bluuebunny/crossref_metadata_2025 huggingface dataset:
Management of three‐dimensional intrafraction motion through real‐time DMLC tracking
Authors: Sawant Amit , Venkat Raghu , Srivastava Vikram , Carlson David , Povzner Sergey , Cattell Herb , Keall Paul
Published: May 2008

Tumor tracking using a dynamic multileaf collimator (DMLC) represents a promising approach for intrafraction motion management in thoracic and abdominal cancer radiotherapy. In this work, we develop, empirically demonstrate, and characterize a novel 3D tracking algorithm for real‐time, conformal, intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT)‐based radiation delivery to targets moving in three dimensions. The algorithm obtains real‐time information of target location from an independent position monitoring system and dynamically calculates MLC leaf positions to account for changes in target position. Initial studies were performed to evaluate the geometric accuracy of DMLC tracking of 3D target motion. In addition, dosimetric studies were performed on a clinical linac to evaluate the impact of real‐time DMLC tracking for conformal, step‐and‐shoot (S‐IMRT), dynamic (D‐IMRT), and VMAT deliveries to a moving target. The efficiency of conformal and IMRT delivery in the presence of tracking was determined. Results show that submillimeter geometric accuracy in all three dimensions is achievable with DMLC tracking. Significant dosimetric improvements were observed in the presence of tracking for conformal and IMRT deliveries to moving targets. A gamma index evaluation with a 3%– criterion showed that deliveries without DMLC tracking exhibit between 1.7 (S‐IMRT) and 4.8 (D‐IMRT) times more dose points that fail the evaluation compared to corresponding deliveries with tracking. The efficiency of IMRT delivery, as measured in the lab, was observed to be significantly lower in case of tracking target motion perpendicular to MLC leaf travel compared to motion parallel to leaf travel. Nevertheless, these early results indicate that accurate, real‐time DMLC tracking of 3D tumor motion is feasible and can potentially result in significant geometric and dosimetric advantages leading to more effective management of intrafraction motion. In order to visually illustrate the algorithm, a movie of MLC tracking for a conformal field has been added to the submission as EPAPS.
Patterns of Intoxication of Shellfish in the Gulf of Maine Coastal Waters
Authors: Hurst John W. , Yentsch Clarice M.
Published: May 2008

There is considerable variability of intoxication in Mytilus edulis leading to Paralytic Shellfish Poisoning (PSP) along the Gulf of Maine coast. When samples from the same sampling location are collected and analyzed on a sufficiently frequent basis, patterns are evident. The patterns are (1) There are areas of high and low probability of shellfish toxin on the Maine coast. (2) Within the high probability areas, the timing at different stations is similar although there is intraannual variability. (3) Toxin rise can occur any time during vernal warning, the most probable timing being spring or late summer. (4) Toxin levels at offshore stations (e.g. Monhegan Island) are frequently much higher than toxin levels at nearshore and inshore stations. These patterns are useful as tracers of bloom dynamics.Key words: Paralytic Shellfish Poisoning, PSP; shellfish toxins, dinoflagellates, bloom dynamics, red tide, Gonyaulax tamarensis var. excavata, Mytilus edulis
Estimating the Average Age of First Birth in Marine Mammals
Authors: DeMaster Douglas P.
Published: May 2008

The average age of sexual maturity and the average age of first birth should not be estimated with identical models. The two parameters often differ by at least 1 y because, among marine mammals, ovulation and parturition take place in different years because of the relatively long gestation period. Furthermore, the assumptions necessary to estimate the average age of sexual maturity cannot be made to fit the data used to estimate the age of first birth. Equating the two models is essentially equivalent to assuming that each ovulation will result in a birth. The described procedure lends itself well to age-specific data. Comparisons between populations should be with a Chi-square goodness-of-fit test.Key words: reproduction, marine mammals, sexual maturity
Steelhead Trout (Salmo gairdneri) on the North Shore of the Gulf of St. Lawrence, near Sept-Îles, Québec
Authors: Whoriskey jr. Frederick G. , Naiman Robert J. , Heinermann Peter H.
Published: May 2008

Fourteen steelhead trout (Salmo gairdneri) were captured in the Matamek and Moisie rivers on the North Shore of the Gulf of St. Lawrence, near Sept-Îles, Québec, in the late summer and early fall of 1979. Steelhead trout are not indigenous to this area. The relatively large numbers of fish taken and their presence in these two rivers on the North Shore may indicate an expanding distribution and a potential threat of colonization in this area of pristine Atlantic salmon (Salmo salar) habitat.Key words: steelhead trout, Salmo gairdneri; geographic range, exotic fish
Gross Growth Efficiency of Fish (K1) Based on Field Observations of Annual Growth and Kinetics of Persistent Environmental Contaminants
Authors: Niimi A. J.
Published: May 2008

The gross growth efficiency of fish (K1) in the field was estimated by incorporating concepts from fish physiology and environmental toxicology into a growth model. Using lake trout and coho salmon as examples, annual growth was estimated from age vs. weight relationships, and food intake was estimated from annual increases in body burden of polychlorinated biphenyls (PCB). Log K1 is suggested to decrease over the life span of a fish.Key words: growth efficiency, annual growth, fish, contaminants
Physical Control of Phytoplankton Production under Sea Ice (Manitounuk Sound, Hudson Bay)
Authors: Legendre L. , Ingram R. G. , Poulin M.
Published: May 2008

