bluuebunny/crossref_metadata_2025 huggingface dataset:
An In Situ Study of Cadmium and Mercury Stress in the Plankton Community of Lake 382, Experimental Lakes Area, Northwestern Ontario
Authors: Marshall J. S. , Parker J. I. , Mellinger D. L. , Lawrence S. G.
Published: April 2011

Four in situ experiments with small-volume (28-L) enclosures were conducted in Experimental Lakes Area Lake 382 to assess the effects of inorganic mercury and cadmium on the plankton community. Additions of 0.9 × 10−8 mol Cd/L caused significant reductions of crustacean zooplankton density, zooplankton community similarity, zooplankton species diversity, and dissolved oxygen concentration over 3-wk periods. Additions of 1.0 × 10−8 mol Hg/L caused reductions similar to those of 0.9 × 10−8 mol Cd/L. Phytoplankton primary productivity was reduced by additions of 2.0 × 10−8 mol Hg/L but not by 1.0 × 10−8 mol Hg/L. On a molar concentration basis, the toxicities of inorganic mercury and cadmium were quite similar. Significant changes in lake plankton communities may occur at molar concentrations above 0.2 × 10−8 mol/L. Potentially toxic concentrations of cadmium may occur in many contaminated lakes, but toxic concentrations of mercury probably occur in few lakes.Key words: Precambrian Shield lakes, plankton communities, phytoplankton, zooplankton, cadmium, mercury toxicity
Competition Between Brook Trout (Salvelinus fontinalis) and Brown Trout (Salmo trutta) for Positions in a Michigan Stream
Authors: Fausch Kurt D. , White Ray J.
Published: April 2011

Competition between brook trout (Salvelinus fontinalis) and brown trout (Salmo truttta) was studied by measuring characteristics of daytime positions held by brook trout before and after removal of the brown trout from 1800 m of a stream. We used four criteria as indices of position quality: "water velocity difference" (the difference between velocity at the focal point and in the fastest current within 60 cm of the fish), water depth, distance to stream bed, and lighting. After brown trout removal, brook trout larger than 15 cm chose resting positions with more favorable water velocity characteristics and more often in shade. The position shift was greatest for the largest brook trout, those of 20–30 cm. Feeding positions of brook trout changed little upon brown trout removal according to our criteria. The shift in resting positions of brook trout after release from competition with brown trout indicates that brown trout excluded brook trout from preferred resting positions, a critical and scarce resource. The combined effects of such interspecific competition, differential susceptibility to angling, differential response to environmental factors, and predation of brown trout on juvenile brook trout may account for declines of brook trout populations while brown trout populations expand in many streams of the northeastern United States where the two species are sympatric.Key words: brook trout, brown trout, competition, ecological release, microhabitat use, resting positions, feeding positions, stream, Michigan
Labeling Fish with an Activable Element Through Their Diet
Authors: Michibata Hitoshi
Published: April 2011

Stable samarium, one of the rare earth elements, was fed to medaka (Oryzias latipes) and goldfish (Carassius auratus). The concentration of samarium in the labeled fish was determined by neutron activation analysis. In O. latipes, samarium was detectable even 1 yr after the labeled diet was eaten. In C. auratus, samarium was retained in the fifth branchial arch, scales, and gills.Key words: fish marking, Oryzias latipes, Carassius auratus, activation analysis, activable tracer, samarium
Relative Effectiveness of Two Ichthyoplankton Sampling Techniques
Authors: Cada Glenn F. , Loar James M.
Published: April 2011

Two common ichthyoplankton sampling devices, a pump and a conical plankton net, were evaluated for their relative effectiveness in collecting various sizes of clupeid larvae in the headwaters of Watts Bar Reservoir in eastern Tennessee. Triplicate surface pump and towed-net samples were taken during both day and night on three dates in June 1979 to detect any diel differences in sampler effectiveness. Clupeid larvae, 4–10 mm long, were collected in numbers large enough to make meaningful statistical comparisons of the two techniques. The differences in the mean densities of most length groups between nighttime pump and tow samples were not statistically significant. During the day, however, the pump collected significantly more 4-mm larvae and the towed net collected more 5- to 10-mm larvae. Our results indicate that under conditions by which these samplers are commonly deployed in open waters, most sizes of young shad larvae exhibited a greater ability to avoid the pump sampler than the towed net during the daytime.Key words: ichthyoplankton, pump, nets, fish larvae, avoidance
An Index of Littoral Zone Complexity and Its Measurement
Authors: Kent Clement , Wong Jonathan
Published: April 2011

The littoral zone is important in lake ecosystems. It affects physical, chemical, and biological processes of the whole lake. We first describe patterns in the shoreline lengths of a lake drawn from maps of different scales. Second, we show that these patterns or "measurement laws" hold for many different lakes. We then use "fractal" measuring theory to provide a unifying explanation of these empirical results. Fractal theory also makes new predictions about the statistical properties of groups of lakes. Patterns in our data were consistent with these predictions. Finally, we discuss how physical and geomorphological processes can give rise to fractal patterns in the landscape.Key words: fractal, geomorphology, littoral, morpho-edaphic index, shoreline development index
Biochemical and Serological Characteristics of Ontario Isolates of Yersinia ruckeri
Authors: Stevenson R. M. W. , Daly J. G.
Published: April 2011

