Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 162-173). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 153-165).

No description available.

Les captures accessoires et les rejets sont inhérents à la pêche depuis toujours mais ce n’est que récemment, avec l’intérêt croissant pour l’approche écosystémique des pêches, qu’une attention particulière est portée à ces sujets aussi bien dans le domaine de la recherche que celui de la gestion des pêches. Le travail présenté dans cette thèse porte sur l’estimation, la caractérisation et la gestion des captures accessoires et des rejets de la pêcherie thonière tropicaleeuropéenne à la senne des océans Atlantique et Indien. La thèse est basée sur les données de livre de bord et celles collectées par les observateurs embarqués à bord des navires de pêche français et espagnols dans le cadre du programme européen de collecte de données DCF (Data Collection Framework). Les prises accessoires et les rejets des océans Atlantique et Indien sont évalués à partir de méthodes statistiques de complexités variables en fonction des questions posées : estimations globales versus locales et/ou par mode de pêche. Une analyse des précisions et biais d’estimation est présentée ainsi qu’une étude comparative des méthodes d’estimation des prises accessoires. Les caractéristiques des prises accessoires et des rejets sont également détaillées. Cette thèse propose un panorama assezcomplet des problématiques liées à la capture accessoire et aux rejets de la pêcherie thonière tropicale européenne à la senne. Elle fait également des propositions pour améliorer la qualité des estimations, réduire les prises accessoires et valoriser les rejets. / Bycatch and discards has always been inherent in fishing but it is only recently, with the growing interest in ecosystem approach to fisheries, that particular attention is paid to these topics both in research and fisheries management.The work presented in this thesis focuses on the estimation, characterization and management of bycatch and discards in the European tropical tuna purse seine fishery of the Atlantic and Indian Oceans. The thesis is based on logbook data andon data collected by observers on board the French and Spanish fishing vessels in the framework of the European data collection programme DCF (Data Collection Framework). Bycatch and discards of Atlantic and Indian Oceans are estimated from statistical methods of various level of complexity according to the questions : global versus local estimations and/or by fishing mode. An analysis of precision and bias in bycatch estimates and a comparative analysis of methods for estimating bycatch are presented. The characteristics of bycatch and discards are also detailed. This thesis proposes a complete overview of issues related to bycatch and discards of the European tropical tuna purse seine fishery. It also makes suggestions to improve the quality of estimates, to reduce bycatch and to valorize the discards.

The objectives of this study were to measure injuries and impairments directly observed from gags Mycteroperca microlepis caught and released within a large-scale recreational fishery, develop methods that may be used to rapidly assess the condition of reef fish discards, and estimate the total portion of discards in the fishery that suffer latent mortality. Fishery observers were placed on for-hire charter and headboat vessels operating in the Gulf of Mexico from June 2009 through December 2012 to directly observe reef fishes as they were caught by recreational anglers fishing with hook-and-line gear. Fish that were not retained by anglers were inspected and marked with conventional tags prior to release. Fish were released in multiple regions over a large geographic area throughout the year and over multiple years. The majority of recaptured fish were reported by recreational and commercial fishers, and fishing effort fluctuated both spatially and temporally over the course of this study in response to changes in recreational harvest restrictions and the Deepwater Horizon oil spill. Therefore, it could not be assumed that encounter probabilities were equal for all individual tagged fish in the population. Fish size and capture depth when fish were initially caught-and-released also varied among individuals in the study and potentially influenced recapture reporting probabilities. The Cox proportional hazards regression model was used to control for potential covariates on both the occurrence and timing of recapture reporting events so that relative survival among fish released in various conditions could be compared. A total of 3,954 gags were observed in this study, and the majority (77.26%) were released in good condition (condition category 1), defined as fish that immediately submerged without assistance from venting and had not suffered internal injuries from embedded hooks or visible damage to the gills. However, compared to gags caught in shallower depths, a greater proportion of gags caught and released from depths deeper than 30 meters were in fair or poor condition. Relative survival was significantly reduced (alpha (underline)<(/underline)0.05) for gags released in fair and poor condition after controlling for variable mark-recapture reporting rates for different sized discards among regions and across months and years when individual fish were initially captured, tagged and released. Gags released within the recreational fishery in fair and poor condition were 66.4% (95% C.I. 46.9 to 94.0%) and 50.6% (26.2 to 97.8%) as likely to be recaptured, respectively, as gags released in good condition. Overall discard mortality was calculated for gags released in all condition categories at ten meter depth intervals. There was a significant linear increase in estimated mortality from less than 15% (range of uncertainty, 0.1-25.2%) in shallow depths up to 30 meters, to 35.6% (5.6-55.7%) at depths greater than 70 meters (p < 0.001, R2 = 0.917). This analysis demonstrated the utility of the proportional hazards regression model for controlling for potential covariates on both the occurrence and timing of recapture events in a large-scale mark-recapture study and for detecting significant differences in the relative survival of fish released in various conditions measured under highly variable conditions within a large-scale fishery.

