bluuebunny/crossref_metadata_2025 huggingface dataset:
Predation of Juvenile Pacific Salmon by the Common Merganser (Mergus merganser) on Eastern Vancouver Island. I: Predation during the Seaward Migration
Authors: Wood C. C.
Published: April 2008

Predation of juvenile salmonids by the common merganser (Mergus merganser) was investigated during the period of seaward migration in two streams where fish populations are enhanced by spawning channels and hatcheries. Observation of foraging behaviour and crop-gullet contents indicated that, during this period, mergansers foraging on freshwater reaches of the streams ate juvenile salmonids almost exclusively whereas those foraging on tidal waters rarely ate salmonids. Maximum rates of salmonid mortality were estimated by assessing merganser abundance and the pattern of foraging activity on fresh versus tidal waters. Maximum mortality rate declined as fish abundance increased (i.e. mortality was depensatory) in all cases where the effects of prey size-selection could be ignored owing to an overwhelming abundance of one prey species. Bounds on maximum mortality rate by species for the entire migration period were computed under different hypotheses about the prey size-selection habits of mergansers; maximum mortality rate did not exceed 10% for any salmonid species over the entire seaward migration.
Predation of Juvenile Pacific Salmon by the Common Merganser (Mergus merganser) on Eastern Vancouver Island. II: Predation of Stream-Resident Juvenile Salmon by Merganser Broods
Authors: Wood C. C.
Published: April 2008

Predation of stream-resident juvenile salmonids by broods of the common merganser (Mergus merganser) was investigated in three streams on eastern Vancouver Island from 1980 to 1982. Daily fish consumption by merganser ducklings was estimated to range from 80% of body weight for ducklings at 10 d of age to 40% of body weight for those at 40 d of age. Merganser ducklings were never observed to eat juvenile salmonids on tidal waters, but did eat them on the freshwater reaches of streams studied. Typically, broods inhabited only the freshwater reaches of their natal stream while young, but spent progressively more time foraging on tidal waters as they grew older. The biomass of broods (and hence potential consumption) on fresh water was estimated by reconstructing the history of individual broods from census data. These results suggest that merganser broods consumed on the order of 82 000–131 000 coho salmon (Oncorhynchus kisutch) fry in the Big Qualicum River between June 10 and August 25. This is equivalent to 24–65% of the observed wild smolt production from this system, assuming that these fry would otherwise have survived as well as uneaten fry.
Phosphorus Species in the Surficial Sediments of Lakes of Eastern North America
Authors: Ostrofsky Milton L.
Published: April 2008

Species of phosphorus, total iron, and organic matter were determined from surficial profundal sediments of 66 lakes of eastern North America. The lakes represented a broad range of lake type, from oligotrophic to eutrophic and from soft water to moderately alkaline. The sediment characteristics were less variable than the lake characteristics. Highly significant correlations were found between percent loss on ignition and sedimentary organic phosphorus and between sedimentary iron and NH4Cl-extractable, NaOH-extractable, HCl-extractable, total inorganic, and total phosphorus in the sediments. There was no relationship between spring total phosphorus or alkalinity and any sediment character measured. The results suggest that lakes with high sedimentary iron have disproportionately higher concentrations of NH4Cl and NaOH-extractable phosphorus, two species that are most likely to contribute to internal loading of phosphorus.
An Analysis of Errors in Catch Projections for Canadian Atlantic Fish Stocks
Authors: Rivard Denis , Foy Malcolm G.
Published: April 2008

Two techniques were used to identify and evaluate the components of error inherent in the catch projection method used in the assessment of Canadian Atlantic fish stocks. Firstly, a retrospective analysis was used to evaluate, for the projections made in 1979 and 1981, the impact of the actual error made in input variables such as catch-at-age, mean weight-at-age, recruitment, and stock size. Secondly, the variance of projections was estimated from the variance of input variables. From the retrospective analysis, the principal causes of error in catch projections were identified as the estimation of stock size, as well as the estimation and forecast of fishing mortalities for the projection years. The difference between actual catch and assumed catch for the first year of a 2-yr projection did not appear to be a major source of bias for catch projections. The coefficients of variation of the catch projected at F0.1 were estimated as follows: 15–20% for the projections of Atlantic cod (Gadus morhua) catches; 25–50% for those of haddock (Melanogrammus aeglefinus); 28% for those of pollock (Pollachius virens); 16% for those of redfish (Sebastes sp.); and 35–42% for those of herring (Clupea harengus). The uncertainties associated with abundance estimates for prerecruited age-groups and estimates of stock size emerged as key factors in the projections. Also important was the effect of uncertainties associated with the forecast of reference fishing mortalities (partial recruitment coefficients × F0.1) for the projection period, e.g. uncertainties resulting from changes in fish catchability, in fleet behavior, and in fishing patterns.
A Model for Comparing Fish Density Estimates from Seine Catches and from Echo Integration
Authors: Mulligan T. J. , Kieser R. , Gjernes T.
Published: April 2008

A model for comparing acoustic and nonacoustic fish density values yields estimates for the ratio of the biases and the variances for the two sets of density measurements. The model compares seine catches and echo integration values. The correlation between the two sets of measurements is 0.98. The data seem to be well described by the model. A discussion is included of the role such comparisons might play in research or fisheries management, for fish behavior studies, for comparison of the relative precision of each technique, and for selecting individual measurements which should be duplicated.
Components Analysis of Instream Escapement Methods for Pacific Salmon (Oncorhynchus spp.)
Authors: Shardlow Tom , Hilborn Ray , Lightly David
Published: April 2008

