bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Metals on the Biomass Production Kinetics of Freshwater Copepods
Authors: Borgmann U. , Cove R. , Loveridge C.
Published: May 2008

The effects of cadmium, copper, mercury, lead, and arsenic on the growth and mortality rates of a natural assemblage of copepods using natural food and water were determined. A seasonal cycle in toxicity was observed for all the metals except arsenic. Lead toxicity appeared to be related to the ash-free dry weight of the seston, but the reason for the variation in toxicity of cadmium, copper, and mercury remain unknown. The chronic toxicity of some metals differs much less between copepods and daphnids than does acute toxicity. The mathematical relationship between growth and mortality rates and metal concentration is discussed and a technique for calculating a sublethally toxic concentration is described.Key words: copepods, heavy metals, biomass production, cadmium, copper, mercury, lead, arsenic, toxicity
Effect of Number of Marked Fish and Years of Repetition on Precision in Studies of Contribution to a Fishery
Authors: Reisenbichler R. R. , Hartmann Jr. N. A.
Published: May 2008

Methods are developed for predicting the expected precision for studies of the contribution of fish to a fishery, based upon the number of fish marked and the number of years an experiment is repeated. Studies concerned with estimating catch–release ratios, comparing catch–release ratios, and comparing distributions of catch are considered. It is suggested that releases of marked fish should be repeated for at least three or four broods, and often there is little advantage in releasing more than 50 000 marked fish per release group. Although we explicitly address studies of contribution to ocean fisheries, the methods apply directly to a broad range of studies involving marked fish, from evaluations of harvest rates on catchable-trout plants to estimates of catch–escapement ratios for Pacific salmon.Key words: precision, experimental design, number of fish to mark, number of years to release marked fish, catch–release ratios, distribution of catch
Bongo Net Retention Rates as Effected by Towing Speed and Mesh Size
Authors: Colton Jr J. B. , Green J. R. , Byron R. R. , Frisella J. L.
Published: May 2008

A comparison of 0.253- and 0.333-mm mesh bongo net retention rates at towing speeds of 1.5 and 3.5 knots showed no significant mesh size related variation in filtration efficiency or in abundance of larval herring at either towing speed. For 1.5-knot tows there was no significant mesh size difference in larval herring length frequency distribution. For 3.5-knot tows, the distributions of lengths were significantly different for the two mesh sizes. The condition of herring larvae was noticeably better in the 1.5-knot tow samples (3%, of yolk-sac larvae caught in 3.5-knot tows had their yolk sac intact compared to 50% from 1.5-knot tows). Feeding incidence was higher for larvae caught in 1.5-knot tows (71%) than for larvae caught in 3.5-knot tows (50%).At a towing speed of 3.5 knots the 0.253-mm mesh zooplankton displacement volumes were significantly greater than the 0.333-mm mesh displacement volumes. At a towing speed of 1.5 knots the difference in displacement volumes was not significant. Adult Oithona spp. and Pseudo-Paracalanus spp., unidentified copepodites, and adult and juvenile Hyperia spp. were caught in significantly greater numbers by the 0.253-mm mesh net at both towing speeds. The 0.253-mm/0.333-mm abundance ratios were greatest for the smaller and more abundant invertebrate taxa. The variation in zooplankton retention rates resulted in large part from differences in mesh size, although catching efficiency was also influenced by tow speed. A substantial proportion of the food items in the guts of all size groups of larval herring consisted of taxa which were not retained by either mesh net (invertebrate eggs, copepod nauplii, Oithona spp., and Pseudo-Paracalanrrs spp. copepodites). Size was the most important factor in prey selection and the average size of food items increased with increased length of herring larvae. On the basis of this analysis, sampling strategies are suggested for future surveys. Key words: bongo nets, retention rates, ichthyoplankton, larval herring, zooplankton, feeding incidence
Diets of Ictalurus nebulosus and Pomoxis nigromaculatus altered by diflubenzuron
Authors: Colwell A. E. , Schaefer C. H.
Published: May 2008

Diflubenzuron was applied to five experimental ponds, yielding a mean concentration of 13 μg/L. Residues in the water declined below detectable limits (0.2 μg/L) by 14 d posttreatment. Young-of-the-year black crappie (Pomoxis nigromaculatus) and brown bullhead (Ictalurus nebulosus) accumulated diflubenzuron and then eliminated all residues by 7 d posttreatment. No fish mortalities occurred after the treatment. For 1 mo following treatment, stomach content analyses indicated major alterations in the diets of the fish. Growth rates and condition factors of the fish 3 mo after treatment were similar to control fish in four untreated ponds.Key words: diflubenzuron, Pomoxis nigromaculatus, Ictalurus nebulosus, condition factor, growth, aquatic invertebrates
Direct Determination of Apatite in Lake Sediments
Authors: Reid R. P. , Pharo C. H. , Barnes W. C.
Published: May 2008

