The federally endangered June sucker (Chasmistes liorus mictus), which is endemic to Utah Lake, UT, historically spawned in all significant tributaries flowing into Utah Lake. However, due to a variety of anthropogenic changes, June sucker spawning is now primarily restricted to the Provo River, the largest tributary to Utah Lake. The purpose of this study was to gain a better understanding of the spawning and early life history of the June sucker. My specific objectives were to determine (1) what environmental factors attract or deter June suckers to certain Utah Lake tributaries for spawning; (2) what cues June suckers to migrate upstream to spawn; (3) if June suckers use more than one tributary for spawning; and (4) what limiting factors exist in these smaller tributaries. I performed weekly trap-netting surveys and installed passive integrated transponder tag interrogation systems into five Utah Lake tributaries during the spring of 2008 to determine if suckers were using multiple tributaries for spawning and to determine the timing and number of fish migrating upstream to spawn. I coupled the trap-netting data (staging) and migration data (tributary use) with a suite of biotic and abiotic environmental variables in a random forest model to establish the strongest relationships that exist between fish migration and environmental factors. I found that June sucker were present at the mouths of all tributaries sampled and migrated up three of the five tributaries during the spawning season. The Provo River was the tributary most used. Evidence of reproduction was found in four of the five tributaries by the presence of larval June sucker. The random forest model, for staging, indicated that lower total dissolved solids of the tributaries influenced higher catch per unit effort at the mouths of the tributaries, but explained only 33% of the variance. The random forest model, for tributary use, performed very well, explaining 85% of the variance and indicated discharge was the most important variable for upstream migration. Specifically, the ascending limb of the hydrograph appeared to cue migration and the descending limb cue spawning. I also found the most likely limiting factors in the smaller tributaries are degraded water quality and available spawning habitat. Results from this study show fish are selecting less degraded streams for spawning. Stream restoration projects, in the smaller tributaries, would likely increase the spawning habitat for June suckers and aid their recovery.

No description available.

Density-dependence is considered one of the most important regulators of population growth, and it has been documented across a wide variety of species. Typically, population growth rate and components thereof decline with increasing density (i.e., negative density-dependence); however, in species that exhibit high population densities and social behavior, positive density-dependence (i.e., Allee effect) may occur at low density. June sucker, a federally endangered lake sucker endemic to Utah Lake, Utah, USA, occurred historically at high density, and it exhibits coordinated feeding behavior. These characteristics indicate a potential for the existence of an Allee effect at current low population densities. To determine effects of density on growth, survival, and diet, I experimentally manipulated density of young June sucker in replicated enclosures in a natural environment. Larval June sucker were placed in enclosures at four different densities, and growth, survival, and diet of fish, and availability of prey (to determine selectivity) were measured at two time intervals. Both individual growth and survival were significantly lower at the lowest density compared to higher densities, indicative of a component Allee effect. Diets of individuals at low densities were more selective than diets of individuals at intermediate and high densities, suggesting a change in feeding strategy with density. Reduced growth and survival at low density suggests that corresponding, highly selective, feeding strategies may be less efficient than feeding strategies employed at higher densities. Allee effects appear to be an important consideration for recovery of this endangered species, and such effects may be common in historically abundant, but currently rare species.

Due to the endangerment of the June sucker (Chasmistes liorus), the lower two miles of Hobble Creek, Utah has been the focus of several restoration efforts. The portion of the creek between Interstate 15 and Utah Lake has been moved into a more "natural" channel and efforts are now being made to expand restoration to the east side of the freeway. This thesis reports on three different parts of a sedimentological analysis performed on Hobble Creek. The first part is a data set that contains information about the particle size distribution on the bed of Hobble Creek between 400 W and Interstate 15 in Springville, Utah. Particle size distributions were obtained for eleven sub-reaches within the study section. Particle size parameters such as D50 were observed to decrease from an average of 72 mm to 24 mm downstream from the 1650 W crossing and Packard Dam. Streambed armoring was observed along most of the reach. This data set can be used as input for PHABSIM software to determine the location and availability of existing spawning material for June sucker during a range of flows. The second part of this thesis compares predictions from four bed-load transport models to bed-load transport data measured on Hobble Creek. In general, the Meyer-Peter, Muller and Bathurst models overpredicted sediment transport by several orders of magnitude while the Rosgen and Wilcock methods (both calibrated models) were fairly accurate. Design channel dimensions resulting from the bed-load transport predictions diverged as a function of discharge. Once validated, the models developed in this section can be used by design engineers to better understand sediment transport on Hobble Creek. The models may also be applied to other Utah Lake tributaries. The third section of the thesis introduces a detailed survey data set that covers the Hobble Creek floodplain on the shifted section between Interstate 15 and Utah Lake with an approximate 10 foot resolution grid. Water surface elevations at two flows, along with invert, fence, saddles, and other points, are labeled in the survey. A comparison with a survey completed last year did not reveal any significant lateral changes caused by the 2010 spring runoff. Due to the potential importance of the side ponds to June sucker survival, this data set can be used to monitor sedimentation in the side ponds. It may also be used in a GSSHA model to determine the magnitude of flow that is required before each side pond will be connected to the main channel.