In polar and subpolar seas, there are numerous accounts of phytoplankton blooms in the upper water column under the ice. Various mechanisms have been invoked to explain these blooms: the seeding of the underlying surface water by algal cells (epontic flora) released from the melting ice, the optimization of light utilization by the cells, and the stabilization of the upper water column by the low-salinity melting water. From studies conducted in Manitounuk Sound (Hudson Bay), it is proposed that phytoplankton blooms under the ice probably result from the simultaneous deepening of both the photic layer (seasonal light increase) and the stratified layer (low-salinity melting water). In ice-covered seas, the release of ice algae superimposes itself on the phytoplankton bloom, resulting in the observed algal increase under melting ice.Key words: phytoplankton, under-ice blooms, ice flora, stability, nutrients, Hudson Bay
Influence of Substrate Composition and Suspended Sediment on Insect Predation by the Torrent Sculpin, Cottus rhotheus
Authors: Brusven M. A. , Rose S. T.
Published: May 2008

Studies conducted in laboratory streams showed that torrent sculpins (Cottus rhotheus) congregated in regions of limited cover when exposed to a sand substrate. When cobbles were added, their distribution was more uniform. Various combinations of sand, pebbles, and cobbles significantly influenced sculpin predation on the stonefly Hesperoperla pacifica, the mayfly Ephemerella grandis, and the caddisfly Rhyacophila vaccua. During 24-h tests, each species experienced 95–100% predation when tested on sand substrates. When different combinations of cobbles and pebbles were added, predation was appreciably reduced. Sculpin predation on H. pacifica, Hydropsyche sp., and Heptagenia solitaria was influenced more by substrate than suspended sediments when substrate and suspended sediment (0–1250 mg∙L−1) were tested interactively. Predator avoidance tactics differed among prey species as changes were made in the physical characteristics of the environment.Key words: predator–prey, sculpin, insects, suspended sediment, substrate, turbidity, behavior
Rates of Digestion of Different Prey in Atlantic Cod (Gadus morhua), Ocean Pout (Macrozoarces americanus), Winter Flounder (Pseudopleuronectes americanus), and American Plaice (Hippoglossoides platessoides)
Authors: Macdonald J. Stevenson , Waiwood Kenneth G. , Green Roger H.
Published: May 2008

Stomachs of ocean pout (Macrozoarces americanus), Atlantic cod (Gadus morhua), winter flounder (Pseudopleuronectes americanus), and American plaice (Hippoglossoides platessoides) were removed and dissected 5, 12, 20, and 30 h after the fish had fed voluntarily to test the evacuation rates of three different prey species. Two evaluation procedures were used: a visual index of recognizabiiity, and a graphical analysis of percent of each prey recovered versus time since feeding. Three decay models were tested for goodness of fit to the evacuation data. The polychaete worms were the first to become unrecognizable, followed by amphipods. These species showed significantly different rates of evacuation when compared with the bivalves which were recognizable for the longest time. The exponential decay curve gave the best overall fit to the data. However, a linear model gave a good or better fit to the decay rate of the bivalve. The evacuation rates of different prey should be considered in estimating daily rations of fish in their environment.Key words: digestion, stomach content, food organism, Yoldia sapotilla, Tmetonyx cicada, Nephtys incisa
Effects of Drilling Muds on Behavior of the American Lobster, Homarus americanus, in Water Column and Substrate Exposures
Authors: Atema Jelle , Leavitt Dale F. , Barshaw Diana E. , Cuomo M. Carmela
Published: May 2008

Studies were conducted to explore the effects of drilling muds on various aspects of lobster behavior directly related to survival in the field. Toxicity of different drilling muds varied from immediately lethal to adult lobsters to apparently harmless to postlarval stages, with a variety of intermediate effects. Both the chemical toxicity in the water column and the physical effects of covering the substrate with drilling mud were studied, and both interfered with normal lobster behavior. The studies are mainly concerned with postlarval lobsters (stages IV and V), i.e. just after settling on the bottom. They were tested in 36-d chronic exposures (7 mg/L) and in seminatural aquaria with 1-mm layers of drilling mud covering the substrate. Toxicity in the water column manifested itself in feeding and molting delays, severe delays in shelter construction, increased walking and swimming, unprovoked tail flipping, and lethargy. A natural bay mud used as a control caused no such effects. Physical effects of substrate cover were apparent in experiments with 1-, 2-, and 4-mm layers of drilling mud and similar layers of a mixture of bentonite and barite covering a natural mud substrate. In depths of 4 mm both kinds of substrate cover caused severe delays in shelter construction and in quality of burrows constructed. Thus, substrates with 4-mm to perhaps as little as 1-mm covering of drilling mud may cause increased exposure of lobsters to predators and currents, resulting in the substrate becoming unsuitable for lobster settling and survival.Key words: drilling muds, lobster, behavior, toxicity, shelter construction, molting, feeding, survival
PCB Uptake by Five Species of Fish in Lake Michigan, Green Bay of Lake Michigan, and Cayuga Lake, New York
Authors: Jensen A. L. , Spigarelli S. A. , Thommes M. M.
Published: May 2008