Escapement counts of Pacific salmon (Oncorhynchus spp.) have played a critical role in the development of fisheries science. We describe the components of instream escapement counts which are (1) an estimate of the number of fish in the stream at specific times, (2) a method for interpolation between visits to estimate total number of fish present at any time and (3) an instream residence time parameter to determine total number of fish that spawned for the entire run. Estimation of number of fish present at any time depends on species, observation method, stream habitat type, and observer experience. Our generalized model accounts for all of these factors in a biologically meaningful manner. Data were collected by five methods for three species of salmon which were counted past a weir; however, the number of fish present was unknown to observers. Counts for walking found, on average, 20% of fish present, for rafting 43%, for swimming 63%, for fixed wing 85%, and for helicopter 100%. The reliability of different methods as an index of abundance was similar, despite variation in the proportion of the fish observed by each method. Subsampling of specific stream sections provided a good index of abundance.
Short-Term Effects of Zooplankton Manipulations on Phosphate Uptake
Authors: Hamilton Daniel T. , Taylor William D.
Published: April 2008

Samples of epilimnetic water were collected, manipulated to alter their zooplankton fauna, and incubated in situ for 24 h. We hypothesized that removal and concentration of zooplankton would decrease and increase phosphate turnover time, respectively, and that the presence of zooplankton would increase the accumulation of added 32PO4 by algae (particles greater than 1.0 μm) relative to bacteria (particles 0.2–1.0 μm). Although the treatments produced significant changes in turnover time and size distribution, neither hypothesis was supported; removal of zooplankton did not decrease turnover time, and it reduced the dominance of 0.2- to 1.0-μm particles in phosphorus uptake. However, concentrating microzooplankton frequently increased turnover time. Zooplankton removal caused a relative increase in ciliates, suggesting that these protozoa may be limited by their predators rather than by resource levels. Our results suggest that microzooplankton were the most important grazers and that the nutrient environment of phytoplankton was not directly affected by mesozooplankton. Phosphate dynamics were probably determined by bacteria, the protozoan predators of bacteria, and the supply of dissolved organic carbon.
Infectious Hematopoietic Necrosis Virus Detected by Separation and Incubation of Cells from Salmonid Cavity Fluid
Authors: Mulcahy D. , Batts W. N.
Published: April 2008

Infectious hematopoietic necrosis (IHN) virus is usually detected by inoculating susceptible cell cultures with cavity ("ovarian") fluid (CF) from spawning females. We identified additional adult carriers of virus in spawning populations of steelhead trout (Salmo gairdneri) and sockeye salmon (Oncorhynchus nerka) by collecting nonerythrocytic cells from CF samples by low-speed centrifugation, culturing the cells for at least 7 d at 15 °C, and then testing the culture medium for virus. Virus appeared in the cultured cells from some samples of CF that remained negative during incubation. In additional samples of CF from these species, the virus titer increased in cultured cells compared with the titer in the original CF sample. With chinook salmon (O. tshawytscha), no negative samples converted to positive during incubation, but the virus titer was retained in incubated CF cells, but not in cell-free CF.
Winter and Spring pH Depressions in Northern Wisconsin Lakes Caused by Increases in pCO2
Authors: Kratz Timothy K. , Cook Robert B. , Bowser Carl J. , Brezonik Patrick L.
Published: April 2008

Seasonal variation in pH in six clearwater northern Wisconsin lakes (mean pH 5.9–7.8; mean total alkalinity 9–830 μeq∙L−1) encompasses an annual range of 1.0–1.5 units in each lake, with lowest values characteristically occurring during the late winter and early spring. In detailed investigations of one lake, we evaluated strong acid inputs, shifts in pCO2, and changes in organic acids as possible mechanisms for pH depression. Our results indicate that seasonal pH depressions are caused largely by pCO2 increases under the ice. Despite an acidic snowpack the pH depression could not be attributed to input of acid meltwater because total alkalinity did not change in the lake. Our results emphasize the importance of using measurements other than pH in investigating the causes of acid dynamics of natural waters.
Life Stage and Population Variation in Resistance and Tolerance ofHyalella azteca(Amphipoda) to Low pH
Authors: France R. L. , Stokes P. M.
Published: April 2008

Lethality experiments revealed that resistance of Hyalella azteca (Amphipoda) to low pH was directly related to size and developmental stage. Exposure of adults to water below pH 5.0 during pulses of acid snowmelt, or of juveniles to below pH 5.5 through gradual lake acidification, could result in population decline. Hyalella azteca from moderately acidic Ontario lakes (pH 5.6–5.7) survived longer at lethal pH than did amphipods from circumneutral lakes (pH 6.4–7.2) where spring pH depressions do not occur. Resistance and tolerance to low pH was neither readily lost by tolerant amphipods exposed to neutral water for 10 d nor readily gained by nontolerant amphipods exposed to sublethal low pH for a similar duration. This absence of physiological plasticity of individual H. azteca suggests that population differences in acid tolerance may result from processes of selective mortality with or without a genetic basis.
Microbial Activity and Ultrastructure of Mineral-Based Marine Snow from Howe Sound, British Columbia
Authors: Amy Penny S. , Caldwell Bruce A. , Soeldner A. H. , Morita Richard Y. , Albright L. J.
Published: April 2008

