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Se realizó un estudio para identificar y cuantificar las especies presentes en la pesquería artesanal de enmalle dirigida a merluza común (Merluccius gayi gayi) entre enero y septiembre de 2010. Se registró la captura en 98 lances de pesca realizados por 45 embarcaciones de 14 caletas distribuidas entre las regiones de Valparaíso y del Biobío. La especie objetivo fue la más relevante en las capturas en todas las regiones. La presencia de 24 taxones fueron registradas como fauna acompañante, no obstante sólo 4 especies presentaron una frecuencia relativa de ocurrencia mayor al 50% de los lances realizados en alguna de las regiones. Estas especies fueron jaiba limón (Cancer porteri), jaiba paco (Platymera gaudichaudii), langostino colorado (Pleuroncodes monodon) y lenguado (Hippoglossina macrops), las cuales explicaron la mayor proporción (>70%) de la fauna acompañante total en número. Mediante métodos de clasificación y ordenación basados en la composición de especies, se determinó la existencia de 4 grupos asociados a las regiones geográficas y al rango de profundidad donde se realizaron los lances de pesca, mientras que los tamaños de malla usados en las redes tendrían una influencia menor en la explicación de los grupos identificados.

Summary To determine the selectivity of gillnets in the Chilean artisanal fishery for the Chilean hake Merluccius gayi gayi, an experimental net was used with three mesh sizes (5.2, 6.8 and 7.6 cm). A total of 2279 specimens of Chilean hake were caught (24–56 cm total length, TL), mainly via gilling and snagging. The catch proportion below the size of sexual maturity SSM50% (37 cm TL) for each mesh size tested was estimated. Models were fitted separately according to the sex to compensate for differences in size compositions, with the males fitted to a binormal model and females fitted to the normal location model. Analysing both sexes combined, the model with the lowest deviance was lognormal, with estimated modal lengths of 30.9, 40.2 and 43.9 cm TL for meshes of 5.2, 6.8 and 7.6 cm, respectively. The estimated selectivity factor (SF) indicates that the modal size matches the SSM50% with a mesh size of 6.2 cm, while the length of retention of 50% (l50) coincides with the SSM50% with a mesh size of 7.6 cm.

Para caracterizar agregaciones de langostino colorado (Pleuroncodes monodon) y langostino amarillo (Cervimunida johni), se utilizó un sistema de filmación remolcado sobre fondos marinos situados en la región de Coquimbo, Chile. Las filmaciones fueron realizadas en 2009 y 2010, a profundidades variables entre 102 y 215 m, a partir de las cuales se estimaron densidades medias por filmación entre 3 y 63 ind m-2 para P. monodon y entre 0,2 y 2,8 ind m-2 para C. johni. Igualmente, se registró la presencia de parejas de C. johni en julio de 2009 (~200 m de profundidad), presumiblemente en proceso de apareamiento. Los resultados indicaron que el sistema de filmación remolcado es un medio efectivo de registro de ejemplares de ambas especies, permitiendo tanto la caracterización cuantitativa del stock sobre el fondo, como la observación de su comportamiento y hábitat. El sistema tiene perspectivas de uso en la evaluación directa de abundancia y en la caracterización del hábitat tanto en términos bióticos como abióticos.

Summary The size selectivity of alternative codends for nylon shrimp and yellow squat lobster was studied off the Chilean coast using the covered codend technique. Various mesh sizes (47 and 63 mm mesh opening) and shapes (diamond and square) in the codends were used. For both species, substituting the DM47 codend with the DM63 codend significantly increased 50% retention length (l50). The change of diamond (DM47) to square mesh (SM47) had a positive effect in size selectivity for nylon shrimp. For yellow squat lobster, no significant effect was observed when changing the diamond (DM63) to square mesh (SM63). Selectivity data were modeled by considering explanatory variables such as ‘codend catch weight’ and ‘vessel’. Increases in the catch significantly reduced the l50 for both species whereas the vessel factor was not significant. Finally, using the length at first maturity as a reference value, the authors concluded that the DM47 codend failed to protect the immature portion of either stock, thus the DM63 codend is recommended.

