Biology of growth of Hoplias aff. malabaricus (Bloch, 1794) in a shallow pampean lake Argentina

The trahira Hoplias aff. malabaricus is a top predator in pampean shallow lakes and is highly appreciated by recreational anglers and artisanal fishermen. Trahira growth from Yalca shallow lake was determined by lepidological analysis and age validated by marginal increment. When growth was fitted to the von Bertalanffy model, annual classes exhibited a bimodal pattern as a result of the presence of spring and summer annual cohorts associated with a three month spawning season, each period in turn showing different growth patterns. The trahira population-age structure at Yalca shallow lake showed a truncated profile with very low numbers of large adults and few individuals older than three to four years, thus producing an unbalanced length-structure population. Growth parameters and growth performance were similar to the corresponding parameters estimated for other shallow pampean lakes of the region, but strongly diverged from the data for those populations inhabiting subtropical and tropical environments. Such differences could be accounted for by dissimilarity in metabolic rates associated with thermal differences accompanying seasonal variability among latitudes as well as by the development of adaptive physiologic and demographic responses to cope with the high thermal amplitude and hydrologic instability observed in pampean lakes.A traíra Hoplias aff. malabaricus é um predador de topo encontrado em lagoas rasas nos Pampas, muito apreciada nas pescas comerciais e esportivas. O crescimento da traíra no lago Yalca foi determinado através de análises lepidológicas, validadas a partir do incremento marginal. O crescimento foi ajustado ao modelo de von Bertalanffy, sendo que as classes de tamanho anuais apresentaram padrão bimodal devido à presença de coortes de primavera e verão, associadas à uma longa estação reprodutiva com diferentes padrões de crescimento. A estrutura etária da traíra do lago Yalca apresentou um perfil truncado, com um número pequeno de adultos de maior porte e poucos indivíduos com mais de três ou quatro anos, produzindo uma estrutura em tamanho desbalanceada. Os parâmetros e a performance de crescimento foram similares aos estimados para outros lagos rasos da região, mas fortemente divergentes de populações encontradas em ambientes tropicais e subtropicais. Tais diferenças podem estar relacionadas à diferentes taxas metabólicas associadas à variação térmica sazonal entre latitudes e ao desenvolvimento de respostas adaptativas fisiológicas e demográficas em resposta aos padrões termais altamente variáveis e instabilidade hidrológica observados nos lagos da região dos Pampas.Fil: Balboni, Leandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Colautti, Dario César. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Baigún, Claudio Rafael M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); Argentin

Age and growth of Pseudoplatystoma corruscans (Siluriformes: Pimelodidae) at the confluence of the Paraná and Paraguay rivers

The age and growth of Pseudoplatystoma corruscans, is analyzed on specimens landed in Puerto Antequera, Province of Chaco, Argentina. The study is based on length frequency distribution of 1192 individuals and growth marks of 293 pectoral spines. Previously to age assignation based on spines readings, we performed analyses that ruled out age-associated resorption of rings and corroborated the annual periodicity of mark formation. The average sizes of the radius of each ring were obtained, and the total length of fish were back-calculated to the time of the ring formation, by the regression model fitted between the total radius of the spines to the respective sizes of each fish. Such data showed a good fitting to growth models of von Bertalanffy, Gompertz and logistic for both sexes separately. Results indicate that the study of the species growth must be carried out for each sex separately and that the fishing regulations must consider this characteristic of the species since the current management guidelines could be promoting differential capture by sexes.Fil: Balboni, Leandro. Ministerio de Agricultura, Ganadería, Pesca y Alimento; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Vargas, Facundo. Gobierno de la Provincia de Chaco. Ministerio de Planificación Ambiente e Innovación Tecnológica; ArgentinaFil: Colautti, Dario César. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; Argentin

Cambios en los indices biológicos de la tararira, hoplias malabaricus (bloch, 1794) en un ciclo anual en la Laguna Yalca, provincia de Buenos Aires, Argentina