Apatite is a common accessory mineral in the source rocks for the glacial debris supplying sediments to many Canadian lakes. A method has been developed which uses scanning electron microscopy and energy dispersive X-ray emission spectrometry for direct identification of apatite. This method has been used to examine the apatite content of various size fractions in Kamloops Lake sediments. Apatite concentrations obtained by this direct examination correlate well (r > 0.999) with apatite concentrations determined by chemical analyses and indicate that, in addition to comprising as much as 70% of the total phosphorus load, apatite may comprise as much as one-third of the "dissolved" (< 0.45 μm) inorganic phosphorus load. Consequently the use of classical (e.g. Vollenweider 1968; Vollenweider and Dillon 1974) methods of estimating lake trophic state from inorganic phosphorus concentrations in lake water must be done with care, recognizing that the bulk of inorganic phosphorus in lakes deriving sediment from glaciated igneous or metamorphic terrains may be in the form of apatite.Key words: apatite, lake, trophic state, phosphorus load, scanning electron microscopy
Natural Sources and Requirements of Phosphorus for Fishes
Authors: Nakashima Brian S. , Leggett William C.
Published: May 2008

The hypothesis that daily consumption of natural prey provides a source of phosphorus sufficient to meet growth and metabolic requirements of fishes is examined. Fish may be capable of utilizing available phosphorus directly from the water; however, this source is negligible in comparison to dietary intake. Experiments were designed to test the effect of different dietary phosphorus levels, chosen to approximate those of natural prey items, on growth of juvenile perch at temperatures encountered during the growing season. Rations were based upon estimates of daily food consumption for perch in Lake Memphremagog. Growth was significantly temperature-dependent and independent of dietary phosphorus levels. Phosphorus:ash ratios of whole fish were not significantly different among diet treatments or between the initiation and termination of the growth experiment. Excretion of phosphorus was positively related to phosphorus intake.Key words: absorption efficiency, daily ration, growth, Lake Memphremagog, nutrition, Perca flavescens, phosphorus budget, yellow perch
Quantitative Measurements of Euphausiids Using a 120-kHz Sounder and Their in situ Orientation
Authors: Sameoto D. D.
Published: May 2008

Biomass and density of euphausiids were estimated using a 120-kHz sounder during 2 y in the Gulf of St. Lawrence. Simultaneously, biological samples were taken with two types of multiple opening and closing nets: MOCNESS-type and BIONESS. Correlations for biomass and density estimates between the acoustic and biological data range from 0.391 to 0.791. Acoustic data showed that a high percentage of euphausiids avoided the MOCNESS-type net during the day. A comparison of the relationship between biological and acoustic data for both years showed that the BIONESS sampler captured euphausiids more efficiently during both day and night. Target strength of the euphausiids estimated from acoustic and biological data showed that it was lower than would be expected if the animals were oriented horizontally. Photographs taken from the BIONESS sampler at depths having acoustic scattering layers showed that the average orientation of euphausiids changed with time, the average orientation being closest to horizontal during daytime. Orientation changed from 27° from the horizontal at 14:00 to 51° during 02:00. The effect of orientation on target strength is discussed.Key words: euphausiids, acoustics, orientation, biomass, underwater photography, multiple net samplers, zooplankton
La mesure du pH en milieu estuarien sur l'échelle NBS
Authors: Pelletier E. , Lebel J.
Published: May 2008

An adjustment is proposed to the classical method of measuring pH in an estuarine and inshore environment. The reproducibility obtained is ±0.005 pH units for 95% of analyzed samples. The use of a secondary standard with high ionic strength makes it possible to follow and correct the slow drift of electrodes which usually happens when a long series of analyses is made on board. The method is estimated to be accurate to ±0.010 pH units and does not appear to be sensitive to abrupt variations of ionic strength of successive samples. The use of this simple and practical method can contribute to a better knowledge of pH variability in estuaries.
Stimulation of Nitrate Uptake and Photosynthesis by Molybdenum in Castle Lake, California
Authors: Axler R. P. , Gersberg R. M. , Goldman C. R.
Published: May 2008

The uptake rates of 15NO3 and 14CO2 by the natural phytoplankton community at Castle Lake, California, were measured in situ as responses to 5 μg∙L−1 additions of molybdenum. Stimulation of both nitrate uptake and photosynthesis occurred in water samples containing only relatively high amounts of nitrate. This response to added molybdenum disappeared as the growing season progressed and nitrate was depleted in the euphotic zone. Although molybdenum stimulated nitrate uptake by 55% in water collected from the lower euphotic zone, it did not increase the rate of CO2 uptake because at that depth the rate of photosynthesis was most limited by light intensity and not by nitrogen. An analysis of molybdenum bioassays from 1959 to 1963 is integrated with these findings and points to the importance of molybdenum for phytoplankton growth during the early portion of the growing season when nitrate concentrations in the euphotic zone are maximal.Key words: molybdenum, nitrate, nitrate uptake, micronutrient bioassays
Variability of Dentin Deposits in Tursiops truncatus
Authors: Hui Clifford A.
Published: May 2008

Dentin is deposited in approximately annual cycles in Tursiops truncatus for at least the first 11 yr. There were no consistent differences in the dentinal layer count between the left and right sides nor between the mandible and maxilla in the teeth of nine animals studied. The posterior teeth, however, have a greater number of growth layer groups (GLGs). The differences in the number of GLGs among teeth of the same individual increase unpredictably when there are more than about 15 GLGs in the posterior teeth. Only minimal age may be determined using dentinal counts.Key words: age determination, dentin, dolphins, odontocetes, teeth, Tursiops
Estimation of Biological Power Functions from Group Measurements
Authors: Cammen Leon M.
Published: May 2008