Electron microscopy and biochemical measurements of heterotrophic and enzymatic activities were made on marine snow and underlying sediments collected from Howe Sound, British Columbia. SEM showed the marine snow to be accretions of comminuted phytoplankton, fecal pellets, cellular material, and mineral particles bonded by films and coatings of an amorphous material. The amount of amorphous substance decreased as Howe Sound became increasingly marine. Rod, cocoidal, and filamentous bacteria were cultured from the marine snow. Heterotrophic microbial activity increased seaward and was found to be higher in marine snow than in underlying sediments. Phosphatase, protease, laminarinase, and xylanase were also more active in marine snow whereas sulfatase activity was found to be higher in the sediments. β-Glucosidase activity was demonstrated in marine snow only at sampling stations isolated from outer Howe Sound and the Strait of Georgia by a submarine sill.
Diel Activity and Foraging Behavior of Juvenile American Lobsters, Homarus americanus
Authors: Lawton Peter
Published: April 2008

The activity of wild-caught juvenile American lobsters, Homarus americanus (20–46 mm carapace length (CL)), was monitored in the laboratory using time-lapse video recording techniques. Behavioral time-budget analyses indicated that juvenile lobsters are nocturnally active within or close to available shelter. Mussels, Mytilus edulis, provided as prey were picked up, apparently nonselectively, when lobsters ventured out from shelter and were immediately taken back to shelter for consumption. Such shelter-related or central-place foraging behaviors may minimize risk from predation during transition to the wide-ranging activity pattern typical of larger lobsters. Increased hunger led to greater light-phase activity, primarily shelter-related foraging behavior, among individually monitored lobsters. Dominant lobsters in CL-matched pairs also exhibited this behavior pattern, but spent less time within shelter and feeding during dark phases due to involvement in agonistic interactions. Subdominant lobsters spent the least time in shelter, often remained inactive in open areas of tanks, and foraged predominantly during light phases. Increase in predation risk due to adoption of these behaviors may be the major consequence of subdominant status rather than a reduction in food intake.
An Egg-Mass Census Method for Tracking Fluctuations in Yellow Perch (Perca flavescens) Populations
Authors: (Buck) Newsome G. E. , Aalto S. K.
Published: April 2008

Extreme annual fluctuations among yellow perch (Perca flavescens) populations are common and have been related to changes in the physical environment during early stages of the development of a year-class. However, critical investigations of these relationships are often hampered by the lack of accurate techniques for estimating abundance. In this paper an egg-mass census technique is described, and statistical procedures which provide population estimates with confidence limits are given. Also discussed are results of preliminary investigations of environmental factors which may have a dramatic affect on the year-class strengths of perch. Winds play an important role in determining recruitment rates. Wind-generated internal seiches may result in thermal shocking of perch embryos which subsequently affects juvenile survival.
Food and Habitat Utilization by Juvenile Salmonids in the Campbell River Estuary
Authors: Macdonald J. Stevenson , Birtwell I. K. , Kruzynski G. M.
Published: April 2008

Salmonid behaviour and abundance in several microhabitats within the Campbell River estuary was observed monthly, from May to July, by divers using snorkels and face masks. Concurrent vertical profiles of physical and biological parameters at each microhabitat were taken to characterize habitats frequented by the fish. Data were collected at high and low tide to record behavioural reactions to changes in water velocity, salinity, and temperature associated with tidal height and salt wedge intrusion. Samples of plankton collected at each microhabitat were compared with stomach contents of salmonids caught nearby to determine if interspecific differences in diet could be correlated with differences in the habitats they occupied. Fish occurred in loose assemblages, aligned with the current, feeding near estuarine banks. As water velocities increased with the ebbing tide, the fish concentrated in a shear region near the mouth of a slough and behind large rocks and submerged vegetation. At both high and low tide, larger coho (Oncorhynchus kisutch) and chinook salmon (Oncorhynchus tshawytscha) (usually hatchery reared) were in deeper, frequently more saline water and further from shore than the smaller conspecifics. Hatchery chinook, however, were also seen in sloughs where water velocity was low. Marine influence as reflected in plankton composition and salmonid diet was greater in the outer estuary and in the deep salt water that intrudes the inner regions of the estuary. Differences in the habitats occupied by the fish were reflected in differences in their diets.
Bioaccumulation and Metabolism of Tri- and Dialkyllead Compounds by a Freshwater Alga
Authors: Wong P. T. S. , Chau Y. K. , Yaromich J. L. , Kramar O.
Published: April 2008

A freshwater green alga, Ankistrodesmus falcatus, exposed to solutions of trialkyllead, dialkyllead, and inorganic lead (II) compounds (1 mg/L) for 24 h accumulated these compounds with concentration factors of about 100, 2000, and 20 000, respectively. Incubation of this alga with trimethyllead and dimethyllead species over a long period (28 d) revealed the ability of the organism to metabolize these compounds. The metabolic processes for trimethyllead followed a dealkylation sequence with the formation of dimethyllead and lead (II) compounds. The alga not ony accumulated dimethyllead, but also contained significant amounts of trimethyllead and lead (II) compounds. Neither chemical disproportionation reactions nor photodecomposition could account for the quantities produced.
Mitochondrial DNA Analysis of Pacific Northwest Populations ofOncorhynchus tshawytscha
Authors: Wilson Gary M. , Thomas W. Kelly , Beckenbach Andrew T.
Published: April 2008

