bluuebunny/crossref_metadata_2025 huggingface dataset:
Stock–Recruitment Dynamics and the Maximum Population Growth Rate of the Barndoor Skate on Georges Bank
Authors: Gedamke Todd , Hoenig John M. , DuPaul William D. , Musick John A.
Published: April 2009

In 1998, the barndoor skate Dipturus laevis was reported to have been locally extirpated in parts of its northern range and to be potentially on the brink of extinction. Managers were faced with assessing the species with virtually no information other than a limited number of individuals observed in annual groundfish surveys. Since that time, a number of the primary life history parameters have been estimated, but the population dynamics of the species remain largely unexplored. In this study, we use information from the National Marine Fisheries Service (NMFS) annual groundfish surveys to investigate two critical components of barndoor skate population dynamics: the relationship of recruitment to spawner abundance and the maximum population growth rate. A strong stock–recruitment relationship was found in the fall survey data, suggesting that recruitment is closely tied to spawner abundance. The Ricker and Beverton–Holt stock–recruit models were fitted to the survey data, and estimates of the slope at the origin was generated. These parameters provided an estimate of the maximum annual reproductive rate, which was then converted to an estimate of the instantaneous maximum population growth rate of 0.37–0.38 per year. A second analysis was also conducted using a Leslie matrix and data from the NMFS survey. Observed rates of population change were used to estimate early life history parameters and incorporate density dependence into the density-independent framework of a Leslie matrix demographic model. From this method, the instantaneous maximum population growth for the barndoor skate was estimated to be 0.36–0.48 per year. Our results suggest that the species is more resilient to fishing pressure than previously believed and is capable of growing at an instantaneous rate in excess of 35% at low population sizes.
The Role of Ciscoes as Prey in the Trophy Growth Potential of Walleyes
Authors: Kaufman Scott D. , Morgan George E. , Gunn John M.
Published: April 2009

Analysis of the growth characteristics of 215 populations of walleye Sander vitreus across Ontario revealed that female walleyes reached larger asymptotic lengths in lakes in which ciscoes Coregonus artedi provided a relatively large prey species for them. The stomach contents of walleyes from a set of intensively studied lakes revealed that walleyes of all sizes depended on ciscoes but that ciscoes were most important to larger walleyes. In lakes without ciscoes, the walleye diet closely tracked the availability of young-of-year yellow perch Perca flavescens; when such prey were in short supply, walleyes consumed invertebrates. The prey size in walleye stomachs was significantly larger in lakes with ciscoes, but the probability of finding empty stomachs was also greater. This suggests that although walleyes in lakes with ciscoes foraged less often, more energy was available for growth. Exceptions to this general pattern occurred when ciscoes were too large to be consumed by walleyes or ciscoes were absent but small prey (i.e., yellow perch) were very abundant. We propose that lakes without ciscoes will provide higher catch rates for anglers, whereas those with ciscoes (particularly small ciscoes) are more likely to provide opportunities for trophy size fish.
Sex-Specific Natural Mortality of Arrowtooth Flounder in Alaska: Implications of a Skewed Sex Ratio on Exploitation and Management
Authors: Wilderbuer Thomas K. , Turnock Benjamin J.
Published: April 2009

Conservative fisheries management in Alaskan waters typically limits harvest to maintain a target biomass of female spawners (40% of the female biomass observed in the absence of fishing). This harvest calculation does not consider the male population level for a species. If natural mortality rates (M) differ between sexes and if females outlive males, then a reduction in males relative to females could diminish the reproductive potential of the stock. This problem was examined in the present study by estimating separate sex-specific M-values for the arrowtooth flounder Atheresthes stomias in Alaska, where females are almost always found at higher proportions than males during trawl surveys. Age data indicated that females outlive males, and estimates of M ranged from 0.10 to 0.33 for females and from 0.16 to 0.51 for males. Based on four estimation methods, male M was consistently higher than female M. Simulated harvest scenarios in which male M and selectivity were varied indicated that increasing male M and lowering the age of males at first capture skewed the sex ratio even more toward females; in the most extreme harvest scenario, the percentage of females in the population was as high as 89% (Gulf of Alaska) and 96% (Bering Sea). Because reproductive success under a skewed sex ratio is probably linked to reproductive behavior, we developed a simple conceptual model to consider three reproductive strategies that differed in the number of females (1–3) that could be paired with a single male. Although a population's reproductive potential was much more resilient to changes in sex ratio for 1:2 or 1:3 (male : female) pairings (reduced by only 15% when the population was 70% female), the fishing mortality rate (F) that corresponded to a reduction in egg fertilization was much higher than the target F (i.e., that maintained biomass at 40% of the unfished biomass) and exceeded overfishing levels when the population was over 80% female.
Using Species Composition Data from a Trawl Survey to Determine Potential Bycatch of the Commercial Trawl Fishery for Horseshoe Crab Limulus polyphemus in the Middle Atlantic Bight
Authors: Graham Larissa J. , Murphy Brian R. , Hata David
Published: April 2009

