bluuebunny/crossref_metadata_2025 huggingface dataset:
Paleomagnetism of Canadian Arctic permafrost; Quaternary magnetostratigraphy of the Mackenzie Delta
Authors: Wang Y. , Evans M. E.
Published: April 2011

A total of 357 samples taken from two long cores (Taglu, Kumak) drilled in the Mackenzie River delta have been investigated paleomagnetically. Remanence and susceptibility were measured in the field while the samples were still frozen. Profiles of susceptibility (5772 measurements) permit lateral correlation and imply that the average accumulation rate at Taglu was ~50% greater than that at Kumak, which lies 15 km to the southwest. Polarity reversals were found in both cores. The Matuyama–Brunhes boundary occurs at depths of 152 and 111 m at Taglu and Kumak, respectively; corresponding depths for the Gauss – Matuyama boundary are 356 and 243 m. In addition to the major chrons, we also find evidence of the Olduvai and Jaramillo subchrons. The chronology based on these data suggests that a major change in sedimentation history occurred about 1.5 Ma ago. This feasibility study thus suggests that paleomagnetism has chronological potential in permafrost environments that are currently important in frontier hydrocarbon exploration and as natural gas hydrate reservoirs.
The Bell Lake group and Anton Complex: a basement – cover sequence beneath the Archean Yellowknife greenstone belt revealed and implicated in greenstone belt formation
Authors: Isachsen C. E. , Bowring S. A.
Published: April 2011

U–Pb zircon and monazite geochronology indicates the presence of a >2.93 Ga basement (Anton Complex) and >2.8 Ga cover sequence (Bell Lake group) beneath the 2.70 to >2.72 Ga Kam Group of the Yellowknife greenstone belt in the southern Slave Province. The Bell Lake group comprises remnants of a quartzite – rhyolite – banded iron formation succession. The ages of detrital zircons from the quartzite unit constrain its deposition to be younger than 2.92 and range up to 3.7 Ga. U–Pb ages for gneisses beneath the Bell Lake group are in excess of 2.93 Ga and they are locally overlain by the quartzite. The contact between the tholeiitic to calc-alkaline Kam Group and the Bell Lake group is poorly exposed and equivocal. Approximately 6 km higher in the section, the Ranney chert, a felsic volcaniclastic layer, separates 2.70 – 2.72 Ga tholeiitic to calc-alkaline upper Kam Group rocks from a lower tholeiitic section containing sheeted-dike complexes. Zircons from the Ranney chert yield Pb –Pb ages ranging from 2.72 to >2.8 Ga. The older ages suggest proximity of older basement during deposition of mostly tholeiitic lower Kam Group volcanic rocks in an extensional setting, followed by deposition of the upper Kam Group, which is more arc-like in character, on this earlier-formed tholeiitic crust beginning at 2.72 Ga.
Apatite fission-track dating of the Cowichan fold and thrust system, southern Vancouver Island, British Columbia
Authors: England T. D. J. , Currie L. D. , Massey N. W. D. , Roden-Tice M. K. , Miller D. S.
Published: April 2011

The Cowichan fold and thrust system on southern Vancouver Island comprises a linked system of folds and thrust faults in crystalline and sedimentary rocks of the Wrangellia terrane and its sedimentary cover, the Upper Cretaceous Nanaimo Group, and Upper Paleocene to Lower Eocene sandstones of the Chuckanut Formation. Apatite fission-track analysis indicates that cooling below the closure temperature of fission-track retention in apatite (100 ± 20 °C) for both the Island Plutonic Suite from the Wrangellian basement and the Nanaimo Group occurred at ~ 50–40 Ma (Middle Eocene). Thrusting is interpreted to have occurred immediately prior to this time in the Middle Eocene, but after post-Cretaceous regional burial of the Turonian to Maastrichtian Nanaimo Group and deposition of Upper Paleocene and Lower Eocene sandstones, which are involved in the deformation. These timing constraints support the hypothesized temporal linkage between contraction and uplift of Wrangellia during the Middle Eocene and continued margin-normal contraction of the Pacific Rim terrane (± the Crescent terrane) at ~ 45 Ma.
Age and paleoecological significance of an early postglacial fossil assemblage near Marathon, Ontario, Canada
Authors: Bajc Andrew F. , Morgan Alan V. , Warner Barry G.
Published: April 2011

Organic materials recovered from deltaic deposits confined to the Black River Valley near Marathon, Ontario, provide information on lake-level history and local ecology for the region. Radiocarbon samples provide the first age determinations (ca. 8200 BP) for the post-Minong III – IV lake phases along the northeast corner of the Lake Superior basin. A minimum of 49 Coleoptera taxa and 22 vascular plant taxa indicate coniferous-forest and riparian communities. Overbank deposition along rivers flowing from the ice margin provided temporary ponds colonized by sedges and other aquatic plants and animals. Many records for both animals and plants illustrate occurrences of western and Arctic disjunct species in early Holocene time. Some "western" Coleoptera might still be present as disjuncts in the Marathon region.
Foredune development on Îles de la Madeleine (Quebec), Atlantic Canada
Authors: Giles P. T. , McCann S. B.
Published: April 2011

