bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of chronic environmental acidification and a summer global warming scenario: protein synthesis in juvenile rainbow trout (Oncorhynchus mykiss)
Authors: Reid S D , Dockray J J , Linton T K , McDonald D G , Wood C M
Published: April 2011

Protein synthesis (Ks), net accretion (Kg), and degradation (Kd) in liver, gills, and white muscle were measured using a flooding dose of [3H]phenylalanine in juvenile rainbow trout chronically exposed (90 days) to softwater in the presence or absence of sublethal acidity (H2SO4, pH 5.2) alone or in combination with a 2°C elevation in the normal temperature profile over the months of June-September 1993 (control temperature range 13-24°C). Chronic sublethal exposure to low pH reduced protein synthesis and degradation in both the gill and liver with little apparent impact on white muscle. As a result, protein was increased in the affected tissues. This suggested that both liver and gill have some capacity to compensate for the effects of acid exposure. The 2°C elevation in the normal temperature profile resulted in a slight increase in protein turnover in both gills and liver. However, during the period of peak water temperature, the 2°C elevation in temperature triggered a dramatic reduction in the protein turnover rates in these tissues. The exact mechanism by which these modifications in protein turnover occurred could not be clearly established. Overall, environmental acidification in combination with a summer global warming scenario would decrease fish growth and survival, most notably during periods of peak temperatures.
Comparison of accuracy, precision, and sensitivity in elemental assays of fish otoliths using the electron microprobe, proton-induced X-ray emission, and laser ablation inductively coupled plasma mass spectrometry
Authors: Campana S E , Thorrold S R , Jones C M , Günther D , Tubrett M , Longerich H , Jackson S , Halden N M , Kalish J M , Piccoli P , de Pontual H , Troadec H , Panfili J , Secor D H , Severin K P , Sie S H , Thresher R , Teesdale W J , Campbell J L
Published: April 2011

The elemental composition of fish otoliths is of considerable interest to those who wish to reconstruct temperature, migration, or environmental histories of individual fish based on assays of the otolith growth sequence. However, reported differences in otolith elemental composition among studies may be due in part to performance differences among four of the most popular instruments for targeted elemental analysis: wavelength-dispersive electron microprobe (WD-EM), energy-dispersive electron microprobe (ED-EM), proton-induced X-ray emission (PIXE), and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). To rigorously compare the sensitivity, accuracy, and precision of these four analytical tools, the International Otolith Composition Experiment distributed blind-labelled real and artificial otoliths of known but varied elemental composition to eight laboratories for assay of 10 selected elements. No one instrument type was sensitive to each element, nor was any one instrument preferred for use in all assays. In general however, abundant elements such as Na and K could only be measured accurately with an electron microprobe, while the trace elements required PIXE or LA-ICPMS. Strontium could be measured with considerable accuracy and precision by WD-EM, PIXE, and LA-ICPMS. The presence of significant, and occasionally large, differences among laboratories suggests that comparisons among published studies should be made cautiously and only after appropriate calibration.
Influence of catchment topography on water chemistry in southeastern Québec Shield lakes
Authors: D'Arcy Pierre , Carignan Richard
Published: April 2011

For 30 Canadian Shield lakes of southeastern Quebec, catchment slope and lake morphometry account for 50-70% of the variability of chlorophyll a (Chl a), dissolved organic carbon (DOC), total phosphorus (TP), NO3- , and NH4+ . Dissolved organic carbon, TP, Chl a, Ca, and Mg are negatively related to catchment slope, whereas NO3- and NH4+ increase with increasing slope. Concentrations of more conservative constituents (SO42-, Na, K) increase with decreasing elevation as a result of higher evapotranspiration and lower precipitation at low elevations. Catchment variables (slope, drainage area, percent wetlands) are as good predictors of Chl a (r2 = 0.7) as are water chemistry variables (TP, Ca, Mg, and pH). Dominant vegetation (deciduous vs. coniferous) has little or no influence on lake water chemistry. Hydrogeological data for the Canadian Shield suggest that, during periods of high runoff, the development of waterlogged areas and the importance of overland flow on saturated soils are inversely proportional to catchment slope. We propose that the strong influence of catchment slope on water quality is due to slope-dependent seasonal waterlogging, which determines the fate (retention or export to surface waters) of dissolved substances produced within and moving through the forest floor.
Managing growth overfishing with multiannual compromise strategies
Authors: Marchal P
Published: April 2011

Most of the Northeast Atlantic stocks are currently fished above the biological reference points (e.g., Fmax). In attempting to achieve such targets, advisers and managers have faced two main problems. First, it is impractical to (i) simultaneously maximize yields, stabilize fisheries, and safeguard stocks and (ii) optimize both short- and long-term outcomes for the industry. Second is the lack of predictability, several years ahead, in factors influencing decisions. This study addresses these twin issues by exploring the relative performances of various multiannual and compromise (or composite) management strategies. Multiannual fishing efforts are set in advance for a ``resolution'' period of several years, at the end of which they are updated. They are calculated to satisfy a prior weighted compromise amongst three criteria: (i) minimizing fishing effort variability, (ii) minimizing catch variability, and (iii) reaching a ``mobile target:'' the latter is defined with a second weighted compromise between the long-term target and the fishing effort at the beginning of the resolution period. A safe and optimal balance between all the short- and long-term fishery outcomes is found with a 5-year resolution period, during which the mobile target is split into 40-60% of the long-term target, and 60-40% of the fishing effort at the start of the resolution period, while criteria i, ii, and iii are weighted equally.
A new recorder for simultaneously recording the activity and oxygen consumption of small benthic invertebrates
Authors: Wilhelm Frank M , Lasenby David C , Wilhelm Ralph M , Plante Ron
Published: April 2011

