bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of wave disturbance and substrate slope on sediment characteristics in the littoral zone of small lakes
Authors: Cyr Hélène
Published: April 2011

Sediment characteristics in the littoral zone of lakes affect the distribution, biomass, and productivity of benthic organisms and affect chemical exchanges with the water column, yet we know very little about their distribution. I tested whether sediment water and organic matter content were related to site exposure and to basin morphology by comparing sediments along 12 transects in three small lakes (area <150 ha). The distribution of sediment water content in small lakes differed from the general patterns described for large lakes and ocean. Sediment water content was generally high in shallow waters (<2-5 m), decreased sharply to 30-50% within 20 m from shore, and increased again in the deeper portion of the littoral zone. Fine sediments were retained in the shallow littoral zone (<1.5 m) at sites with mean fetch <150 m. The maximum depth at which sediments were mixed increased with increasing depth of the wave-mixed layer and with increasing slope of the substrate. The organic matter content (OM) of littoral sediments was closely related to their water content (WC) (log(OM) = -4.7 + 3.0 log(WC), r2 = 0.77, P < 0.001), and sediment organic content was very similar in the upper and lower portions of the littoral zone.
The TRANSAQUA model applied to zebra mussels (Dreissena polymorpha) used for the biomonitoring of 137Cs and 106Ru contamination
Authors: Garnier-Laplace J , Vray F , Baudin J P , Jourd'heuil L
Published: April 2011

The dynamics of contamination of the zebra mussel (Dreissena polymorpha) by two artificial radionuclides, 106Ru and 137Cs, were quantified in a simplified experimental ecosystem. Main sources of contamination (water, phytoplankton, and other natural suspended matter) were considered. The kinetic constants of accumulation and elimination governing each transfer in the ecosystem were used to calibrate the TRANSAQUA model (TRANSfer of radionuclides along AQUAtic food chains). This model was run to simulate the time series of pollutant concentrations within a population of zebra mussels in the Rhone River downstream of the Marcoule fuel reprocessing plant. The ecological parameters considered included the seasonal cycle of phytoplankton and the mussel clearance rate. The TRANSAQUA model was validated on the basis of a comparison between the simulated results and the data from quarterly gamma spectrometry measurements of samples from the mussel population. Almost all field data were within the range of simulated concentrations, except a few points sampled just after periods of flood or low water. For 106Ru, the water pathway was predominant for the whole mussel, almost reaching 80%. For 137Cs, the ingestion of natural suspended matter, other than phytoplankton, was the main route explaining the contamination of the entire mussel.
Population-specific variation in body dimensions of adult chinook salmon (Oncorhynchus tshawytscha) from New Zealand and their source population, 90 years after introduction
Authors: Kinnison Michael , Unwin Martin , Boustead Nelson , Quinn Thomas
Published: April 2011

Chinook salmon (Oncorhynchus tshawytscha) transplanted from the Sacramento River, California, U.S.A., to New Zealand in the 1900s colonized many South Island rivers, which now show significant population-specific phenotypic variation. To characterize this variation, we conducted a morphometric analysis of two New Zealand populations and the fall-run Battle Creek population at the Coleman Hatchery, the apparent ancestral stock. Variation in length at age, weight at length, fin lengths, hump depth, snout length, and caudal peduncle width was detected among populations. Sexually mature Battle Creek and New Zealand chinook salmon were consistently identifiable from morphometric data (97.7% classification accuracy), largely through differences in caudal peduncle width and hump depth. The two New Zealand spawning populations, although distinguishable in morphology in 1994 (mean of 80% correct classification), did not classify as well using the same discriminant functions in 1995 (mean of 62.7% correct), suggesting interannual multivariate effects. Little variation was observed between the two mainstem river populations in adults collected shortly after entering freshwater. Although the genetic or environmental causes for the differences between populations have yet to be determined, our results provide empirical evidence of phenotypic divergence over decadal time scales. This work may be relevant to considerations in the development and monitoring of salmon recovery and conservation programs.
Benthic invertebrate distributions in the San Joaquin River, California, in relation to physical and chemical factors
Authors: Leland Harry V , Fend Steven V
Published: April 2011

The invertebrate fauna of nontidal portions of the lower San Joaquin River and its major tributaries is described in relation to water quality and habitat using canonical correspondence analysis, autecological metrics, and indicator species analysis. A large-scale (basin-wide) pattern in community response to salinity (sulfate-bicarbonate type) was detected when standardized, stable substratum was sampled. Community structure, taxa richness, and EPT (ephemeropterans, plecopterans, and trichopterans) richness varied with dissolved solids concentration (55-1700 mg total dissolved solids ·L-1), and distributions of many taxa indicated salinity optima. Distinct assemblages associated with either high or low salinity were evident over this range. Large-scale patterns in community structure were unrelated to pesticide distributions. Structure and taxa richness of invertebrate assemblages in sand substratum varied both with salinity and with microhabitat heterogeneity. The benthic fauna generally was dominated by a taxa-poor assemblage of specialized psammophilous species, contributing to a weaker relationship between community structure and water quality than was observed using standardized substratum. Habitat types and associated dominant species were characterized using indicator species analysis. Species assemblages did not vary substantially with irrigation regime or river discharge, indicating that structure of invertebrate communities was a conservative measure of water quality.
Sonar systems and aquatic organisms: matching equipment and model parameters
Authors: Horne John K , Clay Clarence S
Published: April 2011

