bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of increasing winter rearing habitat on abundance of salmonids in two coastal Oregon streams
Authors: Solazzi M F , Nickelson T E , Johnson S L , Rodgers J D
Published: April 2011

We used a BACI (before-after-control-impact) experimental design to examine the effects of increasing winter habitat on the abundance of downstream migrant salmonids. Two reference streams and two treatment streams were selected in the Alsea and Nestucca basins of Oregon. Population parameters for juvenile coho salmon (Oncorhynchus kisutch), age-0 trout (Oncorhynchus spp.), steelhead (Oncorhynchus mykiss), and coastal cutthroat trout (Oncorhynchus clarki) were estimated each year for 8 years in each stream. Stream habitat was modified to increase the quality and quantity of winter habitat during the summers of 1990 (Nestucca Basin) and 1991 (Alsea Basin). Complex habitat was constructed by adding large woody debris to newly created alcoves and dammed pools. Numbers of coho salmon summer juveniles and smolts increased in the treatment streams relative to the control streams during the posttreatment period. Overwinter survival of juvenile coho salmon also increased significantly in both treatment streams posttreatment. Summer trout populations in the treatment streams did not change, but downstream migrant numbers the following spring did increase. These increases suggest that winter habitat was limiting abundance of all three species.
Reconstruction of pinniped diets: accounting for complete digestion of otoliths and cephalopod beaks
Authors: Bowen W D
Published: April 2011

The recovery of sagittal fish otoliths and cephalopod beaks from fecal samples is an important source of information about the diets of marine mammals. Nevertheless, diet reconstructions are biased to some extent because of the partial and complete digestion of these prey structures. Although some authors have used correction factors to account for partial digestion of otoliths, none to date have corrected for the number of otoliths and cephalopod beaks that are completely digested, termed number correction factors (NCFs). Data from nine studies of captive pinnipeds show that corrections for the complete digestion of otoliths and cephalopod beaks range from 1.0 to 25.0 in the 28 prey species. Correction factors ranged from 1.0 to 10.0 in cases where seals could exercise by swimming during the experiment. In several species, NCFs vary inversely with prey length. The effect of applying NCFs will depend on the relative proportion of prey species in the diet and the NCFs of these species. Nevertheless, estimates of the species composition of marine mammal diets will benefit from the use of NCFs. Finally, standardization of experimental protocols and attention to the estimation of variability are needed to provide more reliable NCFs.
Modelling the probability of salmonid egg pocket scour due to floods
Authors: Lapointe Michel , Eaton Brett , Driscoll Steve , Latulippe Christian
Published: April 2011

Flood disturbance plays a key but complex role in structuring lotic ecosystems. Empirical models proposed here allow salmonid resource managers to quantify the probability of egg pocket scour during floods and to predict how the expected losses vary with flood strength and reach characteristics. The models are based on comparisons between published salmonid egg pocket depth criteria and statistics on the intensity and spatial distribution of scour and fill produced by three flood events of widely different magnitudes in three separate reaches of a gravel-cobble Atlantic salmon (Salmo salar) river in the Saguenay region, Quebec. A simple substrate mobility index, based on reach-scale geomorphic characteristics and flood hydraulics, was shown to provide useful predictions (R2up to 74%) of the fraction of the area of potential spawning zones undergoing flood scour greater than 30 cm. Any Atlantic salmon egg pockets present in these deeply scoured areas would be destroyed. The models also predict the distribution of fill (net rise in bed) potentially causing fry entombment at redds. The flood disturbance data suggest that average probability of scour of an Atlantic salmon egg pocket in the study reaches ranges from under 5% for frequent-recurrence spring floods to approximately 20% for an extreme, multicentenary-recurrence flood.
Digestive enzyme and gut surfactant activity of detritivorous gizzard shad (Dorosoma cepedianum)
Authors: Smoot James C , Findlay Robert H
Published: April 2011

Measuring digestive enzyme and surfactant activities tested specialization of gizzard shad (Dorosoma cepedianum) digestive physiology to a detritivorous feeding strategy. Digestive enzyme activity was measured in adult and larval gizzard shad using fluorescently labeled artificial substrates. Surfactant activity in gizzard shad was measured by comparing gut juice drop diameters over a range of dilutions. Enzyme activity in the ceca region of adult gizzard shad was high for esterase, beta-glucosidase, lipase, and protease. Enzyme activity was lower in posterior intestine sections than in anterior intestine sections, although protease activity remained high for the greatest distance in the intestine. Micelles were detected in adult gizzard shad gut juice, and surfactant activity was greatest in the ceca region. Larval gizzard shad protease activity was similar to that of adult fish, and surfactants were below their critical micelle concentration. Gizzard shad coupled digestive physiology with gut anatomy to obtain nutrients from detritus, and these adaptations may explain elevated growth rates observed in these fish when they are planktivorous.
Regional differences in rates and patterns of North American inland lake invasions by zebra mussels (Dreissena polymorpha)
Authors: Kraft Clifford E , Johnson Ladd E
Published: April 2011