The foredune, in this cool-temperate, sediment-abundant, relatively high wind and wave energy environment, is generally a single ridge with a mean height of 5.1 m (max. 11.4 m) and width of 25–35 m. Pioneer vegetation is dominated by Ammophila breviligulata. Four foredune types were identified: scarped, scarped with blowouts, scarped with incipient foredune, and nonscarped, the first being the most common, occupying more than 50% of the shoreline. Foredune erosion and retreat is occurring at an average rate of 0.8 m∙a−1. The marked differences in dune character between the west and east coasts of the islands are related to differences in wave energy and shoreline dissipativeness. The higher energy west coast exhibits more dynamic dunes with more frequent blowouts, which may develop into parabolic forms.
Within- and among-population variation in the trophic position of a pelagic predator, lake trout (Salvelinus namaycush)
Authors: Vander Zanden M Jake , Shuter Brian J , Lester Nigel P , Rasmussen Joseph B
Published: April 2011

Many aquatic consumers have flexible feeding habits, and the diet and trophic position of a species can be expected to vary both within and among populations. In this study, we quantify the importance of both within- and among-population trophic variation for lake trout (Salvelinus namaycush) using stable isotope designations of trophic position from 13 Ontario and Quebec lakes. Lake-to-lake differences explained 78% of the total variation in lake trout trophic position. Analysis using both stable isotopes and published dietary data demonstrated that the trophic position of lake trout failed to increase appreciably as a function of animal body size. This finding was attributed to weak predator size - prey size relationships as well as to there being no relationship between prey fish trophic position and body size. The variance in trophic position of a population reflects the extent to which individuals forage as trophic specialists; however, we did not identify any one factor that was correlated with within-population trophic variation. Our finding that much of the total variation in trophic position represents among-population differences indicates that considering the average trophic position of a population does not mask substantial within-population trophic variation.
Seasonal photoreactivity of dissolved organic matter from lakes with contrasting humic content
Authors: Lindell Måns J , Granéli H Wilhelm , Bertilsson Stefan
Published: April 2011

We studied seasonal variability in photodegradation of dissolved organic carbon (DOC) resulting from artificial ultraviolet-A (UV-A) and UV-B irradiation. Water samples were taken approximately monthly from the surface layers of two oligotrophic lakes with contrasting humic content, situated in southern Sweden. Lake water was filter-sterilized (0.2 μm) and exposed to artificial UV radiation in quartz tubes. Potential DOC photodegradation, measured as a photoproduction of dissolved inorganic carbon (DIC) and oxalic, malonic, formic, and acetic acid in irradiated samples, was observed throughout the sampling period. In addition, exposure to UV radiation resulted in a decrease in DOC, absorbance, and humic substance fluorescence. The photoproduction of DIC and the low molecular weight (LMW) organic acids varied seasonally, being generally higher in winter and spring (December-May), while DOC appeared to become less photoreactive after the extensive exposure to solar radiation during summer. Production rates of both DIC and LMW organic acids were approximately eight times higher in the humic lake despite that the DOC concentration was only two times higher than in the clearwater lake. This is most probably due to the high input of allochthonous DOC and the resulting higher absorbance to DOC ratio in the humic system. Furthermore, the longer hydraulic residence time in the clearwater system could have resulted in an accumulation of residual DOC, recalcitrant to further photodegradation.
Patterns of metamorphic age and length in marine fishes, from individuals to taxa
Authors: Benoît Hugues P , Pepin Pierre , Brown Joseph A
Published: April 2011

We present a summary of variability in age and length at metamorphosis for marine fishes. Data from the literature were partitioned into taxonomic, population, and individual levels of resolution to examine the factors affecting the timing of metamorphosis. Temperature appears to be a dominant influence on timing, likely due to its effect on growth rate. Interspecifically, length at metamorphosis correlated poorly with that at hatching but was significantly related to temperature. This pattern was inconsistent for population-level comparisons. Metamorphic age decreased exponentially with increasing temperature in interspecific and population-level comparisons but did not covary with length for either level of resolution. This suggests that age at metamorphosis largely reflects the time required to grow to a given metamorphic length. Within populations, the correlation between metamorphic age and length increases with growth rate, a reflection of variance in age and length. A strong exponential relationship between mean metamorphic age and length and their associated variability (SD) exists, with a slope greater than unity in both cases (i.e., variability increases relative to the mean). With these relationships, we can infer the manner in which individual variability in metamorphic traits is generated throughout ontogeny. These results are considered in light of recruitment variability in marine fishes.
Energetic consequences of reproduction in Atlantic cod (Gadus morhua) in relation to spawning level of somatic energy reserves
Authors: Lambert Yvan , Dutil Jean-Denis
Published: April 2011

