bluuebunny/crossref_metadata_2025 huggingface dataset:
Bythotrephes cederstroemi (Schoedler) in Muskoka Lakes: First Records of the European Invader in Inland Lakes in Canada
Authors: Yan Norman D. , Dunlop Warren I. , Pawson Trevor W. , MacKay Lori E.
Published: June 2008

The large predaceous European zooplankter Bythotrephes cederstroemi is now present in eight large recreational lakes in south-central Ontario, Canada: Lake Muskoka, Lake Joseph, Lake Rosseau, Fairy Lake, Mary Lake, Peninsula Lake, Lake Vernon, and Go Home Lake. These observations represent the first evidence that B. cederstroemi has invaded inland lakes in Canada, and we suggest that close monitoring is now needed to establish whether or not pelagic food webs of the lakes will respond.
Modeling Effects of FADs and Islands on Movement of Skipjack Tuna (Katsuwonus pelamis): Estimating Parameters from Tagging Data
Authors: Kleiber P. , Hampton J.
Published: June 2008

From an experiment with ordinary dart tags, we have found evidence of the effect of fish-aggregating devices (FADs) and of islands on the movements of skipjack tuna (Katsuwonus pelamis) around the Solomon Islands. By fitting a fish movement model to the tag data, we were able to estimate mortality and movement parameters (including diffusivity), parameters of a function that models FAD attraction, and a separate parameter of island attraction. Diffusivity was high enough to effectively distribute fish throughout the island archipelago (approximately 150 000 km2) within a few months. Estimates of FAD parameters indicate that the presence of up to four or five FADs in an area approximately 50 × 50 km can reduce the propensity for skipjack to leave that area by approximately 50%, but that deploying additional FADs in such an area does not significantly increase their effectiveness in holding skipjack. Estimates of the island attraction parameter imply that the propensity of skipjack for movement away from the archipelago is less than half the propensity for movement within it.
Modeling Predator–Prey Dynamics in a Fluctuating Environment
Authors: Collie Jeremy S. , Spencer Paul D.
Published: June 2008

Large fluctuations in the abundance of marine fish are revealed in scale deposits from before the twentieth century and are thought to be environmentally induced. We investigated how a fluctuating environment and predation may combine to cause abrupt shifts in fish abundance on decadal time scales. For example, the biomass of Pacific herring (Clupea pallasi) off Vancouver Island appears to be negatively related to sea surface temperature (SST) and the abundance of its predator, Pacific hake (Merluccius productus). We used first-order differential equations to develop a two-species, predator–prey model forced with stochastic variability. A nonlinear, predator functional response potentially gives rise to multiple equilibrium abundance levels. Environmental variability was simulated as "red noise" (variance is a decreasing function of frequency) with a spectrum derived from SST data. Stochastic variations caused the predator–prey abundances to shift between high and low equilibrium levels. Fishing the prey population can precipitate collapses to the low equilibrium level and prolong the time to recovery. When run with actual catches and SST anomalies from 1951 to 1988, the model simulated prey abundances with a pattern similar to the observed herring biomass.
Sensitivity of Optimum Harvest Strategy Estimates to Alternative Definitions of Risk
Authors: Megrey Bernard A. , Hollowed Anne Babcock , Baldwin Rebecca T.
Published: June 2008

A stochastic age-structured bioeconomic simulation model was developed as a tool for evaluating economic returns to a fishery from alternative harvest policies. The model, which was applied to the Gulf of Alaska walleye pollock (Theragra chalcogramma) fishery, combines the dual goals of protection of the base stock and efficient use of the public resource into an explicit objective function. This paper presents the results of several experiments in which the simulation model is used to examine the sensitivity of the optimum harvest strategy estimates to alternative definitions of risk and assumptions regarding recruitment. Alternative definitions of risk consider assumptions about stock productivity, threshold biomass, economic factors, and hybrid formulations. The bioeconomic extension of the population dynamics model is used to quantify differences in the estimates of optimum fishing mortality obtained from the different risk definitions. Model results demonstrate that estimates of optimal fishing mortality and economic return to the fishery are sensitive to the specific definition of risk used to manage the fishery. The recruitment assumption turned out to be more important to optimum harvest strategy estimates than did risk definitions.
Use of Gaming Procedures in Evaluation of Management Experiments
Authors: Walters Carl
Published: June 2008

Management often involves debate about whether to maintain some conservative, status quo policy or to experiment with some risky alternative that may produce higher long-term value. In comparing such alternatives, a key modelling problem is to predict the transient response pattern that will occur if an experimental approach is adopted but is not successful (stock collapses or fails to recover, enhancement makes no net conributution to catches, etc.), in terms of how long it will take to detect and react to the failure. Prediction of such transients involves modelling not only future data gathering and statistical analysis, but also how future managers will react to the information. Management gaming involving real managers may be the simplest and most efficient way to make such predictions. Application of gaming procedures to fisheries development and hatchery production examples indicates that such procedures may not only help in prediction, but also are useful for management training and clarification of objectives and priorities.
Uncertainty and Risk Evaluation in Stock Assessment Advice for U.S. Marine Fisheries
Authors: Rosenberg Andrew A. , Restrepo Victor R.
Published: June 2008