Το πρόβλημα της αυξημένης σύλληψης υπομεγεθών ατόμων τσιπούρας (Sparus aurata, Linnaeus 1758) στις ιχθυοσυλληπτικές εγκαταστάσεις της λιμνοθάλασσας Μεσολογγίου-Αιτωλικού τις τελευταίες δεκαετίες έχει αποκτήσει σοβαρές διαστάσεις. Το φαινόμενο αυτό εκτός του ότι συνιστά περιβαλλοντική απειλή έχει επιφέρει σημαντική μείωση της εμπορικής αξίας του αλιεύματος με αποτέλεσμα τη συρρίκνωση του εισοδήματος των αλιέων. Η παρούσα εργασία μελετά την επιλεκτικότητα νέων τροποποιημένων ιχθυοπαγίδων που έχουν εγκατασταθεί στη λιμνοθάλασσα στο πλαίσιο μιας πρωτοβουλίας για την αντιμετώπιση του συγκεκριμένου προβλήματος. Η παρακολούθηση αυτής της πρωτοβουλίας έδειξε ότι οι νέες ιχθυοπαγίδες συμβάλλουν στη διαφυγή των υπομεγεθών ψαριών, οπότε και στη μείωση των ποσοτήτων των απορριπτόμενων ψαριών διασφαλίζοντας έτσι τη βιωσιμότητα του ιχθυοπληθυσμού. Επίσης, αυξάνονται τα έσοδα της αλιευτικής εκμετάλλευσης και βελτιώνεται η καθημερινότητα των αλιέων δεδομένου ότι δε μεσολαβεί το στάδιο του διαχωρισμού των μη εμπορεύσιμων από τα εμπορεύσιμα ψάρια. Οι διαφυγές των ψαριών από τις ιχθυοπαγίδες φάνηκε να επηρεάζονται από την αφθονία του αλιεύματος και πιο συγκεκριμένα σε περιπτώσεις μεγάλης αφθονίας παρατηρήθηκε να δυσχεραίνεται η διαφυγή των υπομεγεθών ψαριών από τις ιχθυοπαγίδες. Ενδεχομένως, αυτό να δημιουργεί την ανάγκη επέκτασης της τροποποιημένης επιφάνειας των ιχθυοπαγίδων. Η παρούσα εργασία αποτελεί πηγή σημαντικών πληροφοριών στη λήψη μέτρων με στόχο τη βελτίωση του προτύπου της αλιευτικής εκμετάλλευσης της λιμνοθάλασσας. / The problem of increased capture of undersized individuals of gilthead seabream (Sparus aurata, Linnaeus, 1758) at the Messolonghi - Etoliko lagoon fish traps, the last decades has become serious. This phenomenon apart from the ecological threat has decreased the commercial value of the catch thus leading to a reduction of the fishermen income. The present study investigates the selectivity of new fish traps installed in the lagoon in order to deal with this problem. It was found that modified traps contribute to the escapement of undersized individuals thus decreasing the discards as well as ensuring the sustainability of fish population. Furthermore, new traps exploitation leads to an increase of the income. Also, there is no need to sort undersized fish from the catch thus improving the daily lives of the fishermen. Fish escapement was found to be affected by the abundance of fish catch. In more details, high abundance was observed to make fish escapement difficult. Perhaps, this highlights the need of modified area extension. The present study reflects a source of useful information to take into consideration for the improvement of the lagoon fishery exploitation.

