bluuebunny/crossref_metadata_2025 huggingface dataset:
Fixation Shrinkage of Herring Larvae: Effects of Salinity, Formalin Concentration, and Other Factors
Authors: Hay D. E.
Published: June 2008

The most important factors affecting the degree of larval shrinkage of Pacific herring (Clupea harengus pallasi) larvae during fixation are the salinity and formalin concentrations and initial larval size. In low formalin concentrations (2–5% formalin) shrinkage increased from less than 2% shrinkage at low salinities to about 10% shrinkage in seawater formalin. In high formalin concentrations (20–30% formalin) shrinkage was fairly uniform, ranging from about 3% shrinkage in low salinities to about 5% in seawater. Shrinkage in fixatives stored at 0, 5, 10, 20, and 30 °C was slightly higher (1–2%) at the higher temperatures. Buffering agents and starvation had no effect on shrinkage. Small, young larvae shrank relatively more than larger older larvae.Key words: herring larvae, fixation, shrinkage, formalin, salinity
Pathogenesis of Infectious Hematopoietic Necrosis Virus in Adult Sockeye Salmon (Oncorhynchus nerka)
Authors: Mulcahy Dan , Burke John , Pascho Ron , Jenes C. K.
Published: June 2008

The concentration of infectious hematopoietic necrosis (IHN) virus was determined in eight organs and two body fluids from each of 60 adult sockeye salmon (Oncorhynchus nerka). Included in the sample were 4 males and 56 prespawning, spawning, or spent female fish. All fish were infected, and virus was present in nearly all organs. There was an overall tendency for the mean concentration to increase in many of the organs over time as the fish progressed in ripeness. In prespawning females, IHN virus could be detected in all organs and in ovarian fluid but not in serum; the incidences were highest in the gills, spleen, and pyloric ceca, and the titers were highest in the pyloric ceca and liver. Incidences of infection in the organs were higher in spawning than in prespawning females and higher still in spent females in which the incidence of virus was 100% in all organs except brains (78%) and sera (67%). Virus concentrations in organs or fluids ranged from 5 to 4.0 × 109 plaque-forming units per millilitre. In males, the highest incidences of virus were found in gills, pyloric ceca, and liver. The gills were the only organ in which the virus concentration in males exceeded that of females.Key words: infectious hematopoietic necrosis, IHN, fish virus, viral pathogenesis, sockeye salmon
Fickian Transport and the Dispersal of Fish Larvae in Estuaries
Authors: Fortier L. , Leggett W. C.
Published: June 2008

We studied the regulation of ichthyoplankton dispersion in the two-layer circulation of the St. Lawrence upper estuary by determining larval abundance and vertical distribution during high frequency sampling at three stations in May, June, and July, 1979. Monthly variations in capelin (Mallotus villosus) and Atlantic herring (Clupea harengus harengus) abundance were in agreement with the seasonal trends previously reported. Capelin larvae were concentrated in the surface layer, a situation which resulted in seaward drift. No significant growth was observed over the 60-d sampling period indicating continuous recruitment to, and removal from, the sampling area. Herring larvae were concentrated in the deep layer and were carried landward. The average size of herring larvae increased from the downstream to the upstream stations. Short-term fluctuations in the abundance and vertical distribution of the two species were interpreted in terms of the Fickian representation of transport for partially mixed estuaries. The major source of variation in abundance, at a given station, was the tidal advection of horizontal gradients. Capelin larvae and herring larvae smaller than 10 mm did not actively cross the pycnocline and were not submitted to the diffusive effect of the vertical current shear. The dispersal of these larvae was apparently passive. Herring larvae larger than 10 mm performed diel vertical migrations across the pycnocline and were dispersed in the horizontal plane at a faster rate than a passive contaminant of the environment. We conclude that the Fickian approach can be profitably applied to studies of dispersal and mortality of early larval stages of fish in estuaries.Key words: ichthyoplankton, St. Lawrence estuary, dispersion, transport, vertical distribution, diel migrations, variability, abundance, tidal mixing, Fickian
Interactions multispécifiques: répartition spatio-temporelle des larves de capelan (Mallotus villosus), d'éperlan (Osmerus mordax) et de hareng de l'Atlantique (Clupea harengus harengus) an sein de la communauté planctonique de l'estuaire moyen du Saint-Laurent
Authors: Courtois R. , Simoneau M. , Dodson J. J.
Published: June 2008

The study of the spatial and temporal organization of the planktonic community of the middle estuary of the Saint Lawrence River revealed that fish larvae were distributed in such a way as to minimize interactions between species. Smelt (Osmerus mordax) larvae were distributed upstream whereas capelin (Mallotus villosus) and Atlantic herring (Clupea harengus harengus) larvae were found downstream in June 1979. Capelin larvae were more abundant at the surface (0–20 m) whereas herring larvae were concentrated in deeper waters (20–60 m). The ecological separation observed was maintained by multiple physical factors and appeared to be the consequence of species-specific reproductive strategies. The abundance of chaetognaths, euphausiids, and amphipods in deeper waters suggests that these forms could be important predators of fish larvae. Herring larvae may be particularly vulnerable because of their distribution in deep water. Capelin larvae which are very abundant in June could also be vulnerable to predation during the diurnal migrations of the macroplankton. Smelt larvae appear to be little affected by predation from these forms as a result of their distribution in fresher waters.
Resting Cysts of the Toxic, Red Tide Dinoflagellate Gonyaulax excavate in Bay of Fundy Sediments
Authors: White Alan W. , Lewis Carrie M.
Published: June 2008