We applied a bioenergetic model to describe uptake of polychlorinated biphenyls (PCBs) by lake trout (Salvelinus namaycush), brown trout (Salmo trutta), lake whitefish (Coregonus clupeaformis), coho salmon (Oncorhynchus kisutch), and chinook salmon (Oncorhynchus tshawytscha) in Lake Michigan; lake trout and lake whitefish in Green Bay of Lake Michigan; and lake trout in Cayuga Lake, New York. The model describes PCB uptake in terms of metabolism, food consumption, size, and growth. Concentrations of PCBs differ significantly among species; for the same species there are large differences among habitats. The pattern of PCB uptake by brown trout is different from that of the other species. Application of the model with uptake and metabolic parameters estimated by Norstrom et al. describes the trend in the brown trout data; to describe uptake for other species we increased the exponent of weight for metabolism γ. An increase in γ changes the shape of the relation between PCB concentration and body weight from asymptotic to non-asymptotic. In all species tested except brown trout, uptake of PCBs was not asymptotic and concentrations did not approach an equilibrium; accumulation of contaminants was first rapid, decreased toward a plateau, and then began a second rapid increase. Simulation studies indicate that differences in PCB concentrations among species and in the same species among different environments result from differences in metabolic parameters, exposure, size, and rate of growth.Key words: PCBs, bioenergetic model, contaminant uptake, toxicology, fish, Great Lakes, salmon, trout, whitefish
Corrected Analysis of the Ability to Detect Reductions in Year-Class Strength of the Hudson River White Perch (Morone americana) Population
Authors: Vaughan Douglas S. , Winkle Webster Van
Published: May 2008

This analysis presents a correction of that presented in Van Winkle et al. (1981; Can. J. Fish. Aquat. Sci. 38: 627–632). An exact solution is obtained based on the noncentral t-distribution to replace the incorrect solution based on the central t-distribution used in our earlier analysis. Our new results, although less pessimistic than before, still are not encouraging. They indicate that variability in baseline data is so great that data from 10 additional years are not adequate for detecting even substantial (> 50%) reductions in mean year-class strength, and that at least 20 years of data collection would be required to detect an actual 50% reduction in mean year-class strength, given a Type II error of 50%.Key words: fractional reduction, impingement, power plant, statistical power, Type I and Type II errors, white perch, year-class strength
Daily Growth Increments in Otoliths of Starry Flounder (Platichthys stellatus) and the Influence of Some Environmental Variables in Their Production
Authors: Campana Steven E. , Neilson John D.
Published: May 2008

Tetracycline injected into juvenile starry flounders (Platichthys stellatus) was incorporated into the periphery of the sagittal otoliths within 24 h. The resulting band, visible under ultraviolet light, was used as a dated mark on the otolith growth increments. This technique was used to verify that increments were laid down on a daily basis, both in field and laboratory environments. Subdaily increments were visible in otoliths of fishes reared under most environmental conditions. The production of daily increments in juvenile starry flounders preconditioned to a natural environmental regime was unaffected by photoperiod or temperature fluctuation, suggesting the presence of an internal circadian rhythm.Key words: starry flounder, Platichthys stellatus; otoliths, daily rings, growth increments, circadian, tetracycline
Life History Variations of Anadromous Cisco (Coregonus artedii), Lake Whitefish (C. clupeaformis), and Round Whitefish (Prosopium cylindraceum) Populations of Eastern James–Hudson Bay
Authors: Morin Roderick , Dodson Julian J. , Power Geoffrey
Published: May 2008

Differences in life history among three species of anadromous coregonines from La Grande River, James Bay, were significant with lake whitefish (Coregonus clupeaformis) and round whitefish (Prosopium cylindraceum) displaying reproductive patterns more typical of harsh northern environments and characteristic of "K-selection," relative to cisco (Coregonus artedii). Interspecific differences at La Grande River were more apparent than intraspecific differences in life history traits of cisco and lake whitefish over the James–Hudson Bay range. Although cisco exhibit decreasing reproductive effort independent of growth over the North American range, thus conforming to life history theory, both growth and reproductive effort are reduced northwards over their James–Hudson Bay range. The observations suggest that physiological constraints related to the shorter growing season at the northern limit of cisco's coastal Hudson Bay range may overwhelm expected coadapted life history traits. Lake whitefish exhibit reduced reproductive effort independent of variations in growth northwards over their North American and James–Hudson Bay coastal range; this suggests coadaptation of life history traits that permit survival at northern sites.Key words: reproduction, growth, life history theory, anadromous coregonines, James–Hudson Bay
Coastal Water Mass Replacement: Its Effect on Zooplankton Dynamics and the Predator–Prey Complex Associated with Larval Capelin (Mallotus villosus)
Authors: Frank Kenneth T. , Leggett William C.
Published: May 2008

We examined the hypothesis that the onshore wind-regulated initiation of larval emergence and drift in capelin (Mallotus villosus) was adaptive. Onshore winds were found to induce rapid water mass exchange in coastal Newfoundland resulting in the replacement of cold, high-saline, predator-laden waters with warmer, less-saline waters in which the abundance of an important fraction of the predator community was reduced 3- to 20-fold and zooplankton densities in the edible size fraction were increased 2- to 3-fold. In situ enclosure experiments indicate that the synchronous emergence of larval capelin during onshore winds, coupled with the reduced predator density at this time, results in predator satiation. Wind-induced elevations of the biomass of the edible zooplankton size fraction can produce fivefold increases in the daily growth rate of larval capelin. Capelin larvae thus initiate their drift and first feeding in a wind-induced "safe site." The abundance of eggs and larvae of 11 other marine fish species were also found to be associated with this "safe site" water mass.Key words: capelin, Mallotus villosus; water mass replacement, predation, feeding, growth, larval fish, survival, wind effects, drift, dispersal, enclosures, zooplankton
Les métaux lourds comme indicateurs d'origine géographique de l'anguille d'Amérique (Anguilla rostrata)
Authors: Moreau Guy , Barbeau Claude
Published: May 2008