During testing hatchery and wild fish from Ontario sources, we isolated bacteria that had sufficient characteristics in common with Yersinia ruckeri to suggest they were strains of this organism. Three isolates from brook trout (Salvelinus fontinalis), rainbow trout (Salmo gairdneri), and cisco (Coregonus artedii) biochemically resembled the sorbitol-fermenting Serovar II strain of Y. ruckeri, but gave cross reactions with antiserum to the Hagerman strain, Serovar I. A fourth isolate from brown trout (Salmo trutta) appeared to be different from the three previously described serovars. A fifth isolate previously obtained from muskrat (Ondatra zibethica) intestine biochemically and serologically corresponded to the Hagerman serovar. We suggest that the geographic range of Y. ruckeri and variations in its biochemical and serological properties are greater than previously believed. These findings are of significance in diagnosis and regulation of enteric redmouth disease of salmonids.Key words: Yersinia ruckeri, enteric redmouth, ERM, bacterial disease, fish health protection
Alterations in the Cellular and Subcellular Structure of Marine Teleosts and Invertebrates Exposed to Petroleum in the Laboratory and Field: A Critical Review
Authors: Malins Donald C.
Published: April 2011

Laboratory studies with individual petroleum components, model mixtures of hydrocarbons, fractions of petroleum, and whole oil have demonstrated, mostly at high exposure concentrations, an association between petroleum and various cellular/subcellular alterations in marine organisms. Recent evidence, notably from studying the effect of the AMOCO CADIZ oil spill, suggest that cellular/subcellular alterations also result from exposing marine organisms to petroleum in the field. In marine environments, however, it is still generally not possible to predict the type or degree of impact of petroleum on organisms because little information is available on the influence of myriad natural and man-induced environmental variables on its fate and effects.Key words: marine invertebrates and teleosts, petroleum, pollution, aromatic hydrocarbons, acute/chronic exposures, cellular/subcellular changes, pathological changes, morphology, mutagenesis, DNA binding, laboratory studies, field studies
Aquatic Invertebrates from the Smoking Hills, N.W.T.: Effect of pH and Metals on Mortality
Authors: Havas Magda , Hutchinson T. C.
Published: April 2011

Experiments were conducted on planktonic crustaceans and insect larvae from acidic and alkaline tundra ponds at the Smoking Hills, N.W.T. to determine their tolerance to low pH and elevated levels of potentially toxic elements, including Al. The crustaceans (Daphnia middendorffiana, Diaptomus arcticus, Lepidurus arcticus, Branchinecta paludosa), which are found only in alkaline ponds, died rapidly below pH 4.5. The insect larvae (Orthocladius consobrinus and Limnephilus pallens) from the same alkaline ponds were able to survive for extended periods at pH 3.5, though they do not occur in acidic waters at the Smoking Hills. The red chironomid (Chironomus riparius) is restricted to acidic ponds although it was able to survive not only at pH 2.8, but also in pond water of pH 8.2.Water from an acidic pond (pH 2.8) was markedly more toxic to crustaceans than water from an alkaline pond (pH 8.2) when both were adjusted to pH 4.5. Elevated concentrations of aluminum may account for this additional toxicity of the acidic pond water. Levels reached 20 mg/L Al, and in experiments with Al, additions to the alkaline waters and to the acidic pond waters, after metal removal, caused toxicity to the crustaceans.The absence of crustaceans from acidic ponds at the Smoking Hills may be due to their extreme sensitivity to low pH. The similarly restricted distribution of certain of the insect larvae, in contrast, cannot be explained this simply. Metal concentrations in acidic ponds impose an added stress. Aluminum was found to be the key additional factor to that of H+ ion concentration.Key words: acidic ponds, tundra ponds, Smoking Hills, bioassays, zooplankton, insect larvae, crustaceans, Daphnia, Diaptomus, Lepidurus, Brachinecta, Chironomus, Orthocladius, Limnephilus, heavy metals, aluminum, calcium, sodium, iron, zinc, nickel
Nonlinear Relation Between Smolts and Adults in Babine Lake Sockeye Salmon (Oncorhynchus nerka) and Implications for Other Salmon Populations
Authors: Peterman Randall M.
Published: April 2011

Data on sampling variability in smolt abundance for Babine Lake sockeye salmon (Oncorhynchus nerka) are combined with a previous analysis to calculate a more accurate estimate of the degree of nonlinearity in the relation between smolts and adults. Results indicate significant within-stock nonlinear mortality, large variability in mortality which tends to obscure any smolt-to-adult relation, or both. Analysis of age structure data identifies the first 15 mo of marine life as the period when most of this nonlinear or relation-masking mortality occurs. I also calculate the amount of smolt measurement error below which other salmon stocks are classed as having nonlinear marine survival. A distinct separation between even and odd brood year marine survival of Babine Lake sockeye suggests interactions with pink salmon. Juvenile pink salmon (O. gorbuscha) abundances correlate positively with residuals in Babine Lake sockeye survival for the same seaward migration year. This suggests a depensatory mortality effect which occurs later in the marine life stage than the possible within-population compensatory effect. Depensation is plausible because the size of pink fry equals that of sockeye smolts by August in coastal waters, permitting mutual swamping of predators. The paper concludes with implications for further enhancement.Key words: density dependence, marine survival, measurement error, enhancement, depensation, nonlinear, variability
Substrate Preference Behavior of Juvenile American Lobsters, Homarus americanus, in Gravel and Silt–Clay Sediments
Authors: Pottle Robert A. , Elner Robert W.
Published: April 2011