Mitochondrial (mt) DNA restriction endonuclease assays of seven populations of Oncorhynchus tshawytscha from British Columbia and Alaska disclosed six distinct maternal (clonal) lines, of which three were represented by more than one individual. The three major lines were not population specific. Of the British Columbia fish sampled, 41 belong to clonal line A (82% of the 50 fish sampled in British Columbia). Clonal line C contained 10 fish from Alaskan sites only. Clonal line B contained 20 fish from both British Columbia and Alaska sites. Intraspecific mtDNA sequence divergence is low (less than 1% in ail cases) compared with other species surveys of this sort. Comparison with protein electrophoretic studies of O. tshawytscha reveals similar levels of population structuring. A database of mtDNA fragment sizes produced by the 14 restriction endonucleases is included.
Influence of Vegetation and Hydrology on the Humus Budgets of Labrador Lakes
Authors: Engstrom Daniel R.
Published: April 2008

A mass-balance approach is used to explore the effect of several hydrologic and geographic variables on humic matter concentrations in surface waters of Labrador–Ungava. Water-color measurements from 67 dilute oligotrophic lakes are used to evaluate model predictions of aquatic humus concentration from basin hydrology, catchment vegetation, and internal loss rates. The major trend in water color in the Labrador region — increasing north to south — results from differences in external humus loading from catchment vegetation and soils. Hydrologic influences on aquatic humus concentrations reside in the dilution of catchment drainage by direct precipitation to the lake — effective only when catchments are small — and in water residence time which controls losses due to mineralization and sedimentation.
Frequency of Sampling Required for Monitoring the Niagara River
Authors: El-Shaarawi A. H.
Published: April 2008

Water samples have been collected routinely at the head and mouth of the Niagara River since 1983 and analyzed for their chemical and physical characteristics. Statistical techniques are given for estimating the (1) frequency of sampling the river at two locations within a given year and (2) number of years required for monitoring the river in order to detect a linear trend in its water quality.
Laboratory Apparatus for Studying the Behaviour of Organisms in Vertically Stratified Waters
Authors: Birtwell I. K. , Kruzynski G. M.
Published: April 2008

An aquarium system is described which was designed to examine the locomotor activity of juvenile salmon under simulated estuarine conditions. A stable, vertically stratified water column can be established and dissolved oxygen, salinity, water velocity, and light intensity varied during operation under continuous-flow or recirculating conditions. Examples of stratification stability and application to studies of fish behaviour in relation to hypoxia are also presented.
Identification of Planktonic Sea Scallop Larvae (Placopecten magellanicus) (Gmelin)
Authors: Tremblay M. J. , Meade L. D. , Hurley G. V.
Published: April 2008

Methods for the collection, processing, and identification of planktonic sea scallop larvae (Placopecten magellanicus) (Gmelin) are described. Bivalve larvae collected from the Bay of Fundy were compared with cultured P. magellanicus larvae. Sea scallop larvae collected from the plankton can be tentatively identified based on shape and size; examination of the larval hinge structure allows confirmation.
A General Model for Simulation of Stock and Fleet Dynamics in Spatially Heterogeneous Fisheries
Authors: Hilborn Ray , Walters Carl J.
Published: April 2008

A simple simulation model of stock and fleet dynamics is described that allows rapid exploration of the dynamics of fisheries in a spatially heterogeneous environment. The model simulates how fishermen allocate their search effort among spatial areas in relation to differential catch rates, prices, or area-specific desirabilities. The model runs in a few seconds per simulated year on an IBM microcomputer in interpreted BASIC, although both age structure and space are explicitly represented. The importance of exploring dynamic behavior of fisheries systems is discussed.
On Managing Variable Marine Fisheries
Authors: Getz Wayne M. , Francis Robert C. , Swartzman Gordon L.
Published: April 2008

Marine fisheries are difficult to manage because they are highly variable; yet the stock must be protected from over exploitation and possible collapse. Here we demonstrate that the most important source of uncertainty in estimating long-term productivity of a fishery is the degree of density dependence in the stock–recruitment relationship and not the environmental factors that influence annual recruitment rates. We evaluate the performance of three harvest policies in managing dynamically contrasting fisheries and conclude that close to maximum expected sustainable yield can be obtained by policies that have very different implications for short-term yields. In stochastic fisheries, the variability inherent in the stock can be ignored in determining optimal effort levels or it can be transferred into the fishery by allowing yield and effort levels to vary considerably. Thus it is relatively easy for the manager to ensure long-term maximization of yield. The hard problem is finding a suitable compromise between short-term stability of the fishery and long-term viability of the stock.
Influence of Three Life History Strategies on the Information Content of Stock–Recruitment Data
Authors: Welch David W.
Published: April 2008

