bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between isotope half‐life and prostatic edema for optimal prostate dose coverage in permanent seed implants
Authors: Villeneuve Maxime , Leclerc Ghyslain , Lessard Etienne , Pouliot Jean , Beaulieu Luc
Published: May 2008

The robustness of treatment planning to prostatic edema for three different isotopes (, , and ) is explored using dynamical dose calculations on 25 different clinical prostate cases. The treatment plans were made using the inverse planning by simulated annealing (IPSA) algorithm. The prescription was 144, 127, and 125 Gy for , , and , respectively. For each isotope, three dose distribution schemes were used to impose different protection levels to the urethra: , , and . Eleven initial edema values were considered ranging from 1.0 (no edema) to 2.0 . The edema was assumed to resolve exponentially with time. The prostate volume, seed positions, and seed activity were dynamically tracked to produce the final dose distribution. Edema decay half‐lives of 10, 30, and 50 days were used. A total of 675 dynamical calculations were performed for each initial edema value. For the isotope, limiting the urethra to leads to a prostate under 140 Gy for initial edema values above 1.5. Planning with urethra at provides a good response to the edema; the prostate remains higher than 140 Gy for edema values up to 1.8 and a half‐life of 30 days or less. For , the prostate is under of the prescription dose for approximately , , and of edema values for urethra , , and , respectively. Similar behavior is seen for and the center of the prostate becomes “cold” for almost all edema scenarios. The magnitude of the edema following prostate brachytherapy, as well as the half‐life of the isotope used and that of the edema resorption, all have important impacts on the dose distribution. The isotope with its longer half‐life is more robust to prostatic edema. Setting up good planning objectives can provide an adequate compromise between organ doses and robustness. This is even more important since seed misplacements will contribute to further degrade dose coverage.
A fast, accurate, and automatic 2D–3D image registration for image‐guided cranial radiosurgery
Authors: Fu Dongshan , Kuduvalli Gopinath
Published: May 2008

The authors developed a fast and accurate two‐dimensional (2D)–three‐dimensional (3D) image registration method to perform precise initial patient setup and frequent detection and correction for patient movement during image‐guided cranial radiosurgery treatment. In this method, an approximate geometric relationship is first established to decompose a 3D rigid transformation in the 3D patient coordinate into in‐plane transformations and out‐of‐plane rotations in two orthogonal 2D projections. Digitally reconstructed radiographs are generated offline from a preoperative computed tomography volume prior to treatment and used as the reference for patient position. A multiphase framework is designed to register the digitally reconstructed radiographs with the x‐ray images periodically acquired during patient setup and treatment. The registration in each projection is performed independently; the results in the two projections are then combined and converted to a 3D rigid transformation by 2D–3D geometric backprojection. The in‐plane transformation and the out‐of‐plane rotation are estimated using different search methods, including multiresolution matching, steepest descent minimization, and one‐dimensional search. Two similarity measures, optimized pattern intensity and sum of squared difference, are applied at different registration phases to optimize accuracy and computation speed. Various experiments on an anthropomorphic head‐and‐neck phantom showed that, using fiducial registration as a gold standard, the registration errors were in overall translation and in overall rotation. The total targeting errors were , , and for the targets at the distances of 2, 6, and 10 cm from the rotation center, respectively. The computation time was less than 3 s on a computer with an Intel Pentium 3.0 GHz dual processor.
Dedicated breast computed tomography: Volume image denoising via a partial‐diffusion equation based technique
Authors: Xia Jessie Q. , Lo Joseph Y. , Yang Kai , Floyd Carey E. , Boone John M.
Published: May 2008

Dedicated breast computed tomography (CT) imaging possesses the potential for improved lesion detection over conventional mammograms, especially for women with dense breasts. The breast CT images are acquired with a glandular dose comparable to that of standard two‐view mammography for a single breast. Due to dose constraints, the reconstructed volume has a non‐negligible quantum noise when thin section CT slices are visualized. It is thus desirable to reduce noise in the reconstructed breast volume without loss of spatial resolution. In this study, partial diffusion equation (PDE) based denoising techniques specifically for breast CT were applied at different steps along the reconstruction process and it was found that denoising performed better when applied to the projection data rather than reconstructed data. Simulation results from the contrast detail phantom show that the PDE technique outperforms Wiener denoising as well as adaptive trimmed mean filter. The PDE technique increases its performance advantage relative to Wiener techniques when the photon fluence is reduced. With the PDE technique, the sensitivity for lesion detection using the contrast detail phantom drops by less than when the dose is cut down to of the two‐view mammography. For subjective evaluation, the PDE technique was applied to two human subject breast data sets acquired on a prototype breast CT system. The denoised images had appealing visual characteristics with much lower noise levels and improved tissue textures while maintaining sharpness of the original reconstructed volume.
Frequency distribution of the nanoparticle magnetization in the presence of a static as well as a harmonic magnetic field
Authors: Weaver John B. , Rauwerdink Adam M. , Sullivan Charles R. , Baker Ian
Published: May 2008