Respiration studies of small benthic invertebrates are generally completed without regard to the inclusion of a substrate or the quantification of activity in the experimental chamber. We describe a new activity monitoring system for continuously recording the activity and oxygen consumption of small benthic invertebrates in water with the presence of a substrate. We used the freshwater amphipod Diporeia hoyi to test the new system. Activity rates were significantly higher without sediment than with sediment, and oxygen consumption was directly related to activity. Future invertebrate respiration studies, especially those with infaunal organisms, will benefit from such a system by allowing researchers to determine possible test condition - treatment interactions.
Density, size-at-age, and distribution of young Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in deep river pools
Authors: Bremset Gunnbjørn , Berg Ole Kristian
Published: April 2011

A comparison of populations of juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in four deep pools (maximum depths 2.0-4.0 m) and 12 shallow riffles in three rivers showed significantly higher density, size-at-age, and biomass of the pool-dwelling salmonids. There were 2.5 times more parr per unit of area in the pools compared with the riffles (95.3 and 37.5 parr/100 m2, respectively, p = 0.0053). The pool-dwelling trout had a larger size-at-age than riffle specimens, and the pool-dwelling salmon were larger than those found in the riffles in three of four cases (p < 0.001). The relative biomass of salmonid parr in two of the investigated pools was 6.9 and 12.0 g/m2 compared with the means of 1.6 and 3.7 g/m2 in the riffles. There are two possible explanations that are discussed for the larger size-at-age of the fish in the deep pools: (i) movements of large, dominant parr into the pools as they grow older or (ii) favorable conditions in the pools that give pool-dwelling fish an energetic advantage. In contrast with established theory, the current data show that deep pools are favorable habitats for both young Atlantic salmon and brown trout.
An approach to describing ecosystem performance ``through the eyes of salmon''
Authors: Mobrand Lars E , Lichatowich James A , Lestelle Lawrence C , Vogel Thomas S
Published: April 2011

The intent of this paper is to show that discussion of watershed health and salmon (Oncorhynchus sp.) performance can incorporate a much greater degree of complexity without loss of clarity. We can and should include more temporal-spatial detail, more life history complexity, and more watershed-specific information. The framework and performance measures used in watershed management generally, and salmon management specifically, are inadequate. The bottleneck metaphor is cited all too frequently as a basis for discussion. The bottleneck analogy is useful in understanding capacity, but capacity alone cannot explain observed responses of salmon populations to environmental change. An argument can be made that where protection and enhancement of weak stocks is the priority, productivity is a more critical variable. However, a framework built only around productivity and capacity is also not sufficient. It neglects the need for connectivity of habitats that salmon must pass through to complete their life histories. Adding life history diversity as the third component of performance provides the time and space structure needed to deal with connectivity while also allowing for integration of populations where they mingle.
Age, growth, and maturation of Lolliguncula brevis (Cephalopoda: Loliginidae) in the northwestern Gulf of Mexico with a comparison of length-frequency versus statolith age analysis
Authors: Jackson G D , Forsythe J W , Hixon R F , Hanlon R T
Published: April 2011

Over 2000 individuals of Lolliguncula brevis were collected from 1975 to 1979 in the northern Gulf of Mexico off the Texas coast; their growth and reproductive biology were analyzed by traditional fisheries methods (ELEFAN analysis of the length-frequency data). From 1994 to 1996, 112 squid were captured in Galveston Bay, near Galveston Island, Texas, and their age and growth determined by statolith increment analysis. The results were strikingly different between the two approaches. Length-frequency analysis of growth overestimated life span by a factor of three to seven times. Statolith increment counts, verified by laboratory growth validation experiments, indicate that this species is very short-lived, in the order of 100-200 days depending on temperature. A slight increase in temperature during the early stage of development can greatly shorten the life span. This study provides evidence that increased temperature during a squid's early growth period could markedly accelerate growth. Mature individuals occurred throughout the year, although there were many more mature males collected than females. Gonad growth and maturation in L. brevis appear to be associated more with size than with individual age. There is now compelling evidence that length-frequency analysis should be abandoned as a technique for determining squid growth.
Effects of CO2on competition between a cyanobacterium and eukaryotic phytoplankton
Authors: Caraco N F , Miller R
Published: April 2011