Nonlinear regression can be used to estimate the parameters of power functions (Y = αXβ) when the only available data are group measurements of the dependent variable and individual measurements of the independent variable. Possible applications are to length–weight and weight–metabolism relations of natural populations of organisms.Key words: power functions, length–weight relations, metabolism–weight relations, nonlinear regression
Detection of Corynebacterium salmoninus by Direct Fluorescent Antibody Test
Authors: Bullock G. L. , Griffin B. R. , Stuckey H. M.
Published: May 2008

A direct fluorescent antibody test (FAT) was developed for detecting Corynebacterium salmoninus, causative agent of bacterial kidney disease. The direct procedure was found to be as specific as the previously described indirect test, and requires only 7 min—about [Formula: see text] as much time—to perform. A comparison of the direct FAT with the Gram stain for sensitivity of detecting the bacterium indicated the fluorescent procedure to be 100 to 1000 times more sensitive. Furthermore, the FAT is highly effective and efficient for screening large numbers of samples.Key words: Corynebacterium salmoninus, detection, bacterial kidney disease, direct fluorescent antibody test
Statistical Problems in Studies of Temperature Preference of Fishes
Authors: Mathur Dilip , Silver Carl A.
Published: May 2008

When the laboratory determined acute temperature preference vs. acclimation relationship of fishes is analyzed, the correct assessment of degrees of freedom is central to analyses of covariance, analysis of variance, and regression analysis. Many investigators have assumed that recordings of fish positions in a horizontal temperature gradient trough made at 1 -min intervals in a test of 20-min duration represent 20 degrees of freedom. Such an assumption can arbitrarily allow an investigator to increase or decrease the number of degrees of freedom by simply shortening or lengthening the time intervals for observation of the position of fish in the trough. We contend that each temperature preference test provides only one data point (single degree of freedom) even though an investigator may have used more than one fish in a test. Failure to recognize this distinction may lead to erroneous conclusions from data. For illustrative purposes, we reanalyzed three sets of published data using the correct number of degrees of freedom. The reanalysis showed that the significant values were overstated.Key words: statistics, analysis, sample size, temperature, preference, fishes
Stocks are Chameleons: Plasticity in Gill Rakers of Coregonid Fishes
Authors: Lindsey C. C.
Published: May 2008

The characters that apparently render a stock of fish distinctive may in reality be a reflection of the presence or absence of other fish species with which the stock shares its environment. Over the northern hemisphere, the whitefish genera Coregonus, "Leucichthys," and Prosopium offer striking examples of morphological characters being displaced because of coinhabiting species. Whenever one of the groups is missing, another tends to shift its gill rakers so as to fill in the vacant part of the spectrum in gill-raker counts. Plankton-feeding lake whitefish (Coregonus clupeaformis) having many long gill rakers exist in several lakes sympatrically with bottom-feeding lake whitefish having fewer and shorter gill rakers, but only if the even more specialized plankton-feeding species of ciscoes are absent. Lake whitefish in Yukon Territory have on the average fewer rakers in those lakes that contain ciscoes than in those that do not. Artificial transplants demonstrate that gill-raker characteristics can change quickly in a new environment. Gill-raker count is less subject to phenotypically induced variation from environmental influences than are most morphological characters, but it is not immune. Partial hybridization, where bimodal populations are maintained by a balance between gene flow and selection, also poses special problems for the stock concept. When employing even relatively stable characters such as gill-raker counts, one should beware that the "stocks" may be chameleons which shift their appearance in response to the biological color of their surroundings.Key words: coregonids, whitefish, gill rakers, phenotypic variation, hybridization, selection, transplants, stocks
Changes in the Average Size and Average Age of Pacific Salmon
Authors: Ricker W. E.
Published: May 2008

Of the five species of Pacific salmon in British Columbia, chinook salmon (Oncorhynchus tshawytscha) and coho salmon (O. kisutch) are harvested during their growing seasons, while pink salmon (O. gorbuscha), chum salmon (O. keta), and sockeye salmon (O. nerka) are taken only after practically all of their growth is completed. The size of the fish caught, of all species, has decreased, but to different degrees and over different time periods, and for the most part this results from a size decrease in the population. These decreases do not exhibit significant correlations with available ocean temperature or salinity series, except that for sockeye lower temperature is associated with larger size. Chinook salmon have decreased greatly in both size and age since the 1920s, most importantly because nonmaturing individuals are taken by the troll fishery; hence individuals that mature at older ages are harvested more intensively, which decreases the percentage of older ones available both directly and cumulatively because the spawners include an excess of younger fish. Other species have decreased in size principally since 1950, when the change to payment by the pound rather than by the piece made it profitable for the gill-netters to harvest more of the larger fish. Cohos and pinks exhibit the greatest decreases, these being almost entirely a cumulative genetic effect caused by commercial trolls and gill nets removing fish of larger than average size. However, cohos reared in the Strait of Georgia have not decreased in size, possibly because sport trolling has different selection characteristics or because of the increase in the hatchery-reared component of the catch. The mean size of chum and sockeye salmon caught has changed much less than that of the other species. Chums have the additional peculiarity that gill nets tend to take smaller individuals than seines do and that their mean age has increased, at least between 1957 and 1972. That overall mean size has nevertheless decreased somewhat may be related to the fact that younger-maturing individuals grow much faster than older-maturing ones; hence excess removal of the smaller younger fish tends to depress growth rate. Among sockeye the decrease in size has apparently been retarded by an increase in growth rate related to the gradual cooling of the ocean since 1940. However, selection has had two important effects: an increase in the percentage of age-3 "jacks" in some stocks, these being little harvested, and an increase in the difference in size between sockeye having three and four ocean growing seasons, respectively.Key words: Pacific salmon, age changes, size changes, fishery, environment, selection, heritability
Comparative Survival and Growth of Planted Wild, Hybrid, and Domestic Strains of Brook Trout (Salvelinus fontinalis) in Ontario Lakes
Authors: Fraser J. M.
Published: May 2008