Zebra mussels (Dreissena polymorpha) have spread rapidly in North America by dispersal within connected bodies of waters. This study provides the first systematic evaluation of rates of zebra mussel dispersal to inland lakes separated from source populations by functional dispersal barriers. Plankton samples were examined for this exotic species from 140 lakes during a 3-year period (1995-1997). Infestations were detected in 19% of lakes surveyed: seven of 28 Indiana lakes (25%), 15 of 49 Michigan lakes (31%), but only five of 63 Wisconsin-Illinois lakes (8%). Annual rates of infestation varied from 0 to 12%·year-1 among the three regions. Wisconsin-Illinois lake infestations were only detected in 1995 and 1996, whereas new Indiana and Michigan infestations were detected in all three years. Lakes with surface areas less than 100 ha had lower infestation rates than larger lakes. Incidental sightings of inland lake colonization within the study region qualitatively supported observed regional differences in rates and spatial patterns of colonization. These results demonstrate that the spread of zebra mussels into inland lakes is not occurring as rapidly as through connected waterways, and rates of inland lake colonization vary according to regional conditions and lake size.
Distribution, hydrologic transport, and cycling of total mercury and methyl mercury in a contaminated river-reservoir-wetland system (Sudbury River, eastern Massachusetts)
Authors: Waldron Marcus C , Colman John A , Breault Robert F
Published: April 2011

Riparian wetlands contaminated with Hg from an industrial point source were found to be important sites of production and release of methyl mercury (MeHg) in a 40-km reach of the Sudbury River in eastern Massachusetts. Stream discharge and concentration measurements were used to calculate annual mean loads for total Hg (ΣHg) and MeHg in contaminated river reaches, a reservoir, and a riparian wetland downstream from the industrial source. Budgets based on these loads indicate that the annual mean ΣHg load increased sixfold in a reach receiving flow from the point source, but the annual mean MeHg load did not increase. About 23% of the ΣHg load was removed by sedimentation during flow through the reservoir. Net production of MeHg in the reservoir was similar to that reported elsewhere for lakes receiving Hg from atmospheric deposition only. ΣHg concentrations and loads increased significantly as the river passed through the riparian wetland reach. On the basis of flooded wetland area, net production of MeHg was 15 times greater in the wetland reach than in wetland-associated drainages described in other studies.
An in situ assessment of mercury contamination in the Sudbury River, Massachusetts, using transplanted freshwater mussels (Elliptio complanata)
Authors: Beckvar Nancy , Salazar Sandra , Salazar Michael , Finkelstein Ken
Published: April 2011

Freshwater mussels (Elliptio complanata) were transplanted into the Sudbury River, Massachusetts, to evaluate the bioavailability of total Hg and methyl mercury (MeHg) and the potential impacts to resident species. The principal Hg source is the Nyanza Superfund site, a former textile dye production facility. Mussels (initial tissue concentrations = 640 ng Hg·g dry weight-1 and 120 ng MeHg·g dry weight-1) were transplanted to eight locations in the Sudbury River watershed for 12 weeks. Tissue total Hg concentration increased significantly in mussels at the station closest to the Nyanza site (950 ng Hg·g dry weight-1). Mussel growth, which increased downstream with distance away from the site, was significantly negatively correlated with tissue concentrations of total Hg (r = -0.95) and positively correlated with average temperature (r = 0.85). Due to growth differences, uptake was best assessed by changes in content. Tissue total Hg and MeHg burdens were greatest in mussels at two stations closest to the Nyanza site, with less Hg accumulated in downstream mussels. However, the MeHg content in mussel tissue increased significantly at all Sudbury River stations, indicating that MeHg was bioavailable in all portions of the river evaluated.
Density-dependent intercohort interactions and recruitment dynamics: models and a bull trout (Salvelinus confluentus) time series
Authors: Paul Andrew J , Post John R , Sterling George L , Hunt Carl
Published: April 2011

A simple theoretical model shows that mechanisms of density-dependent survival that result in stable dynamics for populations with only intracohort interactions during the juvenile phase can produce cyclic behaviour when cohorts interact together. We compared these theoretical results with a time series (1971-1985) on juvenile bull trout (Salvelinus confluentus) from Eunice Creek, Alberta. Abundance of bull trout in Eunice Creek ranged over two orders of magnitude over the 15 years. By assigning age-classes to the abundance data (using a probabilistic length-frequency analysis), we assessed yearly survival rates for age-classes 1-3. Survival rates for age-classes 1 and 2 were negatively correlated (P < 0.05) with the effective density (an index of total consumption) of all juvenile bull trout in Eunice Creek. These observations support the hypothesis that different age cohorts of juvenile bull trout do interact. Using a stochastic version of the model and parameter values estimated from Eunice Creek, we hypothesize that even moderate levels of adult mortality (an average adult spawns during two seasons) coupled with random variation in the density-independent component of juvenile mortality can result in an apparent cyclic pattern for bull trout. Finally, stock- recruitment relationships for these populations are not represented by a single average curve.
Factors affecting the swimming endurance and catchability of Atlantic cod (Gadus morhua)
Authors: Winger Paul D , He Pingguo , Walsh Stephen J
Published: April 2011

