Diets of the sole Solea vulgaris Quensel, 1806 and Solea senegalensis Kaup, 1858 in the lower estuary of the Guadiana River (Algarve, southern Portugal): Preliminary results

The feeding habits of two major species of sole, the common sole Solea vulgaris Quensel, 1806 and the Senegalese sole Solea senegalensis Kaup, 1858 were studied in the lower estuary of the Guadiana River (Algarve, southern Portugal). An evaluation of the number, weight, and feeding coefficient of prey types showed that S. vulgaris feed on a limited variety of prey (only Polychaeta and Tanaidacea) and present low-intensity feeding activity, with small differences in diet between seasons. S. senegalensis also have a low-diversity diet (with only one more taxa, Amphipoda), but exhibit more intense feeding activity which varies seasonally, although with little seasonal variation in the relative importance of the main preys. The diet composition of these two species suggests feeding specialization.Se han examinado los hábitos alimentarios de dos especies importantes de lenguado, Solea vulgaris Quensel, 1806 y Solea senegalensis Kaup, 1858, en el bajo estuario del río Guadiana (en el Algarve, sur de Portugal). La actividad depredadora de S. vulgaris es escasa y la variedad de sus presas limitada (únicamente poliquetos y tanaidaceos), con una ligera variación estacional de la dieta. S. senegalensis también se alimenta de una variedad reducida de presas, aunque con un taxón más (anfípodos), y tiene una actividad depredadora mayor, que varía estacionalmente, aunque no hay variaciones en la importancia relativa de la presa con la estación del año. La composición de la dieta de estas dos especies sugiere la especialización de su alimentación.Instituto Español de Oceanografí

Trammel net catch species composition, catch rates and metiers in southern European waters: A multivariate approach

We identified and quantified the effect of season, depth, and inner and outer panel mesh size on the trammel net catch species composition and catch rates in four southern European areas (Northeast Atlantic: Basque Country, Spain; Algarve, Portugal; Gulf of Cadiz, Spain; Mediterranean: Cyclades, Greece), all of which are characterised by important trammel net fisheries. In each area, we conducted, in 1999-2000, seasonal, experimental fishing trials at various depths with trammel nets of six different inner/outer panel mesh combinations (i.e., two large outer panel meshes and three small inner panel meshes). Overall, our study covered some of the most commonly used inner panel mesh sizes, ranging from 40 to 140 mm (stretched). We analysed the species composition and catch rates of the different inner/outer panel combinations with regression, multivariate analysis (cluster analysis and multidimensional scaling) and other 'community' techniques (number of species, dominance curves). All our analyses indicated that the outer panel mesh sizes used in the present study did not significantly affect the catch characteristics in terms of number of species, catch rates and species composition. Multivariate analyses and seasonal dominance plots indicated that in Basque, Algarve and Cyclades waters, where sampling covered wide depth ranges, both season and depth strongly affected catch species compositions. For the Gulf of Cadiz, where sampling was restricted to depths 10-30 m, season was the only factor affecting catch species composition and thus group formation. In contrast, the inner panel mesh size did not generally affect multidimensional group formation in all areas but affected the dominance of the species caught in the Algarve and the Gulf of Cadiz. Multivariate analyses also revealed 11 different metiers (i.e., season-depth-species-inner panel mesh size combinations) in the four areas. This clearly indicated the existence of trammel net 'hot spots', which represent essential habitats (e.g., spawning, nursery or wintering grounds) of the life history of the targeted and associated species. The number of specimens caught declined significantly with inner panel mesh size in all areas. We attributed this to the exponential decline in abundance with size, both within- and between-species. In contrast, the number of species caught in each area was not related to the inner mesh size. This was unexpected and might be a consequence of the wide size-selective range of trammel nets. (c) 2006 Elsevier B.V All rights reserved

Estimation of gillnet and hook selectivity for Carangoides fulvoguttatus (Forsskal, 1775) captured off Kanyakumari coast of India

Selectivity and fishing powers of multi-mesh gillnets with mesh sizes of 13.5, 14, 14.5 and 15 cm and hooks No. 5, 6, 7 and 8 were studied using the experimental catch data of the carangid Carangoides fulvoguttatus (Forsskal, 1775). The selectivity curves, parameters and residual plots for different models viz., normal scale, normal location, log-normal, gamma and bi-normal models were produced applying the SELECT (Share Each Length Class Total) methodology which has been incorporated in the software GILLNET (Generalised Including Log-Linear N Estimation Technique). The models were evaluated using the statistical tools viz., model deviance, dispersion parameter and residual plots to determine the best fit of the selectivity data. The uni-normal model, normal scale was found as best fit for the gillnet catch data while bi-normal was identified as suitable model for the hook catch data. The mesh size of 14.5 cm and hook No. 5 performed better than the other modeled meshes and hooks respectively. Gillnet selectivity data did not converge into bi-normal model due to single mode of capture. However, the hook catch data converged into bi-normal model with two modes of selection curve. Over dispersion was found common in catch data obtained from both gears due to larger size of fishes caught and demonstrated lack of fit in both selection data