In the laboratory, early stage juvenile American lobsters, Homarus americanus, showed a preference for spending time and selecting shelters in gravel when given a choice between silt–clay deposited over gravel versus gravel substrates. Lobsters excavated shelters in the gravel by various combinations of pushing, plowing, and carrying stones with their chelae, third maxillipeds, and walking legs. Burrows in silt–clay were invariably adjacent to supporting structures. Our observations on shelter modifications and occupancy indicate that juvenile lobsters are active primarily, but not exclusively, at night. The juvenile lobsters frequently changed shelters during the initial 3 d before a status quo was established. We hypothesize that ocean dumping of silt–clay over gravel may increase spatial competition among juvenile lobsters for shelter in remaining gravel habitat.Key words: shelter, burrowing, competition, ocean dumping
Ecological Responses of Hydropsychid Caddisflies to Stream Regulation
Authors: Hauer F. Richard , Stanford Jack A.
Published: April 2011

Based on the river continuum theory and preliminary investigation in the upper Flathead River (British Columbia and Montana), we expected a sequential change in the hydropsychid fauna from large Arctopsychinae species in low-order streams to smaller Hydropsychinae in the higher-order rivers. Parapsyche elsis was found in small 1st- and 2nd-order streams and was replaced by Arctopsyche grandis as the dominant net-spinning caddisfly in 3rd- and 4th-order creeks. Three Hydropsychinae species first appeared in 4th-order creeks and became dominant in the 5th-order river, although A. grandis was still present. Site-specific degree-days (annual) increased progressively down the longitudinal gradient from 1200 degree-days in low-order, high-mountain streams to 2400 degree-days in the 5th-order river. However, hypolimnion tail waters from the regulated South Fork altered the thermal regime in the 6th-order mainstream from an expected 2600 annual degree-days to 2050 degree-days. The diurnally fluctuating discharge pattern from the hydroelectric dam also resulted in sloughing of attached algae into the river seston. The decrease in annual degree-days and increase in sestonic particulate organic matter produced conditions similar to those in 4th-order creeks. Hydropsychids responded to the effects of stream regulation by reflecting population structure found in lower-order creek reaches. Arctopsyche grandis was the dominant collector-filter feeder in the regulated mainstream river segment and Hydropsychinae abundance was significantly lower than in unregulated, 5th-order river segments. We interpret the alteration of environmental parameters and corresponding faunal response as a reset of the river continuum caused by stream regulation.Key words: Hydropsychidae, Trichoptera, river, ecosystem, stream regulation, Flathead River, stream continuum, zoobenthos, temperature, particulate organic matter
Discount Factors and Risk Aversion in Managing Random Fish Populations
Authors: Mendelssohn Roy
Published: April 2011

The effects of changes in the discount factor as compared with the effects of changes in risk aversion are examined for a simple stochastic model of fish population dynamics. Numerical results suggest that both optimal harvesting strategies and the resulting population dynamics are insensitive to changes in the discount factor, whereas changes in the degree of risk aversion in the utility function do cause significant changes in both. When risk averse utility functions are viewed as total revenue curves with marginal prices that decrease with supply, the results suggest that the more sensitive price is to supply, then the resulting optimal harvesting policy is smoother. Theoretical results are presented which suggest these results are robust beyond the specific model.Key words: discount factors, risk aversion, population dynamics, randomness
Ability of Standard Toxicity Tests to Predict the Effects of the Insecticide Diflubenzuron on Laboratory Stream Communities
Authors: Hansen Stephen R. , Garton Ronald R.
Published: April 2011

We assessed the ability of a standard set of freshwater single-species toxicity tests to predict accurately effects of the insecticide diflubenzuron (1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea) on complex laboratory stream communities. The single-species tests complied with requirements prescribed for establishing freshwater quality criteria and included nine freshwater animal acute tests, five freshwater animal chronic tests, and one freshwater algal test. The stream communities were stocked from a natural source, equilibrated for 3 mo and then treated with diflubenzuron for 5 mo. Effects on these stream communities were assessed at the functional group level using biomass and diversity for the analysis. The single-species tests adequately predicted the concentrations of diflubenzuron which affected these stream communities; the most-sensitive test species, insects and crustaceans, were up to an order of magnitude more sensitive than the observed community effects. The single-species tests were less successful in predicting the exact nature of the community level effects. Those effects resulting from direct lethality to component species were clearly predicted; indirect effects due to altered interspecies interactions could only be predicted with an a priori knowledge of the system's trophic dynamics.Key words: toxicity, diflubenzuron, streams, community effects, toxicity testing
Population Characteristics of Juvenile Coho Salmon (Oncorhynchus kisutch) Overwintering in Riverine Ponds
Authors: Peterson N. P.
Published: April 2011