Matched plantings of domestic strain and interstrain hybrid (or wild strain) brook trout (Salvelinus fontinalis) were made annually in nine small Precambrian Shield lakes during 1973–77. Recoveries of planted fish were made by gillnetting and/or angling during 1974–80. In six study lakes, hybrids (and wild strains) were recovered at rates two to four times greater than the domestic strain; in three lakes recoveries were similar. Most domestic strain trout were caught in the year following planting whereas recoveries of hybrids and wild strains were spread over 3–4 yr. Each kilogram of hybrid (or wild) planted yielded 5.6 kg (1.2–12.3); each kilogram of domestic strain planted yielded 0.8 kg (0.2–2.1). Lakes containing only minnows and sticklebacks yielded the highest returns of brook trout; lakes containing competitive species yielded low returns. Rapid growth of brook trout occurred in lakes containing only minnows and sticklebacks; slowest growth was noted in lakes supporting white suckers (Catostomus commersoni). Domestic strain brook trout and the matched hybrid grew at approximately the same rate within a lake and in seven of the nine lakes ate the same food. The performance of the Nipigon × domestic hybrid qualifies it for consideration as a replacement for the domestic brook trout presently planted in Ontario lakes.Key words: planting, brook trout, trout strain, hybrid, Precambrian Shield, survival, stock
Structure and Affinities of Freshwater Sea Lamprey (Petromyzon marinus) Populations
Authors: Brussard Peter F. , Hall Marjorie Collings , Wright Janet
Published: May 2008

We have examined genetic differentiation at 23 loci in 12 populations of sea lamprey, Petromyzon marinus, by means of starch gel electrophoresis. Based on two measures of overall genetic distance and two clustering methods, our analysis shows that there are three genetically distinct groups of lamprey in eastern North America: (1) anadromous populations plus those in Lake Champlain, (2) populations in Lake Erie and the upper Great Lakes, and (3) populations in Lake Ontario and three interior New York Lakes (Cayuga, Seneca, and Oneida). Analysis of population subdivision using contiguity partitions and simultaneous test procedures (STP) confirms the above conclusions and offers additional insight into the genetic structure of lamprey in this area.Key words: sea lamprey, Petromyzon marinus; genetic variation, electrophoresis, population structuring
Historical Evidence for Discrete Stocks of Lake Trout (Salvelinus namaycush) in Lake Michigan
Authors: Brown Jr. E. H. , Eck G. W. , Foster N. R. , Horrall R. M. , Coberly C. E.
Published: May 2008

Although few biological data exist on the now extinct native lake trout, Salvelinus namaycush, of Lake Michigan, historical records and interviews with former commercial fishermen strongly suggest that this once widespread resource was composed of a number of discrete spawning populations or stocks. A natural division of the resource into distinct stocks is consistent with the size of Lake Michigan and its varied physiography. The native trout may have undergone subtle genetic changes over the millennia, although we cannot determine whether the physical and behavioral differences represented different genotypes or only temporary effects of the local environment. Because of physiographic similarities among the upper Great Lakes and probable interchanges of lake trout during the last glacial period, we recommend that progeny of extant wild stocks, particularly from Lake Superior, are genetically most suitable for recolonizing Lake Michigan. Moreover, the hatchery-held parents of such fish should be infused periodically with genes of the wild or feral donor populations. Despite the sound historical basis for these recommendations, we also recognize that sufficiently high stocking rates coupled with a reduction of heavy exploitation may be even more important than heritability in obtaining self-sustaining populations.Key words: lake trout, discrete stocks, Lake Michigan, historical changes, phenotype, homing, extinction, planted strains, rehabilitation
Variation among Stocks of Walleye (Stizostedion vitreum vitreum): Management Implications
Authors: Colby Peter J. , Nepszy Stephen J.
Published: May 2008