This paper describes some of the ways that the uncertainty in fisheries scientific advice has been communicated to managers for different fisheries in the United States in the past several years. Describing the uncertainty can be important in allowing managers to weigh the benefits and losses of different management strategies and to allay concerns about the effects of process, measurement, and model errors on the scientific advice, even if a formal decision theoretic risk analysis has not been carried out. The four general steps in analyzing uncertainty and assessing risk are estimation of the uncertainty in the assessment of current stock status due to measurement error, evaluation of the impacts of potential model errors on the assessment, stochastic projections incorporating estimation error and process errors to investigate the impacts of different management options, and assessment of risk using simple utility functions. At least one of these steps has been included in assessment analyses of about 20 major U.S. fisheries. All of these steps have been incorporated in the scientific advice on a few fisheries to date and should be attempted whenever possible to improve the information available to fishery managers.
Sediment Transport in a Small Stream following Two Successive Forest Fires
Authors: Beaty K. G.
Published: June 2008

The transport of stream bedload sediment was monitored continuously in a small stream from 1975 to 1982 following forest fires in 1974 and 1980. The stream is located in the east subcatchment (170 ha) of Lake 239 in the Experimental Lakes Area, northwestern Ontario. Precipitation, stream discharge, bedload transport, and concentration of suspended materials were measured quantitatively and organic debris was observed and collected. Bedload transport increased 20-fold following the first fire and threefold after the second. Particle sizes tended to increase during the period of study. Bedload data suggest a recovery period of 5–6 yr following the first fire and a shorter one following the second. A mass budget of material load transported in a single year following recovery indicated a dominance of dissolved load (87%), followed by suspended load (10%), and bedload (3%).
Sensitivity of Estimates of Seasonal Phytoplankton Photosynthesis to Sampling Frequency
Authors: Schindler E. U. , DeBruyn E. R. , Fee E. J. , Shearer J. A.
Published: June 2008

Phytoplankton photosynthesis was monitored once or twice weekly in an oligotrophic Canadian Shield lake in northwestern Ontario during the ice-free season for 6 yr. These data sets were subsampled in various ways to determine how the precision of estimates of ice-free season phytoplankton photosynthesis was affected by sampling frequency. Deviations were as large as 20% if a measurement was not taken before thermal stratification was established in the spring, or if samples were taken at monthly intervals during the ice-free season. Shorter sampling intervals (1, 2, and 3 wk were tested) all resulted in deviations of about 10%. Taking samples irregularly (every day for the 3 d subsequent to rainfall events ≥ 5 mm) instead of at regular time intervals did not reduce deviations.
Phosphorus Budgets and Stoichiometry during the Open-Water Season in Two Unmanipulated Lakes in the Experimental Lakes Area, Northwestern Ontario
Authors: Campbell P.
Published: June 2008

A comparative mass-balance approach is used to describe and quantify phosphorus (P) cycles during the open-water season in two unmanipulated Experimental Lakes Area (ELA) lakes. A bimodal cycle generally prevailed, in which water-column total phosphorus (TP = total dissolved P plus sestonic particulate P) peaked just after ice-out and again late in the summer. Changes in mass of water-column TP were often much larger than corresponding net external inputs. Shifts of P to and from either zooplankton or fish in the water column do not explain the P residuals. Rather, the bottom sediments must have been adding P to the water column. Short-term regeneration of P from the bottom sediments also probably occurs in artificially eutrophied ELA lakes. The mechanism of regeneration is probably biological. Other aspects of P cycling and P stoichiometry are discussed, particularly in relation to nutrient control of population structure and the function of primary and secondary producers.
Effects of Lake Size on Nutrient Availability in the Mixed Layer during Summer Stratification
Authors: Fee E. J. , Hecky R. E. , Regehr G. W. , Hendzel L. L. , Wilkinson P.
Published: June 2008

Fluxes to the summer mixed layer of N, Si, and P were estimated in a size series of northwestern Ontario Canadian Shield lakes. Increasing turbulence caused upward fluxes through the thermocline to increase with lake size for nutrients that increased in concentration below the thermocline (soluble reactive Si, total inorganic N, and NO3−; but not total N or any form of P). Precipitation and terrestrial runoff were equally important sources of N and P in all but very small lakes (< 100 ha), where precipitation supplied much more than runoff. Runoff was the only important source of Si, except in very large lakes (> 100 000 ha) where mixing through the thermocline was important. N2-fixation was unimportant except in intermediate-sized fakes (700–2000 ha). Si fluxes nearly equaled phytoplankton requirements, but N and P were below requirements, and recycling within the mixed layer must be the most important source of these nutrients. N and P deficits increased progressively with lake size, implying that the efficiency of nutrient recycling increased with lake size; mixed layers in large lakes are more turbulent and thicker than in small lakes and these processes increase the probability of nutrient regeneration within the mixed layer.
Effects of Lake Size on Phytoplankton Nutrient Status
Authors: Guildford S. J. , Hendzel L. L. , Kling H. J. , Fee E. J. , Robinson G. G. C. , Hecky R. E. , Kasian S. E. M.
Published: June 2008