Depuis 2002, les pays membres de l’Union Européenne (UE) collectent, gèrent et fournissent des données nécessaires à la gestion des pêches et des rejets en particulier. Dans ce contexte, les programmes d’observation à la mer collectent des données à bord des navires de pêche sur la composition et la quantité des captures, y compris des rejets. En s’appuyant sur ces données, cette thèse a pour but d’analyser les variabilités spatio-temporelles des débarquements et des rejets de la pêche afin de contribuer à leur gestion. Pour cela, une méthode de cartographie basée sur des grilles à mailles variables a été développée. Cette méthode a été conçue pour produire des cartes pluriannuelles, annuelles et trimestrielles des débarquements et des rejets par espèce ou groupe selon le métier de pêche.Une plateforme basée sur des technologies Big Data a ensuite été utilisée avec pour objectifs d’affiner et d’automatiser la méthode de cartographie. Grâce à un système de stockage en ligne et un système d’analyse à haute performance, un grand nombre de cartes a ainsi pu être produit automatiquement par métier en regroupant ou non les années, les trimestres et les espèces. Finalement, l’utilité des cartes produites pour la gestion des rejets a été démontrée, en particulier dans le cadre de l’Obligation de Débarquement (Règlement (UE) n° 1380/2013). En s’appuyant sur des données de coûts et de revenus de flottilles, ces cartes permettent d’envisager des stratégies d’évitement de zones et/ou périodes de pêche propices aux captures non-désirées minimisant l’impact sur les performances économi / Since 2002, the European Union (EU) Members States collect, manage and supply data forthe management of fisheries and specifically of discards. In this context, at-sea observer programmes collect data on-board fishing vessels on the composition and quantity of catch, including discards. Based on these data, this study aims to analyse the spatio-temporal distribution of landings and discards so as to contribute to their management. In doing so, amapping method based on nested grids has been developed. This method has been designed to produce pluriannual, annual and quarterly maps of landings and discards per species or group of species according to the fishing metier.A platform based on Big Data technologies has then been used with the objectives of refining and automating the mapping method. Using an online storage system and a high-performance computing system, a large number of maps were produced automatically per métier, grouping or not years, quarters and species. Finally, the usefulness of the produced maps for managing discards has been demonstrated, particularly regarding the Landing Obligation (Regulation (UE) n° 1380/2013). Based on fleet cost and revenue data, these maps open up possibilities for identifying fishing zones and/or periods to be avoided (i.e., high bycatch) while minimising the impacts on fleet’s economic performances.

Η μικρή παράκτια αλιεία αποτελεί σημαντικό τμήμα του αλιευτικού κλάδου στnν Ελλάδα και τη Μεσόγειο και χαρακτηρίζεται από υψηλή ετερογένεια και πληθώρα ιδιαιτεροτήτων. Η διαχείριση της απαιτεί την εξέταση βιολογικών, αλλά και κοινωνικών και οικονομικών παραμέτρων. Στην παρούσα εργασία αναπτύχθηκε μία τυπολογία της ελληνικής μικρής παράκτιας αλιείας με βάση βιολογικά, κοινωνικά και οικονομικά χαρακτηριστικά. Στη συνέχεια η εργασία εστιάστηκε στον Πατραϊκό Κόλπο, όπου μελετήθηκε η δραστηριότητα της τοπικής μικρής παράκτιας αλιείας, η συνολική παραγωγή και η παραγωγή ανά μονάδα αλιευτικής προσπάθειας, η σύνθεση του αλιεύματος, τα απορριπτόμενα και η κατά μήκος σύνθεση των αλιευμάτων. Οι νομοί της Ελλάδας στρωματοποιήθηκαν βάσει του αριθμού των αλιέων και της εξάρτησης από την αλιεία και πραγματοποιήθηκαν συνεντεύξεις αλιέων. Επιβεβαιώθηκε η ποικιλία εργαλείων και ειδών-στόχων και η έντονη χωρική ετερογένεια. Το κυρίαρχο πρότυπο αλιευτικής δραστηριότητας εμφάνισε εποχικές διακυμάνσεις (20 ημέρες δραστηριότητας μηνιαίως το καλοκαίρι, 13 ημέρες το χειμώνα), παρουσίασε όμως τοπικές ιδιαιτερότητες. Οι κύριες