To distinguish whether there is a causal link between cyanobacterial dominance and low CO2and (or) the associated high pH, we ran duplicate competition experiments using a factorial design of CO2by alkalinity. In various treatments, three concentrations of alkalinity (ca. 50, 500, and 5000 µequiv. ·L-1) and CO2(ca. 1.3, 13, and 130 µM) generated three pH values (ca. 7, 8, and 9). At the end of about a 1-week incubation, Aphanizomenon flos aquae was the only cyanobacterium present, while the chlorophytes Scenedesmus and Selenastrum along with unidentified flagellates comprised the eukaryotic phytoplankton. The treatments had a dramatic effect on cyanobacterial biomass, which varied from >90% to 0% of the total phytoplankton biomass across treatments. Variation in percent cyanobacteria was better related to pH than to CO2. At pH 8 and 9, percent cyanobacteria was relatively high at all CO2concentrations. Only at pH 7 was percent cyanobacteria negatively related to CO2concentration. These results demonstrate both direct and indirect effects of CO2on cyanobacterial dominance but suggest that, for A. flos aquae, the indirect impact of CO2(pH alteration) is most important. The impact of CO2on this cyanobacterium, therefore, depends on the alkalinity of the system.
Trophic interactions between yellow perch (Perca flavescens) and their benthic prey in a littoral zone community
Authors: Cobb Susan E , Watzin Mary C
Published: April 2011

Yellow perch (Perca flavescens) growth rates in northern Lake Champlain have declined in recent years while densities have increased, suggesting resource limitation. At high densities, predators have the potential to influence prey communities, but these effects can be highly complex. Using in situ mesh cages in an unmanipulated littoral zone setting, we examined the effects of two densities (0.5 and 1.5/m2) of yellow perch on (i) their growth and (ii) the abundance of major prey groups in the benthic community. Yellow perch growth rates were significantly lower in the high-density treatment than in the low-density treatment. Because site characteristics were not manipulated, measured covariates reflecting sediment and vegetation variation between cages were used to help clarify treatment effects on benthos. Fish predation on invertebrate prey was significant only in the high-density predator treatment for three of the six prey groups examined (predatory chironomids, prey chironomids, and isopods). For this littoral zone community, availability and abundance of benthic prey strongly influenced yellow perch growth rates; but the effect of yellow perch predation on benthic community structure was only moderate.
Effects of inorganic sediment and food concentrations on energetic processes of the zebra mussel,Dreissena polymorpha: implications for growth in turbid rivers
Authors: Madon Sharook P , Schneider Daniel W , Stoeckel James A , Sparks Richard E
Published: April 2011

We examined the effects of inorganic suspended sediment (0, 1, 10, and 100 mg ·L-1) and food concentrations (0.1, 0.5, and 2.0 mg particulate organic matter (POM) ·L-1) on clearance, ingestion, respiration, feces, and pseudofeces production rates and assimilation efficiencies of adult zebra mussels (Dreissena polymorpha) under laboratory conditions at 20 ± 1°C. Food quality indices (the proportion of inorganic to organic material in feeding suspensions = IO ratios) ranged from 0.304 to 63.04. Suspended inorganic sediment above 1 mg ·L-1greatly reduced clearance rates, ingestion rates, and assimilation efficiencies of zebra mussels, and ingestion of POM was maintained only at high food concentrations. Pseudofeces were produced copiously by zebra mussels in the 100 mg ·L-1sediment treatment, and there appeared to be an increased metabolic cost associated with pseudofeces production. Declining food quality caused exponential declines in clearance, ingestion, and absorption rates, water processing potential, and assimilation efficiencies, with the sharpest declines between IO ratios of 0.304 and 5.0. IO ratios in turbid rivers often exceed 1.71, our experimental threshold where scope for growth for zebra mussels was zero. We contend that zebra mussels in turbid rivers may exhibit low growth potential and may not stabilize at the high population densities seen in their lake counterparts.
Pup production and population trends of the grey seal (Halichoerus grypus) in the Gulf of St. Lawrence
Authors: Hammill M O , Stenson G B , Myers R A , Stobo W T
Published: April 2011

Grey seal (Halichoerus grypus) pup production of the Gulf of St. Lawrence component of the Northwest Atlantic grey seal population was determined for the 1984-1986 and 1989-1990 periods using mark-recapture methods. Pup production estimates based on recaptures from shot samples from Anticosti Island ranged from 5436 (SE = 672) to 6955 (SE = 1183) for 1984-1986. An independent estimate for 1984-1986, based on animals captured on Sable Island, was 7431 (SE = 1414) to 8633 (SE = 2827). Mark-recapture estimates of pup production for 1989 and 1990 from shot samples collected from Anticosti Island were 8825 (SE = 3164) and 9156 (SE = 2652), respectively. The estimates based on animals captured on Sable Island varied from 7295 (SE = 2118) to 8116 (SE = 846) for 1989-1990. Both the Anticosti Island and Sable Island recovery samples underestimate 1989 pup production due to hunting which removed 1612 pups from the population before they could disperse. The Gulf component of the Northwest Atlantic grey seal population is increasing at an annual rate of 7.4% (SE = 2.2).
Enhanced gut fullness and an apparent shift in size selectivity by radiated shanny (Ulvaria subbifurcata) larvae in response to increased turbulence
Authors: Dower John F , Pepin Pierre , Leggett William C
Published: April 2011