The National Marine Fisheries Service has encouraged regional management councils to develop fisheries ecosystem plans that, among other things, identify the bycatch species within each fishery and describe each species' spatial and temporal distribution. Horseshoe crabs Limulus polyphemus have been harvested along the eastern coast of the USA since the 1800s; however, a fishery management plan was only recently created for this species, and bycatch in the horseshoe crab trawl fishery has not been quantified. We identified species likely to be caught as bycatch in the commercial fishery by using species composition data from a fishery-independent horseshoe crab trawl survey conducted in 2005 and 2006. Seventy-six taxa were caught, including 47 finfish species from 33 families. Skates (family Rajidae) comprised more than one-half of the total biomass caught, and horseshoe crabs comprised one-third of the total biomass. Catch per unit effort (kg/km towed) was greatest for little skate Leucoraja erinacea, winter skate Leucoraja ocellata, horseshoe crab, and clearnose skate Raja eglanteria. We also caught species that are currently on the World Conservation Union's Red List (e.g., Atlantic sturgeon Acipenser oxyrinchus) and unmanaged within U.S. waters (e.g., cownose ray Rhinoptera bonasus and smooth dogfish Mustelus canis). Nonmetric multidimensional scaling was used to cluster sites based on species abundance. The sites strongly clustered into two distinct groups, suggesting that species composition differs between northern and southern sites. Bottom water temperature was a significant factor in determining species composition, explaining almost 70% of the variation in species composition among sites. The results of this study provide managers with a better understanding of which nontarget populations may be affected by the horseshoe crab trawl fishery, a first step in understanding the broader ecosystem-level effects of this fishery.
Effects of Variable Mortality and Recruitment on Performance of Catch-Curve Residuals as Indicators of Fish Year-Class Strength
Authors: Catalano Matthew J. , Dutterer Andrew C. , Pine William E. , Allen Micheal S.
Published: April 2009

We built a simulation model to assess the performance of catch-curve residuals as an index of year-class strength for a short-lived and a long-lived fish life history type across a range of assumed values for the variation in recruitment (CVR) and fishing mortality (CVF). The magnitude of CVR strongly influenced the utility of catch-curve residuals in assessing year-class strength. The probability of finding a significant correlation between catch-curve residuals and true recruitment values exceeded 0.9 when CVR was greater than 0.5 for the long-lived and greater than 1.0 for the short-lived life history types. This suggests that larger recruitment values have a greater probability of being successfully “tracked” through the age structure. Conversely, the magnitude of interannual variation in fishing mortality weakly influenced the performance of catch-curve residuals. The inspection of individual catch-curve residuals relative to the known recruitment values that produced them showed considerable scatter, indicating that the utility of this metric in assessing individual year-class strength is small. Sensitivity analyses showed that the performance of catch-curve residuals improved modestly with equal sampling vulnerability across ages and decreased slightly with increased fishing mortality. Our results suggest that catch-curve residuals can serve as a rudimentary measure of recruitment under ranges of recruitment and mortality variation similar to those frequently observed in field studies.
Size at Implantation Affects Growth of Juvenile Steelhead Implanted with 12-mm Passive Integrated Transponders
Authors: Tatara Christopher P.
Published: April 2009

Passive integrated transponder (PIT) tags have led to greater understanding of fish growth, survival, predation, migration, behavior, and the effects of human-caused environmental manipulation. Technological advances have reduced the size of PIT tags, permitting their implantation into smaller fish. To reap the benefits of PIT tag technology, implantation must not adversely impact growth, survival, or behavior. Steelhead Oncorhynchus mykiss parr reared in a natural-like environment were implanted with 12-mm PIT tags, and implantation effects on growth rate were measured. Steelhead had fork lengths ranging from 45 to 96 mm after 4 weeks of rearing in an outdoor stream channel. Thirty (17.4%) of the 172 steelhead parr that were under 74 mm at the time of PIT tag implantation had instantaneous growth rates of 0 [loge (g)]/d or less, while all parr (n = 72) over 75 mm exhibited positive growth rates. Logistic regression indicated that fork length at implantation was significantly related to the probability of positive growth rates (P < 0.001). For steelhead parr that exceeded 74 mm at implantation, the probability of experiencing positive growth was greater than 95%. The data suggest that fork length of steelhead parr should be above 74 mm at implantation to minimize negative growth effects associated with 12-mm PIT tags.
Movements of Prespawn Adult Atlantic Salmon Near Hydroelectric Dams in the Lower Penobscot River, Maine
Authors: Holbrook Christopher M. , Zydlewski Joseph , Gorsky Dimitry , Shepard Steven L. , Kinnison Michael T.
Published: April 2009