During the winter of 1980–1981 sediment samples were collected from 115 stations throughout the southern Bay of Fundy to determine the distribution and abundance of Gonyaulax excavata resting cysts. An improved, semiquantitative method of cyst enumeration was developed for this purpose. Resting cysts of G. excavata were widely dispersed in the Bay, occurring both offshore and inshore, including the intertidal zone. The great majority of cysts occurred in a large, extremely rich deposit located offshore in the southwestern Bay of Fundy in a zone of fine brown mud at depths of 80–160 m. The location of this deposit was consistent with hydrographic and sedimentary processes in the Bay. Cyst concentrations ranged from 2000 to 8000 cysts∙cm−3 wet sediment at many stations in the approximately 2000-km2 deposit. Mouse bioassay tests of cyst extracts (prepared by sonication or boiling) indicated that the cysts were toxic, containing 2–5 × 10−5 μg saxitoxin (STX) equivalent per cyst — the same range as for G. excavata motile cells in culture. Results support the view that the wintertime acquisition of G. excavata toxins by offshore and inshore molluscan shellfish is caused by ingestion of cysts. Results suggest that the offshore seed bed serves as the primary source of the motile cells which initiate the annual G. excavata bloom in the Bay of Fundy.Key words: cysts, Gonyaulax excavata, dinoflagellate blooms, red tide, paralytic shellfish toxins, shellfish toxicity, sediments, Bay of Fundy
A General Theory for Analyzing Catch at Age Data
Authors: Fournier David , Archibald Chris P.
Published: June 2008

We present a general theory for analyzing catch at age data for a fishery. This theory seems to be the first to address itself properly to the stochastic nature of the errors in the observed catch at age data. The model developed is very flexible and accommodates itself easily to the inclusion of extra information such as fishing effort data or information about errors in the aging procedure. An example is given to illustrate the use of the model.Key words: cohort analysis, virtual population analysis, maximum likelihood estimation, aging errors
A Statistical Method for Evaluating the Reproducibility of Age Determination
Authors: Chang William Y. B.
Published: June 2008

The coefficients of variation and the index of precision provide a statistical test of reproducibility of aging between readers. Because the coefficients of variation and the index of precision incorporate the averaged year-class of a fish species, they are free from the shortcoming of the percent agreement method. Because variance is a better estimator than absolute difference, the coefficient of variation is a stronger estimator than the index of average percent error in providing a test statistic.Key words: age determination, coefficients of variation, index of precision, average percent error, percent agreement
Detecting Ecosystem Responses to Anthropogenic Stress
Authors: Schindler D. W.
Published: June 2008

Recent ecological work on aquatic populations, communities, and ecosystems is reviewed for advances which show promise as early indicators of anthropogenic stress in aquatic ecosystems. Work at the Experimental Lakes Area (ELA) in northwestern Ontario indicates that among the earliest of responses to stress are changes in species composition of small, rapidly-reproducing species with wide dispersal powers such as phytoplankton, and the disappearance of sensitive organisms from aquatic communities. Work elsewhere illustrates that the incidence of morphological abnormalities in benthic invertebrates is also highly sensitive to pollution stress. For several categories of pollutants, this sensitivity of benthic organisms may be due to the greater concentrations of pollutants in sediments than in the water column. Variables reflecting ecosystem functions such as primary production, nutrient cycling, and respiration, were not altered by eutrophication, acidification, or cadmium addition at ELA, and are relatively poor indicators of early stress. Species diversity of phytoplankton was also insensitive to low levels of stress. Mesocosm experiments appear to be fruitful for addressing chemical- or plankton-related problems, but are less useful for addressing community- or ecosystem-level questions. Among population-level approaches, life-table population studies of invertebrates appear to be the most sensitive early indicators of stress on ecosystems.Relative sensitivities of freshwater and forested terrestrial ecosystems exposed to airborne pollutants are compared. Primary production seems to be reduced at a much earlier stage of air pollution stress in terrestrial ecosystems than in aquatic systems. Soils, like lake sediments, tend to be sinks for pollutants. This may protect the pelagic regions of lakes from influxes of toxins that would occur if watersheds and sediments were unreactive, but cause additional stresses to the fauna and flora of soils and sediments. In extreme cases, high concentrations of toxins may inhibit the replacement of terrestrial producers.The importance of long-term monitoring in distinguishing natural from anthropogenic stress is discussed. It is suggested that paleoecological techniques be rapidly developed and calibrated with whole-ecosystem experiments to resolve certain inadequacies of past monitoring records.
Exchange of Nutrients Between Sediments and Water After 15 Years of Experimental Eutrophication
Authors: Schindler D. W. , Hesslein R. H. , Turner M. A.
Published: June 2008