We explore the properties of the signal from magnetic nanoparticles. The nanoparticle signal has been used to generate images in magnetic particle imaging (MPI). MPI promises to be one of the most sensitive methods of imaging small numbers magnetic nanoparticles and therefore shows promise for molecular imaging. The nanoparticle signal is generated with a pure sinusoidal magnetic field that repeatedly saturates the nanoparticles creating harmonics in the induced magnetization that are easily isolated from the driving field. Signal from a selected position is isolated using a static magnetic field to completely saturate all of the particles outside a voxel enabling an image to be formed voxel by voxel. The signal produced by the magnetization of the nanoparticles contains only odd harmonics. However, it is demonstrated experimentally that with the addition of a static magnetic field bias even harmonics are introduced which increase the total signal significantly. Further, the distribution of signal among the harmonics depends on the static bias field so that information might be used to localize the nanoparticle distribution. Finally, the field required to completely saturate nanoparticles can be quite large and theory predicts that the field required is determined by the smallest nanoparticles in the sample.
Single and dual energy attenuation correction in PET/CT in the presence of iodine based contrast agents
Authors: Rehfeld Niklas S. , Heismann Björn J. , Kupferschläger Jürgen , Aschoff Philip , Christ Gunter , Pfannenberg Anna C. , Pichler Bernd J.
Published: May 2008

In present positron emission tomography (PET)/computed tomography (CT) scanners, PET attenuation correction is performed by relying on the information given by a single CT scan. The scaling of the linear attenuation coefficients from CT x‐ray energy to PETgamma energy is prone to errors especially in the presence of CT contrast agents. Attenuation correction based upon two CT scans at different energies but performed at the same time and patient position should reduce such errors and therefore improve the accuracy of the reconstructed PET images at the cost of introduced additional noise. Such CT scans could be provided by future PET/CT scanners that have either dual source CT or energy sensitive CT. Three different dual energy scaling methods for attenuation correction are introduced and assessed by measurements with a modified NEMA 1994 phantom with different CT contrast agent concentrations. The scaling is achieved by differentiating between (1) Compton and photoelectric effect, (2) atomic number and density, or (3) water‐bone and water‐iodine scaling schemes. The scaling method (3) is called hybrid dual energy computed tomography attenuation correction (hybrid DECTAC). All three dual energy scaling methods lead to a reduction of contrast agent artifacts with respect to single energy scaling. The hybrid DECTAC method resulted in PET images with the weakest artifacts. Both, the hybrid DECTAC and Compton/photoelectric effect scaling resulted also in images with the lowest PET background variability. Atomic number/density scaling and Compton/photoelectric effect scaling had problems to correctly scale water, hybrid DECTAC scaling and single energy scaling to correctly scale Teflon. Atomic number/density scaling and hybrid DECTAC could be generalized to reduce these problems.
Geometric calibration of a mobile C‐arm for intraoperative cone‐beam CT
Authors: Daly M. J. , Siewerdsen J. H. , Cho Y. B. , Jaffray D. A. , Irish J. C.
Published: May 2008

A geometric calibration method that determines a complete description of source‐detector geometry was adapted to a mobile C‐arm for cone‐beam computed tomography (CBCT). The non‐iterative calibration algorithm calculates a unique solution for the positions of the source , detector , piercing point , and detector rotation angles based on projections of a phantom consisting of two plane‐parallel circles of ball bearings encased in a cylindrical acrylic tube. The prototype C‐arm system was based on a Siemens PowerMobil modified to provide flat‐panel CBCT for image‐guided interventions. The magnitude of geometric nonidealities in the source‐detector orbit was measured, and the short‐term and long‐term ( months) reproducibility of the calibration was evaluated. The C‐arm exhibits large geometric nonidealities due to mechanical flex, with maximum departures from the average semicircular orbit of and (for the piercing point), and and (for the source and detector), and , , and (for the detector tilt/rotation). Despite such significant departures from a semicircular orbit, these system parameters were found to be reproducible, and therefore correctable by geometric calibration. Short‐term reproducibility was (subpixel) for the piercing point coordinates, for the source‐detector and , for the source‐detector , and for the detector angles. Long‐term reproducibility was similarly high, demonstrated by image quality and spatial resolution measurements over a period of 6 months. For example, the full‐width at half‐maximum (FWHM) in axial images of a thin steel wire increased slightly as a function of the time between calibration and image acquisition: , 0.63, 0.66, 0.71, and at , , 1 day, 1 month, and 6 months, respectively. For ongoing clinical trials in CBCT‐guided surgery at our institution, geometric calibration is conducted monthly to provide sufficient three‐dimensional (3D) image quality while managing time and workflow considerations of the calibration and quality assurance process. The sensitivity of 3D image quality to each of the system parameters was investigated, as was the tolerance to systematic and random errors in the geometric parameters, showing the most sensitive parameters to be the piercing point coordinates and in‐plane positions of the source and detector . Errors in the out‐of‐plane position of the source and detector and the detector angles were shown to have subtler effects on 3D image quality.
Vaired Effects of Clear-cut Logging on Predators and Their Habitat in Small Streams of the Cascade Mountains, Oregon
Authors: Murphy Michael L. , Hall James D.
Published: May 2008