Acoustic telemetry was used to assess riverine behavior and passage success for prespawn male adult Atlantic salmon Salmo salar in the lower Penobscot River, Maine, in 2005 (n = 10) and 2006 (n = 25). Only 3 of 10 (30%) and 2 of 25 (8%) tagged Atlantic salmon successfully passed all three dams between the head of tide and presumed spawning habitat in 2005 and 2006, respectively. Migrants that failed to pass the second upstream dam frequently fell back into the estuary (3 of 4 in 2005; 17 of 23 in 2006), and few successfully reascended Veazie Dam at the head of tide. Fallback behavior was associated with temperatures exceeding 22°C and may reflect a strategy for coping with thermal stress and migratory delays. Atlantic salmon were also observed to actively seek out thermal refuge near one of the dams. Passage data were compared with results from previous telemetry studies that used Carlin tags and radio telemetry from 1987–1990 and 1992, and passive integrated transponder tags from 2002–2004. For all 10 years of study combined, median passage success was 64, 72, and 93% for the three dams. While 2006 may represent an uncommonly poor year for upstream passage at these dams, median cumulative passage past two of these dams was only 71% and ranged from 8% to 87% among years. Study results indicate that poor upstream passage severely limits migratory success in this system, particularly during periods of high discharge. Planned removal of two of these lower river dams is expected to improve migratory success for adult Atlantic salmon in the Penobscot River system.
Migration Patterns and Spawning Distribution of Adult Hatchery Sockeye Salmon Released as Parr from Net-Pens in Lake Wenatchee, Washington
Authors: Murdoch Andrew R. , Tonseth Michael A. , Miller Todd L.
Published: April 2009

Artificial propagation of sockeye salmon Oncorhynchus nerka interrupts the early phases of their life history cycle, typically between the egg and smolt stages. Sockeye salmon reared initially in a hatchery and subsequently released as parr from freshwater net-pens suspended in a lake cannot imprint on a specific tributary water source. As a result, the spawning distribution of returning adults may differ from that of naturally produced fish. We used radio tags and carcass surveys to determine whether the spawning distribution and location of adult hatchery sockeye salmon reared and released from net-pens in Lake Wenatchee, Washington, were similar to the spawning distribution and location of their naturally produced counterparts. Over 2 years, 100 hatchery sockeye salmon were radio-tagged and tracked to their spawning location. No radio-tagged sockeye salmon were found spawning in Lake Wenatchee, the lake outlet, or other nearby rivers. All radio-tagged sockeye salmon that were tracked into tributaries of Lake Wenatchee spawned in locations (i.e., river reaches) similar to those of naturally produced fish. Based on carcass surveys, the spawning distribution of hatchery sockeye salmon among spawning tributaries was different from that of naturally produced fish; this difference was attributed to the inability of hatchery fish to imprint on a natal stream during their early life history. Although the spawning distribution among tributaries differed between hatchery and naturally produced fish, the mean difference was small (10.8%) and ranged between 0% and 29%.
The Number of Redds Constructed per Female Spring Chinook Salmon in the Wenatchee River Basin
Authors: Murdoch Andrew R. , Pearsons Todd N. , Maitland Travis W.
Published: April 2009

The number of redds in a watershed is routinely used to monitor the population status of Pacific salmon Oncorhynchus spp. One limitation of this approach is that spawning escapement estimates derived from redd counts often assume one redd per female. We tested this assumption on spring-run Chinook salmon O. tshawytscha in the Wenatchee River watershed, Washington. Female spring Chinook salmon (N = 3,590) were injected with passive integrated transponder (PIT) tags at Tumwater Dam and were monitored annually on the spawning grounds over a 3-year period. Female Chinook salmon were observed on 75% of the 1,784 redds that were counted, and PIT-tagged females were detected on 42% of the redds. Of the female Chinook salmon detected on the spawning grounds, only 10 were detected on more than one redd. The number of redds constructed per PIT-tagged female (1.01 redds/female) was identical during each year of the study despite differences in the abundance of spawners. These results support the common assumption of one redd per female spring Chinook salmon.
The Effect of Deposited Fine Sediment on Summer Survival and Growth of Rainbow Trout in Riffles of a Small Stream
Authors: Harvey Bret C. , White Jason L. , Nakamoto Rodney J.
Published: April 2009

Elevated fine-sediment inputs to streams can alter a variety of conditions and processes, including the amount of fine sediment stored in riffles. We sought to measure the influence of deposited fine sediment on the survival and growth of juvenile rainbow trout Oncorhynchus mykiss (106–130 mm fork length) using a field experiment that included 18 enclosures in riffles of a small northwestern California stream. The experiment included six replicates of three levels of deposited fine sediment (low, background, and high) that embedded riffle cobbles at 0, 50, and 100%, respectively. Only 1 of 12 fish survived in high-sediment enclosures, while survival of fish in low- and background-sediment treatments equaled or exceeded 50%. Low- and background-sediment treatments could be distinguished from each other by a difference in fish growth: fish in the low-sediment treatment gained mass, on average, while all surviving fish in the background-sediment treatment lost mass. In addition to providing relatively high survival and growth benefits for juvenile rainbow trout, low-sediment experimental units were colonized at significantly higher rates by other vertebrates, particularly coastal giant salamanders Dicamptodon tenebrosus. The amount of stored fine sediment in small streams may substantially influence the total amount of habitat available to vertebrates at the watershed scale.
Morphometric and Meristic Differences among Bluehead Suckers, Flannelmouth Suckers, White Suckers, and Their Hybrids: Tools for the Management of Native Species in the Upper Colorado River Basin
Authors: Quist Michael C. , Bower Michael R. , Hubert Wayne A. , Parchman Thomas L. , McDonald David B.
Published: April 2009

