bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial variation in environmental characteristics of Atlantic salmon (Salmo salar) rivers
Authors: Elliott Scott R , Coe Treva A , Helfield James M , Naiman Robert J
Published: April 2011

Rivers and streams occupied by anadromous Atlantic salmon (Salmo salar) occur across a diverse array of landscapes. This article describes the general ecology of these rivers and streams, including many of the physical and biological variables that are important characteristics of all lotic systems. For analytical purposes, the geographic range of Atlantic salmon rivers is divided into five regions, based on geomorphology and climate. The physical habitat available to anadromous Atlantic salmon is diverse. The geology varies from granitic bedrock to volcanic and glacial substrates, which influence a broad array of other ecological variables, ranging from water chemistry to catchment morphology (e.g., river length). Flood regimes and system hydrology are dependent, as expected, on climate. Many of the catchments receive substantial precipitation in the form of snow; rivers in four of the five regions experience primarily spring freshets. Aquatic temperatures are also variable, representing close to the full range of thermal tolerance of S. salar, with lows just above 0°C in the northernmost latitudes to summer highs in western Europe approaching 25°C. Most rivers are best characterized as oligotrophic with relatively low annual primary productivity. However, physical factors such as availability of suitable spawning and rearing habitat, as well as aquatic temperature and flow regimes, may drive anadromous productivity. In general, most of the rivers have been modified by flow regulation and many suffer from impacts related to other anthropogenic disturbances, principally riparian forest clearing for agriculture, forestry, and urban development. We conclude that the rivers and streams occupied by anadromous Atlantic salmon are diverse across the species' range and have been heavily impacted by anthropogenic disturbances.
Interspecific competition and juvenile Atlantic salmon (Salmo salar): on testing effects and evaluating the evidence across scales
Authors: Fausch Kurt D
Published: April 2011

A review of 17 controlled experiments of interspecific competition between juveniles of Atlantic salmon (Salmo salar) and other fishes revealed relatively little evidence to judge competitive effects at any scale. More than half were unreplicated and so inadequate to test either the existence or relative strength of interspecific competition. Most replicated experiments used one of two designs appropriate to address questions of interest, such as whether nonnative species affect Atlantic salmon via competition or whether interspecific competition from coevolved salmonids is greater than intraspecific competition. Replicated experiments spanned a broad range of spatial and temporal scales, and one well-designed field experiment yielded the strongest inference at useful scales. Nonnative salmonids being introduced worldwide into Atlantic salmon waters have the potential to invade, so experiments testing their effects are most urgently needed. Overall, juvenile coho salmon (Oncorhynchus kisutch) are suspected to have the greatest effect, partly due to their inherent size advantage. The potential for complex interactions or indirect effects to modify effects of nonnative species is completely unknown but may be important and needs investigation.
The marine phase of the Atlantic salmon (Salmo salar) life cycle, with comparisons to Pacific salmon
Authors: Hansen L P , Quinn T P
Published: April 2011

Atlantic salmon (Salmo salar) are distributed over large areas in the north Atlantic Ocean. They usually move very quickly from freshwater to oceanic areas, whereas there is considerable variation among Pacific salmon in early marine movements. In some areas, Atlantic salmon of exploitable size are sufficiently abundant that commercial high seas fisheries have developed. Such areas are off west Greenland, where North American and European fish are harvested, and in the Norwegian Sea, north of the Faroe Islands, where mainly European fish are exploited. Atlantic salmon feed on a wide range of large crustaceans, pelagic fish, and squid in the marine environment, supporting the hypothesis that Atlantic salmon are opportunistic feeders. In the ocean the salmon grow relatively quickly and the sea age when they become sexually mature depends on both genetics and on growing conditions. Natural marine mortality of salmon is highest during the first few months at sea and the major mortality factor is probably predation. However, marine mortality of Atlantic salmon has increased in recent years, apparently correlated with a decline in sea surface temperatures. Similar relationships between environmental conditions and the growth and survival of Pacific salmon have been reported. Atlantic salmon life histories most closely mimic stream-type chinook salmon or steelhead trout among the Pacific species. Finally, Atlantic and Pacific salmon return to their home rivers with high precision and possible mechanisms controlling the oceanic homing migration are presented and discussed.
Implications of temporal and spatial scale for Atlantic salmon (Salmo salar) research
Authors: Folt Carol L , Nislow Keith H , Power Mary E
Published: April 2011

The Atlantic salmon (Salmo salar) is a model species for studying scale issues (i.e., the extent, duration, and resolution of a study or natural process) in ecology. Major shifts in behavior and habitat use over ontogeny, along with a relatively long life span and large dispersal and migration distances, make scale issues critical for effective conservation, management, and restoration of this species. The scale over which a process occurs must be linked to the research design and we illustrate this with a discussion of resource tracking by Atlantic salmon. Identifying scale inconsistencies (e.g., when a process is evident at one scale but not another) is shown to be an effective means by which some scale-dependent processes are understood. We review the literature to assess the temporal and spatial scales used in Atlantic salmon research and find most current studies appear to sacrifice spatial and temporal extent for increased resolution. Finally, we discuss research strategies for expanding the temporal and spatial scales in salmon research, such as conducting multiple scales studies to elucidate scale inconsistencies, identifying mechanisms, and using techniques and approaches to generalize across studies and over time and space.
40Ar/39Ar ages of detrital muscovite within Lower Cambrian and Carboniferous clastic sequences in northern Nova Scotia and southern New Brunswick: implications for provenance regions
Authors: Dallmeyer R. D. , Keppie J. D. , Nance R. D.
Published: April 2011