Phytoplankton nutrient status measurements (C/P, C/N, C/chlorophyll, N/P, alkaline phosphatase activity, and N debt) were measured for 6 yr in seven remote Canadian Shield lakes. Lakes Nipigon and Superior were also studied for 2 yr. These lakes varied in surface area from 29 to 8.223 × 10 ha, they all stratified fully during the summer and had water renewal times > 5 yr. All lakes were severely P deficient; however, the large lakes (> 2000 ha) were consistently less P deficient than small lakes. A growth-rate indicator (photosynthesis normalized to particulate C) agreed with nutrient status indicators, in that small lakes had lower rates than large lakes. Total P was a good predictor of chlorophyll, but factors related to lake size (temperature and mixed depth) were equally good or better predictors of nutrient status. Decreasing mean water column light intensity could not explain the lower P deficiency of large lakes. The deeper, more energetic mixed layers in large lakes apparently cause P to be recycled more efficiently. Extrapolation of observations or experimental results from small to large lakes requires recognition that phytoplankton in large lakes are less nutrient deficient and may have higher growth rates.
Biomanipulation of Lake 221 in the Experimental Lakes Area (ELA): Effects on Phytoplankton and Nutrients
Authors: Findlay D. L. , Kasian S. E. M. , Hendzel L. L. , Regehr G. W. , Schindler E. U. , Shearer J. A.
Published: June 2008

Lake 221 was dominated by omnivorous perch (Perca flavescens); the addition of northern pike (Esox lucius) resulted in trophic changes that eventually affected the phytoplankton community. Two years following the introduction of pike, perch were greatly reduced. Subsequently, Chaoborus abundance increased, rotifer and cladoceran abundance and biomass decreased, and the large-bodied cladoceran Daphnia catawba increased. The phytoplankton community shifted from chlorophyte to cyanophyte codominance with dinoflagellates. Phytoplankton biomass and phosphorus (P) increased because of nutrient recycling and excretion by pike and zooplankton. In years three and four, algal biomass and the ratio of suspended to dissolved P decreased because a larger portion of dissolved P was bound in an increased bacterial population. Phytoplankton cell size and production decreased, but the production:biomass ratio increased. In year five, chrysophytes dominated as phytoplankton biomass and production increased and bacterial abundance declined. Phytoplankton responses were primarily an indirect result of the introduction of piscivorous fish, which altered internal nutrient recycling.
Patterns in Algal Recruitment from Sediment to Water in a Dimictic, Eutrophic Lake
Authors: Hansson Lars-Anders , Rudstam Lars G. , Johnson Timothy B. , Soranno Patricia , Allen Yvonne
Published: June 2008

In the large, dimictic, and highly productive Lake Mendota (Wisconsin, USA), the recruitment rates from sediment to water were determined for some characteristic and dominating algal species during a 1-yr cycle. Quantifying recruitment in relation to abundance in the water on a whole-lake basis revealed that recruitment usually accounted for less than 1% of the total standing stock of each species per day, indicating that recruitment may not be an important population variable in Lake Mendota, but may instead function as an inoculum for future growth in the water column. The recruitment of Cryptomonas erosa and Ceratium hirundinella showed a dephasing among sites, suggesting that algae on the sediment surface rise into the water column in response to some depth-related cue. With the exception of one recruitment period for Aphanizomenon, no recruitment was recorded below the thermocline during the stratification period, indicating that a variable associated with stratified conditions affected algal movements from the hypolimnion to the euphotic zone. We argue that the understanding of recruitment patterns from sediment to water is a key factor in managing algal blooms in highly productive lakes.
Overwintering of Adult Northern Atlantic Cod (Gadus morhua) in Cold Inshore Waters as Evidenced by Plasma Antifreeze Glycoprotein Levels
Authors: Goddard Sally V. , Wroblewski J. S. , Taggart C. T. , Howse K. A. , Bailey W. L. , Kao M. H. , Fletcher G. L.
Published: June 2008

Adult Atlantic cod (Gadus morhua) are known to produce antifreeze glycoproteins in response to cold temperatures. Our laboratory studies demonstrated that blood plasma levels in adult cod were positively correlated with the number of days they spent in subzero water. Between April 1991 and June 1993, we monitored concentrations of antifreeze glycoproteins in the plasma of late juvenile and adult cod in Trinity Bay, Newfoundland, and used the results to estimate how long cod had been exposed to low water temperatures. A consideration of these data in conjunction with detailed temperature profiles of the area taken over the course of the study allowed us to deduce the distribution of cod in relation to the temperature field. This study provides evidence that (1) blood antifreeze glycoprotein levels can be used to deduce the recent thermal history of cod in the wild and (2) after their inshore summer feeding period, considerable numbers of adult cod overwintered inshore in Trinity Bay in subzero water, producing antifreeze glycoproteins as temperatures fell below 0 °C. From May onwards, "cold-adapted" cod moved into warming surface waters, where they became available to an early inshore trap fishery.
A Relationship between Fraser River Discharge and Interannual Production of Pacific Salmon (Oncorhynchus spp.) and Pacific herring (Clupea pallasi) in the Strait of Georgia
Authors: Beamish Richard J. , Neville Chrys-Ellen M. , Thomson Barbara L. , Harrison Paul J. , St. John Mike
Published: June 2008