Hybridization with nonnative fishes is a major factor influencing the status of native catostomids in the Colorado River basin. In Wyoming, hybridization with nonnative white suckers Catostomus commersonii is a particular concern in the conservation of native bluehead suckers C. discobolus and flannelmouth suckers C. latipinnis. The purpose of this study was to describe the meristic and morphometric characteristics of bluehead suckers, flannelmouth suckers, white suckers, and their hybrids from Muddy Creek, Wyoming, for which genotypic data were available to verify the classification of individual fish as pure species or hybrids. We also sought to develop discriminant function models that can be used in the field. Bluehead suckers and flannelmouth suckers had more lateral line scales, shorter and narrower heads, and narrower caudal peduncles than white suckers. Bluehead suckers and bluehead sucker × white sucker hybrids had a cartilaginous biting ridge in their mouth. Important characteristics for discriminating among these taxa included the number of postdorsal lateral line scales and the exterior width of the mouth. The discriminant function correctly classified 100% of the bluehead suckers and bluehead sucker × white sucker hybrids. Flannelmouth suckers, white suckers, and flannelmouth sucker × white sucker hybrids lacked a cartilaginous biting ridge. The number of postdorsal scales, caudal peduncle depth, and ratio of mouth length to the interior width of the mouth discriminated among taxa without a ridge. The discriminant function correctly classified 100% of the flannelmouth suckers, 92% of the white suckers, and 91% of the flannelmouth sucker × white sucker hybrids. None of the white suckers or flannelmouth sucker × white sucker hybrids were misclassified as flannelmouth suckers. Our results suggest that native bluehead suckers and flannelmouth suckers, nonnative white suckers, and hybrids of these species can be accurately identified by a few, easily measured meristic and morphometric characteristics.
Comparison of Failure Time Analysis and Abbott's Formula for Estimating Survival of Organisms Entrained at Power Stations
Authors: Young John R.
Published: April 2009

During the 1970s and 1980s, numerous studies were conducted to estimate the survival of ichthyoplankton following passage through power plant cooling systems. These studies generally used Abbott's formula to adjust the observed survival of organisms collected at the discharge for sampling mortality, as measured at the intake. The U.S. Environmental Protection Agency (USEPA) criticized these past studies for methodological faults (including the data analysis methods) on the basis that Abbott's formula may introduce a bias if sample sizes are small or unequal at the intake and discharge locations, sampling mortality is high, the samples contain organisms that were already dead, or the organisms are heterogeneous with respect to their probability of surviving entrainment. The effects of these issues on the bias and precision of entrainment survival estimates calculated using Abbott's formula and using failure time analysis were determined from simulated samples. Failure time analysis produced estimates that were minimally biased in terms of the issues raised by the USEPA and often more accurate and precise than Abbott's formula estimates. The failure time models were applied to experimental data used to estimate sampling stress at the Indian Point Generating Station in 1980 and supported the equality of sampling stress at the intake and discharge samplers, a critical requirement for obtaining unbiased survival estimates.
Precision of Hard Structures Used to Estimate Age of Bowfin in the Upper Mississippi River
Authors: Koch Jeff D. , Quist Michael C. , Hansen Kirk A.
Published: April 2009

The bowfin Amia calva has traditionally been considered a nuisance species that competes for resources with more desirable fish species. However, an emerging market for bowfin roe has increased the species' economic importance and raised awareness associated with the lack of information on its ecology and population dynamics. Furthermore, few studies have investigated the utility and precision of hard structures used to estimate bowfin age. The objective of this study was to examine the precision of age estimates obtained from sectioned pectoral fin rays, otoliths, scales, gular plates, and branchiostegal rays of bowfin collected from the upper Mississippi River. Structures from 255 bowfin were examined. Otoliths, scales, and branchiostegal rays were excluded from analyses because of poor readability. Sectioned pectoral fin rays provided the highest between-reader agreement and lowest variation between age estimates.
Capture Efficiency and Size Selectivity of Channel Catfish and Blue Catfish Sampling Gears
Authors: Buckmeier David L. , Schlechte J. Warren
Published: April 2009

We used proportional recapture data from mark–recapture experiments to directly estimate capture efficiency (percentage of fish captured per standard level of effort) and size selectivity (for 50-mm size-groups) of catfish sampling gears. Hoop-net series were evaluated for collecting channel catfish Ictalurus punctatus, and low-frequency, pulsed DC electrofishing was evaluated for collecting blue catfish I. furcatus. To examine spatial and temporal variability, capture efficiency and size selectivity were estimated in river and reservoir habitats during June, July, and September 2005. Selectivity of experimental gill nets was also assessed. Capture efficiency of hoop nets for channel catfish was consistent across months and between river and reservoir habitats (2.7–14.3% per 12 hoop-net series). Capture efficiency of low-frequency electrofishing was low (frequently, ≤1% per 120 min) and variable; recapture rates were greatest in river habitat during July and September. Hoop-net series collected representative samples of channel catfish between 250 and 556 mm total length. Likewise, blue catfish between 250 and 855 mm were fully vulnerable to low-frequency electrofishing. Although fish smaller than 250 mm were captured, they were frequently underrepresented in the catch of both gears. Size selectivity was not affected by habitat or month sampled for either gear type or either species. Capture efficiency of experimental gill nets was very low for both channel catfish and blue catfish (about 0.2% in 46 gill-net nights), and gill nets were more size selective than other gears. Based on our findings, hoop-net series and low-frequency electrofishing provide accurate size structure data for adult channel catfish and blue catfish, respectively, from both river and reservoir habitat types. Hoop-net series also provide consistent estimates of channel catfish relative abundance; however, relative abundance data for blue catfish collected with low-frequency electrofishing should be used with caution due to observed variability in capture efficiency.
Hatch Timing Variations among Reservoir Gizzard Shad Populations: Implications for Stocked Sander spp. Fingerlings
Authors: Zweifel Richard D. , Hale R. Scott , Bunnell David B. , Bremigan Mary T.
Published: April 2009