Fil: Balboni, Leandro. Instituto Tecnológico de Chascomús, IIB-INTECH. Chascomús; ArgentinaFil: Colautti, Darío César. Instituto de Limnología Dr. Raúl A. Ringuelet (ILPLA). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Baigún, Claudio Rafael Mariano. Instituto Tecnológico de Chascomús, IIB-INTECH. Chascomús; Argentin

Cambios en los indices biológicos de la tararira, <i>Hoplias malabaricus</i> (Bloch, 1794) en un ciclo anual en la laguna Yalca, provincia de Buenos Aires, Argentina

The tararira is a top predator of paramount importance in Pampean lakes. The goal of this study is to assess the change of different biological indices of this species in Yalca Lake on a yearly basis. Also we attempt to determine the relationship between within indices variations and with water temperature (WT) and light hours (LH). Monthly captures were performed during 2006/2007 estimating the relative condition factor (Kn), gonadosomatic index (GSI), liposomatic index (LSI), hepatosomatic index (HSI) and somatosomatic index (SSI). The Kn and GSI presented significant temporal differences in both sexes, showing highest values from december to february, coincident with the reproductive cycle. The LSI displayed values close to cero not showing a stable trend, whereas the HSI presented highest and lowest values from may to july and from april to september respectively for both sexes. Finally the SSI exhibited differences between sexes with the maximum values between march and september. Males showed a positive and significant relationship between Kn and WT. In females this pattern was also noted between GSI and LH and between KN vs WT, but was negative between GSI vs SSI and SSI vs LH. We conclude that the use of different biological indices in this species allows following the maturation cycle and their associated metabolic processes being the observed variation patterns related to high seasonally physiological processes.Instituto de Limnología "Dr. Raúl A. Ringuelet

Cambios en los indices biológicos de la tararira, <i>Hoplias malabaricus</i> (Bloch, 1794) en un ciclo anual en la laguna Yalca, provincia de Buenos Aires, Argentina

The tararira is a top predator of paramount importance in Pampean lakes. The goal of this study is to assess the change of different biological indices of this species in Yalca Lake on a yearly basis. Also we attempt to determine the relationship between within indices variations and with water temperature (WT) and light hours (LH). Monthly captures were performed during 2006/2007 estimating the relative condition factor (Kn), gonadosomatic index (GSI), liposomatic index (LSI), hepatosomatic index (HSI) and somatosomatic index (SSI). The Kn and GSI presented significant temporal differences in both sexes, showing highest values from december to february, coincident with the reproductive cycle. The LSI displayed values close to cero not showing a stable trend, whereas the HSI presented highest and lowest values from may to july and from april to september respectively for both sexes. Finally the SSI exhibited differences between sexes with the maximum values between march and september. Males showed a positive and significant relationship between Kn and WT. In females this pattern was also noted between GSI and LH and between KN vs WT, but was negative between GSI vs SSI and SSI vs LH. We conclude that the use of different biological indices in this species allows following the maturation cycle and their associated metabolic processes being the observed variation patterns related to high seasonally physiological processes.Instituto de Limnología "Dr. Raúl A. Ringuelet

Cambios en los indices biológicos de la tararira, <i>Hoplias malabaricus</i> (Bloch, 1794) en un ciclo anual en la laguna Yalca, provincia de Buenos Aires, Argentina

The tararira is a top predator of paramount importance in Pampean lakes. The goal of this study is to assess the change of different biological indices of this species in Yalca Lake on a yearly basis. Also we attempt to determine the relationship between within indices variations and with water temperature (WT) and light hours (LH). Monthly captures were performed during 2006/2007 estimating the relative condition factor (Kn), gonadosomatic index (GSI), liposomatic index (LSI), hepatosomatic index (HSI) and somatosomatic index (SSI). The Kn and GSI presented significant temporal differences in both sexes, showing highest values from december to february, coincident with the reproductive cycle. The LSI displayed values close to cero not showing a stable trend, whereas the HSI presented highest and lowest values from may to july and from april to september respectively for both sexes. Finally the SSI exhibited differences between sexes with the maximum values between march and september. Males showed a positive and significant relationship between Kn and WT. In females this pattern was also noted between GSI and LH and between KN vs WT, but was negative between GSI vs SSI and SSI vs LH. We conclude that the use of different biological indices in this species allows following the maturation cycle and their associated metabolic processes being the observed variation patterns related to high seasonally physiological processes.Instituto de Limnología "Dr. Raúl A. Ringuelet