The influence of a lower condition on reproductive investment, somatic energy losses, and postspawning condition of Atlantic cod (Gadus morhua) was examined under the hypothesis that females, in response to lower available energy reserves, would reduce reproductive investment in order to limit somatic energy losses. Laboratory experiments revealed that female cod with high prespawning condition factors ended reproduction in better condition than females with low prespawning condition factors. Fecundity and total egg dry weight were significantly lower in poor-condition females. The loss in somatic mass and energy in these poor-condition females was nevertheless higher, in relative terms, than the losses experienced by females in good condition. Consequently, energy reserves invested in reproduction by poor-condition females increase their risk of mortality. In the northern Gulf of St. Lawrence during the early 1990s, reproductive females had lower fecundities and were in worse prespawning and postspawning condition. The condition of spent females suggested a greater impact of changes in environmental conditions on adult than on immature cod. Reproductive potential and possibly recruitment may have suffered from that situation and could have contributed to the failure of that stock to recover despite the moratorium on commercial fishing.
Analysis of microsatellite DNA resolves genetic structure and diversity of chinook salmon (Oncorhynchus tshawytscha) in Californias Central Valley
Authors: Banks Michael A , Rashbrook Vanessa K , Calavetta Marco J , Dean Cheryl A , Hedgecock Dennis
Published: April 2011

We use 10 microsatellite DNA markers to assess genetic diversity within and among the four runs (winter, spring, fall, and late fall) of chinook salmon (Oncorhynchus tshawytscha) in California's Central Valley. Forty-one population samples are studied, comprising naturally spawning and hatchery stocks collected from 1991 through 1997. Maximum likelihood methods are used to correct for kinship in juvenile samples and run admixture in adult samples. Through simulation, we determine the relationship between sample size and number of alleles observed at polymorphic microsatellite markers. Most samples have random-mating equilibrium proportions of single and multilocus genotypes. Temporal and spatial genetic heterogeneity is minimal among samples within subpopulations. An FSTof 0.082 among subpopulations, however, indicates substantial divergence among runs. Thus, with the exception of our discovery of two distinct lineages of spring run, genetic structure accords with the diverse chinook life histories seen in the Central Valley and provides a means for discrimination of protected populations.
Mercury in the Sudbury River (Massachusetts, U.S.A.): pollution history and a synthesis of recent research
Authors: Wiener James G , Shields Pamela J
Published: April 2011

We review the transport, fate, and bioavailability of mercury in the Sudbury River, topics addressed in the following five papers. Mercury entered the river from an industrial complex (site) that operated from 1917 to 1978. Rates of mercury accumulation in sediment cores from two reservoirs just downstream from the site decreased soon after industrial operations ended and have decreased further since capping of contaminated soils at the site in 1991. The reservoirs contained the most contaminated sediments (some exceeding 50 μg Hg·g dry weight-1) and were depositional sinks for total mercury. Methyl mercury concentrations in biota did not parallel concentrations of total mercury in the sediments to which organisms were exposed, experimentally or as residents. Contaminated wetlands within the floodplain about 25 km downstream from the site produced and exported methyl mercury from inorganic mercury that had originated from the site. Natural burial processes have gradually decreased the quantity of sedimentary mercury available for methylation within the reservoirs, whereas mercury in the lesser contaminated wetlands farther downstream has remained more available for transport, methylation, and entry into food webs.
Stratigraphy and historic accumulation of mercury in recent depositional sediments in the Sudbury River, Massachusetts, U.S.A.
Authors: Frazier Bradley E , Wiener James G , Rada Ronald G , Engstrom Daniel R
Published: April 2011

The distribution and deposition of sedimentary mercury in the Sudbury River were linked to an industrial complex (Nyanza site) that operated from 1917 through 1978. In two reservoirs just downstream from the Nyanza site, estimated rates of mercury accumulation increased markedly in the 1920s and 1930s, were greatest during 1976-1982, decreased within 5 years after industrial operations ceased, and have decreased further since capping of contaminated soil at the Nyanza site was completed in 1991. The most contaminated sediments were typically buried, yet the 0- to 1-cm stratum remained substantially contaminated in all cores. Mercury accumulating in the surficial, reservoir sediments was probably from continuing, albeit much lesser, inputs from the Nyanza site, whereas recent inputs to downstream wetland areas were attributed to recycling of sedimentary mercury or to mercury from unidentified local sources. In the reservoirs, burial of highly contaminated sediments is gradually decreasing the amount of sedimentary mercury available for methylation. In downstream wetlands, however, sedimentary mercury seemed to be more available than that in the reservoirs for physical transport and biogeochemical cycling.
Spatial variability in growth and mortality of the red sea urchin, Strongylocentrotus franciscanus, in northern California
Authors: Morgan Lance E , Botsford Louis W , Wing Stephen R , Smith Barry D
Published: April 2011

Natural and fishing mortality rates of the red sea urchin, Strongylocentrotus franciscanus, in northern California were estimated from growth increment and size distribution data under the assumption of a constant recruitment rate. Mean asymptotic test diameter, standard deviation of asymptotic test diameter, growth rate coefficient, and natural mortality rate were first estimated for three nominally unharvested sites, Bodega Marine Reserve, Caspar Closure, and Salt Point. These estimated growth and mortality parameters differed among sites, leading to substantially different yield-per-recruit surfaces. Estimates of fishing mortality rate from size distributions collected at 11 harvested sites were then calculated based on the growth and natural mortality estimates obtained from the Caspar Closure and Bodega Marine Reserve sites. Estimates of fishing mortality rate ranged from 0.11 to 1.87·year-1. The alongshore pattern of fishing mortality rate was moderately correlated with landings and effort, but the spatial pattern of rare, strong recruitment events also appeared to influence values of fishing mortality rate. The positive bias in estimates of fishing mortality rate due to recruitment variability indicated that our observed pattern in estimated values for fishing mortality rate could have been caused by the historical spatial pattern of interannual variability in recruitment.
Changes in species composition of the demersal fish community in nearshore waters of Kodiak Island, Alaska
Authors: Mueter Franz J , Norcross Brenda L
Published: April 2011