Identification of races, strains, or subpopulations of walleye (Stizostedion vitreum vitreum) by examining differences in the morphology or biochemistry has met with relatively limited success. Although there is some genotypic evidence for stock discreteness, most evidence points to differences (age, growth, fecundity, maturity) which are believed to be phenotypic expressions induced by the environment. Thus, in the absence of clear genetic evidence, the biological differences are the reliable means of identifying and managing walleye stocks.Walleye populations are spatially distinct, varying greatly in their rate of growth, rate of maturity, and longevity throughout their distributional range. Any genotypic expression of these population characteristics would probably be masked by environmental influences. There is no concrete evidence that differences in growth, age to maturity, fecundity, and longevity among walleyes are inheritable. The possibility of southern walleye populations being obligative riverine spawners suggests genetic differences, but this needs to be substantiated.Some of the physiological variables used to delineate the responses of stocks to their environment can be useful as management tools to measure their responses to various disturbances, for example, exploitation and habitat modification. Measurement of specific fecundity indicates the relative ability of species to replace themselves. Measurements of mean age of the catch and age of onset of sexual maturity provide information used in protecting the brood stock and rate of maturity indices are more recent examples of these management initiatives.The trend in time responses (mean age, age to maturity, catch per unit effort, etc.) to exploitation of walleye stocks in the Great Lakes and larger inland lakes illustrate the appropriateness of monitoring these variables. Age to maturity, mean age of the catch, and fecundity will also be useful variables in determining the compensatory reserve to population reduction among walleye stocks inhabiting various energy and nutrient regimes. Using examples of heavily exploited walleye populations, we have made an initial attempt to show the degree of compensation in different energy regimes. A crisis curve is given to warn when various walleye stocks are in danger of collapse due to commercial overexploitation.Key words: walleye, phenotypic and genotypic difference, stock, distribution, rate of maturity, fecundity, walleye management
Community Consequences of Fish Stock Diversity
Authors: Ryder R. A. , Kerr S. R. , Taylor W. W. , Larkin P. A.
Published: May 2008

Genotypes are variable among fish stocks, and these limit potential niche. In turn, realized niche is further constrained by the interaction of abiotic and biotic environmental factors, together with fishery exploitation. Selection pressures by these three factors provide feedback on genotypes, modifying potential niches. The steady-state consequence of this process is a harmonic community of co-evolved stocks. Using community size structure as one of our criteria, we trace the effects of the major classes of perturbation on harmonic communities, and discuss their management implications.Key words: harmonic community, co-evolution, fish stock, management, genetics, biotic and abiotic environmental factors, niche
Guidelines for the Culture of Fish Stocks for Resource Management
Authors: Hynes J. D. , Brown Jr. E. H. , Helle J. H. , Ryman N. , Webster D. A.
Published: May 2008

Examples of desired genetic changes produced in fish by selective breeding are contrasted with those of unintentional and often harmful genetic changes resulting from artificial propagation over prolonged periods, e.g. reduced longevity and reduced temperature tolerance. Evidence for undesired effects caused by the hatchery environment on captive fish stocks is also presented, e.g. precocity, inappropriate feeding behavior, and the risks posed by artificial rearing techniques are discussed. Methods for identifying both genetic and environmentally induced changes are outlined along with experimental designs for distinguishing between them. Some practical recommendations are offered for establishing, developing, and maintaining brood stocks in hatcheries and for managing wild fish populations in ways that maximize genetic variability while avoiding the occurrence of undesirable changes. Adherence to the recommended procedures will improve progress in fisheries rehabilitation efforts.Key words: fish culture, genetics, environmental effects, brood stocks, resource management
Genetic Aspects of Fisheries Rehabilitation Programs
Authors: Krueger Charles C. , Gharrett Anthony J. , Dehring Terrence R. , Allendorf Fred W.
Published: May 2008

The stocking of indigenous or exotic fish species is often a desirable aspect of fisheries rehabilitation programs. Two strategies are proposed for the choice of fish for stocking. The first plan involves making separate collections of fish from each of several genetically different populations, performing all possible crosses between the different sources, and then stocking the progeny. In contrast to selective breeding programs, this strategy maximizes genetic variability and then relies on the environment for the selection of the most appropriate genotypes. The second plan is to sample populations from waters environmentally similar to those being rehabilitated that may contain preadapted genotypes. Application of this strategy should consider the use of gene banks or natural refugia as a source of preadapted genetic variability. When gene flow may occur between stocked fish and local populations, the second strategy should be used in favor of the first to minimize the impact on native gene pools. When choosing fish to implement either strategy, it is important to know the distribution of genetic variability within and between populations to sample adequately the variability present.Key words: stocking, genetics, fisheries, rehabilitation, natural selection, exotic introductions, genetic introgression, gene banks, Great Lakes
The Stock Concept, Discreteness of Fish Stocks, and Fisheries Management
Authors: MacLean J. A. , Evans D. O.
Published: May 2008