Cambios en los indices biológicos de la tararira, Hoplias malabaricus (Bloch, 1794) en un ciclo anual en la laguna Yalca, provincia de Buenos Aires, Argentina

The tararira is a top predator of paramount importance in Pampean lakes. The goal of this study is to assess the change of different biological indices of this species in Yalca Lake on a yearly basis. Also we attempt to determine the relationship between within indices variations and with water temperature (WT) and light hours (LH). Monthly captures were performed during 2006/2007 estimating the relative condition factor (Kn), gonadosomatic index (GSI), liposomatic index (LSI), hepatosomatic index (HSI) and somatosomatic index (SSI). The Kn and GSI presented significant temporal differences in both sexes, showing highest values from december to february, coincident with the reproductive cycle. The LSI displayed values close to cero not showing a stable trend, whereas the HSI presented highest and lowest values from may to july and from april to september respectively for both sexes. Finally the SSI exhibited differences between sexes with the maximum values between march and september. Males showed a positive and significant relationship between Kn and WT. In females this pattern was also noted between GSI and LH and between KN vs WT, but was negative between GSI vs SSI and SSI vs LH. We conclude that the use of different biological indices in this species allows following the maturation cycle and their associated metabolic processes being the observed variation patterns related to high seasonally physiological processes.La tararira es un depredador tope de suma importancia en los lagos pampeanos. El objetivo de este estudio es evaluar el cambio anual de diferentes índices biológicos de esta especie en la laguna&nbsp; Yalca. También intentamos determinar la relación entre las variaciones de los índices y con la temperatura del agua (WT) y las horas de luz (LH). Se realizaron capturas mensuales durante 2006/2007, estimando el factor de condición relativa (Kn), el índice gonadosomático (GSI), el índice liposomático (LSI), el índice hepatosomático (HSI) y el índice somatosomático (SSI). Kn y GSI presentaron diferencias temporales significativas en ambos sexos, mostrando los valores más altos desde diciembre hasta febrero, coincidiendo con el ciclo reproductivo. El LSI mostró valores cercanos a cero que no mostraron una tendencia estable, mientras que el HSI presentó valores más altos y más bajos de mayo a julio y de abril a septiembre, respectivamente, para ambos sexos. Finalmente el SSI exhibió diferencias entre sexos con los valores máximos entre marzo y septiembre. Los machos mostraron una relación positiva y significativa entre Kn y WT. En las hembras, este patrón también se observó entre GSI y LH y entre KN vs WT, pero fue negativo entre GSI vs SSI y SSI vs LH. Concluimos que el uso de diferentes índices biológicos en esta especie permite seguir el ciclo de maduración y sus procesos metabólicos asociados, siendo los patrones de variación observados relacionados con los procesos fisiológicos de alta estacionalidad

Ecología poblacional de la tararira, <i>Hoplias argentinensis</i> (Rosso, González-Castro, Bogan, Cardoso, Mabragaña, Delpiani, Díaz de Astarloa, 2018) en la cuenca baja del río Salado

