Dissertations / Theses: 'Trawling'

1

Udoff, Geoffrey. "An Alternate Trawling Method: Reduced Bycatch and Benthic Disturbance Achieved with the Wing Trawling System." ScholarWorks@UNO, 2016. http://scholarworks.uno.edu/td/2217.

Full text

Abstract:

The Wing Trawling System (WTS) was tested as an alternative to traditional shrimp capture methods in the Gulf. Compared to an otter trawl, this trawl was conceived to reduce bycatch, retain shrimp catch, and minimize seafloor disturbance. Through seventy-one paired tows, the WTS was assessed against a standard otter trawl. The WTS was found to reduce bycatch by 63-65% and reduce shrimp catch by 30-35%. Additionally, I measured the depth of the scars produced by both trawls and quantified the turbidity of the plumes behind them. The scars left by the WTS and the otter trawl were between 9.9 cm-13.6 cm. The turbidity behind the WTS was 18.6 NTU, while the turbidity behind the otter trawl was 206.8 NTU. In conclusion, the WTS offers an alternative to an otter trawl that reduces bycatch and the impact trawling has on the seafloor but results in a significant amount of shrimp loss.

APA, Harvard, Vancouver, ISO, and other styles

2

Alves, Fábio Rui Lima. "Traits of benthic assemblages subjected to different trawling pressure." Master's thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/12618.

Full text

Abstract:

