFN-γ within hours to a few days. Splenic and liver lymphocytes were obtained from LVS-infected mice and analyzed for IFN-γ mRNA by reverse transcription-PCR, for intracellular cytokine expression by multiparameter flow cytometry, and for ex vivo production of IFN-γ protein by enzyme-linked immunosorbent assay. Cells producing IFN-γ were readily detectable by day 3 after infection, and numbers progressively increased through days 5 to 7. Importantly, the cell types responsible for IFN-γ production were much more varied than expected: these included not only NK cells and T cells, which might be predicted, but also other cells, including dendritic cells (DCs), “NK DCs,” NK T cells, and neutrophils. Most importantly, since RAG-1 knockout mice appeared to exhibit a frequency of IFN-γ-producing cells comparable to that of intact wild-type mice, early IFN-γ production by innate immune cells does not depend on the presence of T or B cells.
Tick-Borne Transmission of Two Genetically DistinctAnaplasma marginaleStrains following Superinfection of the Mammalian Reservoir Host
Authors: Leverich Christina K. , Palmer Guy H. , Knowles Donald P. , Brayton Kelly A.
Published: June 2008

Strain superinfection affects the dynamics of epidemiological spread of pathogens through a host population. Superinfection has recently been shown to occur for two genetically distinct strains of the tick-borne pathogenAnaplasma marginalethat encode distinctly different surface protein variants. Superinfected animals could serve as a reservoir for onward transmission of both strains if the tick vector is capable of acquiring and transmitting both strains. Whether competition among strains during development within the tick vector, which requires sequential invasion and replication events, limits colonization and subsequent transmission to a single strain is unknown. We tested this possibility by acquisition feedingDermacentor andersoniticks on a reservoir host superinfected with the genetically distinct St. Maries and EMΦ strains. Although the St. Maries strain consistently maintained higher bacteremia levels in the mammalian host and the EMΦ strain had an early advantage in colonization of the tick salivary glands, individual ticks were coinfected, and there was successful transmission of both strains. These results indicate that a genetically distinctA. marginalestrain capable of superinfecting the mammalian host can subsequently be cotransmitted and become established within the host population despite the presence of an existing established strain.
Variability of Particulate Matter in a Small Coastal Inlet
Authors: Kranck Kate
Published: June 2008

Total suspended particulate matter concentration and grain size spectra, total and living particulate carbon, and dissolved nitrogen and carbon were measured at stations along the length of Petpeswick Inlet and over several tidal cycles. Distinct particle populations were associated with the water at the head and at the mouth of the inlet. Mixing of water masses and temporal periodicities cause variance in particle concentration and spectral shape which correspond to seasonal, tidal, and seiche variations. To explain the last, a process of transformation of organic matter between dissolved and particulate states by aggregate formation and breakup in response to turbulent changes is proposed.Key words: Petpeswick Inlet, Nova Scotia, particulates
Ambient Oxygen Tension and Transition to Anaerobic Metabolism in Three Species of Freshwater Fish
Authors: Burton Dennis T. , Heath Alan G.
Published: June 2008

Rainbow trout (Salmo gairdneri), bluegill (Lepomis macrochirus), and brown bullhead (Ictalurus nebulosus) were exposed to a gradual (over several hours) reduction in dissolved oxygen. Muscle and liver lactic and pyruvic acid concentrations were measured at seven environmental [Formula: see text]. The response was an increase in anaerobic metabolism of the resting fish at a threshold [Formula: see text] that varied with the species and acclimation temperature. A lower anaerobic threshold occurred after acclimation to cold in rainbow trout and possibly bluegill; cold acclimated brown bullhead did not metabolize anaerobically when held in water for 20 min with an oxygen tension near zero. The anaerobic thresholds correspond reasonably well to the relative positions of the blood oxygen dissociation curves for the three species. Only in the trout, however, does the anaerobic threshold found in this study compare to the critical oxygen tension (PC; [Formula: see text] below which aerobic metabolism becomes dependent on [Formula: see text] in the water). PC is far higher in both the bluegill and brown bullhead than the anaerobic threshold which suggests a reduction in overall energy expenditure in these species at rest when in water of low dissolved oxygen.Key words: anaerobic metabolism, lactate/pyruvate ratios, muscle, liver, rainbow trout, Salmo gairdneri; bluegill, Lepomis macrochirus; brown bullhead, Ictalurus nebulosus
An Evaluation of Gulland's Method for Fitting the Schaefer Model
Authors: Roff D. A. , Fairbairn D. J.
Published: June 2008