The information content of stock–recruitment (SR) data is examined for three population models incorporating different life history characteristics. These models represent (i) a population whose recruitment is totally independent of stock size, (ii) a semelparous population whose recruitment is dependent on the abundance of the adult age group, and (iii) an iteroparous population whose recruitment is equally dependent on the abundance of several age groups. Fourier analysis of these age structures shows that the recruitment data (i) are completely uninformative about SR processes at all frequencies, (ii) are equally informative about SR processes at all frequencies, and (iii) contain more information about SR processes at some frequencies than at others. In particular, the SR information content of the latter model is shown to be zero at certain frequencies, so that all such recruitment variability can be removed from the data by filtering before examining the SR relationship. A numerical example is presented for the last model.
Potential of Eimeria sardinae (Apicomplexa: Eimeridae) Oocysts for Distinguishing between Spawning Groups and between First- and Repeat-Spawning Atlantic Herring (Clupea harengus harengus)
Authors: McGladdery Sharon E.
Published: April 2008

Prevalence of Eimeria sardinae oocysts was closely correlated with the maturity stage of the testes of Atlantic herring (Clupea harengus harengus). Prevalence was low in testes of immature fish, increased in ripe and spawning fish, and decreased in postspawning fish. No correlation was found between prevalence and age of spawning herring. The uniformly high prevalences in mature fish indicated the efficiency of transmission on the spawning grounds, where infective oocysts are released. Infection of first-spawning herring (approximately age 3) indicated that the oocysts may be dispersed to surrounding areas or immature fish may associate with spawning aggregations. Therefore, this parasite could not be used to distinguish first from repeat spawners. Prevalence oF E. sardinae peaked in May and September, and possibly in June and early July, thereby distinguishing two, and possibly three, spawning groups. A previous study indicated no correlation between maturity stage and infections by E. sardinae in northeastern Atlantic herring. The difference between the two sides of the Atlantic is attributed to greater mixing of immature and adult herring around spawning grounds and/or greater dispersal of infective oocysts from spawning grounds in the northeastern Atlantic, compared with those in the northwest.
Escape Behaviour and Use of Cover by Young-of-the-Year Brook Trout, Salvelinus fontinalis
Authors: Grant James W. A. , Noakes David L. G.
Published: April 2008

The distance between young-of-the-year (YOY) brook trout (Salvelinus fontinalis) and an approaching observer when the trout first fled (reactive distance) was significantly shorter in areas of high cover than in areas of low cover. Reactive distance was negatively correlated with foraging rate in one stream but not in another. These results provide some support for a recent economic model of escape behaviour. Three measures of willingness to take risks while foraging, reactive distance, latency to forage after a disturbance, and use of foraging sites with overhead cover, increased with increasing body size of YOY brook trout. We suggest that stream-resident salmonids become more wary with increasing size because the relative benefits of growing quickly, and hence taking risks while foraging, decrease with increasing body size.
Emigration and Production of Hatchery Coho Salmon (Oncorhynchus kisutch) Stocked in Streams Draining an Old-growth and a Clear-cut Watershed
Authors: Bilby Robert E. , Bisson Peter A.
Published: April 2008

Downstream movement of coho salmon fry (Oncorhynchus kisutch) stocked in old-growth and clear-cut watersheds occurred in three phases: (1) a brief period of heavy emigration immediately after stocking, (2) relatively little movement throughout most of the summer, and (3) intermittent heavy emigration during early autumn freshets. Coho emigrated whenever a streamflow change ≥ 3%∙d−1occurred, but movement nearly ceased at flows above a certain level. Temperature changes were less important than discharge in triggering movement. When high densities were stocked, emigrant fry were smaller than residents. When low densities were stocked, emigration after the initial pulse of downstream movement was generally lower and there were no size differences between emigrants and residents. Production in the clear-cut was greater than in the old-growth watershed. Proportionately fewer fish emigrated from the old-growth stream, but when population densities were high, mortality in the old-growth exceeded the clear-cut. Greater emigration from the clear-cut site was possibly related to a scarcity of pools. Although the old-growth stream possessed better rearing habitat, less food may have been available, as suggested by gross photosynthesis rates 50% lower than in the clear-cut stream. Coho production therefore appeared to be most strongly influenced by trophic conditions, while volitional residency was most strongly influenced by habitat quality.
Latent Effects of Pulse Exposure to Aluminum and Low pH on Size, Ionic Composition, and Feeding Efficiency of Lake Trout (Salvelinus namaycush) Alevins
Authors: Gunn John M. , Noakes David L G.
Published: April 2008

No mortality of lake trout (Salvelinus namaycush) embryos occurred during 5 d of exposure to aluminum concentrations of 0, 100, and 200 μg∙L−1in low-pH (pH 5.0) water or during 21- and 32-d recovery periods, but alevins from the high-Al exposure were smaller in length, had less calcified skeletons, had reduced (18–22%) whole-body concentrations of Ca2+and K+, and were less effective predators on Daphnia magna. These latent effects of pulse exposure to acidic Al-rich water may help explain the disappearance of lake trout populations from lakes with relatively high ambient pH.
Chemical Analysis of Muscle from Walleye (Stizostedion vitreum vitreum) with Myofibrogranuloma, a Chronic Myopathy
Authors: Kelly R. K. , Klaverkamp J. F. , Hunt R. V. , Nielsen O.
Published: April 2008