We examined the species composition of the demersal fish and shrimp community in seven different areas in the nearshore waters of Kodiak Island based on trawl survey data. A major part of the variability in the data set was attributed to trends over time, indicating a significant change in species composition in the early 1980s. Results agree with work by others and show a shift from a community dominated by shrimp and small forage fishes to one dominated by large piscivorous gadid and flatfish species. The shift occurred rather abruptly in most areas between 1980 and 1982, but the pattern of change differed significantly among areas. Correlations between trends in the two groups of species were weak but were consistent with the hypothesis that the decline in shrimp and forage fishes followed, rather than preceded, the increase in large piscivorous fishes. The results suggest predation as a possible mechanism to explain the observed changes.
Gillnet selectivity and size and age structure of an alpine Arctic char (Salvelinus alpinus) population
Authors: Finstad Anders G , Jansen Peder A , Langeland Arnfinn
Published: April 2011

The aim of the present study was to address possible implications of biased sampling for the commonly adopted uni- and bi-modal size structures and unimodal age structures in Arctic char (Salvelinus alpinus) populations. Multimesh gill nets were used to sample an allopatric population of Arctic char in an alpine lake in central Norway. Direct estimates of gillnet selectivity for different length-classes of Arctic char were obtained by mark-recapture experiments and by successive removal methods. The observed size and age structure in gillnet samples was significantly different from the estimated size and age structure of the Arctic char population when catches were corrected for gillnet selectivity. An observed unimodal size and age structure was a direct result of gillnet selectivity, as smaller and younger fish were underrepresented in gillnet catches. Moreover, an abrupt increase in gillnet selectivity for large Arctic char was related to a niche shift to cannibalism. A model that explains bimodal size distributions in gillnet catches as a result of ontogenetic behavioural change is presented. Complex ontogenetic growth and mortality patterns that have been suggested to be essential in structuring modal Arctic char populations were superfluous in explaining the observed modal population structure in the present study.
An evaluation of alternative procedures using the Bou-Rouch method for sampling hyporheic invertebrates
Authors: Hunt Gary W , Stanley Emily H
Published: April 2011

This study assesses the influence of well design, pumping rate, and sample volume on hyporheic invertebrate density and richness estimates in three streams differing in sediment composition. A comparison of five well designs, i.e., temporary wells with no pores and with 4-, 6-, and 8-mm pores along the lower 15 cm and permanent wells with 6-mm pores, revealed no significant differences in either total invertebrate densities or taxon richness. Pumping rates, i.e., 1.5 versus 4 L·min-1, significantly affected density estimates at two streams and taxon richness at one of the three streams, shown by higher values at the faster pumping rate. A comparison of five sample volume sizes, i.e., 0.5, 1.0, 1.5, 2.0, and 2.5 L, indicated that smaller sample volumes produced significantly higher estimates of density, while larger sample volumes gave significantly higher estimates of taxon richness. These results underscore the importance of maintaining consistent pumping rates and sample volume sizes throughout the course of a study.
Growth variation and water mass associations of larval silver hake (Merluccius bilinearis) on the Scotian Shelf
Authors: Jeffrey Jennifer A , Taggart Christopher T
Published: April 2011

Otolith microstructure is shown to be ideal for assessing age and growth in silver hake (Merluccius bilinearis) larvae and is used to examine growth among individuals and cohorts. Larvae collected from Western Bank, Scotian Shelf, in September, October, and November 1997 defined three monthly cohorts identified using inferred hatch dates. Total length-at-age relations did not differ between the September and October cohorts despite substantial differences in growing degree-day (435 versus 318°C·d) and zooplankton (potential prey index) wet biomass (0.15 versus 0.27 g·m-3). Larvae collected off-bank in September exhibited a growth advantage of >0.10 mm·d-1 relative to larvae collected on-bank. Greater variability in growth rate within cohorts and among water masses implies that cohort-averaged growth and survival (based on growth) estimates can be biased by overrepresentation of a single water mass. The focus on growth variability, and its relationship to survival, should be on individuals within cohorts and not on cohort-averaged estimates. We hypothesize that growth, and perhaps survival, in silver hake larvae on the Scotian Shelf is most easily explained by variation in physical oceanographic processes.
Nutrient-chlorophyll relationships: an evaluation of empirical nutrient-chlorophyll models using Florida and north-temperate lake data
Authors: Brown Claude D , Hoyer Mark V , Bachmann Roger W , Canfield Jr Daniel E
Published: April 2011