Gulland's method for fitting the Schaefer model is examined using data from 19 groundfish stocks. The relationship between catch per unit effort and averaged effort may arise from statistical artifacts due to the method itself or from the way the fisheries develop. The prevalence of these artifacts in the actual data suggest that this method cannot be statistically justified.Key words: catch/effort data, surplus production model, Schaefer model
Use of Biochemical Genetic Variants for Identification of Sockeye Salmon (Oncorhynchus nerka) Stocks in Cook Inlet, Alaska
Authors: Grant W. S. , Milner G. B. , Krasnowski P. , Utter F. M.
Published: June 2008

We used the geographic distributions of biochemical genetic variants in sockeye salmon (Oncorhynchus nerka) to describe features of its population structure and to identify stocks in commercial catches from the central fishing district of Cook Inlet, Alaska. Allelic frequencies for 6 polymorphic loci were determined for samples of 13 spawning areas using starch gel electrophoresis and were used as the basis of stock classification. The level of genetic variation, estimated by average heterozygosity, was 4.6%. Likelihood ratio tests for heterogeneity among allelic frequencies indicated a significant degree of heterogeneity among spawning areas within the Susitna and Kenai rivers, but not among the spawning areas within the Kasilof River. These tests also indicated that for the Kasilof River, where multi-year samples were taken, allelic frequencies were not significantly different for two consecutive years. Cluster analysis of genetic similarities between samples indicated that the samples from the Kasilof River were distinct from samples of the Kenai and Susitna rivers, but that Kenai and Susitna River samples were not distinct from one another. Maximum likelihood estimates of the stock composition of samples collected from the set- and drift-gillnet fisheries were made on a weekly basis during the commercial fishing season. These estimates indicated that Susitna River fish predominated in the 1976 run into Cook Inlet.Key words: sockeye salmon, Oncorhynchus nerka; stock identification, biochemical genetic variation, population genetics, Cook Inlet, electrophoresis
Measurement of Oxidation in Fish Oil and its Effect on Vitamin E Nutrition of Rainbow Trout (Salmo gairdneri)
Authors: Hung S. S. O. , Cho C. Y. , Slinger S. J.
Published: June 2008

Peroxide value (PV), anisidine value, and thiobarbituric acid (TBA) number were compared as methods for measuring oxidation in fish oils and fish diets. PV was the method of choice for estimating oxidation in the oil. Methods for measuring moderately oxidized oil after being mixed in the diets are discussed. Analyses of dietary samples revealed that the TBA numbers and percentages of polyunsaturated fatty acids were not greatly altered by the addition of moderately oxidized fish oil and by the long-term storage (24 wk) of the diet at room temperature. However, endogenous α-tocopherol levels in the diet were significantly (P < 0.05) reduced by both the addition of moderately oxidized oil and by 24-wk storage. The level of supplemental DL-α-tocopheryl acetate was not changed by the treatments. Fish fed the experimental diets showed no significant differences in body weight gain, feed/gain ratio, mortality, carcass composition, hematocrit, or plasma glutathione peroxidase activity. However, the α-tocopherol concentration in their livers was significantly (P < 0.05) increased by raising the levels of supplementary DL-α-tocopheryl acetate.Key words: oxidized oil, vitamin E, diet stability, Salmo gairdneri
Energy Dynamics of the Eutrophic Chironomid Chironomus plumosus f. semireductus from the Bay of Quinte, Lake Ontario
Authors: Johannsson Ora E.
Published: June 2008