Pantosteus, a subgenus of Catostomus, includes the mountain sucker (Catostomus playthyrnchus), whose speculated older origins in the Miocene/Pliocene can provide insight into the ancient geographical events of western North America. We believe that major geologic events influencing the diversification of mountain suckers include the rise of the Colorado Plateau, the connections between the ancient Snake River system and the Lahontan system and subsequently the connection of the Snake River system to the Columbia Basin, dispersal of mountain suckers across the continental divide, as well as the Pleistocene Bonneville flood. If this is true, we should see evidence of geologic separation and timing through studying the phylogenetics of the mountain sucker. In order to clarify relationships of the mountain sucker with respect to other Pantosteus species, we examined cytochrome b (cyt b) sequences for 144 mountain suckers, 24 other Pantosteus species, and ten outgroup species. Phylogenetic relationships among haplotypes were constructed based on maximum likelihood and Bayesian criterion. In an effort to provide better resolution at some nodes, we also sequenced additional mitochondrial genes (ND1, ND2, ATPase, ND4L, ND4, ND5, ND6, and cyt b) for a subset of 44 individuals taken from the major clades obtained from the cyt b phylogentic analyses. Trees from this data set were also constructed under maximum likelihood and Bayesian criterion. All phylogenetic analysis revealed that mountain sucker are paraphyletic, with two major clades of mountain suckers separated by other members of the subgenus Pantosteus. One clade included two sub-clades, one from the upper Snake River drainage/northern Bonneville/Green River drainage Basins and the other from the southern Bonneville Basin. The other major clade included sub-clades from the Lahontan Basin, Columbia River Basin, and Upper Missouri River Basin. Molecular clock analysis revealed that Pantosteus likely split from Catostomus during the Miocene and that major speciation events within Pantosteus occurred during the Pliocene and Pleistocene. Genetic structuring and gene flow estimates for mountain sucker populations, with groupings based on major drainage basins, were calculated with AMOVA and Fst estimates in Arlequin and revealed that most of the genetic structuring was explained by variation among drainage basins with limited gene flow occurring between drainage basins. Based on this study, the role of the Colorado Plateau's geologic history in the evolution of the mountain sucker remains unclear. However, all other geologic events as discussed in this study seem to have played a significant role in the evolution of the mountain sucker.

Swimming performance strongly influences fitness in aquatic organisms and is closely tied to external body morphology. Although this connection has been closely examined at the individual and species level, few studies have focused on this relationship as it pertains to functional group assemblages. Using functional groups based on similarities in habitat use and morphology, I tested the hypothesis that swimming performance can be reliably predicted by functional group composition. I measured swimming performance as burst speed using a simulated predator attack and as prolonged speed using a step-endurance test in a laboratory flume. I measured morphology using geometric morphometric techniques. A difference in swimming behavior in four of the seven species was observed in the step-endurance test. Benthic species exhibited bracing behavior as an alternative to body-caudal fin (BCF) propulsion in the prolonged speed trials. Swimming performance exhibited a weak relationship with functional groups based on habitat or morphology. Rather a species-based model was the best predictor of swimming performance. Although species exhibited variation in swimming performance, body size was the strongest predictor of absolute swimming performance across all models. Relative swimming performance (measured in body lengths/sec) was negatively related to body size. The results of this study suggest that functional groups are not always reliable predictors of performance and they necessitate empirical testing to validate their effectiveness. This study also provides critical swimming performance data for previously unstudied Great Basin fishes which could be valuable for predicting fish passage through culverts, weirs and fish ladders.