We studied the relationship between microscale turbulence and feeding success of larval radiated shanny (Ulvaria subbifurcata) in Conception Bay, Newfoundland, during a 3-week period in July-August 1995. Although previous studies had suggested that the relationship between turbulent velocity and larval feeding rates should be dome shaped, we found no evidence of such a functional relationship. Rather, differences in larval feeding success were evident only when days were grouped as either "high turbulence" or "low turbulence" on the basis of Richardson number. Feeding conditions (i.e., prey concentration and composition) were not significantly different on high- versus low-turbulence days. Nonetheless, U. subbifurcata larvae (3-14 mm standard length) contained significantly fewer items in their guts on high-turbulence days. These prey items, however, were (on average) significantly larger than those found in guts on low-turbulence days; the net result was that significantly greater volumes of food were found in larval guts on high-turbulence days. Turbulent velocity did not affect between-day variation in RNA:DNA ratios of the larvae. We suggest that what appears to be a shift in size selectivity by U. subbifurcata larvae under increased turbulence may result from larvae having a higher probability of capturing large prey under increasingly turbulent conditions.
Factors that regulate the zooplankton community structure of a turbid, hypereutrophic Great Lakes wetland
Authors: Lougheed Vanessa L , Chow-Fraser Patricia
Published: April 2011

We sampled zooplankton from mid-May to early September over 2 years to study the spatial and seasonal distribution of animals in a large urban wetland of Lake Ontario. Samples were from several habitat types including open water, vegetated areas, fast-flow areas, and a sewage lagoon. Mean seasonal densities ranged from 17 individuals/L (5 µg/L) in fast-flow areas to 1800 individuals/L (1100 µg/L) in low-flow, highly vegetated areas. All of our sites were dominated by herbivorous rotifers (e.g., Brachionus sp., Polyarthra sp., Keratella sp.), small herbivorous cladocerans (Bosmina longirostris; mean length <300 µm), cyclopoid nauplii, and medium-sized cladocerans (e.g., Moina micrura; mean length 300-600 µm), which were absent from the most eutrophic sites. The high levels of inorganic suspended solids in the marsh appeared to select against large filter feeders such asDaphnia and allowed smaller zooplankton to dominate. Multivariate analyses indicated that the zooplankton distribution was related to flow rate, extent of macrophyte cover, and level of site degradation. If the forthcoming carp (Cyprinus carpio) exclusion from Cootes Paradise Marsh results in increased macrophyte growth, we predict that zooplankton biomass will increase and that the zooplankton community may shift to larger forms.
Responses of Ohio River and Lake Erie dreissenid molluscs to changes in temperature and turbidity
Authors: Thorp James H , Alexander, Jr. James E , Bukaveckas Bonny L , Cobbs Gary A , Bresko Kurt L
Published: April 2011

To predict possible effects of global climatic change (via changes in ambient water temperatures and suspended sediments) on two exotic bivalves (zebra mussel, Dreissena polymorpha, and quagga mussel, Dreissena bugensis), we evaluated survival and growth at three temperatures (ambient, ambient + 2°C, and ambient + 4°C) and two turbidities (ambient and twice ambient) in outdoor tanks for approximately 3 months during both warm and cool seasons. We compared responses of zebra and quagga mussels from southwestern Lake Erie and zebra mussel from the Ohio River at Louisville, Kentucky. Experimental increases in temperature significantly enhanced growth rates in fall - early winter but not during summer - early fall. Elevated temperatures increased mortality in the warm season but not in the cool season. Zebra mussel survived better (especially the Ohio River population) than did quagga mussel at high temperatures. Inorganic turbidity had few detectable effects; relationships, where significant, varied with temperature and species. Based on these experiments and related laboratory studies, we predict that populations of Dreissena in the Ohio River and farther south will suffer overall if water temperatures increase. In contrast, more northern populations of Dreissena will probably benefit from predicted climatic change and may extend their range to higher latitudes and altitudes.
Pre- and post-season tagging models: estimation of reporting rate and fishing and natural mortality rates
Authors: Hearn William S , Pollock Kenneth H , Brooks Elizabeth N
Published: April 2011

Brownie et al. (1985, U.S. Fish Wildl. Serv. Resour. Publ. 156, p. 159) presented models for tag returns from multiple taggings of animals when tagging is done twice per year. Here, we present a reformulation of their model suitable for pre- and post-season fishery tag return studies. Under this model, it is possible to estimate fishing mortality, natural mortality, and reporting rate from the tag return data alone. (Under once-a-year tagging models, the reporting rate usually has to be estimated externally.) We consider two special cases: (i) a pulse fishery and (ii) a continuous fishery over part of the year. An artificial example and simulation results are presented to illustrate the methodology and the properties of the various estimators. Unlike for catch-based methods, the correlation between estimates of fishing mortality and natural mortality is moderate. While pre- and post-season tagging studies are likely to be difficult to run in practice, other methods of estimating reporting rate are also difficult to implement, and therefore, this approach may prove quite useful, especially in fisheries that have heavy exploitation rates.
Hyporheic zone chemistry and stream-subsurface exchange in two groundwater-fed streams
Authors: Hill Alan R , Lymburner Donna J
Published: April 2011

