bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors affecting the timing of surface scums and epilimnetic blooms of blue-green algae in a eutrophic lake
Authors: Soranno P A
Published: April 2011

Blue-green algal blooms, which can occur mixed throughout the epilimnion or as scums at the lake surface, develop in response to a variety of factors. However, it is still unclear what conditions suggest that blooms are imminent or how far in advance blooms can be forecast. I assessed the predictability of surface scums and epilimnetic blooms from limnological, physical, and meteorological variables using data sampled daily during summer and fall 1993 in Lake Mendota, Wisconsin. Daily chlorophyll a (a measure of blue-green algal biomass) was correlated to some weather, physical, and grazing variables at lags ranging from 0 to 9 days. Conditions immediately preceding surface scums were variable, making predictions difficult. However, during surface scums, Secchi disk depth, wind velocity, atmospheric pressure, and precipitation were significantly different than when the scums were absent. Based on predictors examined in this study, I developed criteria that identify the conditions sufficient for scums to form. In Lake Mendota, conditions sufficient for surface scum formation (proper weather and water column conditions and a pre-existing algal population) occur much more often than scums are observed. This study shows the importance of weather in determining both epilimnetic blue-green algal biomass and surface scum formation.
The energetic implications of the diel onshore-offshore migration by dace(Phoxinus eosxP. neogaeus) in a small oligotrophic lake
Authors: Gauthier S , Boisclair D
Published: April 2011

We assessed the energetic implications of onshore-offshore migrations executed by dace (Phoxinus eos times P. neogaeus). We estimated growth, consumption, and activity rates for dace allowed to migrate and for dace restricted to the littoral zone during 45 days. We also estimated the growth and consumption rates of a permanent littoral resident, the pumpkinseed sunfish (Lepomis gibbosus) kept with migrating dace and compared these values with those obtained for sunfish kept with dace restricted to the littoral zone. Dace migrated from the littoral towards the pelagic zone at dusk and returned to the littoral zone at dawn. On average, 70% of the daily ration of dace was obtained during the migration. Consumption and activity rates of dace that executed diel migrations were twice those estimated for dace restricted to the littoral zone. Average growth of dace allowed to migrate was 0.38 g wet mass, but fish resticted to the littoral lost 0.36 g wet mass. Growth and consumption rates of sunfish were not affected by the confinement of dace in the littoral zone. The survival of dace in the presence of a littoral competitor and a pelagic predator appears closely linked to the energetic advantages associated to diel onshore-offshore migrations.
Effects of intrapopulation variability on von Bertalanffy growth parameter estimates from equal mark–recapture intervals
Authors: Smith E B , Williams F M , Fisher C R
Published: April 2011

The effects of intrapopulation variability on the parameter estimates of the von Bertalanffy growth equation have received discussion in the literature. Here we evaluated the effects of intrapopulation variability, using computer simulations, on four commonly used methods for estimating the von Bertalanffy growth parameters: the Ford-Walford plot, Ricker's method, Bayley's method, and Fabens' method. Intrapopulation variability in growth rates (k) and maximum sizes ( L infinity ) plus initial size distributions and measurement error, were tested for their effects on the accuracy of the parameter estimates using simulated mark-recapture data with equal recapture intervals. Fabens' method and a modified Ford-Walford plot provided the most accurate estimates in all cases, but when intrapopulation variability was large, they performed poorly. With moderate intrapopulation variability, the bias in estimates was small although between-sample variance was quite large. Biased initial size distributions without either small or large size classes cause a magnification of the estimation errors. Without knowledge of the degree of intrapopulation variability in a natural population, large errors of unknown magnitude in parameter estimation can result, and care should be taken when interpreting these estimates. However, if this variability can be quantified, then approximate parameter estimate errors can be obtained.
Using mark-recapture to estimate the numbers of a migrating stage-structured population
Authors: Myers R A , Hammill M O , Stenson G B
Published: April 2011

A model is presented for the joint analysis of mark-recapture data and stage- or age-structured data that allows the population abundance, birth rates, and migration rates to be estimated in situations where standard methods may be unreliable. The model assumes that birth rates follow a continuous distribution and that migration can be described by a simple Markov process. Application of the model is illustrated using mark-recapture and stage-structured data for grey seal (Halichoerus grypus) pup production in the Gulf of St. Lawrence and resulted in estimates of 9800 and 10 500 pups produced in 1989 and 1990, respectively.
Influence of extended water column mixing during the first 2 years of hypolimnetic oxygenation on the phytoplankton community of Amisk Lake, Alberta
Authors: Webb D J , Robarts R D , Prepas E E
Published: April 2011