Growth and survival of stocked Sander spp. fingerlings can be influenced by timing of stocking in relation to the peak in density of larval gizzard shad Dorosoma cepedianum. However, coordinating stockings to coincide with peaks in gizzard shad density is difficult due to temporal variation in spawn timing among reservoirs. We used weekly estimates of larval gizzard shad density and length distributions to identify dates of peak hatching and peak total density in Ohio reservoirs and to explore the influence of spring water temperature regimes on timing of peak larval density. Gizzard shad density peaked over 21–32 d among reservoirs but generally varied by 12 d or less among years for any given population. Density peaks were driven by hatching, as larvae smaller than 10 mm accounted for a majority of the gizzard shad collected on the peak date. Peaks in gizzard shad density corresponded to water temperatures of 17–22°C and occurred most frequently when water temperatures had been stable or rising. Reservoirs in the southern portion of the state were 2–5°C warmer than northern reservoirs throughout the spring; thus, gizzard shad spawning and date of peak larval density were earliest in southern reservoirs and became progressively later for populations in more northerly reservoirs. Historical stocking dates for fingerling walleyes S. vitreus and saugeyes (sauger S. canadensis × walleye) in Ohio reservoirs indicated that southern reservoirs were often stocked after the expected peak in gizzard shad density and northern reservoirs were stocked before the peak. A statewide approach to stocking that incorporates latitudinal variations in gizzard shad hatch timing whereby southern reservoirs are stocked earliest would better align stockings with peak gizzard shad density, potentially improving survival of fingerling walleyes and saugeyes.
How well do we understand the impacts of alien species on ecosystem services? A pan‐European, cross‐taxa assessment
Authors: Vilà Montserrat , Basnou Corina , Pyšek Petr , Josefsson Melanie , Genovesi Piero , Gollasch Stephan , Nentwig Wolfgang , Olenin Sergej , Roques Alain , Roy David , Hulme Philip E ,   DAISIE partners
Published: April 2009

Recent comprehensive data provided through the DAISIE project (www.europe‐aliens.org) have facilitated the development of the first pan‐European assessment of the impacts of alien plants, vertebrates, and invertebrates – in terrestrial, freshwater, and marine environments – on ecosystem services. There are 1094 species with documented ecological impacts and 1347 with economic impacts. The two taxonomic groups with the most species causing impacts are terrestrial invertebrates and terrestrial plants. The North Sea is the maritime region that suffers the most impacts. Across taxa and regions, ecological and economic impacts are highly correlated. Terrestrial invertebrates create greater economic impacts than ecological impacts, while the reverse is true for terrestrial plants. Alien species from all taxonomic groups affect “supporting”, “provisioning”, “regulating”, and “cultural” services and interfere with human well‐being. Terrestrial vertebrates are responsible for the greatest range of impacts, and these are widely distributed across Europe. Here, we present a review of the financial costs, as the first step toward calculating an estimate of the economic consequences of alien species in Europe.
Clinical Research Networks for Neurological Emergencies: An Evidentiary Review
Authors: Storer Andrew
Published: April 2009

Consensus groups believe that clinical research networks are a more effective method of conducting clinical research than stand-alone sites. For example, clinical research networks have increased patient recruitment, decreased financial overhead, and allowed for coordinated research efforts, resulting in decreased duplication within high-cost research infrastructure. To date, there is little evidence describing the benefits and effectiveness of clinical research networks.
Genetic erosion and population resilience in Daphnia longispina O.F. Müller under simulated predation and metal pressures
Authors: Lopes Isabel , Martins Nelson , Baird Donald J. , Ribeiro Rui
Published: April 2009