American eels (Anguilla rostrata) were sampled from the St. Lawrence River and many of its tributaries. Heavy metal concentrations (Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Zn) in muscles were analyzed in relation to collection site, age, length, and weight of the specimens. Among the essential heavy metals, zinc, copper, and especially manganese can be used to distinguish the samples by their origin. In the Saguenay River, which is contaminated by mercury wastes, it is possible to distinguish two types of eels according to their mercury content, weight, and length leading to the hypothesis that these two types lived in different parts of the drainage system. The metal concentrations in the eels seem to depend on the availability of these metals in the bottom sediments. Analysis by flexible grouping and principal coordinates yields groups that are not sufficiently homogeneous and distinct to conclude to a specific pattern of heavy metal contents for all the different origins.
Habitat and Food Segregation of Dwarf and Normal Arctic Charr (Salvelinus alpinus) from Vangsvatnet Lake, Western Norway
Authors: Hindar Kjetil , Jonsson Bror
Published: May 2008

The aim of the present study was to test possible habitat and food segregation between two charr morphs in Vangsvatnet Lake. The charr population of Vangsvatnet consists of one pale phenotype with parr marks along the flanks and poorly developed spawning coloration (dwarf charr), and another phenotype with silvery flanks in nonbreeding condition and bright red spawning colors (normal charr). The habitus of the two morphs indicated that they were adapted to different niches during the growth season. The analyses of distribution and food showed that there was marked habitat and food segregation between the two morphs during summer, when dwarf charr dwelled deep-benthic and normal charr roamed in the limnetic zone. The segregation broke down in periods of food abundance, indicating that the habitat segregation was due to intraspecific competition for food. A comparison of charr morphs of Vangsvatnet with the nearby Lønavatnet Lake suggested that the number of charr morphs is adapted to local environmental conditions, among which lake morphology, food availability, and other fish species are important. We hypothesize that the number of charr morphs within a locality depends on the number of available niches during the growth season.Key words: polymorphism, camouflage, distribution, ontogeny, intra- and inter-specific competition
Thermal Habitat Shifts by Fishes at the Thermocline in Lake Michigan
Authors: Crowder Larry B. , Magnuson John J.
Published: May 2008

We documented thermal habitats of Lake Michigan fishes by bottom trawling at the intersection of the thermocline and the lake bottom near Grand Haven, Michigan. Fish distribution by temperature strata was surveyed during day and night on September 7–13, 1977, and repeated on August 27–September 1, 1979. In the interim, bloaters (Coregonus hoyi) had increased substantially. By comparing these two periods, we suggest that bloaters dramatically altered the thermal distribution of adult alewife (Alosa pseudoharengus). While comprising less than 1% of the trawl catch in 1977, bloaters comprised 42% in 1979. Bloaters were the most-abundant species from 5 to 16 °C in 1979. Adult alewife shifted their thermal distribution from 11 to 16 °C in 1977 to 4 to 8 °C in 1979. This shift is interpreted in terms of competition for food and thermal habitat, or predation by salmonids. The idea that the altered thermal distribution of alewife results from competitive interactions with bloaters is favored by existing data.Key words: competition, fishes, habitat partitioning, Lake Michigan, niche shift, predation, salmonids, temperature, thermocline
Relationship of Fishing Mortality to Natural Mortality and Growth at the Level of Maximum Sustainable Yield
Authors: Deriso R. B.
Published: May 2008

Fishing mortality constraints are derived for fishes harvested at the maximum sustainable yield (MSY) determined by a delay-difference population model. Those constraints depend upon rates of natural mortality and growth as well as a simple constraint placed on abundance of the exploited population. The results are generalized for a wider class of population models where it is shown that MSY fishing mortality is constrained often to be less than the fishing mortality which maximizes yield per recruit. Fishing mortality rates are lower in the delay difference model in comparison to MSY fishing rates in the logistic model, when a quadratic spawner–recruit curve is applied.Key words: delay-difference model, logistic model, fishing mortality, maximum sustainable yield, yield per recruit
Ocean Sciences in Relation to Living Resources
Authors: Bakun Andrew , Beyer Jan , Pauly Daniel , Pope John G. , Sharp Gary D.
Published: May 2008