The phytoplankton community, physical variables, and nutrient and chlorophyll a (Chl a) concentrations were monitored during the first two of six open-water seasons of hypolimnetic oxygenation in double-basined Amisk Lake, Alberta. Deep mixing of the water column in the treated basin (Zmax = 34 m) in spring was enhanced by hypolimnetic oxygenation. Oxygenation began in June 1988, when stratification was likely already established, but subsequent year-round treatment favoured an extended spring diatom bloom (Asterionella formosa and Cyclotella spp.), followed by a delay in the development of, and reduction in the severity of, cyanobacterial blooms (Aphanizomenon flos-aquae and Anabaena flos-aquae) in 1989. Historically, mean summer Chl a and total phosphorus (TP) concentrations in the euphotic zone (0-6 m) of the treated basin were 15.9 ± 1.6 and 33.5 ± 1.5 µg ·L-1, respectively, indicating a eutrophic lake. In 1988 and 1989, mean summer Chl a (10.0 ± 0.6 and 8.1 ± 0.7 µg ·L-1, respectively) and TP concentrations (29.0 ± 0.5 and 22.5 ± 0.9 µg ·L-1, respectively) in this stratum were lower than historic values (P < 0.05), indicating that the trophic status of Amisk Lake had shifted towards mesotrophy.
Effects of hypolimnetic oxygenation on water quality in Amisk Lake, Alberta, a deep, eutrophic lake with high internal phosphorus loading rates
Authors: Prepas E E , Burke J M
Published: April 2011

Year-round injection of pure oxygen into the hypolimnion of one of two basins in Amisk Lake during 1988-1993 changed dissolved oxygen (DO) and nutrient concentrations in both lake basins without eliminating thermal stratification. Changes were greatest in the treated basin and during 1990-1993, when an upgraded injection system operated; injection rates of <<= 1.3 t · day-1increased mean summer hypolimnetic DO concentrations from 1.0 (1980-1987) to 4.6 mg ·L-1(1990-1993). Summer hypolimnetic DO depletion rates nearly doubled relative to the pretreatment period. Mean summer hypolimnetic total phosphorus (TP) concentrations decreased from 123 to 56 µg · L-1, despite low iron to phosphorus ratios near the sediments. Similarly, mean hypolimnetic ammonium concentrations declined from 120 to 42 µg ·L-1. Epilimnetic TP and chlorophyll a concentrations decreased to 87 and 45%, respectively, of pretreatment summer means. Oxygen consumption rates in the treated basin were lower in winter than in summer; injection rates of <<= 0.8 t ·d-1increased mean winter deepwater DO concentrations from 2.5 to 7.2 mg ·L-1. In winter, mean deepwater TP concentrations decreased from 96 to 51 µg ·L-1. Oxygenation enhanced deepwater circulation in the treated basin in summer and winter. No changes were seen in two other reference basins during the study period. The hypolimnetic oxygen injection technology developed at Amisk Lake can be a cost-effective management tool for lakes with high hypolimnetic oxygen depletion rates related to high internal nutrient loading rates.
Distribution of littoral fishes in structurally complex macrophytes
Authors: Weaver M J , Magnuson J J , Clayton M K
Published: April 2011

By considering patchiness in the littoral vegetation, we were able to distinguish within-lake distributions among species and between young-of-the-year and yearling-and-older fishes. We characterized the macrophytes in Lake Mendota, Wisconsin, along transects using rake grabs to estimate species diversity and sonar charts to estimate the patchiness at 1-m intervals. We discerned two distinct littoral fish assemblages, one characterized by rock bass (Ambloplites rupestris) and smallmouth bass (Micropterus dolomieu) in unvegetated areas and another by a diverse assemblage in vegetated areas. Patchiness of macrophytes, not simply abundance, determined variations in the specific structure of the fish assemblage: e.g., yellow perch (Perca flavescens) were more dominant and abundant where vegetation was species rich and structurally complex as well as abundant. Young-of-the-year and yearling-and-older fishes differed in their distribution patterns: e.g., age 0 bluegill (Lepomis macrochirus) were more abundant where Eurasian watermilfoil was abundant and patchy and yearling-and-older bluegill where vegetation was more dense and species rich. Furthermore, yearling-and-older black bullhead (Ameiurus melas) and brown bullhead (Ameiurus nebulosus) were more common in patchy macrophyte beds than in species-rich vegetation. The largest catches of age 0 white bass (Morone chrysops) occurred at sites with sandy shallow beaches and patchy milfoil beds farther offshore. These patterns were discerned because we assessed macrophyte structural complexity at multiple scales and we separated young-of-the-year from older fishes.
Population viability and spatial fish reproductive strategies in constant and changing environments: an individual-based modelling approach
Authors: LePage C , Cury P
Published: April 2011

A spatially explicit individual-based model (IBM) helps to explain how two reproductive strategies, described as obstinate and opportunist, may be acting at the population level. Factors such as the spatial structure and the dynamics of the environment, the shape of the reproductive function, and spawning season duration are considered. Five simulations are presented to explore the importance of these factors in the success of two reproductive strategies experiencing in a first step, a constant, and in a second step, a changing environment. Simulations show that the obstinate strategy is characterized by high inertia and mainly selects optimal environmental conditions in the long term, whereas the opportunist strategy maintains diversity in site choice and allows the individual to explore environmental variability. Under drastic environmental changes, only a population combining both strategies avoids extinction. A low percentage of opportunists (about 1%) coupled with a high proportion of obstinates (about 99%) ensure population viability. Similar percentages have been observed in nature for philopatric species. The respective percentages of inertia and innovation that are needed in the functioning of natural systems are discussed.
The loss of hyperosmoregulatory ability in migrating juvenile American shad,Alosa sapidissima
Authors: Zydlewski J , McCormick S D
Published: April 2011

