Search

The present study characterizes the reproductive cycle of Venerupis senegalensis (=V. pullastra) from Ria de Aveiro (Portugal) as well as its nutrient storage and exploitation strategy. The reproductive cycle followed a seasonal cycle that correlated negatively with sea surface temperature, and comprised a ripe stage in winter followed by a spawning period that began in late winter and ended in the early summer. This extended spawning may be an advantageous strategy for the species because it ensures a continuous supply of settlers. Gametogenesis began in late summer/early autumn and intensified with the decrease in temperature during autumn. The condition index increased even during the spawning period, which indicates that there is rapid recovery and that reserves are accumulated during late summer and used later in the gametogenic process. Proteins did not contribute significantly to gametogenesis and the glycogen pattern is typical of conservative species, since gametogenesis depends largely on the amount of glycogen stored. The lipid storage and utilization cycle showed that gametogenesis took place in autumn/winter and that energy reserves were accumulated in summer., El presente estudio caracteriza el ciclo reproductivo de Venerupis senegalensis (= V. pullastra) en la Ría de Aveiro (Portugal) así como su estrategia de almacenamiento y explotación de los nutrientes. El ciclo reproductivo de esta especie sigue un ciclo estacional que se correlaciona negativamente con la temperatura del agua del mar, que coincide con un estado de madurez en el invierno, seguido de un periodo de desove que se inicia a finales de invierno y termina a principios del verano. Este periodo de puesta prolongado puede ser una estrategia ventajosa para la especie, ya que garantiza un suministro continuo de larvas. La gametogénesis comenzó a finales del verano/inicios de otoño y se intensificó con la disminución de la temperatura durante el otoño. El aumento del índice de condición, todavía durante la puesta, indica una recuperación rápida y una acumulación de reservas a finales del verano, que serán utilizadas en el siguiente proceso de gametogénesis. Las proteínas no contribuyen significativamente a la gametogénesis y el ciclo de glucógeno es típico de las especies conservadoras, una vez que la gametogénesis depende, en gran medida, de la cantidad de glucógeno almacenado. El almacenamiento de lípidos y su utilización indica la gametogénesis en el otoño/invierno, así como el proceso de acumulación de energía en verano.

RESUMO: A principal razão que me levou a escolher este estágio e esta intervenção, foi o facto de gostar muito de trabalhar com jovens. Esse gosto, aliado à paixão que tenho pelo exercício e saúde, trouxe-me para um projecto que visa alterar e promover estilos de vida saudáveis em jovens obesos com idades entre os 12 e os 16 anos de idade. O estágio teve a duração de 10 meses, de Outubro de 2010 a Julho de 2011. Começamos com a definição dos protocolos a implementar e das tarefas a realizar. A primeira dessas tarefas, centrava-se no recrutamento da amostra que pretendíamos para desenvolver o estudo. Paralelamente ao projecto TOP, colaborámos também nas consultas de obesidade pediátrica no Hospital de Santa Maria, o que nos permitiu recrutar jovens que iam às consultas e incluí-los no projecto TOP. Após termos efectuado o recrutamento, começámos com as aulas práticas e teóricas. Essas aulas ocorriam na Universidade Lusófona, todos os sábados, das 10 às 12 horas. Eram sempre da nossa responsabilidade as aulas práticas, e as teóricas quando se falava de exercício. Nas aulas práticas realizavam-se circuitos, jogos tradicionais, jogos colectivos, e jogos que promovessem a competição saudável e a inter-ajuda, visto que ali todos os participantes tinham um objectivo comum. Durante o ano foram realizadas duas colónias de férias, onde organizámos outro tipo de actividades, nomeadamente mini-golf e caminhadas na zona do Jamor. Tanto as colónias de férias, como as avaliações eram da nossa inteira responsabilidade, desde a preparação, à execução e realização das mesmas. De referir que, tendo em conta os resutados obtidos, os participantes que melhoraram na sua capacidade cardiovascular apresentaram igualmente melhoras ao nível da composição corporal, nomeadamente com a diminuição do perímetro da anca e do perímetro acima das cristas ilíacas. Importa ainda referir que ocorreram melhorias significativas (p, Orientador: António Palmeira ; co-orientador: Sandra Martins