Increases in the concentrations of nitrogen and phosphorus occurred in the water column of Lake 227 during 15 years of fertilization with phosphoric acid and sodium nitrate. The sources of the increases were deduced by comparing the budgets of N and P to the budget for sodium, using a simple model, and from the chemistry of sediment pore water.Total inventories for sodium since fertilization began confirmed that the element was almost perfectly conservative, as expected. When model results for phosphorus and sodium were calculated, the apparent increase in phosphorus was found to be due entirely to lower water renewal rates during recent years. This agrees with the observation that phosphorus concentrations in sediment pore water did not change between 1975 and 1982. Both phosphorus and sodium in the lake have been in equilibrium with external loading for the past several years.In contrast, the observed increase in nitrogen could not be accounted for by the decreased water renewal rate, implying that the element was either becoming more efficiently recycled or that there was an increasing, unmeasured external source of the element. An increase in pore water ammonium between 1975 and 1982 was balanced by an increase in the concentration in overlying waters, so that diffusive fluxes did not change. Increasing blooms of nitrogen-fixing bluegreen algae after 1975 indicate that N2 fixation is the increasing source of nitrogen to the lake. No tendency for the nitrogen:sodium ratio to stabilize has been observed, indicating that the nitrogen budget has still not reached a new steady state.
Phytoplankton Community Responses to Nutrient Addition in Lake 226, Experimental Lakes Area, Northwestern Ontario
Authors: Findlay D. L. , Kasian S. E. M.
Published: June 2008

Inclusion of phosphorus in fertilizer added to one of two basins of a small lake, between which water exchange was greatly reduced by a vinyl sea-curtain, significantly increased epilimnetic phytoplankton biomass, and altered species composition. Over an 8-yr period, the average biomass of phytoplankton in the basin receiving carbon, nitrogen, and phosphorus (in ratios of 10:5:1) increased 4 to 8 times and the biomass in the basin receiving only carbon and nitrogen (in ratios of 10:5) increased 2 to 4 times over non-fertilized years. The basin receiving all three nutrients consistently had blooms in late summer which were dominated by nitrogen fixing species of cyanophytes. In comparison with unfertilized reference lakes, the proportion of phytoplankton in fertilized basins which was available to zooplankton as food was 10 times greater in the basin receiving all three nutrients, and two times greater in the basin receiving only nitrogen and carbon. When fertilization of both basins was stopped, species composition and levels of biomass reverted within a year to the composition and biomass levels of phytoplankton observed in the reference lakes and remained at those levels for 2 further years of study.
Population Dynamics of Lake Whitefish (Coregonus clupeaformis) During and After the Fertilization of Lake 226, the Experimental Lakes Area
Authors: Mills K. H. , Chalanchuk S. M.
Published: June 2008

Responses of an unexploited population of lake whitefish (Coregonus clupeaformis) to the fertilization of Lake 226 in the Experimental Lakes Area, northwestern Ontario, are described for the fifth through eighth years of fertilization (1977–80) and for three years after fertilization was terminated (1981–83). A vinyl curtain separated Lake 226 into two basins. One basin (L226NE) received additions of phosphorus, nitrogen, and carbon; the other (L226SW) received nitrogen and carbon. Lake whitefish in L226NE were faster growing, had higher condition (k), were more numerous, had higher survival from age 0 to age 1, had greater biomass, and had greater production than L226SW whitefish from 1977 to 1980. Some of these effects continued in 1981 and 1982 after fertilization was terminated, but only biomass differences remained by 1983.
Detection of Handling Mortality and its Effects on Jolly–Seber Estimates for Mark–Recapture Experiments
Authors: Arnason A. N. , Mills K. H.
Published: June 2008

Handling mortality occurs in mark–recapture experiments if animals handled and released in a given sample have a higher mortality rate than animals that were alive but not sampled. This violates the assumption of equal survival required for forming the Jolly–Seber estimates of population abundance, survival, and recruitment. We show that handling mortality can produce very large biases in these estimates, and we develop a test to detect it. We investigate the power of this test and find that quite large biases can be produced at handling mortality rates that are too low to be detected. We recommend methods to prevent handling mortality from occurring in fish sampling experiments and methods to reduce bias in the estimates. The test and the bias corrections are applied to mark–recapture data for a lake whitefish (Coregonus clupeaformis) population and to data from simulated mark–recapture experiments. Because of unavoidable inadequacies in the detection and reduction of bias due to handling effects, we strongly recommend that fisheries biologists take great care to prevent its occurrence.
Reproductive Impairment of the Crayfish Orconectes virilis in Response to Acidification of Lake 223
Authors: France Robert L.
Published: June 2008

Reproductive characteristics of crayfish (Orconectes virilis) were examined during 1979–81 in four small Canadian Shield basins in the Experimental Lakes Area, northwestern Ontario. One of these lakes, Lake 223 (L223), has been experimentally acidified since 1976. Egg resorption, fertilization, and rate of development were not seriously affected by lake acidification to pH 5.1. Incomplete hardening of the glair–cement compound forming the egg capsule membrane and stalk resulted in a loss of eggs from the pleopods, causing the L223 population to suffer decreased reproduction. On an egg production basis, the reproductive impairment (defined as the % decrease in number of viable eggs prior to hatching) in reference populations averaged 3.2 ± 1.8 (95% C.I.) compared to levels of 18.7, 36.2, and 29.4% during 1979–81 in L223 at pH 5.2–5.6. Direct mortality of eggs accounted for little of the reduced natality in the L223 population and did not occur in reference lakes. Loss of crayfish populations exposed to lake acidification will probably result from reproductive failure before lake water becomes acid enough to be directly toxic to mature crayfish.
Histopathological Changes in the Gills of Pearl Dace, Semotilus margarita, and Fathead Minnows, Pimephales promleas, from Experimentally Acidified Canadian Lakes
Authors: Leino Richard L. , Wilkinson Peter , Anderson Jon G.
Published: June 2008