Mestrado em Biologia Marinha Over time, fishing techniques improved as a response to the needs of Human populations. Alongside with the increase of fishing activities important changes in the marine ecosystems were also observed (e.g. overexploitation of stocks and habitat loss or degradation). Overfishing, bycatch, discards and ghost-fishing are some of the most discussed impacts of fishing activities, but the effect of bottom trawling should not be underestimated, since it has been proven to have a significant impact of benthic communities. Up to now the knowledge about fisheries impact on deep-sea benthic macrofaunal assemblages is scarce in Europe and, for all we know, even more in Portuguese fishery grounds. However, assessing fisheries impacts on marine ecosystems and ensuring fisheries sustainability is essential to achieve proper management of the sector and for the conservation of marine resources. In this context, the present study was carried out aiming to investigate the impact of continued trawling on benthic macrofaunal assemblages from deep muddy grounds of the burrowing crustacean Nephropsnorvegicus (Norway lobster) by comparing towed and untowed stations regarding their biodiversity, density, biomass, trophic structure, life style and body size spectra. Seven stations were studied along a transect of a highly Fished zone (Area 1, Stations 1 and 2), a Non-fished zone (Area 2, Stations 3, 4 and 5) and another Fished zone (Area 3, stations 6 and 7) during a cruise carried out in September 2012 onboard the RV Garcia del Cid (Consejo Superior de Investigaciones Cientificas) in the framework of the project IMPACT (Universidade do Algarve). In general Fished zones showed decreased heterogeneity and although the results of the multivariate analysis support a significant difference between Fished and Non-fished areas the comparisons of the biodiversity (number of families, H’, EF(n)), density and biomass in Fished and Non-fished zones are inconclusive, inconsistent or even contradict most of the literature predictions. When the trophic structure and life style spectra of the assemblages are compared the decreased heterogeneity of the Fished zones is confirmed but other patterns emerge such as the higher relative contribution of free living organisms, especially meiofaunal predators, grazers and browsers in Fished zones in contrast with the higher relative contribution of tubiculous animals in Non-fished zones, the dominance of deposit feeders over detritus feeders in Fished areas and the presence of large suspension feeders in Non-fished zones. The interpretation of the observed taxonomic and trophic structure of the assemblages is complex and must take into account sources of variability introduced by unwanted alterations of the sampling strategy and habitat heterogeneities in the study area. Overall this study constitutes a good asset for the knowledge of bottom trawling impact on macrofaunal assemblages from deep-sea habitats. It is at this point impossible to estimate the impact of 60 years of bottom trawling and regular monitoring studies are desirable. Some methodological issues arose which can be used as recommendations for future assessments of trawling impacts and monitoring of seafloor integrity: selection of adequate control area(s) must consider habitat heterogeneity, selection of the sampling gear must consider the possible selectivity of smaller samplers; the number of replicates per stations should be sufficiently large to ensure representativeness of biodiversity, abundance and biomass assessment and significance of the comparative tests; and finally, trophic structure, life style and body size spectra showed to be good indicators of change and therefore they should become a more common tool on the assessment of trawling impact. Ao longo do tempo, as artes de pesca têm vindo a evoluir como resposta às crescentes necessidades da população Humana. Ao mesmo tempo que a indústria pesqueira tem vindo a crescer têm-se vindo a observar importantes mudanças nos ecossistemas marinhos (ex. sobreexploração de recursos pesqueiros e perda ou degradação da biodiversidade). A sobre-pesca, pesca de espécies acessórias, rejeições e pesca fantasma são os impactos causados pelas pescas que geram maior preocupação, mas o efeito devastador de pesca de arrasto no fundo oceânico não deve ser subestimado, devido ao seu reconhecido impacto nas comunidades bentónicas. Até aos dias de hoje o conhecimento acerca do impacto em comunidades bentónicas de mar profundo é escasso na Europa e ainda menor em fundos oceânicos Portugueses. Contudo, a avaliação dos impactos da indústria pesqueira em fundos marinhos e nos seus ecossistemas é essencial para obter uma gestão apropriada do setor e para um uso mais sustentável dos recursos biológicos. Neste contexto, este estudo tem como objectivo avaliar o impacto da contínua pressão das pescas de arrasto em comunidades de macrofauna bentónica em fundos lamosos de mar profundo nos habitats do crustáceo Nephrops norvegicus (Lagostim), através da comparação de fundos impactados com fundos nãoimpactados, considerando a análise da biodiversidade, densidade, biomassa, estrutura trófica, espectro de tamanhos e modos de vida. Foram estudadas sete estações ao longo de um transeto, das quais, as primeiras duas estações (estações 1 e 2, área 1) correspondem a uma zona impactada, as seguintes três estações a uma zona não sujeita a pesca de arrasto (estações 3, 4 e 5, área 2,) e, por fim, duas estações (estações 6 e 7, área 3) novamente sujeitas a pressões de pesca de arrasto. A expedição oceanográfica foi realizada em Setembro de 2012 a bordo do navio RV Garcia del Cid (Consejo Superior de Investigaciones Cientificas) inserido no projecto IMPACT (Universidade do Algarve). De um modo geral, as zonas pescadas mostram uma menor heterogeneidade e embora os resultados da análise multivariada suportem uma diferença significante entre zonas pescadas e não-pescadas, as comparações de biodiversidade (número de familias, H’, EF(n)), densidade e biomassa) em zonas pescadas e não-pescadas são inconclusivas, inconsistentes e por vezes contraditórias quando comparadas com a literatura. Quando a estrutura trófica e o estilo de vida das comunidades são comparados, a pequena heterogeneidade nas zonas pescadas é confirmada, mas outros factores emergem, como a contribuição de animais de mobilidade livre, especialmente predadores de meiofauna e raspadores em zonas pescadas, em contraste com a alta contribuição de animais tubículos em zonas não-pescadas, a dominância de detritívoros que se alimentam de matéria orgânica associada ao sedimento sobre detritívoros que se alimentam de matéria orgânica particulada, em zonas pescadas e a presença de grandes suspensívoros em zonas não-pescadas. A interpretação dos resultados taxonómicos e da estrutura trófica é complexa e deve ter em conta variações introduzidas por alterações não esperadas na estratégia de amostragem e diferenças de habitat das zonas estudadas. No geral, este estudo contribui para o conhecimento do impacto de pescas de arrasto em comunidades de macrofauna bentónica de ambientes marinhos profundos. Nestas condições é dificil avaliar quais os efeitos de 60 anos de pressões de pesca de arrasto e futuros estudos são desejáveis. Surgiram alguns problemas metodológicos, o que pode servir como recomendações para futuros estudos de impactos de pesca de arrasto e monitorização da integridade dos fundos oceânicos: uma boa selecção de áreas controlo deve ser considerada; a seleção de tipos de amostradores deve ter em conta a selectividade de amostradores menores; o número de réplicas por estação deve ser suficiente para garantir representatividade da biodiversidade, abundância e biomassa, e a significância de testes comparativos; e por fim, estrutura trófica, espetro de tamanhos e modo de vida mostraram ser bons indicadores de diferenças entre as duas zonas, logo deveriam ser usados mais regularmente na avaliação de impactos de pesca de arrasto.

APA, Harvard, Vancouver, ISO, and other styles

3

Sterling, David J. "Modelling the physics of prawn trawling for fisheries management /." The Gap, Qld. : Sterling Trawl Gear Services, 2005. http://adt.curtin.edu.au/theses/available/adt-WCU20050921.093622.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Sterling, David John. "Modelling the physics of prawn trawling for fisheries management." Thesis, Curtin University, 2005. http://hdl.handle.net/20.500.11937/2573.