ενασχολήσεις (métiers) που πραγματοποιούνται σε πανελλήνιο επίπεδο αναγνωρίστηκαν ως συνδυασμοί αλιευτικού εργαλείου, είδους-στόχου, εποχής και περιοχής με πολυμεταβλητή ανάλυση. Οι αλιείς παρουσίασαν χαμηλό μορφωτικό επίπεδο και υψηλή μέση ηλικία, υψηλά ποσοστά παραμονής στον τόπο γέννησης και διαπιστώθηκε έντονη παρουσία της οικογένειας στο επάγγελμα. Οι αλιείς χωρίστηκαν σε τρεις ομάδες εξάρτησης από την αλιεία βάσει του ποσοστού του εισοδήματος που προέρχεται από το ψάρεμα, οι οποίες εμφάνισαν διαφορές σε χαρακτηριστικά όπως η μέση ηλικία, το μήκος του σκάφους, οι ημέρες δραστηριότητας και το εισόδημα από το ψάρεμα. Στη συνέχεια μελετήθηκε η μικρή παράκτια αλιεία του Πατραϊκού Κόλπου με δειγματοληψίες σε αλιευτικές εξορμήσεις. Η αλιευτική παραγωγή ήταν κατά μέσο όρο 12 Kg ανά αλιευτική εξόρμηση. Συνολικά, αναγνωρίστηκαν 102 είδη αλιευμάτων. Αναπτύχθηκε μία μεθοδολογία αναγνώρισης ενασχολήσεων σε περιπτώσεις περιορισμένου αριθμού δεδομένων, όπως συχνά συμβαίνει στη Μεσόγειο. Οι ενασχολήσεις που αναγνωρίστηκαν παρουσίασαν διαφορές στην ποσότητα και στη σύνθεση του αλιεύματος και ομαδοποιήθηκαν σε μετα-ενασχολήσεις με σκοπό την αποτελεσματικότερη δειγματοληψία της αλιευτικής δραστηριότητας. Η μελέτη των απορριπτομένων ανέδειξε τρεις αιτίες απόρριψης: χαμηλή εμπορικότητα (78% της απορριφθείσας ποσότητας), καταστροφή των αλιευμάτων κατά την παραμονή τους στο νερό (5%) και μείωση της ποιότητάς τους εξαιτίας κακών χειρισμών του ψαρά (17%). Υψηλό ποσοστό απόρριψης παρουσίασαν οι ενασχολήσεις παραγαδιών και μανωμένων διχτύων με μικρό άνοιγμα ματιού. Από τα δεδομένα ατομικού μήκους των αλιευμάτων πραγματοποιήθηκαν συγκρίσεις κατά μήκους σύνθεσης ανάμεσα σε διαφορετικές ενασχολήσεις και εποχές του έτους. Στις περισσότερες περιπτώσεις διαπιστώθηκαν διαφορές. Η μελέτη της επίπτωσης της εφαρμογής του ελάχιστου επιτρεπόμενου μεγέθους εκφόρτωσης έδειξε μικρό ποσοστό υπομεγεθών ατόμων στο αλίευμα βάσει τόσο των σημερινών σε ισχύ μεγεθών όσο και βάσει αυτών που πρόκειται να εφαρμοστούν σύμφωνα με τον Οδικό Χάρτη για την Αναθεώρηση της Κοινής Αλιευτικής Πολιτικής, σε επίπεδο είδους όμως παρουσιάστηκαν εξαιρέσεις. Η παρούσα εργασία αποτελεί τη βάση για την ανάπτυξη μεθοδολογίας για τη μελέτη της μικρής παράκτιας αλιείας στην Ελλάδα και την πραγματοποίηση συγκριτικών μελετών σε ευρωπαϊκή κλίμακα σε αυτόν τον λίγο μελετημένο αλιευτικό κλάδο. / Small-scale fisheries are an important fisheries sector in Greece and the Mediterranean. They are characterized by high heterogeneity and a multitude of particularities. The management of small-scale fisheries requires taking into account biological as well as social and economical elements. In the present study, a typology of Greek small-scale fisheries was developed based on biological, social and economical parameters. Consequently, the study focused in the Patraikos Gulf, where elements such as the fishing activity of the local fleet, catch and catch per unit of effort, species composition, discards and length composition of individuals caught were examined. The prefectures of Greece were stratified considering the number of fishermen and local dependence on fisheries and interviews of fishermen were carried out. The multitude of fishing gears and target species and the intense spatial heterogeneity was confirmed. The major activity pattern identified was seasonal (20 days of activity in summer, 13 in winter), however local particularities arose. The main métiers practiced were identified as combinations of fishing gear, target species, area and season. Concerning socio-economical elements, the fishermen generally had low education, high average age, tendency to remain in their place of birth and the profession is attached to the family. The fishermen were categorized into three dependence groups, based on the percentage of income originating from fisheries. Significant differences were identified among these groups considering variables such as mean fishermen age, vessel size, days of activity and income from fishing. Consequently, the small-scale fisheries of the Patraikos Gulf were studied