The swimming endurance of Atlantic cod (Gadus morhua), native to the cold waters off the east coast of Newfoundland and Labrador, was investigated under laboratory conditions. Using a swimming flume, endurance was tested at swimming speeds ranging from 0.6 to 1.3 m·s-1using water temperatures from 0.0 to 9.8°C ( mean = 3.2°C, SD = 2.8) and fish lengths from 41.0 to 86.0 cm ( mean = 57.8 cm, SD = 10.5). The results revealed that swimming speed was the only significant factor affecting the endurance of cod. The maximum sustained swimming speed (Ums) was predicted to be 0.66 m·s-1. Statistical analysis of the data was conducted using failure time analysis. The hazard, or risk of exhaustion, was found to increase rapidly with increasing swimming speed, i.e., there was a decrease in the probability of cod achieving a given swimming endurance. Probability curves for the endurance of cod were calculated for different swimming speeds. The findings suggest that the catching efficiency of commercially targeted cod (>41.0 cm) by otter trawls may be highly sensitive to changes in towing speed while being independent of both fish length and water temperature.
Cumulative effects of pulp mill and municipal effluents on epilithic biomass and nutrient limitation in a large northern river ecosystem
Authors: Scrimgeour Garry J , Chambers Patricia A
Published: April 2011

Large-scale patterns in epilithic biomass and nutrient status were evaluated at 33 sites located upstream and downstream of point-source anthropogenic effluents in the Athabasca and Wapiti-Smoky rivers in Alberta, Canada. Multiple regression showed that epilithic chlorophyll a was significantly (p < 0.0001) related to concentrations of dissolved inorganic nitrogen and marginally (p = 0.06) significantly related to soluble reactive phosphorus. Epilithic biomass was up to 50 times higher immediately downstream of point-source inputs compared with sites upstream and those 20-150 km downstream. Data from nutrient diffusing substrata showed that the epilithon at 18 of the 33 sites was nutrient limited, while 14 sites showed no nutrient limitation; interpretation of the remaining site was inconclusive. Of the 18 nutrient-limited sites, six were nitrogen limited, five were phosphorus limited, and seven were co-limited. Multiple discriminant function analysis showed that the combined concentration of soluble reactive phosphorus and dissolved inorganic nitrogen was a significant discriminator between deplete and replete sites.
A bioeconomic model of marine sanctuaries on Georges Bank
Authors: Holland Daniel S
Published: April 2011

An empirically estimated fleet dynamics model for New England trawlers is integrated with spatial, age-structured models of primary groundfish species on Georges Banks, southern New England, and the Gulf of Maine. This bioeconomic model is used to explore how permanent marine sanctuaries on Georges Bank might affect catches, revenues, and spawning stock of principal groundfish species in New England. The simulations explore how the location of sanctuaries relative to major ports and their orientation relative to seasonal movement patterns of fish stocks impact their effectiveness and the distribution of benefits across groups of fishers from different ports. The simulation results also demonstrate that the impacts of sanctuaries can vary greatly across species, sometimes increasing yields for some while decreasing yields for others. While the specific results from the simulations reflect the characteristics of the New England groundfish fishery, the modeling methodology and some general conclusions are applicable to other fisheries.
Protandry in Pacific salmon
Authors: Morbey Yolanda
Published: April 2011

Protandry, the earlier arrival of males to the spawning grounds than females, has been reported in several studies of Pacific salmon (Oncorhynchus spp.). However, the reasons for protandry in salmon are poorly understood and little is known about how protandry varies among and within populations. In this study, protandry was quantified in a total of 105 years using gender-specific timing data from seven populations (one for pink salmon (O. gorbuscha), three for coho salmon (O. kisutch), two for sockeye salmon (O. nerka), and one for chinook salmon (O. tshawytscha)). Using a novel statistical procedure, protandry was found to be significant in 90% of the years and in all populations. Protandry may be part of the males' strategy to maximize mating opportunities and may facilitate mate choice by females.
Abundance estimation and capture of sablefish (Anoplopoma fimbria) by longline gear
Authors: Sigler Michael F
Published: April 2011

Longline surveys in Alaska measure sablefish (Anoplopoma fimbria) relative abundance and are the primary information source used for abundance and quota estimation. Hook timer, on-bottom (soak) time, hook density, hook pattern, bait type, and bait condition experiments and mathematical models were used to evaluate the performance of the longline surveys for estimating sablefish relative abundance. The rate that sablefish encountered the longline gear decreased with on-bottom time independently of sablefish density in the sampled area. Sablefish were adept at locating available baits, even when few remained. The decrease in encounter rate appears related to odor concentration at the leading edge of the odor plume. The ability to locate baits, even when few remain, differs from previous models of fish capture by longline in which the probability that a fish located a bait was proportional to the number of available baits. Decreased encounter rate and the ability to locate baits efficiently imply that longline catch rates likely provide an accurate index of fish abundance if the on-bottom time is long enough to cover the period when most fish encounter the gear and the initial bait density is high enough that baits remain available throughout the soak; the weak link between catch rate and abundance is the unknown extent that factors such as temperature and food availability affect the proportion of fish caught.
Changes in sediment viral and bacterial abundances with hypolimnetic oxygen depletion in a shallow eutrophic Lac Brome (Quebec, Canada)
Authors: Ricciardi-Rigault Mahaut , Bird David F , Prairie Yves T
Published: April 2011