Survival and growth from immigration to smolt outmigration differed substantially between pond populations of juvenile coho salmon (Oncorhynchus kisutch). In Pond 1 (the deeper, less-productive pond) overall survival was 78% but average fish weight increased only 49%, whereas in Pond 2 (the shallow, more-productive pond) survival was only 28% but average fish weight increased 94%. Diet of resident coho in the early spring was characterized by chironomid larvae and newly emerged adults in Ponds 1 and 2, respectively. Manipulation of pond morphometry may have potential for enhancing coho stocks.Key words: coho, pond, winter habitat, survival, growth, diet
An Evaluation of the Wet Oxidation Technique for Use in Determining the Energy Content of Seston Samples
Authors: Newell Roger I. E.
Published: April 2011

Many of the techniques available to determine energy content have problems inherent in their use on samples with a high proportion of inorganic minerals. One technique which may readily be used on such samples is wet oxidation, in which the sample is quantitatively chemically oxidized. However, this technique is infrequently used because of a potentially significant underestimation of energy content, due to incomplete oxidation of nitrogenous compounds. For a number of plant and animal tissues, wet oxidation with potassium dichromate gave values for energy content within ±3.0% of the value determined by bomb calorimetry.Seston samples on glass fiber filters may also be quickly and accurately analyzed using this procedure. The conversion from either weight loss on ignition or carbon and nitrogen content to energy content, using literature-derived conversion factors, is extremely inaccurate. Conversion of the wet oxidation values to carbon content gave inconsistent results, if the carbon content of the samples is required this should be determined directly by C:N analysis, or by quantifying the CO2 liberated by wet oxidation.Key words: wet oxidation, seston analysis, energy budgets, calorimetry, weight loss on ignition, CHN analysis
Reproductive Strategy of Dwarf and Normal Arctic Charr (Salvelinus alpinus) from Vangsvatnet Lake, Western Norway
Authors: Jonsson Bror , Hindar Kjetil
Published: April 2011

In this paper, we investigate the reproductive strategy maintaining dwarf and normal phenotypes of an Arctic charr (Salvelinus alpinus) population. Both morphs occurred together in the spawning area, but the peak abundance of dwarf spawners was significantly deeper, and later in the spawning period, than normal spawners. Both phenotypes attained sexual maturity at the same age and did not differ in length-specific fecundity or egg diameter. Our data support the hypothesis that the females matured sexually at the age that maximizes their fitness within the constraints imposed by growth and survival. The two female morphs appeared not to have equal fitness; these differences may be due to random events. The males were more heterogeneous by size than the females when maturing sexually. This may be due to intrasexual competition between males making large males the principal spawners. The dwarf males may circumvent the effects of intrasexual competition by mimicking immature fish, sneak at the redds of normal females, and participate in the spawning acts of normal charr pairs. Also, they may fertilize the eggs of dwarf females spawning in deeper areas.The two charr morphs developed from a uniform young phenotype (parr). The dwarf spawners were precocious individuals maturing sexually in their parr stage, whereas normal spawners had a color shift, analogous to smoltification in anadromous charr, before they attained sexual maturity. The different spawning coloration of the two morphs may be due to sexual selection.Key words: spawning, growth, fecundity, mortality, sexual selection, maturing strategy
Acute Toxicity of Cyanide to Rainbow Trout (Salmo gairdneri) Acclimated at Different Temperatures
Authors: Kovacs Tibor G. , Leduc Gérard
Published: April 2011

The toxicity of cyanide (HCN) to juvenile rainbow trout (Salmo gairdneri) acclimated for 3 wk at 6, 12, and 18 °C was determined at these temperatures by flow-through bioassays, in the cyanide concentration range of 0.018–0.087 mg∙L−1. The 96-h median lethal concentrations (LC50) were 0.028 ± 0.004 mg∙L−1 at 6 °C, 0.042 ± 0.004 mg∙L−1 at 12 °C, and 0.068 ± 0.004 mg∙L−1 at 18 °C. Warm acclimated rainbow trout survived longer in lethal concentrations of cyanide. Toxicity curves clearly showed the temperature effect on the acute toxicity of cyanide is concentration dependent. At slowly lethal concentrations, cyanide is more toxic at lower temperatures, whereas at rapidly lethal levels the reverse occurs; the reversal takes place at 0.10 mg∙L−1 HCN.Key words: cyanide, acute toxicity, temperature, rainbow trout
Production Modeling Using Mortality Estimates
Authors: Csirke J. , Caddy J. F.
Published: April 2011

Two new approaches to applying the logistic model to fisheries data are suggested; these do not employ information on fishing effort, but use the overall mortality rate (Z) for the population as a direct index of fishing mortality rate (F). The first approach suggests fitting a parabola between annual yield and mean annual Z, and provides an independent estimate of natural mortality M; the second suggests fitting a straight line directly between catch rate and mean annual Z. Both approaches use data sources that are statistically independent and encourage a smooth transition from an early use of production models in a developing fishery into the use of more elaborate analytical models as the data base accumulates.Key words: Theory of production modeling, logistic population growth, use of mortality parameters in fitting
Mercury Speciation in Water
Authors: Ramamoorthy S. , Cheng T. C. , Kushner D. J.
Published: April 2011