Investigations on juvenile American shad (Alosa sapidissima) revealed several physiological changes associated with downstream migration. Plasma chloride decreased 20% in wild juvenile shad during the autumn migration. Migrants had lower condition factor and hematocrit than non-migrant shad captured by beach seining. Gill Na+,K+-ATPase activity of migrant shad was higher than non-migrant; a 2.5-fold increase was observed in 1993, while a 57% increase was observed in 1994. Similar changes were observed in laboratory studies of shad maintained in fresh water under simulated natural temperature and photoperiod. Plasma chloride dropped 68% and gill Na+,K+-ATPase activity increased 3-fold over a 3-month period. Decreased plasma chloride was associated with increased mortality. Increases in gill Na+,K+-ATPase activity decreases in plasma chloride and osmolality, and incidence of mortality were delayed and moderated, but not eliminated, in shad maintained at constant temperature (24°C). Shad did not survive in fresh water past December regardless of temperature regime. In seawater, all shad survived and showed no perturbation of plasma chloride at 24°C or simulated natural temperature (above 4°C). The decline in hyperosmoregulatory ability, as influenced by declining temperatures, may serve as a proximate cue for autumnal migration.
Condition and energy reserves of Atlantic cod (Gadus morhua) during the collapse of the northern Gulf of St. Lawrence stock
Authors: Lambert Y , Dutil J -D
Published: April 2011

Interannual variations and seasonal cycles in condition and energy reserves were investigated for the northern Gulf of St. Lawrence cod (Gadus morhua) before and during the collapse of the stock. Significant decreases in cod condition between the late 1980s and the early 1990s coincided with the reduction in biomass. Cod exhibited clear seasonal variations in condition factor (Fulton's K), energy reserves, and tissue composition. Maximum K (0.87-0.91) and highest hepatosomatic index (HSI; 4.3-5.7%) occurred during the autumn while minimum levels occurred in spring. In May, the levels of condition (K, 0.69-0.74; HSI, 2.2-3.0) were below those reported for other stocks. In spring during spawning, a proportion of the wild cod had condition and energy reserves that were within the range that resulted in mortality among unfed fish held in the laboratory. Feeding experiments also indicate that the condition of wild cod in fall was lower than that observed for well-fed fish held in the laboratory. The decline in the condition and energy reserves of cod during several consecutive years may have lowered the productivity of the northern Gulf of St. Lawrence stock. This, along with overfishing, could have contributed to the collapse of this stock.
Early embryonic cleavage pattern, hatching success, and egg-lipid fatty acid composition: comparison between two cod (Gadus morhua) stocks
Authors: Pickova J , Dutta P C , Larsson P -O , Kiessling A
Published: April 2011

Baltic cod (Gadus morhua), from a brackish environment, were compared with oceanic (Skagerrak) cod in terms of early embryonic cleavage pattern, hatching success, and egg-lipid fatty acid composition. The influence of diet on these variables was investigated by analysing eggs from the Baltic stock, caught during three successive years and given controlled food for 24, 7, and 2 months, respectively, before the experiment commenced. Skagerrak cod eggs contained twice as much arachidonic acid (AA) in the phospholipid (PL) fraction as eggs from the Baltic cod, regardless of the length of time the Baltic cod had been kept in captivity and fed a control diet. Correlation between hatching rate and docosahexaenoic (DHA; 22:6n-3)/ eicosapentaenoic acid (EPA; 20:5n-3) ratio was significant (r2 = 0.56) as well as hatching rate and AA content of the PL fraction (r2 = 0.61). Symmetry during development, which was correlated to egg viability, was higher for eggs from Skagerrak than those from the Baltic stock. We suggest that AA content and DHA/EPA ratio of the PL fraction are important factors influencing egg viability and possibly also egg symmetry.\b Further, it appears that the factor(s) influencing the composition of the PL fraction is mostly related to stock rather than to diet.
Quantifying “no net loss” of productivity of fish habitats
Authors: Minns C K
Published: April 2011

A net change equation is derived for assessing no net loss of productivity of fish habitat (NNL). NNL is the guiding principle of the Canadian policy for the management of fish habitat. The equation provides a middle ground between the extremes of no conservation and no development. Projects affecting fish habitat are accountable for the productive capacity in loss areas and the difference between current and future productivities in modified areas. The equation implies quantitative conservation targets overall and loss-offsetting equivalencies in modified habitat areas. Generalization of the net change equation to heterogeneous habitats is illustrated with a development in a coastal wetland on the Great Lakes. The net change framework has implications for linkages between suitable habitat supply and fish population dynamics. Area fish habitat management plans envisioned in the policy and site-level net change assessments are connected. Quantitative ways are proposed for simultaneous assessment of NNL and ``harmful alteration, disruption, or destruction'' of fish habitat, as required in the Canadian Fisheries Act. Defensible methods for applying the net change equation are superior to earlier nonquantitative approaches. If the available science is insufficient, the precautionary principle is recommended. Future development steps for the quantitative net change framework are suggested.
Winter oxygen conditions in ice-covered rivers: the impact of pulp mill and municipal effluents
Authors: Chambers P A , Scrimgeour G J , Pietroniro A
Published: April 2011