Assemblages of aquatic vertebrate and insect predators were inventoried in streams in old-growth and logged coniferous forests in the western Cascades of Oregon to assess effects of clear-cut logging on stream communities. Effects associated with logging depended on stream size, gradient, and time after harvest. Clear-cut sections where the stream was still exposed to sunlight (5–17 yr after logging) generally had greater biomass, density, and species richness of predators than old-growth (> 450-yr-old) forested sections. Increases were greatest in small (first-order), high gradient (10–16%) streams, where clear-cut sites had both greater periphyton production and coarser streambed sediment than old-growth sites of similar size and gradient. Effects on predators were mixed in larger, lower gradient streams, where clear-cut sites showed accumulation of sediment and relatively small increases in periphyton production. Second-growth logged sections (12–35 yr after logging), reshaded by deciduous forest canopy, had lower biomass of trout and fewer predator taxa than old-growth sites.Key words: trout, salamanders, insects, logging, sediment, periphyton, watershed management
DNA Homology Studies of Selected Flexibacteria Associated with Fish Disease
Authors: Pyle Stephen W. , Shotts Jr. Emmett B.
Published: May 2008

Seventeen strains of gliding bacteria (flexibacteria) associated with fish disease were evaluated with DNA homology techniques. The data support our earlier report that isolates from warmwater fish may be considered as a separate group from isolates of cold-water fish. DNA analysis indicates that at least four of the warmwater isolates studied are genetically identical and that one other warmwater isolate is sufficiently unrelated to these four organisms to indicate a strain, or possibly a species difference, based on the results of work with enteric bacteria. Based on a selected reference organism, results indicate three groups within the cold-water isolates, each with varying degrees of relatedness. A strain of Flexibacter columnaris, included as an unlabeled reference, demonstrated a low degree of relatedness to the labeled reference strains.Key words: DNA homology, flexibacteria, hydroxyapatite, Flexibacter columnaris
Regional Variation in the Size of Maturity of Two Species of Tanner Crab (Chionoecetes bairdi and C. opilio) in the Eastern Bering Sea, and Its Use in Defining Management Subareas
Authors: Somerton David A.
Published: May 2008

Minimum size limits for the commercial harvest of tanner crab (Chionoecetes bairdi and C. opilio) are based on the sizes of sexual maturity. Establishing such size limits in the eastern Bering Sea is complicated by a large regional variation in the size of maturity. A computer technique was developed which partitioned the eastern Bering Sea into subareas that were relatively homogeneous with respect to the size of maturity. The best partitioning for C. bairdi was a separation of the eastern Bering Sea into two subareas along 167°15′N longitude. No acceptable partitioning could be found for C. opilio. The size of 50% maturity for male C. bairdi was estimated to be 108.9 mm carapace width in the western subarea and 117.0 mm in the eastern subarea. The size of maturity upon which the current minimum size for C. bairdi is based is nearly the same as the size estimated for the western subarea but significantly less than the size estimated for the eastern subarea.Key words: crabs, size of maturity, Chionoecetes bairdi, Chionoecetes opilio, tanner crab, eastern Bering Sea
Compositional Changes on Freshwater Leaching of the Marine Algae Nereocystis luetkeana and Macrocystis integrifolia
Authors: Whyte J. N. C. , Englar J. R. , Borgmann P. E.
Published: May 2008

An assessment of the chemical components in Nereocystis luetkeana and Macrocystis integrifolia before and after sequential freshwater leaching demonstrated that a high degree of separation of inorganic from organic elements was achieved by freshwater leaching of both algae with a high proportion of the proteinaceous and polysaccharide material being retained. Significant retention in di- and tri-valent cations present as minor and trace elements was observed and the retention of iodine suggested its partial inclusion as a covalently bound element. Even after exhaustive leaching alginate was almost totally retained in both residual algal tissues, essentially as a combined salt of potassium, sodium, and polyvalent ions with the latter imparting a net insoluble nature to the molecule. Fucoidan was the principal polysaccharide leached from both algae and was solely responsible for the mucilaginous nature of chopped Nereocystis and Macrocystis. Potassium, sodium, and chloride ions accounted for the major losses on leaching both algae and could be removed prior to drying and transportation of these plants as sources of alginate salts. The virtual loss of all mannitol and chloride suggested that intracellular constituents were the major leachates while the cell wall components were essentially retained. Commercial implication of these results are considered.Key words: Nereocystis luetkeana, Macrocystis integrifolia, marine algae, inorganic elements, alginate, fucoidan, mannitol, protein, water leaching
Wind Regulation of Emergence Times and Early Larval Survival in Capelin (Mallotus villosus)
Authors: Frank Kenneth T. , Leggett William C.
Published: May 2008