using data from sampling of fishing operations. The catch weighted about 12 Kg per operation on average and a total of 102 species were recorded. A methodology for the identification of métiers using a limited dataset, as is often the case in the Mediterranean, was developed. The métiers identified showed significant differences in catch quantity and composition and were grouped in meta-métiers to facilitate fishing activity sampling schemes. The study of discards revealed three reasons for discarding: low commercial value (78% of discards), destruction of the catch before gear retrieval (5%) and bad handling of the catch o board (17%). High discard ratio was recorded for the longline and small-size mesh trammel net métiers. Using data of individual length per species comparisons were carried out among métiers and seasons that in most cases revealed significant differences. The study of the effect of minimum landing sizes legislation showed a low percentage of undersized individuals regarding both the legislation currently in effect and the proposed one by the Roadmap for the Reform of the Common Fisheries Policy of the European Union, but exceptions arose for certain species. The present work is the foothold for the development of a methodology for studying small-scale fisheries in Greece and for carrying out comparative studies in a European scale concerning this understudied fishing sector.

Tese(doutorado) - Universidade Federal do Rio Grande, Programa de Pós–Graduação em Oceanografia Biológica, Instituto de Oceanografia, 2012. / Submitted by Cristiane Gomides (cristiane_gomides@hotmail.com) on 2013-10-11T16:45:36Z No. of bitstreams: 1 Luciano.pdf: 10791164 bytes, checksum: abbbf3e63dd24039e4b6f6fb89af6147 (MD5) / Approved for entry into archive by Sabrina Andrade (sabrinabeatriz@ibest.com.br) on 2013-10-17T17:51:18Z (GMT) No. of bitstreams: 1 Luciano.pdf: 10791164 bytes, checksum: abbbf3e63dd24039e4b6f6fb89af6147 (MD5) / Made available in DSpace on 2013-10-17T17:51:18Z (GMT). No. of bitstreams: 1 Luciano.pdf: 10791164 bytes, checksum: abbbf3e63dd24039e4b6f6fb89af6147 (MD5) Previous issue date: 2012 / Os peixes da família Macrouridae apresentaram uma das maiores biomassas entre os peixes demersais em cruzeiros de pesquisa no Sudeste-Sul do Brasil entre 300-600m. Embora não sejam alvo da pesca no Brasil, estão entre os principais itens no descarte da pesca de arrasto no talude, sofrendo impacto similar às espécies-alvo. Dados de dois cruzeiros sazonais de arrasto de fundo foram utilizados para analisar a distribuição, abundância, densidade, composição de comprimentos e estimativas de biomassas para sete espécies de Macrouridae do talude superior do Sudeste-Sul do Brasil: Coelorinchus marinii, Malacocephalus occidentalis, M. laevis, Lucigadus ori, Hymenocephalus billsam, Ventrifossa macropogon e V. mucocephalus. A biomassa total foi estimada em 5,5 e 8,3 kt, respectivamente, no inverno-primavera e verão-outono, das quais C. marinii e M. occidentalis compuseram 98%. Amostras mensais da pesca comercial foram adicionalmente usadas para analisar a ecologia trófica das quatro espécies mais abundantes no talude superior do Sul do Brasil. Foram analisadas a composição da dieta, as mudanças ontogenéticas, as variações sazonais, a sobreposição alimentar intra e interespecífica, a fauna parasitária e aspectos da morfologia funcional relacionada à alimentação. C.marinii consumiu presas pequenas da infauna, epifauna, plâncton, nécton e carcaças, aproveitando presas em manchas ou agregações. M.occidentalis apresentou certa seleção por presas maiores e de coluna d’água, além de caranguejos e carcaças. As duas espécies apresentaram mudanças ontogenéticas e variações sazonais na composição da dieta, ocasionando mudanças nos padrões de sobreposição, mas em geral houve uma baixa sobreposição alimentar. As distintas morfologias funcionais encontradas refletiram em diferenças na dieta e nas estratégias de alimentação das espécies. Para C.marinii e M.occidentalis foram contruídos mapas com densidades, áreas de desova, índice