Two studies were conducted to examine changes in sediment viral and bacterial abundances following hypolimnetic oxygen depletion. Both studies, a spatiotemporal field study and a core incubation experiment set under controlled conditions, demonstrated that bacterial and viral abundances decreased significantly (43-48% for bacteria and 36-38% for viruses) and in a nearly identical pattern when submitted to changes in the oxygen status of their milieu. The consistency of the results strongly suggests that the shift in both population densities is essentially caused by the onset of anoxia, either directly or indirectly. We suggest that the decline in abundance is due to the disappearance of strictly aerobic bacteria and their associated viruses and not due to stress-induced viral lysis. We also show that the P content of the lysed microbial community can represent an important source of P released from the sediments.
Growth patterns of Labrador Sea Atlantic salmon postsmolts and the temporal scale of recruitment synchrony for North American salmon stocks
Authors: Friedland Kevin D , Reddin David G
Published: April 2011

We measured postsmolt growth patterns from scales of Atlantic salmon postsmolts captured in the Labrador Sea and adult returns from stocks at the southern end of the range of salmon in North America. Because Labrador Sea postsmolts are believed to represent the juvenile nursery for the entire stock complex, the growth variation for southern stocks may yield insights on the time scale of stock mixing during the postsmolt year. Circuli spacing patterns were extracted from the scales of 1525 salmon for 3 smolt years. For 2 of the 3 years, growth trajectories for fish from the southern stocks intersected the trajectories for Labrador Sea postsmolts after 4-5 circuli pairs. The time that it takes to deposit a circulus during the spring and summer seasons suggests that distribution patterns for regional groups begin to overlap or stocks begin to experience similar environmental conditions by June or July of the postsmolt year, or 1 to 2 months after their migration to sea. In some years, however, it would appear that this mixing does not occur until fall. These data provide the first indication of the time scale of events during the postsmolt year that regional influences may be acting on stocks to produce synchronous recruitment.
Effects of fish predation in erosional and depositional habitats in a temperate stream
Authors: Rosenfeld Jordan
Published: April 2011

Combined effects of predation by benthic and drift-foraging fish (prickly sculpin (Cottus asper) and coho salmon (Onchorhynchus kisutch) parr) on benthic invertebrate community and trophic structure were evaluated in Mayfly Creek, a previously fishless stream in the Coast Range Mountains of British Columbia. The role of microhabitat (substrate) in mediating predation effects was assessed by comparing invertebrate community structure on unglazed ceramic tiles and gravel baskets nested within enclosures. The role of macrohabitat was evaluated by placing enclosures in pool and riffle habitats. Effects of fish predation were most pronounced on tile substrate and in riffle habitat and least pronounced on gravel substrate in pool habitat. The presence of fish caused a decrease in abundance of larger-bodied herbivores (primarily the mayflies Ameletus and Baetis) and had positive indirect effects on algae and smaller invertebrates (primarily Orthocladiinae chironomids and nemourid stoneflies), probably through competitive release. In contrast with herbivores, detritivorous invertebrates were less influenced by fish predation and more highly correlated with the abundance of organic detritus. The distribution and abundance of detritivores in Mayfly Creek appear to be primarily influenced by bottom-up forces (implying resource limitation), while grazers in algal-based food chains are more strongly influenced by top-down effects (fish predation).
Bioavailability of sediment-bound metals for Vallisneria americana Michx, a submerged aquatic plant, in the St. Lawrence River
Authors: St-Cyr Louise , Campbell Peter GC
Published: April 2011

We have assessed the bioavailability of sediment-bound metals (Cd, Cr, Cu, Ni, Pb, and Zn) in the St. Lawrence River using a rooted aquatic plant, Vallisneria americana Michx, as the biomonitor species. The host sediments were subjected to a sequential leaching procedure to determine the partitioning of the metals present in the surficial oxic stratum; previously published equations were then used to estimate the free metal ion concentrations at the root-sediment interface. Suspected metal accumulation in foliage from point-source pollution of the water column obscured sediment-plant relationships at several sampling stations, but in general, plant metal concentrations could be predicted on the basis of sediment geochemistry (including sediment metal concentrations). Metal concentrations in Vallisneria tissues correlated more closely with estimates of bioavailable sediment-bound metal than with total metal concentrations in sediments, particularly for Cd, Pb, and Zn. Roots proved to be better bioindicator organs than shoots for monitoring sediment contamination. Overall, the results demonstrate that Vallisneria would be a useful biomonitor species of metal contamination in the St. Lawrence River.
Potential contact statistics for measuring scale-dependent spatial pattern and association: an example of northern cod (Gadus morhua) and capelin (Mallotus villosus)
Authors: O'Driscoll Richard L , Schneider David C , Rose George A , Lilly George R
Published: April 2011

Analysis of simulated data showed that potential contact statistics could be used to describe spatial pattern in sample density data. Potential contact is a new method, analogous to Ripley's K function for mapped point pattern analysis. Potential contact can be used to describe spatial pattern and association over a range of scales without grouping data and is robust against the presence of zeros. The statistical output is ecologically interpretable, as a measure of the degree of contact between individuals. This new technique was applied to examine changes in the spatial distribution of Atlantic cod (Gadus morhua) off Newfoundland, Canada, from 1985 to 1994, a period that encompassed a collapse of the cod stock. Sample data from bottom-trawl surveys indicated that cod were aggregated in patches with dimensions of 100-250 km. During the period of cod decline in the 1990s, spatial structure changed in three ways: the number of patches decreased, patch size shrank, and contact with conspecifics at small (10-20 km) scales fell. Cod were broadly associated with capelin (Mallotus villosus), a major prey species. Spatial distribution of capelin changed over the same time period as changes in cod distribution, and there was no evidence that contact between cod and capelin decreased.
Influence of body weight, swimming characteristics, and water temperature on the cost of swimming in brook trout (Salvelinus fontinalis)
Authors: Tang Ming , Boisclair Daniel , Ménard Chantal , Downing John A
Published: April 2011