Thesis (MScAgric)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Grapevine trunk diseases are responsible for reduced wine and table grape production world-wide. Trunk disease infections are caused by xylem-inhabiting pathogens which include species of Botryosphaeriaceae, Diatrypaceae, Hymenochaetales and Diaporthales, as well as Phaeomoniella chlamydospora and Phaeoacremonium spp. Winter pruning wounds are regarded as the main infection-sites for trunk disease pathogens. However, the role of sucker wounds as portals of trunk disease infections has been minimally investigated. Knowledge of the potential role of grapevine trunk pathogen infections that occur through sucker wounds is important for better wound protection strategies. The aim of this study was to determine the role of grapevine sucker wounds as portals of entry for trunk disease pathogens and to assess the use of Trichoderma spp. for sucker wound protection. The susceptibility of sucker wounds to different trunk disease pathogens was assessed from natural as well as artificial infections. In addition the duration of sucker wound susceptibility in the field was also ascertained. Sucker wounds were sampled from three wine and two table grape vineyards during 2011 and 2012 in the Western Cape province of South Africa. Thereafter, fungal isolations were made from 161 sucker wounds and the cultures were identified based on cultural and morphological characteristics as well as the internal transcribed spacer regions and 5.8S ribosomal RNA gene. Sixty-two percent of the wounds were naturally infected by at least one of the trunk pathogens. Phomopsis (Po.) viticola (46%; 18%), Diplodia (D.) seriata (30%; 9%) and Phaeomoniella (Ph.) chlamydospora (27%; 5%) were the most predominant trunk disease pathogens isolated from sucker wounds of field wine and table grape cultivars, respectively. Lower incidences of Phaeoacremonium aleophilum (18%), Eutypella sp. (3%), Cryptovalsa ampelina (2%), Diplodia sp. (1%) and Neofusicoccum australe (1%) were obtained, however, only from wine grapes. Sucker wounds on 1-year-old potted grapevine plants of Chardonnay cultivar were inoculated with spore suspensions of Eutypa lata, N. parvum, Pa. aleophilum, Ph. chlamydospora and Po. viticola in the glasshouse. After 4 months all the inoculated pathogens could be re-isolated at the following incidences: N. parvum (85%), Ph. chlamydospora (75%), Po. viticola (65%), Pa. aleophilum (55%) and E. lata (45%). Sucker wound susceptibility was further ascertained under field conditions on 12-year-old Cabernet Sauvignon vines by artificial inoculation of the same pathogen species. After 5 months three pathogens could be re-isolated at the following incidences: Po. viticola (65%), N. parvum (32.5%) and Ph. chlamydospora (7.5%). The duration of susceptibility of field sucker wounds to Ph. chlamydospora was assessed for a period of 4 weeks. The wounds remained susceptible for 4 weeks with a decline in susceptibility after one week. This study showed that sucker wounds are susceptible to the major trunk disease pathogens and thus could play an important role in grapevine trunk disease epidemiology. In the second part of this thesis a possible management strategy to prevent infections of sucker wounds was investigated. The use of Trichoderma (T.) harzianum against two trunk pathogens on sucker wounds was tested in the field. Additionally the sensitivity of T. harzianum and T. atroviride was tested in vitro against 16 fungicides that are used to control powdery mildew, downy mildew, Botrytis rot and Phomopsis cane and leaf spot. In October 2012, sucker wounds were made on 1-year-old wood of Cabernet Sauvignon and spray-treated with Eco-77® immediately after desuckering, and then inoculated with spore suspensions of either Ph. chlamydospora or Po. viticola after 24 hours. After 5 months, isolations were made from the sucker wounds to evaluate the efficacy of the Trichoderma treatment. Trichoderma harzianum reduced the incidence of Ph. chlamydospora by 66.65%. Although the incidence of Po. viticola was reduced by 15.37%, it was not significantly different from the control treatment. The inhibition of mycelial growth and conidial germination of T. harzianum and T. atroviride were screened against 16 fungicides. The fungicides were applied at 0, 0.25, 0.5, 1 and 2 times the recommended dosages. Systemic fungicides boscalid, metrafenone and trifloxystrobin, as well as contact fungicides quinoxyfen and meptyldinocap were least