Speciation of mercury in water and in the air above the water was studied. The effects of hydrogen peroxide, bacterial growth medium, and both living and dead bacteria (Escherichia coli and Pseudomonas aeruginosa) were tested. Both living and dead bacteria transport metallic mercury from water into air. The amount of total Hg produced in the head space was similar in living or dead bacterial and hydrogen peroxide systems, [Formula: see text]. Hydrogen peroxide stabilized Hg2+ in the system. Partition coefficients were calculated from the corrected concentrations in the head space using literature solubility values for air/water phases. It is possible that Hg0 could be produced biologically or/and abiologically in a microenvironment within suspended particulate matter under favorable conditions. Further movement into air or subsequent transformation would depend on the physicochemical properties of the bulk water.Key words: mercury speciation, water, bacterial growth medium, living and dead bacteria
Predation by Sharks on the Grey Seal (Halichoerus grypus) in Eastern Canada
Authors: Brodie Paul , Beck Brian
Published: April 2011

The increase in population size of the grey seal (Halichoerus grypus) off eastern Canada over the past 20 yr may be attributed to a decrease in shark stocks, their supposed predators. Reduction of the shark population is presumed to have resulted from a directed longline fishery and, of greater significance, from a change in the fishery for swordfish (Xiphias gladius) from selective harpooning to pelagic longlining, which has produced a large bycatch of sharks. The resulting enhanced survival of grey seals is reflected in greater infestation of commercially important fish species by the codworm (Phocanema decipiens).Key words: grey seals, harbour seals, sharks, swordfish, codworm, predation, fisheries
Predator–Prey Relationships for Juvenile Chinook Salmon, Oncorhynchus tshawytscha, Feeding on Zooplankton in "in situ" Enclosures
Authors: English Karl K.
Published: April 2011

Juvenile chinook salmon, Oncorhynchus tshawytscha, were raised in 90-m3 mesh enclosures in Saanich Inlet, B.C. The enclosures permitted ample water and zooplankton circulation while retaining 5–6 g juvenile salmon. Mean growth rate was 1.8% wet body weight/d over 6 wk. Weekly growth rates ranged from 3.9%/d while food was abundant, to −0.5%/d when food was scarce. Zooplankton concentration inside and outside enclosures without fish were not significantly different. Organisms associated with the sides of the enclosures (non-pelagic) were not a major contributor to the growth of the juvenile chinook. There was a strong relationship between the fish growth rates and the abundance of 1.4- to 4.5-mm zooplankton. Rates of successful search varied directly with the size and inherent contrast of a prey item. The minimum rate of successful search was 2.3 m3/h for salmon feeding on 1.4- to 4.5-mm zooplankton. This rate of successful search, while far greater than previously suspected, is still within the visual capabilities of the juvenile salmon. The enclosed salmon grew rapidly on zooplankton concentrations that were 1/1000 of those required to sustain similar growth rates in tank experiments.Key words: predator–prey relationship, planktivorous salmonid, marine, "in situ" enclosures, search efficiency
Influence of Sediment on Anthracene Uptake, Depuration, and Biotransformation by the Amphipod Hyalella azteca
Authors: Landrum Peter F. , Scavia Donald
Published: April 2011

Uptake, depuration, and biotransformation rates of anthracene were determined for Hyalella azteca (Amphipoda, Crustacea) in both the presence and the absence of sediment. The mean rate constant ± SE for uptake from water was the same for cases with or without sediment, 255 ± 76 mL∙(g animal wet weight)−1∙h−1. The rate constant for uptake of sediment-associated anthracene was 19 ± 5 g dry sediment∙(g animal wet weight)−1∙h−1 for an organic sediment. Depuration increased by a factor of three in the presence of sediment. Sediment-associated anthracene, compound sorbed to sediment and in pore water, was estimated to contribute 77% of the steady-state body burden. These animals, and presumably other benthic organisms exposed to toxicants in organic sediments, are at higher risk than animals not associated with sediments. Further, bioconcentration factors based on the ratio of body burden to water concentration are overestimates for H. azteca and other benthic organisms that obtain a large proportion of their body burden from sediment.Key words: anthracene, Hyalella azteca, sediment, PAH
Effort Dynamics of the Northern California Dungeness Crab (Cancer magister) Fishery
Authors: Botsford Louis W. , Methot Jr. Richard D. , Johnston Warren E.
Published: April 2011

Knowledge of the dynamic response of fishing effort to abundance is essential to a complete understanding of the cycles in catch in the northern California Dungeness crab fishery. In this fishery there is a lagged response of harvest rate to changes in abundance that is caused either by a time lag in fishermen entering and leaving the fishery following changes in abundance, a lag in market expansion and contraction following changes in abundance, or a combination of both. The time lag in this response appears to have decreased over the past 30 yr. This lagged response is a potential cause of the cycles. However, neither of the two potential cyclic mechanisms examined here, a predator–prey mechanism (with man as the predator) and a price-dependent escapement mechanism (with price dependent on past catch), is a cause of these cycles. Although time-varying effort does not cause the cycles, it does have a substantial effect on the resulting catch record and population dynamics. If there is a density-dependent recruitment mechanism in this population as proposed earlier, the presence of this lagged response would cause the period of observed cycles to be longer than would be expected on the basis of population dynamics alone. Hence, previous estimates of the expected period of cycles from various population mechanisms are low. Removal of this response is a potential means of stabilizing this fishery.Key words: effort, Dungeness crab, harvest rate, predator–prey, price, stability, age, cycles
Reliability in Measuring Diet Overlap
Authors: Wallace Richard K. , Ramsey John S.
Published: April 2011