Catch composition, catch rates and size selectivity of three long-line methods in the Algarve (southern Portugal)

Three long-line methods have been studied in the Algarve: 1) small-hook long-line for inshore (less than 30 m) ‘white' sea breams (Sparidae); 2) small-hook long-line for deeper water (40-60 m) ‘red' sea breams; and 3) deep water (500-700 m) semi-pelagic long-line for hake Merluccius merluccius (Linnaeus, 1758). Selectivity studies were carried out with three hook sizes in the first two cases: Mustad round-bent Quality 2369 hooks, numbers 15, 13, and 11, baited with a standardsized razor-shell Ensis siliqua (Linnaeus, 1758). Four hook sizes (numbers 10, 9, 7, and 5) of Stell round-bent, eyed hooks were used in the semi-pelagic long-line selectivity study, baited with a half of a standard-sized sardine. Some factors affecting catch composition and catch rates of the small hook long-lines were also evaluated: bait, gangion length, setting time, fishing ground, and depth. Species diversity was relatively high, with 40, 36 and 27 species, respectively, in the three studies. However, the catches were dominated by a limited number of species. Catch rates (number of fish per 100 hooks) were variable ( 5 %; 20 %), with a general decrease in catch rate with increasing hook size in all the studies. In general, the catch size distributions for the different hook sizes for each species were highly overlapping, with little or no evidence of differences in size selectivity. Hooks caught a wide size-range for each species, with few or no illegal-sized fish, in most cases. Some implications of these results for the management of multi-species, multi-gear fisheries are discussed.Tres artes de palangre han sido estudiados en Algarve: 1) palangre de anzuelo pequeño para espáridos de aguas costeras (menos de 30 m); 2) palangre de anzuelo pequeño para espáridos rojos de aguas mas profundas (40-60 m); y 3) palangre semipelágico de profundidad para merluza Merluccius merluccius (Linnaeus, 1758). En los dos primeros casos, los estudios de selectividad han utilizado anzuelos de tres tamaños: round bent marca Mustad modelo 2369 (números 15, 13 y 11), utilizando como cebo pedazos de navajas Ensis siliqua (Linnaeus, 1758) de la misma talla. En el estudio de selectividad con el palangre semipelágico se han utilizado cuatro tamaños de anzuelo (números 10, 9, 7 y 5) round hook de la marca Stell, con media sardina como cebo. Se evalúan, también, otros factores que afectan a la composición y a la tasa de captura de los palangres equipados con anzuelo pequeño: cebo, longitud de la puntera, hora de largada del aparejo, área de pesca y profundidad. La diversidad de especies en los tres estudios ha sido relativamente elevada: 40, 36 y 27 especies, respectivamente. Sin embargo, las capturas han sido dominadas por un número reducido de especies. Las tasas de captura (número de peces por 100 anzuelos) han variado ( 5 %; 20 %), observándose en los tres estudios un descenso general de las tasas de captura con el aumento del tamaño del anzuelo. De forma general, se ha observado una fuerte sobreposición de las distribuciones de las capturas con los diferentes tamaños de anzuelo para cada especie, con poca o ninguna evidencia de diferencias en la selectividad por talla. Los tamaños de anzuelo probados han capturado un rango de tallas amplio para cada especie, con escasa o ninguna captura de peces de talla ilegal en la mayoría de los casos. Se discuten algunas implicaciones de estos resultados en la gestión de pesquerías incluyendo varias especies y varios artes de pesca.Instituto Español de Oceanografí

Competition between static gear of the small-scale fisheries in Algarve waters (southern Portugal)

Parallel fishing trials with 0.30 mm diameter monofilament gill nets and longlines using small hooks were carried out in the Algarve (southern Portugal) over a one-year period, 1997-1998, with the objective of comparing species composition, catch rates, discards and size ranges. Four hook sizes of 'Mustad' brand, round bent, flatted sea hooks (numbers 15, 13, 12 and 11) and four mesh sizes of 25, 30, 35 and 40 mm (nominal bar length) of gill nets were used in the trials. Overall, 84 species were caught, with gill nets taking 71 species and longlines 54 species and with 41 species caught by both gears. The amount of discarding was higher for gill nets than for longlines. The catch species composition differed between the two gears, with the commercially valuable sea breams dominating the longline catches whereas small pelagics were relatively more important in the gill nets. Multivariate analysis showed a clear separation between the different sizes of the two gears both in terms of numbers and weights per species. Algarve gill netters and longliners fish the same species assemblage on the same fishing grounds, but have clearly different impacts in terms of catch species composition, catch rates and sizes. This information will be useful for the improved management of these small-scale, multi-species, multi-gear fisheries, where different gears compete for scarce resources. In particular this study provides a basis for a more rational allocation of licenses and control of fishing effort