Detrital muscovite from lowermost Cambrian sequences exposed in the Avalon Composite Terrane in Nova Scotia and New Brunswick record 40Ar/39Ar plateau ages of ca. 625–600 Ma. These are interpreted to date times of cooling in source areas. The regional distribution of coarse-grained detrital muscovite in Lower Cambrian rocks of Avalonian overstep sequences suggests a source region of dimensions considerably larger than any presently exposed in Appalachian segments of the Avalon Composite Terrane. Late Proterozoic tectonic reconstructions locate the Avalon Composite Terrane adjacent to northwestern South America, thereby suggesting a possible source within Late Proterozoic PanAfrican – Brasiliano orogens. Detrital muscovite from clastic sequences of the proximally derived, Lower Carboniferous (Tournaisian) Horton Group and the more distal Upper Carboniferous (Westphalian D – Stephanian) Pictou Group in Nova Scotia records 40Ar/39Ar spectra that define plateau ages of ca. 390–380 Ma (Horton Group) and and ca. 370 Ma (Pictou Group). Finer grained fractions from samples of the Horton Group display more internally discordant age spectra defining total-gas ages of ca. 397–395 Ma. A provenance for the finer muscovite may be found in southern Nova Scotia where Cambrian–Ordovician turbidites of the Meguma Group display a regionally developed micaceous cleavage of this age. The ca. 390–380 Ma detrital muscovites probably were derived from granite stocks presently exposed in proximal areas of northernmost Cape Breton Island. A more distal source for the ca. 370 Ma detrital muscovites in the Pictou Group is suggested by its original extensive distribution, although a local, possibly recycled, source may also have been present. The presence of only 400–370 Ma detrital muscovite suggests a rapidly exhumed orogenic source with characteristics similar to those of crystalline rocks presently exposed in the Cape Breton Highlands and (or) the Meguma Terrane.
The role of gravity and magma in the structural evolution of a deformed Archean volcanic centre, Timmins, Ontario, Canada
Authors: Beavon Roy V.
Published: April 2011

A deformed bimodal subaqueous volcanic centre in the western Archean Abitibi Subprovince of the Canadian Shield contains structures comparable with those of relatively undisturbed igneous complexes. Similarities include an annular fold pattern initiated by structural doming and downsagging of basaltic flows prior to the terminal felsic volcanism. During this cycle an ancestral dome was ruptured by a northeasterly regional graben defined by fossil fault scarps preserved beneath the terminal volcanic deposits. Fissure vents developed along the northwest boundary of the graben, gradually drained the underlying magma chamber, and transformed the crest of the dome into a central collapse basin surrounded by an annular anticlinal uplift marking the inner periphery of the former dome. Basalts on the basinward side of the fissure vents became detached along interflow argillites and glided into the central collapse, forming secondary gravity folds within the uppermost basalts. Subaqueous deposition of felsic debris occurred in the graben and subsiding collapse basin, succeeded by postvolcanic turbidites. The annular folds were modified by two phases of regional deformation, separated by an episode of Archean molasse sedimentation along the reactivated south boundary of the paleograben.
The Late Wisconsinan deglacial history of the east-central Taseko Lakes area, British Columbia
Authors: Huntley David H. , Broster Bruce E.
Published: April 2011

Late Wisconsinan Fraser Glaciation retreat-phase deposits and landforms in the east-central Taseko Lakes area, British Columbia, are used to demonstrate a four-phase model of deglaciation. During phase I, at the onset of ice retreat, the Cordilleran Ice Sheet occupied much of the study area, blocking southward drainage of Fraser River. Phase II was marked by the deglaciation of uplands and plateaux. Meltwater drainage patterns were controlled by stagnating glaciers confined to valleys. Phase III commenced as remnant ice in the Fraser Valley downwasted to between 850 and 760 m elevation. At this time, interlobate glacial lakes formed in hanging valleys east of Fraser River. Drainage of glacial lakes occurred subglacially, and was accompanied by disintegration of remnant ice and an increase in mass movements in valleys. These events were followed by decreased sedimentation rates, reflecting lower meltwater volumes and exhaustion of unstable glacial debris during phase IV. Postglaciation valley fill was subject to fluvial degradation and terracing as modern drainage patterns became established.
Tectonic and paleogeographic significance of Late Ordovician conodonts in the Canadian Appalachians
Authors: Nowlan Godfrey S. , McCracken Alexander D. , McLeod Malcolm J.
Published: April 2011