Intraspecific diet overlaps were calculated for young-of-the-year largemouth bass (Micropterus salmoides), juvenile bluegills (Lepomis macrochirus), and inland silversides (Menidia beryllina) by randomly dividing collections of each species into two sets, measuring the diet (average of the volume percentage) and calculating the diet overlap by Schoener's method. The randomization process and overlap calculation were repeated 30 times and an upper confidence limit (95%) for intraspecific overlap was determined. Upper confidence limits of intraspecific overlap were generally below the 100% overlap expected if diets were adequately characterized. Intraspecific overlap varied with collection date, fish species, and size of sample. Increasing sample size did not increase intraspecific overlap when the larger sample included a wider size range of fish. The upper confidence limit of intraspecific overlap can be used as a measure of reliability for interspecific diet overlap calculations. We suggest that intraspecific overlaps approaching 100% indicate high reliability for the corresponding interspecific overlap value. The intraspecific overlap is most useful in judging the reliability of interspecific overlap when sample size is limited.Key words: diet overlap, intraspecific overlap, interspecific overlap
A New Method for Allotting Effort to Individual Species in a Mixed-Species Trawl Fishery
Authors: Westrheim S. J.
Published: April 2011

A new method is described which allots fishing effort to individual species in a multi-species trawl fishery in northern Hecate Strait, British Columbia. All-species effort and individual species' landings are arranged by depth in selected area–time cells. In each area–time cell, each species is allotted the all-species effort expended in the depth intervals containing the rank-1 (most) and rank-2 (next-most) landings of that species. Comparison of the new option method with the conventional qualification method indicated that the latter method underestimated expended effort, particularly for less important species. Trends in effort and CPUE did not differ appreciably among methods. The new option method is deemed to be superior to the conventional qualification method.Key words: effort allotment, multispecies trawl fisher, Hecate Strait, western Canada
Analysis of the Biological and Demographic Parameters of Northern Sand Lance, Ammodytes dubius, from the Newfoundland Grand Bank
Authors: Winters G. H.
Published: April 2011

Biological characteristics and population dynamics of northern sand lance (Ammodytes dubius) population on the Grand Banks were investigated in the period 1968–79. Sand lance were distributed mainly in the shallower areas of the Grand Banks, particularly in the northeast and southeast areas. Through an examination of reproduction parameters I conclude that spawning occurs principally during the period November–January. Growth rates of Grand Bank sand lance are within the range of those described for the Scotian Shelf and are well correlated with temperature variations. Abundance indices, derived from groundfish surveys, indicate a substantial increase in abundance since the 1960s, and this increase is attributable to increased recruitment and reduced natural mortality. From correlation analyses I suggest that the decline in the Grand Bank population of Atlantic cod (Gadus morhua) may be responsible for the reduced mortality rates and increased abundance of Grand Bank sand lance during the 1970s.
Early Marine Mortality of Marked Juvenile Chum Salmon (Oncorhynchus keta) Released into Hood Canal, Puget Sound, Washington, in 1980
Authors: Bax Nicholas J.
Published: April 2011

The average daily loss in numbers from a group of fluorescently marked, hatchery-reared, juvenile chum salmon (Oncorhynchus keta) remaining in the nearshore zone following their release from the hatchery into southern Hood Canal, Washington State, was estimated at 38–49%. This estimated loss was then adjusted by the estimated maximum emigration of marked fish from the sampling area and the average daily mortality over a 2- and a 4-d time period estimated at between 31 and 46%. These estimates are an order of magnitude higher than estimates of the average daily mortality of naturally emigrating juvenile pink salmon (O. gorbuscha) from the Bella Coola River, British Columbia, over a 40-d time period (Parker 1968). The two studies are contrasted and it is suggested that daily mortality is highly variable over the 40 d subsequent to saltwater entry, with mortality higher initially, particularly for those fish remaining close to their point of saltwater entry.
Unionid Growth Curves Derived from Annual Rings: A Baseline Model for Long Point Bay, Lake Erie
Authors: McCuaig Janet M. , Green Roger H.
Published: April 2011

Growth curves for Lampsilis radiata and Anodonta grandis collected in July 1981 at three stations in Long Point Bay, Lake Erie, were determined based on measured lengths at annual winter shell rings. A Walford Plot technique was used to convert annual growth-in-length increments to length vs. age growth models. For the two species, we used simulated baseline and environmental impact data to illustrate the use of baseline growth models in testing for long-term environmental deterioration.
Genetic Differentiation in the Face of Gene Flow: A Study of Mussel Populations from a Single Nova Scotian Embayment
Authors: Gartner-Kepkay K. E. , Zouros E. , Dickie L. M. , Freeman K. R.
Published: April 2011