toxic to Trichoderma spp. isolates. For the conidial germination assay, boscalid, trifloxystrobin, penconazole and metrafenone (systemic) plus quinoxyfen and folpet (contact) were compatible with Trichoderma spp. These fungicides were regarded as being compatible with Trichoderma spp. isolates because they gave mean percentage inhibitions of less than 50% at all the tested dosages. Spiroxamine and pyrimethanil gave the highest mean percentage inhibitions for both mycelial inhibition and conidial germination. The findings of this study showed that T. harzianum can protect sucker wounds against Ph. chlamydospora in the field. Furthermore, some fungicides applied for the control of powdery mildew and Phomopsis cane and leaf spot can be alternatively or simultaneously applied with T. harzianum and T. atroviride, however, this will have to be verified with field trials. / AFRIKAANSE OPSOMMING: Wingerd stamsiektes is wêreldwyd verantwoordelik vir verminderde wyn- en tafeldruif produksie. Stamsiektes word veroorsaak deur patogene wat in die xileem voorkom, insluitend verskeie spesies in die Botryosphaeriaceae, Diatrypaceae, Hymenochaetales en Diaporthales, asook Phaeomoniella chlamydospora en Phaeoacremonium spp. Winter snoeiwonde word beskou as die hoof bron van infeksies vir stamsiekte patogene. Die rol van suierwonde as poorte van infeksie vir stamsiektes is nog nie goed bestudeer nie. Kennis van die potensiële rol van wingerd stamsiekte patogeen infeksies wat deur suierwonde plaasvind is belangrik vir die formulasie van beter wondbeskerming strategieë. Die mikpunt van hierdie studie was om die rol van suierwonde as ingangsportale vir wingerd stamsiekte patogene te bepaal en om die gebruik van Trichoderma spp. vir suierwond beskerming te evalueer. Die vatbaarheid van suierwonde vir verskillende stamsiekte patogene is geëvalueer vanuit natuurlike, sowel as kunsmatige infeksies. Die duur van suierwond vatbaarheid in die veld is ook bepaal. Suierwonde is versamel vanuit drie wyn- en twee tafeldruif wingerde gedurende 2011 en 2012 in die Wes Kaap provinsie van Suid Afrika. Hierna is swam isolasies gemaak vanuit 161 suierwonde en die kulture is geïdentifiseer volgens kultuur en morfologiese kenmerke, sowel as die interne transkribeerde spasieerders en 5.8S ribosomale RNA geen. Twee-en-sestig persent van die wonde was geïnfekteer deur ten minste een van die stamsiekte patogene. Phomopsis (Po.) viticola (46%; 18%), Diplodia (D.) seriata (30%; 9%) en Phaeomoniella (Ph.) chlamydospora (27%; 5%) was die mees algemene stamsiekte patogene wat, respektiewelik, vanuit die wyn- en tafeldruif kultivars verky is. Laer hoeveelhede Phaeoacremonium aleophilum (18%), Eutypella sp. (3%), Cryptovalsa ampelina (2%), Diplodia sp. (1%) en Neofusicoccum australe (1%) is verkry, en slegs vanaf wyndruiwe. Suierwonde op 1-jaar oue Chardonnay wingerdplante in potte is in die glashuis geïnokuleer met spoorsuspensies van Eutypa lata, N. parvum, Pa. aleophilum, Ph. chlamydospora en Po. viticola. Na 4 maande kon al die geïnokuleerde patogene her-isoleer word teen die volgende hoeveelhede: N. parvum (85%), Ph. chlamydospora (75%), Po. viticola (65%), Pa. aleophilum (55%) en E. lata (45%). Suierwond vatbaarheid is verder geëvalueer onder veld kondisies op 12-jaar oue Cabernet Sauvignon plante deur kunsmatige inokulasie van die selfde patogeen spesies. Na 5 maande kon drie patogene her-isoleer word teen die volgende hoeveelhede: Po. viticola (65%), N. parvum (32.5%) en Ph. chlamydospora (7.5%). Die duur van vatbaarheid van suierwonde teen Ph. chlamydospora in die veld is geevalueer oor ‘n periode van 4 weke. Die wonde het vatbaar gebly vir 4 weke met ‘n afname in vatbaarheid na ‘n week. Hierdie studie demonstreer dat suierwonde vatbaar is vir die hoof wingerd stamsiektes en dus ‘n belangrike rol in die epidemiologie van wingerd stamsiektes kan speel. In die tweede deel van hierdie tesis is ‘n moontlike bestuurs-strategie ondersoek om infeksie van suierwonde te verhoed. Die gebruik van Trichoderma (T.) harzianum teen twee stampatogene op suierwonde is getoets in die veld. Verder is die in vitro sensitiwiteit van T. harzianum en T. atroviride getoets teen 16 fungisiedes wat gebruik word in die beheer van poeieragtige meeldou, donsskimmel, Botrytis vrot en Phomopsis streepvlek. Gedurende Oktober 2012 is suierwonde gemaak op 1-jaar oue hout van Cabernet Sauvignon en onmiddelik behandel met Eco-77® na suiering. Wonde is dan geïnokuleer met spoorsuspensies van óf Ph. chlamydospora óf Po. viticola