Myofibrogranuloma (MFG), a chronic myopathy of unknown origin, is a rare disease of walleye (Stizostedion vitreum vitreum). We studied 15 cases observed in adult walleye during 1975–85 from seven lakes in southern Manitoba and northwestern Ontario and from one lake in North Dakota. Two of the lakes (Pelican Lake, Man., and Lake Sakakawea, ND) had a higher number of overt cases in 1984 and 1985. The inorganic analyses of representative samples of diseased muscle revealed that the ratio of potassium to sodium ions in the afflicted skeletal muscle was significantly depressed from the normal. Selenium was elevated. Calcium levels averaged 55 times normal in the muscle lesions where excessive calcium deposition was also readily demonstrable by histochemical staining with nuclear fast red. Magnesium levels were significantly depressed (i.e. 0.7 times normal) in diseased muscle. In contrast, copper (1.71 ± 0.57), iron (9.23 ± 4.56), zinc (25.48 ± 9.33), and aluminum (2.80 ± 1.14) concentrations (micrograms per gram wet wt ± SD) were generally 5- to 10-fold greater in the muscle lesions than in muscle from healthy walleye. The physiological significance of the latter data was unclear.
Effects of Snow and Ice on the Annual Cycles of Heat and Light in Saqvaqjuac Lakes
Authors: Welch Harold E. , Legault John A. , Bergmann Martin A.
Published: April 2008

The annual cycles of temperature, ice and snow cover, and light are described for small Saqvaqjuac lakes (63°30′N). Summer thermal stratification occurred but was not persistent. Annual heat budgets were slightly higher than for temperate lakes and increased with increasing mean depth; latent heat of fusion constituted one half to one third of the total heat flow. Ice thickness reached a maximum of 1.6–2.2 m, depending upon winter snow cover, and a thin layer (≈5 cm) of white ice occurred in some years. Ice-out was a partial function of mean June temperature. The open-water season lasted 2–3 ms. Light attenuation through white and candled ice, snow, and water was measured. About 28% of the annual surface irradiance penetrated the unfrozen water, about half that which would have been absorbed under ice-free conditions. Extinction coefficients were inversely correlated with mean depth and positively correlated with nutrient status.
Influence of Interannual Variations in Winter Sea Temperature on Fecundity and Egg Size in Pacific Herring (Clupea harengus pallasi)
Authors: Tanasichuk R. W. , Ware D. M.
Published: April 2008

Data for 2937 fish, collected from seven locations over five years, were analysed to evaluate the effects of sea temperature and stock biomass on size-specific ovary weight and fecundity at spawning. Ovary weight did not vary significantly between years or locations. Size-specific fecundity was higher in 1983, when coastal waters were abnormally warm because of a strong El Niño – Southern Oscillation event. The effect of location was equivocal: one stock that overwintered in warm water tended to have a higher fecundity. Mean sea temperature between 60 and 90 d before spawning (in spring) best accounted for variations in size-specific fecundity. Temperature may influence fecundity by regulating gonadotropin concentration and consequently pre-ovulatory atresia. We hypothesize that the trade-off between fecundity and egg size is adaptive. A theoretical analysis of the early life history of Pacific herring suggests that, to maximize survival to metamorphosis, egg size should decrease and fecundity increase with temperature when the larval growth rate Q10 is less than the mortality rate Q10. Our model seems to explain the differences in egg size between recruit and repeat spawners, and between stocks of Atlantic herring that spawn in different seasons.
Ovarian Development and Oocyte Diameter as Maturation Criteria in Pacific Herring (Clupea harengus pallasi)
Authors: Hay D. E. , Outram D. N. , McKeown B. A. , Hurlburt M.
Published: April 2008

Seasonal changes in ovaries of Pacific herring (Clupea harengus pallasi) are described. Vitellogenic and resting oocytes could be distinguished histologically by size during early development. Resting oocytes had a mean diameter of about 80 μm and a maximum of about 150 μm. Oocytes larger than 150 μm were vitellogenic and indicate early sexual maturation. An alternative non-histological method of determining oocyte diameter, involving physical separation of oocytes, yielded good maturity estimates, rapidly and simply.
Marking Nonfeeding Salmonid Fry with Dissolved Strontium
Authors: Yamada S. Behrens , Mulligan T. J.
Published: April 2008

Chemical marking is a simple, inexpensive, and rapid technique for marking young salmon. We have marked nonfeeding embryos by adding strontium to their rearing water. Strontium, a harmless element in its natural form, resembles calcium chemically and is therefore readily incorporated into bone. Our data show that the best time for inducing a Sr mark into nonfeeding salmon fry is after hatching, when bone development begins. The addition of 1 μg Sr/mL to the rearing water of salmon fry for a period of 49 d resulted in a 10-fold increase in their vertebral Sr concentration. As the salmon grew, the induced mark became diluted in a predictable manner, but was still detectable after 169 d.
Alternative Recruitment Models of Adams River Sockeye Salmon, Oncorhynchus nerka
Authors: Collie Jeremy S. , Walters Carl J.
Published: April 2008