Full text

Abstract:

Management of prawn trawling fisheries is a difficult task due to the competing interests of strongly motivated stakeholders and interest groups. This occurs because prawn trawling operations are technically complex, require large capital investments and exhibit high running costs while owners have limited property rights over the resources that they harvest. Prawn stocks are public resources and are managed with a view to provide maximum benefit to the broad community. Additionally their exploitation also involves the incidental capture of significant numbers of other animals of no commercial value (bycatch) and causes impacts on seabed morphologies, which are involved in many diverse ecosystem processes. At the policy level an intention to manage trawl fisheries in a comprehensive way is backed by a mandated approach that is designed to capture all of the above issues and interests. That approach is termed Ecological Sustainable Development (ESD). The work in this thesis is designed to produce a prediction tool for prawn trawling performance that is based on modelling the physical nature of prawn trawling activities. It is proposed that the resulting tool is essential for working to manage the multi-dimensional aspects of prawn trawling fisheries. Three discrete objectives for the thesis are; to expand and improve an existing Prawn Trawling Performance Model (PTPM) so that it is more accurate and relevant to a broader range of questions, to evaluate the capacity of the PTPM to predict the performance characteristics of real prawn trawling operations in terms of both engineering and catching performance and to investigate the problem space surrounding prawn trawl fisheries to identify and develop applications for the model. A rudimentary PTPM (Sterling 2000b) is expanded through the analysis of further empirical data collected for model and full-scale trawl gear.ght area of improvement to the PTPM were considered and in all cases significant changes were made. The accuracy of the new form of the model is here tested by comparing performance predictions with measurements of trawling performance for a variety of industrial trawl systems operated in the Queensland East Coast Trawl Fishery and also through comparing predicted trawling performance with prawn catches returned for trawlers operating in the Northern Prawn Fishery over the years 1970 to 2000. In the first case, errors in predicting swept area rate, considered an important performance parameter, were less than 5%. Fine scale issues were explored using the available sea mal data and a number of areas of concern within the model are highlighted. These relate to accurately quantifying the forces involved in the interaction of the trawl gear with the seabed and accurately accounting for the interaction between components within trawl systems. In the second case, the results suggest that between 50% and 60% of the variation in the seasonal catching performance of trawlers in the NPF is explained by predictions of swept area rate derived by the PTPM from the available data for that fishery. A comprehensive survey of applications for the PTPM is conducted in context with approaching the management of prawn trawling fisheries using the principles of ESD as defined by the National Strategy for ESD (1992). The Northern Prawn Fishery is used as a case study to explore in finer detail applications for the PTPM. Issues arising from the implementation of some of the applications are discussed.

APA, Harvard, Vancouver, ISO, and other styles

5

Sterling, David John. "Modelling the physics of prawn trawling for fisheries management." Curtin University of Technology, School of Physical Sciences, 2005. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=16093.

Full text

Abstract:

Management of prawn trawling fisheries is a difficult task due to the competing interests of strongly motivated stakeholders and interest groups. This occurs because prawn trawling operations are technically complex, require large capital investments and exhibit high running costs while owners have limited property rights over the resources that they harvest. Prawn stocks are public resources and are managed with a view to provide maximum benefit to the broad community. Additionally their exploitation also involves the incidental capture of significant numbers of other animals of no commercial value (bycatch) and causes impacts on seabed morphologies, which are involved in many diverse ecosystem processes. At the policy level an intention to manage trawl fisheries in a comprehensive way is backed by a mandated approach that is designed to capture all of the above issues and interests. That approach is termed Ecological Sustainable Development (ESD). The work in this thesis is designed to produce a prediction tool for prawn trawling performance that is based on modelling the physical nature of prawn trawling activities. It is proposed that the resulting tool is essential for working to manage the multi-dimensional aspects of prawn trawling fisheries. Three discrete objectives for the thesis are; to expand and improve an existing Prawn Trawling Performance Model (PTPM) so that it is more accurate and relevant to a broader range of questions, to evaluate the capacity of the PTPM to predict the performance characteristics of real prawn trawling operations in terms of both engineering and catching performance and to investigate the problem space surrounding prawn trawl fisheries to identify and develop applications for the model. A rudimentary PTPM (Sterling 2000b) is expanded through the analysis of further empirical data collected for model and full-scale trawl gear. ght area of improvement to the PTPM were considered and in all cases significant changes were made. The accuracy of the new form of the model is here tested by comparing performance predictions with measurements of trawling performance for a variety of industrial trawl systems operated in the Queensland East Coast Trawl Fishery and also through comparing predicted trawling performance with prawn catches returned for trawlers operating in the Northern Prawn Fishery over the years 1970 to 2000. In the first case, errors in predicting swept area rate, considered an important performance parameter, were less than 5%. Fine scale issues were explored using the available sea mal data and a number of areas of concern within the model are highlighted. These relate to accurately quantifying the forces involved in the interaction of the trawl gear with the seabed and accurately accounting for the interaction between components within trawl systems. In the second case, the results suggest that between 50% and 60% of the variation in the seasonal catching performance of trawlers in the NPF is explained by predictions of swept area rate derived by the PTPM from the available data for that fishery. A comprehensive survey of applications for the PTPM is conducted in context with approaching the management of prawn trawling fisheries using the principles of ESD as defined by the National Strategy for ESD (1992). The Northern Prawn Fishery is used as a case study to explore in finer detail applications for the PTPM. Issues arising from the implementation of some of the applications are discussed.