na 24 uur. Na 5 maande is isolasies gemaak vanaf suierwonde om die doeltreffendheid van van die Trichoderma behandeling te evalueer. Trichoderma harzianum het die voorkoms van Ph. chlamydospora met 66.65% verminder. Alhoewel die voorkoms van Po. viticola verminder is met 15.37%, was dit nie ‘n beduidende verskil in vergelyking met die kontrole behandeling nie. Die inhibisie van miselium groei en konidia ontkieming van T. harzianum en T. atroviride is getoets teen 16 fungisiedes. Die fungisiedes is aangewend teen 0, 0.25, 0.5, 1 en 2 keer die aanbevole dosisse. Sistemiese fungisiedes boscalid, metrafenone en trifloxystrobin, sowel as kontak fungisiedes quinoxyfen en meptyldinocap was die minste toksies teen Trichoderma spp. Gedurende die konidia ontkiemingstoets was boscalid, trifloxystrobin, penconazole en metrafenone (sistemies) en quinoxyfen en folpet (kontak) versoenbaar met Trichoderma spp. Die fungisiedes is beskou as bruikbaar met Trichoderma spp. isolate omdat hulle gemiddelde persentasie inhibisies van minder as 50% teen al die getoetste dosisse gelewer het. Spiroxamine en pyrimethanil het die hoogste gemiddelde persentasie inhibisie gelewer vir beide die miselium inhibisie en konidia ontkieming. Die bevindings van hierdie studie het gewys dat T. harzianum suierwonde kan beskerm teen Ph. chlamydospora in die veld. Verder sou sommige fungisiedes wat aangewend word vir die bestuur van poeieragtige meeldou en streepvlek moontlik alternatiewelik of gelyktydig met T. harzianum en T. atroviride aangewend word, alhowel dit met veldproewe bevestig moet word.

During the reservoir production life reservoir pressure will decline. Also after water breakthrough the fluid column weight will increase as hydrostatic pressure will increase because of increased water and oil mixture density. In this case, reservoir pressure may not be enough to lift up the fluid from bottom to the surface. These reasons decrease or even may cause to stop flowing of fluids from the well. Some techniques must be applied to prevent the production decline. Artificial lift techniques are applied to add energy to the produced fluids. It increases production rate by reducing down-hole pressure and so that by increasing the drawdown. Artificial lift techniques increase production either by pumping the produced fluid from the bottom to the surface or reduce bottom-hole pressure by reducing the fluid column weight as a result of decreased fluid mixture density. Artificial lift is used worldwide in approximately 85% of the wells, thus its impact in overall efficiency and profitability of production operations cannot be overemphasized. The most important problem is how to select optimum artificial lift techniques by taking into consideration the reservoir, well, environmental conditions. Selection of poor technique could cause decrease in efficiency and low profitability. As a result, it will lead to high operating expenses. Several techniques have been developed for selection of optimum artificial lift techniques. Expert Systems (ES) is the most suitable technique used in these selection techniques. Because the use and availability of required parameters is easy. Also in this selection method most of the artificial lift techniques are analyzed rather than other selection techniques. Expert Systems program mainly consist of three modules: (1) Expert Module, (2) Design Module, and (3) Economic Module. By entering required data to the system, program automatically suggests the feasible artificial lift techniques those might be used referring to given data. In this thesis work the artificial lift selection criteria and Expert Systems available in the literature have been studied. A Microsoft Windows based program has been developed to predict suitability of artificial lift methods for a given set of wells and produced fluid parameters. For the selected artificial lift method (i.e. sucker rod pump, ESP, gas lift, hydraulic pump, PCP) the program is able to perform basic calculations for the given data. Different case studies have been performed by running the program with actual data from fields. Well data of Venezuela, Azerbaijan and Iranian oil fields has been used in case studies. The results have been compared with previous studies those have been done on these fields with other selection techniques and current artificial lift techniques are being applied in selected wells. The obtained program results have been overlap with current real field application and previous studies.