Factors regulating the emergence and survival of capelin (Mallotus villosus) larvae from their beach gravel nest sites were investigated in the spring and summer of 1978 and 1979. In both years, the pattern of larval emergence was characterized by intermittent abrupt increases in the numbers of larvae in the nearshore waters and corresponding precipitous declines in the density of preemergent larvae in the beach gravel. Both events were strongly correlated with onshore wind-induced wave action which disturbed the beach. Larval emergence patterns were unrelated to changes in tidal amplitude or day–night variation. The generality of this wind-induced larval emergence hypothesis was tested and confirmed using published data from two separate studies conducted at three different Newfoundland sites during 1927, 1929, 1930, and 1941. The density of larvae in the beach gravel was positively correlated with the length of time separating the occurrence of onshore winds. The result was a pronounced temporal clumping of larvae hatching at different times, periodic releases of large numbers of larvae into the aquatic environment, and a progressive deterioration in the physical condition of larvae emerging as beach residence time increased. The frequency of onshore winds during the hatching period was 50% greater in 1979 relative to 1978. Egg densities were similar in 1978 and 1979 but larval densities (no./m3) in the nearshore environment were 60% greater in 1979. This increase in larval density conformed to the increase in the proportion of larvae exiting the beach in good physical condition in 1979.Key words: capelin, Mallotus villosus; Newfoundland, larval emergence, larval survival, wind, population biology, beach spawning, coastal environments, year-class strength
Comparison of Sympatric Dwarf and Normal Populations of Least Cisco (Coregonus sardinella) Inhabiting Trout Lake, Yukon Territory
Authors: Mann G. J. , McCart P. J.
Published: May 2008

A normal (205– to 340-mm fork length at maturity) and a dwarf (85– to 135-mm fork length at maturity) form of least cisco (Coregonus sardinella) exist sympatrically in Trout Lake, Yukon Territory. Dwarf ciscoes have significantly fewer gill rakers, lateral lines scales, and pyloric caeca and significantly more vertebrae, on the average, than normal ciscoes. Dwarf cisco mature earlier than normals (age 3 vs. age 6); however, normals are longer lived (maximum age 23 vs. age 14) and may produce nearly 30 times the annual complement of eggs produced by dwarf cisco. Spawning of dwarf cisco may precede that of the normals, and there is some evidence of both spatial segregation of the two forms by selective schooling and of differences in food habits.Key words: least cisco, Coregonus sardinella; dwarfing, Yukon, North Slope, life history
Aeromonas salmonicida: Relationship between Extracellular Growth Products and Isolate Virulence
Authors: Cipriano Rocco C. , Griffin Billy R. , Lidgerding Burton C.
Published: May 2008

Extracellular growth products, extracted from culture supernatants of Aeromonas salmonicida by precipitation with ammonium sulfate and ethanol, were resolved into four fractions by ion-exchange chromatography. Although one of these (fraction II) possessed leukocytolytic activity, virulence of the pathogen was not associated with leukocytotoxicity. A positive correlation was established, however, between virulence and the toxicity of extracted material to cultured rainbow trout gonad (RTG-2) cells. The crude material and fractions II and III from virulent isolates were more toxic to RTG-2 cells than were similar preparations from avirulent isolates. Preparations from virulent isolates caused hemorrhaging, lesion development, and mortality when injected intramuscularly into brook trout (Salvelinus fontinalis) and Atlantic salmon (Salmo solar). Rainbow trout (Salmo gairdneri) were more resistant and lesions could be produced only with fraction II. Fraction II also possessed proteolytic activity.Key words: Aeromonas salmonicida, furunculosis, pathogenicity, salmonids, extracellular products, cytotoxicity, leukocytolysis, proteolysis, fishes
Relationship Between Destructive Grazing by the Sea Urchin, Strongylocentrotus droebachiensis, and the Abundance of American Lobster, Homarus americanus, on the Atlantic Coast of Nova Scotia
Authors: Wharton W. G. , Mann K. H.
Published: May 2008

Relationships between percentage cover of macroalgae, population structure of sea urchins (Strongylocentrotus droebachiensis), and the history of the lobster fishery were examined at nine sites distributed along the Atlantic coast of Nova Scotia from Guysborough County in the northeast to Pubnico in the southwest. At Pubnico there was dense algal cover and a small number of urchins living in crevices, and at Cape Sable there was an area of transition, but at all other sites there were urchin-dominated barren grounds. When the population structure of the urchins was compared with that previously observed in St. Margaret's Bay before, during, and after destruction of beds of kelp (Laminaria spp. and Agarum) by overgrazing, it was concluded that kelp bed destruction occurred on the coast north of Halifax prior to 1970, and on the coast south of Halifax after 1970. From the records of American lobster (Homarus americanus) catches it was concluded that a critical decline in catches at each site occurred a few years after kelp bed destruction. Information from various sources is synthesized into a coherent theory of the relationship between lobsters, other predators, sea urchins, and kelp.Key words: lobsters, Homarus americanus; sea urchins, Strongylocentrotus droebachiensis; destructive grazing, kelp, Laminaria, Agarum
Developmental Responses of Juvenile Daphnia rosea to Experimental Alteration of Temperature and Natural Seston Concentration
Authors: Neill William E.
Published: May 2008