Acoustic technology is an accepted and important component of aquatic research and resource management. Despite the widespread use of echosounders, few guidelines aid in the choice of appropriate sonar system parameters for acoustic surveys. Choice of acoustic carrier frequency is analogous to the choice of spotlight colour used to illuminate a painting. Three primary biological factors influence the scattering of sound by aquatic organisms: swimbladder presence, organism length, and organism behaviour. We illustrate the influence of these factors on the amplitude of backscattered echoes using a Kirchhoff-ray mode scattering model to quantify fish and zooplankton backscatter as a function of carrier frequency, fish length, and swimbladder aspect. Model results illustrate that echo amplitudes from aquatic organisms are largely dependent on the presence or absence of a swimbladder. Target strengths generally increase with increasing carrier frequency and organism length. Swimbladder angle relative to the incident sound wave affects scattering amplitudes at all frequencies. Measurements of backscatter from swimbladdered fish are relatively robust when the ratio of fish length to acoustic frequency wavelength ranges between 2 and 10. As fish length to frequency wavelength ratios increase, echo amplitudes become more dependent on aspect and peak when the swimbladder is perpendicular to the acoustic wavefront.
Microsatellite gene diversity analysis in anadromous arctic char,Salvelinus alpinus, from Labrador, Canada
Authors: Bernatchez Louis , Dempson J Brian , Martin Sylvain
Published: April 2011

We analysed six loci among 257 Arctic char (Salvelinus alpinus) representing seven locations in Labrador and Newfoundland to provide a first assessment of microsatellites gene diversity in anadromous char and to determine the geographic scale of population structuring within the species. The number of alleles per locus varied between 9 and 48, and gene diversity ranged from 0.190 to 0.968. Significant FSTand differences in allele frequencies were observed among most samples, as well as heterozygous deficiency, which was indicative of a Wahlund's effect. These results implied the existence of genetically distinct populations on a microgeographic scale (less than 10 km) and that our samples represented an admixture of char from those populations that interchange among rivers for owerwintering, in congruence with tagging investigations. These results indicate that microsatellites potentially offer more sensitivity than allozymes and mitochondrial DNA to infer fine-scale population structure in anadromous arctic char.
Competition between larval lake herring (Coregonus artedi) and lake whitefish (Coregonus clupeaformis) for zooplankton
Authors: Davis Bruce M , Todd Thomas N
Published: April 2011

Diet and growth of larval lake herring (Coregonus artedi) and lake whitefish (Coregonus clupeaformis) were compared in mesocosm experiments in a small mesotrophic lake in southeastern Michigan. Fish were sampled from single-species and mixed assemblages in 2-m3 cages for 8 weeks during April and May. Both species initially ate mostly cyclopoid copepodites and small cladocerans (Bosmina spp.). Schoener's index of diet overlap showed considerable overlap (70-90%). Lake whitefish ate Daphnia spp. and adult copepods about 2 weeks earlier than did lake herring, perhaps related to their larger mean mouth gape. Lake whitefish were consistently larger than lake herring until the eighth week, especially in the sympatric treatments. Lake whitefish appeared to have a negative effect on the growth of lake herring, as lake herring in mixed-species treatments were smaller and weighed less than lake herring reared in single-species treatments. The diet similarities of lake whitefish and lake herring larvae could make them competitors for food in the Great Lakes. The greater initial size of lake whitefish could allow them to eat larger prey earlier and thereby limit availability of these prey to lake herring at a crucial period of development.
Model complexity and catch-age analysis
Authors: Richards Laura J , Schnute Jon T
Published: April 2011

Catch-age analysis has become a standard tool of fisheries stock assessment. Modern catch-age models can contain dozens or even hundreds of parameters to be estimated. In this paper, we compare the performance of a typically complex catch-age model with a simpler model in which the population age structure is represented only by the annual mean age. We find that the population trajectory estimated from the simple model is in general agreement with the trajectory from the catch-age analysis. We suggest that the simple model can serve as both an intuitive and quantitative aid to interpreting results from the complex model. For example, the contrast between models highlights the role of technically complex assumptions. To some extent, errors in the age structure data cancel in calculating the mean age. Thus, our analysis suggests options available for investigating stocks where only summary age data are reliable.
Effects of chronic sublethal ammonia and a simulated summer global warming scenario: protein synthesis in juvenile rainbow trout (Oncorhynchus mykiss)
Authors: Reid Scott D , Linton T K , Dockray J J , McDonald D G , Wood C M
Published: April 2011