Relationships between feeding rate, temperature, body size, and time of day were investigated and collated with seasonal assimilation efficiencies of in situ chironomids to construct a picture of chironomid energetics over the year. Temperature controlled feeding rate, and larval size and time of day exerted no effect. The temperature optimum plateaued between 22.0 and 24.5 °C, decreasing logarithmically outside this range. Both assimilation efficiency (AE) and organic content of the food varied seasonally, but were not correlated. Periods of high AE corresponded with the latter part of Melosira or Melosira–Stephanodiscus blooms, while periods of low AE occurred between diatom blooms and during the late summer blue-green bloom. Consequently, growth fluctuated throughout the year, being a result of the interaction of temperature and AE. Anabolic processes dominated at AE greater than 3.5%. Maximum net growth efficiency (NGE) was attained when AE ≥ 6% and temperature ≥ 15 °C. NGE was more sensitive to changes in AE than temperature. Instantaneous growth rate, however, was more sensitive to changes in temperature. Daily ingestion (mg) exceeded body weight by as much as 460–480%, which equals the sediment-processing capacity of freshwater detritivores.Key words: chironomid, feeding rate, assimilation efficiency, instantaneous growth rate, net growth efficiency, algal community, Bay of Quinte
Least Squares Regression Estimates of the Schaefer Production Model: Some Monte Carlo Simulation Results
Authors: Uhler Russell S.
Published: June 2008

Both analytical methods and Monte Carlo experiments are used to determine the amount of bias in the regression estimates of the Schaefer model when it is estimated with catch and effort data. It is shown that the use of the catch–effort ratio and effort as regressors leads to the classical errors in variables problem which produces asymptotically biased parameter estimates. Since the seriousness of the bias, and even its direction in the case of certain formulations of the model, cannot be determined by analytical methods, Monte Carlo simulation experiments were used. Four variations of the Schaefer model were investigated; two of which come from a discrete formulation of the model and two of which come from a continuous formulation. The least squares regression estimates of all formulations result in substantial bias although one formulation is considerably better than the others.Bias in the optimal levels of the population size, the harvest rate, and fishing effort are also calculated. It is found that under likely conditions regarding the model equation errors that the optimal population size and harvest rate may be as much as 40–50% in error depending on the model used. In general, however, the bias in these quantities is much smaller than the bias in the parameter estimates themselves.Key words: Schaefer model, Monte Carlo, optimal fishery management, errors in variables, biased estimates
Interactive Effects of Metals in Mixtures on Biomass Production Kinetics of Freshwater Copepods
Authors: Borgmann Uwe
Published: June 2008

The effect of metal mixtures on the biomass production rates of natural assemblages of copepods was predicted by assuming that metal-induced increases in the inverse of the growth rate (i.e. the growth time) are additive. The average observed growth time increase, ΔGTobs in 14 binary mixtures of the metals Cd, Cu, Hg, Pb, Zn, and As was 17% larger than the average calculated growth time increases, ΔGTcal (assuming additivity), indicating a slight but statistically significant synergism. Synergism in multimetal mixtures appears to be cumulative, since the average ΔGTobs was 53% greater than the average ΔGTcal in mixtures containing five metals simultaneously. One of the 15 possible binary mixtures (Zn:As) of the six metals tested demonstrated a large divergence between ΔGTobs and ΔGTcal. For all other metal mixtures studied, most of the toxicity is accounted for by the summation of noninteractive, single, metal effects.Key words: copepods, metal toxicity, metal interactions, biomass production, cadmium, copper, mercury, lead, zinc, arsenic
Organic Flocculation and Hydroextraction: Two New Methods for Phytoplankton Concentration from Lakes
Authors: Bitton Gabriel , Beaver John R. , Farrah Samuel R.
Published: June 2008

The organic flocculation method was about as effective as the hydroextraction method, recovering 71–96% and 88–94%, respectively, of algal cells from lakes. Chlorophyll recovery-was, however, less efficient, ranging from 42 to 56%. Both methods are simple and inexpensive and can be conducted under field conditions.Key words: phytoplankton, hydroextraction, organic flocculation
Estimating Stock Composition in Mixed Stock Fisheries Using Morphometric, Meristic, and Electrophoretic Characteristics
Authors: Fournier D. A. , Beacham T. D. , Riddell B. E. , Busack C. A.
Published: June 2008