Nutrient-chlorophyll (CHL) relationships were developed using a large data set collected in Florida over the last 10 years consisting of monthly total phosphorus (TP), total nitrogen (TN), and CHL concentrations from 360 lakes. The precision of these and five additional published relationships was examined. The 95% confidence interval for the best available TP-CHL model is 30-325% of the calculated CHL value. Analysis of associated Florida monthly nutrient and CHL data indicate that the TP-CHL relationship is sigmoid, although a linear response is found for TP concentrations in the range of 3-160 µg·L-1. The maximum CHL responses for a sigmoid curve and straight line are similar for TP concentrations of 3-100 µg·L-1. Both relationships describe P limitation when the CHL response falls on or near the line and provide a benchmark to evaluate other limiting or colimiting factors that are indicated when the CHL response falls below the line. Florida and global data are similar, exhibiting a lessening of slope above a TP concentration of 100 µg·L-1. A global median line is derived from a large population of lake data for use in general lake management.
Predicted impact of zebra mussel (Dreissena polymorpha) invasion on water clarity in Lake Mendota
Authors: Reed-Andersen Tara , Carpenter Stephen R , Padilla Dianna K , Lathrop Richard C
Published: April 2011

Lake Mendota, which is plagued by periodic cyanobacterial blooms, is typical of many lakes in the Laurentian Great Lakes region that are vulnerable to zebra mussels (Dreissena polymorpha) but have yet to be invaded. We coupled removal estimates with chlorophyll production estimates in a dynamic model to predict the likely impact of mussel-mediated removal of phytoplankton on water clarity across a range of hypothetical zebra mussel densities. Models were fit to chlorophyll and temperature data collected biweekly from Lake Mendota during 1977-1993. When we assumed daily epilimnetic circulation, the percentage of days when the chlorophyll concentration exceeded 50 µg·L-1 was decreased threefold at mussel densities as low as 1000 mussels·m-2. When we assumed less frequent epilimnetic circulation, the density of mussels required to substantially improve water clarity increased dramatically. We predict that zebra mussel invasion would lead to increased water clarity in Lake Mendota. Cyanobacterial blooms would be reduced but not eliminated. Negative impacts on other lake processes following zebra mussel invasion could outweigh the benefits of lower phytoplankton concentrations.
Suitability criteria analyzed at the spatial scale of redd clusters improved estimates of fall chinook salmon (Oncorhynchus tshawytscha) spawning habitat use in the Hanford Reach, Columbia River
Authors: Geist David R , Jones Julia , Murray Christopher J , Dauble Dennis D
Published: April 2011

We improved our predictions of fall chinook salmon (Oncorhynchus tshawytscha) habitat use by analyzing spawning habitat at the spatial scale of redd clusters. Spatial point pattern analyses indicated that redd clusters in the Hanford Reach, Columbia River, were consistent in their location from 1994 to 1995. Redd densities were 16.1 and 8.9 redds·ha-1 in 1994 and 1995, respectively, and individual redds within clusters were usually less than 30 m apart. Pattern analysis also showed strong evidence that redds were uniformly distributed within the clusters where interredd distances ranged from 2 to 5 m. Redd clusters were found to occur predominantly where water velocity was between 1.4 and 2 m·s-1, water depth was 2-4 m, and lateral slope of the riverbed was less than 4%. This habitat use represented a narrower range of use than previously reported for adult fall chinook salmon. Logistic regression analysis determined that water velocity and lateral slope were the most significant predictors of redd cluster location over a range of river discharges. Overestimates of available spawning habitat lead to nonachievable goals for protecting and restoring critical salmonid habitat. Better predictions of spawning habitat may be possible if cluster-specific characteristics are used.
Do logging and forest fires influence zooplankton biomass in Canadian Boreal Shield lakes?
Authors: Patoine A , Pinel-Alloul B , Prepas E E , Carignan R
Published: April 2011

Zooplankton biomass was assessed in 20 reference lakes, nine logged-watershed lakes, and nine burned-watershed lakes during three summers following watershed disturbances by logging or wildfires. Biomass of cladocerans, calanoids, cyclopoids, and rotifers was quantified in the 38 lakes for the first year following disturbances. Limnoplankton biomass in four size fractions was quantified during 3 years following disturbances. One year after disturbances, burned-watershed lakes supported 59% more biomass of the rotifer size fraction of limnoplankton (100-200 µm) than reference lakes, while logged-watershed lakes supported 43% less of calanoid biomass. Two years after disturbances, differences in limnoplankton biomass between burned-watershed lakes and reference lakes were more pronounced than during the first year, while logged-watershed lakes supported levels of limnoplankton biomass no different from those of reference lakes. Three years after disturbances, no significant variations could be detected among the three groups of lakes for any of the limnoplankton size fractions. The proportion of watershed area impacted by logging activities was on average less than half the proportion impacted by wildfires. Nonetheless, both types of disturbances seemed to have opposite effects on the zooplankton biomass during the first year, and the effects did not extend beyond 2 years.
Larval fish diversity on the Scotian Shelf
Authors: Shackell N L , Frank K T
Published: April 2011