A need for accurate estimates of juvenile development rates of Daphnia rosea from oligotrophic lakes prompted this investigation into the combined effects of temperature and natural seston concentrations on growth of neonates. Significant effects of seston concentration and temperature and especially their interaction were detected upon survival, number of prereproductive instars, growth increment per instar, and duration of development. Low summertime seston concentrations that were sufficient for good survival and growth at a low rearing temperature (12 °C) generally produced high mortality, slow development, and reduced biomass increments at higher temperature (21 °C). Further, poor growth and survival under low seston – high temperature conditions were exaggerated in August compared with May, suggesting possible seasonal changes in natural seston quality and/or juvenile daphnid physiology. In contrast, higher food levels typical of springtime conditions produced excellent survival and growth regardless of the test temperature employed or season examined. Food limitation of daphnid development was thus dependent upon both temperature and food concentration within the range of conditions commonly observed in oligotrophic lakes. Extrapolation of development rates measured under only a limited range of food–temperature conditions or taken from literature values should be done cautiously.Key words: Daphnia, development, juvenile, seston, food, temperature, growth, survival, Cladocera, oligotrophic
The Effect of Phosphorus Limitation on Algal Growth Rates: Evidence from Alkaline Phosphatase
Authors: Smith Ralph E. H. , Kalff Jaap
Published: May 2008

The inducible enzyme alkaline phosphatase (APA) was used to quantify phosphorus limitation of freshwater phytoplankton growth in situ. Natural phytoplankton communities from oligotrophic–eutrophic Lake Memphremagog were grown at phosphorus-limited rates of 0.06–0.93 per day in continuous, lake water cultures. APA varied inversely with phosphorus-limited growth rate and was little influenced by the community composition changes that occurred in culture. Compared to cultures, average in situ APA in Lake Memphremagog during the ice-free season was low, and suggested phosphorus-limited growth rates greater than 0.6 per day in even the most oligotrophic parts of the lake. Although algal abundance varies with total phosphorus among most north-temperate zone lakes, including Lake Memphremagog, our data show that average community growth rates are normally high and change relatively little over a fourfold range of total phosphorus concentration.Key words: alkaline phosphatase, phytoplankton, growth rate, phosphorus
Particle-Size-Conversion Efficiency and Total Animal Production in Pelagic Ecosystems
Authors: Borgmann Uwe
Published: May 2008

A method is described for defining conversion efficiency in pelagic ecosystems on the basis of particle size, rather than trophic level, this permits calculation of a size-corrected biomass function which can be used to describe total animal production by taking into account biomass losses resulting from carnivorous feeding in multitrophic level systems. This, in turn, permits the determination of potential fish production, for any given size fish, from experimental data on zooplankton production using simple equations. Little knowledge of trophic interactions is required. The potential fish production resulting from microzooplankton production in the Burlington Canal is calculated. Keywords: conversion efficiency, production, pelagic ecosystem, particle-size spectrum
Inshore–Offshore Sedimentation Differences Resulting from Resuspension in the Eastern Basin of Lake Erie
Authors: Bloesch J.
Published: May 2008

From June through October 1978 sediment traps were moored at three stations in an inshore–offshore transect in the Eastern Basin of Lake Erie. Settling fluxes measured with the traps exposed close to lake bottom were rather similar at all three stations during summer stratification, averaging 6.1 g∙m−2∙d−1 for dry weight, 293 mg∙m−2∙d−1 for particulate organic carbon (POC), 38 mg∙m−2∙d−1 for particulate nitrogen (PN), and 5.44 mg∙m−2∙d−1 for particulate phosphorus (PP). A comparison of the hypolimnetic traps with the epilimnetic traps at the offshore station indicated that considerable resuspension takes place even in summer. During fall, however, the nearshore sedimentation rates were markedly increased because of storm-induced bottom resuspension. By comparing the trap catches with sediment cores taken at all three stations, a resuspension model for dry weight, POC, and PN was developed. The calculations showed that newly formed organic material is resuspended and redeposited more frequently at nearshore locations than offshore. This repeated nearshore resuspension enhances decomposition of detritus, as shown by low relative phytoplankton activity in the hypolimnetic traps, and results in horizontal transport of fine-grained organic matter in the offshore direction. The significant POC and PN concentration differences found in the inshore–offshore transect of the bottom sediments can be explained by these two processes.Key words: sedimentation, sediment traps, sediment cores, resuspension, inshore–offshore differences
A Rapid High-Performance Liquid-Chromatographic Method for Simultaneously Determining the Concentrations of TFM and Bayer 73 in Water During Lampricide Treatments
Authors: Dawson V. K.
Published: May 2008