Made available in DSpace on 2014-12-17T14:56:09Z (GMT). No. of bitstreams: 1 JoaoMAN.pdf: 3978536 bytes, checksum: e28a273c6981fff29b2c335fd3ee11ce (MD5) Previous issue date: 2005-03-11 / This work proposes a computer simulator for sucker rod pumped vertical wells. The simulator is able to represent the dynamic behavior of the systems and the computation of several important parameters, allowing the easy visualization of several pertinent phenomena. The use of the simulator allows the execution of several tests at lower costs and shorter times, than real wells experiments. The simulation uses a model based on the dynamic behavior of the rod string. This dynamic model is represented by a second order partial differencial equation. Through this model, several common field situations can be verified. Moreover, the simulation includes 3D animations, facilitating the physical understanding of the process, due to a better visual interpretation of the phenomena. Another important characteristic is the emulation of the main sensors used in sucker rod pumping automation. The emulation of the sensors is implemented through a microcontrolled interface between the simulator and the industrial controllers. By means of this interface, the controllers interpret the simulator as a real well. A "fault module" was included in the simulator. This module incorporates the six more important faults found in sucker rod pumping. Therefore, the analysis and verification of these problems through the simulator, allows the user to identify such situations that otherwise could be observed only in the field. The simulation of these faults receives a different treatment due to the different boundary conditions imposed to the numeric solution of the problem. Possible applications of the simulator are: the design and analysis of wells, training of technicians and engineers, execution of tests in controllers and supervisory systems, and validation of control algorithms / Este trabalho prop?e um simulador computacional para po?os de petr?leo com trajet?ria vertical, equipados com eleva??o artificial por bombeio mec?nico (BM). O simulador ? capaz de representar o comportamento din?mico de sistemas de BM e avaliar numericamente diversos par?metros relevantes ao mesmo, permitindo a f?cil visualiza??o de diversos fen?menos pertinentes ao processo, tudo isso, de forma conveniente e a custos e tempos menores, do que experimentos com po?os reais. A simula??o utiliza um modelo baseado no comportamento din?mico da coluna de hastes, o qual pode ser representado por uma equa??o diferencial parcial de segunda ordem. A partir deste modelo, pode-se verificar a ocorr?ncia de diversas situa??es comumente vivenciadas em campo. A simula??o conta ainda com anima??es em 3D, facilitando o entendimento f?sico do processo, devido a uma melhor interpreta??o visual dos fen?menos. Outra caracter?stica importante ? a emula??o dos principais sensores utilizados na automa??o de BM. A emula??o dos sensores ? feita atrav?s de uma interface microcontrolada entre o simulador e controladores industriais, de maneira que os controladores interpretem o simulador como um po?o real. No simulador foi desenvolvido um m?dulo de falhas onde s?o implementadas seis diferentes condi??es de falhas. Estas pertencem ao grupo dos principais problemas encontrados em sistemas de BM. Assim, a an?lise e verifica??o destes problemas, atrav?s do simulador, d? ao usu?rio a oportunidade de identificar tais situa??es que s? poderiam ser observadas em campo. A implementa??o destas condi??es recebe um tratamento diferenciado em virtude das diferentes condi??es de contorno impostas ? solu??o num?rica do problema. Diversas aplica??es s?o encontradas para o simulador, dentre elas: a parametriza??o e an?lise de po?os, a aplica??o em cursos de capacita??o t?cnica para t?cnicos e engenheiros, a realiza??o de testes em controladores, sistemas supervis?rios e a valida??o de algoritmos de controle

In group work, the sucker-effect is a motivational loss in which effort is reduced due to feeling taken advantage of when other group members intentionally avoid work, known as free-riding. No previous studies on the sucker-effect have investigated moderating factors that can be attributed to the free-rider. The purpose of this study was to explore if agreeable behavior of a free-rider would moderate the sucker-effect, and if so, to what extent. Using an experimental design, students (n = 20) at Södertörn University served as participants. A systematic allocation toone of two conditions was used, the less agreeable and more agreeable. During the experiment a participant and a confederate worked in dyadson a disjunctive cooperative jigsaw puzzle task. The manipulation was the free-riding confederate's level of agreeableness. Self-rated effort andactual performance were measured. Using Mann-Whitney U-tests (α =.05, two-tailed), no significant differences were found in either of thedependent variables. In fact, by and large, no sucker-effect was observed at all. Other than manipulating the confederate's level of agreeableness, the design allowed for much more interaction in the dyads than previous studies on the sucker-effect have. It is discussed whether this interaction might have created an ingroup feeling, leading to the prevention of asucker-effect. In this study it thus seems that the free-rider's level of agreeableness does not moderate the sucker-effect. Also, meaningful interaction between group members might prevent a sucker-effect fromoccurring at all. However, due to the study's small sample size, theseresults are not definitive and should be taken with caution.