Conodonts of Late Ordovician age are well represented in Laurentian parts of eastern Canada, but are rare in the Appalachian orogenic belt. They are known from the Anticosti Basin, the Matapedia Belt, and the Exploits Subzone of the Dunnage Zone. Two new discoveries are described: one from unnamed strata on Markey Brook, west-central New Brunswick, and one from the Goss Point Formation (Avalon Zone, southwestern New Brunswick). Faunas from the Anticosti Basin are of undoubted Midcontinent Faunal Region affinity. Those from the Matapedia Belt are highly mixed both paleoecologically and provincially, containing elements of shallow- and deep-water Midcontinent affinity and elements typical of the Atlantic Faunal Region. Faunas from the Exploits Subzone and Markey Brook are also mixed, suggesting endemic faunas of Atlantic affinity with local influx of Midcontinent faunas from Laurentia. The Goss Point Formation, previously believed to belong to the Mascarene Group (a Silurian cover sequence on the Avalon Zone), also yields mixed faunas. Provincial mixing of all faunas east of the Anticosti Basin suggests that Late Ordovician faunas around Iapetus Ocean may have been more homogeneous than earlier Ordovician faunas. Therefore, the Iapetus Ocean may have been smaller or current patterns may have changed to permit trans-Iapetan migration. A strong global pattern of provincialism for Late Ordovician conodonts is recognized and a new Australasian Province is proposed. Conodonts permit identification of a previously unrecognized Ordovician volcano-sedimentary succession that has economic and tectonic implications for the region.
Distribution shifts and overfishing the northern cod (Gadus morhua): a view from the ocean
Authors: Rose G A , deYoung B , Kulka D W , Goddard S V , Fletcher G L
Published: April 2011

Research on northern cod (Gadus morhua) from 1983 to 1994 indicated that a southward shift in distribution in the early 1990s was real and not an artifact of sequentially fishing down local populations. In the early 1990s, seasonal fishery and survey data showed distribution changes where there was no fishery, and large tonnage and densities (450 000 t, densities fourfold higher than 1980s levels) appeared in the south concurrent with declines in the north. All fishery, acoustic, and trawl survey indices increased in the south, while the stock declined. Southern-caught cod in the early 1990s exhibited northern characteristics: (i) antifreeze production capacities above historical norms and equivalent to those of northern fish, (ii) vertebral counts above historic norms and equalling northern counts, and (iii) declines in size-at-age to levels associated with northern fish. The cause of the shift is thought to be a combination of abiotic (climate) and biotic (capelin (Mallotus villosus)) environmental changes and cumulative long-term fisheries effects on cod behavior. The shifted distributions increased vulnerability to Canadian and foreign fisheries and led to a rapid decline in abundance, both before and after the moratorium on fishing in Canadian waters in 1992. Rebuilding will occur in three steps: environmental restoration, recolonization by adults, and enhanced recruitment across the shelf.
Response of yellow perch (Perca flavescens) in Oneida Lake, New York, to the establishment of zebra mussels (Dreissena polymorpha)
Authors: Mayer C M , VanDeValk A J , Forney J L , Rudstam L G , Mills E L
Published: April 2011

We used long-term data on Oneida Lake, New York, to evaluate hypotheses about the effects of introduced zebra mussels (Dreissena polymorpha) on yellow perch (Perca flavescens). We detected no change in survival, diet, or numbers of young-of-the-year (YOY) yellow perch. YOY growth increased in association with zebra mussel introduction and was marginally correlated with zooplankton size, which increased after zebra mussel introduction. Low numbers of YOY in recent years did not explain their increased growth rate. The percentage of age 3 and older yellow perch that consumed zooplankton and benthos increased after zebra mussel introduction. Water clarity, which has increased since zebra mussel introduction, was inversely related to the percentage of the adult population with empty stomachs and positively related to the percentage that consumed benthos. The percentage of adult yellow perch that consumed zooplankton was positively related to zooplankton size. Despite the increase in percentage of adults consuming both types of invertebrate prey, we detected no changes in adult growth associated with zebra mussel introduction. This suggests that the principal effects of zebra mussels on yellow perch in Oneida Lake were not via benthic pathways but through modifications of water clarity and zooplankton. Thus far, these effects have not been negative for the yellow perch population.
Variations in pallial organs and eulatero-frontal cirri in response to high particulate matter concentrations in the oyster Crassostrea gigas
Authors: Barillé Laurent , Haure Joël , Cognie Bruno , Leroy Anne
Published: April 2011

Variations in gill, palp, and adductor muscle areas and in the length and spacing of eulatero-frontal cirri (EFC) were investigated in specimens of the Japanese oyster (Crassostrea gigas) within the same bay in two nearby sites (15 km) differing in turbidity. Significant variations occurred on a small geographical scale. In particular, individuals from the higher turbidity zone had smaller gills and larger labial palps. For a standard oyster (1 g dry body weight), gill area was 25% larger in oysters from the low-turbidity zone, while palp area was 66% larger in oysters from the high-turbidity zone. No difference was observed for total adductor muscle area. Intersite differences in the mean length of EFC and in the distance between two adjacent cirri sampled on ordinary filaments in the midregion of the gill were studied by image analysis. Cirri tended to be longer and more evenly spaced in oysters from the higher turbidity zone, although differences were not significant at the 5% probability level. The geometric characteristics of the EFC were apparently not modified in response to high turbidity, although the wide individual variability observed may have prevented detection of ciliary adaptation.
Coho salmon (Oncorhynchus kisutch) transgenic for a growth hormone gene construct exhibit increased rates of muscle hyperplasia and detectable levels of differential gene expression
Authors: Hill James A , Kiessling Anders , Devlin Robert H
Published: April 2011