We describe a conditional maximum likelihood procedure for estimating stock composition in a mixed-stock fishery, provided that samples can be collected from the contributing stocks in isolation from each other and that characters exist that differ significantly between stocks. The procedure presented can use discrete (electrophoretic, meristic) or continuous (morphometric) data or any combination of these data. The procedure is tested by simulations and is used to estimate stock compositions of chum salmon (Oncorhynchus keta) sampled in a test fishery near Vancouver Island, B.C., in 1981. The estimated composition in the test fishery agreed closely with the results of previous tagging studies in the same area.
Periodicity of Egg Laying and Egg Age Distributions in Planktonic Cladocera
Authors: Tessier Alan J.
Published: June 2008

In natural populations of planktonic Cladocera, I observed significant diel, molt cycle, and cohort periodicity of egg laying. Diel cycles of egg laying were pronounced in one population of Daphnia galeata mendotae; most females laid eggs only at dawn. There was a strongly negative correlation between diel egg laying cycles of coexisting Daphnia species. Egg laying in two Daphnia populations cycled with a period approximating the egg development times, suggesting a synchronization of individual molt cycles. Noncontiguous reproduction was characteristic of a population of Holopedium gibberum. Adults reproduced synchronously and then died; there was little overlap of generations.
An Evaluation of Morphometrics and Meristics for Stock Separation of Pacific Herring (Clupea harengus pallasi)
Authors: Meng Hans Jürg , Stocker Max
Published: June 2008

We conducted an analysis to determine if Pacific herring (Clupea harengus pallasi) stocks occurring in different localities in British Columbia waters could be separated using morphometric and meristic characters. Discriminant function analysis was applied to morphometric and meristic characters taken from food herring samples. Herring found in northern British Columbia waters were detectably different from those found in the Strait of Georgia. We recommend using meristic characters for separation on a broad geographic scale and using "best" morphometric characters for finer resolution within the established broader groups. We defined a set of 12 best morphometric characters for further large-scale studies.
Empirical Prediction of Crustacean Zooplankton Biomass and Profundal Macrobenthos Biomass in Lakes
Authors: Hanson John Mark , Peters Robert Henry
Published: June 2008

We used data taken from the literature to develop and compare several estimators of crustacean zooplankton biomass (49 lakes) and profundal macrobenthos biomass (38 lakes). Both mean zooplankton biomass (r2 = 0.72, P < 0.001) and mean profundal macrobenthos biomass (r2 = 0.48, P < 0.001) correlated better with mean total phosphorus concentration than with Secchi depth, mean depth, maximum depth, or lake surface area. Mean total phosphorus concentration was also superior to mean chlorophyll a concentration (r2 = 0.57, P < 0.001) as an estimator of zooplankton biomass, but data were insufficient to evaluate chlorophyll a concentration as an estimator of macrobenthos biomass. Inclusion of maximum depth as a variable in a multiple regression resulted in a slight but significant (P < 0.030) improvement in the zooplankton–total phosphorus relationship (R2 = 0.75, P < 0.001). Inclusion of lake surface area as a variable in a multiple regression significantly (P < 0.001) improved the predictive power of the profundal macrobenthos–total phosphorus relationship (R2 = 0.59, P < 0.001).
Optimal versus Unregulated Industry Behavior in a Beverton–Holt Multicohort Fishery Model
Authors: Stollery K.
Published: June 2008

Canadian government policy toward fisheries in recent years has shifted emphasis from maximizing the sustainable catch level toward maximizing economic yield taking account of fishing costs and revenues. I have provided a model for the determination of the optimal catch rate and mesh size for maximum economic yield in a Beverton–Holt model employing many age cohorts. The optimal effort and mesh size are compared with those predicted for an unregulated fishery. While the analysis is mainly limited to steady state, an attempt is also made to determine the optimal disequilibrium response to environmentally caused exogenous changes in recruitment.
Analysis of Echo Counting Data: A Model
Authors: Kieser R. , Mulligan T. J.
Published: June 2008