We identified years of anomalously high and low discharge from the Fraser River and compared these years with indices of anomalously high and low production of Pacific salmon (Oncorhynchus spp.) and Pacific herring (Clupea pallasi). For chinook (O. tshawytscha) and coho salmon (O. kisutch), we found that brood years that went to sea in a year when the Fraser River discharge was very high compared with the previous year virtually never had an index of production that was higher than the previous year. Similarly, brood years that went to sea in a year when the Fraser River discharge was very low compared with the previous year almost never had an index of productivity that was lower than the previous year. The analysis identified a weaker association between extreme discharge anomalies and chum salmon (O. keta) production. A close association was not found between extreme discharge anomalies and pink salmon (O. gorbuscha), sockeye salmon (O. nerka), or herring production. The relationships identify a connection between annual fluctuations in river flow and production of some marine fishes and may be of use in forecasting abundance changes.
Dietary Variation in a Freshwater Fish Species: Relative Contributions of Biotic Interactions, Abiotic Factors, and Spatial Structure
Authors: Magnan Pierre , Rodríguez Marco A. , Legendre Pierre , Lacasse Sylvain
Published: June 2008

We used multivariate analyses to examine which variables among the environmental and spatial components can best account for dietary variation in a freshwater fish, brook trout, Salvelinus fontinalis. The diet composition of brook trout was quantified in 37 lakes of the Laurentian Shield, Québec, Canada. Among the 25 measured environmental variables, fish species composition, sampling date, macrophyte abundance, and trout body length were the best predictors of diet composition. The total variation in diet composition was partitioned into four components: pure environmental 21.6%, pure spatial 23.2%, shared 19.9%, and unexplained 35.3%. A significant spatial trend in diet composition existed even after accounting for the main effects measured by the environmental variables. The two sets of spatial variables, when combined with the environmental descriptors, extracted different components of the dietary variation. The study allowed us to (1) highlight the role of spatial structure in diet variation of brook trout, (2) determine the relative contribution of both environmental and spatial components, and (3) generate testable hypotheses concerning mechanisms underlying the observed structure. Dependent variables other than diet composition, such as the density of different species at different sampling sites, can be used within the same statistical framework in studies of community ecology.
Development and Effect of Female Size on Egg and Juvenile Production in the Neogastropod Buccinum cyaneum from the Saguenay Fjord
Authors: Miloslavich Patricia , Dufresne Louise
Published: June 2008

The size at sexual maturity, the developmental timing and biology, and the biochemical (protein, glycogen, and lipid) content of eggs and juveniles were determined in two female size groups of the buccinid Buccinum cyaneum. Males reach sexual maturity at a smaller size (27 mm in shell length) than females (37 mm). A total of 33 females spawned in the laboratory starting in November 1991. The egg capsules were concave, measured 6.3 mm in diameter, and contained between 300 and 1000 eggs measuring 240 μm in diameter. Between 1 and 10 embryos developed. The others underwent chromatin degeneration within 3–4 wk and became nurse eggs. Between 1 and 10 crawling juveniles emerged 9 mo later in July and August and measured 2.5 ± 0.3 mm in shell length. The number of eggs and developing embryos within egg capsules increased with the size of the female. However, the quality of the juvenile at hatching, both in size and in biochemical content, did not vary significantly with female size.
Patterns in the Abundance and Composition of Fishes among Beds of Different Macrophytes: Viewing a Littoral Zone as a Landscape
Authors: Chick John H. , Mclvor Carole C.
Published: June 2008

To determine if the density, biomass, species density (number of fish species per square metre), and species composition of juvenile and forage fish (fish ≤ 100 mm SL) differed among macrophyte types, we sampled fishes monthly from beds of Hydrilla verticillata, Panicum hemitomon, and Potamogeton illinoensis in two areas of Lake Okeechobee, Florida, from December 1989 to December 1990. Fish density and biomass differed significantly among the three macrophytes despite our design having relatively low statistical power to detect such differences. Densities and biomass were highest in H. verticillata (196 fish∙m−2, 30 g∙m−2), intermediate in P. hemitomon (60 fish∙m−2, 12 g∙m−2), and lowest in P. illinoensis (31 fish∙m−2, 6 g∙m−2). Trends among macrophytes were consistent throughout the year despite significant variation among months. Fish species density did not vary significantly among macrophyte types. However, the relative abundances of fishes differed significantly among macrophyte types. Patterns in fish abundance and relative species composition led us to infer that beds of different macrophyte types constitute distinct microhabitats for fish and structure the littoral zone of Lake Okeechobee into a mosaic landscape.
Hydrological exchange and sediment characteristics in a riverbank: relationship between heavy metals and invertebrate community structure
Authors: Gibert Janine , Plénet Sandrine , Marmonier Pierre , Vanek Vladimir
Published: June 2008