This paper examines the concept and definition of fish stocks and the processes that influence discreteness of these stocks in light of the tactics necessary for the application of the concept in management. Two approaches to the definition of stocks are discussed. These differ in the extent to which management inputs other than biological ones are considered. We consider definition to be less important than the adoption and development of a stock concept to provide a genetic perspective for fisheries management. The two central levels of the stock concept — the subdivision of species into local populations and the adaptive nature of genetic differences between these populations — are discussed with respect to the interlinked set of ecological and genetic processes that result in subdivision and determine the discreteness of these stocks. Genetic discreteness usually implies some restriction of gene flow, and spatial and temporal mechanisms of isolation are discussed with examples from the STOCS symposium. The structure of subdivided populations is seen as the result of behavioral processes that are one component of a set of coadapted traits, which collectively constitute a life history strategy. The necessity for managers to develop a new integrated view of species, which incorporates both ecological and genetic arguments, is discussed.Key words: stock concept, life history, gene flow, ecological and genetic discreteness, local adaptation stock management
Assessing and Managing Man's Impact on Fish Genetic Resources
Authors: Thorpe J. E. , Koonce J. F. , Borgeson D. , Henderson B. , Lamsa A. , Maitland P. S. , Ross M. A. , Simon R. C. , Walters C.
Published: May 2008

Historically, human activities have adversely affected the genetic resources of many fish species. We suggest that a continuum of vulnerability to loss of genetic resources exists for fishes. Primary determinants of vulnerability are extent of stock structure in populations and fundamental life history features, such as length of juvenile period, sex ratio, and fecundity. The genetic basis for this trend is the relationship between the subdivided state of a population (its stock structure) and important processes of genetic change, which include selection, gene flow, and genetic drift. We relate various human activities to their effects on genetic resources through these genetic processes, and we review various lines of evidence for a relationship between stock structure and genetic diversity. In general, we found that those species whose populations are subdivided into nearly isolated stocks (e.g. Pacific and Atlantic salmon) are more vulnerable to directional changes in genetic composition as well as reduction in overall genetic diversity through loss of some stocks. We also found that similar changes will be difficult to detect, if they occur at all, in less stock-structured species like walleye.Key words: stock structure, genetic diversity
Larval Cohort Succession in Herring (Clupea harengus) and Capelin (Mallotus villosus)
Authors: Lambert Timothy C.
Published: May 2008

Complexities of herring (Clupea harengus) stocks previously alluded to are here explored in detail. Analysis of polymodal larval populations of both herring and capelin (Mallotus villosus) from a number of localities reveals the presence of a succession of larval cohorts over time. Separation of these cohorts in time and space is quantified and similarities and differences between species are indicated. The concept of "feeding range" can be applied in explanation of this cohort phenomenon. I suggest that this reproductive strategy serves to limit intraspecific competition and divides a limited food supply more equitably among the total larval population.
Reproductive Strategies of Demersal and Pelagic Spawning Fish
Authors: Lambert T. C. , Ware D. M.
Published: May 2008

The spawning tactic of herring (Clupea harengus) wherein batches of eggs are deposited leading to a succession of larval cohorts is elaborated. We found the time interval between cohorts to be a function of larval growth rate as well as larval mouth size. In view of the relationship with growth rate we suggest a continuum of reproductive strategies with "bet hedging" by herring at one extreme and an "all at once" egg release by Atlantic mackerel (Scomber scombrus) at the other.
Uptake and Accumulation of Inorganic Tin by a Freshwater Alga, Ankistrodesmus falcatus
Authors: Wong P. T. S. , Maguire R. J. , Chau Y. K. , Kramar O.
Published: May 2008

Uptake of Sn by Ankistrodesmus falcatus occurred very rapidly. The alga accumulated 2.3 and 4.1 mg Sn/g dry weight of cells after 2 and 60 min of incubation, respectively, in the presence of 46 μgSn/L of medium. Increasing Sn concentrations in the medium resulted in a steady increase in the Sn concentrations in the cells. At 6 mg of Sn and 3 mg of dry weight of cells in 1 L of medium, the cells had accumulated 100 mg Sn/g dry weight of cells, representing 10% of the dry cell mass. The uptake of Sn from the medium and the release of Sn from the cells were not affected by other metals (Pb, As, Zn, Cd, Hg, Sb, and Cu). Addition of EDTA, however, caused an immediate and rapid release of 60% of Sn from the cells. Heat-killed cells took up Sn faster and to a higher level than living nonheated cells. About 85% of Sn taken up by the cells was recovered in the cellular polysaccharide fraction and 15% in the protein fraction, while the lipid and the small molecular weight metabolites accounted for 0.2% of the total Sn.
Phosphate Exchange Between Littoral Sediments and Overlying Water in an Oligotrophy North-Temperate Lake
Authors: Twinch A. J. , Peters R. H.
Published: May 2008

The soluble phosphate equilibrium between aerobic sediment and overlying water was examined in intact cores of marginal sediment and water from Lake Memphremagog. Radiotracer experiments demonstrated a dynamic phosphate exchange between sediments and water under steady-state conditions. Perturbations of this equilibrium in batch and continuous-flow systems show that aerobic sediment can act as a phosphate source or sink, depending on the phosphate concentration of the overlying water. The existence of an oxidized microzone on the sediment surface does not preclude phosphate release when concentrations in the overlying water drop below the equilibrium concentration. Under natural conditions, soluble reactive phosphorus concentrations in the surface waters of Lake Memphremagog are always lower than the equilibrium concentrations measured in this study. This suggests that aerobic marginal sediments may serve as a phosphate source in lakes where algal demand maintains low levels of soluble phosphate in the water.
Short-Term Colonization Patterns of Lotic Macroinvertebrates
Authors: Ciborowski Jan J. H. , Clifford Hugh F.
Published: May 2008