We examined larval fish diversity on the Scotian Shelf using data, representing 91 genera, collected during the Scotian Shelf Ichthyoplankton Program from 1978 to 1982. Two diversity indices (genus richness (GR) and Shannon's entropy (H)) were relatively lower from December to February-March and relatively higher and stable from April to September-October. Taxon composition changed seasonally. Total median log abundance (log10(number of individuals + 1)·1000 m-3) was low from December to February, increased in March, was stable from April to June, and declined from July to October. Our results suggest that the abundance trends of most taxa were not coincident with either a spring or fall bloom of calanoid copepods. Log GR was significantly positively related to H (r = 0.62, p < 0.001, n = 1853). A negative exponential best described the relationship between log GR and log abundance (R2 = 0.77; log GR = 1.37(1  e-(1.13)(log abundance)), p < 0.001, n = 2357). Shannon's H was not related to log abundance in winter or in summer-fall and was negatively correlated in spring-summer (r = -0.12, p = 0.003, n = 593). Thus, diversity increases with abundance but the composition is dominated by relatively fewer genera at higher levels of abundance. Western - Sable Island banks had higher levels of GR and abundance in all seasons. Additional banks were diverse and productive during warmer months.
Century-long effects of forest harvest on the physical structure and autotrophic community of a small temperate lake
Authors: Scully N M , Leavitt P R , Carpenter S R
Published: April 2011

The effects of forest clearcut and regrowth on a small (8.1 ha) stained lake were studied using a 200-year record of fossil carotenoids and chlorophylls. Comparison of high-resolution cores recovered from exposed, sheltered, and reference lake basins showed that annual laminations of sediments ceased concomitant with logging (ca. 1870-1890), indicating a fundamental change in the lake mixing regime. Biological responses to forest harvest included elimination of deepwater populations of anaerobic photosynthetic bacteria and reduced abundance of metalimnetic chrysophytes. Photosynthetic bacteria remained absent for over 100 years, while sediment laminae and chrysophytes have only returned since around 1970. In contrast, populations of epilimnetic phytoplankton (cyanobacteria, chlorophytes, cryptophytes) were unaffected by the clearcut. Analysis of sediment profiles did not reveal evidence of eutrophication or of increased flux of organic matter following watershed disturbance. Instead, fossil records were most consistent with increased wind stress, leading to deeper water column mixing in fall and reduction in deepwater anoxia, the main factor promoting sediment laminations and populations of photosynthetic bacteria. Such century-long disturbance may be common in small, stratified boreal lakes that lack physical shelter due to landforms.
Multiple lineages of the mitochondrial DNA introgression fromPungitius pungitius(L.) toPungitius tymensis(Nikolsky)
Authors: Takahashi H , Takata K
Published: April 2011

We applied mitochondrial DNA (mtDNA) restriction fragment length polymorphism analysis to trace the maternal lineages and compare the intrapopulation mtDNA variabilities of two ninespine stickleback species, Pungitius pungitius (L.) and Pungitius tymensis (Nikolsky), in which occasional natural hybridization was detected. mtDNA phylogenies constructed by neighbor-joining and Wagner parsimony methods resolved two divergent clades differing by an average nucleotide divergence of 5.94%. All P. pungitius mtDNA haplotypes fall within a single clade. In contrast, P. tymensis appeared paraphyletic; nine of the 13 mtDNA haplotypes found in P. tymensis were grouped within the P. pungitius clade, but the remaining four were of the other clade. The former nine mtDNA variants were very close to the sympatric P. pungitius mtDNA halotypes. These observations suggest that the nine P. tymensis haplotypes originated and introgressed from sympatric P. pungitius and that the introgressed mtDNA haplotypes have a polyphyletic origin in each region. The high incidences of the mtDNA introgression in northern and central Hokkaido may be due to a warmer climate than that of the other regions. The recipient P. tymensis populations had significantly higher mtDNA variation than those observed in the sympatric donor species populations, suggesting the sudden population growth during or after the mtDNA substitution processes.
Modeling relationships between landscape-level attributes and snorkel counts of chinook salmon and steelhead parr in Idaho
Authors: Thompson William L , Lee Danny C
Published: April 2011

Knowledge of environmental factors impacting anadromous salmonids in their freshwater habitats, particularly at large spatial scales, may be important for restoring them to previously recorded levels in the northwestern United States. Consequently, we used existing data sets and an information-theoretic approach to model landscape-level attributes and snorkel count categories of spring-summer chinook salmon (Oncorhynchus tshawytscha) and steelhead (Oncorhynchus mykiss) parr within index areas in Idaho. Count categories of chinook salmon parr were negatively related to geometric mean road density and positively related to mean annual precipitation, whereas those for steelhead parr were negatively related to percent unconsolidated lithology. Our models predicted that chinook salmon parr would be in low count categories within subwatersheds with >1 km·km-2geometric mean road densities and (or) <700 mm mean annual precipitation. Similarly, steelhead parr were predicted to be in low count categories in subwatersheds with >30% unconsolidated lithology. These results provide a starting point for fish biologists and managers attempting to map approximate status and quality of rearing habitats for chinook salmon and steelhead at large spatial scales.
Population effects of shrimp trawl bycatch on Atlantic croaker
Authors: Diamond Sandra L , Cowell Lindsay G , Crowder Larry B
Published: April 2011