The Intergovernmental Oceanographic Commission's Resolution XI-17 on Ocean Sciences in Support of Living Resources specifies that programs should be formulated in applied ocean research related to fishery problems. In this report we identify some types of needed research. We discuss the relative importance of the various life history stages to the question of resource variation regarding difficulties in sampling or studying on relevant scales. Our report stresses identification and accounting for causal climate-driven ambient variations. Some testable hypotheses relating the larval stages are given as examples of useful research. We also describe research needed on predation and species interactions. Examples of specific systems where important ecological processes need intense study are given. Upwelling areas, coral reefs, tropical and shelf demersal fisheries, and the open ocean fisheries each require different types and scales of study. The importance of data accessability and multidisciplinary research activities, beginning with dialogues between the ocean research and fishery resource scientists is paramount to successful completion of these tasks. The examples provided may stimulate further effort to identify resource research problems and programs for resolving them.Key words: ocean science, living resources, life history cycles, fishery recruitment, predation, species interactions, fish eggs and larvae, vertical stability of the ocean, advection, convergence and divergence, upwelling systems, coral reefs, tropical demersal fisheries
An Arctic Intertidal Population of Macoma balthica (Mollusca, Pelecypoda): Genotypic and Phenotypic Components of Population Structure
Authors: Green Roger H. , Singh Shiva M. , Hicks Beverly , McCuaig Janet M.
Published: May 2008

In July 1980 we collected live Macoma balthica from populations at two tide levels near Fort Churchill, Man., Canada. Upper lethal temperature tolerances were determined for clams from the mean low water (MLW) tidal level and from 1.1 m above MLW tidal level, after which all specimens were hard frozen for later electrophoretic analysis. Of 22 loci evaluated, the following were polymorphic: AKP, ACP, EST, LAP, MDH, and ME. Genotypes at these loci were related to tide level, growth rate, tolerance to high temperature, and age. Analysis of shell annual rings verified an earlier report of much faster growth in the higher tide level population. Growth rate and degree of heterozygosity are both higher at 1.1 m than at MLW. Degree of heterozygosity increases with age, suggesting selection against homozygotes. At 1.1 m, but not at MLW, individuals with higher growth rates have lower tolerance to high temperatures and a higher degree of heterozygosity. Similar patterns are described for the six individual loci.
Validation of Age Estimation in the Harp Seal, Phoca groenlandica, Using Dentinal Annuli
Authors: Bowen W. D. , Sergeant D. E. , Øritsland T.
Published: May 2008

We investigated the validity and accuracy of age estimation in harp seals, Phoca groenlandica, using a sample of 155 known-age teeth from seals age 3 mo to 10 yr. Under transmitted light, transverse sections of harp seal canine teeth showed distinct incremental growth layers (IGLs) in the dentine. The first growth-layer group (GLG), representing Ist-year growth, consists of two IGLs: an outer layer of opaque dentine, bounded by the neonatal line, and an inner layer of translucent dentine. Subsequent GLGs, each representing 1 yr of growth, generally consist of three IGLs: an outer layer of interglobular dentine deposited during the annual molt in April, a middle layer of opaque dentine formed during the northward spring migration (May–June), and an inner layer of translucent dentine formed from July to March. We show that dentinal GLGs can be used to estimate the absolute age of harp seals. The accuracy of the method decreases with age. Only 72.4% of estimates of 0-group seals were correct using only transverse sections. These errors were virtually eliminated (99.0% correct age determination) when the tooth root was examined. Based on a single examination of a transverse section, the probabilities of correctly estimating age are 0.983, 0.889, 0.817, and 0.553 at ages 1, 2, 3, and 4 + yr, respectively, when clearly inaccurate tag-tooth associations are omitted. The respective probabilities are only slightly higher when age is based on the average of five blind readings, being 1.0, 0.889, 0.833, and 0.625. Beyond age 3 yr, existing data are insufficient to estimate reliably the accuracy of age determined by counting GLGs.
Use of An Age-Dependent Mark–Recapture Model in Fisheries Research
Authors: Pollock K. H. , Mann R. H. K.
Published: May 2008

An age-dependent generalization of the Jolly–Seber mark–recapture model for fish populations subject to birth, death, and migration is illustrated using data from a study on northern pike (Esox lucius) in Dorset, England. These data show strong evidence of differential survival with age. We estimate the average annual survival rate to be 50% for the pike aged 2 or more years and 34% for those of age 1 yr. We believe that this age-dependent mark–recapture model could be very useful for a wide range of fisheries research and management problems. Often in fisheries work the assumption that survival is independent of age has not been examined critically. We present guidelines helpful in designing mark–recapture studies. This includes a useful design which increases precision and also allows population size estimation to be robust to unequal catchability (heterogeneity or trap response) within an age-class.
Bioaccumulation and Effects of Cadmium and Zinc in a Lake Michigan Plankton Community
Authors: Marshall J. S. , Parker J. I. , Mellinger D. L. , Lei C.
Published: May 2008

We conducted four in situ experiments in the southern basin of Lake Michigan to determine the responses of the plankton community to additions of cadmium (3 μg/L) and zinc (15, 30, 60, and 90 μg/L) as well as the bioaccumulation of zinc by different species of crustacean zooplankton. Total cadmium and zinc concentrations in treated enclosures (accounting for pretreatment lakewater concentrations of ~ 20 ng Cd and ~ 1 μg Zn per litre) were calculated from measurements of 109Cd and 65Zn with known specific activities.Zinc significantly reduced zooplankton populations and several other properties of community structure and function at concentrations much lower than those previously reported to be toxic to zooplankton and well below the levels established for protection of freshwater life. Zinc additions as low as 15 μg/L significantly reduced chlorophyll a, primary productivity, dissolved oxygen, specific zooplankton populations, zooplankton species diversity, and community similarity within 2 wk. Populations of several zooplankton species were severely reduced by 15 μg/L; for example, the population of the rotifer Conochilus unicornis was reduced to less than 1% of that in controls. Secondary, indirect effects included significant increases of a few populations, including Bosmina longirostris and Keratella cochlearis, for zinc additions of 15 and 30 μg/L. Most of the populations and community properties that we measured showed somewhat different percentage reductions in response to a given zinc addition at different times, but their relative (rank) values at different times were similar. Specific zooplankton populations were more sensitive to zinc than community similarity indices, and species diversity indices were relatively insensitive. Bioaccumulation of zinc by different species of crustaceans increased with added zinc but showed few significant differences among species. The small differences among species could, nevertheless, partially account for some of the observed changes in zooplankton community structure.
Bottlenose Dolphins, Tursiops truncatus, Can Detect Oil
Authors: Geraci J. R. , St. Aubin D. J. , Reisman R. J.
Published: May 2008