Ecological aspects of 75 megabenthic bivalve species found on the south coast of Portugal (from Vila Real to Sagres) were studied based on the information provided by seasonal bivalve surveys from 2000 to 2007 (8600 hauls, simultaneously using a razor shell dredge and a clam dredge). Of the 75 species identified, 36 occurred less than 30 times, and thus were considered rare in the area. The remaining 39 bivalves were analysed according to their occurrence, bathymetric distribution, geographic preferences, seasonal preferences, burying-depth, beach exposure and river mouth proximity. All species belonging to the Pharidae and Solenidae families (razor shells) and most Tellinidae were significantly more frequent in the razor shell dredge (indicating deeper burying in the sediment), whilst the families Cardiidae and Donacidae were significantly more frequent in the clam dredge (indicating that these species are probably closer to the sediment surface). As for the season, most bivalve species occurred similarly in both seasons (19 sp; 49%), but a large proportion were more abundant during the autumn surveys (17 sp., 44%), whereas only three species were commoner during the spring surveys. Most species belonging to the families Cardiidae and Mactridae were commoner in the autumn surveys. The spatial distribution differed between species and cluster analysis identified four communities with greater geographic affinity. Species belonging to the family Cardiidae were preferably found in the western part (WB) and the eastern part (S) of the study area, whereas the families Donacidae, Mactridae and Tellinidae occurred mainly in the central area (EB) and the eastern (S) coastal sectors. Overall, shallower species (modal depth at 3-6 m) showed greater occurrences and abundances than the deeper ones, and the depth pattern observed did not change between seasons. Donacidae and Mactridae (except Mactra glauca) were represented essentially by shallow species, whereas Cardiidae (except Acanthocardia tuberculata and Cerastoderma edule) included mostly species occurring in deeper waters. Bathymetric sequence of species distribution within some families was observed., Se estudiaron algunos aspectos ecológicos de 75 especies de bivalvos megabentónicos en la costa meridional de Portugal (desde Vila Real a Sagres), basados en la información obtenida a lo largo de varios muestreos estacionales realizados entre el año 2000 y 2007 (8600 muestras). Las muestras se obtuvieron utilizando simultáneamente un rastro para capturar navajas y un rastro para capturar almejas). De los 75 taxones identificados, 36 aparecieron menos de 30 veces, considerándose raros en el área. De los 39 taxones de bivalvos restantes se analizaron los patrones de presencia, distribución batimétrica, preferencias geográficas y estacionalidad y se relacionaron con la profundidad de enterramiento, la exposición de las playas y la proximidad a desembocaduras de ríos. Todas las especies de las familias Pharidae, Solenidae (navajas) y la mayor parte de Tellinidae fueron más frecuentes en el rastro para capturar navajas, indicando una mayor profundidad de enterramiento en el sedimento, mientras que las familias Cardiidae y Donacidae fueron significativamente más frecuentes en el rastro para capturar almejas, indicando que estas especies se encuentran más cercanas a la superficie del sedimento. La mayoría de especies presentaron abundancias similares a lo largo de todo el año (19 especies, 49%), pero una gran proporción fueron más abundantes en los muestreos de otoño (17 especies, 44%), mientras que sólo 3 especies fueron más comunes en primavera. La mayoría de especies de las familias Cardiidae y Mactridae fueron más comunes en otoño. La distribución espacial fue distinta para cada especie y el análisis de clasificación jerárquica mostró 4 comunidades con mayor afinidad geográfica. Las especies pertenecientes a la familia Cardiidae se encontraron preferentemente en la parte occidental de la zona de estudio (WB) y en la oriental, mientras que las familias Donacidae, Mactridae y Tellinidae aparecieron principalmente en los sectores central (EB) y oriental (S) del área. Las especies de distribución más somera (profundidad modal 3-6 m) fueron más frecuentes y abundantes en general que las especies de más profundidad y este patrón no cambió entre primavera y otoño. Donacidae y Mactridae (excepto Mactra glauca) estuvieron representadas fundamentalmente por especies someras, mientras que los Cardiidae (excepto Acanthocardia tuberculata y Cerastoderma edule) estuvieron representados principalmente por especies de profundidad. En algunas familias se observó una distribución batimétrica secuencial.