We performed respirometry experiments to estimate the spontaneous swimming costs of brook trout (Salvelinus fontinalis) for 24 combinations of fish weight (3.5, 17, and 32 g), water temperature (4, 12, and 18°C), and respirometer size (27, 54, and 108 L). Fish swimming characteristics were estimated for each experiment using videocamera recordings and image analysis. Under our experimental conditions, average swimming characteristics of fish, such as swimming speed and turning and acceleration rates, varied from 2.5- to 29-fold. Our data, alone or combined with similar published results on brook trout weighing 1 g, indicated that fish weight was the only variable that could explain a statistically significant proportion of the variations of spontaneous swimming costs for that species (r2 = 0.91). Our work confirms, with a wider range of experimental data, that spontaneous swimming costs of fish are 3- to 22-fold (8-fold average difference) more energy demanding than predicted by forced swimming models developed using fish swimming at constant speeds and directions in flumes.
Effect of unstable aluminium chemistry on Arctic char (Salvelinus alpinus)
Authors: Poléo Antonio BS , Bjerkely Frode
Published: April 2011

Arctic char (Salvelinus alpinus) were exposed to a non-steady-state Al-rich medium (pH 5.8, total Al 480 µg·L-1, total organic C 3.0 mg C·L-1, Ca2+ 2.9 mg·L-1, temperature 7.5°C). An Al-poor medium (pH 5.2 and 5.8, total Al 99 µg·L-1, total organic C 3.0 mg C·L-1, Ca2+ 2.9 mg·L-1, temperature 8.0°C) acted as control. The Al-rich medium was acutely toxic to the Arctic char. Total mortality (percent) and mortality rate (LT50) were highest in fish exposed to the Al-rich medium immediately after mixing and decreased systematically with water residence time (e.g., from 65 h at 1 min to 124 h at 3 min to more than 400 h at 15 min). Gill morphology changes, Al gill deposition, and haematological parameters revealed significant effects of Al, which all correlated with water residence time. Signs of acclimation or high difference in Al tolerance between individuals were observed. This indicates that effects of Al in fish are dependent on the degree of Al polymerisation and supports earlier indications that Arctic char are relatively tolerant of acidic Al-rich water.
Role of chemical and physical variables in regulating microcystin-LR concentration in phytoplankton of eutrophic lakes
Authors: Kotak Brian G , Lam Angeline K-Y , Prepas Ellie E , Hrudey Steve E
Published: April 2011

A survey of eutrophic to hypereutrophic hardwater lakes in central Alberta was conducted to test the hypotheses that the concentration of the cyanobacterial toxin microcystin-LR (MC-LR) in phytoplankton is regulated by environmental factors that affect both the biomass of the main producer of the toxin, Microcystis aeruginosa, and the concentration of the toxin in the cells. Of all environmental factors examined, total phosphorus was the strongest correlate of both M. aeruginosa biomass and cellular MC-LR (expressed as micrograms per gram of M. aeruginosa). Microcystis aeruginosa biomass was also strongly negatively related to the total nitrogen to total phosphorus ratio (TN:TP) and inorganic nitrogen (NO2-+ NO3-, NH4+). A univariate regression model of TN:TP explained the most variation in MC-LR concentration (expressed as nanograms of cellular toxin per litre) in mixed phytoplankton communities. This study indicated that MC-LR dynamics in phytoplankton of lakes was related to changes in the concentration and ratio of phosphorus and nitrogen.
Population dynamics of rainbow smelt (Osmerus mordax) in Lakes Ontario and Erie: a modeling analysis of cannibalism effects
Authors: Lantry Brian F , Stewart Donald J
Published: April 2011

We used a stochastic stage-based matrix model (annual time step) and a bioenergetics model (daily time step) to simulate population dynamics, production, consumption, and conversion efficiency for rainbow smelt (Osmerus mordax) populations in Lakes Ontario and Erie. Cannibalism on young-of the-year (YOY) smelt by yearlings was the only scenario that reproduced alternate-year recruitment cycles observed in Lakes Ontario and Erie. Assuming constant survivorship and 5% variation in cannibalism, less than one YOY consumed per yearling smelt per year in both lakes could produce fluctuations greater than those observed. We found that at estimated daily mortality rates and during the pelagic phase of larvae only, 2% of the yearling smelt in Lake Erie and 5.1% in Lake Ontario need to consume one YOY per day to induce the observed abundance fluctuations. Bioenergetics simulations of alternating recruitment produced fluctuations in simulated values for annual gross production of approximately 6-7 and 31-59% for the Lake Ontario and Lake Erie smelt populations, respectively.
European eel (Anguilla anguilla): prediction of spawner escapement from continental population parameters
Authors: Feunteun Eric , Acou Anthony , Laffaille Pascal , Legault Antoine
Published: April 2011