The first metre of bed sediments of the Rhône River functions as a filter for fluxes of heavy metals and epigean organisms between surface and interstitial environments. To study the efficacy of this bank filtration, three sampling stations were established at increasing distances from pumping wells, resulting in a gradient of hydraulic characteristics. Station A, a permanent downwelling area with very high hydraulic gradients, low hydraulic conductivity, low oxygen content, and rather high metal concentrations contained a fauna exclusively composed of epigean organisms. At station B, intermediate hydraulic gradients, high hydraulic conductivity near the surface, and variable direction of water exchanges resulted in well-oxygenated pore water and a diversified fauna with hypogean and epigean species. Finally, at station C, low hydraulic gradient, low hydraulic conductivity, low water exchange, and high sediment metal concentrations resulted in low pore-water oxygen concentrations and low interstitial fauna density and diversity. At this site, low oxygen content and low biodiversity were related to the clogging of shallow sediments and low filtration efficiency. Thus, bank filtration efficiency, a property that depends mainly on natural or human-induced hydraulic gradients and sediment granulometry, determines pore-water chemistry, metal distribution, and faunal composition in the shallow interstitial environments of the Rhône River.
The influence of error on population estimates from catch-age models
Authors: Schnute Jon T. , Richards Laura J.
Published: June 2008

Catch-age analysis has become a standard tool for modern stock assessment, where it is recognized that population estimates are linked to estimates of the natural mortality rate M. We use state space models and simulation–estimation cycles to evaluate the performance of catch-age analysis. In particular, we design a simulation model with realistic measurement and process error. We then examine how effectively unknown parameters and population sizes can be obtained from an estimation model simplified to conform with common assumptions. We describe circumstances in which, simultaneously with all other parameters, M is estimable from traditional catch-age data. Increased fishing contrast improves estimates of some model parameters, but not M. The variance ratio ρ relating process error in recruitments with measurement error in the abundance index must be specified in the estimation. We consider both true and ad hoc choices for ρ. In general, estimation models perform better when the true ρ is specified and measurement error is low, so that recruitment error is the dominant source of model variability. Thus, well-designed data collection programs are critical to the correct interpretation of actual fishery data.
Relationship between respiration rate of juvenile brook trout (Salvelinus fontinalis), water temperature, and swimming characteristics
Authors: Tang Ming , Boisclair Daniel
Published: June 2008

We estimated the cost of spontaneous swimming and the swimming characteristics of juvenile brook trout for 21 combinations of water temperature (3.5, 6, 9, 12, 15, 18, and 20.7 °C) and respirometer volume (27, 54, and 108 L). Spontaneous swimming costs were estimated as the oxygen depletion in the respirometers corrected for biological oxygen demand of the water and standard metabolism of the fish. Spontaneous swimming costs varied 9-fold among our experiments. Swimming characteristics, such as the average and the variance of speed, acceleration, and turning rates, were determined using a pair of video cameras. Swimming characteristics varied 2- to 10-fold among experiments. Speed and turning rate tended to increase with water temperature up to 18 °C and decreased at 20.7 °C. Water temperature (r2 = 0.44) was the only variable that could explain a significant portion of the variations of spontaneous swimming costs between 3.7 and 20.7 °C. Variance of speed (partial R2 = 0.32) and the average turning rate (partial R2 = 0.34) explained 53% of the variation between 3.7 and 18 °C. Average speed never explained more than 35% of spontaneous swimming cost variation.
Swimming performance and predator avoidance by mummichog (Fundulus heteroclitus) larvae after embryonic or larval exposure to methylmercury
Authors: Weis Judith S. , Weis Peddrick
Published: June 2008

Embryos of the mummichog, Fundulus heteroclitus, were exposed to 5 and 10 μg/L methylmercury throughout development; these are concentrations below those that cause teratological effects. Larvae were maintained in clean seawater or in water with methylmercury, and tested for swimming performance by chasing them with a glass rod. Swimming performance improved with larval age. Larvae that had been exposed to methylmercury as embryos swam greater distances than controls, while those that were exposed only as larvae swam less than controls. The effects of the embryonic exposure diminished over time, and the larval environmental conditions took precedence. Larvae were also tested with two predators, the grass shrimp, Palaemonetes pugio, and 1 -year-old mummichogs. Those that had been exposed to mercury as embryos (which swam more than controls) or as larvae (which swam less than controls) were more susceptible to predation than controls. The increased swimming of those exposed as embryos may have reflected greater activity, making them more likely to attract the predator's attention, while the slower swimming of those exposed as larvae could make them easier to capture.
Empirical and theoretical analyses of correction of time-series bias in stock-recruitment relationships of sockeye salmon (Oncorhynchus nerka)
Authors: Korman Josh , Peterman Randall M. , Walters Carl J.
Published: June 2008

Using data from 30 sockeye salmon (Oncorhynchus nerka) stocks and Monte Carlo simulations, we examined the importance of time-series bias on estimates of optimal harvest rate, optimal escapement, and sustainable yield. We compared the performance of the least-squares procedure for fitting a Ricker curve with an existing bias-correction method. Simulations showed that the effect of time-series bias is greatest for low-productivity stocks that exhibit a high degree of autocorrelation among residuals of the stock-recruitment relationship. A strong inverse empirical relationship between autocorrelation and stock productivity among the 30 stocks suggests that time-series bias is a more important concern for low-productivity northern stocks than for more productive southern stocks. The corrected method reduced bias in optimal escapement estimates under a limited set of conditions but at the price of increased variance in the estimates. For a constant escapement goal policy, using the bias correction thus resulted in sustainable yields slightly lower than or equal to expected values for 28 of the 30 stocks compared with yields obtained using the standard least-squares estimation method. We demonstrate the value of using a decision theoretic approach to evaluate the performance of estimation methods.
Hydrochemical response of upland Precambrian Shield catchments to additions off H2SO4and NH4NO3during snowmelt
Authors: Allan Craig J.
Published: June 2008