Transgenic coho salmon (Oncorhynchus kisutch) containing a growth hormone gene construct were compared with nontransgenic coho salmon in terms of gross anatomy, muscle cellularity, muscle enzyme activity, and differential gene expression. Transgenic fish were found to have significantly higher numbers of small-diameter muscle fibres in both the dorsal and lateral region of the somitic muscle, suggesting that they grow by greater rates of hyperplasia relative to slower growing nontransgenic fish. Higher levels of activity were found for phosphofructokinase and cytochrome oxidase in white muscle of the transgenic fish. This difference indicates a higher glycolytic and aerobic requirement in the muscle of transgenic fish. Subtractive hybridisation of muscle RNA of transgenic fish from control fish provided a library of cDNAs whose expression is upregulated in the transgenic fish. This library contains genes that may be involved in, or related to, both high growth rates and muscle hyperplasia. We have sequenced a number of fragments and have found a preponderance of myosin light chain 2 mRNAs, consistent with a putative high level of expression in the early stages of muscle fibre construction.
Natural mortality from poor condition in Atlantic cod (Gadus morhua)
Authors: Dutil Jean-Denis , Lambert Yvan
Published: April 2011

The extent of energy depletion was assessed in Atlantic cod (Gadus morhua) in spring and early summer (1993-1995) to assess relationships between poor condition and natural mortality. Several indices of condition were compared in wild fish in the northern Gulf of St. Lawrence and in fish exposed to a prolonged period of starvation in laboratory experiments. Discriminant analyses classified only a small fraction of the wild fish as similar to cod that did not survive and a much larger fraction as similar to cod that survived starvation. This percentage increased from April to May and peaked in June 1993 and 1994. Condition factor and muscle somatic index allowed a clear distinction between live and dead fish. Muscle lactate dehydrogenase activity suggested that cod had experienced a period of negative growth early in 1993, 1994, and 1995. Fish classified as similar to starved individuals were characterized by a higher gonad to liver mass ratio than others. Reproduction may have a negative impact on survival not only in spring but also later into summer, as some individuals were found not to have recovered by late summer. This study shows that natural mortality from poor condition contributed to lower production in the early 1990s.
Predicting fish abundance using single-pass removal sampling
Authors: Mitro Matthew G , Zale Alexander V
Published: April 2011

Three-pass removal data for juvenile rainbow trout (Oncorhynchus mykiss) along bank areas of the Henrys Fork of the Snake River, Idaho, were used to construct a mean capture probability (MCP) model to predict abundance from single-pass catch data. We evaluated the MCP model by simulation. The precision of the MCP model was poor when predicting abundance within a specific bank unit. MCP model prediction intervals were about 7.5 times greater than three-pass removal intervals. However, the MCP model performed about the same as three-pass removal for predicting total abundance in a river section from multiple bank samples. We evaluated how the MCP model can be used to improve precision of total abundance estimates. Reallocating effort to sample 150 bank units by single-pass removal rather than 50 bank units by three-pass removal resulted in a 48% increase in prediction interval precision for a simulated population of 10 000 fish. Precision also increased when allocating effort to sampling more bank units of smaller length versus fewer bank units of longer length. Sampling 1500 m of bank as one hundred 15-m bank units increased precision by about 28% versus sampling fifty 30-m bank units and by about 50% versus sampling twenty-five 60-m bank units.
Patterns in fish species composition across the interface between streams and lakes
Authors: Willis Theodore V , Magnuson John J
Published: April 2011

We compared fish species compositions among four site types (lake, lake mouth, stream mouth, stream) along the gradient from stream to lake for 12 tributary mouths. Comparison of species richness, rarefaction species diversity, and species density all supported the same pattern: stream-mouth sites contained the highest number of species, followed by stream sites, lake-mouth sites, and lake sites, even though lake and lake-mouth sites yielded more individuals and were larger in area and volume. Principal components analysis formed three clusters of mixed sites based on similarities in dominant fish species rather than designations of lake, lake mouth, etc. Rank order assemblage tests revealed that species composition of tributary-mouth sites was similar in only one quarter of the systems sampled; other systems showed a transition from "lake" to "stream" species compositions at or near the tributary mouth. Species assemblage comparisons within site types between systems revealed low consistency in the composition of stream-mouth sites and high consistency for the other site types. We concluded that the tributary mouth fits the definition of an ecotone and speculate that the difference in hydrologic and geomorphic properties of streams and lakes played a role in the patterns that we saw on either side of the tributary mouth.
Seasonality in phosphorus release rates from the sediments of a hypereutrophic lake under a matrix of pH and redox conditions
Authors: Penn Michael R , Auer Martin T , Doerr Susan M , Driscoll Charles T , Brooks Carol M , Effler Steven W
Published: April 2011