The high-performance liquid-chromatography (HPLC) procedure requires only minutes per sample, is specific, and is relatively sensitive (limit of detection < 0.005 mg/L for both chemicals). A combined buffer (pH 4) and internal standard (3-chlorodiphenylamine) reagent is added to the water sample, which is injected through a Sep Pak C18 disposable cartridge. The cartridge adsorbs and retains both the lampricides and the internal standard. The quantitative elution of the three chemicals from the cartridge with a small volume of methanol effectively concentrates the sample and provides sample cleanup. The methanol extract is then analyzed directly by HPLC on an MCH 10 reverse phase column by using a methanol:0.01 mol/L acetate buffer (87:13, v:v) as the mobile phase at 2 mL/min and detected by ultraviolet spectrophotometry at 330 (or 254) nm. A microprocessor data system further facilitates the procedure by quantifying off-scale peaks and yielding results directly in units of concentration (mg/L).Key words: sea lamprey, lampricides, methodology, chromatographic techniques, 3-trifluoromethyl-4-nitrophenol, 2′,5-dichloro-4′-nitrosalicylanilide, streams
A Comparison of Different Phosphorus Fractions as Predictors of Particulate Pigment Levels in Lake Memphremagog and its Tributaries
Authors: Peters Robert Henry , Bergmann Martin
Published: May 2008

The amounts of colored particulate material (measured by reflectance) in surface waters of Lake Memphremagog and its tributaries were regressed against concentrations of total phosphorus and several of its component fractions: soluble phosphorus, particulate phosphorus, soluble reactive phosphorus, orthophosphate, large molecular weight phosphorus (> 5000 mol wt) and small molecular weight phosphorus (< 400 mol wt). The correlations were examined to see if one of these fractions was a better predictor of seston concentration, and presumably of other biologically related lake properties, than total P, and to determine if riverine samples differed from lake waters in the relation between concentrations of P and suspended particulates. Total P correlated with colored particulates in both lotic and lentic samples as well as or better than any other fraction. Although river samples showed greater variation than lake samples, the regression lines describing the relations were similar in both lakes and rivers.Key words: phosphorus fractions, lakes, rivers, empirical models, particulate concentration, seston
Selection of Bottom Type by Groundfishes of the Scotian Shelf
Authors: Scott J. S.
Published: May 2008

Catches (numbers per tow) of 25 species of groundfish of the Scotian Shelf were estimated for five different bottom types on which the tows were made. An index of selectivity was calculated for each species. Selectivity ranged from highly specific in shallow-water species on sand and gravel bottom, to broad in deep-water species associated mainly with mud and silt bottoms, and in semipelagic species. Gradation in bottom-sediment particle size from northeast to southwest is correlated with clines in shallow-water fish abundance. Bottom type and water depth are correlated with each other and with fish distribution.Key words: bottom type, groundfish, sediment type
Vitamin C and Disease Resistance in Channel Catfish (Ictalurus punctatus)
Authors: Durve V. S. , Lovell R. T.
Published: May 2008

Channel catfish (Ictalurus punctatus) fingerlings were fed semipurified diets containing 0–150 mg/kg of vitamin C for 14 wk and subsequently at two temperature regimes infected with the pathogenic bacterium Edwardsiella tarda. Mortality rates were determined 96 h after infection. A supplemental vitamin C level of 30 mg/kg of diet was sufficient for normal growth and for prevention of deficiency signs such as lordosis, scoliosis, and a reduction in bone collagen formation. However, increased resistance against infection was provided when the level of supplemental vitamin C was increased to the highest dietary level, 150 mg/kg, at a water temperature of 23 °C. At 33 °C, increasing the supplemental level of vitamin C had significantly less effect on resistance against infection. The difference in response at the two temperatures indicates that the vitamin C requirement for resistance to infection is possibly higher when channel catfish are infected at lower temperatures, where the natural resistance is reduced, than when infected at a temperature near optimum for the natural resistance mechanisms of the fish.Key words: vitamin C, channel catfish, disease resistance, Edwardsiella tarda, infection
Timing and Relative Intensity of Size-Selective Mortality of Juvenile Chum Salmon (Oncorhynchus keta) During Early Sea Life
Authors: Healey M. C.
Published: May 2008

Available evidence indicates that mortality of juvenile salmon during early sea life is high and probably size dependent. I used scale analysis to determine the timing and relative intensity of size-selective mortality in chum salmon (Oncorhynchus keta) during early sea life. Significant size-selective mortality could be demonstrated only over the time period that the fish were laying down circuli 2–4 on their scales. The relative intensity of mortality for different sizes of fish suggested that mortality was strongly size selective over the size range 45–55 mm fork length. No particular mortality agent could be identified, but the size range involved corresponds with the size at which chum salmon move from very shallow water and nearshore habitat to open water pelagic habitat.Key words: size-selective mortality, salmon, early sea life
Lake Erie Oxygen; The Prehistoric Record
Authors: Delorme L. D.
Published: May 2008