Depressions in dissolved oxygen (DO) commonly occur in ice-covered rivers and can be further exacerbated by anthropogenic inputs. To assess the impact of pulp mill and municipal effluents on under-ice oxygen, temporal and spatial patterns in DO were examined for the Athabasca River, Alberta, Canada. Start-up of a bleached kraft mill in 1957 was associated with the lowest late-winter (February-March) DO concentrations ever recorded. Improvements in mill technology since 1977 coincided with increases (P < 0.05) in late-winter DO concentrations at two of three downstream sites and an amelioration in both the magnitude and downstream extent of the DO sag. During recent years (1988-1993), effluent loading resulted in sag and recovery zones over small spatial scales (tens of kilometres) and also contributed to large-scale (hundreds of kilometres) linear declines in DO. A review of oxygen conditions in ice-covered rivers throughout the world likewise showed that DO concentrations decreased linearly with distance below effluent outfalls for most river reaches with effluent concentrations >1%. Our observation that depressions in DO in ice-covered rivers increase with distance downstream raises concerns about safeguarding oxygen levels in northern rivers, especially in view of increasing development in these areas.
Influence of temperature on size-dependent predation by a fish (Gasterosteus aculeatus) and a jellyfish (Aurelia aurita) on larval capelin (Mallotus villosus)
Authors: Elliott J K , Leggett W C
Published: April 2011

We compared the size-dependent mortality patterns of newly emerged larval capelin (Mallotus villosus) at three different temperatures (3, 9, and 15°C) when exposed to predation by threespine stickleback (Gasterosteus aculeatus) and moon jellyfish (Aurelia aurita). Controlled experiments were conducted in both microcosms (38 L) and mesocosms (3100 L). Some temperature-related trends were evident in experiments with sticklebacks, but not with jellyfish. Sticklebacks fed selectively on smaller capelin larvae at 15°C, were nonselective at 9°C, and fed on larger larvae at 3°C. There was no prey size selection by A. aurita at any of the temperatures examined. Our findings support the view that the direction and magnitude of size-selective predation vary depending on the predator-prey assemblage and environmental conditions examined.
Sex-related growth of European eel, Anguilla anguilla, with focus on median silver eel age
Authors: Holmgren K , Wickström H , Clevestam P
Published: April 2011

Silver eels, Anguilla anguilla, migrating downstream were monitored for 15 years since being stocked in 1980 as cultured fingerlings in a Swedish lake. Females were larger than males in each separate year, but mean growth rate was higher in males than in females. This discrepancy was due to different age distributions, with 64.5% of the males migrating after four or five growing seasons, while 86.3% of the females grew for 10-15 seasons before migration. Otolith length in the glass eel stage was independent of sex, and it was not correlated with year of migration. With focus on median year of migration, otolith lengths after one, two, and three growing seasons were significantly larger in males than in females. This was mainly due to a higher otolith length increase during the first growing season, i.e., before the eels were stocked in the lake. These results are inconsistent with the view that female eels generally grow faster than males.
Mixed-stock analysis of Atlantic coast striped bass (Morone saxatilis) using nuclear DNA and mitochondrial DNA markers
Authors: Wirgin Isaac I , Waldman John R , Maceda Lorraine , Stabile Joseph , Vecchio Victor J
Published: April 2011

Striped bass (Morone saxatilis) stocks comingle along the northeastern United States and Canadian coasts and support mixed-stock fisheries in which stock compositions fluctuate widely. Many approaches to stock analysis of these populations have been tried. The recent use of mitochondrial DNA (mtDNA) haplotype frequency data showed promising results, despite low levels of mtDNA variation; to improve resolution, we used a single-copy nuclear DNA (nDNA) probe with two mtDNA markers (major length variants and Taq I variants), alone or in combination. Striped bass reference collections were from the Hudson River and Chesapeake Bay, and mixed-stock collections (1989 and 1991) were from eastern Long Island, New York. The combination of the nDNA and mtDNA major length variant data provided lower but still quite high resolution potential (Dst = 0.417) in mixed-stock analysis (1991 collection) than the combination of all three markers (Dst = 0.552). However, unlike the Hudson River stock, the Chesapeake Bay stock is composed of multiple substocks that vary significantly in the frequencies of Taq I variants; this among-substock variation destabilizes the Chesapeake Bay reference data set and the resultant mixed-stock estimates. Thus, we recommend an approach based on composite nDNA and mtDNA major length variant markers.
Energetics and survival of virgin and repeat spawning brown trout (Salmo trutta)
Authors: Berg Ole Kristian , Thronæs Eivind , Bremset Gunnbjørn
Published: April 2011

Smaller virgin spawners of a stunted population of brown trout (Salmo trutta) had higher specific energy content than repeat spawners, indicating that once maturation has started, the trout does not completely recover from its first spawning. Males had higher amounts of total and specific energy after spawning compared with females (adjusted for length differences). The greatest energy expenditures were recorded among spawning females (specific total energy losses of about 20%, which were twice the losses of male spawners). Repeat females lost 40% of their fat content. The gonads of the females accounted for 20% of the total protein content. The loss in carcass protein and fat for the spawners was greater than the corresponding loss in visceral fat and protein. Survival rates paralleled the amounts of energy expended in reproduction. Overall survival rate of first-time spawning males (females) was about 0.90 (1.00), while the corresponding value for repeat spawners was about 0.65 (0.50). It is predicted that brown trout from a stunted population should make a relatively small investment in reproduction and thus represent a case of low investment among iteroparous fish species.
Chemical trends and status of small lakes near Sudbury, Ontario, 1983-1995: evidence of continued chemical recovery
Authors: Mallory M L , McNicol D K , Cluis D A , Laberge C
Published: April 2011