En esta tesis se propone conocer la ecología de la tararira, denominada hasta hace poco como Hoplias malabaricus y recientemente identificada como Hoplias argentinensis. Este cambio implica que los resultados obtenidos son de los primeros para la especie. Por tratarse de un predador tope, reviste interés desde el punto de vista ecológico y pesquero, en los cuerpos de agua pampásicos. Es sabido que el área de estudio representa su límite meridional de distribución natural debido a las bajas temperaturas e inestabilidad hidrológica que además afectarían la dinámica de sus poblaciones. Considerando lo planteado se propusieron las siguientes hipótesis y objetivos generales: Hipótesis - El funcionamiento biológico y poblacional de tararira en las lagunas pampeanas se encuentra regulado fundamentalmente por factores ambientales (ej. fotoperiodo, temperatura y precipitaciones) y por lo tanto es densoindependiente. - Dado que el ambiente determina que la abundancia poblacional de la especie resulte muy variable en el tiempo, las pautas de manejo deben ser dinámicas. Objetivos generales: - Evaluar diferentes tópicos de la biología de la tararira H. argentinensis en las lagunas de la cuenca baja del río salado y su sincronización con la estacionalidad. - Analizar diferentes aspectos de la dinámica poblacional de la tararira y su respuesta a las variables ambientales. - Describir cuestiones relevantes de la ecología de esta especie en las lagunas pampeanas de la cuenca baja del río Salado - Sobre la base de los conocimientos generados, proponer pautas de manejo para el aprovechamiento sostenible de la especie. Con el objetivo de testear las poblaciones de tararira se realizaron muestreos en 5 lagunas de la cuenca baja del río Salado, con características ambientales, fisonómicas y topográficas diferentes. La regularidad de muestreo fue mensual en una de ellas (Yalca) y estacional en las otras (Lacombe, El Burro, Vitel, y Chascomús). Se emplearon artes de pesca activos (ranio y red de arrastre) y pasivos (espineles, trampas, red agallera y red trasmallo) y se estimaron las capturas por unidad de esfuerzo tanto en número como en peso para cada arte de pesca y laguna resultando más eficientes los espineles y las trampas. Los ejemplares capturados se distribuyeron en un amplio rango de tallas, aunque en todas las lagunas se observó un grupo diferente de tallas predominantes. No se registraron ejemplares menores a 220 mm de longitud estandar. Se trataron diferentes aspectos reproductivos durante un ciclo anual, su relación con el índice gonadosomático eviscerado (IGSe), índice hepatosomático eviscerado (IHSe), índice somatosomático (ISS) y el índice de condición relativo eviscerado (Kne), como así también con temperaturas promedio del agua (TA), horas luz (HL) y precipitación promedio porcentual (PPP). Los valores de IGSe en las hembras, presentaron los valores más altos y con mayor dispersión a mediados de primavera, cayendo hacia fines de verano, indicando que éste es el periodo reproductivo, ya que durante los meses fríos los IGSe fueron bajos y poco dispersos. En el caso de los machos el IGSe no mostró cambios significativos durante el ciclo anual. Los valores de ISS en hembras presentaron patrón opuesto al presentado por el IGSe durante el ciclo anual. En cambio, para los machos no se observaron tendencias. El IHSe presentó un patrón de cambio de valores medios similares en ambos sexos, con marcas máximas entre mayo y noviembre para la Yalca y entre mayo y julio en el resto de las lagunas. El análisis de correlación entre los índices biológicos y los parámetros ambientales reveló relaciones significativas positivas entre el IGSe con TA, Horas luz HL y PPP, y negativas entre el IGSe con ISS y el ISS con HL y PPP en el caso de las hembras. Por lo tanto, se comprobó que los parámetros ambientales considerados, cumplen un rol en la regulación de la fisiología general y de ciclo de maduración ovárico en particular. En este sentido, las horas luz representarían al factor que modula de manera general la maduración de los ovarios, y el incremento del nivel hidrométrico producto de las precipitaciones, acompañado del incremento de las temperaturas, activaría la maduración final de las gónadas y el desove de la especie. Este proceso pudo describirse macroscópicamente a partir de los cambios de aspectos de las gónadas (6 estadios para las hembras y 4 para los machos). El análisis de diámetros ovocitarios, permitió detectar dos tandas de tamaños de ovocitos con modas bien definidas, evidenciando la existencia de maduración parcelada y la capacidad de desovar más de una vez entre los meses de noviembre a enero. La fecundidad, presentó una relación significativa de tipo lineal con el peso y con el volumen del ovario. La fecundidad parcial (número de ovocitos maduros o por hembra) promedio, fue de 11432 (±4414,89 ± 6240-19323). La capacidad de desovar en más de una oportunidad en sintonía con disparadores ambientales como indicadores de