Protein synthesis, net accretion, and degradation in liver, gill, and white muscle and ribosomal translational efficiency and protein synthesis capacity in liver and gill were measured using a flooding dose of [3H]phenylalanine in juvenile rainbow trout (Oncorhynchus mykiss). The fish were chronically exposed (90 days) in hardwater to the presence or absence of sublethal ammonia (70 µmol total ammonia ·L-1) alone or in combination with a 2°C elevation in the normal temperature profile over the months of June-September 1993 (ambient temperature range 13-22°C). Chronic sublethal exposure to ammonia had little impact on gill protein synthesis and degradation (protein turnover) and even less in muscle. However, in the liver, both protein synthesis and degradation were stimulated following 60 days of the sublethal ammonia exposure. The 2°C elevation in temperature 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 inhibited protein dynamics in these tissues. Overall, elevated environmental ammonia in combination with a summer global warming scenario would challenge the ability of fish to adapt to alterations in the quality of their environment, most notably during periods of peak temperatures.
The temporal-spatial pattern of vertical migration by the freshwater copepod Skistodiaptomus oregonensis relative to predation risk
Authors: Ghan David , McPhail J D , Hyatt K D
Published: April 2011

Skistodiaptomus oregonensis vertical migration in Kennedy Lake and Paxton Lake may be an adaptation to avoid predation by threespine stickleback (Gasterosteus aculeatus). In Kennedy Lake, juvenile sockeye salmon (Oncorhynchus nerka) and the mysid Neomysis mercedis are also predators that potentially drive the vertical migration. A corollary of the hypothesis that predation selects for vertical migration is that the extent and timing of the vertical migration decreases predation risk. This corollary is tested for each of the potential predators. Laboratory experiments indicate that stickleback feeding rate decreases below 1.6 µE ·s-1 ·m-2. In Kennedy and Paxton lakes, S. oregonensis occupied depths below this light intensity during the day. Furthermore, as S. oregonensis ascended at dusk and descended at dawn, they remained within light intensities that reduced stickleback predation rate. In Kennedy Lake, hydroacoustic data coupled with information in the literature on feeding behaviour of juvenile sockeye indicate that this species move to surface waters to feed before sunrise and after sunset. Vertically migrating S. oregonensis are near the surface during the twilight feeding periods of juvenile sockeye. The timing of S. oregonensis vertical migration also does not reduce the time it is in contact with the predator N. mercedis.
Benefits and costs of vertical migration by the freshwater copepod Skistodiaptomus oregonensis: testing hypotheses through population comparison
Authors: Ghan David , Hyatt K D , McPhail J D
Published: April 2011

The benefits and costs of vertical migration behaviour of the freshwater lacustrine copepod, Skistodiaptomus oregonensis, is explored through the study of two migrating and two nonmigrating populations. The association of vertical migration with the presence of pelagic threespine stickleback (Gasterosteus aculeatus) is consistent with the hypothesis that the adaptive benefit of vertical migration by S. oregonensis is avoidance of predatory stickleback. The hypothesis of avoidance of juvenile sockeye salmon (Oncorhynchus nerka) predation is not supported. Skistodiaptomus oregonensis do not migrate in the lake with the highest juvenile sockeye abundance but do migrate in the lake where juvenile sockeye are absent. A foraging efficiency hypothesis does not explain migration behaviour; neither food abundance nor food distribution distinguish lakes where S. oregonensis migrate from lakes where they do not migrate. Neither a bioenergetic efficiency hypothesis nor a thermal advantage hypothesis explain migration behaviour; temperature structures are similar in all four lakes examined. Vertical migration appears to be the result of a trade-off between predator avoidance and resource acquisition. Phytoplankton food is less concentrated in the deep habitat where S. oregonensis reside during the day. Furthermore, migrators contain less phytoplankton food in their guts than nonmigrators.
Discarding practices for commercial gadoids in the North Sea
Authors: Stratoudakis Yorgos , Fryer Robert J , Cook Robin M
Published: April 2011

Understanding fishers' discarding behaviour, and anticipating their reactions to changes in the biological or regulatory characteristics of a fishery, are important for dealing with the problem of discarding. In this paper, we investigate the discarding of haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), and Atlantic cod (Gadus morhua) in the North Sea, using data collected by scientific observers onboard Scottish demersal vessels. We describe discarding on each trip by species-specific discard curves and explore how these curves depend on biological and regulatory variables. There are large differences in the size of discarded fish between inshore and offshore areas, with offshore-operating vessels discarding larger fish (high-grading). Increases in legal landing size correspond to immediate increases in the size of discarded fish, particularly for haddock and cod in inshore areas. In general, discarding practices for haddock and cod are similar over time and consistent across gears, whereas decisions for the lesser valued whiting are more variable and can be affected by the catch composition.
Influence of salmon carcasses on stream productivity: response of biofilm and benthic macroinvertebrates in southeastern Alaska, U.S.A.
Authors: Wipfli Mark S , Hudson John , Caouette John
Published: April 2011