This study investigated the effects of nonselective predation (culling) and metal toxicity on the genetic diversity of laboratory populations of the cladoceran Daphnia longispina. Populations, comprising five clones differing in their sensitivity to lethal concentrations of a metal-rich mine drainage effluent, were subjected to all possible combinations of three levels (absent, weak, and strong) of each stressor. Observed population densities were compared to those expected from a life history experiment, and clone frequencies were determined by allozyme profiling. Culling did not affect population density, although clonal diversity was higher than the control. Populations stressed by mine drainage recovered to their initial densities within 12 days, though the most sensitive genotypes disappeared under both weak and strong metal stress levels. Because the surviving resistant clones were shown to be the most sensitive ones to other chemicals (Cd and H+), it is suggested that successive inputs of partially lethal concentrations of different chemicals can lead to the disappearance of the population, even if the time between inputs is large enough to allow density recovery. These results suggest that changes in abundance are not enough to evaluate ecological effects of chemicals on the environment and information on co-tolerance and multiple tolerance within populations is highly valuable to prevent their extinction. Moreover, populations exposed to low levels of both stressors showed clonal diversity levels identical to controls, highlighting the importance of low level effects of nonselective stressors in the maintenance of high clonal diversity levels in Daphnia populations, and thus further supporting the intermediate disturbance hypothesis.
Arsenate toxicity for wheat and lettuce in six Chinese soils with different properties
Authors: Cao Qing , Hu Qin-Hong , Baisch Cristoph , Khan Sardar , Zhu Yong-Guan
Published: April 2009

To assess soil arsenic (As, in the form of arsenate) toxicity to plants, 6-d root elongation tests on wheat (Triticum aestivum L.) and lettuce (Lactuca sativa) were conducted in six Chinese soils freshly spiked with As. Plants were treated with 7 or 10 levels of As to establish concentration-effect curves. Median effective concentration and 10% effective concentration values were derived with regression analysis to measure As toxic potencies, and no-observed-effect concentration was determined by comparison with a control to elucidate thresholds of As to the two plant species. The median effective concentration values for As varied from 159 to 683 mg/kg for wheat and 59 to 426 mg/kg for lettuce, and the 10% effective concentration values varied from 79 to 270 mg/kg for wheat and 20 to 156 mg/kg for lettuce. The result suggests that lettuce is a more sensitive species for monitoring soil As contamination. With the same level of As spiked, soil toxicity for a plant showed a tendency of fluvoaquic soil toward red soil or black soil toward paddy soil. The phytotoxicity of As was negatively correlated with soil amorphous iron content extracted with ammonium oxalate. The overall results from the present work illustrate the necessity of considering soil properties in assessing soil As contamination.
Kinetics of the Reaction of Citric Acid With Calcite
Authors: Alkhaldi M. H. , Nasr-El-Din H. A. , Sarma H.
Published: April 2009

The previous studies of citric-calcite have been limited to core flood tests, and bench scale experiments. However, the reaction kinetics of citric acid-calcite has not been measured. This paper gives, for the first time, the kinetics of citric-calcite reaction, which will provide a better way to model the performance of citric acid as a stand-alone stimulation fluid.

In this paper, the rotating disk was used to study citric-calcite reaction at pressure of 1,000 psi, temperature values from 25 to 50°C, citric acid concentrations of 1 to 7.5 wt%, and disk rotational speeds of 100 to 1,000 rpm. The reaction of citric acid with calcite is dependent on the initial citric acid concentration, disk rotational speed, and the temperature value. For example, at 50°C, the reaction is reaction rate-limited at high rotational speeds, rpm > 500, using high initial citric acid concentrations (3, 5, 7.5 wt%), while at low acid concentrations (1,2 wt%), the reaction is mass-transfer limited even at high rotational speeds, 1,000 rpm. Calcium citrate formation is also dependent on both the initial citric acid concentration, and the rotational speed. More calcium citrate forms at high initial citric acid concentrations, especially at high rotational speeds.

Calcium citrate precipitation occurred at the reacted calcite surface, even at low initial citric acid concentration, 1 wt%. Due to this precipitation, the equilibrium of citric-calcite reaction was disturbed, and the reaction shifted towards the forward reaction (toward the products). Therefore, the overall reaction rate was mainly governed by the rate of the forward reaction, and hence, it was molded by a new simplified reaction rate equation, rate = kf {Ka1*CB}n/2. The average value of the reaction order (n) was found to be equal to 0.833. In addition, the value of the reaction constant (kf) was determined at various temperatures. The effect of temperature on the reaction order was found to follow Arrhenius law, where the activation energy was found to be equal to 63.1 kJ/mol.
Re-commissioning of Mothballed Pipelines Offshore California: A Success Story of Cleaning, Pigging, Monitoring and Integrity Management
Authors: Wylde Jonathan J.
Published: April 2009

Three unused intra-field pipelines exist between two platforms in a producing complex located offshore California. The complex produced 2,200 BOE/d and the project was to bring an offline platform online in order to boost production. The platform had not produced since 1999 and the pipelines had not seen active duty since that time.

The major challenge for this project was the condition of the intra-field pipelines and the requirement to provide the US Minerals Management Service (MMS) with a robust integrity management strategy in this environmentally sensitive area of the Pacific Ocean.

This paper gives details on the external pipeline condition as determined by ROV coupled with cathodic potential measurements. Further details are given on how the pipelines were intelligently pigged including the chemical cleaning procedure that enhanced the efficacy of the pigging runs.

The well start-up strategy and a description of the operating conditions of the facilities and pipelines are given. The corrosion mitigation and monitoring strategy form the bulk of discussions. Details are also given on the initial batch treatments to establish a protective chemisorbed film on the pipelines as well as the subsequent maintenance of these films. The discussion of the monitoring strategy includes direct electrochemical monitoring using ER probes in addition to indirect monitoring using amine residuals, iron and manganese counts and corrosion coupons. Final details are given on the successful start up of the platform and pipelines and the success of the integrity management strategy.