Two of three upland Precambrian Shield catchments received additions of H2SO4and NH4NO3prior to snowmelt in 1989 and 1990; loading levels were equivalent to 18 kg∙ha−1∙yr−1as SO42−and 2.62 kg∙ha−1∙yr−1as N. The third catchment served as a reference. The manipulated catchments retained 96–98% of the added NH4+, 73–94% of the added NO3−, 31–48% of the added SO42−, and 72–92% of the added H+. Proton neutralization was attributed to increased cation export (Ca2++ Mg2++ Na++ K++ Aln++ Mn2++ Fe2+: 26–53%) and SO42−retention (48–67%). The protonation of weak organic acids accounted for a 13–34% decline in organic anions during snowmelt. No significant change in dissolved organic carbon export was observed. In manipulated catchments, inorganic monomeric Al export increased from 30 to 80% over reference levels, and the ratio of inorganic to organic monomeric Al changed from < 1.0 to 2.7. Differences in response of the manipulated catchments were attributed to differences in soil thickness and the extent of forest cover. Interannual differences in responses were attributed to differences in snow accumulations, melt sequences, and hydrologic flushing of catchment soils.
Experimental acidification of a poor fen in northwestern Ontario: effects on emergence of Chironomidae (Diptera)
Authors: Rosenberg David M. , Wiens Allen P. , Bilyj Bohdan , Armstrong Llwellyn
Published: June 2008

The effects of experimental acidification and N fertilization on chironomid emergence from a poor fen in northwestern Ontario were studied from 1984 to 1989. Experimental treatments did not affect the numbers of chironomids emerging weekly, the timing of emergence, or species composition of emergence during the study period. Weekly emergence counts were higher (P < 0.05) from the periphery of the fen than the central part. Total seasonal emergence was higher from the area previously burned in a forest fire than the unburned part of the fen, although the difference was not statistically significant. Stability of species composition, despite experimental treatments and physiographic differences in the fen, may be a widespread characteristic of Canadian acidic peatlands.
Ecological effects of blooms of filamentous green algae in the littoral zone of an acid lake
Authors: Turner Michael A. , Townsend Bruce E. , Robinson Gordon G. C. , Hann Brenda J. , Amaral John A.
Published: June 2008

Ecological effects of blooms of filamentous green algae (FGA) were studied in an experimentally acidified lake (pH 4.5) at the Experimental Lakes Area in northwestern Ontario, Canada. Blooms of FGA influenced the energy balance, chemical cycling, physical features, and biological conditions in the littoral zone. Photosynthetic capacity of the FGA, dominated by Zygogonium, was greater than that of acidified epilithon, the normally dominant littoral algal association, partially offsetting acidification-induced oligotrophication in the littoral zone. Intra- and inter-annual variability of FGA growth was large, however, so that FGA were an unreliable energy source for the littoral food web. Nutrient uptake varied with the degree of FGA growth; e.g., FGA were occasionally the largest phosphorus pool in the epilimnion. Nitrogen dynamics of FGA varied seasonally causing acidification in spring and summer, and alkalinization in fall. The blooms also affected epilimnetic cycling of dissolved inorganic carbon. Peak blooms prevented as much as 90% of the light from reaching the lake bottom. Local depletions of oxygen resulting from FGA decomposition also posed potential risks for animals using the FGA as habitat.
Fate of60Co and134Cs added to the hypolimnion of a Canadian Shield lake
Authors: Bird G. A. , Stephenson M. , Roshon R. , Schwartz W. J. , Motycka M.
Published: June 2008

Tritium (3H), cobalt-60 (60Co), and cesium-134 (134Cs) were added to the anaerobic hypolimnion of a Canadian Shield lake during the summer of 1989 to simulate the nuclear fuel waste disposal scenario in which nuclides are assumed to enter the bottom of a lake with deep groundwater flow. The radionuclides initially remained confined to the hypolimnion and there was little loss from the water. Lake mixing during autumn turnover resulted in the rapid loss of60Co (first order rate constant, k, is 0.036 d−1) and much slower loss of134Cs (k = 0.006 d−1) from the water to sediment over the next 41 and 238 d, respectively. One year after the addition, <1% of the60Co and134Cs and 6% of the tritiated water added to trace water movement had been lost to the outflow. About 6% of the60Co and 19% of the134Cs remained in the water column. Loss rates to the sediment observed following autumn turnover in the present study were slower than those previously observed from the epilimnion; however, there was little difference in the amount of60Co and134Cs remaining in the water after 1 year when the input was to the hypolimnion as opposed to the epilimnion.
Deformities in the menta of chironomid larvae from the Experimental Lakes Area, Ontario
Authors: Bird G. A. , Rosentreter M. J. , Schwartz W. J.
Published: June 2008