To establish colonization of gravel-filled trays by aquatic invertebrates, we used concurrent simultaneous placement/sequential removal and sequential placement/simultaneous removal sampling schedules over 12-d intervals in a river of central Alberta. Colonization trays collected more taxa and greater numbers of animals than did unit area (Hess) samples of the natural substrate. There was no correlation between rank of abundance of the 10 most prevalent taxa found in colonization trays and in Hess samples. The two sampling schedules produced significantly different estimates of colonization rate and numbers for 6 of 10 abundant taxa. From hypothetical colonization curves derived for Baetis tricaudatus Dodds larvae from information on drift tendencies and settling abilities, we suggest that temporal pattern of tray colonization is strongly dependent on fluctuations in mean current velocity and short-term changes in upstream benthic density.
Quantification of Wood Habitat in Subtropical Coastal Plain Streams
Authors: Wallace J. Bruce , Benke Arthur C.
Published: May 2008

To assess the importance of woody debris in two relatively unaltered Coastal Plain streams in the southeastern United States, a line intersect technique, developed by foresters, was used to estimate volume, mass, surface area, and spatial distribution. The ash-free dry mass of in-channei woody material was 6.5 kg/m2of stream channel bottom in the sixth-order Ogeechee River and 5.0 kg/m2in the fourth-order Black Creek. Most wood is located near the erosional bank in these meandering streams. These wood mass estimates are much higher than expected for middle-order streams and are similar to those from several small headwater streams in other regions. Due to their very low slopes (<0.02%), these streams appear to have insufficient stream power to move large woody material. Snag, or woody, habitat is the major stable substrate in these sandy-bottomed streams and is a site of high invertebrate diversity and productivity. In-channel snag surface area per square metre of channel bottom was 0.249–0.433 m2in the Ogeechee and 0.191–0.379 m2in Black Creek, depending on the hydrograph stage. With invertebrate biomass of 6.6 g dry mass/m2of snag surface, this results in an invertebrate biomass of at least 1.88 g/m2of channel bottom. Wood is also important to fishes, providing a rich source of invertebrate food, habitat, and cover. In addition to its obvious biological role, wood enhances the ability of a stream to process and conserve nutrient and energy inputs and has a major influence on the hydrodynamic behavior of the river. The quantification of wood habitat seems mandatory to assess past or potential impacts of snag removal on ecosystem processes in low-gradient streams.
Nearshore Ichthyoplankton of a North Temperate Estuary
Authors: Powles H. , Auger F. , FitzGerald G. J.
Published: May 2008

Composition of ichthyoplankton in the nearshore zone (0–6 km from shore) of the St. Lawrence estuary showed important differences from that farther offshore. In particular, larvae of herring (Clupea harengus harengus), winter flounder (Pseudopleuronectes americanus), and smooth flounder (Liopsetta putnami) made up a greater proportion of the ichthyoplankton than in published surveys farther offshore. Peak catches of larval herring were 1–2 orders of magnitude higher than in offshore waters. Winter flounder and smooth flounder larvae were significantly more abundant [Formula: see text] from shore than 1–6 km offshore; significant abundance gradients were not found for other species. Nearshore areas have received considerably less effort than offshore areas in earlier studies, and we suggest that more intensive studies in the nearshore zone, at least for those species mentioned, would be of importance for elucidating early life history processes and for estimating spawning biomass based on ichthyoplankton surveys.
Osmoregulatory and Hematological Responses of Rainbow Trout (Salmo gairdneri) to Extended Environmental Acidification
Authors: Giles M. A. , Majewski H. S. , Hobden B.
Published: May 2008

The dose-dependent relationships of several physiological responses to acid were examined in rainbow trout (Salmo gairdneri) exposed for 22 d to water at pH 4.2–6.0. Significant increases in ventilatory and cardiac rates occurred at pHw < 4.9. Hematocrit and hemoglobin concentration increased progressively with acid stress at pHw < 5.5. Plasma calcium, magnesium, sodium, and chloride concentrations were reduced and plasma phosphate elevated in acid-exposed fish. Seasonal differences were observed in the quantitative responses to acid exposure in the relationship between hematocrit and hemoglobin concentration and in the plasma concentrations of calcium and magnesium. The fractional contribution of sodium and chloride to plasma osmolality decreased linearly with increasing hydrogen ion concentration, and the change in plasma sodium, chloride, and osmolality per unit change in pHwwas 35.2 mmol/L, 39.7 mmol/L, and 47.4 mosmol/kg, respectively, in the pH range of 4.5–5.2. We concluded that the discrepancy between the reduction in plasma osmotic pressure and the combined reduction in the major plasma electrolytes is a result of the elevation in concentration of an unidentified plasma solute which offsets 40–45% of the expected reduction in osmotic pressure.
Changes in Populations and Drift of Stream Invertebrates Following Lampricide Treatment
Authors: Dermott R. M. , Spence H. J.
Published: May 2008