Echo counting is a standard tool for the estimation of fish density and hence population. Density estimates are readily obtained using an uncalibrated, stable echo sounder with accurate time-varied gain. We extended a standard nonstochastic echo pulse counting model to include the analysis of single fish echo traces as they are obtained from the sounder chart recorder. The trace counting analysis depends strongly on the overlap in the insonified volumes between successive sounder transmissions. An equation for the nonoverlapping volume is given in terms of range, distance between transmissions, and effective beam angles. The near and far range limits of the model are given and the errors associated with the commonly used approximations to the correct model are shown. A generalization of the model considers the analysis of data from a tilted transducer. A sensitivity analysis gives a qualitative indication of the model's performance for echoes from fish with a realistic target strength distribution. Single fish echo returns are analyzed by the echo pulse and trace counting methods to illustrate the model.
Prediction of Chlorophyll a Concentrations in Florida Lakes: Importance of Aquatic Macrophytes
Authors: Canfield Jr. Daniel E. , Shireman Jerome V. , Colle Douglas E. , Haller William T. , Watkins II Curtis E. , Maceina Michael J.
Published: June 2008

Chlorophyll a concentrations in Lake Pearl, Florida, increased as the percentage of the lake's total volume infested with aquatic macrophytes decreased. Using data from 32 Florida lakes having a wide range of limnological characteristics, we demonstrated that predictions of chlorophyll a concentrations could be improved by including a term for the percentage of the lake's total volume infested with macrophytes in existing nutrient–chlorophyll models. Our best-fit multivariate regression equation was[Formula: see text]where CHLA is the chlorophyll a concentration (milligrams per cubic metre), TN is the total nitrogen concentration (milligrams per cubic metre), TP is the total phosphorus concentration (milligrams per cubic metre), and PVI is the percentage of the lake's total volume infested with macrophytes. By use of this equation, we assessed the potential effect of aquatic macrophytes on chlorophyll yields and Secchi disc transparencies in lakes of different trophic status.
Small-Scale Covariability in the Abundance of Fish Larvae and Their Prey
Authors: Fortier L. , Leggett W. C.
Published: June 2008

We studied the covariability in the abundance of larval fish and rnicrozooplankton at a fixed station of the St. Lawrence upper estuary. Hourly sampling during 129 h combined with net and tidal circulations allowed us to resolve spatial scales of approximately 2 km to several tens of kilometres. Low-frequency fluctuations in the abundance of larval capelin (Mallotus villosus) and larval Atlantic herring (Clupea harengus harengus) reflected the advection past the station of successive cohorts. Large-scale horizontal gradients in abundance and length were apparently formed at the emergence of the larvae from the spawning beds. The majority of capelin larvae we sampled had not yet completely exhausted their yolk reserves. There was no indication that differential mortality or active swimming had produced a concordance between the distribution of this species and the distribution of microzooplankton. Herring larvae resorbed their yolk sac and began mandatory exogenous feeding during the period of sampling. Tidal and subtidal patterns of variation in the abundance of this species and microzooplankton became significantly coherent after the resorption of the vitelline reserves. The possible mechanisms giving rise to coherence at these two different scales are considered in light of published information on the feeding behavior and swimming capacity of herring larvae.
Crab Response to Prey Density Can Result in Density-Dependent Mortality of Clams
Authors: Boulding E. G. , Hay T. K.
Published: June 2008

Field experiments involving recovery of marked clams showed that even adult native littleneck clams (Protothaca staminea) could suffer high mortality to cancrid crabs. The mortality rate increased with clam density, suggesting that these crabs preferentially forage in areas of higher prey density. Acoustic telemetry showed that at least one of the crabs, Cancer productus, is sufficiently mobile to search large areas while foraging. This is important for understanding the effects that these large, mobile predators have on the distribution and the abundance of their prey and may explain the high incidence of crab predation seen in mariculture operations where the density of clams is artificially raised.
Opportunistic Cyclopoid Prédation on Fish Larvae
Authors: Hartig John H. , Jude David J.
Published: June 2008

Exceptional spring spawning of yellow perch (Perca flavescens) in an inland coastal lake resulted in very high larval fish densities (up to 41 900/1000 m3) and facultative predation by adult female Diacyclops thomasi on newly hatched larvae (maximum predation density: 8740/1000 m3), as evidenced by cyclopoid attachment to fish larvae in field collections. This predation suggests that larval fish mortality and possibly cyclopoid population growth are affected. Opportunistic cyclopoid predation on fish larvae may also alter zooplankton community structure by changing the feeding pattern of cyclopoids. Lack of significant predation on other species of fish larvae is probably due to temporal and spatial asynchrony of predator and prey, low probability of encounter, robust nature of certain fish species, and effective swimming and escape ability.
Abundance and Distribution of Humpback Whales (Megaptera novaeangliae) in West Greenland Waters
Authors: Perkins Judith S. , Balcomb III Kenneth C. , Nichols Jr. George , DeAvilla Marisa
Published: June 2008