This study was conducted to determine if salmon carcasses (from spawning adults) increased stream biofilm ash-free dry mass (AFDM) and benthic macroinvertebrate abundance in southeastern Alaska, U.S.A. Thirty-six once-through artificial streams were situated along, and received water and drifting invertebrates from, a natural stream. Two treatments (salmon carcass, control) were sampled six times during a 3-month period in a randomized incomplete block design with a 2 x 6 factorial treatment structure. Additionally, two natural stream sites were sampled once for biofilm and macroinvertebrates, one site receiving 75 000 adult salmon migrants during 1996 and the other upstream of spawning salmon. While biofilm AFDM was 15 times higher in carcass-enriched reaches of Margaret Creek, there were no detectable treatment differences in the artificial streams. Total macroinvertebrate densities were up to eight and 25 times higher in carcass-enriched areas of artificial and natural streams, respectively; Chironomidae midges, Baetis and Cinygmula mayflies, and Zapada stoneflies were the most abundant taxa. The increased biofilm in Margaret Creek and macroinvertebrate abundance in both systems suggest that salmon carcasses elevated freshwater productivity. This marine-based positive feedback mechanism may be crucial for sustaining aquatic-riparian ecosystem productivity and long-term salmonid population levels.
Assessing the indicator properties of zooplankton assemblages to disturbance gradients by canonical correspondence analysis
Authors: Attayde José Luiz , Bozelli Reinaldo Luiz
Published: April 2011

The indicator properties of zooplankton assemblages in a coastal lagoon were evaluated, by means of canonical correspondence analysis, along environmental gradients of trophic state and marine influence caused by anthropogenic impact. Changes in zooplankton species composition were significant indicators of environmental heterogeneity patterns. Species diversity was insensitive to eutrophication but decreased with increasing marine influence. The rotifer species Brachionus plicatilis and Synchaeta bicornis as well as cirriped nauplii were good indicators of mesohaline conditions. The rotifer species Asplanchna brightwelli, Brachionus angularis, Brachionus falcatus, Filinia terminalis, and Polyarthra remata were good indicators of eutrophic conditions. The other species investigated were good indicators of oligohaline and mesotrophic conditions. The rotifer genus Brachionus proved to be a better indicator organism for these environmental gradients than the entire zooplankton assemblage. Hence, this taxon can be considered a target taxon for more intensive monitoring and conservation planning. The method used here to assess the indicator properties of species assemblages and to select target taxa can be widely applied in any aquatic ecosystems to any group of organisms, spatial and temporal scales, and environmental gradients.
Improving the stock-recruitment relationship in Icelandic cod (Gadus morhua) by including age diversity of spawners
Authors: Marteinsdottir Gudrun , Thorarinsson Kristjan
Published: April 2011

The size of the Icelandic cod stock has been gradually declining since the middle of this century. Recruitment has been poor over an extended period of time and much below the long-term average since 1985. Except for the concurrent decrease in stock size and recruitment during this period, the stock size - recruitment relationship is weak. This relationship is improved by including the age composition of the spawning stock. Spawning stock age diversity in each year from 1955 to 1992 was estimated with the Shannon index using the number of mature fish in each age group. By including information on age composition, 31% of the total variation in recruitment was accounted for by the model with stock size, age diversity, and the interaction between the two, compared with less than 15% by single factor models of either age diversity or stock size. These results indicate that age diversity is an important component in stock-recruitment models and that one of the management goals for fish species should be to maintain high age diversity in the spawning stocks.
Estimating gillnet selectivity using nonlinear response surface regression
Authors: Helser Thomas E , Geaghan James P , Condrey Richard E
Published: April 2011

We present a method of estimating the selectivity of experimental gill nets in which type A and type B curves are solved for simultaneously as a response surface using nonlinear regression. The modeling approach provides a general statistical framework for estimating selectivity parameters, evaluating different functional forms of the selectivity model, and testing for differences between models. We applied this approach to the gillnet catches of Louisiana spotted seatrout (Cynoscion nebulosus) in a five-panel experimental net from data collected from 1988 to 1995. The selectivity of the experimental gill nets for female and male spotted seatrout could be described by a common response surface that was based on a four-parameter normal probability density function (r2 = 0.95). By estimating type A and type B curves simultaneously the model was able to explain 74% more variation in the data than when compared with methods that estimate type B curves for each size-class individually. Statistical comparison of annual response surfaces was not significantly different (p > 0.05) and suggests that the estimation approach was relatively insensitive to interannual variation in population size composition.
Monitoring organic pollution and eutrophication in the Grand River, Ontario, by means of diatoms
Authors: Rott Eugen , Duthie Hamish C , Pipp Eveline
Published: April 2011