condiciones favorables, sumado al cuidado parental, conformarían los rasgos principales de la estrategia reproductiva de la especie. Se analizó la edad y el crecimiento de la tararira, a partir de la lectura de marcas en escamas. Se reconocieron dos cohortes con un máximo de 5 edades. La estructura de edades de la población de tarariras en la laguna Yalca se caracterizó por la baja frecuencia de individuos mayores a tres años. Mediante análisis de incremento marginal se evidenció un patrón estacional de crecimiento, donde la máxima tasa se alcanza durante los meses de calor y se minimiza en los meses con temperaturas por debajo de 15 ºC. Los parámetros de la curva de von Bertalanffy para las cohortes identificadas fueron para la cohorte, 1 Lt∞= 623,60, K= 0,43, t0=0,34 y para la cohorte 2, 1 Lt∞= 514,51, K= 0,73, t0=0,35. No se detectaron diferencias significativas en el crecimiento entre sexos. A partir de la estructura de edades de la población se obtuvo la curva de mortalidad de la especie en la laguna Yalca: Nt=1817,857 e -1,466t. El elevado valor de mortalidad es factible que presente grandes oscilaciones en función de las variaciones climáticas e hidrológicas particulares en que se desarrollen las poblaciones ya que influyen profundamente en la dinámica poblacional de la especie. El análisis de la producción de una cohorte en Yalca indicó que la máxima biomasa se obtiene cuando las tarariras llegan a 1,75 años de edad. Respecto a los hábitos alimenticios se registró un elevado número de estómagos vacíos y que 10 especies de peces compusieron la dieta de H. argentinensis, representando 80 % del total de los ítems alimenticios. El número total de peces ocupó más del 92% en la composición de la dieta. Entre los peces, el bagarito, Parapimelodus valenciennis triplicó los valores en número y peso respecto del resto de los ítems alimentarios, quedando como el componente más relevante de la dieta seguido por otros peces de pequeño porte. El análisis integral de los resultados y las observaciones realizadas durante el estudio, permiten determinar que el funcionamiento de las poblaciones de tararira en la región pampeana se encuentra regido de manera global por factores denso-independientes entre los que se destacan las horas luz, la inestabilidad hídrica y la temperatura, que afectan sensiblemente y de manera diferente a la especie, año a año, determinando reclutamientos disímiles en número de ejemplares y cambios amplios en las tasas decrecimiento y mortalidad. Esta dinámica, polarizada en ciclos plurianuales, posee fuertes implicancias socioeconómicas provocando el apogeo y ocaso de pesquerías basadas en la especie. El desafío de los administradores pesqueros es generar normas de manejo asumiendo la alta variabilidad de las poblaciones de la especie para maximizar el rendimiento de la pesca.The aim of this thesis is to study the ecology of the tararira, previously known as Hoplias malabaricus and recently identified as Hoplias argentinensis. This change implies that the results obtained in this thesis are among the first for the species. As a top predator, it is of interest from an ecological and fishing point of view in Pampean water bodies. The study area is within the southern limit of its natural distribution, where the low temperatures and hydrological instability would also affect the dynamics of its populations. Taking these considerations into account, the following hypotheses and general objectives were proposed: Hypotheses Biological and population functioning of the tararira in Pampean shallow lakes is mainly regulated by environmental factors (eg: photoperiod, temperature and precipitations) and therefore, it is density-independent. Given that the environment determines that the population abundance of the species is highly variable over time, management guidelines must be dynamic. General objectives - To evaluate different topics of tararira H. argentinensis biology in the shallow lakes of the lower basin of the Salado River and their synchronization with seasonality. - To analyze different aspects of the population dynamics of the tararira and its response to environmental variables. - To describe relevant issues of the ecology of this species in the Pampean shallow lakes of the lower Salado River basin. - To propose management guidelines for sustainable use of the species, based on this new knowledge. In order to test tararira populations, regular seasonal samplings were carried out in five shallow lakes of the lower Salado River basin, with different environmental, physiognomic and topographic characteristics. Sampling regularity was monthly in one of them (Yalca) and seasonal in the others (Lacombe, El Burro, Vitel, and Chascomús). Active (ranio and trawl) and passive (longlines, traps, gillnet and trammel net) fishing gear were used and the catches per unit of effort were estimated both in number and weight for each fishing gear and waterbody, resulting more efficient longlines and traps. The captured