Using photoidentification of individual humpback whales (Megaptera novaeangliae) and mark–recapture calculations in 1981 (mark) and 1982 (recapture), the population of this species that occurs in summer along the West Greenland coast between 63 and 70°N was estimated to be less than 200 whales. Whale distribution, however, was not random. Humpbacks were found clustered on Fyllas Banke (Godthaab District) during July and August in both years. Only a few individuals were scattered within a 240-km radius of this location. No West Greenland humpbacks have been seen in other known western North Atlantic feeding areas and vice versa.
Interspecific Relations among Fish Species in South Bay, Lake Huron, 1949–84
Authors: Henderson Bryan A. , Fry F. E. J.
Published: June 2008

Of the nine species caught in pound and gill nets in South Bay, Lake Huron (lake whitefish (Coregonus clupeaformis), rainbow smelt (Osmerus mordax), lake trout (Salvelinus namaycush), splake (S. namaycush × S. fontinalis), burbot (Lota lota), lake hering (Coregonus artedii), alewife (Alosa pseudoharengus), white sucker (Catostomus commersoni), and yellow perch (Perca flavescens)), only yellow perch, white sucker, and lake whitefish were significantly related to the abundances of all other fish species (multiple regression) from 1965 to 1984. For the longer period (pound nets 1949–84), all but smelt, burbot, and white sucker were dependent upon variations in the abundance of the nine other species. For the same period (1965–84) and species (nine), the abundances only of yellow perch and white suckers were significantly and positively related in two basins of the Bay. None of the inverse correlations between species abundances was significant in both basins. Within the Outer Basin, only the correlations between alewife and lake herring (r = −0.49, r = −0.45) and yellow perch and white sucker (r = +0.55, r = +0.47) were significant in the same direction for both time periods (1949–64 and 1965–84, respectively). We concluded that there was little evidence that the abundances of species were affected significantly by interspecific influences.
Lake Superior Revisited 1984
Authors: MacCallum Wayne R. , Selgeby James H.
Published: June 2008

The Lake Superior fish community has changed substantially since the early 1960s, when control of the sea lamprey (Petromyzon marinus) became effective. Self-reproducing stocks of lake trout (Salvelinus namaycush) have been reestablished in many inshore areas, although they have not yet reached pre-sea lamprey abundance; offshore lake trout are probably at or near pre-sea lamprey abundance. Stocks of lake whitefish (Coregonus clupeaformis) appear to have fully recovered; commercial catches are at or above historical levels. Lake herring (Coregonus artedii) are recovering rapidly in U.S. waters and are abundant in western Canadian waters. The population of rainbow smelt (Osmerus mordax), which declined in the 1970s, is recovering. Pacific salmon (Oncorhynchus) are becoming more abundant as a result of increased stocking in U.S. waters and are reproducing in most suitable tributaries; they have become significant in anglers' creels.
Recent Changes in the Aquatic Food Web of Eastern Lake Ontario
Authors: Christie W. J. , Scott K. A. , Sly P. G. , Strus R. H.
Published: June 2008

During the past 10 yr there have been dramatic increases in piscivorous populations of walleye (Stizostedion vitreum) in the Bay of Quinte and of planted lake trout (Salvelinus namaycush) and double-crested cormorants (Phalacrocorax auritus) in the Kingston basin of Lake Ontario. This paper documents changes in the prey stocks shared by these piscivores, including reduction in size and abundance of the slimy sculpin (Cottus cognatus) with subsequent stock equilibration and unabated reduction in the size and abundance of rainbow smelt (Osmerus mordax), both owing to predation pressure from the lake trout. The third primary prey species, alewife (Alosa pseudoharengus), has not yet suffered severely from the depredations of the piscivores. Symptoms of the effects are discernible, however, and the implications of a possible collapse are discussed. Lake trout survival and growth have not yet been affected by the changes in prey availability, but their diet has shifted both in response to their own expanded size composition and relative abundance of the three prey species. Increased utilization of alewife makes the hunting of the trout more pelagic. Problems of obtaining representative samples of the prey are discussed.
An Ecological Approach to Fisheries Assessment
Authors: Dickie L M. , Kerr S. R. , Schwinghamer P.
Published: June 2008