We monitored 23 chemical parameters in 161 lakes northeast of Sudbury, Ontario, in most years between 1983 and 1995 to determine whether lake chemistries were responding to reduced local SO2 emissions. Lakes were typically small (median 4.0 ha, 4.5 m deep), rapid flushing, and acid stressed (median pH 5.58, acid-neutalizing capacity (ANC) 7.1 µequiv. ·L-1). Forty percent of the lakes declined significantly in SO4, base cations, and Al levels from 1983 to 1995, but only 12 and 16% increased in ANC and pH, respectively. Chemical trends were influenced by local climate; pronounced improvements occurred in response to drought conditions (1986 and 1987), but rapid deterioration followed the wet year in 1988. With more typical precipitation levels since 1989, a pattern of gradual improvement returned. Connected, rapid-flushing lakes, those on low or moderately sensitive bedrock, and peatlands showed the greatest improvements in pH and ANC whereas glacial headwaters and lakes on highly sensitive bedrock showed the least improvement. These results confirm that some recovery continues to occur following local emission reductions. However, many small Sudbury area lakes remain very degraded and unsuitable for acid-sensitive biota. Further emission reductions, including long-range sources, may be necessary to restore chemical conditions to critical levels sufficient to support further biological recovery.
Application of Bayesian decision analysis to management of a sockeye salmon (Oncorhynchus nerka) fishery
Authors: Robb Christina A , Peterman Randall M
Published: April 2011

We developed a decision-making framework for management of a sockeye salmon (Oncorhynchus nerka) fishery on the Nass River, British Columbia, that explicitly accounts for uncertainties in (i) the stock-recruitment relationship, (ii) annual recruitment, (iii) run timing, and (iv) catchability. The method used Monte Carlo simulation within a decision analysis framework and used Bayesian statistics to calculate probabilities for parameter values in the Shepherd stock-recruitment model. The decision dealt with when to open a fishery, upstream of all normal fishing areas, that is intended to harvest fish that are considered surplus to spawning requirements. The optimal decision rule for opening this fishery depended on (i) the relative importance of different management objectives and (ii) the range of shapes of the stock-recruitment relationship that were admitted as possible within the decision analysis. The management decision that was optimal if we assumed a dome-shaped stock-recruitment relationship was not optimal when we admitted the possibility of other shapes of the relationship. Therefore, given the variability in salmon stock-recruitment data, uncertainty in the shape of the stock-recruitment relationship should be routinely considered in analyses of management decisions.
Responsiveness of the interrenal tissue of yellow perch (Perca flavescens) from contaminated sites to an ACTH challenge test in vivo
Authors: Girard Caroline , Brodeur Julie C , Hontela Alice
Published: April 2011

The effects of chronic toxic stress on the hypothalamo-pituitary-interrenal (HPI) axis were investigated in yellow perch (Perca flavescens) captured at a reference site (Lake Memphremagog) and two sites contaminated with heavy metals and organic contaminants (Ile Perrot and Iles de la Paix, Lake St. Louis) in spring, summer, and fall. Cortisol secretion of the fish was stimulated in situ by an acute capture stress or by an i.p. injection of 4 IU/100 g body mass of porcine corticotropin (ACTH1-39). The response to both these challenges was lower in perch from the highly contaminated site than in perch from the reference site in the spring but not in summer. In fall, fish from the highly contaminated site had, as in spring, a lower response to ACTH than fish from the reference site. The reduced ability of perch to respond to capture stress or to ACTH indicates that the interrenal tissue in fish from contaminated sites is functionally impaired. Cortisol-impaired fish also had abnormal carbohydrate metabolism. The reduced ability of wild fish from contaminated sites to respond to a standardized ACTH challenge may be used as an early indicator of contamination-induced chronic stress.
Pelagic distribution of lake trout (Salvelinus namaycush) in small Canadian Shield lakes with respect to temperature, dissolved oxygen, and light
Authors: Sellers Todd J , Parker Brian R , Schindler David W , Tonn William M
Published: April 2011

The distribution of lake trout (Salvelinus namaycush) with respect to water temperature, dissolved oxygen, and light intensity was surveyed in three small Canadian Shield lakes at the Experimental Lakes Area, northwestern Ontario. Based on hydroacoustic and gillnet surveys, there was considerable variation among lakes in temperatures occupied by lake trout during the summer. During the day, lake trout were concentrated at 4-8°C in Lake 375, broadly distributed from 6 to 15°C in Lake 442, and concentrated in the epilimnion at 19°C in Lake 468. At night, lake trout in all lakes occupied epilimnetic waters at 19-20°C. Lake trout inhabited highly oxygenated water, with 75-90% of fish at >6 mg dissolved oxygen ·L-1 throughout the spring and summer in all three lakes. Light intensity did not affect lake trout distribution in Lake 468 but may have contributed to lake trout daytime descent into cool waters in Lakes 375 and 442. We suggest that previously assumed niche boundaries of lake trout do not adequately describe critical habitat for the species in small lakes, the same lakes that are likely most sensitive to erosion of such habitat.
Abdomen allometry, ovary development, and growth of female snow crab, Chionoecetes opilio (Brachyura, Majidae), in the northwestern Gulf of St. Lawrence
Authors: Alunno-Bruscia Marianne , Sainte-Marie Bernard
Published: April 2011