Submitted by Joana Lopes Dias (jdias@ubi.pt) on 2015-07-16T15:09:53Z No. of bitstreams: 1 tese.pdf: 5255415 bytes, checksum: 896ed669e4fb098aec4036a2f54f2355 (MD5) Made available in DSpace on 2015-07-16T15:09:53Z (GMT). No. of bitstreams: 1 tese.pdf: 5255415 bytes, checksum: 896ed669e4fb098aec4036a2f54f2355 (MD5) Previous issue date: 2009

The purple dye murex, Bolinus brandaris (Linnaeus, 1758), is a muricid gastropod common throughout the Mediterranean and along the Moroccan and Portuguese Atlantic coasts. In the present study, we confirmed the diploid chromosome number of 2n = 70 for this species, and established for the first time the karyotype, which comprised 12 metacentric, 15 submetacentric and eight subtelocentric chromosome pairs. To facilitate cytotaxonomic comparisons, we carried out a comparative karyological analysis through multidimensional scaling between B. brandaris and three other 2n = 70 muricid species (Hexaplex trunculus, Ocenebra erinaceus, and Stramonita haemastoma) for which chromosomal measurements have been previously published. The interpretation of the ideograms and the statistical analysis highlighted the closest similarity of B. brandaris and H. trunculus compared to S. haemastoma and O. erinaceus. Indeed, B. brandaris and H. trunculus showed the smallest dissimilarities both for relative length and arm ratio, with O. erinaceus presenting intermediate values, whereas the highest dissimilarities were found between H. trunculus and S. haemastoma for both data. The karyotypes of B. brandaris and H. trunculus (subfamily Muricinae) presented the highest proportions of metacentric chromosomes compared to the other two muricids analysed, suggesting that those karyotypes could be considered primitive within the 2n = 70 Muricidae studied so far. (C) 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96, 185-193. Fundacao para a Ciencia e Tecnologia (FCT) [SFRH/BPD/18961/2004, SFRH/BPD/26348/2006]; PROMAR; Tecnologias de Producao Aquicola [22-05-01-FDR-0009] info:eu-repo/semantics/publishedVersion

The artisanal fishery for muricid gastropods in the Ria Formosa lagoon (Algarve coast, southern Portugal) is a locally important fishing activity because the banded murex (Hexaplex trunculus) and the purple dye murex (Bolinus brandaris) are greatly appreciated seafoods with high commercial value in the Portuguese seafood market. An integrated study was implemented to monitor the muricid gastropod fishery with the artisanal fishing gear (“wallet-line”) through monthly experimental fishing operations carried out during one year. The aim was to describe the fishing operations and fishing gear, to estimate the fishing yield, to characterise the target species catch composition, and to identify by-catch species and discards. The “wallet-line” is neither a species-specific nor a size-selective fishing gear, because the catches comprised a variety of by-catch species and a high proportion of commercially under-sized target species. The vast majority of the by-catch is discarded immediately on board, so mortality is presumably negligible. The CPUE of both target species and by-catch species decreased during consecutive fishing days, mainly due to declining bait attraction. Considering the overall information gathered on this fishing activity, some management measures are proposed for this artisanal fishery, which might ultimately contribute to the long-term sustainable exploitation of the fishing resource., La pesquería artesanal de gasterópodos murícidos en la laguna Ría Formosa (costa del Algarbe, sur de Portugal) constituye una actividad pesquera importante porque la corneta (Hexaplex trunculus) y la cañaílla (Bolinus brandaris) son mariscos muy apreciados con alto valor comercial en el mercado Portugués. Se aplicó un estudio integrado para controlar la pesquería de gasterópodos murícidos con el arte de pesca artesanal “wallet-line” a través de pescas experimentales mensuales desarrollados durante un año. El objetivo fue describir las operaciones de pesca y el arte de pesca, para estimar el rendimiento pesquero, caracterizar la composición de las capturas de las especies objetivo, identificar las especies procedentes de las capturas no dirigidas y descartadas. El arte de pesca “wallet- line” no es ni específica para cada especie ni selectiva por tallas, ya que las capturas incluyen una variedad de especies procedentes de capturas no dirigidas y una alta proporción de especies objetivo de talla inferior a la permitida. La amplia mayoría de capturas no dirigidas son descartadas a bordo inmediatamente, y por tanto la mortalidad es presumiblemente insignificante. La CPUE tanto de las especies objetivos como de las no dirigidas disminuyó durante días de pesca consecutivos debido principalmente a la disminución de la atracción de los cebos. Teniendo en cuenta la información global recopilada en esta actividad pesquera, se proponen algunas medidas de gestión para esta pesquería artesanal, que podrían finalmente contribuir a la explotación sostenible del recurso pesquero a largo plazo.