Despite evidence of depensatory interactions among year-classes of Adams River sockeye salmon (Oncorhynchus nerka), the best management policy is one of equal escapement for all year-classes. We fit alternative models (Ricker model and Larkin model) to 32 yr of stock–recruitment data and checked, using simulation tests, that the significant interaction terms in the Larkin model are not caused by biases in estimating the parameters. We identified a parameter set (Rationalizer model) for which the status quo cyclic escapement policy is optimal, but this set fits the observed data very poorly. Thus it is quite unlikely that the Rationalizer model is correct or that the status quo escapement policy is optimal. Using the fitted stock–recruitment parameters, we simulated the sockeye population under several management policies. The escapement policy optimal under the Ricker model is best overall because of the high yields if it should be correct. If the three stock–recruitment models are equally likely to be correct, the simulations predict that adopting a constant-escapement policy would increase long-term yield 30% over the current policy and that an additional 15% increase in yield could be obtained if the policy were actively adaptive.
Incidence and Effects of Sea Lamprey (Petromyzon marinus) Parasitism on Breeding Pink Salmon (Oncorhynchus gorbuscha) from the Carp River, Eastern Lake Superior
Authors: Noltie Douglas B.
Published: April 2008

The potentially important effect of Great Lakes pink salmon (Oncorhynchus gorbuscha) numbers on the population dynamics of parasitic sea lamprey (Petromyzon marinus) has thus far remained unassessed. This study reveals that despite their small size, pink salmon from the Carp River, eastern Lake Superior, sustain parasitism at rates and in body locations similar to other Great Lakes salmonids. In general, the incidence of sea lamprey parasitism increased with salmon length. Differences in marking rates between male and female salmon were attributable to their dimorphism in size: female pink salmon grew slower than males and bore more fresh wounds than males when sampled. Lamprey attacked fish of similar sizes in 1983 and 1984, but smaller ones in 1985. This parasitism had a negative impact on host breeding potential: marked fish were in poorer condition than unmarked ones. Marked males invested less biomass in gonad than did unmarked males, and wounded males occupied the spawning grounds for less time, thus reducing their reproductive potential. These results indicate that the population dynamics of both species may be determined in part by their mutual interaction.
Testing Predictions of Marine Fish and Shellfish Landings from Environmental Variables
Authors: Drinkwater K. F. , Myers R. A.
Published: April 2008

Previous studies by Sutcliffe and co-workers using exploratory analysis found correlations between environmental variables and lagged annual catch for several Gulf of St. Lawrence and Gulf of Maine fish and shellfish stocks. The present study tests these relationships using recent data. For 6 of the 13 stocks investigated, correlations between the 9–14 yr of new catch data and that predicted from the environmental models remained high (r > 0.5) and of the same sign; however, individually none was statistically significant (p > 0.05) after accounting for the loss of degrees of freedom due to the high autocorrelation in the data. The hypothesis of an overall environmental effect on the landings was considered. It could not be substantiated as the correlation coefficient for 5 of the 13 stocks reversed sign using the new data, but changes in fishing effort are believed to mask detection of environmentally induced variability in the landings of many stocks. The utility of environmentally based predictions was also tested. Overall, the mean deviations of the predicted catch based on environmental regressions were similar to predictions based on the long-term means but were higher than predictions using lagged catch. Environmentally based predictions of landings for invertebrate stocks were generally more accurate than those for fish stocks.
Processes and Causes of Lake Acidification during Spring Snowmelt in the West-Central Adirondack Mountains, New York
Authors: Galloway James N. , Hendrey George R. , Schofield Carl L. , Peters Norman E. , Johannes Arland H.
Published: April 2008

The surface and outlets of two headwater lakes acidified during the 1978, 1979, and 1980 spring snowmelt periods. The decrease in pH was accompanied by an increase in nitrate whereas the other strong acid anion, SO42−, remained relatively constant. Chemical mass-balance calculations, using data from the Integrated Lake–Watershed Acidification Study, indicate that the peak in acidification observed in the Adirondack Mountains in the spring is caused by (1) a dilution of base cations (Ca2+, Mg2+, Na+, and K+) and associated alkalinity by snowmelt, (2) an increase in NO3−concentration in the acidified portion of the lakes, and (3) the constant elevated concentration of SO42−. At Woods Lake, the NO3−that accumulated in the snowpack plus that deposited from the atmosphere during snowmelt was sufficient to account for the increased NO3−in and transported from the lake. At Panther Lake, an additional source of NO3−was needed and was believed to be contributed by nitrification in the upper soil horizons. If atmospheric deposition of sulfur is reduced, low-alkalinity systems like Woods and moderate-alkalinity systems like Panther will be less likely to develop strong acidity during spring acidification.
Intraspecific variation in Hydrogen Ion and Aluminum Toxicity inBufo americanusandAmbystoma maculatum
Authors: Clark Karen L. , LaZerte Bruce D.
Published: April 2008