Two trained bottlenose dolphins, Tursiops truncatus, were tested for their ability to detect visually 12 different oils and 22 oil mixtures confined at the surface in small cylinders. Detection thresholds were established in tests using progressively lighter substances. The animals detected 6-mm slicks of crude, residual, and refined motor oils, and diesel slicks thicker than 17 mm. They could not detect 6-mm thicknesses of leaded gasoline or transparent mineral oil. One dolphin's ability to detect oil improved with experience. While blindfolded, one dolphin could detect 12-mm-thick samples of two crude oils, Bunker C and mineral oil, but only when the latter two were churned and contained air bubbles. We conclude that dolphins detect the thicker concentrations of oil that occur near the source of an oceanic spill, but not lightly colored or refined products that tend to disperse into thin films.
Feasibility of Snow Clearing to Improve Dissolved Oxygen Conditions in a Winterkill Lake
Authors: Barica J. , Gibson J. , Howard W.
Published: May 2008

Although periodic mechanical snow removal from the surface of an experimental plot on Rock Lake, southern Manitoba, between January and February, did not provide an expected increase of dissolved oxygen levels that would reduce the likelihood of fish winterkill in the localized area of the lake, it provided a basis for analyzing the practicality and feasibility of the method. The minimum lake area to be kept clear of snow for prevention of winterkill was calculated to be 15% of the total lake area. Snow clearing should start soon after freeze-up to provide at least 0.3 g∙m−2 d−1 dissolved oxygen needed to compensate for bacterial oxygen uptake during the winter months.
Salmonid Whirling Disease: Dynamics of Experimental Production of the Infective Stage — the Triactinomyxon Spore
Authors: Markiw Maria E.
Published: May 2008

In two trials, spores of the myxosporean Myxosoma cerebralis were added to aquaria containing specific-parasite-free tubificid oligochaetes held at 12.5 °C. After 104–113 d, the tubificids gave rise to and released actinosporean spores of triactinomyxon form, the alternate life stage of M. cerebralis and the initiator of salmonid whirling disease. Production of triactinomyxon spores peaked during days 154–190, and then declined almost as abruptly as it had risen. The triactinomyxon spores were released at trace levels for 9 mo after they first appeared. In a second trial, 26–50 million triactinomyxon spores were produced. The approximate yield from each tubificid was 730–3420 spores. The prevalence of experimentally infected tubificids was about 20%.
Growth of Lampsilis radiata (Bivalvia: Unionidae) in Sand and Mud: A Reciprocal Transplant Experiment
Authors: Hinch Scott G. , Bailey Robert C. , Green Roger H.
Published: May 2008

To examine the effects of habitat on shell growth and form, freshwater unionid clams (Lampsilis radiata) were reciprocally transplanted between a sandy and a muddy site in Inner Long Point Bay, Lake Erie. There were significant differences in the initial shell dimensions of the two populations, with the sand clams being larger and less obese than the mud clams. Pretransplant growth rate analysis, using annual rings, showed that long-term growth in the sand was greater than that in the mud. After 16 wk the transplanted clams were recovered. Overall growth rate was affected by the source of the clams, while transplant destination affected shape change (height growth per unit length growth). This suggests that shell growth rates may be under direct genetic control, while shell shape can be adaptively modified by environmental cues.
Further Analysis of Population Trends in the Northwest Atlantic Harp Seal (Phoca groenlandica) from 1967 to 1985
Authors: Roff Derek , Bowen W. Don
Published: May 2008

We examined changes in the age structure of the northwest Atlantic harp seal (Phoca groenlandica) population from 1967 to 1983. Through this period there has been a statistically significant population increase in the proportion of seals aged 2–6 yr. Precise estimation of the rate of increase is hindered by a tendency for immature seals to be overrepresented in samples of molting males. Two methods were developed to correct for this bias; these provide a minimum estimate of the proportion of seals aged 2–6 yr present in 1967. Utilizing a simulation model, we showed that the unadjusted and adjusted age distributions are both extremes and that the correct distribution probably lies between them. In both cases the data are more consistent with an increasing than a decreasing population, given the level of catch experienced by this population up to 1982. Recent total catches of 75 000 or less in 1983 and 1984 are substantially below the most conservative estimates of replacement yield in 1985 and will result in a further, more rapid population increase.
Current Response and Agonistic Behavior in Newly Emerged Fry of Chinook Salmon,Oncorhynchus tshawytscha, from Ocean- and Stream- Type Populations
Authors: Taylor Eric B. , Larkin P. A.
Published: May 2008