alimentar, proporções de sexos e de imaturos/maturos, que foram relacionadas aos processos oceanográficos, fornecendo uma visão sobre as estratégias de vida e processos que regulam os padrões de distribuição e abundância. Ambas as espécies apresentaram variação sazonal na extensão e localização das áreas de desova. A maioria das fêmeas de C.marinii estavam maturas (90%), sugerindo que assentam ao fundo simultaneamente à maturação e que os juvenis são pelágicos, enquanto M.occidentalis apresentou muitos juvenis e poucas fêmeas maturas, assentando ao fundo bem antes da maturação. São identificados e descritos três processos responsáveis pelos padrões de distribuição e abundância encontrados nestas espécies. Sugere-se que áreas encontradas com elevadas biomassas de Macrouridae (carniceiros) sejam causadas por zonas de ocorrência semipermanente de processos de mesoescala (e.g. vórtices). Esses processos aumentam a produtividade e possibilitam elevadas biomassas de organismos de vida-curta encontradas em camadas superiores, e por outro lado, aumentam a concentração, mortalidade e disponibilidade de carcaças desses organismos, favorecendo predadores carniceiros. Esses processos podem ser responsáveis por inconsistências nas biomassas de magafauna e macrofauna encontradas em alguns estudos, onde biomassas de megafauna foram da mesma ordem de grandeza ou maiores que as de macrofauna, contradizendo o princípio Eltoniano. / Macrourids are among the most abundant and diverse demersal fishes in all deep oceans, including the Southwestern Brazilian continental slope. Although not targeted by Brazilian fisheries, they suffer impact similar than the target species, being among the most discarded fishes by deep bottom trawling. Trophic Ecology: Data from research surveys and commercial fishing were used to analyze the trophic ecology of four species inhabiting the upper slope of southern Brazil: Coelorinchus marinii, Malacocephalus occidentalis, M. laevis and Lucigadus ori. For the two abundant ones, ontogenetic changes, seasonal variations, intra- and interspecific dietary overlap, parasite fauna and aspects of functional morphology are also described. C.marinii had an extremely diverse diet, preying infauna, epifauna, plankton, necton and carcasses. M.occidentalis fed on larger and nektonic prey, but also included crabs and carcasses in the diet. Both species showed ontogenetic shifts and seasonal variations in diet composition, both leading to changes in intra- and interspecific diet overlap patterns. Species showed quite distinct feeding anatomy and proportions of body with mouth size, reflecting on feeding strategies. There was little interspecific food overlap. In most cases when the diet was more similar there was a spatial segregation. The coexistence of these species appears to be facilitated by the development of different functional morphologies and feeding strategies. A considerable portion of the diet of these species is due to the consumption of carcasses of pelagic and mesopelagic organisms, and even insects, bypassing the benthic trophic web. Conservative (minimum) estimates of the mean weight of carcasses in diet ranged from 3 to 20%, increasing with the size of the predators and towards deeper waters. C.marinii showed a lower consumption of carcasses and a high proportion of mesopelagic fishes and cephalopods, however, the analysis of the feeding morphology and prey size leads to believe that most of these two groups of prey were consumed as carcasses. This source of food bypass the detritus food chains and connect the concentrations of macrourids to fluctuations in the abundance of epi and mesopelagic organisms and to oceanographic processes that increase their concentration and mortality (e.g. mesoscale anticyclonic eddies). Distribution, Biomass and Oceanography: Data from two seasonal bottom trawl surveys were used to provide information on distribution, abundances, densities, sizecomposition and biomass estimates for seven species: Coelorinchus marinii, Malacocephalus occidentalis, M. laevis, Lucigadus ori, Hymenocephalus