Variation in hydrogen ion and aluminum toxicity was measured among clutches in one Bufo americanus population from a pond with pH 5.96 and both among clutches and ponds in four Ambystoma maculatum populations from ponds with pH levels from 4.44 to 6.19. There was significant variation among clutches, but in general, B. americanus hatching success was reduced at pH 4.1 compared with pH6.0. At pH 4.1,200 μg Al/L caused even greater embryonic mortality. Aluminum toxicity did not vary among clutches; however, variation in acid tolerance was such that clutches with the highest hatching success at pH 6.0 had the lowest hatching success at pH 4.1. Hatching success of A. maculatum also varied among clutches, but in general, hatching success was lower at pH 4.3 than at pH 6.0, and 200 μg Al/L at pH 4.3 increased hatching success compared with when no aluminum was present. Variation in acid tolerance among pond populations was so large that one population had higher hatching success at pH 4.3 than at pH 6.0. Ambystoma maculatum hatching success was not related to diameter of the perivitelline space just prior to hatch. The wide variation in acid tolerance among clutches of B. americanus and among populations of A. maculatum suggests that laboratory studies using small numbers of clutches may not adequately represent the response of the natural populations.
Predator-Induced Changes in Thermoregulation of Bluegill, Lepomis macrochirus, from a Thermally Altered Reservoir
Authors: Fischer Jr. Robert U. , Standora Edward A. , Spotila James R.
Published: April 2008

In the absence of a predator, small bluegill (Lepomis macrochirus) had a mean upper avoidance temperature of 30.0 °C as compared with 29.8 °C for large bluegill. In the presence of a predator (Micropterus salmoides), bluegill upper avoidance temperatures were significantly higher; however, predator size did not influence this relationship. In the presence of a small and large bass, small bluegill had a mean upper avoidance temperature of 34.0 and 33.9 °C, respectively, while large bluegill had a mean upper avoidance temperature of 33.8 and 33.1 °C. The preferred temperatures of large bluegill [Formula: see text] were statistically higher than that of small bluegill [Formula: see text]. There was no significant difference in the preferred temperatures for bluegill from heated and normothermic sites.
Evidence of Acidification Effects on Stream Insect Communities in Central Ontario Between 1937 and 1985
Authors: Hall Ronald J. , Ide Fredric P.
Published: April 2008

Aquatic insect surveys were conducted in two low-alkalinity streams in Algonquin Provincial Park, Ontario, Canada, that were first studied 48 yrs ago (1937–42). At a site where current spring pH fluctuations are small (pH 6.4–6.1), most of the same taxa that were present in 1984–85 were observed during the original surveys. However, at sites where large spring pH depressions are currently observed (pH 6.4–4.9), many mayfly and stonefly taxa that were present 48 yr ago and that are known to be intolerant of low pH (pH <5) were not recorded in 1984–85. An invasion of acid-tolerant mayfly and stonefly taxa occurred at sites with large pH depressions. Species replacements from acid-sensitive to acid-tolerant insects suggest that poorly buffered surface waters in this region have acidified sometime within the last five decades.
Nearshore Occurrence of Submersed Aquatic Macrophytes in Relation to Wave Action
Authors: Chambers Patricia A.
Published: April 2008

The minimum depth of occurrence of submersed aquatic macrophytes (zmin) was measured along undisturbed shorelines of four lakes in southern Quebec and found to be strongly correlated (r = 0.86, P < 0.001) with depth of surface wave mixing (zw; calculated from wind velocity and fetch). The slope of the relation did not differ significantly from 1.0 (t-test, P > 0.10) and the intercept did not differ from 0.0 (t-test, P > 0.10). These results support the hypothesis that the nearshore occurrence of submersed aquatic macrophytes is related to wave action.
Population Dynamics of the Peruvian scallop Argopecten purpuratus during the El Niño Phenomenon of 1983
Authors: Wolff Matthias
Published: April 2008

Population size, growth, and mortality rates of the Peruvian scallop (Argopecten purpuratus were studied during the El Niño event of 1983 in the fishing area off Pisco, Peru. Gonadal index and larval abundance of this scallop as well as measurements of in situ temperature, dissolved oxygen, and plankton volumes were taken to record spawning activity and environmental conditions. The scallop population size exceeded 60 times that of "normal" years. It is thought to be due to a significant increase in survival rate of larval and juvenile scallops and/or intensified spawning activity with subsequent recruitment in the warm El Niño waters. Only small scallops (15–45 mm shell height) showed accelerated growth due to elevated temperatures. Total mortality (Z) was estimated as 2.5 and natural mortality (M) as 1.0. the hypothesis is proposed that A. purpuratus is a relict of a tropical/subtropical fauna inhabiting the Peruvian and Chilean waters in the Miocene, which has maintained its warmwater characteristics during evolution in the cold upwelling water because of periodic post-Miocene El Niño events.
Biochemical Genetic Survey and Stock Identification of Chum Salmon (Oncorhynchus keta) in British Columbia
Authors: Beacham T. D. , Gould A. P. , Withler R. E. , Murray C. B. , Barner L. W.
Published: April 2008

We examined genetic variability using electrophoretic analysis of 83 chum salmon (Oncorhynchus keta) stocks in British Columbia and used regional differences in genotypic frequencies of seven polymorphic loci to estimate stock compositions in a number of commercial and experimental test fisheries. Chum salmon from five regions could be discriminated: Queen Charlotte islands, north and central coast, west coast of Vancouver Island, the Fraser River and its tributaries, and the south coast (rivers draining into Johnstone Strait and the Strait of Georgia). Allelic frequencies from 33 stocks were generally stable over a period of 2 yr or more. South coast chum salmon was the dominant run migrating through upper Johnstone Strait in October 1982–85. The genetic method of stock identification provided managers with the relative proportions of Fraser River and other groups of chum salmon in a number of fisheries and allowed managers to regulate more effectively the exploitation rate of Fraser River chum salmon.