Diatom analysis discriminates between the impacts on river water quality of treated urban wastewaters and diffuse nutrient sources from farmland. Evaluation of organic pollution and trophic levels in the Grand River, Ontario, using two diatom indices shows a clear differentiation among 10 sampling sites over a distance of 214 km. Sites in the central reaches that are influenced by both urban discharges and agricultural runoff have the lowest water quality. The ranking of sites according to both diatom indices is consistently independent of substratum and seasonality. Ordination of samples by multivariate analysis results in a primary separation of the spring and summer communities and a secondary separation of upper, central, and lower reaches. Substratum differences are only apparent at the tertiary level, and mainly for midsummer samples from the upper reaches. Canonical correspondence analysis shows that the largest portion of the observed variability in species composition can be explained by a seasonal gradient related to temperature and by longitudinal gradients of nitrate-nitrogen, conductivity, and chloride. Differences in species composition between nutrient-rich sites and polluted sites are identified. Compared with a study conducted in the 1960s, the Grand River shows clear signs of increased eutrophication.
Crustacean zooplankton species richness: single- and multiple-year estimates
Authors: Arnott Shelley E , Magnuson John J , Yan Norman D
Published: April 2011

Richness estimates are dependent on the spatial and temporal extent of the sampling programme and the method used to predict richness. We assessed crustacean zooplankton richness in eight Canadian Shield lakes at different temporal and spatial scales using three methods of estimation: cumulative, asymptotic, and Chao's index. Percent species detected increased with the number of spatial, intraannual, or interannual samples taken. Single samples detected 50% of the annual species pool and 33% of the total estimated species pool. This suggests that previous estimates of zooplankton richness, based on single samples in individual lakes, are too low. Our richness estimates for individual lakes approach the total number of zooplankton found in some regions of Canada, suggesting that each lake has most taxa at some time, the majority being very rare. Single-year richness estimates provided poor predictions of multiple-year richness. The relationship between richness and environmental variables was dependent on the method of estimation and the number of samples used. We conclude that richness should be treated as an "index" rather than an absolute and sampling efforts should be standardized. We recommend an asymptotic approach to estimate zooplankton richness because the number of samples taken influenced it less.
Detection of Atlantic herring (Clupea harengus) schools in shallow waters using high-frequency sidescan sonars
Authors: Trevorrow Mark V , Claytor Ross R
Published: April 2011

This work examines results from field trials in April and May 1996 exploring the feasibility for estimating spawning Atlantic herring (Clupea harengus) abundance using a 330-kHz sidescan sonar in a shallow coastal region near Escuminac, New Brunswick. Herring schools were observed using both towed and fixed-location, azimuthally scanning techniques at ranges up to 100 m in water depths of 3-6 m. The schools were typically linear in shape, with lengths of 100-280 m, thickness of 4-14 m, and peak acoustic target strength near -12 dB. Using acoustic ray-tracing analysis, surface- and bottom-reflected multipaths from an ensemble of targets are shown to increase the echo amplitude and reverberation time, producing large overestimates (4-27 times actual) in herring densities when using echo-integration. Using the acoustic simulations to compensate for this reflection focusing, average population densities near 11 ·m-3 were estimated, with the schools comprising 10 900 - 103 000 individuals. These total school sizes and densities were consistent with expectations for spawning herring.
Recent international agreements and the precautionary approach: new directions for fisheries management science
Authors: Richards Laura J , Maguire Jean-Jacques
Published: April 2011

The dynamics of exploited fish populations can be highly uncertain and the precautionary approach to fisheries management addresses such uncertainties. The precautionary approach is now embodied in several international agreements, including (i) the UN Straddling Fish Stocks and Highly Migratory Fish Stocks Agreement and (ii) the FAO Code of Conduct. We discuss how application of these agreements will change the daily operations of many fisheries agencies. Contrary to past practices, the absence of adequate scientific information can no longer be a reason for postponing or failing to take conservation measures. Future harvest strategies will be based on stock-specific reference points and predefined decision rules. However, more research is required to quantify uncertainties associated with reference point definitions and their practical application in a management context. In addition, future research will emphasize environmental issues with extensive data requirements, such as ecosystem impacts of fishing. Data collection will remain a core business activity; agencies must address the costs of maintaining shared and documented data archives over the long term.
Individual variation and interrelationships between swimming performance, growth rate, and feeding in juvenile rainbow trout (Oncorhynchus mykiss)
Authors: Gregory T Ryan , Wood Chris M
Published: April 2011

Variation among individuals in specific growth rate (SGR), feeding, and two measures of swimming performance and their possible interrelationships were investigated in juvenile rainbow trout (Oncorhynchus mykiss) kept in groups on either satiation or half-satiation rations. Maximum sustainable velocity (Ucrit) was measured as an index of aerobic swimming performance and stamina (fatigue time in a fixed-velocity test at 6 body lengths ·s-1) as an index of anaerobic performance. Individual performance in both of these tests was found to be significantly repeatable. Trout fed on half-satiation ration exhibited significantly lower mean values of SGR and body size and higher levels of aggression-related fin damage, but no significant differences in stamina, relative or absolute Ucrit, glycogen content, or plasma cortisol. However, in these fish, there was a significant negative relationship between SGR and relative Ucrit, a significant positive relationship between SGR and stamina, and a significant positive relationship between SGR and total daily meal. None of these relationships were seen in fish fed to satiation. Plasma cortisol and tissue glycogen stores were not related to SGR. These results indicate that under the intensified competition of restricted ration, there are trade-offs between growth, feeding, and different types of swimming performance.
Does mortality select size or growth potential in young sockeye salmon (Oncorhynchus nerka)? A simulation based on otolith - fish size relationships
Authors: Meekan M G , Ryan DAJ , Dodson J J , Good S P
Published: April 2011