billsam, Ventrifossa macropogon and V. mucocephalus. The total biomass was estimated in 5.5 and 8.3 kt respectively in winter-spring and summer-autumn. C.marinii and M.occidentalis comprised 98% of the biomass. For these two abundant species, surface maps were made with spawning areas, feeding index, sex and immature/mature ratios, and were related to oceanographic processes, providing insights on strategies and important processes regulating distribution and abundance patterns. Both species showed a marked seasonal variation in the extent and location of spawning areas. Most C.marinii females were mature (90%), suggesting an early maturation during pelagic phase and acquiring demersal habit just prior the onset of maturation, while M.occidentalis showed few matures females and settle to bottom well before maturity. Temperature rather than depth seems to be the main factor regulating the batimetric distribution of both species. We describe three processes responsible for distribution and abundance patterns found in these species. Differentpatterns of spatial segregation were found in both species, related with depth, sex and maturity. It is suggested that areas with high biomass Macrouridae (scavengers) are induced by zones of occurrence semi-permanent mesoscale processes (e.g. eddies). These processes increase productivity and enable large biomass of short-lived organisms found in the upper layers, and also increase the concentration, mortality and availability of carcasses, favoring scavenger predators. These processes may be responsible for inconsistencies in biomass of megafauna and macrofauna found in some studies, where biomass of megafauna was of the same order of magnitude or larger than macrofauna, contradicting the Eltonian principle. It is suggested that future studies attempt to relate mesoscale processes with the biomass of potential short-lived prey in surface waters and higher biomass of scavengers. This work highlights the importance of the study of ocean dynamics, combining biological and oceanographic observations, trying to understand the role of mesoscale physical processes on the distribution and abundance patterns of species.

La pesca d'arrossegament practicada al mar Mediterrani incideix sobre un rang batimètric molt ampli i afecta a nombrosos tipus de fons que presenten comunitats molt diversificades, on les espècies de peixos, crustacis, cefalòpodes, altres mol·luscs, equinoderms i d'altres macroorganismes epibentònics interaccionen entre si. D'aquí la importància de caracteritzar amb una aproximació multiespecífica els fons explotats, com la que aquí hem dut a terme, prenent en consideració no tan sols les espècies d'interès comercial sinó totes les espècies que conformen la comunitat. Els objectius concrets d'aquesta tesi estan centrats en l'estudi qualitatiu i quantitatiu dels descartaments produïts per la pesca d'arrossegament que efectua la flota espanyola en la zona del Golf de Lleó, i en aspectes relacionats a millorar la selectivitat de les xarxes emprades canviant el disseny de la malla tradicional per malla quadrada.El mostreig s'ha dut a terme a bord d'una embarcació d'arrossegament comercial, amb una freqüència setmanal, dins el període comprès entre març del 1998 i març del 2000. En total s'han analitzat 68 pesques. Totes les mostres estudiades provenen del primer vol del dia i s'han capturat a fondàries entre 50 i 500 metres.De tot el volum capturat durant l'estudi s'han identificat un total de 307 espècies pertanyent a diversos grups taxonòmics. El grup taxonòmic majoritari és el dels peixos amb 133 espècies, seguit dels crustacis, els cefalòpodes, els equinoderms i finalment el grup d'altres invertebrats. L'espècie més capturada en nombre a la pesquera del Golf de Lleó ha estat la cervellina (Leptometra phalangium) i les més capturades en biomassa han estat la sardina (Sardina pilchardus) i el lluç mediterrani (Merluccius merluccius smiridus).Pel total de la captura la fracció descartada en nombre d'individus representa el 71% mentre que la biomassa descartada és de