Data from two headwater streams in southern Ontario provide support for conceptual models that suggest that hyporheic zone influence on stream nutrient retention is determined by the extent of surface-groundwater exchange and subsurface chemical transformation rates. The hyporheic zone (>10% stream water) was delineated by a chemical mixing equation using differences in background stream and groundwater chloride concentrations and by injections of chloride to stream flow. Good agreement between the two methods confirmed that the extent of stream-groundwater exchanges can be successfully estimated using background conservative ions as a tracer technique. During low stream flows in May-October the depth of the hyporheic zone was 2-15 cm in a 12-m sand-bottom pool, debris dam, pool reach of Glen Major stream and 15-20 cm in a 16-m gravel riffle reach of Duffin Creek. Differences between observed NO3concentrations and concentrations predicted from background chloride indicated depletion of NO3in the hyporheic zone at a few locations in Glen Major and at 5-10 cm depth throughout the Duffin Creek reach. NO3and NH4injected into stream water were reactive at only a few hyporheic sites in the streams. Upstream-downstream comparisons during injections indicated that stream retention was minor.
Models for tagging data that allow for incomplete mixing of newly tagged animals
Authors: Hoenig John M , Barrowman Nicholas J , Pollock Kenneth H , Brooks Elizabeth N , Hearn William S , Polacheck Thomas
Published: April 2011

The Brownie models for tagging data allow one to estimate age- and year-specific total survival rates as well as tag recovery rate parameters. The latter can provide estimates of exploitation rates if the tag reporting, tag shedding, and tag-induced mortality rates can be estimated. A limitation of the models is that they do not allow for newly tagged animals to have different survival rates than previously tagged animals because of lack of complete mixing. We develop a model that allows for the animals to be incompletely mixed, or not fully recruited, into the population during the entire year in which they are tagged. There is a penalty in terms of precision associated with the use of this model. To increase the precision, we also developed a model for which it is assumed that animals become fully mixed (recruited) after a portion of the year has elapsed. Sometimes, animals must be tagged after the fishing season has begun. In this case, newly tagged animals experience fishing and natural mortality for only a fraction of the year. The partial-year non-mixing model can be modified to account for this situation.
A new method for estimating the morphometric size at maturity of crabs
Authors: Watters George , Hobday Alistair J
Published: April 2011

Existing techniques for estimating the morphometric size at maturity of crabs are based on assumptions that may be unnecessary. Here we demonstrate a new method of detecting changes in relative growth (or allometric) relationships and estimating morphometric size at maturity. This method involves fitting several smoothing splines to relationships between body size and claw size, selecting the "best" spline, and finding this spline's maximum second derivative. The body size where the second derivative of the best spline is maximized estimates the morphometric size at maturity. Monte Carlo simulations suggest that uncertainty and bias in the estimate of morphometric size at maturity can be decreased by measuring a large number of crabs from a wide range of body sizes. Our spline method does not require a priori assumptions about the shape of the relative growth relationship; it can detect multiple changes in the relative growth rate; and it is robust to outliers. The modeling technique may also be used to identify regions of allometric change in other types of relationships. We demonstrate the new technique by estimating the morphometric size at sexual maturity for males of both brachyuran (Chionoecetes tanneri) and anomuran (Paralomis spinosissima and P. formosa) crabs.
Sex-specific life history strategies in capelin (Mallotus villosus)?
Authors: Huse Geir
Published: April 2011

The life history of capelin (Mallotus villosus) is presently suggested to be sex specific: while males follow a semelparous batch-spawning strategy, females are iteroparous. This hypothesis is based on predictions from a life history simulation model of Barents Sea capelin that shows that iteroparity is more profitable than semelparity for females, but for males, semelparity with several matings with females may be as profitable as iteroparity. These predictions are supported by (i) reports of males mating with several females during a spawning season, (ii) males having a lower gonadosomatic index than females and instead spending their energy on mating and somatic growth, and (iii) an observed higher mortality for males after spawning. The Darwinian fitness of female capelin is limited by the amount of eggs they can carry, and offspring production may only be increased by undertaking several spawning seasons with yearly intervals. Added together, these indices suggest that male and female capelin follow different life history strategies.
Quantifying the uptake and release of cadmium and copper by the opossum shrimp Mysis relicta preying upon the cladoceran Daphnia magna using stable isotope tracers
Authors: Smokorowski K E , Lasenby D C , Evans R D
Published: April 2011

Daphnia magna were uniformly labeled with the stable isotope tracers 113Cd and 65Cu and fed to the invertebrate predator Mysis relicta to determine the levels of release, assimilation, accumulation, egestion, and excretion of Cd and Cu when consumed in food alone. Samples were analyzed using ICP-MS and data analyzed using a mass balance model. The sloppy feeding behaviour of mysids resulted in the release of metals from the prey Daphnia in particulate and soluble forms. Mysids have been observed to consume selectively the soft-body portion of Daphnia, resulting in the discarding of particulates, mainly exoskeleton, while eating. The trade-off of a higher handling time is a highly assimilable diet. Assimilation efficiencies of the two metals (72% for Cd and 21% for Cu) were considerably higher than previously published values for M. relicta, likely due to a previous overestimation of metal egestion. Excretion appears to be an important mechanism by which mysids rid their body of assimilated metals, resulting in the further transfer of metals into the readily available dissolved phase. After a 94-h depuration period, 47% of ingested Cd and 53% of ingested Cu remained associated with the mysids in either the gut, body, or exoskeleton.
Diel foraging cycles and interactions among juvenile Atlantic cod (Gadus morhua) at a nearshore site in Newfoundland
Authors: Grant Scott M , Brown Joseph A
Published: April 2011