Growth and maturation of female snow crab (Chionoecetes opilio) in the northwestern Gulf of St. Lawrence were elucidated using carapace size-frequency distributions, indices of molting activity, ovarian mass, and laboratory and field measures of growth per molt. Females develop in three major stages: immature, with narrow abdomen and no detectable ovaries; prepubescent, with narrow abdomen and previtellogenic followed by vitellogenic ovaries; and adult, with broad abdomen and reproductive capability. Additionally, there is an ephemeral pubescent stage represented by females temporally close to the maturity molt. A reduction in the rate of carapace and abdomen growth occurs at the passage from immature to prepubescent, because energy is diverted into germinal growth, and adulthood is reached at a terminal molt to maturity. The pattern of abdomen growth relative to carapace is complex, consisting in successive phases of low, high, and again low positive allometry with increasing size of immature-prepubescent females. Over the period 1989-1996, a few females became adult at instar VIII at 4.5 years postlarval age, but more commonly, maturity occurred at instars IX and X at ages of 5.5 and 6.5 years, respectively. Average size at maturity may be temperature dependent, and within cohorts, larger females may mature earlier than smaller females.
Evaluation of factors related to increased zooplankton biomass and altered species composition following impoundment of a Newfoundland reservoir
Authors: Campbell Christine E , Knoechel Roy , Copeman Douglas
Published: April 2011

Zooplankton biomass and species composition were monitored in Cat Arm Lake and Reservoir on Newfoundland's Great Northern Peninsula from 1983 to 1993. Zooplankton biomass increased approximately 19-fold in the oligotrophic reservoir following impoundment in 1984, relative to biomass in the preexisting lake. Microcrustaceans Cyclops scutifer and Daphnia dubia, either rare or absent from Cat Arm Lake prior to impoundment, were consistently measurable components of the zooplankton community by 1993. Similar changes elsewhere have been attributed to both increased water retention time and enhanced phytoplankton biomass, factors whose effects are usually interdependent. In Cat Arm, there were no increases in either phytoplankton biomass or primary productivity during the first 3 years of impoundment, and natality of the dominant cladoceran, Daphnia catawba, did not increase. Summer water retention time increased from preimpoundment levels of 4 days in 1983 to 338 days in 1993. Zooplankton biomass was significantly correlated with water retention time (Spearman's rs = 0.72, p = 0.04) and showed no significant correlation with phytoplankton biomass, primary productivity, nutrient concentrations, pH, colour, or epilimnetic temperature. Changes in the zooplankton community in this subarctic system can thus be attributed most directly to a decrease in losses due to washout.
River-specific target spawning requirements for Atlantic salmon (Salmo salar) based on a generalized smolt production model
Authors: Chaput G , Allard J , Caron F , Dempson J B , Mullins C C , O'Connell M F
Published: April 2011

Atlantic salmon (Salmo salar) management in eastern Canada is based on ensuring that there is sufficient spawning escapement to meet an egg deposition target that maximizes the production of smolts. Using available egg deposition to smolt production data, we show that the present strategy of basing spawning targets on the presence-absence of lacustrine habitat for the rearing of juvenile salmon is a valid approach. We further show that a general smolt production model that accounts for this difference in available habitat when combined with the biological characteristics of the recruiting adults provides river-specific spawning targets. Targets corresponding to maximum yield tend to be less than half the target values currently used. A target representing the egg deposition for 90% of maximum yield serves as an example of a risk-averse strategy. The lower target values relative to those currently used are in large part determined by low sea survivals. The targets that we derived for four example rivers would correspond to the currently used target egg depositions if the long-term sea survivals were 2-3 times those observed in the last 6 years.
Postglacial fish dispersal from the Mississippi refuge to the Mackenzie River basin
Authors: Rempel L L , Smith D G
Published: April 2011

Wisconsinan glaciation had a profound impact on fish faunas in North America, and deglaciation led to the dispersal of approximately 28 species from the Mississippi glacial refuge into the Mackenzie River basin. A hypothesized dispersal 11 500 years ago via glacial lakes Agassiz and Peace is difficult to verify and hydrologic linkage between these lakes was sporadic and short lived. Geomorphic evidence indicates that glacial Lake Agassiz drained into the Mackenzie basin via the Clearwater River, Saskatchewan, 9900 years ago and created a second opportunity for fish dispersal northward. Fish distribution data indicate a 96% similarity between Mississippi species in the Mackenzie basin and species occupying the former Agassiz-Clearwater corridor. Fifteen species dispersed into the headwaters of the Clearwater River during hydrologic linkage to Lake Agassiz and are now isolated above an 18.5 m waterfall. Previous genetic data suggest lake trout (Salvelinus namaycush) used the Agassiz-Clearwater corridor for two-way dispersal between Beringia and the Great Lakes basin. Lake whitefish (Coregonus clupeaformis) populations of Mississippi origin are distinguished by a marker allele of glucose-3-phosphate dehydrogenase, G3PDH-1*b, that is absent from modern populations within the former Lake Peace region and the distribution of Mississippi whitefish across Canada is best resolved by our Agassiz-Clearwater dispersal hypothesis. Our research substantially alters the interpretation of fish biogeographic patterns in Canada and generates testable hypotheses for future studies.
Fossil pigments as indicators of phototrophic response to salinity and climatic change in lakes of western Canada
Authors: Vinebrooke Rolf D , Hall Roland I , Leavitt Peter R , Cumming Brian F
Published: April 2011