Periodic anoxia as a symptom of eutrophication has lasted for hundreds, maybe thousands, of years in the central basin of Lake Erie. Fossil ostracode remains in sediment cores show that a common species, Candona caudata, has been able to survive despite periodic anoxia because of its tolerance to low dissolved oxygen (as low as 2.3 mg/L at 16.5 °C) and a short life cycle of weeks to several months. These qualities have enabled it to survive despite oxygen levels below 2.3 mg/L. Two other species, Candona subtriangulata and Cytherissa lacustris, that were expected in the sediment cores were not present. They were not able to cope with periodic low oxygen levels because of their requirement for higher dissolved oxygen (5.6 mg/L at 11.5 °C, 3.0 mg/L at 12.8 °C) and a life cycle of about 1 yr. This condition appears to have been common in the lower part of some of the sediment cores examined. A time-transgressive change in carbon concentration occurred in the surficial sediments of the central basin. A decrease in carbon started in the Sandusky basin around 4000 yr ago and gradually extended itself to the middle of the central basin by 1220 A.D. The loss of carbonate in the upper part of the sediment profile probably resulted from trapping of carbon dioxide, produced by the decomposition of organic material by oxidation and bacterial activity, in the hypolimnion.Key words: Lake Erie, periodic anoxia, ostracodes, inorganic carbon, organic carbon
Biological Half-lives of Polychlorinated Biphenyl (PCB) Congeners in Whole Fish and Muscle of Rainbow Trout (Salmo gairdneri)
Authors: Niimi A. J. , Oliver B. G.
Published: May 2008

The biological half-life [Formula: see text] of 31 dichloro- to decachloro-biphenyl congeners were monitored for 105 d in adult rainbow trout (Salmo gairdneri) that were exposed to a single oral dose. In whole fish [Formula: see text] increased from 5 d to no apparent elimination as the number of chlorines on the biphenyl increased. This structure–activity relationship was not as evident in muscle where [Formula: see text] ranged from < 5 to 127 d. We suggest the decline in muscle resulted from decreasing lipid levels and the redistribution of congeners within the fish. From structure–activity analysis of [Formula: see text] in whole fish we conclude that elimination is enhanced for those congeners with lower chlorine content, with no chlorine substitutions in the ortho positions, and those with two unsubstituted carbons that are adjacent (vicinal) on the biphenyl. A significant decline in total PCB content in whole fish, equivalent to a [Formula: see text] of 219 d, was partly due to the composition of the PCB mixture administered, and the selective elimination of the lower chlorinated biphenyls.
An Allocation Model of Growth and Reproduction in Fish
Authors: Roff Derek A.
Published: May 2008

A simple model is proposed to describe the pattern of allocation of resources into growth and reproduction. This model assumes that there is a fixed amount of surplus energy which may be channeled into either somatic or gonadal tissue. The change in weight or length of a fish can be predicted from this model from the surplus energy and the gonadosomatic index. Evidence is presented that in many species the gonadosomatic index can be assumed to be a constant. Surplus energy can also be estimated by inverting the growth equations. With this information it is possible to examine the consequences on Darwinian fitness of changes in the age at maturity or the allocation to reproduction as measured by changes in the gonadosomatic index. The allocation model is validated using data on the growth of American plaice, Hippoglossoides platessoides. It is shown that the reproductive strategy of American plaice cannot be accounted for on the basis of the trade-off between growth and reproduction.
Orthophosphate Turnover Time in Shallow Productive Lakes
Authors: Prepas E. E.
Published: May 2008

Orthophosphate turnover times were measured in 18 small and medium-sized lakes in western Canada. Turnover times in eight thermally stratified lakes were similar to those of other Canadian lakes: moderately rapid (up to 42 min) in the spring, increasing to very rapid (3–16 min) during July and August. Turnover times in the shallow (i.e. those which mixed intermittently during summer) productive lakes were far more variable, ranging from 17 min to 17 h in spring and 2 min to 36 h during July and August. For individual shallow lakes turnover times remained constant for particular summers. One shallow lake was studied over two summers. In the first summer, turnover times were extremely slow (7–36 h) and in the second summer they were extremely rapid (2–11 min). Therefore I suggest that the mechanisms controlling nutrient limitation in shallow productive lakes are not constant, and can vary dramatically from year to year.
Analysis of Catch/Effort Data: A Comparison of Three Methods
Authors: Roff Derek A.
Published: May 2008

The models of Schnute and Deriso are compared with a simple autoregressive model (SA model). Comparisons are made using both stepwise and omnibus prediction. In the latter case predictions are made for at least 3 or 10 yr ahead. The SA model is shown to be consistently better at predicting both catch and catch-per-unit effort than either of the other two models. Furthermore, the percentage error is frequently sufficiently small to make the predictions useful for stock assessment. It is shown that in practice the Schnute and the Deriso models are variants of the SA model. It is suggested that catch and effort data cannot be used to establish equilibrium catches. The reasons for this are that unique equilibria probably do not exist and the catch/effort data are generally too unreliable to detect anything except major fluctuations in population size. It is suggested that catch-and-effort data can be used by adopting strategies designed to track the population fluctuations.
Temperature-Sensitive Period of Sex Determination in the Atlantic Silverside, Menidia menidia
Authors: Conover David O. , Fleisher Mark H.
Published: May 2008