Phosphorus release rates were measured on intact sediment cores collected from the major depositional basin of Onondaga Lake, a dimictic, calcareous, hypereutrophic system in Syracuse, N.Y., U.S.A. Release experiments were conducted under a matrix of redox and pH conditions to investigate the importance of Ca- and Fe-related physicochemistry on sediment cores collected seasonally, i.e., during the spring, summer, fall, and winter periods. Strong seasonal variation in P release was observed, with rates ranging from ~3 to 38 mg P·m-2·day-1. This variation is attributed to changes in redox status and P concentration gradients at the sediment-water interface. An oxidized microlayer at the sediment-water interface partially inhibits sediment P release under isothermal, well-mixed conditions in the spring and fall. Phosphorus trapped in the oxic microlayer (sorption) is freed when the microlayer is chemically reduced at the onset of anoxia and high P release rates are observed. The oxidized microlayer serves to regulate seasonality in rates of sediment P release but does not influence long-term sediment-water exchange. It is proposed that the long-term P release process is best represented by a time-weighted annual average rate, calculated here to be ~10 mg P·m-2·day-1.
Bioaccumulation and differential partitioning of polychlorinated biphenyls in freshwater, planktonic food webs
Authors: Berglund Olof , Larsson Per , Ewald Göran , Okla Lennart
Published: April 2011

The planktonic food chain phytoplankton - zooplankton - young-of-the-year roach (Rutilus rutilus) was studied in 19 lakes in southern Sweden to investigate the bioaccumulation of polychlorinated biphenyls (PCBs). The ΣPCB concentrations did not steadily increase with increasing trophic level. The ΣPCB concentrations in zooplankton (400 ng·g lipid-1) were lower than in both phytoplankton (660 ng·g lipid-1) and fish (890 ng·g lipid-1), which did not differ significantly. Lipid content explained 40% of the total variation in dry weight normalised ΣPCB concentrations in the samples. The PCBs were differentially partitioned between the trophic levels. The logBMFs (biomagnification factors, concentration in predator/concentration in prey) were a function of the logKowof the PCB congeners. The logBMFzoo/phytovalues were < 0 for all PCB congeners on a lipid weight basis, and the logBMFfish/zoovalues were < 0 for PCB congeners with logKow> 6. We conclude that no PCBs had higher lipid-normalised concentrations in zooplankton than in phytoplankton and the most lipophilic PCBs had moderately higher concentrations in roach than in zooplankton. PCBs with logKow> 6 decreased in concentration from phytoplankton to zooplankton to roach. We suggest that the concept of biomagnification did not apply to the planktonic food chain investigated in these lakes.
Comparison of techniques of back-calculation of growth and settlement marks from the otoliths of three species ofDiplodusfrom the Mediterranean Sea
Authors: Vigliola Laurent , Harmelin-Vivien Mireille , Meekan Mark G
Published: April 2011

We developed a model of back-calculation of fish size from otoliths that could accommodate both changes in the relationship between otolith and somatic growth that occur through time and variation in growth rates among individuals. We used this model to back-calculate estimates of size and growth from otoliths of three species of Diplodus from the Mediterranean Sea. The outcomes of our model were compared with those of three other models and with growth curves estimated directly from populations of fish in the field. We found that our new model produced estimates of size-at-age that were closer to those observed in the field than the biological intercept, time-varying growth, and body proportional models. Comparison of profiles of increment width from otoliths of newly settled and juvenile Diplodus puntazzo and Diplodus vulgaris showed that these species formed a settlement mark, where increment width declined at settlement. In contrast, a settlement mark was not evident in the otoliths of Diplodus sargus. However, settlement of all species coincided with a sharp decline in somatic growth rate. Thus, growth rate may provide a means of estimating the timing of settlement in species that do not display a marked change in increment width.
Comparisons within and between years resulting in contrasting recruitment of Pacific hake (Merluccius productus) in the California Current System
Authors: Mullin Michael M , Goetze Erica , Beaulieu Stace E , Lasker Jacqueline M
Published: April 2011

In a search for correlates and possible causes of the difference in recruitment success of Pacific hake (Merluccius productus) of the 1981 and 1984 year-classes, we analyzed (by optical plankton counter) the distribution into sizes of preserved zooplankton samples from stations with and without larval hake in winter and spring of these two years. We also assessed the onshore/offshore distributions of larvae, potential for geostrophic and Ekman transport, and their overall survival rates. Cluster analyses of biovolume spectra led to the development of a simple ratio of "medium" to "small + large" zooplankton that statistically separated stations within a year where larval hake were likely to be found from those where they were unlikely to be found. This biovolume ratio was independent of temperature, and the same ratio statistically distinguished stations where larval hake tended to occur in spring 1998. However, we found no property or process that might explain why the 1984 year-class was spectacularly successful.
A stable isotope evaluation of the structure and spatial heterogeneity of a Lake Superior food web
Authors: Harvey Chris J , Kitchell James F
Published: April 2011