The proactive work gave MMS assurance on the continued integrity of the pipeline, protection of production, and of the environment.
A New MIC Control Strategy in Low Velocity Gas Gathering Pipelines
Authors: Smith C. , Li C. , Bedard T. , Kimler J.
Published: April 2009

Internal corrosion related failures in oil and gas gathering systems are increasing, especially in conditions categorized as "low risk" by computer modeling. Such systems usually exhibit, low pressure, low temperature sweet gas production, and relatively low total dissolved solid content waters. The failure rate is commonly influenced by two major factors; 1) undiagnosed microbiologically influenced corrosion (MIC) mechanisms, and 2) the unappreciated impact of corrosive chemical biocides used to treat sessile and planktonic bacteria. Low velocity gas gathering systems are particularly difficult to treat for MIC as a result of pigging challenges and the tendency for corrosive biocides to concentrate in the water phase over time. Here we report a new water soluble quaternary ammonium compound, didecyldimethylammonium bicarbonate/carbonate (DDABC), that acts as an MIC corrosion control agent against common oilfield bacteria. At the proper dilution, DDABC also acts as a thin film forming anodic inhibitor on steel. Supporting lab and field tests indicate this inhibitor is effective in competitive evaluations against glutaraldehyde, THPS, and quaternary ammonium chloride based agents. In a field trial reported herein, DDABC reduced the failure rate of a 1,653 km low velocity gas gathering field to approximately one-sixth the original rate in a 20 month field trial.
An Innovative Cement Formula To Prevent Gas Migration Problems in HT/HP Wells
Authors: Al-Yami A. S. , Nasr-El-Din H. A. , Al-Humaidi Ahmad
Published: April 2009

Gas Migration through cement columns has been an industry problem for many years. The most problematic areas for gas migrations occur in deep gas wells. To control gas migration, cement densities required to successfully cement the zone could be as high as 170 pcf (Pounds per Cubic Foot). As cement slurry sets, hydrostatic pressure is reduced on the formation. During this transition, reservoir gases can travel up through the cement column resulting in gas being present at the surface. The permeable channels, from which gas flows, cause operational and safety problems at the well site.

Current high density cement formulations do not provide good gas migration prevention due to settling and subsequent increase in permeability. To address the settling problem and reduce permeability of cement, a formula that resulted in great gas prevention was developed.

A gas migration set-up helped in testing and optimizing cement formulations to measure gas flow through cement columns. The gas migration set up consisted of the following components: computer, data acquisition, full-length permeability determination, two partial length permeability determinations, cement volume change measurement, gas flow meter, and electronic filtrate weight determination. The pressure and temperature limitations are 2,000 psi maximum and 350°F. Different chemicals for gas migration prevention were evaluated. Special types of cements were designed and evaluated for possible use for cementing gas wells. Addition of inert particles to cement and their effect on gas migration prevention was investigated.

In this paper, a new cement system was developed and resulted in significant gas prevention. The performance of this system outperforms available formulations and has great potential to improve wellbore isolation in deep gas wells.
Low Dosage, High Efficiency and Environment Friendly Inhibitors: A New Horizon in Gas Hydrates Mitigation in Production Systems
Authors: Kannan Krupa , Punase Aarti
Published: April 2009

Presently, gas hydrates formation pose problems, causing flow restrictions, in gas and oil industry including drilling operations (particularly in deep water), production process, well workovers where gas and water come into contact at equilibrium conditions. Traditional hydrate control methods of insulation and/or thermodynamic or chemical inhibition may not provide the desired level of hydrate protection at an economic price. Low-Dosage Hydrate Inhibitors (LDHIs) are a proven technology to control hydrates in numerous applications and are instrumental in reducing the total cost of operations. Low dosage Inhibitors are either kinetic, thermodynamic inhibitors or anti- aglomerants, which either prevent hydrate formation or remove the hydrates that are already formed respectively.

Therefore, this paper focuses on introduction to such low dosage inhibitor which can perform all the functions like prevention of formation of hydrate nuclei (like kinetic or thermodynamic inhibitors) and dispersing the already formed ones in flowlines (like anti- agglomerants). This paper proposes the use of Cationic polymers like cationic starch (from a high amylose carbohydrate source) in low concentration with addition of Polyethylene Oxide (PEO) as a new Gas Hydrates inhibitor.

The polymer with PEO, dissolved in water, can be introduced in petroleum fluid using mechanical equipment or utilized in treating fluid prior to substantial formation of the hydrates. As observed from an experimental analysis, these positively charged polymers interfere with nucleation of hydrates, increase induction time of gas hydrate nucleation, suppress memory effect, and act as antifreeze and thereby controlling hydrates.