This paper describes the assessment of silver European eel (Anguilla anguilla) escapement based on a "sedentary" population fraction analysis in a 60-km2 watershed of northern Brittany (France). Downstream migration fluxes were monitored using eel traps and related to environmental factors. Intensive electrofishing and fyke-net fishing were conducted to assess eel biomass, densities, and population structure. A total of 564 eels, including 81 silver eels, were PIT tagged. In 1996, 616 eels were caught in the catchment including 68 silver eels (11%). During the following downstream migration period, 12 of the PIT-tagged silver eels, among a total of 678, were recaptured in the downstream traps. Seven were recaptured in the catchment in 1997. It was shown that (i) only about 20% of the silver eels present in the catchment emigrated during the following year, (ii) 12% stayed in the catchment including two (3.4%) that recovered yellow eel characteristics, and (iii) the other eels either died or settled in the catchment but were not recaptured. It was also estimated that 2% (650 eels) of the population (34 000 eels) among 3000 silver eels considered "emigration candidates" emigrated each year,.
Pelagic fishes and the cod recruitment dilemma in the Northwest Atlantic
Authors: Swain D P , Sinclair A F
Published: April 2011

Like most other stocks of Atlantic cod (Gadus morhua) in the Northwest Atlantic, cod in the southern Gulf of St. Lawrence declined to low abundance in the early 1990s. Recovery has been slow in contrast with the rapid recovery from similar levels of abundance in the mid-1970s. This difference reflects remarkably high prerecruit survival of cod in the earlier period of low abundance rather than unusually poor survival in the 1990s. The period of high prerecruit survival of cod coincided with the collapse of herring (Clupea harengus) and mackerel (Scomber scombrus) stocks resulting from overfishing. These pelagic fishes are potential predators or competitors of the early life history stages of cod. We report a strong negative relationship between the biomass of these pelagic fishes and recruitment rate of southern Gulf cod. This is consistent with the recent suggestion that the success of large predatory fishes may depend on "cultivation" effects in which the adults crop down forage fishes that are predators or competitors of their young. Our results also point to the possibility of a triangular food web involving cod, seals, and pelagic fishes, making it difficult to predict the effect of a proposed cull of seals on the recovery of cod.
Stream temperature responses to forest harvest and debris flows in western Cascades, Oregon
Authors: Johnson Sherri L , Jones Julia A
Published: April 2011

Stream temperature controls the rates of many biotic and abiotic processes and is influenced by changes in streamside land use practices. We compiled historic stream temperature data and reestablished study sites in three small basins in the H.J. Andrews Experimental Forest in the western Cascades, Oregon, to reexamine the effects on and recovery of stream temperatures following removal of riparian vegetation. Maximum stream temperatures increased 7°C and occurred earlier in the summer after clear-cutting and burning in one basin and after debris flows and patch-cutting in another. Diurnal fluctuations in June increased from approximately 2 to 8°C. Stream temperatures in both basins gradually returned to preharvest levels after 15 years. The influence of the primary factor controlling stream temperatures, shortwave solar radiation, was amplified following removal of riparian vegetation, and conduction between stream water and nearby soils or substrates also appeared to be an important factor. Shifts in the timing of summer maxima and greater increases in early summer stream temperatures could impact sensitive stages of aquatic biota.
Field test of a new method for tracking small fishes in shallow rivers using passive integrated transponder (PIT) technology
Authors: Roussel J -M , Haro A , Cunjak R A
Published: April 2011

A new method for tracking small fishes in shallow streams based on passive integrated transponder (PIT) technology, using a portable reading unit, was investigated. The device consists of a chest-mounted palmtop computer, a reader, and a 12-V battery enclosed in a backpack, connected to a 60-cm-diameter coil antenna mounted on a 4-m-long pole. The method was field tested with wild Atlantic salmon, Salmo salar, parr using transponders 23.1 mm long and 3.9 mm in diameter surgically implanted in the peritoneal cavity of the fish. Laboratory experiments indicated no posttagging mortality for fish > 84 mm in fork length and no tag loss when sutures were used. In the field, tag detection distance was up to 1 m. While moving the antenna above the stream surface, the operator could locate a fish's position to within a square metre. Experiments indicated that more than 80% of tagged parr, on average, were detected by the reader. The technique is a useful alternative to standard radiotelemetry in small-scale environments because PIT tags can be implanted in smaller-bodied fishes and fine-scale movements of individuals can be studied. It can be applied to address numerous questions in the fields of animal behaviour, habitat use, and population dynamics.
Modeling the potential effects of climate change on leaf pack processing in central Appalachian streams
Authors: Buzby Karen M , Perry Sue A
Published: April 2011

A computer simulation model was constructed to evaluate some of the projected impacts of climate change, including elevated temperatures and increased frequency and magnitude of floods and droughts, on leaf pack processing in central Appalachian streams. The model simulated microbial processing, invertebrate consumption, and transport along a 1-km second-order stream. We examined the effects of wet and dry years with and without a 2°C temperature increase. Both invertebrates and microbes processed more leaf material under the elevated temperature scenarios; however, the invertebrate response was greater than the microbial response. In the model, microbial processing is represented as a linear function of temperature; a nonlinear response might produce different results. Invertebrates processed a greater percentage of the inputs in wet than in dry years, while microbial processing rates were unaffected. A 20-year flood event occurring in November, January, or March caused more than 50% of the leaf inputs to be exported, leaving little detrital material available for invertebrate consumption. The timing of the flood event made little difference to the simulation results. All climate change scenarios resulted in decreases, sometimes substantial, in coarse particulate organic matter availability to shredders during the summer months.
Interrenal metallothionein and cortisol secretion in relation to Cd, Cu, and Zn exposure in yellow perch, Perca flavescens, from Abitibi lakes
Authors: Laflamme J -S , Couillard Y , Campbell P GC , Hontela A
Published: April 2011

