Elson Leal

Bio: Elson Leal is an academic researcher from Valparaiso University. The author has contributed to research in topics: Gonadosomatic Index & Engraulis. The author has an hindex of 7, co-authored 19 publications receiving 125 citations. Previous affiliations of Elson Leal include University of Concepción.

Variability in oocyte size and batch fecundity in anchoveta (Engraulis ringens, Jenyns 1842) from two spawning areas off the Chilean coast

Abstract: Utilising histological preparations of ovaries from Engraulis ringens females collected in two contrasting spawning habitats along the Chilean coast, we assess the variability in oocyte size and batch fecundity during the peak spawning seasons in three years. The effects of female size (length and weight), batch fecundity and mean sea surface temperature on oocyte size were also examined. Results showed larger oocytes and lower batch fecundity in females from the southern area. Oocyte volume differences persisted inter-annually and were not explained by differences in female sizes. Since ovary weight was similar between areas, the cost of producing larger oocytes in the south population seems to be a fecundity reduction. The latitudinal variations in oocyte number and size seem to be determined by the predominant environmental conditions in each habitat. Hence, female E. ringens seem to adapt their reproductive tactics by producing eggs sizes and quantities that favour survival of their offspring under the environmental conditions in which they are to develop.

Actividad reproductiva y longitud de madurez de sardina austral Sprattus fuegensis en el mar interior de Chiloé, Chile

Abstract: Resumen es: La sardina austral, Sprattus fuegensis, ha sido recientemente identificada en las capturas de peces pelagicos en el mar interior de Chiloe, sur de Chile....

Parámetros de historia de vida de la anchoveta Engraulis ringens Jenyns, 1842, en la zona centro norte de Chile Life history parameters of anchoveta Engraulis ringens Jenyns, 1842, in central north Chile

Abstract: In the central north of Chile (25°00'S-32°10'S) an anchoveta fishery (Engraulis ringens) operates on a small scale. In spite of being controlled by total allowed catches, the life history parameters used to estimate its abundance remain unknown. We estimated the basic biological parameters as growth, maturity and natural mortality for anchovy inhabiting the Chilean central north. The von Bertalanffy parameters were an annual growth rate (k) of 0.91 year -1 , asymptotic length (L ∞ ) at 18.72 cm, and age at zero length (t o ) of -0.01 year. The maximum value of the gonadosomatic index in September and the high frequency of mature stages between July and December, support that the main spawning period of anchoveta in the area would occur from August to October of each year. The mean maturity length (L m50% ) was estimated at 12.5 cm and the natural mortality (M) was 1.30 year -1 . The biological

Parámetros de historia de vida de la anchoveta Engraulis ringens Jenyns, 1842, en la zona centro norte de Chile

Abstract: In the central north of Chile (25°00?S-32°10?S) an anchoveta fishery (Engraulis ringens) operates on a small scale. In spite of being controlled by total all...

Distribucion, batimetria y alimentacion de epigonus crassicaudus de buen, 1959 (perciformes: epigonidae) en la costa de chile

Abstract: Se estudio la distribucion batimetrica y latitudinal de besugo (Epigonus crassicaudus) en la costa de Chile analizando los registros de la pesqueria y a traves de informacion complementaria recopilada desde los lances de pesca realizados en la evaluacion directa de merluza comun. Adicionalmente, se reportan antecedentes sobre los habitos alimenticios de besugo a traves de analisis del contenido estomacal de ejemplares recolectados en la zona central de Chile. Segun la informacion de la actividad comercial, el recurso concentraria su distribucion entre Valparaiso (33°04'S) y Puerto Montt (41 °46'S). Sin embargo, el crucero de evaluacion, registra capturas positivas de besugo desde su limite norte de operacion (29°00'S). En relacion a la batimetria, tanto la frecuencia de lances positivos como la captura, mostraron un patron coincidente en ambas fuentes de informacion, evidenciando una concentracion del recurso en el rango de profundidad de 300 a 400 m. Respecto de la alimentacion, las presas mas consumidas por E. crassicaudus fueron organismos planctonicos representados por eufausidos y estomatopodos. Apareciendo ocasionalmente algunos componentes del bentos en su dieta. Los resultados del presente estudio sugieren que E. crassicaudus presentaria habitos migratorios desde el pelagos al bentos, determinado por la oferta ambiental de alimento, concentrando su distribucion sobre la plataforma y talud continental. Ademas se confirmo una distribucion latitudinal mas amplia del recurso de la reconocida a traves de informacion exclusiva de la pesqueria.