There are significant genetic differences among populations of the blue mussel, Mytilus edulis, from six localities in St. Margaret's Bay, N.S., Canada, despite the presence of gene flow. The populations are differentiated into two groups, those at the head of the bay where ambient conditions fluctuate widely during the year, and those at the mouth of the bay where conditions (particularly salinity) fluctuate to a lesser degree. Three isoenzyme loci, i.e. leucine aminopeptidase 1, peptidase 2, and phosphoglucose mutase, show a clear shift in the predominant frequencies, from slow migrating alleles at the mouth of the bay to faster migrating alleles at the head of the bay. This shift is a microgeographic parallel of the pattern we observed in 1980 on a macrogeographic scale. A genetic comparison of these populations with those studied previously shows that allele "populations" cluster according to their environment and not according to geographical proximity. We conclude that differences in allele frequencies among localities index heterogeneity among environmental conditions, and that the sensitivity to environmental selective forces varies from locus to locus.
Winter Distribution of Juvenile Coho Salmon (Oncorhynchus kisutch) Before and After Logging in Carnation Creek, British Columbia, and Some Implications for Overwinter Survival
Authors: Tschaplinski P. J. , Hartman G. F.
Published: April 2011

Numbers of juvenile coho salmon (Oncorhynchus kisutch) in streams are reduced substantially in winter compared to those that occur in summer. Most of this reduction occurs early in autumn with the onset of the first seasonal freshets. Stream sections containing adequate winter habitat in the form of deep pools, log jams, and undercut banks with tree roots and debris lost fewer fish during freshets and maintained higher numbers of coho in winter than sections without these habitat characteristics. These features provide shelter and reduce stream velocities. Microhabitats occupied by coho juveniles in winter after logging were unchanged from those described before logging — all microhabitats were characterized by low water velocities (≤ 0.3 m/s). Up to 48% of the coho population inhabiting stream sections with adequate shelter remained there by midwinter (Jan. 3). This percentage was typical of stream sections where at least some trees remained after logging. Streamside trees stabilized the banks and prevented their collapse. In contrast, two of three study sections that had been clear-cut logged had unstable banks which collapsed during winter freshets. Almost no coho remained in these sections in winter. Many coho emigrate from the main stream to seek the shelter of low-velocity tributaries and valley sloughs concurrent with the decline of coho populations in Carnation Creek during autumn and early winter. This seasonal shift in distribution reverses in the spring when large numbers of coho reenter the main stream. Fish overwintering in these sites have a high apparent survival rate. Before logging a 4-yr mean of 169 ± 44 coho entered one tributary (a slough called 750-m site) in autumn. Of these numbers entering, 72.2% came out in spring. During and after logging, an annual mean of 288 coho entered the same site. The apparent survival rate during and after logging was 67.4%, essentially unchanged from the prelogging value. Logging has neither reduced the numbers of coho juveniles that enter such sites in autumn to overwinter, nor reduced the numbers leaving these sites to reenter Carnation Creek in spring.
Sea Urchins in the Saint Lawrence Estuary: Their Abundance, Size-Structure, and Suitability for Commercial Exploitation
Authors: Himmelman John H. , Lavergne Yves , Axelsen Fritz , Cardinal André , Bourget Edwin
Published: April 2011

Quantitative transects were made at nine locations along the Saint Lawrence Estuary, Québec, to examine changes in the abundance and size-structure of populations of the green sea urchin, Strongylocentrotus droebachiensis, in relation to the estuarine gradient. Near the seaward extremity of the estuary, sea urchin densities are very high and small urchins are particularly abundant in shallow water. In contrast, midway up the estuary, small urchins are scarce in shallow water, probably because they cannot tolerate the periodic drops in surface salinities which occur there. Where urchin densities are high, urchin grazing severely limits algal production, and because of low algal food availability, the urchin growth rate is exceedingly low. In the Upper Estuary, urchin numbers are low and no urchins are found near the surface. There is feeble recruitment of urchins, and the near absence of urchins of intermediate size suggests that there is a high probability that juveniles are killed before they reach intermediate size. The urchin growth rate is accelerated because of the abundance of algae present, and below 10 m deep some juveniles survive through the intermediate size range. After they reach 40–50 mm in diameter, they can move up to the 2- to 10-m-depth zone and can tolerate the periods of hypo-osmotic conditions which occur there. Suitable populations for commercial use are most likely found where salinity or winter ice conditions reduce urchin numbers to a level permitting greater algal abundance and an elevated somatic and gonadal growth of the remaining urchins.
An Echo Counting and Logging System (ECOLOG) for Demersal Fish Size Distributions and Densities
Authors: Dickie L. M. , Dowd R. G. , Boudreau P. R.
Published: April 2011

Target strength of fish is dependent on their size, behavior, and density, and uncertainties about these parameters under field conditions affect the interpretation of acoustic survey data. The echo counting and logging system, ECOLOG, appears to offer information on these important parameters. The dual-beam system is described and results of a test cruise are analyzed. Published data on the relation of target strength to fish size are used to generate an "acoustic size-composition" from otter-trawl catches. Correspondence between the converted otter-trawl samples and acoustic data suggest that the system is generating direct information on demersal fish size and density and may thus be useful in verifying the results of echo sounder surveys. Main components of variation among samples and between sampling methods are ascribable to small-scale spatial heterogeneity of size distributions, although day–night behavior differences contribute significantly to the total heterogeneity.
An Effective Method for Tagging Marine Polychaetes
Authors: Joule Bruce J.
Published: April 2011