The concentrations of Zn, Cu, and Cd in the interrenal tissue and liver of yellow perch, Perca flavescens, sampled in six lakes in the mining region of Abitibi (Quebec) revealed a gradient of contamination: reference lakes, intermediate-contaminated lakes, and highly contaminated lakes. Interrenal and hepatic metallothionein concentrations followed a similar gradient, and there was a strong relationship between metallothionein and total metal (Zn + Cu + Cd) content in the liver and Cu + Cd content in the interrenals. Following a standardized confinement stress test, plasma cortisol and glucose were significantly higher in fish from reference lakes compared with the two most contaminated lakes. No differences in plasma chloride were observed. The secretory response of the interrenal tissue to in vitro stimulation by adrenocorticotropic hormone and dibutyryl cyclic AMP was significantly lower in fish from a contaminated lake compared with fish from a reference lake. Condition factor was significantly lower in yellow perch from the most contaminated lakes. This study demonstrated that a chronic field exposure to base metals increases hepatic and interrenal tissue metallothionein concentrations and disrupts the physiological capacity of yellow perch to generate the normal hormonal stress response.
Effects of experimental clearcut logging on water quality in three small boreal forest lake trout (Salvelinus namaycush) lakes
Authors: Steedman Robert J
Published: April 2011

Water quality was monitored in three 30-ha stratified headwater Precambrian Shield lakes for 5 years before and 3 years after moderate to extensive catchment deforestation. These lakes, which had water renewal times of about a decade, showed only minor changes in water quality by the third year after logging. Water quality response in a lake with moderate deforestation and intact shoreline forest was similar to that in two lakes with extensive upland and shoreline deforestation. By the second and third years after logging, May-September average volume-weighted concentrations of dissolved organic carbon, chlorophyll, total nitrogen, K+, Cl-, and Si had all increased, generally by about 10-40% over predisturbance levels, while Ca2+ and Mg2+ had declined by 10-25%. Dry weather the first year after logging was associated with temporary declines of 10-20% in dissolved organic carbon and chlorophyll.
Sudden appearance of cysts and ellobiopsid parasites on zooplankton in a Michigan lake: a potential explanation of tumor-like anomalies
Authors: Bridgeman Thomas B , Messick Gretchen , Vanderploeg Henry A
Published: April 2011

Cysts on calanoid and cyclopoid copepods, previously reported as tumor-like anomalies (TLAs) in Lake Michigan and Europe, appeared briefly in Patterson Lake, a small Michigan inland lake. Cysts were rare (4% maximum) in samples collected on September 11, 1999, but appeared with high frequency on calanoid adults (49%) and cyclopoid nauplii (73%) in samples collected on October 16. By October 30, cysts were again rare (0.4% maximum). Cysts most commonly appeared on the lateral surface of the animal at the articulation of the 1st and 2nd prosomal segments and often consisted of herniated copepod tissues. Transparent, pyriform cysts co-occurred in low frequency with other types of cysts and are believed to be the trophomeres and gonomeres of ellobiopsid parasites. Histologic manifestations of cysts were diverse; herniations consisted of acellular yolk-like material and apparent host tissue, while cysts thought to be Ellobiopsis contained cells with different degrees of nuclear staining and unusual spherical bodies. Hernias were experimentally induced on live calanoid copepods by piercing the carapace with a fine needle, suggesting that ellobiopsid parasites may cause the hernias by puncturing the carapace of their hosts. Ellobiopsid parasites are common on marine crustacean zooplankton but have been recorded only once before in freshwater.
Phosphorus dynamics in shallow subsurface waters in an uncut and cut subcatchment of a lake on the Boreal Plain
Authors: Evans J E , Prepas E E , Devito K J , Kotak B G
Published: April 2011

Phosphorus dynamics in shallow subsurface waters (<2.5 m depth) were studied in harvested and unharvested subcatchments of a Boreal Plain lake. The organic soil layer was underlain by discontinuous layers of sand and clay glacial till. Total dissolved P (TDP) concentrations (6-798 µg·L-1) of discrete water samples from mineral layers (0.9-2.5 m deep) generally decreased with depth, were negatively related to Ca (rs < -0.7), and were lower in clay. When the groundwater table rose and saturated the organic layer, TDP concentrations increased in the composite (organic mineral layer) but not in the discrete (mineral layer) water samples, indicating that elevated TDP concentrations originate from the near-surface organic layer. TDP concentrations in composite samples were negatively correlated with water table depth (rs = -0.6) and were positively correlated with transmissivity (rs = 0.7) and dissolved organic C concentration (rs > 0.6). In the riparian buffer zone of the harvested subcatchment, TDP concentrations of composite samples decreased during high runoff, but these values remained higher than concentrations in the unharvested subcatchment. However, surface topography and variable depth to confining clay layers resulted in higher groundwater tables in the harvested subcatchment, especially in the cut area. Mean daily TDP export coefficients were similar between the unharvested (14 µg·m-2) and harvested (12 µg·m-2) subcatchments.
Effects of forestry roads on reproductive habitat and exploitation of lake trout (Salvelinus namaycush) in three experimental lakes
Authors: Gunn John M , Sein Rod
Published: April 2011