There is conflicting evidence on the role of size-selective mortality in the demography of populations of young sockeye salmon (Oncorhynchus nerka). A previous field study suggested that increases in mean fork length and otolith size at emergence observed in a cohort of salmon between fry and smolt stages were due to size-selective mortality, such that fry with small fork lengths underwent higher mortality than larger individuals. However, a subsequent study used a simulation to show that such increases could not have been achieved by size-selective mortality without levels of survivorship of the cohort far lower than those that had been observed in the field. To account for field observations, the simulation study proposed that individuals with high metabolic rates had better survivorship, a process that was termed "selection for growth potential." Here, we use a simulation approach to show that size-selective mortality may result in shifts in mean fork length and otolith size at emergence comparable with those observed in the field at total mortalities within the range of estimates of natural values. The contrasting outcomes of earlier simulation work and the present study are probably due to the assumption by the former that otolith and fish size in young salmon were weakly correlated and the use of an inappropriate model of size-selective mortality. We conclude that size-selective mortality can explain the results of previous field studies and that little empirical evidence exists to support the hypothesis of selection for growth potential in cohorts of young salmon.
Vulnerability to predation and physiological stress responses in juvenile chinook salmon (Oncorhynchus tshawytscha) experimentally infected with Renibacterium salmoninarum
Authors: Mesa Matthew G , Poe Thomas P , Maule Alec G , Schreck Carl B
Published: April 2011

We experimentally infected juvenile chinook salmon (Oncorhynchus tshawytscha) with Renibacterium salmoninarum (Rs), the causative agent of bacterial kidney disease (BKD), to examine the vulnerability to predation of fish with differing levels of Rs infection and assess physiological change during progression of the disease. Immersion challenges conducted during 1992 and 1994 produced fish with either a low to moderate (1992) or high (1994) infection level of Rs during the 14-week postchallenge rearing period. When equal numbers of treatment and unchallenged control fish were subjected to predation by either northern squawfish (Ptychocheilus oregonensis) or smallmouth bass (Micropterus dolomieui), Rs-challenged fish were eaten in significantly greater numbers than controls by nearly two to one. In 1994, we also sampled fish every 2 weeks after the challenge to determine some stressful effects of Rs infection. During disease progression in fish, plasma cortisol and lactate increased significantly whereas glucose decreased significantly. Our results indicate the role that BKD may play in predator-prey interactions, thus ascribing some ecological significance to this disease beyond that of direct pathogen-related mortality. In addition, the physiological changes observed in our fish during the chronic progression of BKD indicate that this disease is stressful, particularly during the later stages.
A mtDNA analysis of spatiotemporal distribution of two sympatric larval populations of rainbow smelt (Osmerus mordax) in the St. Lawrence River estuary, Quebec, Canada
Authors: Pigeon Dany , Dodson Julian J , Bernatchez Louis
Published: April 2011

Ecological isolation through resource partitioning is invoked as a major factor for explaining the persistence of genetically distinct yet closely related sympatric populations. Two genetically distinct sympatric populations of anadromous rainbow smelt (Osmerus mordax) exist in the middle estuary of the St. Lawrence River. The persistence of these coexisting populations in sympatry is in conflict with current theoretical concepts predicting population richness. In the present study, we performed mtDNA PCR-RFLP analysis of 922 larvae from 33 sampling stations to test the hypothesis that the larvae belonging to the two sympatric smelt populations of the St. Lawrence middle estuary are spatially segregated and that such segregation may promote the persistence of the populations. Results clearly revealed spatial homogeneity in the relative distribution of larvae from the two populations. Consequently, they did not support our working hypothesis that larvae belonging to the two sympatric smelt populations are spatially segregated. Two alternative explanations may account for the lack of spatial partitioning observed here. Competition may not be important enough to promote resource partitioning at the larval stage. Alternatively, resource partitioning occurs, but not spatially. This study also demonstrated that the effect of historical events may have been as important as contemporary ecological settings in determining genetic population structure in smelt.
Function and dynamics of woody debris in stream reaches in the central Sierra Nevada, California
Authors: Berg Neil , Carlson Ann , Azuma David
Published: April 2011