In coastal Newfoundland, age 0 Atlantic cod (Gadus morhua) settle in shallow, nearshore regions occupied by older conspecifics. Although intercohort cannibalism is common, little is known of the behavioural responses that limit interactions among juvenile cohorts in the wild. We examined the day-night differences in catch and diet of age 0 and age 1 cod to delineate peak foraging activity and resource use in eelgrass (Zostera marina) habitat. Cod exhibited a size-related shift (age 0 to age 1) from feeding predominantly on zooplankton by day to benthos at night. Intercohort cannibalism occurred when age 1 cod were approximately three times larger than their prey. Concentrations of age 0 cod foraged in the water column during the day, ceased feeding at night, and appeared to disperse to the bottom. Seasonally decreasing daylength and prey size contributed to a decline in daily ration, yet age 0 cod still maintained a strict diurnal foraging cycle. The nocturnal decrease in feeding coincided with an increase in the catch of older conspecifics (age 2 and age 3) and increased foraging activity of age 1 cod, suggesting that avoidance of older conspecifics is an important factor influencing the diel foraging and activity cycles of age 0 cod.
Effects of trophic position and lipid on organochlorine concentrations in fishes from subarctic lakes in Yukon Territory
Authors: Kidd Karen A , Schindler David W , Hesslein Raymond H , Muir Derek CG
Published: April 2011

Concentrations of organochlorines in lake trout (Salvelinus namaycush), burbot (Lota lota), and northern pike (Esox lucius) from subarctic lakes in Yukon Territory varied significantly among populations, and these differences could not be ascribed to size or age of the fishes. For each species, lipid content and trophic positioning (measured by stable nitrogen isotope ratios; delta 15N) were significantly different across populations, and the latter differences could not be attributed to variable delta 15N at the base of the food webs. Across lakes, concentrations of up Sigma PCB, Sigma DDT, chlorinated bornanes (CHB), chlordane ( Sigma CHL), chlorobenzenes ( up Sigma CBZ), and hexachlorocyclohexane ( Sigma HCH) in lake trout and northern pike muscle and burbot liver were significantly related to their delta 15N. The slopes of these log organochlorine - delta 15N relations were greatest for more lipophilic contaminants ( Sigma PCB, Sigma DDT, CHB), indicating that they bioaccumulate to a greater degree than less lipophilic contaminants. Lipid significantly predicted organochlorine concentrations both within and among populations of lake trout, and the slopes did not vary significantly with contaminant lipophilicity. Among-lake differences in Sigma HCH in trout muscle were removed by adjusting concentrations by the covariate lipid. Lipid-adjusted concentrations of CHB, Sigma PCB, Sigma DDT, Sigma CHL, and Sigma CBZ in lake trout remained significantly different between lakes, and these differences were attributed to variable food chain lengths.
Predictions on the effect of common carp (Cyprinus carpio) exclusion on water quality, zooplankton, and submergent macrophytes in a Great Lakes wetland
Authors: Lougheed Vanessa L , Crosbie Barb , Chow-Fraser Patricia
Published: April 2011

We conducted a study to examine the relationship between common carp (Cyprinus carpio) exclusion, water quality, zooplankton, and submergent macrophytes. Twelve 50-m2 in situ experimental enclosures were installed in degraded Cootes Paradise Marsh during the carp spawning period in 1995. Enclosures were stocked with two or three carp of similar size, ranging from 13 to 59 cm and in total biomass from 23 to 2100 kg/ha. Turbidity, total phosphorus, and total ammonia concentrations increased predictably with total carp biomass in the enclosures. Although carp had no direct effect on zooplankton community structure, increased turbidity and nutrient load associated with carp activity resulted in reduced total zooplankton biomass. We developed a relationship between species richness and water turbidity for 19 wetlands in the Great Lakes basin which indicated that above an apparent threshold of 20 NTU, there were less than five species of submergent plants, while a more diverse community existed in less turbid systems. We predict that water turbidity in Cootes Paradise Marsh may not be reduced below this threshold value of 20 NTU following carp exclusion. We emphasize the need to consider other factors that may contribute to increases in water turbidity and nutrient concentrations, including wind resuspension and substrate characteristics.
Measurement of primary production and community respiration in oligotrophic lakes using the Winkler method
Authors: Carignan Richard , Blais Anne-Marie , Vis Chantal
Published: April 2011

The precision of the Winkler method can reach 2 µg ·L-1 if a potentiometric end-point detection method if used and if minor modifications to standard protocols are made. The major sources of variability encountered at this precision level are due to the gradual decrease (1-3 µg ·L-1 ·h-1) in apparent O2 which occurs after reagent addition and to thermal expansion and contraction of the samples during storage. These sources of error can, however, be easily minimized or eliminated. The precision of the proposed protocols for Winkler determinations and metabolic rate measurements allows the detection of gross primary production and community respiration rates as low as 0.7 mg C ·m-3 ·h-1 after 4-h incubations. The methods are therefore adequate for metabolic studies in oligotrophic lakes, where epilimnetic production and respiration rates range between 5 and 50 mg C ·m-3 ·h-1.
The dead of winter: size-dependent variation and genetic differences in seasonal mortality among Atlantic silverside (Atherinidae: Menidia menidia) from different latitudes
Authors: Schultz Eric T , Conover David O , Ehtisham Amir
Published: April 2011