We investigated the timing and duration of the temperature-sensitive period of development in the Atlantic silverside, Menidia menidia, by measuring the sex ratio in groups of larvae shifted reciprocally among low and high temperatures as development progressed. The sensitive period of sex determination was dependent on body size, rather than age, and occurred during the middle to later stages of larval development when fish were between 8 and 21 mm in total length. Sex determination was irreversibly fixed earlier in development (i.e. at 15 mm in length) at higher than at lower temperatures. Higher, male-producing temperatures therefore appear to more strongly effect sex determination than do lower, female-producing temperatures. Temperature prior to, or after, the sensitive period had no measurable effect on sex ratio. From histological examination we suggest that gonad differentiation coincided with the end of the temperature-sensitive period. The timing and duration of the temperature-sensitive period in M. menidia is generally similar to the hormone-sensitive period identified in other fishes. Both phenomena reveal a specific developmental period during which the course of primary sex differentiation in fishes is labile.
Internal Phosphorus Load in an Oligotrophic Precambrian Shield Lake with an Anoxic Hypolimnion
Authors: Nürnberg Gertrud K. , Shaw Margo , Dillon Peter J. , McQueen Don J.
Published: May 2008

The release of phosphorus from sediments into the anoxic water of oligotrophic Chub Lake, Ontario, determined with three different methods, showed that the average release rate of 2.2 mg∙m−2∙d−1is much smaller than release rates of more eutrophic lakes (14 mg∙m−2∙d−1). Our hypothesis that anoxic release rates depend on lake trophy was confirmed by the significant positive regression of release rates on lake phosphorus concentrations for 56 lakes from the literature. Despite a comparably small phosphorus release rate, the sediments play an important role in Chub Lake as a source of phosphorus because phosphorus from internal sources is in a highly available form and external loads are small.
Free Amino Acid Pools of Five Species of Freshwater Oligochaetes
Authors: Graney R. L. , Keilty T. J. , Giesy J. P.
Published: May 2008

The concentrations of free amino acids (FAA) were measured in five species of freshwater Oligochaeta (Limnodrilus hoffmeisteri, Tubifex tubifex, Potamothrix moldaviensis, Potamothrix vejdovskyi, and Stylodrilus heringianus) collected from southeastern Lake Michigan. Alanine represented between 23.1 and 41.8% of the total FAA pool and was the most abundant amino acid in all species. Leucine, valine, and glutamic acid were, respectively, the next most abundant and had similar relative concentrations in all species except T. tubifex. In T. tubifex, glutamic acid, asparagine, and aspartate were the second, third, and fourth most abundant FAA, respectively. Relative to other freshwater invertebrates, the total FAA pool of Lake Michigan oligochaetes was small. Differences in innate physiological and/or biochemical processes, dietary intake, and reproductive status may have contributed to the quantitative and qualitative differences observed among species. Identification of individual oligochaetes to species was accomplished by multivariate statistical analysis of the FAA profiles. A potential exists for the application of this technique for identifying immature oligochaetes.
Stunted Lake Trout (Salvelinus namaycush) from the Rocky Mountains
Authors: Donald D. B. , Alger D. J.
Published: May 2008

Lake trout (Salvelinus namaycush) from Sassenach Lake, a subalpine lake in jasper National Park, Alberta, are stunted and grow slower than lake trout from any other known population in North America. Mean weight at age 10 was 125 g and at age 20 was 281 g. The largest fish caught weighed 451 g and was 28 yr old. We attribute the slow growth to the absence in the lake of preferred lake trout foods such as amphipods and other fish species. Males were usually mature at > 75 g, and females were often mature at > 100 g. Fifty percent or more of males and females spawned at age 4 and 7, respectively. The age when [Formula: see text] of females spawn in Sassenach Lake, age 7, was typical for lake trout populations with > 5% but < 40% of the catch older than 10 yr. Thus, age at maturity was not obviously affected by the stunted condition of the population.
Quantifying Changes in British Columbia Dungeness Crab (Cancer magister) Landings Using Intervention Analysis
Authors: Noakes D.
Published: May 2008

Natural or man-induced interventions may cause temporary or permanent changes in the behaviour of biological systems. To determine the impact of future management decisions, it is first necessary to quantify the effects of past interventions on the system. Only then can rational decisions be made so as to ensure that the desired response is achieved. However, time series data are often autocorrelated and this precludes the use of standard statistical tests. The linear stochastic intervention model outlined in this paper takes this autocorrelation into account and provides a procedure for quantifying the impacts of particular interventions. This model is employed to determine if there has been a significant abrupt decrease in Dungeness crab (Cancer magister) landings in British Columbia.
Analysing the Effect of Age Structure on Stock–Recruitment Relationships in Herring (Clupea harengus)
Authors: Rosenberg Andrew A. , Doyle Roger W.
Published: May 2008

A Leslie matrix model, fit by multivariate time series analysis methods, of the southwest Nova Scotia herring (Clupea harengus) stock indicates that there is feedback from mature stock abundance to recruitment. Median smoothing suggests dome-shaped nonlinearity in this stock–recruitment relationship. Evidence for compensatory density dependence appears most strongly in the relationships of abundances of individual mature age groups and total recruitment. We suggest that this arises from the separation in space and time of spawners based on their size or age. This results in the production of distinct larval cohorts. These cohorts and the spawners which produce them are the units relevant for the examination of density-dependent processes, rather than the total numbers of spawners and recruits.