We used stage-within-age based matrix models of Atlantic croaker (Micropogonias undulatus) in the Gulf of Mexico and the South and Mid-Atlantic bights to explore the population-level impacts of shrimp trawl bycatch on estuarine-dependent fishes and to investigate tradeoffs between directed adult fisheries and bycatch mortality. The Gulf model reflected a rapidly declining population, while the Atlantic population showed a modest decline. Elasticity analyses indicated that both populations were more sensitive to the summed survival of adults than first-year survival, particularly in the Gulf. Contrary to our expectations, bycatch mortality on late juveniles was not the most important factor affecting either population of Atlantic croaker, and this result was robust to uncertainty in both adult and late juvenile mortality estimates. Both populations were most sensitive to ocean larva mortality, followed by mortality of estuary larvae and adults in the Gulf and of early juveniles and adults in the Atlantic. Nonetheless, bycatch mortality did have a large negative impact on population growth rates, and reducing late juvenile or adult mortality by about 35% in the Gulf or 5% in the Atlantic should reverse population declines. Bycatch reduction devices currently in use can achieve these desired reductions.
Anchovy foraging: simulating spatial and temporal match/mismatches with zooplankton
Authors: Plagányi Éva E , Hutchings Larry , Field John G
Published: April 2011

Prey abundance is only a useful correlate of fish growth rate if it is considered within a match/mismatch hypothesis framework. We developed a model to explore the extent to which the growth rates of juvenile anchovies (Engraulis capensis) are influenced by temporal and spatial match/mismatches with the copepod Calanoides carinatus, a major component of their diet. The distributions of copepods and anchovies are dynamic, so that predation by anchovy may dramatically impact on its prey's spatial distribution. Predation rates by resident fish were commensurate with the average and maximum specific copepod production rates at fish densities of approximately 1 and 3.5 t·km-2, respectively. The spatial arrangement of fish biomass and the temporal overlap between fish and copepod abundances substantially modified both anchovy and copepod growth estimates. Predicted optimal shoal sizes suggest that additional factors such as predator avoidance or the energetics of maintaining school structure may be important. The model emulated observed variability in anchovy growth rates and confirmed the prediction that the availability of high-sustained abundances of food along the West Coast may be a critical "bottleneck" contributing to the strength of recruitment to the South African pelagic purse-seine fishery.
Relationship between gill Na+,K+-ATPase activity and downstream movement in domesticated and first-generation offspring of wild anadromous brown trout (Salmo trutta)
Authors: Aarestrup Kim , Nielsen Christian , Madsen Steffen S
Published: April 2011

The relationship between smolt status and downstream movement following release was investigated in two stocks of hatchery-reared anadromous brown trout (Salmo trutta). Yearlings from a domesticated stock (DS) and first-generation offspring (F1) of wild anadromous trout were held under identical conditions from August 1997 until the following spring, where they developed smolt characteristics as judged from increasing gill Na+,K+-ATPase activity. Presmolts (low Na+,K+-ATPase activity), smolts (high Na+,K+-ATPase activity), and desmolts (regressed Na+,K+-ATPase activity) were released on three occasions into the River Salten. Using both dye-marked and radiotagged fish, downstream movement was monitored by either trapping 3 km downstream (dye-marked fish) or radiotracking on a daily basis. The experiments showed a positive correlation between smolt status (gill Na+,K+-ATPase activity) and downstream movement. Gill Na+,K+-ATPase activity may therefore be used as an indicator of migratory readiness in brown trout. F1 and DS trout had the highest migration frequency when released as presmolts and smolts, respectively. Despite smaller size, F1 trout had similar or better survival than DS trout after release. Our data suggest that initiation of downstream movement is influenced by an interaction between the previous physiological development of the fish and a discrete level of water discharge or water temperature.
Impacts of major watershed perturbations on aquatic ecosystems
Authors: Carignan Richard , Steedman Robert J
Published: April 2011

This Supplement presents data syntheses and new evidence from temperate (primarily boreal) North American studies of aquatic ecosystem response to episodic watershed deforestation and acid rain. These studies confirm the dominant role of the watershed in modulating aquatic response to terrestrial disturbance and quantify important regional differences related to physiography, vegetation, and drainage patterns. Comparisons of watershed disturbance by wildfire and logging revealed both similarities and differences in aquatic impact and underscore the need for ongoing regional evaluation of forest management models based on simulation of natural disturbance patterns. General quantitative impact models are now available but tend to be regional in scope and relevant primarily to water yield and water quality, rather than to habitat and biota.
Rate of chitobiase degradation as a measure of development rate in planktonic Crustacea
Authors: Sastri Akash R , Roff John C
Published: April 2011

We have developed a method to determine development time (molt rate) in both single and mixed populations of crustacean zooplankton based on turnover of the chitinolytic enzyme chitobiase in the ambient medium. We examined the relationship between body size and chitobiase activity released into the medium following molt in three freshwater cladoceran species, Ceriodaphnia spp., Daphnia pulex, and Daphnia magna. Chitobiase activity increased with body length, and a common relationship was observed among all three species (r2= 0.82, p < 0.0001). Under steady-state conditions in laboratory cultures, the rate of decay of this enzyme in the medium was balanced by its rate of production by molting animals. The rate of decay of the enzyme in the absence of animals was therefore also its rate of production, which is a measure of the average rate of development of the crustacean zooplankton community. Development times for a D. magna culture (2×) and a Ceriodaphnia spp. - D. magna mixed culture were 65.4 vs. 62 h, 59 vs. 67 h, and 46.6 vs. 50 h, respectively, as measured by this "chitobiase method" versus conventional molt rate determinations.
Incorporation of strontium, cadmium, and barium in juvenile spot (Leiostomus xanthurus) scales reflects water chemistry
Authors: Wells Brian K , Bath Gretchen E , Thorrold Simon R , Jones Cynthia M
Published: April 2011