Ecology of fishes

Abstract: In this course, taught at the Pymatuning Laboratory of Ecology in northwest Pennsylvania, students will explore the population, community, and ecosystem ecology of fishes. We will conduct field investigations in streams, lakes, and marshes. Students will attend background lectures, conduct experiments and field surveys, participate in data collection and analysis, and gain experience in the interpretation and presentation of results. We will learn how to integrate math, physics, chemistry, and biology in our study of fishes. In addition, we seek to expose students to current research in fish ecology. Students will participate in the design of experiments, data analysis, and hone their presentation skills. Most importantly, they will leave the course with a greater knowledge of and appreciation for Pennsylvania’s rich diversity of fishes.

Simple methods for estimation of parametersfor assessing exploited fish stocks

Abstract: New methods for estimation of growth and mortality parameters, together with their error estimations, are given, discussing in detail their advantages over the existing ones. A new model called Relative Response model has been designed for estimation of such stocks that are common in tropics where the application of other models are not effective. Demonstrative worksheets are provided to illustrate easy working of the methods. Various proformae for collection of data are appended.

Extending the linear model with R : generalized linear, mixedeffects and nonparametric regression models

Abstract: INTRODUCTION BINOMIAL DATA Challenger Disaster Example Binomial Regression Model Inference Tolerance Distribution Interpreting Odds Prospective and Retrospective Sampling Choice of Link Function Estimation Problems Goodness of Fit Prediction and Effective Doses Overdispersion Matched Case-Control Studies COUNT REGRESSION Poisson Regression Rate Models Negative Binomial CONTINGENCY TABLES Two-by-Two Tables Larger Two-Way Tables Matched Pairs Three-Way Contingency Tables Ordinal Variables MULTINOMIAL DATA Multinomial Logit Model Hierarchical or Nested Responses Ordinal Multinomial Responses GENERALIZED LINEAR MODELS GLM Definition Fitting a GLM Hypothesis Tests GLM Diagnostics OTHER GLMS Gamma GLM Inverse Gaussian GLM Joint Modeling of the Mean and Dispersion Quasi-Likelihood RANDOM EFFECTS Estimation Inference Predicting Random Effects Blocks as Random Effects Split Plots Nested Effects Crossed Effects Multilevel Models REPEATED MEASURES AND LONGITUDINAL DATA Longitudinal Data Repeated Measures Multiple Response Multilevel Models MIXED EFFECT MODELS FOR NONNORMAL RESPONSES Generalized Linear Mixed Models Generalized Estimating Equations NONPARAMETRIC REGRESSION Kernel Estimators Splines Local Polynomials Wavelets Other Methods Comparison of Methods Multivariate Predictors ADDITIVE MODELS Additive Models Using the gam Package Additive Models Using mgcv Generalized Additive Models Alternating Conditional Expectations Additivity and Variance Stabilization Generalized Additive Mixed Models Multivariate Adaptive Regression Splines TREES Regression Trees Tree Pruning Classification Trees NEURAL NETWORKS Statistical Models as NNs Feed-Forward Neural Network with One Hidden Layer NN Application Conclusion APPENDICES Likelihood Theory R Information Bibliography Index

Larval fish distribution, growth and feeding in Patagonian fjords: potential effects of freshwater discharge

Abstract: In fjord systems, freshwater inputs occur by ice melting and river discharge, affecting seawater salinity along fjord and adjacent waters, and potentially the ecology of early life stages of marine fish occurring in the area. During austral spring 2008, a bio-oceanographic cruise was carried out in southern Chile between 47°00′ and 50°09′S, an area influenced by Baker River discharge and ice melting of Northern and Southern Ice Fields, the largest glaciers from Patagonia. Surface salinity and temperature ranged from 1.22 to 32.80, and from 8.11 to 10.68°C, respectively. Larval lightfish Maurolicus parvipinnis (Sternoptychidae) and Falkland sprat Sprattus fuegensis (Clupeidae) were the dominant species, with abundances of 2.2–39.9 larvae 10 m−2 and 3.4–77.1 larvae 10 m−2, respectively. Postflexion stages of both species were collected mainly in surface density fronts. Otolith-based growth analyses estimated linear growth rates of 0.136 mm day−1 for M. parvipinnis of 4.1–15.1 mm, and 0.448 mm day−1 for S. fuegensis of 5.4–20.5 mm. Recent Otolith Growth Index (ROGI), based on the residual analysis of the relationship between increment width of outermost five microincrements and otolith radius, indicates that larval M. parvipinnis collected in low salinity waters showed a reduction of its recent growth rate compared those collected in saltier waters. Also, ROGI was positively correlated with salinity of the water column for larval M. parvipinnis. Gut content analysis showed that large larvae collected near sources of freshwater had lower number of prey in its guts and preyed on different items than fish larvae collected in saltier waters. Therefore, freshwater inputs from rivers and glaciers from Patagonia affected horizontal distribution, recent growth and feeding of larval fish in fjords and channels of southern Chile.