Competition between static gear of the small-scale fisheries in Algarve waters (southern Portugal)

Parallel fishing trials with 0.30 mm diameter monofilament gill nets and longlines using small hooks were carried out in the Algarve (southern Portugal) over a one-year period, 1997-1998, with the objective of comparing species composition, catch rates, discards and size ranges. Four hook sizes of MUSTAD brand, round bent, flatted sea hooks (numbers 15, 13, 12 and 11) and four mesh sizes of 50, 60, 70, and 80 (stretched mesh) (nominal bar length) of gill nets were used in the trials. Overall, 84 species were caught, with gill nets taking 71 species and longlines 54 species and with 41 species caught by both gear types. The amount of discarding was higher for gill nets than for longlines. The catch species composition differed between the two gear types, with the commercially valuable sea breams dominating the longline catches whereas small pelagics were relatively more important in the gill nets. Multivariate analysis showed a clear separation between the different sizes of the two gear types both in terms of numbers and weights per species. Algarve gill netters and longliners fish the same species assemblage on the same fishing grounds, but have clearly different impacts in terms of catch species composition, catch rates and sizes. This information will be useful for the improved management of these small-scale, multi-species, multi-gear fisheries, where different gear types compete for scarce resources. In particular this study provides a basis for a more rational allocation of licenses and control of fishing effort

Reduction of elasmobranch by-catch in the hake semipelagic near-bottom longline fishery in the Algarve (Southern Portugal)

Elasmobranch fish, particularly deep-sea sharks, are the most important component of the by-catch of the hake semipelagic near-bottom 'pedra-e-bola' longline fishery in the Algarve (South Portugal) and most of these fish are discarded. The effects of the removal of the lower hooks were evaluated, in terms of target and by-catch reductions, by quantifying the catches of each hook relative to the distance from the bottom. The analysis showed that most European hake (Merluccius merluccius), the target species of this fishery, were caught in the middle range of the hooks, with very few individuals caught near the bottom, whereas for sharks the situation was the opposite, with most hooked near the bottom. The removal of the lower three pairs of hooks would result in a small reduction in the catch of the target species, but a much more significant reduction in elasmobranch by-catch. In the specific case of the blackmouth catshark (Galeus melastomus), discard mortality would be further minimized due to the fact that the lower hooks capture significantly smaller animals that are always discarded compared with hooks that are more distant from the bottom

An approach to map and quantify the fishing effort of polyvalent passive gear fishing fleets using geospatial data

The use of tracking devices, such as vessel monitoring systems or automatic identification system, enabled us to expand our knowledge on the distribution and quantification of fishing activities. However, methods and models based on vessel tracking data are mostly devised to be applied to towed gears, whereas applications to multi-gear and passive fisheries have been underrepresented. Here, we propose a methodology to deal with geospatial data to map and quantify the fishing effort, as soak time, of passive fishing gears used by a multi-gear fishing fleet. This approach can be adapted to other passive multi-or single-gear fisheries, since it requires only three variables that can be extracted from a pre-classified dataset, to identify the beginning (gear deployment) and the end (hauling) of passive fishing events. As far as we are aware, this is the first time a methodology that allows quantifying the soak time of static passive fishing events, within a polyvalent fishery context, is presented. We argue that the information that can be extracted from such approaches could contribute to improved management of multi-gear and static-gear fisheries and the ecosystem-based approach

Semi-pelagic Longline and Trammel Net Elasmobranch Catches in Southern Portugal: Catch Composition, Catch Rates and Discards

In Portugal, elasmobranch landings have decreased substantially in recent years. In this work, elasmobranch catches in semi-pelagic longlines (1997 and 1998) were compared with those in trammel nets (2000) in the Algarve, southern Portugal areas. In the semi-pelagic longline fi shery, 7 elasmobranch species represented 33.4% (2 185 specimens) of the total fi sh catches. Among the elasmobranch species, the most abundant were Galeus melastomus (63.3%), Etmopterus pusillus (21.7%) and Scyliorhinus canicula (14.2%). Most of these elasmobranchs were discarded (68.3% in total). In the trammel net fi shery, 16 different elasmobranch species represented 4.3% (597 specimens) of total fi sh catches and the most important species were Raja undulata (43.6%) and S. canicula (10.2%). The majority of the elasmobranchs caught in trammel nets had commercial value, and only 5.4% were discarded. In both fi sheries, intra-specifi c catch rates varied with depth. Length-frequency distributions for the only species with relatively high catches in both fi sheries, S. canicula, showed that, in general, trammel nets catch larger specimens and in a narrower length range than do longlines.info:eu-repo/semantics/publishedVersio