l'ordre del 36%. La causa més important en quant a quantitat de rebuig produït és la que respon al compliment de la normativa vigent, ja sigui per les talles mínimes legals o per les captures acompanyants permeses. Els majors descartaments estacionals en termes d'abundància es donen a la primavera i l'estiu, coincidint amb l'època de reclutament de la majoria de les espècies explotades. En canvi, els descartaments estacionals en termes de biomassa són excepcionalment elevats a l'estiu i estan provocats per la captura massiva de sardina (S. pilchardus) durant aquesta època de l'any. El rebuig expressat tant en nombre com en pes disminueix en funció de l'estrat de fondària, essent la quantitat descartada major en l'estrat A (50-200 m) i menor en l'estrat C (>400 m).S'ha comprovat que el disseny de malla quadrada aplicat al cóp de les xarxes d'arrossegament fa augmentar dràsticament, tant en nombre com en pes, el percentatge d'individus escapats, disminuint a la vegada la quantitat de descartament. També s'aconsegueix un augment de la mida de primera captura (L50) de totes les espècies excepte en la bruixa de quatre taques (Lepidorhombus boscii). A més es redueix l'impacte de la pesca sobre els estocs d'individus juvenils, sobretot d'espècies que presenten una secció de cos rodona com el lluç mediterrani (M. merluccius smiridus) i el verat (Scomber scombrus), disminuint així la sobrepesca de creixement i de reclutament al mateix temps que s'assegura i es millora la venda d'exemplars de mida legal. / Multispecies Mediterranean trawl fisheries are carried out in a wide range of depths and affect different bottoms and communities. The demersal resources distributed in the trawl fishing grounds off the south-western Gulf of Lions were studied. The aim of this study is to evaluate qualitatively and quantitatively the amount of discards associated to demersal trawl fisheries in this area and to improve the selectivity of bottom trawl nets introducing square mesh codends. A weekly sampling was conducted with a chartered commercial trawler (length 23 m; 600 HP) between march 1998 to march 2000. All the samples took place during daylight at depths ranging between 50 and 500 m. A total of 68 hauls were analyzed and 307 species were identified. The main taxonomic group are fishes with 133 species followed by crustaceans, cephalopods, echinoderm and other invertebrates. Leptometra phalangium is the most abundant species in number of individuals and Sardina pilchardus and Merluccius merluccius smiridus are the most abundant in biomass.From the total catch discards represented 71% in number of individuals and 36% in biomass. The main reason to discard is the compliance with current legislation in relation to minimum landing size and TAC's.Seasonal discards were important in number of individuals during spring due to recruitment of some commercial species. In summer, large amounts of Sardina pilchardus were discarded due to legal regulations that established TAC's to small pelagic species.Discards decreased with depth. We obtain majors discards in the continental shelf and less in the slope.We realized that square mesh design in codends is better than diamond mesh design. The percentage of individuals and biomass escaped increase in square mesh codends and the fraction discarded decrease. The estimated fifty percent retention length (L50) and selection factors were higher for square mesh codends than diamond mesh codends in the most cases except for Lepidorhombus boscii. Also the L50 obtained with square mesh codends are very close to or coincide with the legal size for the majority of the species studied. This results may be explained by the different body shapes and behaviour of the individuals species. We have observed that square mesh codends contribute to reduce the impact of fisheries in immature and undersized individuals from the stock, especially in species with a round shape body like Merluccius merluccius smiridus and Scomber scombrus. Moreover, the square mesh codends assured that landings are made up of marketable lengths.