The gills of pearl dace form experimentally acidified Canadian ELA lakes 223 (pH 5.2) and 114 (pH 5.8) and fathead minnows from Lake 114 were examined microscopically and compared with gills from unacidified waters. The acid-exposed gills exhibited (1) hyperplastic primary lamellar epithelia, (2) diminished respiratory lamellar surface areas, (3) widened respiratory blood-water barriers, and (4) altered cellular composition and morphology, especially greater numbers of chloride (ionoregulatory) cells with and without apical pits. While little can be said about the effects of acid water on fish based on such a small sample of lakes, the present research does not contradict the views expressed by many investigators that very soft water with a low pH and toxic metal ions has a deleterious effect on gills and the physiological processes associated with them.
Early Responses of Periphyton to Experimental Lake Acidification
Authors: Turner Michael A. , Jackson Michael B. , Findlay David L. , Graham Roger W. , DeBruyn Edwin R. , Vandermeer Elizabeth M.
Published: June 2008

We studied the periphyton in two small lakes acidified experimentally with either sulfuric or nitric acid. For comparison, we monitored periphyton in one previously acidified (sulfuric) lake and in two neutral lakes. Net photosynthesis declined in epilithic periphyton in the middle littoral zone (1–2 m) of both recently acidified basins in response to reduced concentrations of dissolved inorganic carbon. Dark respiration and taxonomic composition remained largely unchanged in this zone. Attached filamentous algae proliferated early [Formula: see text] in the upper littoral zone (< 1 m) of the sulfuric acid basin confirming earlier observations made in the previously acidified lake. These Zygnematales-dominated filamentous algae (largely Mougeotia sp.) developed conspicuously on submerged rock and log surfaces. In contrast, growth on macrophytes was variable in both the neutral and nitric acid systems. We hypothesize that during the early stages of acidification proliferation of filamentous Chlorophyceae is due to selection of algae tolerant of increased H+and better adapted to obtain inorganic carbon at low concentrations, in combination with reduced grazing.
Effects of Low Concentrations of Cadmium on the Crustacean Zooplankton Community of an Artificially Acidified Lake
Authors: Lawrence S. G. , Holoka M. H.
Published: June 2008

The toxic effects of cadmium to total community and individual species of zooplankton generally decreased as pH of the lake was experimentally lowered over a number of years by additions of acids. The biomass of crustacean zooplankton held in small impoundment systems suspended in the lake for fourteen days was reduced by 60–70% when pH was 6.7–6.8 and concentrations of Cd were maintained at 1 μg∙L−1, and by 70–80% when Cd was at 3 μg∙L−1. At a pH of 5.9, however, biomass was reduced only 20–30% in concentrations of Cd of 1 μg∙L−1, and at pH 5.6, biomass decreased by only 20% when subjected to 3 μg∙L−1 Cd. The cladocerans Bosmina longirostris and Holopedium gibberum were the most sensitive to cadmium. Cladocerans were more sensitive to cadmium than calanoid copepods, and both these groups were more sensitive then cyclopoid copepods. The decrease in toxicity of cadmium with increasing H+ may be analogous to the inhibition of uptake of cadmium by calcium.
Limnocorral Studies of Chemical and Biological Acid Neutralization in Two Freshwater Lakes
Authors: Schiff Sherry L. , Anderson Robert F.
Published: June 2008

Twenty-nine 1 m diameter limnocorrals were installed in two Canadian Shield lakes to examine the relative importance of individual acid neutralization processes. Once the water column alkalinity was depleted, the within-lake alkalinity production processes were confined to the lake sediments. The flocculent organic-rich sediments of a shallow dystrophic lake (Lake 114) neutralized acid at a significantly greater rate than the sandy littoral sediments of an oligotrophy lake (Lake 302). Since the water column alkalinity of Lake 114 is much lower than Lake 302, ambient alkalinity is not a good predictor of acid neutralization capacity in the sediments. In both lakes, HNO3 was neutralized at a substantially higher rate than HCl or H2SO4. The rates of nitrate consumption, sulfate consumption, and abiotic acid neutralizing processes are independent of each other. Denitrification to an uncharged end-product is the primary mechanism of NO3− removal. The principal source of non-anion-specific buffering in the enclosure experiments was Ca2+ release from the sediments in Lake 302 and Ca2+ and NH4+ release in Lake 114. There is no significant difference between the organic-rich sediments of Lake 114 and the sandy sediments of Lake 302 in the concentration of exchangeable cations (μeq∙cm−3) for all cations except NH4+ and Mn2+. Alkalinity production in epilimnetic sediments is an important component of the resistance of softwater lakes to anthropogenic acidification.
Experimental Acidification of a Sphagnum-Dominated Peatland: First Year Results
Authors: Bayley S. E. , Vitt D. H. , Newbury R. W. , Beaty K. G. , Behr R. , Miller C.
Published: June 2008