Genetic differences among populations of Atlantic silverside (Menidia menidia) are hypothesized to be evolutionary responses to intense, size-selective winter mortality at high latitudes. Three experiments were conducted to test features of winter mortality. In the first experiment, we varied size and whether food was provided or withheld; temperatures were permitted to follow ambient (New York) wintertime fluctuations. Mortality and depletion of energy reserves were more rapid in the units receiving no food. Small fish died before larger fish in these units, but not in the units receiving food. Energy depletion of fish in the no-food treatment resembled that of fish in the wild. In the second experiment, we varied size and population of origin, representing high-latitude (Nova Scotia), midlatitude (New York), and low-latitude (South Carolina) populations. These fish were provided food and showed minimal depletion of energy reserves, but mortality rates were high when water temperatures were low. Mortality did not vary with size in New York and South Carolina fish, but was highest in intermediate-size fish from Nova Scotia. There was a pronounced population difference in survival rate (Nova Scotia > New York > South Carolina). In the third experiment, food was withheld and extreme low temperatures were moderated. Energy depletion was rapid and small fish died before large fish. We conclude that populations in seasonal environments are likely to be subject to size-selective winter mortality when energy reserves are depleted and that juvenile growth rates have evolved in response to this selection pressure. In addition, high-latitude populations have evolved greater tolerance to other winter stresses associated with low temperatures.
Increased deposition of organic matter, polychlorinated biphenyls, and cadmium by zebra mussels (Dreissena polymorpha) in western Lake Erie
Authors: Dobson Evan P , Mackie Gerald L
Published: April 2011

Biodeposition of organic matter, polychlorinated biphenyls (PCBs), and cadmium (Cd) by zebra mussels (Dreissena polymorpha) was investigated at five stations in the western basin of Lake Erie during the summer of 1992. Biodeposition rates at the five stations were determined by using sediment traps and converted to per unit area values to facilitate comparisons with natural sedimentation rates. Biodeposition of suspended material by zebra mussels was up to 8 times greater than sedimentation in the traps. Concentrations of organic matter, PCBs, and Cd were determined for the biodeposits and the sedimented material. There were no significant differences in concentration of organic matter, PCBs, or Cd between the two types of material. Biodeposition rates per unit area of organic matter, PCBs, and Cd were 8-10 times greater than corresponding values for natural sedimentation; therefore, the natural sedimentation processes of these factors appear to be greatly accelerated in the presence of zebra mussels. Results support the possibility that zebra mussels are altering contaminant movement in western Lake Erie, as well as clarifying the water column by removing suspended material.
Use of passive integrated transponder tags to estimate survival of migrant juvenile salmonids in the Snake and Columbia rivers
Authors: Skalski John R , Smith Steven G , Iwamoto Robert N , Williams John G , Hoffmann Annette
Published: April 2011

Single-release and modified single-release statistical models were evaluated as means to generate reliable survival estimates from release-recapture studies of migrant salmonid smolts in the Snake and Columbia rivers of the northwestern United States. Monte Carlo simulation studies were used to assess robustness of estimation methods to violations of model assumptions. To field test model assumptions, passive integrated transponder tagged chinook salmon (Oncorhynchus tshawytscha) smolts were released on seven consecutive days in 1993 above Lower Granite Dam on the Snake River. These releases were used to estimate sampling variability of survival estimates for comparison with model-based variance estimates and to assess mixing of detected and nondetected individuals. Field results satisfied model assumptions. The average survival estimate from point of release to the tailrace of Lower Granite Dam (31 km) was 0.902 ± 0.004 (mean ± SE). From the tailrace of Lower Granite Dam to the tailrace of Little Goose Dam (60 km) the average survival estimate was 0.859 ± 0.013.
Sexual difference in polychlorinated biphenyl accumulation rates of walleye (Stizostedion vitreum)
Authors: Madenjian Charles P , Noguchi George E , Haas Robert C , Schrouder Kathrin S
Published: April 2011

Adult male walleye (Stizostedion vitreum) exhibited significantly higher polychlorinated biphenyl (PCB) concentrations than similarly aged female walleye from Saginaw Bay (Lake Huron). To explain this difference, we tested the following three hypotheses: (i) females showed a considerably greater reduction in PCB concentration immediately following spawning than males, (ii) females grew at a faster rate and therefore exhibited lower PCB concentrations than males, and (iii) males spent more time in the Saginaw River system than females, and therefore received a greater exposure to PCBs. The first hypothesis was tested by comparing PCB concentration in gonadal tissue with whole-body concentration, the second hypothesis was tested via bioenergetics modeling, and we used mark-recapture data from the Saginaw Bay walleye fishery to address the third hypothesis. The only plausible explanation for the observed difference in PCB accumulation rate was that males spent substantially more time in the highly contaminated Saginaw River system than females, and therefore were exposed to greater environmental concentrations of PCBs. Based on the results of our study, we strongly recommend a stratified random sampling design for monitoring PCB concentration in Saginaw Bay walleye, with fixed numbers of females and males sampled each year.
Strontium:calcium ratios in Atlantic salmon (Salmo salar) otoliths and observations on growth and maturation
Authors: Friedland Kevin D , Reddin David G , Shimizu Nobumichi , Haas Ruth E , Youngson Alan F
Published: April 2011