This study was designed to test the effects of two potential impacts of forest access roads on lake trout (Salvelinus namaycush) lakes in the Boreal Shield ecozone: (i) loss of reproductive habitat through siltation and (ii) increased access and exploitation. During an 9-year study (1991-1999) in Whitepine Lake, access to seven original spawning sites and over 250 alternate spawning sites was progressively removed by covering the substrate with opaque plastic sheeting to simulate siltation. No effects on recruitment of lake trout have yet been detected. Mark-recapture estimates of juvenile (<370 mm fork length) abundance remained high, mean body size did not increase, and emergent alevins continued to be produced from the alternate spawning sites each year. Similar results occurred in a short-term study in Helen Lake. The lack of obvious effects of reproductive habitat loss was in sharp contrast with the rapid and severe effects that fishing pressure exerted on the lake trout population in Michaud Lake where access was improved by construction of a 12-km forest access road. These findings suggest that lake trout can tolerate substantial losses in spawning habitat, but natural populations, particularly in small lakes, must be protected from excessive exploitation.
Pelagic and benthic algal responses in eastern Canadian Boreal Shield lakes following harvesting and wildfires
Authors: Planas Dolors , Desrosiers Mélanie , Groulx S-Raphaëlle , Paquet Serge , Carignan Richard
Published: April 2011

Pelagic and benthic algal biomass and pelagic algal community structure were measured in Boreal Shield lakes impacted by forest harvesting and wildfires (Haute-Mauricie, Québec). Sixteen reference lakes in which the watershed has been unperturbed for at least 40 years, seven harvested lake watersheds (logged in 1995), and nine lake watersheds burnt in 1995 were sampled for 3 years following harvesting or wildfires. From 1996 to 1998, repeated-measures ANOVA showed significant effects between treatment and sampling years for pelagic chlorophyll a (Chl a) and biomass, but for 1997-1998 benthic Chl a, repeated-measures ANOVA showed only significant treatment effects. Chl a concentrations increased 1.4- to 3-fold in perturbed lakes as compared with reference lakes. Areal pelagic Chl a (milligrams per square metre) was lower than estimated littoral Chl a in perturbed lakes. The pelagic algal community was dominated by mixotrophic nanoflagellates in reference lakes. Watershed perturbation induced differential changes in pelagic algal communities: mixotrophic nanoflagellates increased in harvested lakes and photoautotrophic diatoms in burnt lakes. Considering only perturbed lakes, algal biomass was proportional to the fraction of the catchment area perturbed divided by the surface area of lakes in the catchment.
Cause of pH decline in stream water during spring melt runoff in northern Sweden
Authors: Laudon Hjalmar , Westling Olle , Bishop Kevin
Published: April 2011

This study has sought to distinguish the anthropogenic and natural factors that drive episodic pH decline in northern Sweden. Approximately 600 stream water chemistry samples from 12 streams during the spring melt runoff of 1997 and 1998 were collected. Although the acid deposition levels of the region are relatively low (2-4 kg SO42--S·ha-1·year-1), the pH decline in all of the almost two dozen spring melt events ranged from nearly 1 to 3 pH units. By using the sum of base cation concentration as a dilution index and an organic acid pH model, the sources contributing to the pH decrease were quantified. For a majority of the spring melt events, organic acids contributed over 75% of the acidity at peak runoff (minimum pH). In only three of the monitored events was the anthropogenic SO42- contribution as high as that from natural sources. NO3- did not contribute to the pH decline during spring melt in this study. An interannual variation was observed that was probably due to a larger anthropogenic deposition load during the winter of 1997-1998 and a more rapid snowmelt during the spring of 1998.
Application of statistical model selection criteria to the Stock Synthesis assessment program
Authors: Helu S Langitoto , Sampson David B , Yin Yanshui
Published: April 2011

Statistical modeling involves building sufficiently complex models to represent the system being investigated. Overly complex models lead to imprecise parameter estimates, increase the subjective role of the modeler, and can distort the perceived characteristics of the system under investigation. One approach for controlling the tendency to increased complexity and subjectivity is to use model selection criteria that account for these factors. The effectiveness of two selection criteria was tested in an application with the stock assessment program known as Stock Synthesis. This program, which is often used on the U.S. west coast to assess the status of exploited marine fish stocks, can handle multiple data sets and mimic highly complex population dynamics. The Akaike information criterion and Schwarz's Bayesian information criterion are criteria that satisfy the fundamental principles of model selection: goodness-of-fit, parsimony, and objectivity. Their ability to select the correct model form and produce accurate estimates was evaluated in Monte Carlo experiments with the Stock Synthesis program. In general, the Akaike information criterion and the Bayesian information criterion had similar performance in selecting the correct model, and they produced comparable levels of accuracy in their estimates of ending stock biomass.