A poor fen (3.6 ha) in northwestern Ontario was experimentally acidified with HNO3 and H2SO4 to study the effects of acid precipitation on the dominant Sphagnum species and on the chemistry of the surface waters and pore waters. The nitrate concentration in the surface waters of the fen increased from < 0.07 μeq∙L−1[Formula: see text] to between 20–70 μeq∙L−1 during or just after each acidification event. Subsurface [Formula: see text] concentrations remained unchanged and surface [Formula: see text] concentrations returned to background levels within a day. The mire as a whole retained over 99% of the added [Formula: see text], probably due to nitrate assimilation by the Sphagnum. Sulfate concentrations in the surface pools increased from 5 μeq∙L−1 to 130 μeq∙L−1 with acidification and gradually decreased in the following 7 to 14 days. Pore water concentrations of [Formula: see text] decreased and H2S increased indicating sulfate reduction even in the highly acidic environment (pH 4). The decrease in concentration of [Formula: see text] in the surface pools due to SO4 reduction and assimilation was not as rapid as the decrease in [Formula: see text] concentration due to plant assimilation. The dominant Sphagnum species increased in growth with the added [Formula: see text] and [Formula: see text], particularly in the oligotrophic areas of the mire. In the minerotrophic area, only those species isolated from the water table showed increased growth due to acidification. Results here indicate that in the early stages of acidification the mire is capable of taking up the added [Formula: see text] and [Formula: see text], probably in an assimilatory reduction process which generated additional alkalinity in the mire.
Atmospheric Deposition of Nutrients and Major Ions at the Experimental Lakes Area in Northwestern Ontario, 1970 to 1982
Authors: Linsey G. A. , Schindler D. W. , Stainton M. P.
Published: June 2008

Up to 24 chemical parameters have been monitored in individual precipitation events captured in bulk collectors at the Experimental Lakes Area (ELA), from 1970 to 1982. Although sample to sample variation was high, seasonal trends were discernible for several ions. Annual mean concentrations of H+, NO3−, and SO42− were low and quite constant until 1981, but increased dramatically in 1982. Hydrogen ion concentration increased by an average of 0.63 μEq∙L−1 over this period. The order of annual average cation dominance was Ca2+ > NH4+ > H+ > Mg2+ > K+. The dominant anion was SO42−, followed by NO3− > Cl−. Calcium, Mg2+, SO42−, Si, suspended P and N, total dissolved P and N, and total ionic concentrations were greatest in spring and fall, correlating with periods of maximum agricultural activity on the prairies, over 250 km away. Concentrations of NO3− and H+ were higher in snow than in rain, while SO42−, Ca2+, Mg2+, and NH4+ were greater in rain. The total deposition of most substances was higher in summer than in winter, because of the greater proportion of annual precipitation occurring in summer months. A comparison with other sites revealed higher Ca2+ and NH4+ at all sites near agricultural areas, and higher H+, SO42−, and NO3− at sites in eastern North America. A comparison of 1980 bulk versus wet-only chemistry indicated that dryfall contributed 52% of the total annual deposition of Cl−, 22% of the SO42−, 0% of the NO3−, 48% of the Mg2+, 31% of the NH4+, 28% of the Ca2+, and 8% of the Na+. Charge balances were excellent for both wet and bulk samples.
Validating the Use of Radiotracers as Analogs of Stable Metal Behaviour in Enclosed Aquatic Ecosystem Experiments
Authors: Anderson Robert F. , Santschi Peter H. , Nyffeler Urs P. , Schiff Sherry L.
Published: June 2008

Radiotracer experiments were carried out in enclosures in two lakes at the Experimental Lakes Area, North-western Ontario, to study the pathways of trace metal removal from the shallow water columns to the sediments of these lakes. As part of the larger experiment, stable carriers of Fe, Mn, and Zn were added individually to each of three enclosures. Rates of removal to sediments at pH 6.3 and backdiffusion after HCl addition to pH 4.8 of radiotracer 59Fe, 54Mn, and 65Zn were compared to the respective rates of their stable counterparts. Tracer removal and backdiffusion rates in enclosures which received stable carrier additions were further compared with the tracer behaviour in enclosures which received no carrier additions. Radiotracers and stable carriers were removed from the water column at similar rates at pH 6.3, and were remobilized at similar rates from the sediments when the pH of the water column was lowered to 4.8. The presence of the added stable carriers had no effect on the removal or remobilization of Mn or Zn. However, the removal of 59Fe from the water column was slowed slightly by the addition of Fe(III) carrier compared to removal in the other tubes, possibly due to the formation of colloidal phases. These results show that information on the rates of trace metal transport obtained using radiotracers is applicable to stable metal behavior in these freshwater systems. The use of radiotracers to study trace metal geochemistry under natural conditions is preferred to the addition of stable metals which may alter the physical and chemical properties of the suspended particulate matter as occurred after the addition of stable iron. Speciation studies showed that adsorption to ion exchange resins does not provide a reliable indication of the ionic form of metals in lake water.
Method for Estimating Dry Weight of Freshwater Planktonic Crustaceans from Measures of Length and Shape
Authors: Lawrence S. G. , Malley D. F. , Findlay W. J. , Maclver M. A. , Delbaere I. L.
Published: June 2008