Two commercially harvested marine polychaetes, Glycera dibranchiata and Nereis virens, were successfully tagged with coded microwire tags placed in the coelomic cavity. Mortalities incurred during the experimental periods appear to be subject to the animals' sensitivity of being held under laboratory conditions rather than the tagging procedures. Average tag retention for the experiment was 82% among survivors.
Measurements of Dissolved Adenosine Triphosphate in Lake Michigan
Authors: Maki James S. , Sierszen Michael E. , Remsen Charles C.
Published: April 2011

Comparisons of two methods of separating dissolved adenosine triphosphate (dATP) were made, both in the laboratory and in vertical profiles in Lake Michigan. Laboratory work indicated that filtration through a 0.2-μm pore filter or centrifugation of samples gave similar concentrations of dATP. In Lake Michigan, however, the filtration method gave significantly higher dATP concentrations suggesting some adverse filtration effect. Therefore, centrifugation was chosen as the method to determine dATP. Resulting particulate ATP (pATP) concentrations indicated the highest levels of microbial biomass were located below the epilimnion. Feeding by Mysis relicta appeared to decrease pATP but not release much dATP.
Predicting Natural Mortality Rates and Reproduction–Mortality Trade-offs from Fish Life History Data
Authors: Myers R. A. , Doyle R. W.
Published: April 2011

A method for estimating natural mortality and evolutionary constraint on fish life histories is presented based on the assumption that observed life histories are evolutionarily stable. Inverse optimization techniques are used to determine the values of natural mortality, reproduction–mortality trade-offs, and energy conversion efficiencies that would make observed life histories evolutionarily stable. The life history method yields natural mortality estimates comparable with those based on population age–frequency data. Sensitivity analysis is used to determine the robustness of the predictions to errors in parameter estimation and density-dependent factors.
Redundancy of Variables Used to Describe Importance of Prey Species in Fish Diets
Authors: Macdonald J. Stevenson , Green R. H.
Published: April 2011

Information redundancy associated with three measurement variables were examined using food habit data from five species of demersal fish in the lower Bay of Fundy. Number, weight, and percent frequency of occurrence measures of three prey species all load heavily on the first principal component of a PCA and are therefore highly correlated. We conclude that it is probably not necessary to create compound indices of prey species importance when documenting soft-bottom benthic associations or demersal fish food habits. Compound indices add little new information when compared with any single measure.
An Integrated Study of the Factors Influencing the Choice of the Settling Site of Balanus crenatus Cyprid Larvae
Authors: Hudon Christiane , Bourget Edwin , Legendre Pierre
Published: April 2011

Settled larvae of Balanus crenatus were collected at Pointe Mitis, in the St. Lawrence Estuary, Quebec. Four substrata were sampled and observed using scanning electron microscopy (SEM): shells of Mytilus edulis, fronds of Fucus evanescens, and laminated panels immersed for periods of 4 and 8 wk. Following this treatment, 23 variables describing the substratum surface, the cover of inert and biological material, and the gregarious response of the larvae were documented for 200 larvae, and compared with 187 control sites uncolonized by larvae. Significant differences of substratum texture, detritus, and diatom abundance were observed between colonized and uncolonized sites, indicating that the selectivity of the larva is related to the heterogeneity of the substratum. On all substrata, the settling site of the larvae was free of detritus and diatoms, clean surfaces ensuring better adhesion for the individual. To rank the variables on which selection occurred, the χ2 value of a contingency table between each variable and the type of substratum was computed. Variables carrying low χ2 values represented the most constant larval choices irrespective of the type of substratum. Variables related to the microscopic characteristics of the substratum were more important for larval selection than the variables describing the already established barnacle population.
Towards a Better Definition of "Metamorphosis" in Coregonus sp.: Biochemical, Histological, and Physiological Data
Authors: Forstner H. , Hinterleitner S. , Mähr K. , Wieser W.
Published: April 2011

In Coregonus sp. the period between hatching and metamorphosis is characterized by an enhanced involvement of glycolysis in energy metabolism (as reflected by oxygen consumption and enzyme activities) and by the differentiation of the red and pink muscle fibers on which the increasing versatility of swimming performance of the larvae appears to depend. The larval weight of Coregonus sp. increased during the first 150 d of development at 10 °C from 6 to 2000 mg, but the average rate of oxygen consumption decreased only from 639 to 419 μg∙g−1∙h−1. Four types of muscle fibers were distinguished, each with a distinct developmental pattern: red and pink fibers first become observable 25–34 d after hatching, the latter growing more slowly than the former; before this, only white muscles and a characteristic layer of small diameter red fibers are present in Coregonus sp. The activities of the two oxidative enzymes, citrate synthase and cytochrome oxidase, and the activity of hexokinase, increased directly after hatching, reaching a peak within 20–47 d. On the other hand, the three glycolytic enzymes, phosphofructokinase, pyruvate kinase, and lactate dehydrogenase, remained at a constantly low level from hatching to day 40, whereafter their rates of activity began to increase rapidly.