In Ria Formosa cockles (Cerastoderma edule) have traditionally been harvested with a harvesting-knife (HK). However, over the last six years there has been an increase in the use of a hand-dredge (HD) to exploit cockle beds. A comparative study on the impact of these harvesting methods on the benthic macrofauna was undertaken with the aim of evaluating the possible introduction of the hand-dredge in the fishery. Macrofaunal mortality was very low regardless of the gear. However, the total mortality resulting from using the HK was superior to the one observed for the HD. For the same fishing time the hand-dredge covers an area approximately five times greater that the one covered by the knife, with the former yielding 5 times the catch of the latter. Consequently, the use of hand-dredges increases the fishing effort, which may lead to the overexploitation of the cockle populations. Our results revealed that the immediate effect of both gears on macrobenthic communities was similar and minimal. Therefore, we believe that introducing the hand-dredge in the cockle fishery should only be authorised if other management measures, such as daily quotas, closed areas and limiting the number of fishing licenses, are implemented., En la Ría Formosa los berberechos (Cerastoderma edule) han sido tradicionalmente recolectados con un cuchillo de marisqueo. Pero en los últimos seis años ha habido un crecimiento en el uso del rastro de mano en la explotación de los bancos de berberechos. Se ha desarrollado un estudio comparativo sobre el impacto de estos métodos de pesca en la macrofauna bentónica con el objetivo de evaluar una posible introducción de este arte de pesca ilegal. La mortalidad de la macrofauna ha sido muy baja, independientemente de los métodos de pesca utilizados. No obstante, la mortalidad total, resultante del uso del cuchillo de marisqueo, es superior a la que se ha observado con el uso del rastro de mano. Para el mismo tiempo de pesca, el rastro cubre aproximadamente una área cinco veces mayor que el del cuchillo. En consecuencia, el uso del rastro de mano aumenta el esfuerzo de pesca, lo que puede llevar a la sobreexplotación de las poblaciones de berberechos. Nuestros resultados revelan que el efecto inmediato de ambos artes en las comunidades macrobentónicas ha sido semejante y mínimo. Concluimos que la introducción del rastro en la pesca de berberechos sólo debería autorizarse si fueran implementadas otras medidas de gestión de la pesca, como las restricciones diarias de las capturas, áreas cerradas y limitaciones en el número de permisos de pesca.

Nowadays Portugal is under a large process of creation/revision of studies and plans related with land use and territorial planning, mainly due to the end of the lifetime period of the actual Municipal Master Plan, but also because of the creation of the new Metropolitan Authorities of Transportation, which will require Mobility Plans. Even though the Portuguese law doesnÂ’t impose these Mobility Plans at the present moment, there is a general feeling about the importance of the mobility system for the society and economics in general. This is the case in highly density areas, where the need and complexity of the system requires these specific studies in order to obtain an efficient management; or in the case of low-density areas where the risk of loosing competitiveness is too high to ignore the importance of the transportation and mobility system, and the advantage of gaining local and regional competitiveness might increase the importance of the municipality in regional context. This paper intends to provide an innovative approach regarding the provision, at an early stage, of technical support to decision-makers in order to define Mobility and Transportation Policies. The opportunity provided by using adapted SWOT analysis (among others) to identify weakening or potential factors, and how to take advantage of the results, always using a cause and effect approach and a coherent policy in order to obtain high quality and effective studies and politics. The methodology relies on a two-stage process. In the first stage a summary diagnose is provided, using inputs which are supposed to well characterise the territoryÂ’s mobility patterns. Afterwards, in a second phase, these are inter-related and evaluated in order to build-up a table of options, where policies are proposed with a careful attention to its qualitative cross impact with the measures and objectives intended to be achieved. The proposed methodology was applied in the Alcobaça´s Municipality case study, which provided different lines of action in diverse subjects, such as, public and private transportation networks, parking policies and organisation, and territory competitiveness. This study was particularly relevant, since this Municipality is under great pressure of its neighbour municipalities, has a low level of regional importance and a low intra-municipal cohesion. Finally, the general opinion of the decision-makers about this technical approach is presented. Keywords: Mobility; Transportation; Land Planning and Policies; Decision-making Support

This project systematically examines the bivalve dredging process and its physiological and ecological consequences. The literature on ecology and population dynamics of the target species, dredge design and fisheries and the environmental effects of dredging and selectivity of dredging is reviewed. A programme of experimental work, both laboratory and field studies is described in scallop and clam dredge fisheries in European waters; scallop species (UK, France) Pecten maximus, Aequipecten opercularis, clam species (Italy; N. Adriatic) Chamelea gallina, clam species (Portugal) Spisula solida, Donax trunculus, Callista chione. Selectivity measures and dredge design are examined for their consequences in terms of environmental effects. Studies included physical, chemical and biological effects both at individual and community level, and selectivity of dredging. These studies include the use of instrumentation and modelling to describe physical effects and behavioural observations, stress and damage indices, both acute and chronic, to describe environmental effects. In the discussion measurement of environmental effects and selectivity are discussed along with the environmental effects of selectivity parameters, dredge designs and responses to fishing effort. The results are discussed in the context of dredge fishery management.