We used stable isotope analysis to derive trophic relationships and movement patterns for components of the western Lake Superior food web. Trophic linkages implied by previous gut content studies were only marginally supported by stable isotope data. Siscowet lake trout (Salvelinus namaycush siscowet) were the top predators, and trophic overlap between siscowet and lean lake trout (Salvelinus namaycush) was low. Exotic Pacific salmon (Oncorhynchus spp.) occupied a lower trophic position than native piscivores because the latter relied more on coregonids. To evaluate spatial heterogeneity of the food web, we assumed that the adjacent cities of Duluth and Superior (DS) were a point source of 15N, and we measured isotopes of organisms close to and far from DS. Slimy sculpin (Cottus cognatus) were enriched in the DS area relative to other sites, implying that they are relatively sedentary. Rainbow smelt (Osmerus mordax) showed no differences at any sites, implying high vagility. Other organisms showed differences that could not be attributed to DS, implying that other mechanisms, such as trophic ontogeny, were influencing their isotopic signatures.
Trophic cascades in streams: effects of nutrient enrichment on autotrophic and consumer benthic communities under two different fish predation regimes
Authors: Biggs Barry JF , Francoeur Steven N , Huryn Alexander D , Young Roger , Arbuckle Christopher J , Townsend Colin R
Published: April 2011

We tested the hypothesis that differences in top-level predators could mediate the importance of top-down versus bottom-up forces in stream food chains using three streams dominated by Galaxias (fish native to New Zealand) and three dominated by brown trout (Salmo trutta) (an introduced species). These two fish species have quite different predation strategies and energetic requirements. Periphyton in the Galaxias streams formed relatively low biomass (indicative of high invertebrate grazing), whereas periphyton in two of the three trout streams formed relatively high biomass (indicative of lower grazing pressure). Periphyton biomass response to inorganic nutrient enrichment varied by fish type. Invertebrate densities on artificial substrates were higher in the Galaxias streams, with the exception of chironomids. Nutrient enrichment of periphyton led to increases in total invertebrate densities, but these increases were greater in the Galaxias streams where invertebrate predation was thought to be lower. Our results suggest that the specific feeding behavior traits of the consumers should be considered when investigating trophic cascades or predicting effects of bottom-up nutrient enrichment on autotrophy.
In situ survival and growth of three brook trout (Salvelinus fontinalis) strains subjected to acid conditions of anthropogenic origin at the egg and fingerling stages
Authors: Lachance Stephanie , Bérubé Pierre , Lemieux Michel
Published: April 2011

Tolerance to naturally acidic conditions of a Côte-Nord brook trout (Salvelinus fontinalis) strain (Arseneault strain, presumed acid tolerant) does not appear completely genetically mediated, since this tolerance was not evident when the fish were subject to acid conditions of anthropogenic origin. Three wild brook trout strains, at the egg and fingerling stages, were exposed in the field to waters acidified by atmospheric deposition of anthropogenic origin as well as to natural waters typical of the region. Although egg mortality was significantly higher in acid (61.0-85.6%) than in reference (6.3-20.8%) conditions, no differences between strains were noted. Residual density 1 year after stocking with fingerlings was significantly higher (by 56%) in the reference lake than in the acid lake, but differences between strains did not follow any clear tendency. While overall growth was greater in the acid environment, weight yield was lower except for the Arseneault strain. Variations pertaining to gonadosomatic index and percent mature individuals in both males and females seemed linked more to differences in growth than to chemical conditions. Developing a permanent reintroduction program with the Arseneault strain to counter losses of brook trout populations due to acid precipitation in Québec does not appear justified at this time.
Cross-tributary analysis of parr to smolt recruitment of Atlantic salmon (Salmo salar)
Authors: Whalen Kevin G , Parrish Donna L , Mather Martha E , McMenemy James R
Published: April 2011

We used estimates of Atlantic salmon (Salmo salar) parr and smolt density, estimated in three tributaries of the West River, Vermont, U.S.A., to determine (i) if smolt recruitment is density dependent or independent of parr density, (ii) if the proportion of parr migrating as smolts and cohort survival differ among tributaries, and (iii) the effect of parr maturity on smolt production and recruitment variability. We found that parr to smolt recruitment was best described with a linear function providing no evidence for density dependence in the recruitment dynamics of parr and smolts at the tributary scale. The proportion of age-1 parr recruiting to age-2 smolts did not systematically differ among tributaries or years (overall mean ± 95% CL: 18 ± 11%, range = 9-37%), and mean age-1 to age-2 survival ranged less than twofold among tributaries (27-46%) and was independent of cohort density. Survival of age-1 mature (39%) and immature (33%) parr was similar, but probability of smolting for mature parr (0.21) was threefold less than for immature parr (0.76). Quantifying smolt recruitment pathways involving parr maturation helped elucidate the population-level effect of parr maturation on smolt production and recruitment variability.
Population genetics, phylogeography, and systematics of the thornyhead rockfishes (Sebastolobus) along the deep continental slopes of the North Pacific Ocean
Authors: Stepien Carol A , Dillon Alison K , Patterson Amy K
Published: April 2011