In order to improve the inter-specific selectivity of a new bottom trawl design for demersal crustaceans, an experimental attempt was carried out to compare the shrinkage effect in length of net structure accessories, particularly shorter bridles and sweeps, based on previous studies on escape behavior of gadiform fishes. For this purposes, an experimental fishing for nylon shrimp (Heterocarpus reedi) was carried out on board of two trawler vessels. The results showed no significant differences in catch per unit of fishing effort (CPUE) for the target species between gears and significant reductions (p < 0.05) for the most important by-catch species (Merluccius gayi) with the modified gear. In fact, the average CPUE for M. gayi decreased 5.6 kg h-1 (19.2%) and 35.7 kg h-1 (47.5%) for each vessel.

Se realizó la caracterización mensual de las agregaciones de merluza de cola usando registros acústicos obtenidos por equipos SIMRAD EK60 y ES60 a bordo de tres embarcaciones multipropósito que operaron en la Unidad de Pesquería Centro-Sur durante el año 2003, para lo cual se emplearon descriptores morfológicos y batimétricos. En cuanto a su morfología, las agregaciones mostraron una amplia variabilidad, explicada por su nivel de cohesión y tendencia a formar agregaciones de gran extensión horizontal, mientras que batimétricamente se determinó que el 90% de éstas se ubicaron preferentemente entre 300 y 450 m. Existe evidencia de asociación entre diversos descriptores y estos a su vez con otros factores como talla media, temperatura del agua, latitud y mes, lo que permite describir apropiadamente la forma de las agregaciones y su ubicación en la columna de agua. Algunas relaciones relevantes corresponden a: profundidad de las agregaciones respecto a la profundidad del fondo (r = 0,55), altitud de las agregaciones respecto a la profundidad del fondo (r = 0,72), altitud de las agregaciones respecto al índice de profundidad relativa (r = -0,98) y profundidad de las agregaciones respecto a la talla media (r = 0,66).

La evaluación de paneles de escape de malla cuadrada en redes de arrastre de fondo usadas en la pesquería de merluza común se realizó empleando dos metodologías complementarias: lances con sobrecopo y lances alternados. Los lances con sobrecopo permitieron cuantificar la fracción de la captura que escapa a través de los paneles de escape, y determinar la estructura de tallas y pesos medios, estimando longitudes de retención y rangos de selección. Se determinó la fracción bajo 30 y 36 cm de longitud total presentes en el copo y en el sobrecopo, ambos como indicadores del efecto selectivo que éstas producen. Los lances alternados permitieron verificar la disminución de los rendimientos de captura, tanto en número como en peso, aumentando los pesos medios de los ejemplares retenidos y disminuyendo la proporción de ejemplares bajo tallas de referencia, lo que indica la existencia de un efecto de escape en la fracción juvenil del stock.

In 2010, two experiments were carried out in order to study ghost fishing generated by lost or abandoned gillnets. The first experiment was aimed to identify and quantify the number of captured specimens in intentionally abandoned gillnet between 45 and 86 m depth, which were periodically checked up to 156 days after being abandoned. In this experiment, 912 specimens of 12 taxa were caught, mostly invertebrates such as Cancer porteri (81.6%) and Platymera gaudichaudii (9%). After the abandonment, the fish caught were only registered until day 63, while benthic species were captured during all the experiment. The second experiment consisted of checking and registering periodically the loss of height of an abandoned gillnet at 34 m depth in order to determine the reduction of the fishing capacity of the net. After 19 days of abandonment, the functional area of the net was reduced to 40% of the original area, reaching nearly zero after 155 days of abandonment. In order to estimate the potential effect of lost or abandoned gillnets in Chilean hake fisheries (Merluccius gayi gayi), an additional information-collecting process must be carried out, mainly in terms of frequency of gillnets losses.

The behaviour of Chilean hake (Merluccius gayi gayi) in a bottom trawl was observed with an underwater camera positioned in the trawl mouth and in the front of the codend extension. Significant differences were observed in the fish behaviour in the two sections, demonstrating that this species is more active in the mouth of the net. The fish activity was lower in the trawl extension, where the fish were merely carried by the flow into the net.