specimens were distributed in a wide range of sizes, although different groups of predominant sizes were observed in all shallow lakes. No specimens smaller than 220 mm in standard length were recorded. Different reproductive aspects were considered during an annual cycle, their relationships with the eviscerated gonadosomatic index (IGSe), eviscerated hepatosomatic index (IHSe), somatosomatic index (ISS) and eviscerated relative condition index (Kne), as well as with mean water temperatures (TA), daylight (HL) and percentage of mean precipitation percentage (PPP). Female IGSe values were highest and with greatest dispersion in the middle of spring, falling at the end of summer, suggesting that spring is the reproductive period; during cold months the IGSe were low and little dispersed. In the case of males, the IGSe did not show significant changes during the annual cycle. ISS values in females presented the opposite pattern to that of the IGSe during the annual cycle. In contrast, no trends were observed for males. The pattern of change of IHSe presented similar mean values in both sexes, with maximum marks between May and November for Yalca and between May and July in the rest of shallow lakes. Correlation analysis between biological indices and environmental parameters revealed significant positive relationships between IGSe with TA, HL and PPP and negative between IGSe with ISS, and ISS with HL and PPP. Therefore, the considered environmental parameters were found to play a role in regulating the general physiology and the ovarian maturation cycle. In this sense, the daylight hours would be the factor that generally modulates the maturation of the ovaries; the increase in the hydrometric level as a result of the rainfall, accompanied by the increase in temperatures, would activate the final maturation of the gonads and the spawning of the species. This process could be described macroscopically from the changes in the gonads (6 stages for females and 4 for males). The analysis of oocyte diameters allowed the detection of two batches of oocyte sizes with well-defined modes, evidencing the existence of parcel maturation and the ability to spawn more than once from November to January. Fertility presented a significant linear relationship with weight and ovary volume. Average partial fertility (number of mature oocytes or per female) was 11432 (± 4414.89 ± 6240-19323). The ability to spawn more than once, in tune with environmental triggers as indicators of favorable conditions, added to parental care, would be the main features of the reproductive strategy of the species The age and growth of the tararira were analyzed from the scale marks. Two cohorts with a maximum of five ages were recognized. The age structure of the Tararira population in the Yalca shallow lake was characterized by low frequency of individuals older than three years. By means of a marginal increase analysis, a seasonal pattern of growth was evidenced, where the maximum rate is reached during hot months and is minimized in months with temperatures below 15 ºC. Von Bertalanffy parameters curve were for cohort 1, Lt∞= 623.60, K= 0.43, t0=0.34, and for cohort 2, 1 Lt∞= 514.51, K= 0.73, t0=0.35. No significant differences in growth were detected between sexes. Mortality curve of the species was obtained from the age structure of the Yalca population: Nt=1817.857 e -1.466t. High mortality value is likely to present large oscillations depending on the particular climatic and hydrological variations in which populations develop, since they profoundly influence the population dynamics of the species. The analysis of the production of a cohort in Yalca indicated that the maximum biomass is obtained when tarariras reach 1.75 years of age. Regarding feeding habits, a high number of stomachs were empty, and 10 species of fish made up the H. argentinensis diet, representing 80% of the total food items. Fish items total number occupied more than 92% in the diet composition. Among fish items, the bagarito, Parapimelodus valenciennis tripled in number and weight the rest of the food items, remaining as most relevant component of the diet followed by other small fish. Comprehensive analysis of the results and observations made during the study, indicate that functioning of populations of tararira in the Pampean region is globally governed by dense-independent factors. Among them, daylight, hydric instability, temperature are the most relevant, affecting differentially the species populations year after year, determining dissimilar recruitments in number of specimens, as well as wide changes in growth and mortality rates. This dynamics, polarized in multiyear cycles, has strong socioeconomic implications, causing the rise and fall of fisheries based on the species. Challenge for fisheries managers is to generate management standards assuming the high variability of the species' populations to maximize fishing performance.Facultad de Ciencias Naturales y Muse