The effects of 3-trifluoromethyl-4-nitrophenol (TFM) treatment on invertebrate abundance, recolonization, and drift rates were examined in three Great Lakes tributaries, having a wide range of water hardness. In the softwater streams only philopotamid caddisflies and lumbriculid worms were significantly reduced after the TFM treatment, whereas their abundance in the untreated stream sections was unchanged. Treatment of the hardwater stream resulted in a dramatic mortality of leeches. Abundance of soft-bodied oligochaetes and Turbellaria were significantly reduced, while numbers of Simuliidae, Hydropsyche, and Baetis increased 4 d after treatment. Daytime drift rates of the Annelida, Turbellaria, Amphipoda, Glossosomatidae, and Tipulidae increased significantly during the lampricide treatment. Increased drift rates rather than mortality appears to be the major impact of the lampricide on invertebrate communities.
Uptake Efficiency of the Gills of English Sole (Parophrys vetulus) for Four Phthalate Esters
Authors: Boese Bruce L.
Published: May 2008

Uptake efficiencies of the gills of English sole (Parophrys vetulus) for four homologous phthalic acid esters were directly measured and compared with octanol–water partition coefficients (Kow). Test compounds were diethyl phthalate (DEP), butyl benzyl phthalate (BBP), bis(2-ethylhexyl) phthalate (DEHP), and di-n-octyl phthalate (DOC). Mean uptake efficiencies in a single pass through the gills were 11% for DEP (log Kow = 3.2), 42% for BBP (log Kow = 5.8), 3% for DEHP (log Kow = 8.7), and 12% for DOC (log Kow = 9.2). Uptake efficiencies for DEP and BBP were inversely correlated with weight-specific ventilation volume and did not correlate with aqueous concentration. Uptake efficiencies for DOC and DEHP were uncorrelated with any measured parameter. Solubilities of phthalic acid esters were measured by generator column. DEP and BBP had aqueous solubilities similar to published values, but DEHP was 1/700 and DOC was 1/3000 below published solubility values. DOC and DEHP used to determine uptake efficiencies were most likely in colloidal or micellar form, which may be less bioavailable than soluble forms of the compound; this would reduce the apparent uptake efficiency, regardless of Kowvalue.
Benthic Macroinvertebrates Modify Copper and Zinc Partitioning in Freshwater–Sediment Microcosms
Authors: Krantzberg G. , Stokes P. M.
Published: May 2008

The effects of bioturbation on metal dynamics in freshwater–sediment systems were examined. In general, benthic macroinvertebrates caused significant changes in Cu and Zn partitioning among physicochemical forms in the sediment. The proportion of cation-exchangeable and specifically adsorbed Cu observed in Chub Lake (Muskoka–Haliburton) microcosms colonized by chironomids and chaoborids was greater than that for uncolonized sediment. The same relationship held for Cu in Lohi Lake (Sudbury) microcosms supporting a similar benthic community and for Cu and Zn in Port Credit (Lake Ontario) sediments inhabited by tubificids. The ability of tubificid worms to increase sediment Eh was recorded and related to Cu and Zn dynamics. We conclude that macroinvertebrate communities have the potential to increase metal concentrations in the water column, particularly during short episodes of high burrowing activity, and that in situ studies are warranted to verify this potentiality.
Hypolimnetic Oxygen Consumption in Small Lakes
Authors: Fulthorpe Roberta R. , Paloheimo J. E.
Published: May 2008

The hypolimnetic oxygen consumption rates of 28 Ontario lakes were calculated and compared with lake morphology, chemical concentrations, and productivity measures. In most cases, hypolimnia had upper zones where average light intensities were greater than 1% of surface light. In these layers, oxygen dynamics were highly variable from year to year and production rather than consumption was common. The ratio of areal oxygen consumption below the 1% light level to planktonic production corrected for retention was studied as a measure of percent available material decomposed. Using stepwise multiple regressions, we found this parameter to be related to mean thickness of the hypolimnion, lake organic carbon, and iron concentrations. The range of lake productivities in the data set was small and did not explain a significant portion of the variance in areal hypolimnetic depletion rates.
Influence of Sea Temperature upon the Numbers of Grilse and Multi-Sea-Winter Atlantic Salmon (Salmo salar) Caught in the Vicinity of the River Dee (Aberdeenshire)
Authors: Martin J. H. A. , Mitchell K. A.
Published: May 2008

The possible influence of sea temperature upon the age of return of Atlantic salmon (Salmo salar) was examined using the catch and weight data of grilse and multi-sea-winter (MSW) salmon of the Aberdeen Harbour Board caught either within or adjacent to the River Dee (Aberdeenshire). This data set, apart from a 10-yr period of commercial confidentiality, is very suitable because uniformity of effort allowed catch per unit effort to be calculated. Only in the last few years was external pressure (high seas fishing) applied to the system. Various temperature series were examined but the known loci of high seas fishing and the temperature ranges involved suggested that the most relevant series is from the subarctic. Increase in temperature is shown to be associated with larger numbers of fish returning as MSW salmon and fewer as grilse. The average weight of grilse increases with grilse catch numbers. Regression equations for grilse and MSW salmon catch numbers are produced for the period 1877–1972. There is a marked 4-yr periodicity in the grilse catch data. A hypothesis is proposed that the temperature of the subarctic influences the migratory pattern, that fish travel further north into the Arctic/subarctic only during those years when the minimum temperature remains above 2 °C.