Population genetic, phylogeographic, and systematic relationships are elucidated among the three species comprising the thornyhead rockfish genus Sebastolobus (Teleostei: Scorpaenidae). Genetic variation among sampling sites representing their extensive ranges along the deep continental slopes of the northern Pacific Ocean is compared using sequence data from the left domain of the mtDNA control region. Comparisons are made among the shortspine thornyhead (S. alascanus) (from seven locations), the longspine thornyhead (S. altivelis) (from five sites), which are sympatric in the northeast, and the broadbanded thornyhead (S. macrochir) (a single site) from the northwest. Phylogenetic trees rooted to Sebastes show that S. macrochir is the sister taxon of S. alascanus and S. altivelis. Intraspecific genetic variability is appreciable, with most individuals having unique haplotypes. Gene flow is substantial among some locations and others diverged significantly. Genetic divergences among sampling sites for S. alascanus indicate an isolation by geographic distance pattern. Genetic divergences for S. altivelis are unrelated to the hypothesis of isolation by geographic distance and appear to be more consistent with the hypothesis of larval retention in currents and gyres. Differences in geographic genetic patterns between the species are attributed to life history differences in their relative mobilities as juveniles and adults.
Hyporheic discharge of river water into fall chinook salmon (Oncorhynchus tshawytscha) spawning areas in the Hanford Reach, Columbia River
Authors: Geist David R
Published: April 2011

Fall chinook salmon (Oncorhynchus tshawytscha) spawned predominantly in areas of the Hanford Reach of the Columbia River where hyporheic water discharged into the river channel. This upwelling water had a dissolved solids content (i.e., specific conductance) indicative of river water and was presumed to have entered highly permeable riverbed substrate at locations upstream of the spawning areas. Hyporheic discharge zones composed of undiluted ground water or areas with little or no upwelling were not used by spawning salmon. Rates of upwelling into spawning areas averaged 1200 L·m-2·day-1 (95% CI = 784-1665 L·m-2·day-1) as compared with approximately 500 L·m-2·day-1 (95% CI = 303-1159 L·m-2·day-1) in nonspawning areas. Dissolved oxygen content of the hyporheic discharge near salmon spawning areas was about 9 mg·L-1 (±0.4 mg·L-1) whereas in nonspawning areas, dissolved oxygen values were 7 mg·L-1 (±0.9 mg·L-1) or lower. In both cases, dissolved oxygen of the river water was higher (11.3 ± 0.3 mg·L-1). Physical and chemical gradients between the hyporheic zone and the river may provide cues for adult salmon to locate suitable spawning areas. This information will help fisheries managers to describe the suitability of salmon spawning habitat in large rivers.
Spatial and dietary overlap in the Georges Bank groundfish community
Authors: Garrison Lance P
Published: April 2011

Patterns in spatial and trophic resource partitioning in the fish community of the Georges Bank region are identified, accounting for size-based changes in diets. During autumn and spring, this community is divided into geographic assemblages of species that have high spatial overlap. Similarity in spatial distribution is primarily related to similarity in depth preferences, and seasonal differences in species composition within assemblages are related to migrations. There is also important trophic structure within the Georges Bank community separating predators based upon prey size and location in the water column. Ontogenetic changes in diets are an important feature of the trophic structure in this system, particularly in the major piscivores. Seasonal changes in trophic structure reflect both predator and prey migrations. Dietary overlap among predator types is independent of either spatial overlap or depth preferences. There is spatial segregation within trophic guilds, and this spatial partitioning reduces the potential for exploitative competition within this community. Given the observed spatial patterns in trophic structure, the geographic assemblages on Georges Bank may be considered ecologically distinct functional units within this ecosystem.
Transport and development of eggs and larvae of Atlantic cod, Gadus morhua, in relation to spawning time and location in coastal Newfoundland
Authors: Bradbury Ian R , Snelgrove Paul V.R. , Fraser Sandra
Published: April 2011

We provide evidence that variation in location and timing of spawning of Atlantic cod, Gadus morhua, has a major impact on occurrence, distribution, and development of eggs and larvae in a large embayment on the south coast of Newfoundland. Atlantic cod egg densities, measured with a series of ichthyoplankton surveys in Placentia Bay during the spawning and postspawning seasons of 1997 and 1998, were highest during the early spring of both years and decreased through the spring and summer. Egg development stages and larval size suggest that eggs and larvae were released from spawning locations within the bay and developed as they were transported in cyclonic flow from the southeast and around the bay towards the southwest, where late-stage eggs and larvae were found to be most abundant. Although egg densities were generally lower in 1998, late-season egg production during the summer of 1998 was elevated in relation to 1997, providing a possible explanation for the observation that larval total densities were more than an order of magnitude higher in 1998 than in 1997. In terms of larval production, late spawners may be particularly important to successful egg hatching in the coastal waters of Newfoundland.
Habitat selection by juvenile coho salmon in response to food and woody debris manipulations in suburban and rural stream sections
Authors: Giannico Guillermo Roberto
Published: April 2011