In Slim Creek, a tributary to the upper Fraser River east of Prince George, B.C., chinook salmon (Oncorhynchus tshawytscha) fry summer and overwinter in their natal stream before migrating seaward as yearlings; they are "stream-type" in juvenile life history pattern. From the Harrison River, a tributary to the lower Fraser River, chinook fry migrate to the Fraser River estuary sometime during their first spring or early summer; they are "ocean-type." Newly emerged chinook fry from Slim Creek showed a stronger positive current response, were more aggressive in mirror image stimulation tests and intra- and inter-specific (with coho salmon (O. kisutch) fry) stream tank tests, and had larger and more brightly colored median fins than chinook fry from the Harrison River. These differences between Slim Creek and Harrison River chinook fry are in a direction consistent with their different patterns of length of freshwater residence as juveniles, since aggressive behavior, positive rheotaxis, and bright fin coloration are important components of extended stream residence in salmonids.
Size Selectivity of Coho (Oncorhynchus kisutch) Preying on Juvenile Chum Salmon (O.keta)
Authors: Hargreaves N. Brent , LeBrasseur Robin J.
Published: May 2008

Predation may be a major source of size-dependent mortality of Pacific salmon (Oncorhynchus spp.) during early sea life. Our experiments conducted in large saltwater enclosures demonstrated that coho (Oncorhynchus kisutch) are size selective when preying on juvenile chum (O. keta) salmon. Yearling coho (112–130 mm fork length) consumed significantly more smaller chum over a range in prey size of 43–63 mm fork length. We hypothesize that the intensity of size selectivity by coho and other predators is variable, depending on the relative sizes of the predators and prey.
Natural and Acquired Agglutinins toAeromonas hydrophilain Carp (Cyprinus carpio)
Authors: Lamers C. H. J. , Muiswinkel W. B. Van
Published: May 2008

Formalin-killed Aeromonas hydrophila cells (F-Ah) and heat-inactivated and fragmented A. hydrophila cells (H-Ah) both evoked agglutinin titers in carp (Cyprinus carpio) at 21 °C, which persisted for at least 8 mo. The height of the agglutinin response depended on the antigen dose and bacterin. H-Ah injection induced the highest agglutinin production. The peak day of the response was dependent not on antigen dose, but on bacterin type (day 14 and 20 for H-Ah and F-Ah, respectively). Antisera raised against the two bacterins differed in agglutinating properties. F-Ah induced agglutinins which were mainly directed to A. hydrophila lipopolysaccharide (LPS), whereas H-Ah induced activity against other bacterial antigens. Sephadex G200 fractionation of immune (anti F-Ah) and non-immune sera resulted in four and three protein peaks, respectively. The peak of immunoglobulin (Ig) coincided with the first protein peak. ln immune serum, the first peak agglutinated both F-Ah and H-Ah, but the third peak contained only H-Ah agglutinating activity. In non-immune serum, only fractions of the second and third peak showed some agglutination with H-Ah predominantly.
Model for Streamwater Chemistry of a Tributary to Harp Lake, Ontario
Authors: Rustad Steinar , Christophersen Nils , Seip Hans M. , Dillon Peter J.
Published: May 2008

The model is an extended version of the "Birkenes" model and consists of a hydrological submodel with a snow reservoir and two soil reservoirs, a sulphate submodel, and a submodel including H+, Ca2+ + Mg2+, Al, Na+, [Formula: see text], and organic anions. Major processes incorporated are different hydrologic flow patterns during highflow and lowflow, [Formula: see text] adsorption/desorption, ion exchange, weathering, gibbsite solubility, and equilibria with CO2 in soil and stream water. The model reproduces important daily and seasonal trends in the observed streamwater chemistry. Tentative model runs have been carried out to simulate the effects of both a doubling and a 50% reduction in the present sulphur deposition. At present the pH of the stream is generally above 5.7, with values approaching pH 5.3 during snowmelt highflow. According to the simulations, lowflow pH is not sensitive to changes in deposition. At snowmelt highflow, however, a 50% reduction in the deposition could cause a pH increase of 0.2–0.5 unit whereas a doubling could result in pH depressions of 0.5–0.9 unit.
Use of Calcareous Otic Elements (Statoliths) to Determine Age of Sea Lamprey Ammocoetes (Petromyzon marinus)
Authors: Volk Eric C.
Published: May 2008

I examined the possibility that the number of internal bands in calcareous otic elements (statoliths) of sea lamprey ammocoetes (Petromyzon marinus) could be used to estimate age. The correspondence between statolith band number and known ammocoete age was very close for the first 4 yr but less rigorous for the few 7-yr-old specimens examined. This is the first use of calcareous otic elements to determine age in a nonteleost and represents the only direct age determination technique for lampreys. Compared with length–frequency analysis, this method will provide greater reliability of age determinations, essential for investigations on the life history and ecology of sea lampreys.
Factors Affecting Alkalinity Concentrations of Streamwater during Snowmelt in Central Ontario
Authors: Molot Lewis A. , Dillon P. J. , LaZerte B. D.
Published: May 2008