We have developed a method of estimating the dry weight of planktonic crustaceans by using geometric figures of their approximate shape. Measurements of three dimensions are used in conjunction with the formulae to estimate volume, and then, on the basis of a number of assumptions, individual weights are estimated from these volumes. We verified the accuracy of the estimates by comparing them with measured weights of adult cladocerans and copepods and subsequently adjusting the formulae. These data are used to form weight–length relationships for cladoceran species and for developmental groups of copepod species. These weight–length relationships may be useful for estimating the biomass of zooplankters from other lakes when size and shape and method of preservation are similar to those of our organisms. For specimens of different size and shape and for different species, the geometric formulae may be useful.
Survival and Development of Lake Trout (Salvelinus namaycush) embryos in an Acidified Lake in Northwestern Ontario
Authors: Mohr L. C. , Mills K. H. , Klaverkamp J. F.
Published: June 2008

Survival and development of lake trout (Salvelinus namaycush) embryos from L223 in the Experimental Lakes Area, northwestern Ontario, were evaluated from 1979 (pH 5.6) to 1982 (pH 5.1). Survival of L223 embryos was not significantly correlated to lake pH during experimental acidification. Also, embryo mortality in L223 was not significantly different from that of lake trout embryos in two reference lakes, L224 and L468. Survival of L223 embryos was not improved when they were incubated in nonacidified lakes. Embryo mortality was highest in all lakes (33–81%) within 15 d of fertilization. Mortality was negligible from Day 15 until the termination of the seasonal observations (Day 120 or 150). High variability in embryo survival existed between individual females within a single lake. The mean size of eggs from L223 lake trout decreased significantly from 1979 to 1982. Recruitment failures occurred in L223 from 1980 to 1982. We hypothesize that lake trout recruitment failure in L223 occurred between the posthatching period (spring) and actual recruitment into the population as young-of-the-year (fall) and that embryo mortality in this lake was not critical to population recruitment.
Effect of Nutrient Additions on Lower Trophic Levels of an Oligotrophic Lake with a Seasonal Deep Chlorophyll Maximum
Authors: Shortreed Ken S. , Stockner John G.
Published: June 2008

Inorganic nitrogen and phosphorus were added to the surface of selected areas of Sproat Lake, Vancouver Island, British Columbia for varying periods in 1985 and 1986. The lake is monomictic, oligotrophic, and for much of each year has a deep chlorophyll maximum (DCM) located near the bottom of the euphotic zone (20–25 m). Epilimnetic chlorophyll concentrations are low (ca. 0.5 μg∙L−1) in summer, and DCM concentrations are from three to 10 times higher. The diatom Rhizosolenia eriensis was a dominant species in the epilimnion in spring and at the DCM for much of the year, but was rare in the epilimnion during summer, and consequently was not affected by the nutrient additions. Cyclotella spp. were also abundant in spring, were a prominent component of the DCM, and increased in abundance during nutrient additions. The cyanobacterium Synechococcus was the dominant member of the autotrophic picoplankton community and during the nutrient additions densities reached 300 000∙mL−1 (a 10-fold increase). Bacterioplankton numbers also increased during nutrient additions, at times exceeding 3.0 × 106∙mL−1. The DCM was formed and maintained by sinking cells, by occasional active photosynthesis at the DCM, and by an increase in chlorophyll/cell.
Pattern of Solute Movement from Snow into an Upper Michigan Stream
Authors: Stottlemyer R. , Toczydlowski D.
Published: June 2008

Precipitation, snowpack, snowmelt, and streamwater samples were collected in a small gauged watershed draining into Lake Superior during winter 1987–88 to assess the importance of snowmelt pattern and meltwater pathways in the occurrence of solute pulses in streamwater. The snowpack along the south shore of Lake Superior can contain 50% of annual precipitation inputs and 38% of annual ionic inputs including moderate levels of strong acids. Throughout winter, thawed surface soils and small but steady snowpack moisture release promoted movement of snowpack solutes to surface mineral soils. Preferential elution of K+, NH4+, and H+from the snowpack occurred with the initial thaw. Most ions exhibited pulses in snowmelt. Transport of snowpack solutes to the stream during snowmelt was through near-surface soil macropores and overland flow. For those ions with concentrations higher in the snowpack than in the premelt streamwater, K+, NH4+, and H+, the earliest snowmelt pulses had the greatest influence on streamwater chemistry. Unlike other portions of the region with resistant bedrock, the widespread presence of alkaline glacial till provides excess stream acid neutralization capacity (ANC) to buffer acidic inputs. Peak winter streamwater ANC reduction was caused principally by spring melt dilution of base cations and associated alkalinity, constant high SO42−levels, and an increase in NO3−. The maximum reduction in stream ANC was concurrent with overland flow. Relative to its snowmelt concentration, NO3−was highest in streamwater with some stream input likely the result of nitrification and N mineralization.
MULTIFAN a Likelihood-Based Method for Estimating Growth Parameters and Age Composition from Multiple Length Frequency Data Sets Illustrated using Data for Southern Bluefin Tuna (Thunnus maccoyii)
Authors: Fournier D. A. , Sibert John R. , Majkowski Jacek , Hampton John
Published: June 2008