High performance liquid chromatography was used to quantify changes in fossil pigments among 111 saline lakes in British Columbia and to reconstruct past changes in phototrophic communities in three closed-basin prairie lakes. Redundancy analysis of survey data demonstrated that pigment concentrations were greatest in deep stratified lakes but were unaffected by ion concentrations, pH, or conductivity. Algal standing crop (as chlorophyll) was correlated (r = 0.21-0.33, P < 0.01) only with fossil measures of total algal abundance ( beta -carotene, pheophytin a). In contrast, redundancy analysis demonstrated that relative abundance (%) of fossil carotenoids varied with lake chemistry. Lutein-zeaxanthin (from green algae, cyanobacteria) and diatoxanthin (diatoms) replaced fucoxanthin (diatoms, chrysophytes, dinoflagellates) as salinity increased, while alloxanthin (cryptophytes) and myxoxanthophyll (colonial cyanobacteria) were most common in lakes with low Ca2+ and high dissolved organic carbon contents. Ordinations of surficial sediments suggested that post-deposition degradation did not alter the relation between pigment abundance and environmental characteristics. Fossil profiles of chlorophyll b and lutein-zeaxanthin also recorded climatic signals from Antelope and Kenosee lakes. These findings suggest that fossil pigments are well preserved in saline lakes and are capable of recording phototrophic community response to changes in salinity and climate.
A re-evaluation of swimming performance in juvenile salmonids relative to downstream migration
Authors: Peake S , McKinley R S
Published: April 2011

It has been hypothesized that downstream migration of juvenile salmonids is initiated by physiological changes that occur during smoltification, which render the fish unable, or unwilling, to swim against currents that exceed 2 body lengths per second (BL ·s-1). This decline in ability, coupled with the increase in flow rate generally associated with the spring run-off, is thought to result in passive downstream displacement. To test this hypothesis, we measured holding ability of wild Atlantic salmon (Salmo salar) parr and swimming ability of wild, migrating Atlantic salmon smolts in the field under ambient environmental conditions. Atlantic salmon parr (fork length 4.8-13.1 cm) used their pectoral fins to anchor themselves for indefinite (i.e., >200 min) periods in water speeds up to 0.86 m ·s-1. Atlantic salmon smolts (fork length 12.4-21.1 cm) swam indefinitely against currents up to 1.26 m ·s-1, maintained velocities as high as 1.64 m ·s-1for short periods (2-10 min), and made short bursts at speeds up to 1.95 m ·s-1. These findings indicate that absolute swimming performance is not impaired after smoltification and that wild Atlantic salmon smolts are capable of swimming at speeds much greater than 2 BL ·s-1, making it unlikely that they are involuntarily carried to the sea by river currents.
Parentage assignment using microsatellites in turbot (Scophthalmus maximus) and rainbow trout (Oncorhynchus mykiss) hatchery populations
Authors: Estoup Arnaud , Gharbi Karim , SanCristobal Magali , Chevalet Claude , Haffray Pierrick , Guyomard René
Published: April 2011

Eight turbot (Scophthalmus maximus) and eight rainbow trout (Oncorhynchus mykiss) microsatellites were selected for parentage assignment in fish-farmed populations. The number of alleles, gene diversity, polymorphic information content, and the probabilities of exclusion of these loci were 8, 0.76, 0.73, and 0.55 in turbot and 4, 0.65, 0.59 and 0.39 in rainbow trout, respectively. The power of the markers for parentage assignment was assessed by computing the frequency of good and unique decisions (fgu) in a population of genitors defined by its allele frequencies and assuming three different types of mating schemes. The eight turbot microsatellites gave larger maximal mating schemes (the largest mating structure with a fgu >= 0.95) than the eight rainbow trout loci: 1 female (F) mated to 520 males (M) (paternity retrieval scheme), more than 140F x 140M (factorial scheme), and more than 15 000 independent pairs (natural population scheme) for turbot, and 1F x 88M, 34F x 34M, and 7000 independent pairs for rainbow trout. The variation of the fgu values with the number of loci confirmed that the turbot set of microsatellites was more efficient for parentage assignment than the rainbow trout markers.
Estimating season-wide survival rates of outmigrating salmon smolt in the Snake River, Washington
Authors: Skalski John R
Published: April 2011

Standard release-recapture models can provide release-specific estimates of survival probabilities for a group of salmonid smolt released at a particular time and place in the river. However, reliable estimates of season-wide survival for the population of outmigrating smolt are needed in the Snake-Columbia River Basin for careful management of the resource. Alternative estimators are presented to estimate season-wide survival of spring chinook salmon (Oncorhynchus tshawytscha) smolt. Using daily fish tagging, survival for the middle 95% of the migration was estimated to be SS = 0.873 (SE = 0.005) from the tailrace of Lower Granite Dam (RK 695) to the tailrace of Little Goose Dam (RK 635) in 1995. Daily survival estimates were remarkably stable across the migration season with some evidence of decreased survival towards the very end of the migration. Sample size calculations suggest good precision can be attained (i.e., projected SE = 0.01) with tag releases as small as n = 500 fish per day (d = 7) across the outmigration. Less than daily sampling can result in season-wide survival estimates that are too imprecise for many management purposes.
Does lake size affect concentrations of atmospherically derived polychlorinated biphenyls in water, sediment, zooplankton, and fish?
Authors: Paterson Michael J , Muir DCG , Rosenberg B , Fee E J , Anema C , Franzin W
Published: April 2011