With reference to these polymers, their abundant availability, easy application techniques and simple cationization procedure all contribute to its inexpensive and environment friendly usage as gas hydrate inhibitor. This paper provides systematic approach and relevant theoretical explanation for the proposed technique.
Successful Field Application of a High-Temperature Conformance Polymer in Mexico
Authors: Mercado Modesto , Acuna Juan Carlos , Caballero Carlos , Vasquez Julio , Soriano Eduardo
Published: April 2009

Conformance-polymer systems have been successfully applied for many years to control undesired water production from hydrocarbon wells. However, currently available polymers present a number of limitations for high-temperature wells (>250°F) in terms of providing longer gelation times and acceptable thermal stability. This paper presents the successful field implementation of an organically crosslinked polymer (OCP) for high-temperature applications in southern Mexico.

The OCP system is based on a copolymer of acrylamide and t-butyl acrylate (PAtBA) crosslinked with polyethyleneimine (PEI). To date, more than 450 jobs have been performed with the OCP system around the world to address conformance problems, such as water coning/cresting, high-permeability streaks, gravel pack isolation, fracture shutoff, and/or casing-leak repair. Originally, the OCP system had a limited working temperature range from 100° to 250°F. The upper placement temperature of the system was ~250°F because, above this temperature, pumping times were too short. A recently developed carbonate retarder allows reasonable placement times up to 350°F, without the need for cooling down the formation to obtain enough pumping time. The retarder is not detrimental to the thermal stability of the system.

An overview of case histories that used OCP in southern Mexico is presented in this paper. In addition, the development results of the high-temperature conformance polymer are discussed in terms of (1) gelation-time measurement and (2) effectiveness to limit permeability to water and thermal stability in sandpack flow tests at elevated temperatures. To date, more than 70 jobs have been successfully performed worldwide with the OCP at temperatures higher than 250°F.
Prevention of Vertical Gas Flow in a Collapsed Well Using Silicate/Polymer/Urea Method
Authors: Lakatos Istvan , Medic Borimir , Jovicic Dragan , Basic Ivan , Lakatos-Szabo Julianna
Published: April 2009

The overpressurized CO2 field Becej (Serbia) was found in 1951. At the end of 1968, drilling a well, an uncontrolled gas blowout happened and lasted for 209 days. The disaster claimed human lives and huge gas loss until it was spontaneously killed by collapse of the well5. Hence, the substantial loss of reserve (>17 billion m3) became critical and urgent actions had to be taken to stop the vertical gas migration. As a precondition, environmentally friendly chemicals could be used for restriction of vertical gas flow in the collapsed well. Therefore, silicate solution aided by polymer and urea was recommended for the job utilizing its auto-gelation in CO2 rich media. The triangle well pattern was the basis of operation consisting of an observation and a newly drilled directional well that served for injection of the treating solutions. The inverted injection protocol and huge volume of treating solution jointly proved satisfactory to provide extensive pillow around the well filling up also the accumulated debris at the bottom and open vertical hole. Restriction of vertical CO2 migration in and around the collapsed well was successfully completed in the middle of 2007. As a result of treatment, the annual decline of formation pressure was merely 0.03 bar/y compared to 0.9 bar/y before the treatment. Further, other indications in the damaged and the observation wells have shown that the uncontrolled gas flow was considerably restricted or completely stopped. The successful restriction of gas migration into the upper layers (and the atmosphere) preserves the CO2 reserve, limits CO2 and GHGs emission to atmosphere and stabilizes the collapsed well against potential danger of repeated gas blowout.
Identification and Analysis of Biocides Effective Against Sessile Organisms
Authors: Keasler Victor , Bennett Brian , Diaz Raul , Lindemuth Paul , Kasowski Dale , Adelizzi Craig , Santiago-Vazquez Lory Z.
Published: April 2009

Microbiologically influenced corrosion (MIC) is a major problem in the oil and gas industry. Although the exact mechanism by which this occurs is not well understood, it is recognized that byproducts produced by sessile bacteria located on the metal surface are responsible for the corrosion. However, many of the biocide treatment programs that have been developed thus far have focused only on planktonic organisms, ignoring the root cause of the problem. The goal of this research was to develop and implement sessile monitoring and analysis capabilities to assist in biocide selection.

Initial laboratory testing was performed using a representative selection of bacteria inoculated into a closed flow loop system containing removable biostuds. Sessile bacteria populations were analyzed before and after biocide treatment using serial dilutions and denaturing gradient gel electrophoresis (DGGE). A biocide/surfactant combination shown to be effective in the lab was tested in a field trial to demonstrate a correlation between laboratory testing and field use. Data collected in the field was analyzed by quantitative PCR (qPCR) as well as DGGE.

The biocide/surfactant tested in the laboratory led to a 3-log reduction in sessile bacteria without regrowth 24 hours after treatment. Bacterial enumeration determined by serial dilution was confirmed by DGGE analysis. This biocide/surfactant combination was also tested in a field trial where a 3- to 5-log reduction in bacterial numbers was determined by qPCR, a dramatic reduction in bacterial species observed by DGGE, and reduced pitting of the corrosion coupons identified.

In conclusion, we have implemented new testing capabilities that allow us to identify biocides effective at removing sessile organisms in the laboratory. Importantly, we have also shown that these laboratory results are recapitulated in field trials. These methods can now be utilized to ensure that the most efficacious biocide is chosen to mitigate bacterial populations that could potentially cause MIC in an asset-specific manner.