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Abstract. Macrobrachium acanthurus inhabits estuaries and rivers in the western Atlantic. It is not clear whether females migrate towards estuaries to hatch larvae, as reported for other congeneric shrimps. We tested whether females of M. acanthurus exhibit reproductive migrations. The population dynamics of this shrimp was studied in the Ribeira de Iguape River, Brazil. Four sites that differ in position with respect to the coast were sampled monthly during 2007. In M. acanthurus, reproduction was seasonal and reproductive intensity did not vary among study sites. Females brooding early and late embryos were found at all study sites during the reproductive season. No disappearance of reproductive females was observed at the study site located furthest away (,150 km) from the coast. Thus, reproductive females of M. acanthurus do not exhibit reproductive migrations towards estuaries to hatch larvae. Maturity in females was reached at smaller body sizes during the austral summer and spring compared with winter and autumn. Growth rate and body size was sex-specific; males grew slower but attained larger average and final body sizes than females. This information needs to be considered in assessing stocks and establishing sustainable management plans for M. acanthurus in Brazil.

RESUMEN.En Chile los cultivos del ostión del norte Argopecten purpuratus han sido desarrollados intensivamente a partir de la captación de semillas en ambiente natural y desde principios de 1980 con semillas obtenidas en hatchery. Para aportar información sobre el desempeño de semillas de ostión del norte en este estudio se comparó, mediante ANCOVA, el crecimiento en longitud entre cohortes producidas a partir de semillas de ambiente natural y de hatchery en Tongoy, Chile. Se evaluó la consistencia de esta comparación en distintos años y estaciones, comparándose parejas de cohortes producidas simultáneamente en los años 2003 (primavera) Comparison of growth among cohorts obtained Argopecten purpuratus larval recruitment in natural and hatcheryABSTRACT. In Chile crops of the northern scallop Argopecten purpuratus have been developed intensively from seeds obtained in natural environment, and since 1980 from hatchery's seed, when this technique could be controlled and developed. In order to provide information on the performance of seeds of northern scallops in this study growth in length between cohorts produced from seeds obtained in natural environment (CN) and hatchery (CH) in Tongoy (Chile) was compared using ANCOVA. We assessed the consistency of this comparison in different years and seasons. 2006 . These differences indicate that the cohorts of natural environment seeds grew faster than those of hatchery. Inter annual comparison showed significant statistical differences. These results are discussed in terms of the cultivation temperature and the heterozygosity for the growing population.

Most fisheries models are based on dynamic pool assumptions. For sedentary and sessile species, these assumptions are inadequate, because they are spatially distributed in patches that vary in size, density and age structure. A simple bioeconomic model, negative binomial (NEGBIN), is proposed; this model relaxes the dynamic pool assumption without entering into the complexities of a geographically structured model. NEGBIN assumes a probability density function (the negative binomial), to describe heterogeneity in the density distribution over the population range. The model incorporates decision theory and different levels of risk aversion in resource management. The uncertainty associated with alternative fishing strategies, given imperfect knowledge about virgin stock biomass, is also included in the analysis. The model is applied to the Mesodesma donacium (surf clam) fishery in the central northern zone of Chile (South America). Alternative management strategies are evaluated with different levels of risk aversion. In the fisheries literature to date, this approach to evaluating the uncertainty associated with spatial allocation decisions has been rare. It is suggested that this kind of analysis, whether accompanied by quantitative probabilities of alternative states of nature or not, is an alternative way of dealing with risk and uncertainty in spatial allocation decisions.

Una modificación de la ecuación de crecimiento de von Bertalanffy para incluir el efecto de la temperatura en el crecimiento del abalón rojo Haliotis rufescens para su uso en acuicultura A modification to the von Bertalanffy's growth equation to include the effect of the temperature on the growth of Haliotis rufescens for aquacultural use

RESUMEN. Una situación recurrente en el mercado de muchas especies bajo cultivo acuícola es la tendencia en la disminución del precio internacional en oposición al aumento en los costos de los insumos, lo que obliga a la industria a ser innovadora al momento de rentabilizar la inversión. Una opción poco explorada es el aumento del valor de la producción a través de una cuidadosa selección de tamaños y tiempos de cosechas. Las cosechas parciales permiten que calibres subóptimos puedan tener el tiempo necesario de crecimiento hasta alcanzar mejores atributos, al mismo tiempo que la fracción de mejor crecimiento es cosechada y puesta disponible en el mercado. Difiere significativamente de la estrategia alternativa de cosechas totales, donde la totalidad de la producción es cosechada al mismo tiempo. Así, el óptimo económico será resultado del tiempo de primera cosecha (DPC), de la longitud de cosecha (LC), número de cosechas (NC) e intervalo de tiempo (∆t) entre cosechas sucesivas. Mediante un modelo de simulación, alimentado con valores reales de una empresa de cultivo de ostión del norte (Argopecten purpuratus) se analizó el resultado económico de la estrategia de cosechas múltiples. Los resultados indican que las combinaciones alternativas de DPC, LC, ∆t y NC generan distintos niveles de rendimientos económicos, aspecto que debiera ser considerado por los productores. En los escenarios simulados de cosechas, una decisión incorrecta en este sentido podría generar una diferencia del orden de US$ 510.000. Palabras clave: Argopecten purpuratus, ostión del norte, cosechas múltiples, rendimiento económico, acuicultura. Economic effects of the multiple harvests strategy in the culture of northern scallopArgopecten purpuratus: an opportunity to improve competitiveness ABSTRACT. A recurrent situation in the market of many species under culture is the trend in the decline in the international price in opposition to the increase in the costs of inputs, forcing the industry to be innovative at the time of return on the investment. A little explored option is the increase in the value of production through a careful selection of sizes and timing of harvest. Partial harvests allow sub optimal calibers to have the necessary time to grow until reaching best attributes, at the same time that the fraction of better growth is harvested and put available on the market. It differs significantly from the alternative strategy of total harvest, where the entire production is harvested at the same time. Thus, the economic optimum is the result of first harvest time (DPC), the length at harvest (LC), number of harvests (NC) and time interval between successive harvests (∆t). The economic result of the strategy of multiple crops using a simulation model, powered by actual values of a culture firm of northern scallop (Argopecten purpuratus) was analyzed. Results indicate that the alternative combinations of DPC, LC, ∆t and CN generate different levels of economic returns, aspect that should be considered by the producers. In simulated crop...

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