Interannual variation in the diet of non-breeding male Antarctic fur seals, Arctocephalus gazella, at Isla 25 de Mayo/King George Island

The diet of non-breeding male Antarctic fur seals, Arctocephalus gazella, was investigated at Stranger Point, King George Island, through the analysis of scats during three consecutive summer seasons (1996, 1997, 1998). Overall, fish and krill were the most frequent prey occurring, respectively, in an average of 82.9% and 78.8% of samples (n = 131), followed by penguins (22.8%) and cephalopods (17.8%). Myctophids constituted almost 90% of the fish predated, with Electrona antarctica and Gymnoscopelus nicholsi being the most abundant and frequent species consumed. All fish taxa identified were krill feeding species suggesting that seals foraged mainly on a krill and a fish community associated with krill aggregations. However, a seasonal change was observed in the relative proportions of the different prey taxa, with a progressive decrease with time in the occurrence of krill and a concomitant increase of fish, penguins and squid. Possible influence of the strong 1997/98 ENSO event is discussed.Fil: Daneri, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Carlini, A. R.. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; ArgentinaFil: Harrington, Ana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Balboni, Leandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús). Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "Dr. Raúl Alfonsín" (sede Chascomús); ArgentinaFil: Hernandez, C.M.. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas; Argentin

Fish assemblage of a Pampean shallow lake, a story of instability

The aim of this study was to analyze the temporal long term variability of fish assemblage in Chascomús Lake. Data acquisition was based on documented historical research fishing records and experimental fishing program performed from 1999 to 2013. Fish assemblage composition showed a strong temporal variability. Planktivorous species such as Platanichthys platana, Odontesthes bonariensis and Parapimelodus valenciennis accounted for the 70 to 80% of relative abundance becoming alternatively dominant. The iliophagous Cyphocharax voga, the forth dominant species, shared with P. valenciennis the pattern of change in their relative abundance along time. O. bonariensis and P. platana showed high fluctuations in their representation from dominant to almost disappearance during the considered period. Cluster analysis allowed the identification of four different groups of fish assemblage configuration. Two of them grouped the data from historical studies meanwhile the other encompasses the samples taken between 1999-2012, being the discriminant species the mentioned above. Water level, critical temperatures and man basin modifications are discussed as main drivers of species relative abundance shifts. The study highlights the importance to build a long-term assessments to understand how fish assemblage modifications are linked to the typical pampean floods and drought cycles coupled with unfavorable thermal conditions and water management impacts.Fil: Colautti, Dario César. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Instituto de Limnología "dr. Raul A. Ringuelet". Universidad Nacional de la Plata. Facultad de Cs.naturales y Museo. Instituto de Limnología "dr. Raul A. Ringuelet"; ArgentinaFil: Baigún, Claudio Rafael M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "dr. Raul Alfonsin" (sede Chascomus) | Universidad Nacional de San Martin. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas "dr. Raul Alfonsin" (sede Chascomus); ArgentinaFil: Llompart, Facundo Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Maiztegui, Tomás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Instituto de Limnología "dr. Raul A. Ringuelet". Universidad Nacional de la Plata. Facultad de Cs.naturales y Museo. Instituto de Limnología "dr. Raul A. Ringuelet"; ArgentinaFil: Garcia de Souza, Javier Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Instituto de Limnología "dr. Raul A. Ringuelet". Universidad Nacional de la Plata. Facultad de Cs.naturales y Museo. Instituto de Limnología "dr. Raul A. Ringuelet"; ArgentinaFil: Solimano, Patricio José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - la Plata. Instituto de Limnología "dr. Raul A. Ringuelet". Universidad Nacional de la Plata. Facultad de Cs.naturales y Museo. Instituto de Limnología ; ArgentinaFil: Balboni, Leandro. Ministerio de Agricultura, Ganaderia, Pesca y Alimento; ArgentinaFil: Berasain, G.. Provincia de Buenos Aires. Ministerio de Asuntos Agrarios; Argentin