The behaviour of fish by-catch was recorded and characterized by in situ observations in the mouth of a crustacean trawl using an underwater camera system with artificial light, at depths between 106 and 461 m, along the central coast of Chile. The groups or species studied were rattails (family Macrouridae), Chilean hake Merluccius gayi gayi, sharks (orders Carcharhiniformes and Squaliformes), skates (family Rajidae), flatfishes (genus Hippoglossina) and small benthopelagic and demersal fishes (orders Osmeriformes, Stomiiformes, Gadiformes, Ophidiiformes and Perciformes). The fish behaviour was categorized in terms of (1) position in the water column, (2) initial orientation with respect to the trawl, (3) locomotion and (4) swimming speed with respect to the trawl. Rattails, sharks, skates and flatfishes were passive in response to the trawl and showed similar behavioural patterns, with most fishes observed sitting or touching the bottom with no swimming or other activity. Merluccius gayi gayi was the most active species, displaying a wide combination of behavioural responses when the trawl approached. This species showed several behavioural patterns, mainly characterized by swimming forward at variable speed. A fraction of small bentho-pelagic and demersal fishes also showed an active behaviour but always at lower speed than the trawl. The species-specific differences in behaviour in the mouth of the trawl suggest that improvements at the level of the footrope can be made to reduce by-catch, especially of passive species.

Queirolo, D., Hurtado, C. F., Gaete, E., Soriguer, M. C., Erzini, K., and Gutiérrez-Estrada, J. C. 2012. Effects of environmental conditions and fishing operations on the performance of a bottom trawl. – ICES Journal of Marine Science, 69: 293–302. Trawl performance was studied based on net spread and variability in the contact of the footrope with the seabed and their relationship with vessel operations, catch weight, and environmental conditions. Artificial neural networks (ANNs) and generalized additive models (GAMs) were used to model the response of each variable. For the variables net spread and variability in footrope contact (VFC), the ANN models were more accurate than the GAMs, with greater generalization capacity in the validation phase. In the best ANN model for net spread, all variables were significant. The relationship between tow direction and wind direction (tactic) was most important in the sensitivity analysis. Net spread increased with increasing towing speed and windspeed, and decreased with increasing wave height. In the ANN model for VFC, there were differences among vessels, and both scope ratio and catch size were not significant. VFC increased with increasing depth and decreased with increasing towing speed and windspeed. The results demonstrate that both operational variables and environmental conditions affect trawl performance, and suggest that survey protocols designed based on this information might help to improve the precision of biomass estimates.

The species composition and bycatches of a new trawl for crustaceans (Heterocarpus reedi, Cervimunida johni and Pleuroncodes monodon) was studied in central Chile between 2007 and 2009. The spatial and temporal variations of the catch composition were analyzed using univariate and multivariate comparison techniques. In 289 trawl hauls, 72 taxa were recorded, with target species accounting for most of the catch, while the bycatch consisted mainly of Merluccius gayi, Hippoglossina macrops, Coelorinchus aconcagua, Epigonus crassicaudus and Platymera gaudichaudii. 14 species of elasmobranchs were identified, and at least one of these species was present in 50% of the hauls made. The classification and ordination methods showed the existence of three groups, each one associated with a target species, with no significant spatial and temporal effects. The information obtained in this study represents the basis for setting targets in order to reduce the bycatch captured by this trawl. The focused strategy on the most recurring and sensitive species for these fisheries is also discussed. (C) 2011 Elsevier B.V. All rights reserved.

Se llevaron a cabo experiencias tendientes a determinar el momento en que las redes de arrastre utilizadas en la pesquería de crustáceos demersales tienen contacto efectivo con el fondo. Lo anterior permite definir en forma exacta la duración efectiva del lance, siendo este parámetro esencial para las estimaciones de abundancia llevadas a cabo por el método de área de barrido. Este documento describe los resultados obtenidos al incorporar un sensor de contacto que registra su ángulo de inclinación al ser conectado al borlón de la red de arrastre, permitiendo el monitoreo continuo de su desempeño sobre el fondo. Las mediciones de la duración del lance con dicho sensor de contacto se comparan con el método estándar utilizado, discutiéndose sus ventajas con fines de estimación de abundancia