In 1993, we located, measured, and tagged almost 1700 woody debris pieces on six streams in Californias central Sierra Nevada. The stability, geomorphic function, and use by fish for cover of each piece were recorded. In 1994 and 1995, piece movement was quantified and new debris pieces were measured. In the 60 study reaches, debris was not influential in shaping channel morphology and fish cover. Although woody debris was often associated with habitat units, few pieces deflected flow or contributed to the formation of pools or steps. Fish used deep water as cover more often than debris or any other cover type. Medium-sized debris was, however, used in a greater proportion than its availability to fish. Little sediment was stored by debris, and five large pieces stored 85% of the sediment volume measured. Debris frequency and volume did not differ significantly by channel type. After a low stream flow year (19931994), few pieces had moved and few new pieces were identified. After a high-flow season (19941995), 31% of the pieces had either moved or were not found and new pieces represented over 5% of the originally surveyed volume of wood.
Swim speeds and energy use of upriver-migrating sockeye salmon (Oncorhynchus nerka): role of local environment and fish characteristics
Authors: Hinch Scott G , Rand Peter S
Published: April 2011

We used electromyogram (EMG) radiotelemetry to assess swimming activity (e.g., swim speeds), behaviour, and migration speeds (e.g., ground speeds) of individual adult sockeye salmon (Oncorhynchus nerka) migrating through several reaches of the Fraser and Nechako rivers in British Columbia. Using a laboratory swim flume and volitionally swimming adult fish carrying EMG transmitters, we developed relationships between EMG pulse intervals and swim speeds. A bioenergetics model was used to estimate reach-specific energy use per metre for each individual based on the average swim speed, migration time, body size, and river temperature. Migration was most energetically efficient (i.e., migration costs per unit distance traveled were relatively low) for females compared with males, large males compared with small males, and 1995 males compared with 1993 males. In all three cases, differences in swim speed patterns were primarily responsible for differences in energy use. For both sexes and in both years, migrations through reaches that contained a constriction (caused by an island, gravel bar, or large rock outcropping) were energetically inefficient compared with that through reaches with no constrictions. The high energetic costs at constrictions seem to result from long travel times probably caused by turbulent flow patterns that may generate confusing migrational cues.
Egg size, fecundity, and development rate of two introduced New Zealand chinook salmon (Oncorhynchus tshawytscha) populations
Authors: Kinnison Michael T , Unwin Martin J , Hershberger William K , Quinn Thomas P
Published: April 2011

Interpopulation differences in several adult phenotypic traits suggest that New Zealand (NZ) chinook salmon (Oncorhynchus tshawytscha) are evolving into distinct populations. To further investigate this hypothesis, we compared egg sizes, fecundities, and early development rates of chinook from two NZ streams. The two NZ study populations differed in size-adjusted egg weight and gonadosomatic index, but not in size-adjusted fecundity. Egg weight, fecundity, and gonadosomatic index values for both NZ populations were different than values for chinook from Battle Creek, California, the population regarded as the ancestral NZ stock. In contrast, there was little evidence of divergence in juvenile development. Time to hatching did not differ between the two NZ study populations and heritability estimates were small with large standard errors. Evidence of a small difference in alevin growth rate may have represented an effect of yolk conversion mechanics related to egg size. Despite the similarity in development rates under shared conditions, modeling based on temperature records suggests that emergence dates in the two NZ streams may differ by 4-6 weeks, yielding significant phenotypic differences.
Effects of light intensity, water velocity, and species composition on carbon and nitrogen stable isotope ratios in periphyton
Authors: MacLeod Neil A , Barton David R
Published: April 2011

Periphyton was allowed to grow on glass plates suspended in the water column of a small stream under two conditions of light and water velocity, over two seasons, to assess the influence of the thickness of benthic boundary layers on stable isotope fractionation. Isotopic signatures for both carbon and nitrogen in samples of periphyton varied with light intensity and season, but not with current velocity. In summer, periphyton grown under low-light conditions had depleted 13C and 15N values relative to periphyton grown under high light. In autumn, isotopic signatures were generally more depleted than in summer, but did not vary systematically with light intensity or water velocity. These results suggest that isotopic fractionation in periphyton was more strongly influenced by the intensity of metabolic activity than by variations in the thickness of the benthic boundary layer.
Life history variability in response to temperature and Chaoborus exposure in three Daphnia pulex clones
Authors: Walls Mari , Ventelä Anne-Mari
Published: April 2011

In a 21-day life table experiment, we studied the role of temperature, exposure to Chaoborus obscuripes, and their interaction on life history parameters and neck spine development in Daphnia pulex. We used three D. pulex clones collected from different ponds in southwestern Finland. In these ponds, temperature, predation pressure, and the clonal composition of Daphnia populations may vary substantially. Each clone was exposed to Chaoborus-conditioned water or control water at 16 and 20°C. Predator exposure and temperature affected significantly age and size at first reproduction and the total number of offspring in Daphnia. Interaction between predator exposure and temperature approached significance for the age at first reproduction, and the interaction between predator exposure and clone was significant for the same trait. Temperature interacted with clonal origin for all reproductive parameters studied. All three clones showed no or only weak morphological responses to Chaoborus. This indicates that the life history changes observed are independent of neck spine formation and may be adaptive in the presence of invertebrate predation.
Effects of different organic carbon sources on a freshwater plankton community
Authors: Wehr John D , Holen Dale A , MacDonald Molli M , Lonergan Sean P
Published: April 2011