Chironomus spp. larvae in Experimental Lakes Area Lake 382, which received experimental additions of cadmium, were exposed to cadmium concentrations up to approximately 200 ng∙L−1 in water and to about 4 μg∙g−1 in dry sediment, resulting in body burdens of about 3.5 μg∙(g dry weight)−1. Mentum deformities in Chironomus spp. larvae in Lake 382 and five reference lakes ranged from 0 to 16%, which was within the range reported for other contaminated lakes (2 to 83%). The frequency of deformities in Lake 382 was not detectably different either in larvae collected between 1989 and 1992, or in those from reference lakes. Incidence of deformities was higher in four of the five reference lakes than in Lake 382. The constancy of the deformities (confined mainly to the median tooth, commonly with cleft or forked median teeth) is consistent with an inherited genetic effect; therefore, we consider the deformities to be natural abnormalities. We conclude that the low cadmium levels added to Lake 382 did not induce mentum deformities and that background levels of deformities are high (up to 16%) in Experimental Lakes Area lakes. The common occurrence of natural abnormalities must be considered when using chironomid mouthpart deformities as an index of environmental degradation.
Perspectives on the relationship between otolith growth and the conversion of isotope activity ratios to fish ages
Authors: Kimura Daniel K. , Kastelle Craig R.
Published: June 2008

Ageing of fish otoliths using radiometric methods is now becoming widely accepted. Using this methodology, one has the choice of extracting otolith cores or modeling otolith mass growth. Modeling otolith growth forgoes the difficult work of extracting cores, but one is left with the nearly equally daunting task of selecting and validating an otolith growth model and deriving the corresponding decay equations. We note that the mathematical aspects of this problem appear to have been satisfactorily resolved. However, problems of interpretation remain, and it is not clear whether practitioners fully appreciate the sensitivity of their results to growth model selection and interpretation. We note that the two-stage linear growth model appears to be generally misapplied in the literature. Also, we present evidence that the process of using otolith growth curves estimated from annular ring counts to validate the method of counting annular rings can constitute circular reasoning. Although tedious work, extracting otolith cores seems the most valid way to avoid some serious problems in radiometric age determination work.
Rotation of principal stresses near a heated fracture in a bituminous sand
Authors: Ofoegbu G. I. , Curran J. H.
Published: June 2008

The physical processes induced in a bituminous (oil) sand by hot fluid injection consist of the transport of heat and mass and the deformation of the solids skeleton. The roles of heat conduction, convection, and the inelastic stress–strain response of sands in the evolution of stresses in a heated bituminous sand are evaluated in this paper, using the example of hot fluid injection into a vertical slit.Reservoir heating occurs by conduction and convection, whereas heat dissipation occurs mainly by conduction. The heated zone around the slit is small, but, because of stress redistribution due to localized tensile and shear failures, the zone of influence of the induced stresses can be quite large. As a result of the anisotropic temperature gradients caused by the geometry of the heated boundary, rotation of principal stresses occurs in a large area near the slit. Key words: sands, tar sands, injection, fracture, no tension, yielding, strain softening, thermal stress.
Hydraulic conductivity of contaminated natural clay directly below a domestic landfill
Authors: Quigley R. M. , Fernandez F. , Yanful E. , Helgason T. , Margaritis A. , Whitby J. L.
Published: June 2008

The hydraulic conductivity of natural clays in the 1.5 m contamination zone below a 15 year old domestic waste landfill has been determined.Water-soluble contaminants such as chloride, sodium, and dissolved organic carbon have migrated about 1.0 m compared with only 15 cm for copper, zinc, iron, lead, and manganese. The migration, primarily by diffusion, has rendered the clay perfect for assessment of clay–leachate compatibility with respect to hydraulic conductivity, k.Oedometer tests on tube samples of the clay yielded k values of 1.4 × 10−8 cm/s with a slight decrease to about 1 × 10−8 cm/s in the upper 20 cm of clay at the waste–clay interface. Direct measurement of k on "undisturbed" tube samples, reconsolidated to their field stress state and permeated with pore fluid squeezed from adjacent contaminated samples, yielded values of 1.5 × 10−8 cm/s at 1 m depth decreasing to 0.75 × 10−8 cm/s at the interface.The decrease in k near the interface seems to correlate directly with increased pollutant concentration of soluble species, total heavy metal concentration, and a slight decrease in void ratio. The changes in k are so small, however, that for the test leachates and undisturbed test soils at this domestic waste site, it is concluded that the hydraulic conductivity has not changed significantly as a result of contamination. Key words: domestic waste, leachate, hydraulic conductivity, clay barriers, compatibility.
Undrained shear strength from piezocone tests
Authors: Konrad J.-M. , Law K. T.
Published: June 2008

With the advent of piezocones — penetrometers measuring both the mechanical resistance and induced pore pressures near the tip during penetration into the soil — a new interpretation of penetrometer test data is possible. This paper presents a review of available interpretation methods for obtaining the undrained shear strength of soft soils, and introduces a new interpretation taking into account measured pore pressures. The undrained shear strength is considered to be solely related to the ultimate cavity expansion pressure, which is one of the components of the tip resistance. The other component is calculated assuming that effective friction is developed at the cone–soil interface.Parametric studies on the parameters required for strength determination based on the proposed method are also presented. Special self-boring pressuremeter tests to obtain relevant values of soil rigidity index, which is a key parameter for cavity expansion modelling, are described. Tests were conducted at three sites having the characteristics of soft sensitive clay, stiff sensitive clay, and clayey silt. The operational undrained strength mobilized during the cone insertion derived from the proposed model is equal to or lower than the CK0U triaxial strength, which depends on soil brittleness. The proposed approach yields results consistent with known soil behaviour at all three sites. Key words: piezocone penetrometer, pressuremeter, excess pore-water pressure, undrained shear strength, rigidity index, in situ tests, laboratory test.
Reconnaissance of rockslide hazards in Kananaskis Country, Alberta
Authors: Cruden D. M. , Eaton T. M.
Published: June 2008

