Verificación de la edad y crecimiento de besugo Epigonus crassicaudus (de Buen, 1959) admitiendo error en la determinación de la edad Age verification and growth of the Chilean cardinalfish Epigonus crassicaudus (de Buen, 1959

No abstract

Age, growth and natural mortality in Chilean hoki, Macruronus magellanicus, are estimated using samples of saggital otoliths from specimens caught from 1991 to 1996 between 46º and 56º S. The age determination was done by reading of annual growth ring in otoliths. The lengths at different ages were obtained by back calculation and also to actual ages. The validation of the annual formation of otoliths increment was established by the regularity of the deposition of the hyaline and opaque rings in the edge of the otoliths and the marginal increment analysis. This allowed the determination of the formation of an annual hyaline (annulus) in July and an opaque ring in January. The growth was determined following the von Bertalanffy model and the growth parameters were assessed separately for each sex, using a nonlinear adjustment model. The growth parameters between sexes were compared with the T 2 test of Hotelling and the minimum square ratio of Chen et al. (1992). The results indicate that growth was significantly greater in females than in males. The results obtained here are consistent with previous records for the same species from other regions of the Eastern Pacific, the Western Atlantic, as well as with the congeneric species M. novaezelandiae, from the coasts of Australia and New Zealand. The instantaneous coefficient of natural mortality (M) was estimated with empirical methods and catch-curve analysis.

Abstract.-A study of age, growth and natural mortality of southern blue whiting, Micromesistius australis, was conducted using samples collected at latitudes from 46ºS to 56ºS, between 1991 and 1995. The age determination was made by reading annual growth increments in sagitta otoliths. The lengths at different ages were estimated using corrected backcalculated lengths. The annual formation of one hyaline and opaque ring was determined by the analysis of the otolith margin. In the study of growth in length, the traditional models of von Bertalanffy (VBT), the generalized (VBG), and the Gompertz (GOMP) were used. The parameter estimations were performed using a nonlinear function, and maximum likelihood, for each sex and for both sexes pooled together. Based on the coefficient of determination, the sum of the squared residuals and the Akaike criterion (AIC), the most representative model of growth was the traditional von Bertalanffy. The comparison of growth parameters between the sexes by the Hotelling T 2 test and the reason of least squares, indicate a significantly higher growth for females. The growth parameters estimated for Micromesistius australis in the southeastern Pacific are different from those recorded for the southwest Atlantic and New Zealand, as they belong to different stocks. The instantaneous coefficient of natural mortality (M) was estimated by empirical methods that consider the close relationship between M and the growth parameters. The estimated values are lower than those reported in previous studies. Key words: Merlucciidae, otolith, Chilean coastResumen.-Se realizó un estudio de edad, crecimiento y mortalidad natural en merluza de tres aletas, Micromesistius australis, con muestras de especímenes capturados en el periodo 1991-1995 entre las latitudes 46ºS y 56ºS. La determinación de edad se efectuó mediante lectura de anillos crecimiento anual en los otolitos sagitta y las longitudes a distintas edades se estimaron mediante longitudes retrocalculadas corregidas. Se determinó la formación de un anillo hialino y uno opaco anual mediante el análisis estacional del borde. En el estudio del crecimiento en longitud se utilizaron los modelos de von Bertalanffy tradicional (VBT), el generalizado (VBG), y el de Gompertz (GOMP). La estimación de parámetros se realizó por sexo y total, utilizando un modelo no lineal. Sobre la base del coeficiente de determinación, suma de residuales al cuadrado y el criterio Akaike (AIC), el modelo más representativo del crecimiento fue el de von Bertalanffy tradicional. La comparación de parámetros de crecimiento entre sexos mediante el test T 2 de Hotelling y la razón de mínimos cuadrados, indican para las hembras un crecimiento significativamente mayor que los machos. Los parámetros de crecimiento estimados para Micromesistius australis en el Pacífico suroriental son diferentes a los registrados para el Atlántico suroccidental y Nueva Zelanda, debido a que constituyen stocks distintos. El coeficiente instantáneo de mortalidad natural (M) fue estimado por método...

In Chile, salt (NaCl) use per salmon fish farm ranges between 20-30 t yr-1 and is used to prevent and control fungal infections. An increase in salinity in freshwater can have adverse effects on freshwater biodiversity and ecosystem functions and services. We studied the effects of fish-farm effluents on benthic macroinvertebrate communities in a northern Patagonian stream (Chile). Benthic samples were collected at 3 sites near a land-based salmon aquaculture facility (one located 100 m upstream from the fish-farm outlet for effluent, 2 sites located 200 and 400 m downstream from the effluent source). We found changes in benthic macroinvertebrate communities downstream from the effluent, with higher abundances of tolerant taxa and lower abundances of sensitive taxa, which was related to nutrient and salt concentration in the water. We also studied the effects of salinity on macroinvertebrate drift in a mesocosm experiment conducted in recirculating channels, measuring the drift of 2 salt-sensitive macroinvertebrates (Andesiops peruvianus and Smicridea annulicornis), collected from an unpolluted northern Patagonian stream, after exposure to a range of salinity concentration pulses similar to those from fish farms. Our results demonstrate that (1) fish-farm effluent can alter stream macroinvertebrate community composition and dynamics, and (2) such effects are at least partly driven by high salt concentrations in effluent waters.