Concentrations of 90 polychlorinated biphenyl (PCB) congeners were determined in water, surface sediment, zooplankton, and fish collected from eight remote lakes in northwestern Ontario. The lakes vary in surface area from 0.2 to 4848 km2 and receive PCBs only from atmospheric deposition. Systematic differences with lake size in concentrations of Sigma PCBs or in congener distributions were not detected in any of the sample sets, except sediment. Concentrations of Sigma PCBs in surface sediments increased in the largest lakes when expressed on an organic carbon basis because carbon content decreased with lake size. In general, there were few strong correlations among PCB concentrations in water, sediment, or biota and physical, chemical, or biotic conditions at the time of sampling. There was no strong biomagnification of PCBs up the food chain from plankton to piscivorous fish. The results of this study are surprising because many factors that are thought to affect PCB dynamics and bioaccumulation varied systematically with lake size (water temperature, dissolved organic carbon concentrations, particle residence times, food chain length, algal productivity).
Zooplankton community responses to a novel forest insecticide, tebufenozide (RH-5992), in littoral lake enclosures
Authors: Kreutzweiser David P , Gunn John M , Thompson Dean G , Pollard Heather G , Faber Marvin J
Published: April 2011

The effects of tebufenozide (RH-5992), a potential forest insecticide, on zooplankton communities were determined in 16 littoral enclosures in a small forest lake of northern Ontario. Community structure in enclosures treated with 9, 36, or 157 µg tebufenozide/L ( 0.2, 0.7, and 3 times the expected environmental concentration) was compared with natural zooplankton communities in control enclosures. No significant treatment effects on zooplankton communities were detected, even at 3 times the expected environmental concentration. While some changes in community structure of crustacean zooplankton in enclosures occurred through the season, these did not appear to be related to the tebufenozide treatments. Tebufenozide residues in water dissipated following exponential decline kinetics with time to 50% dissipation (DT50) ranging from 32 to 35 days irrespective of initial concentration. There were no differences in pH, dissolved oxygen, conductivity, and phytoplankton abundance among treatment levels (repeated-measures ANOVA, p > 0.07).
Phylogeography and postglacial dispersal of lake trout (Salvelinus namaycush) in North America
Authors: Wilson Christopher C , Hebert Paul DN
Published: April 2011

We used restriction fragment length polymorphism (RFLP) analysis of mitochondrial DNA (mtDNA) diversity to assess the complex postglacial history of lake trout (Salvelinus namaycush) and test existing dispersal hypotheses. A pilot survey with 30 restriction enzymes was carried out on lake trout from 16 geographically representative populations to determine phylogenetically informative characters. Subsequent screening of 1416 lake trout from 93 populations across the species' range with nine variable restriction enzymes showed that lake trout from at least five glacial refugia contributed to extant populations. Three major mtDNA lineages were observed, with sufficient differences to suggest their divergence during the mid-Pleistocene. Geographic and genetic differences within two lineages suggested further vicariant divergence caused by Wisconsinan glacial advances. In contrast with more southern freshwater species, no correlation was observed between the geographic proximity of glacial refugia and relatedness of mtDNA lineages. Current distributions of refugial lineages are readily explained by consideration of timing and connections of proglacial lakes. These lakes facilitated large-scale dispersal from multiple refugia, particularly enabling long-distance dispersal from the Mississippian and northwestern refugia. Proglacial lakes also enabled extensive secondary contact among refugial groups, resulting in high levels of intrapopulation mtDNA diversity within their former boundaries.
Long-term changes in parasites of sockeye salmon (Oncorhynchus nerka) smolts
Authors: Bennett Shannon N , Adamson Martin L , Margolis Leo
Published: April 2011

Parasites were examined in 41 annual samples of sockeye salmon (Oncorhynchus nerka) juveniles originating from lakes in British Columbia: Chilko and Shuswap. Nine species of parasitic helminths and two species of parasitic Crustacea were recovered from various organs. The number of species ranged from three to nine per year. Most (94%) parasites belonged to three tapeworm species, identified as core to the parasite community because they also infected the most hosts. Two of these cestode species are probably maintained by resident freshwater hosts in the lakes. Positive numerical associations were observed between four parasite species pairs. Parasite communities in both lakes were composed of similar species, with the exception of three rare Chilko Lake species that were never recovered from Shuswap Lake. Parasites were often as variable within stock (temporally) as between stocks (geographically), except for the prevalence of Eubothrium sp. and Neoechinorhynchus sp. and mean annual intensity of Proteocephalus sp. and encysted digenetic metacercariae, which were greater at Chilko Lake than at Shuswap Lake. Discrimination between the two lakes based on their parasite community is possible only in extreme cases of infection and thus is of limited use to fisheries officers attempting to distinguish between these stocks.