Relative contributions of changes in base cations and acid anions to alkalinity decreases during spring snowmelt in 1984–86 were analyzed for 15 headwater streams and lake outflows in three central Ontario catchments. During episodes, concentration changes in ions which contributed to alkalinity decreases were partially offset by smaller changes in other ions which contributed to alkalinity increases. The major contributor to alkalinity depressions was base cation dilution by snowmelt water. Akalinity depressions were more likely to be dominated by SO42− increases in streams that were more acidic. Neither nitrate nor organic acid anions were significant contributors to alkalinity depressions. Discharge was highly correlated with alkalinity in a circumneutral stream but not in an acidic stream and is consistent with dilution being less important as a cause of alkalinity depressions as streams become more acidic.
Temporal and Spatial Dynamics of a Coastal Pelagic Species,Sardinella maderensisoff the Ivory Coast
Authors: Mendelssohn Roy , Cury Philippe
Published: May 2008

Variations of fortnightly catch-per-unit-effort (CPUE) of Sardinella maderensis off the Ivory Coast is studied both in time and in space–time. Using multivariate time series models, lagged values of coastal sea surface temperature (SST) and salinity explain 33% of the variation of CPUE during this period. When optimal transformations are estimated, 55% of the variance is explained. The optimal transformations suggest that good catch rates are associated with local upwelling or oceanic frontal structures. However, the model differs significantly from previous models that examine the CPUE for the combined catches of the fleet. The model is shown to produce reasonable forecasts for the next two years. In space–time, evidence is presented that suggests that the migration of the fish between areas is related to movement of structures in the ocean. The relationships between CPUE and the environment are again highly nonlinear, so that linear analysis, such as correlation analysis, will be of limited use in examining these questions.
Effects of Snail Grazing on the Diversity and Structure of a Periphyton Community in a Eutrophic Pond
Authors: Swamikannu Xavier , Hoagland Kyle D.
Published: May 2008

Periphyton diversity was highest at low to intermediate levels of grazing by the freshwater snail Physella and suppressed at high grazer densities, in partial support of the intermediate disturbance hypothesis. For the first time, the response curve of algal biomass versus a range of snail densities was used to establish low, intermediate, and high levels of community disturbance. Physella densities corresponding to these levels were added to net enclosures in a small eutrophic pond, to examine differences in attached algal cell densities and diversity after 20 d. Algal standing crop was enhanced in low and depressed in intermediate and higher grazer treatments. Five categories of attached algal response to grazing were identified: (1) filamentous algae suppressed at high grazing pressure; (2) rosette or filamentous taxa suppressed at moderate to high levels of grazing; (3) algae resistant to grazing via sediment-associated recruitment; (4) low profile algae with highest densities at moderate grazing, and; (5) prostrately attached taxa enhanced at moderate and high grazing levels, in contrast to marine macroalgal communities, the primary mechanism mediating community response to different levels of grazing was the morphology of algal attachment.
Revised Morphological Relationships Within the Amphipod GeneraPontoporeiaandGammaracanthusand the "Glacial Relict" Significance of their Postglacial Distributions
Authors: Bousfield E. L.
Published: May 2008

The Holarctic coastal marine and freshwater members of the amphipod families Pontoporeiidae and Gammaracanthidae reveal much greater taxonomical, distributional–ecological, and physiological diversity than formerly recognized. Pontoporeia is formally divided into three full genera (comprising more than 20 species), namely, Pontoporeia (Kroyer, 1842; Monoporeia, new genus, and Diporeia, new genus. Gammaracanthus is divided into two full genera (encompassing about a dozen species) namely, Gammaracanthus Bate, 1862, and Relictacanthus, new genus; Gammaracanthus is divided into the subgenera Gammaracanthus Bate, and Pseudacanthus, new subgenus. The genera are transferred from family Gammaridae, superfamily Gammaroidea, to family Gammaracanthidae (newly diagnosed herein) within superfamily Eusiroidea. Two lines of evidence refute previous theories (e.g. Hogbom's "sluicing up" theory) concerning the origin and evolution of the so called glacial and marine–glacial crustacean fauna of the northern hemisphere: (1) the broad taxonomic diversity of pontoporeiid and gammaracanthid amphipods; and (2) the regional endemicity of primary freshwater members of Eurasia and North America, between which no intercontinental exchange apparently took place during Pleistocene and recent times. A more credible explanation for such taxonomic and biogeographical diversity requires a much longer time frame (e.g. late Cretaceous to late Tertiary times).
Specificity of the Gustatory Chemoreceptors for CO2and H+in Rainbow Trout (Oncorhynchus mykiss)
Authors: Yamashita S. , Evans R. E. , Hara Toshiaki J.
Published: May 2008

Response characteristics of the gustatory chemoreceptors to CO2and H+were electrophysiologicaliy studied in rainbow trout (Oncorhynchus mykiss) in decarbonated, natural water. The integrated responses of the whole nerve bundle as well as single fibre responses were recorded from the palatine nerve (a branch of VIIth cranial nerve) innervating the anterior palate and inside the upper lip. Gustatory receptors were highly sensitive to both CO2and H+, with estimated threshold concentrations of 4 × 10−5and 5 × 10−5 mol∙L−1, respectively. Responses to CO2were not affected by pH, and adaptation to amino acids and bile salts had little effect on CO2responses. None of the single fibers responding to CO2responded to other gustatory stimuli including amino acids and bile salts. We conclude that rainbow trout distinguish CO2from H+, and further that chemoreceptors for CO2are distinct from those which detect other gustatory stimuli.