This study explored the effects of food and woody debris manipulations on the summer distribution of juvenile coho salmon (Oncorhynchus kisutch) in small suburban streams. To examine fish responses to these factors, three different experiments were carried out in modified sections of two streams. The results showed that the distribution of juvenile coho salmon in a stream section was primarily controlled by the availability and distribution of food among pools and by the presence and density of woody debris. Food, however, played a dominant role because the foraging quality of a pool not only affected the density of fish in it but also the response of those fish towards instream debris. In food-rich stream sections, low proportions of juvenile coho salmon occupied pools with dense woody debris in the spring, which changed towards late summer. In contrast, in food-poor reaches, high proportions of fish were found in pools with abundant debris in the spring. Pools that combined abundant food with sparse woody debris were the most favoured by the fish. It is important that salmonid habitat enhancement projects consider that open foraging areas interspersed with woody debris characterize the type of summer habitat that juvenile coho salmon prefer.
Predation on hatchery-reared lobsters released in the wild
Authors: van der Meeren Gro I
Published: April 2011

Predation on hatchery-reared lobsters (Homarus gammarus) in the wild was studied in order to identify predators in southwestern Norway on rocky and sandy substrates in winter and summer. Lobsters of 12-15 mm carapace length were tagged with magnetic microtags. About 51 000 juvenile lobsters were released on 10 occasions at three locations. Predator samplings were by trammel nets, eel traps, and videorecordings during the 24 h immediately following the releases. In summer, loss to predators occurred on both rocky and sandy substrates. The loss was lower in winter when lobsters were found as prey in predators caught on sand. The risk of fish predation was highest in the first hours after release, when the lobsters were out of shelter. The wrasses Labrus bergylta and Labrus mixtus were the major predators of lobsters, while Atlantic cod (Gadus morhua), shorthorn sculpin (Myoxocephalus scorpius), and crab (Cancer pagurus) were mainly winter predators. Winter predators were never as abundant as summer predators. To minimise predatory loss of reared and costly lobsters, they should be released onto rocky substratum in winter. Due to the damage to the predated lobsters, it was not possible to correlate survival against lobster size.
Landscape controls on phosphorus loading to boreal lakes: implications for the potential impacts of forest harvesting
Authors: Devito K J , Creed I F , Rothwell R L , Prepas E E
Published: April 2011

For 12 low-order lakes in the Western Boreal Forest of Canada, lake position in the groundwater flow system and surface hydrologic connection to wetlands accounted for 57% of the variation in the change in postharvest (1997) relative to preharvest (1996) open-water median total phosphorous concentration ([TP]). Changes in [TP] decreased with calcium and magnesium concentrations, indicating that the largest increases in [TP] are likely to occur in lakes located in areas of groundwater recharge or shallow local discharge. Changes in [TP] increased with the area of wetland connected to the lake, a measure of near-surface hydrologic flushing of TP to the lake. However, the remaining variation (43%) in the TP response of lakes to harvest was not explained by landscape-based criteria. This study illustrates that in landscapes with complex hydrogeology, factors controlling the chemical responses of lakes to disturbance are complex, remain poorly understood, and require further study.
Global block kriging to estimate biomass from acoustic surveys for zooplankton in the western Aleutian Islands
Authors: Kern John W , Coyle Kenneth O
Published: April 2011

Because of patchy distributions and the expense of collecting and processing net samples, zooplankton population data are often characterized by broad confidence intervals, with little detailed information on vertical and horizontal distributions. Although acoustic techniques and optical plankton counters combined with nets can supply much more detailed information on plankton distributions, application of classical statistical procedures to such data may be effected by pseudoreplication from autocorrelation in closely spaced samples. We apply two-dimensional kriging for population mapping and global estimation. The technique utilizes a computational estimator of the global block kriging mean, which can be applied to large data sets common to hydroacoustic surveys. The techniques are outlined using examples from acoustic data taken in the western Aleutian Islands. This technique has two fundamental advantages: (i) it minimizes pseudoreplication by accounting for autocorrelation, permitting rigorous statistical inferences, and (ii) it provides an effective technique for visualizing the results. These advantages may make this a useful technique for identifying changes in the size and distribution of populations.
Understanding krill growth and aging: the contribution of experimental studies
Authors: Nicol Stephen
Published: April 2011

Krill have been viewed as difficult animals to examine experimentally. Consequently, most information on growth and age of these pelagic crustaceans has come from demographic studies on preserved specimens. Only one species of krill, Euphausia superba, has been intensively studied in the laboratory, but the experimental findings on growth and age from these studies have fundamentally altered our perceptions of the population biology of this species. Most other species of krill remain in the preexperimental phase of understanding; thus, there remain considerable uncertainties regarding their growth and longevity. Unfortunately, these uncertainties are often ignored in ecological studies. In this paper, I have examined the role that experimental studies have played in increasing knowledge of the population biology of krill, particularly in the fields of growth and aging. I have indicated where discrepancies exist between field-based and experimental approaches and I outline some approaches for exploring these discrepancies and suggest some potentially fruitful areas for future research.