Kananaskis Country is situated in the Front Ranges of the Canadian Rockies in southwestern Alberta. Sedimentary rock thrust northeastwards forms mountain ridges that trend northwest–southeast parallel to the major thrust faults. Older, Palaeozoic rocks—mainly limestone and dolomite—form the ridges and peaks. Younger, Mesozoic rocks—sandstones, quartzites, siltstones, shales, conglomerates, and coals—are more easily eroded and form mountain passes and valleys.A reconnaissance mapped 228 rockslides, 8 km2 of rockslide debris and 96 km2 of talus. The largest rockslide exceeds 50 × 106 m3. Rockslides are most probable in the Devonian Palliser Formation, then in the Permo-Pennsylvanian Rocky Mountain Group, Mississippian Rundle Group, Devonian Fairholme Group, Mississippian Banff Formation, and the younger detrital rocks. Rockslides are most probable on dip and overdip slopes, followed by reverse-dip slopes, oblique and strike-dip slopes, and underdip slopes. Large rock masses have not slid on slopes below their basic friction angle, [Formula: see text]The reconnaissance shows that certain facilities in valleys below steep mountain slopes are exposed to rockslide hazards, and provides a guide for the location of new facilities. Analyses of two mountain slopes show that there are large, hypothetical hazards in Kananaskis. Rockslides are likely and could be destructive. Key words: Front Ranges, Rocky Mountains, Alberta, rockslides, hazards.
Use of critical state representations of sand in the method of stress characteristics
Authors: Jefferies M. G. , Been K.
Published: June 2008

The limitations of critical state representations of sand behaviour are discussed and it is shown that stress dilatancy is an implicit part of a critical state framework. It is then argued that dilatancy leads to underestimates of bearing capacity factors in the method of characteristics. Kinematic constraints should also be considered in such calculations. Both dilatancy and kinematic constraint may be introduced into a stress characteristics approach while preserving critical state characterization of sand, using the technique known as the method of associated fields. Key words: bearing capacity, critical state, stress dilatancy, method of characteristics.
Adfreezing strength of ice to model piles
Authors: Parameswaran V. R.
Published: June 2008

Results of tests to determine the adfreezing strength of freshwater ice to piles having different surface characteristics show that adfreeze strength increases with increase in the rate of displacement and loading of the pile. Surface coatings such as creosote on wood piles and paint and silicone sealer on metallic piles drastically decrease the adfreezing strength of ice. Key words: adfreezing strength, displacement rate, ice, loading rate, model piles, surface coating.
Stability of circular vertical earth anchors
Authors: Saeedy Hamed S.
Published: June 2008

This study aims to provide an extensive analytical approach for determining the uplift capacity of circular vertical earth anchors and to investigate the soil–anchor interaction. The solution is simplified by utilizing proper dimensionless parameters, in which controlling dimensionless factors [Formula: see text] are produced for a range of values of H/D and angle of internal friction. The factor [Formula: see text] is a pressure ratio representing gravitational and shear strength of the soil, and H/D signifies relative depth, which pertains to anchor geometry. The functional relationship of these parameters was previously studied for H/D ratios up to 6. The present work concludes that the greater the value of H/D the higher the uplift resistance, but with a decreasing rate until a constant value of uplift force is reached. The transitional value of depth, which defines the condition of failure, is a function of the shear strength of the burial soil. This transitional stage indicates the optimum possible value for uplift capacity for a given relative depth (H/D). Key words: tension foundation, uplift capacity, earth anchor load capacity, soil anchor interaction.
Residual strength of smectite-dominated soils from the Kamenose landslide in Japan
Authors: Gibo Seiichi , Egashira Kazuhiko , Ohtsubo Masami
Published: June 2008

The residual strength of smectite-dominated soils from the main slip surfaces of the Kamenose landslide, Japan, was measured by ring shear test, and the relations of the residual strength to the clay fraction content and clay particle orientation were studied. The residual angles of shearing resistance, [Formula: see text], were estimated assuming that the residual cohesion is zero. The magnitude of the residual angle of shearing resistance was dependent on the <2-μm clay fraction content, CF, and on the effective normal stress, [Formula: see text], because of curved strength lines. At [Formula: see text] equivalent to the overburden pressures, the soils had [Formula: see text] of 6–8°. These residual angles of shearing resistance were fitted on the [Formula: see text] – CF line for sand–bentonite mixtures, and exhibited the sliding shear mode.The orientation of smectite particles on shear surfaces showing slickensides was assessed by X-ray diffraction technique. The orientation of smectite particles was found to reduce the residual strength considerably, and this orientation effect was revealed more clearly at low effective normal stresses. Key words: residual strength, particle orientation, landslide, smectite, shear mode, slip surface, slickenside, clay mineral, physicochemical properties, ring shear test.