In this paper, we report on two data sets that have relevance to contemporary ideas on maturation in Atlantic salmon (Salmo salar): (i) an analysis of maturity rate of Atlantic salmon captured in the southern Labrador Sea and (ii) a study of otolith strontium:calcium ratios for maturing and immature Atlantic salmon. A discrimination function based on gonadosomatic indices was developed to classify maturation state of Atlantic salmon caught in Newfoundland and Labrador fisheries during the period 1985-1988. Atlantic salmon believed to be on feeding migrations were found to be in advanced states of sexual development. In an attempt to clarify the meaning of these data, chronological transects of Sr:Ca ratios from the otoliths of maturing and immature one-seawinter fish were collected. Sr:Ca ratios deposited during freshwater residency varied by stock and appeared to reflect the environmental availability of Sr. Sr:Ca ratios deposited during marine residency appeared to reflect somatic growth and sexual development. We detected no differences in the postsmolt Sr:Ca ratios for mature and immature Atlantic salmon from a hatchery stock originating in North America, suggesting that for this stock, little differentiation occurs between the maturity components. Mechanisms by which environment may contribute to the variation in maturation rate of North American Atlantic salmon are discussed.
Natural isotope indicators of fish migration at Prudhoe Bay, Alaska
Authors: Kline, Jr. Thomas C , Wilson William J , Goering John J
Published: April 2011

A dichotomy in the natural stable carbon isotope abundance measured in tissues of obligate freshwater and marine fishes from the Alaskan Arctic coastal plain suggested that the methodology can be used to differentiate recent freshwater from marine feeding in migratory fishes. Natural stable carbon isotope ratio of migratory fishes reflected differences of feeding habitat in relation to known life-history patterns. Use of the stable isotope methodology as a tool for proxy analysis of fish behavior in present and future Arctic environmental monitoring studies is suggested from analysis of age-specific isotopic ratio differences in broad whitefish (Coregonus nasus) and Arctic cisco (Coregonus autumnalis).
Estimation of growth and mortality parameters from size frequency distributions lacking age patterns: the red sea urchin (Strongylocentrotus franciscanus) as an example
Authors: Smith Barry D , Botsford Louis W , Wing Stephen R
Published: April 2011

We present a maximum likelihood procedure for estimating population growth and mortality parameters by simultaneously analysing size frequency and growth increment data. The model uses von Bertalanffy growth with variability among individuals in the two parameters that determine growth rate, and size-dependent mortality. Analyzing growth increments together with size frequencies reduces the statistical confounding of the natural mortality rate with von Bertalanffy's K parameter. We assume steady-state (constant recruitment) conditions for the size distributions; hence the method does not depend on age modes in the distribution. We evaluate the bias and precision of estimates obtained for growth-dominated distributions typical of the red sea urchin (Strongylocentrotus franciscanus) in northern California, although the method and its evaluation could be applied as easily to mortality-dominated or bimodal distributions. The method provides good estimates with sample sizes as low as 200 individuals in a size distribution and 30 growth increments. Results are robust to random variability in recruitment, measurement error, and sampling selectivity up to the size where about one third of the distribution is affected. Estimation of the fishing mortality rate could require size distributions from both an unharvested and a harvested population. Estimates of growth and mortality rates depend critically on reliable growth data.
Quantifying cutthroat trout (Oncorhynchus clarki) predation on sockeye salmon (Oncorhynchus nerka) fry using a bioenergetics approach
Authors: Cartwright Margaret A , Beauchamp David A , Bryant Mason D
Published: April 2011

Although some sockeye salmon (Oncorhynchus nerka) enhancement programs achieve production goals in Alaskan lakes, others like the Margaret Lake project fall well below expected levels. We used bioenergetics model simulations, coupled with field sampling of predator diet and distribution, to quantify the intensity of cutthroat trout (Oncorhynchus clarki) predation on stocked sockeye salmon fry in Margaret Lake during 1993 and 1994. Model results indicated that, by September, cutthroat trout consumed an estimated 34-51 and 32-100% of the 200 000 and 100 000 sockeye salmon fry stocked in May 1993 and 1994, respectively. September hydroacoustic survey results estimated a 82-87% decline of fry in 1993 and 90-93% in 1994. Stomach fullness and evacuation estimates of total consumption were 59% of model estimates after the first fry release in 1994 and 120% of the model estimates after the second release. All approaches to estimating cutthroat trout predation on stocked fry suggested that piscivores played a substantial role in the decline of sockeye salmon fry in Margaret Lake. The ability to estimate consumption is valuable in isolating predator influence on food web dynamics, especially in manipulated systems.