The effect of dredging on bottom structure was assessed, to estimate the damage inflicted on the benthic macrofauna left on the dredge path and to evaluate aggregations of scavengers within the track. Sediment suspended during dredging rapidly resettled both on sand and sandy-mud bottoms. Dredge tracks were deeper on sandy-mud sediments and persisted longer than in sandy sediments. The disappearance of tracks in both sediment types depended both on current strength and wave action. Damage and mortality induced by dredging on the macrobenthic animals left on the dredge path was relatively low. Post-fishing diver observations showed that damaged animals left on the dredge path rapidly attracted scavengers, mainly Ophiura albida. Immediately after the tow ophiuras reached densities 8 times greater in the track region than in the background. However, they dispersed again rapidly because only few damaged fauna were available on the dredge tracks. Undamaged or slightly damaged shellfish started to rebury immediately after escaping from the dredge.

The white clam Spisula solida is harvested along the entire coast of Portugal using mechanical dredges. In this study, the total direct mortality of the macrobenthic community caused by three types of clam dredges (north dredge—ND, traditional dredge—TD, and the metallic grid dredge—GD) used in the S. solida fishery was determined and compared. The relationship between mortality and catching efficiency for each type of dredge was also assessed. Our results showed significant differences for total direct mortality between the ND and both the GD and TD dredges. This difference was largely attributed to the mortality of animals that died in the dredge track as a direct result of the physical damage inflicted by the dredge passing. It was also found that the damage to uncaught individuals is directly related to gear efficiency. The lower catching efficiency of the ND (64%) led to a higher proportion of damaged individuals being left in the dredge path, when compared with the more efficient GD (98%) and TD (90%) dredges. Short and long-term implications of the impact of dredging on the composition of benthic communities are discussed. From fisheries management and ecological points of view, there are obvious advantages to introduce into the bivalve dredge fisheries more efficient and selective dredges in order to reduce the number of damaged individuals and by-catch, and consequently decreasing the impact on the macrobenthic communities.

A study was undertaken on the northwestern coast of Portugal to evaluate the selectivity effect of both tooth spacing and mesh size on the catch of the white clam (Spisula solida). Two typical clam dredges, equipped with different tooth spacing and mesh size, were towed side by side. Three tooth spacing (20, 40 and 60 mm) and three mesh sizes (35, 40 and 50 mm) were investigated. The dredge selectivity experiments were performed by attaching a cover bag with a 20mm mesh to the gear. Individual hauls were analysed by the SELECT model. The Fryer’s mixed model of between-haul variation was also applied to data. The results showed that the space between teeth does not have an effect on selectivity. Tooth length was directly related to the dredge’s capture efficiency. The only factor that contributed to dredge size selection was mesh size. The 50% retention lengths estimated for mesh sizes 30, 40 and 50mm were 25.68, 26.35 and 31.94 mm, respectively. For all mesh sizes, very narrow selection ranges were observed. The most appropriate mesh size to be enforced within the Portuguese northwestern S. solida fishery should be 40 mm.