Deductions based on recent ecological information suggest that while current fishery assessment methodology has captured the main features of fishery production, it may not well anticipate the effects of early natural mortality or of major changes in fishing. We propose here a new methodology based on ecological theory related to a characteristic biomass size spectrum. Theoretical considerations coupled with empirical data on population production appear to take into account high natural mortalities at small sizes and the effects of spatial distribution on production parameters throughout the life history. The resulting models offer a somewhat modified view of the relation of fishery yield to effort and the prospect of population assessments with more modest data requirements.
A review of harvest theory and applications of optimal control theory in fisheries management
Authors: Cohen Yosef
Published: June 2008

Optimal control theory is a useful tool for analysis of general mathematical models of fisheries and harvest strategies. It provides a framework for management decisions, but is too general for direct application to many specific management problems. A review of applications of optimal control theory to fisheries management is presented, with a general audience in mind. Advantages and shortcomings of optimal control theory in the context of fisheries management are discussed with some specific examples.
Ecological Stability in the Context of Multispecies Fisheries
Authors: Pimm Stuart L. , Hyman Jeffrey B.
Published: June 2008

Recent theoretical studies suggest that disrupted communities are not persistent in the face of attempted invasions; moreover, reassembly of a persistent community is likely to prove difficult. It appears that the most likely species to invade a harvested community are those most similar to the harvested species, except in their propensity to be harvested. Most communities are not resistant to removals of top predators; large changes in species composition usually ensue. Large changes in community composition may, however, be associated with small changes in total biomass. Although there is some debate over whether natural communities are, on average, resistant, given species additions, community changes following species introductions appear to be common, especially in harvested or polluted systems where man effects a positive feedback between extinctions and invasions. There are several alternative theoretical relationships between population resilience, variability, and stress; the choices strongly depend on the underlying mathematical model. Multispecies models suggest that the relationship will depend on the relation of the population to other species. Empirical analyses have been highly deficient, primarily because of the failure to distinguish different temporal scales of variability.
Potential Stizostedion Yield as a Function of Chlorophyll Concentration with Special Reference to Lake Erie
Authors: Oglesby Ray T. , Leach Joe H. , Forney John
Published: June 2008

Models for predicting potential fish yield from indices of productivity or standing crop at a lower trophic level have proved most reliable when applied to a specific fish association. Using chlorophyll concentration as the independent variable, we demonstrated that Stizostedion yield was defined by a dome-shaped curve with maximum catch of about 10 kg∙ha−1∙yr−1 occurring between 7.5 and 12.5 mg chlorophyll a∙m−3. We postulate that the ascending and descending portions of the curve represent trophic regions where walleye production is replaced, respectively, by that of salmonid/coregonid- and centrarchid/cyprinid-dominated communities.
Abundance Patterns and Community Attributes of Fishes Relative to Environmental Gradients
Authors: Marshall T. R. , Ryan P. A.
Published: June 2008

Seventy-five lakes of the Canadian boreal forest were examined for patterns of fish species abundance and community structure in relation to gradients of four environmental variables: (1) lake area, (2) mean depth, (3) Secchi disk transparency, and (4) morphoedaphic index (MEI). Mean depth appeared to exert the greatest control on the relative abundance of the species considered. The remaining variables influenced abundance in unique ways, although, as with mean depth, this influence was mainly a consequence of changes in thermal and nutrient regimes. An examination of lower trophic components indicated that these regimes appear to structure food webs, with distinctly different patterns in food webs occurring in dimictic and polymictic lakes. Major shifts in aquatic biota occur in the transition region between lake types. Lakes with these characteristics are at a lower successional state due to environmental unpredictability, as demonstrated by an increasing importance of r- over K-strategists.
Perch (Perca fluviatilis) and Pike (Esox lucius) in Windermere from 1940 to 1985; Studies in Population Dynamics
Authors: Cren E. D. Le
Published: June 2008