We present a method for simultaneously analyzing multiple length frequency data sets. The method utilizes a robust likelihood-based estimation procedure that provides an objective criterion for hypothesis testing. The method is applied to length frequency data from southern bluefin tuna (Thunnus maccoyii) for which independent estimates of growth parameters based on tag return data are available. The estimates of the growth parameters from the new method were found to be in substantial agreement with the values previously obtained for these parameters. The strength of the likelihood approach is demonstrated by discriminating between alternative structural hypotheses for describing the data. The ability to simultaneously analyze multiple samples permits the method to exploit the extra information not available when analyzing samples one by one. The computer program maintains a database of fits to the data which enable the user to organize the results of the analysis. Graphical displays permit the user to view any of the fits, and an interactive graphics routine aids the user to find good initial parameter estimates.
Freshwater Migration as a Determinant Factor in the Somatic Cost of Reproduction of Two Anadromous Coregonines of James Bay
Authors: Lambert Yvan , Dodson Julian J.
Published: June 2008

We tested the hypothesis that the species-specific costs of migration differentially affect reproductive effort and somatic cost of reproduction in sympatric anadromous populations of cisco (Coregonus artedii) and lake whitefish (C. clupeaformis) of James Bay. Reproductive effort, which includes the energy cost of migration, is higher for cisco. Female cisco allocate more energy to reproduction than its total energy gain. The energy invested by lake whitefish in reproduction is approximately equal to its seasonal energy gain. Reproduction results in large differences in the energy content of gonads, viscera, and carcass between reproductive and nonreproductive fish of the same length. Neither cisco nor lake whitefish are able to spawn two years in succession. The somatic energy increase of reproductive female cisco is 121% lower than the somatic energy increase of nonreproductive females; similar comparisons are 89% (female) and 103% (male) for lake whitefish. The energy cost of migration is largely responsible for the higher somatic cost of reproduction observed for cisco. These different somatic costs of migration are related to resource accumulation prior to migration and to differences in the aerobic cost of swimming between the two species in combination with the difficulty of the freshwater migration.
Influence of Freshwater Migration on the Reproductive Patterns of Anadromous Populations of Cisco (Coregonus artedii) and Lake Whitefish (C. clupeaformis)
Authors: Lambert Yvan , Dodson Julian J.
Published: June 2008

We tested the hypothesis that differences in the cost of freshwater migration are responsible for the different reproductive patterns exhibited by the Eastmain River (James Bay) populations of anadromous cisco and lake whitefish, as predicted by species-specific migration costs that result in interspecific differences in energy allocation to growth, survival, and reproduction. In the Eastmain River, cisco spawn at a younger age and a smaller size, have a shorter life span and show a higher fecundity and a higher mortality than lake whitefish. Assuming that the two populations are stable (being only lightly exploited), the two species spawn at an age that maximizes their lifetime fecundity. Either juvenile (between three and age at maturity) and/or adult mortality is of major importance in moulding the observed age at maturity but adult mortality may play a predominant role. Adult mortality is associated with migration, an obligatory cost representing a major proportion of the energy loss experienced by reproductive individuals. The difference in the energy cost of migration between the two species suggests that migration may play a predominant role in producing the different reproductive patterns of cisco and lake whitefish in the Eastmain River and that within the physiological and size constraints of each species, these patterns represent optimal adaptations maximizing fitness.
Sea Surface Temperatures along the Coast of British Columbia: Regional Evidence for a Warming Trend
Authors: Freeland Howard J.
Published: June 2008

Sea-surface temperature has been measured at a large number of sites around the coast of British Columbia for periods well in excess of 50 yr. These time series are long enough to give clear evidence of a large scale secular warming. For the purposes of this paper the daily SST observations are decimated to monthly mean values. The observations are of particular value because observation methods have remained invariant throughout the observation period, and many of the stations are remote from civilisation allowing trends to be estimated that have not been contaminated with urbanization effects. Eighteen out of nineteen stations that are currently being sampled show a warming trend, the one that shows a cooling trend is the shortest time series, only in its eleventh year. The sea-surface temperatures at sites exposed to the Pacific Ocean show very high coherence with global scale air temperature variations but no relationship to the El Niño/Southern Oscillation signal.
Phototrophic Growth of Microalgae with Allantoic Acid or Hypoxanthine Serving as Nitrogen Source, Implications for Purine-N Utilization
Authors: Qliveira Luis , Huynh Hanh
Published: June 2008

Eleven species of marine phytoplankters assigned to seven different taxonomic divisions were tested for their ability to grow on hypoxanthine and some of its derivatives (allantoin, allantoate, urea) to study the mechanism of purine-N utilization in microalgae. All species tested were able to utilize urea, but only six of these were capable of growth on hypoxanthine. Growth on allantoic acid was restricted to six species, while no growth occurred with allantoin. In some species growth occurred only after supplementation of the culture media with Ni2+or it was enhanced by it. These results suggested that purine-N utilization involved the production of urea and its subsequent conversion to utilizable ammonium by the enzyme urease. Demonstration of xanthine dehydrogenase, allantoinase, allantoicase, and urease activities in cell-free extracts of microalgae grown on hypoxanthine and of growth inhibition using the inhibitors allopurinol, 2,6,8-trichloropurine and hydroxyurea confirmed that urea is a major product of hypoxanthine degradation. However, in Pavlova lutheri growth in allantoate or hypoxanthine occurs in the presence of urease inhibitors. This suggests that the catabolic oxidation of purines and their derivatives does not always involve urea production and that purine-N utilization must be studied on a species basis.
Longitudinal Structure of an Agricultural Prairie River System and its Relationship to Current Stream Ecosystem Theory
Authors: Wiley M. J. , Osborne L. L. , Larimore R. W.
Published: June 2008