We examined effects of terrestrial and aquatic detritus on optical, chemical, and biological properties of a planktonic food web in mesotrophic Calder Lake, New York. The 5400-L mesocosms received detritus from terrestrial leaves or aquatic macrophytes (added 1-2 mg dissolved organic C/L). Terrestrial detritus had significant effects on UV-B absorbance (OD250 twofold greater), but humic substances (OD440) remained low. Both C sources resulted in 40% declines in oxygen saturation and two- to threefold increases in dissolved inorganic and total P but no effects on NH4+ or NO3-. Bacterial growth was stimulated by 20% in systems receiving macrophyte C but declined by 50% in systems with terrestrial C. Initially, controls had >60% greater chlorophyll a concentrations than C-amended systems, but mesocosms with macrophyte C exhibited the greatest chlorophyll a concentrations after day 10. Autotrophic nanoflagellates <20 µm (Chrysochromulina parva, Ochromonas) increased in controls but were inhibited in C-amended systems. Cyanobacteria (Coelosphaerium naeglianum, Anabaena, Dactylococcopsis acicularis) numbers increased in mesocosms with macrophyte C; densities of most algal taxa declined in terrestrial-supplemented systems, except certain flagellates (Synura, Cryptomonas, Ceratium hirundinella), which were enhanced. Abundances of heterotrophic nanoflagellates, rotifers, Daphnia pulicaria, and copepod nauplii were stimulated by macrophyte C; only the copepod Mesocyclops edax increased following addition of terrestrial C.
MULTIFAN-CL: a length-based, age-structured model for fisheries stock assessment, with application to South Pacific albacore, Thunnus alalunga
Authors: Fournier Daid A , Hampton John , Sibert John R
Published: April 2011

We introduce a length-based, age-structured model, MULTIFAN-CL, that provides an integrated method of estimating catch age composition, growth parameters, mortality rates, recruitment, and other parameters from time series of fishery catch, effort, and length frequency data. The method incorporates Bayesian parameter estimation, estimation of confidence intervals for model parameters, and procedures for hypothesis testing to assist model development. We apply the method to South Pacific albacore, Thunnus alalunga, fishery data and demonstrate the incorporation of model structure such as spatial heterogeneity, age-dependent natural mortality and movement rates, time series trends and seasonal variation in catchability, and density-dependent growth. Consistency of the results of the albacore analysis with various exogenous sets of biological and environmental data gives credence to the model results.
Consideration of ocean conditions in the management of salmon
Authors: Bisbal Gustavo A , McConnaha Willis E
Published: April 2011

An ecologically based conceptual foundation is presented as a way to incorporate environmental variability in salmon management. The argument addresses the problem of accommodating marine environment variability through actions in freshwater. We argue for an approach that considers marine and freshwater environments as integral components of a larger salmonid ecosystem. This contrasts with previous propositions that either relied heavily on technological fixes in the freshwater environment or questioned the value of any recovery effort designed to withstand overwhelming ocean forces. Salmon management requires a more holistic approach incorporating modern understanding of the salmonid ecosystem and its variability. We suggest two strategies. The first calls for deliberate improvement of estuarine and nearshore ocean conditions through regulation of upstream flows, river operations, hatchery production, and other actions. The second calls for improving the resilience of salmon to a variable environment. This requires relaxing anthropogenic factors that hinder the natural range of salmon life history diversity within and between populations, a survival mechanism that evolved in response to changing conditions. These strategies recognize that although the ocean primarily determines overall salmon abundance, management actions, particularly in freshwater, are critical to the ability of salmon to cope with a variable ocean environment.
Outcome of an inshore spawning event by northern Atlantic cod (Gadus morhua) at a low stock level
Authors: Smedbol R K , Schneider D C , Wroblewski J S , Methven D A
Published: April 2011

A large spawning aggregation of northern Atlantic cod (Gadus morhua) was discovered in a fjord of Trinity Bay, Newfoundland, in April 1995, 3 years after the collapse of this stock and 1 year after the last offshore spawning aggregation was recorded. We hypothesized that spawning by this aggregation would increase the abundance/density of eggs and settled 0-group juveniles above the level of spawning in the bay during recent years. Data from 1995 were compared with ichthyoplankton and postsettlement juvenile surveys conducted in recent years. Egg density was significantly higher in 1995 than the pooled average of two recent years (1991 and 1993). The hypothesized increase in numbers of postsettlement age 0 fish was tested at three different spatial scales: the entire northeast coast of Newfoundland, individual bays, and areas within Trinity Bay. There was no detectable increase in catches of settled age 0 juveniles at any spatial scale. Consequently, while this large spawning aggregation produced locally high egg concentrations, it did not lead to a detectable increase in abundance of newly settled age 0 juveniles in coastal nursery areas. This study did not provide any direct evidence for an increase in recruitment in the inshore region due to the spawning output of locally abundant spawners in Trinity Bay.