We investigated the hypothesis that strontium:calcium (Sr:Ca), cadmium:calcium (Cd:Ca), and barium:calcium (Ba:Ca) composition in scales reflects that of the ambient seawater in which fish were reared under controlled experimental conditions. Juvenile spot (Leiostomus xanthurus) were held in replicate tanks containing four different concentrations of Sr, Cd, and Ba maintained at either 20 or 25°C for a total of 42 days. The elemental composition of scales from these fish was analyzed at the termination of the experiment, using isotope dilution inductively coupled plasma mass spectrometry (ICP-MS). Sr, Cd, and Ba levels in the scales, expressed as ratios to Ca, were linearly related to environmental concentrations, indicating that the elements were incorporated in constant proportions to levels in the ambient water. Temperature had no measurable effect on the uptake of Sr, Cd, or Ba into the scales. Finally, Sr:Ca and Ba:Ca ratios in scales were highly correlated with levels in the otoliths from the same treatment. In all, Sr:Ca, Cd:Ca, and Ba:Ca signatures in scales appear to be representative of the ambient environment and, therefore, may be useful for quantifying life-history characteristics of individual fish.
Environmental constraints on the lipid composition and metabolism of euphausiids: the case ofEuphausia superbaandMeganyctiphanes norvegica
Authors: Mayzaud P , Albessard E , Virtue P , Boutoute M
Published: April 2011

Antarctic (Euphausia superba) and northern krill (Meganyctiphanes norvegica) are characterised by large-scale spatial distributions. Euphausia superba is limited to the Southern Ocean, while M. norvegica is present from the Arctic Ocean to the Mediterranean Sea. Euphausia superba structural lipids showed little mesoscale variability. Specific differences between phosphatidylcholine and phosphatidylethanolamine fatty acid composition exceeded variability related to sampling stations. On a larger scale (Southern Ocean), fatty acid composition of both total polar lipids and phosphatidylcholine confirmed the reduced level of regional variability. Similar comparisons between female M. norvegica collected at two extreme sites in terms of temperature regime (Kattegat and Ligurian Sea) during two seasons (spring-summer and fall-winter) suggested a more complex picture. Levels of phosphatidylethanolamine, lysophosphatidylcholine, and diphosphatidylglycerol showed significant differences between sites. During spring- summer, a lower content of phosphatidylethanolamine and lysophosphatidylcholine was observed for the Ligurian Sea population. Fatty acid composition of total polar lipids was significantly different at both sites. Comparisons between spring-summer populations at both sites showed higher percentages of 22:6n-3 and a lower content in saturated and monoenoic acids for the Ligurian Sea, suggesting some degree of adaptation to temperature regime.
Interpreting the collapse of the northern cod stock from survey and catch data
Authors: Shelton P A , Lilly G R
Published: April 2011

Sequential population analysis reconstructions of the northern cod (Gadus morhus) stock using survey and catch data formed the basis for the scientific advice for substantial reductions in catch quotas in the late 1980s. However, the model failed to provide acceptable reconstructions of the population in subsequent stock assessments when data for the 1990s were added. The model assumes constant age-independent instantaneous rate of natural mortality, accurate catch reporting, and a constant linear relationship between the survey index at age and the population size at age. It seems likely that one or more of these assumptions failed to hold around the time of the collapse. Diagnostic studies were carried out to determine the magnitude of the departure from the assumptions required to allow the model to fit the data. Information related to changes in natural mortality, fishing activity, and survey catchability is reviewed to evaluate the plausibility of departures from model assumptions of the magnitude estimated. It is concluded that unreported deaths caused by the offshore fishery may be most plausible as the main contributing factor to lack of model fit but that factors such as increased natural mortality, and possibly changes in survey catchability, also played a role.
Spatial components of bowhead whale (Balaena mysticetus) distribution in the Alaskan Beaufort Sea
Authors: Schick R S , Urban D L
Published: April 2011

Bowhead whales (Balaena mysticetus) on their fall migration are exposed to oil exploration activities in the Alaskan Beaufort Sea. While previous research into the effect of industrial noise on whale behavior and distribution has noted significant responses, this research has often proceeded from a parametric statistical framework. To account for the presence of spatially autocorrelated and intercorrelated data, we propose a suite of spatial analysis techniques to assess the distribution of bowhead whales relative to oil exploration activities. Using random resampling techniques and Mantel tests, we analyzed the distribution of bowhead whales around active drilling rigs in 1993. Results from the resampling tests indicated that whales were distributed farther from the drilling rig than they would be under a random scenario. Results from the Mantel tests indicated that in 1993, the spatial pattern of bowhead whale distribution was highly correlated with distance from the drilling rig, indicating that the presence of the drilling rig resulted in a significant temporary loss in available habitat. These techniques offer a new perspective on spatial analysis in the marine realm.