The largescale structure of an agriculturally developed prairie river system in central Illinois was examined and compared with predictions from current stream ecosystem theory. High rates of primary productivity (> 15 g carbon∙m−2∙d−1) were characteristic of the watershed, although longitudinal patterns in riparian vegetation, stream temperature, and primary productivity were inverted relative to typical streams in forested uplands. Empirical models of gross primary production and community respiration were developed. Light availability, mediated by both channel shading and turbidity, appeared to be the principal factor limiting primary productivity. Both nitrate and orthophosphorus were found in high concentrations throughout the watershed. Largescale patterns in nutrient availability suggest that landuse patterns, and particularly urbanization, strongly affected spatial and temporal distributions of both nutrients. Differences between prairie river systems and "prototype" structures envisioned by the River Continuum Concept (RCC) derive from the descriptive nature of the RCC, and its inability to incorporate nonstandard distributions of key driving variables. The use of empirical modelling in stream ecosystem studies is discussed.
Causes of Density-Dependent Catchability for Georges Bank Haddock Melanogrammus aeglefinus
Authors: Crecco Victor , Overholtz William J.
Published: June 2008

We used population estimates (VPA) fishing effort and catch data for Georges Bank haddock, Melanogrammus aeglefinus, from 1964 through 1984 to test Paloheimo and Dickie's hypothesis which predicts: (1) that the catchability coefficient (q) from the commercial fishery is inversely related to haddock stock size (N) and stock area (Area); (2) that commercial catch per effort (C/f) data are curvilinearly related to stock abundance; and (3) that search time in the Georges Bank haddock fishery is inversely related to stock abundance. The catchability coefficients for the Georges Bank trawl fishery were inversely related to haddock stock size (r = −0.82, P < 0.001) and stock area (r = −0.75, P < 0.001). There was also a significant curvilinear relationship between commercial C/f and absolute and relative haddock stock biomass from 1964 through 1984. The slope estimate (B + 1) from this relationship was less than 1.0 (r = 4.18 to 8.95, P < 0.001), indicating nonlinearity between C/f and N. Finally, the relative search time expended by the haddock commercial fishery was inversely related to stock size from 1964 through 1984 (r = −0.75, P < 0.001). These results are consistent with the three predictions of the Paloheimo and Dickie hypothesis, suggesting that fishing mortality rates on Georges Bank haddock are a depensatory function of stock biomass.
Comparative Population Dynamics ofDaphnia roseaandHolopedium gibberumin Four Oligotrophic Lakes
Authors: Walters Carl J. , Robinson Donald C. E. , Northcote Thomas G.
Published: June 2008

Seasonal abundance patterns of Daphnia rosea and Holopedium gibberum showed great variability over the period 1974–83 in four coastal montane lakes of British Columbia. Though the lakes differed considerably in size, depth, and history of experimental disturbance (fish introductions, fertilization, plankton harvesting}, these differences apparently had much less influence on seasonal abundance patterns than did interannual variation in environmental factors shared by all the lakes. Spring rates of population increase differed strongly among years and were positively correlated between the two species. The timing and magnitude of summer population maxima also differed significantly among years, but were not correlated between the species. Adult mortality rates tended to increase through each season for both species, but showed no clear correlations either between the species or between years. Annual differences in growth and mortality rates and peak abundances were not associated with any obvious differences in environmental factors (insolation, rainfall, water temperature). There was no evidence of direct competition between the species, in terms of negative correlations in abundance. This is surprising in view of their similar life histories and feeding ecologies.
Response of Phytoplankton in Acidic Lakes in Ontario to Whole-Lake Neutralization
Authors: Molot Lewis A. , Heintsch L. , Nicholls K. H.
Published: June 2008

Changes in phytoplankton community composition were examined in two acidic lakes in Ontario, Bowland and Trout Lakes, to determine whether neutralization (and subsequent stocking with lake trout (Salvelinus namaycush) in the case of Bowland Lake) would reverse acidic characteristics. Miskokway Lake was monitored as an untreated reference lake. Analysis of community percentage similarity showed that year-to-year variability in phytoplankton community structure would have been low in the absence of neutralization. While changes in phytoplankton biovolumes or chlorophyll a concentrations after neutralization were not significant, there were several taxonomic changes: (1) the shift in the Bowland Lake phytoplankton community away from dominance by the cyanophyte, Rhabdoderma, and (2) the dominance of the prymnesiophyte Chrysochromulina breviturrita in the Bowland Lake phytoplankton community in 1985 2 yr after neutralization. It is likely that the major phytoplankton taxonomic changes were direct responses to chemical changes. These results suggest that structural changes (taxonomic) maintained stability of the phytoplankton communities under chemical stress (in terms of standing crop).