During 1998, a study of the European hake (Merluccius merluccius) static gear fishery was undertaken in southern Portugal. This study aimed to compare long-line and gill net catches within the same area in terms of catch composition, fishing yield, by-catch and discards, and specifically for hake, catch size frequency distribution and quality of the fished product. At least 35 species of fish and invertebrates were caught, with hake dominating the catches in terms of both weight and number. The by-catch represented 23% and 15% of the catch in weight for long-lines and gill nets respectively. No illegal sized hake (under 27 cm total length) were caught in either gear during the study period. Discards of non-commercial species were similar for both gears and considered to be negligible (< 3% by weight). Hake discards were significantly different between gears (7% for long-lines and 42% for gill nets, by weight), due to fish deterioration related to soaking time. Higher daily yields were obtained for long-lines (258.37 kg / 9,000 hooks) compared with those for gill nets (127.12 kg / 10 km net). These findings will help to improve the management and conservation of this valuable hake fishery., Durante 1998 se realizó un estudio de la pesquería estática de merluza europea (Merluccius merluccius) en el sur de Portugal. Este estudio estuvo dirigido a comparar las capturas de las redes de enmalle y del palangre dentro de la misma área, en términos de composición, rendimiento pesquero, captura secundaria y descartes. Específicamente para la merluza, se comparó además la distribución de frecuencias de talla y calidad del producto pescado. Se capturaron, por lo menos 35 especies de peces e invertebrados, con la merluza como especie dominante en las capturas, tanto en peso como en número. Las capturas colaterales representaron el 23% y 15% del total de la captura en peso para los palangres y redes de enmalle respectivamente. Durante el periodo de estudio no se capturaron merluzas de talla ilegal (menos de 27 cm de talla total) en ninguna de las artes de pesca. Los descartes de especies no comerciales fueron similares para ambas artes de pesca y se consideraron insignificantes (< 3% en peso). Los descartes de merluza fueron significativamente distintos entre artes de pesca (7% y 42% en peso para palangre y redes de enmalle respectivamente), debido al deterioro de los peces relacionado con el tiempo de permanencia de las artes de pesca en el agua. Se obtuvieron rendimientos diarios más altos para los palangres (258.37 kg / 9,000 anzuelos) que para las redes de enmalle (127.12 kg / 10 km de red). Estos resultados contribuyen a mejorar la gestión y conservación de esta valiosa pesquería de merluza.

A study was undertaken to evaluate the existence of depth segregation between size classes of Donax trunculus populations that occur along the Algarve coast (southern Portugal). Five collecting areas were sampled in the Ria Formosa barrier islands, namely in the Culatra, Barreta and Armona Islands, between March and June 1998. The study was based on size frequency distribution analysis and shell biometric relationships. The size frequency distribution showed the predominance of smaller individuals (< 25 mm) in the renewal area (0.5-1.0 m depth) and the prevalence of larger individuals (? 25 mm) at greater depths (4.0-6.0 m depth). The biometric study revealed the existence of significant differences in the type of growth between size classes in relation to depth distribution and burrowing activity. On the basis of these results, some specific management measures were proposed for this important bivalve fishery, taking into account the distinct fishing strategies and operations (manual and boat-operated dredging) performed at different depths., No disponible

Experiments to assess the effect of mesh size and tooth spacing on the catch of Spisula solida were undertaken with the aim of determining an optimal combination of these two characteristics to minimize the dredging impact on by-catch species. However, our data showed that tooth spacing, mesh size and the interactions between these two factors did not affect the number of damaged macrofaunal individual’s caught. This may be because infauna entered the dredge without passing through the space between the teeth and the mesh of the net bag closed as it was stretched by the weight of the contents, preventing the escape of the caught individuals. Thus, independently of mesh size, when the dredge is towed over the sediment, the retained individuals were injured due to abrasion between animals and/or between animals and debris. The severity of injuries inflicted by dredging on different macrobenthic species is related to their morphology and fragility.

To evaluate a possible introduction of a new dredge in the fishery of Callista chione (Linnaeus, 1758), IPIMAR has conducted a study with the objective of comparing the efficiency of two dredges (traditional dredge and the new dredge design) and evaluating their impact on the benthic community. The experiments were carried out during March 1999 on the Southwest coast of Portugal, from a site off Troia. Three different tow durations of 5, 10 and 20 min were investigated. A total of 24 hauls were accomplished, 4 for each tow duration and dredge. The experiments were conducted by attaching a cover bag with a 20 mm mesh to the gear. After each haul, the catches in the bag and in the cover were sorted separately. All individuals retained were attributed scores on a scale of 1–4 in which 1 equates to good and 4 equates to dead. The results obtained showed that catches from the traditional dredge (TD) are composed of a great fraction of juveniles of C. chione, while in the new dredge (NDD) catches are composed, almost entirely, by individuals with a superior size to the minimum legal length (50 mm). This result indicates that the mesh of the bag of the TD used in the exploitation of this resource is not adequate. For the 3 different tow durations, the mean fishing yield obtained for the NDD was always superior to the TD, due to its greater efficiency in capture. The proportion of by-catch is significantly higher when the TD is used. For all 3 tow duration, the TD caused mortalities on the target species and on the macrobenthic community in the same order of magnitude as the NDD. Since the fishery of C. chione is managed by daily quotas per boat, when using the NDD the impact on the macrobenthic community is reduced by about 50% due to its greater efficiency of capture. Another advantage in the usage of the NDD relatively to the TD, is to allow the smallest individuals (independently of the species) to escape rapidly through the metallic bars on the grid, increasing their probability of survival.