The austral sardine (Sprattus fuegensis) is the target fish resource of a small-scale fishery operating in the Patagonian waters of Chile (41 • 30'S-46 • 00'S). Purse seine boats composed the fleet and landings have fluctuated between 14,344 and 48,589 tons during the period between 2006 and 2014. The stock assessment of the austral sardine utilizes a Statistical Catch-atLength model and this method requires independent estimates of abundance. In order to evaluate the abundance of the austral sardine in the inner sea of the Chilean Patagonia, an acoustic assessment was carried out in Autumn 2013. The study area covered the coastal zone of two administrative regions of Chile, the Los Lagos region in May 2013 and the Aysén region in June 2013. An EK-60 echo sounder permitted to obtain the acoustic data with transducer of 38 and 120 kHz from which echograms were examined to obtain NASC data. A total of 25 fishing set allowed to estimating the species composition and the length structure of the pelagic fish. In addition, fish confined in a jail allowed to estimating the target strength (TS) of the austral sardine. The fishing data and the NASC permitted to evaluate the acoustic biomass of the austral sardine, as well as the biomass of the anchovy (Engraulis ringens) and the common sardine (Strangomera bentincki). The biomass was estimated according to a stratified sampling design, the Gaussian Likelihood Geostatistics technique, and the fit to probability density models. The stratified design included six strata in the Los Lagos region and five strata in the Aysén region, as well as four depth strata (0-50, 50-100, 100-150 and 150-200 m). The stratified estimates of the austral sardine biomass were 118,173 tons (CV=11.6%) in the Los Lagos region and 101,630 tons (CV=9%) in the Aysén region. The estimates of biomass based on Gaussian geostatistics were 122,469 tons (CV=7.6%) in the Los Lagos region and 92,890 (70%) tons in the Aysén region. The best fitting of probability density functions to the acoustic density was log-normal, and allowed to estimate 100,145 tons of austral sardine in the Los Lagos region and 81,965 tons in the Aysén region. The biomass of anchovy was 50,079 tons in the Los Lagos region and 18,668 tons in the Aysén region. The biomass of common sardine was minimal with 5,327 tons in the Los Lagos region only. The estimate of the TS for the austral sardine was -67.59 dB and represented fish between 9 and 17 cm. The study area is spatially heterogeneous, and hydrographical features could determine behaviors of the austral sardine that have not yet described. Therefore, the estimates of biomass here obtained must be regarded as a relative abundance. The basis here obtained will be of importance for monitoring yearly changes in the abundance of the sardine austral.

SUMMARY: Size and shape of fish otoliths are species-specific, but some species also display intraspecific variations. The common sardine, Strangomera bentincki, is a small pelagic fish inhabiting a seasonal upwelling ecosystem off centralsouthern Chile, having two discrete spawning sites along its latitudinal distribution. Otoliths of specimens were collected from commercial catches in Talcahuano and Corral, representing the central and south spawning zones. On the basis of otolith images, size-based shape descriptors were used to detect ontogenetic variation, and morphometric variables (length, breadth, area, perimeter and weight) were used to detect geographical differences in size and shape of otoliths. Outline analysis was studied on the basis of elliptic Fourier descriptors through multivariate statistical procedures. Size-based shape descriptors showed that otolith shape starts to be stable for fish larger than 12 cm total length, which keep an elliptical form. Morphometric variables for fish larger than 12 cm revealed intraspecific variation between central and south zones, which were associated with otolith weight and breadth. Outline analysis did not reveal significant spatial differences, but extreme intraspecific variation was due to the antirostrum, excisure, and posterior part of otoliths. Intraspecific variation in otolith size could be linked to differences in each spawning habitat and related to geographical origin, whose differences are not clearly identified. It is concluded that intraspecific variability in morphometric variables of sardine otoliths revealed geographic differences in size that are not attributable to allometric effects, and that otolith shape was similar between specimens from different geographic origin.Keywords: otolith, outline, shape descriptors, intraspecific, Fourier, sardine, pelagic. RESUMEN: Sobre la variación intra-específica en la morfometría y forma del otolito sagita de sardina común (Strangomera bentincki) en la zona centro-sur de Chile. -El tamaño y la forma de los otolitos de los peces son específicos, pero algunas especies también muestran variaciones intraespecíficas. La sardina común, Strangomera bentincki, es un pez pelágico pequeño que habita en un ecosistema de afloramiento estacional en la zona centro-sur de Chile, y tiene dos áreas discretas de desove a lo largo de su distribución latitudinal. Se obtuvieron otolitos a partir de las capturas comerciales en Talcahuano y Corral, que representan las zonas de desove del centro y sur. Sobre la base de imágenes de otolitos, los descriptores de la forma basados en el tamaño fueron usados para detectar variación ontogenética, y las variables morfométricas (longitud, ancho, área, perímetro, y peso) se utilizaron para detectar diferencias geográficas en el tamaño y la forma de los otolitos. El análisis de contorno fue estudiado sobre la base de los descriptores elípticos de Fourier a través de procedimientos estadísticos multivariados. Los descriptores de forma mostraron que la forma del otolito comienza a ser es...

No abstract

No abstract