The aduit population of perch (Perca fluviatilis) in Windermere was severely reduced by an experimental trap fishery from 1941 to 1947 in one basin and from 1941 to 1964 in the other and has been monitored since. A gillnet fishery for pike (Esox lucius) >550 mm began in 1944 and has continued since. Changes in numbers, recruitment, mortality, growth, biomass, and fecundity have been measured. Summer water temperature and population density affected perch growth; temperature affected pike growth from 1944 to 1959, but not thereafter. A model involving correlations with temperature and negative correlations with abundance of adult perch and 0 group pike explained 90% of variation in perch recruitment for part of the period. Pike recruitment was correlated with temperature. In perch adult mortality rate and growth rate are correlated. Perch numbers are recovering after a 98% adult mortality from disease in 1976. Temperature and size-related predation within and between the two species appear to be the main controlling factors, but the relationships have changed from one part of the period to another.
Colonization of Inland Lakes in the Great Lakes Region by Rainbow Smelt, Osmerus mordax: Their Freshwater Niche and Effects on Indigenous Fishes
Authors: Evans David O. , Loftus David H.
Published: June 2008

Rainbow smelt, Osmerus mordax, have colonized numerous inland lakes in eastern North America, primarily as a result of introductions by humans. Smelt often establish large populations in these lakes and influence indigenous fishes both directly (predation) and indirectly (competition). Smelt have a eurythermal life history, which results in spatial segregation of their larvae, juvenile, and adults, and are omnivorous feeders, eating a range of food types from zooplankton to fish. As a result, smelt interact strongly with a wide spectrum of prey and predator species. Effects on other species are mediated via food web interactions resulting in recruitment and growth changes in some species and redirection of energy flow and storage. Species most often affected are cold-water and cool-water species whose niches are most similar to juvenile and adult smelt. Increased growth rates of Atlantic salmon (Salmo salar) and lake trout (Salvelinus namaycush) and recruitment failure of lake whitefish (Coregonus clupeaformis) are the best documented responses to invasion by smelt. Many other species are probably also affected, although the effects vary greatly between lakes. Variation in the smelt metabolic niche (as expressed by relative growth efficiency) is due to variations in prey size and availability and is reflected in differences in smelt body size between lakes. Smelt body size, in turn, is related to the variable effects that they have on other species.
Modeling and Management in the Presence of Uncertain Inputs
Authors: Vincent T. L
Published: June 2008

Management objectives are often obtained by maintaining a dynamical system at some equilibrium state. It is assumed here that a management program to maintain the system at an equilibrium state has already been specified. However, in the presence of external inputs of an unknown nature, the specified management program is unable to maintain the system in the neighborhood of the equilibrium state. This paper deals with methods for modifying a specified management program so that the system will remain in the neighborhood of the desired equilibrium point in spite of uncertain input. An example is given to illustrate the method.
Biomass Dynamics of Lake Superior Lake Herring (Coregonus artedii): Application of Schnute's Difference Model
Authors: Jacobson Lawrence D. , MacCallum Wayne R. , Spangler George R.
Published: June 2008

Schnute's (1985. Can. J. Fish. Aquat. Sci. 42: 414–429) difference model was used to study the biomass dynamics of lake herring (Coregonus artedii) in Thunder Bay and Black Bay, Lake Superior, during 1948–79. Recruitment to both fisheries appeared to be independent of escapement during previous years. Abundance of lake herring in Black Bay varied without trend during the study period despite a strong peak in effective fishing effort during 1968–70 and a general trend of increasing effort throughout the study period. Abundance of Thunder Bay lake herring declined during 1948–50 and 1959–67 and increased when fishing effort declined. The estimated catchability coefficient for small-mesh gill nets (54–83 mm stretched measure) set in Black Bay for lake herring during November was 0.467/102 km net. The estimated catchability coefficient for small mesh gill nets set in Thunder Bay for lake herring during December was 0.132/102 km net. Estimates of natural mortality rates and recruitment levels for both fisheries were confounded and unreliable. This analysis demonstrates the utility of Schnute's model for management of Great Lakes herring stocks and some difficulties with its application.