APA, Harvard, Vancouver, ISO, and other styles

6

Bloomfield, Helen J. "Compliance and control : a multidisciplinary assessment of prohibited trawling areas." Thesis, University of Newcastle Upon Tyne, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613446.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Stella, Leonie. "Trawling deeper seas : the gendered production of seafood in Western Australia /." Access via Murdoch University Digital Theses Project, 1998. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20040913.155811.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Magorrian, Bridgeen Helen. "The impact of commercial trawling on the benthos of Strangford Lough." Thesis, Queen's University Belfast, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318751.

Full text

APA, Harvard, Vancouver, ISO, and other styles

9

Britton, Adam Robert Corden. "Flight performance, echolocation and prey capture behaviour in trawling Myotis bats." Thesis, University of Bristol, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319104.

Full text

APA, Harvard, Vancouver, ISO, and other styles

10

Stella, Leonie C. "Trawling deeper seas: the gendered production of seafood in Western Australia." Thesis, Stella, Leonie C. (1998) Trawling deeper seas: the gendered production of seafood in Western Australia. PhD thesis, Murdoch University, 1998. https://researchrepository.murdoch.edu.au/id/eprint/346/.

Full text

Abstract:

This thesis explores the sexual division of labour in three worksites associated with the Western Australian Fishing industry: fishers' households, a seafood processing company and fishing vessels. There has been no previous substantial study of the labour of women in Australian fishing industries. My research has been primarily undertaken by interviewing women and men who work in the Western Australian fishing industry, and my findings are presented through a comparison with overseas literature relative to each site. As I found, in the households of fishermen, women do unpaid and undervalued labour which includes servicing men and children; managing household finances and operating fishing enterprises. In seafood processing companies women are allocated the lowest paid and least rewarding work which is regarded as women's work. On-the factory floor issues of class, race/ ethnicity and gender intersect so that the majority of women employed in hands-on processing work are migrant women from a non-English speaking background. The majority of women who work at sea are cook/ deckhands who are confronted by a rigid sexual division of labour, and work in a hyper-masculine workplace. The few other women who have found a niche which enables them to enjoy an outdoor lifestyle while they earn their own living, are those who work as autonomous independent small boat fishers. In each site there is evidence that women, individually and collectively, exercise some power in determining how and where they work, but they remain marginalised from the more lucrative sites of the industry, and have limited access to economic and social power.

APA, Harvard, Vancouver, ISO, and other styles

11

Stella, Leonie C. "Trawling Deeper Seas: the Gendered Production of Seafood in Western Australia." Murdoch University, 1998. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20040913.155811.

Full text

Abstract:

This thesis explores the sexual division of labour in three worksites associated with the Western Australian Fishing industry: fishers' households, a seafood processing company and fishing vessels. There has been no previous substantial study of the labour of women in Australian fishing industries. My research has been primarily undertaken by interviewing women and men who work in the Western Australian fishing industry, and my findings are presented through a comparison with overseas literature relative to each site. As I found, in the households of fishermen, women do unpaid and undervalued labour which includes servicing men and children; managing household finances and operating fishing enterprises. In seafood processing companies women are allocated the lowest paid and least rewarding work which is regarded as "women's work". On-the factory floor issues of class, race/ ethnicity and gender intersect so that the majority of women employed in hands-on processing work are migrant women froma non-English speaking background. The majority of women who work at sea are cook/ deckhands who are confronted by a rigid sexual division of labour, and work in a hyper-masculine workplace. The few other women who have found a niche which enables them to enjoy an outdoor lifestyle while they earn their own living, are those who work as autonomous independent small boat fishers. In each site there is evidence that women, individually and collectively, exercise some power in determining how and where they work, but they remain marginalised from the more lucrative sites of the industry, and have limited access to economic and social power.

APA, Harvard, Vancouver, ISO, and other styles

12

Houston, Robert Duncan. "Prey detection and evaluation by echolocation in aerial feeding and trawling bats." Thesis, University of Bristol, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313009.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

Samy-Kamal, Mohammed. "Evaluation of some management measures for trawling fishery of the western Mediterranean." Doctoral thesis, Universidad de Alicante, 2014. http://hdl.handle.net/10045/45169.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Simpson, Anne W. "An Investigation of the Cumulative Impacts of Shrimp Trawling on Mud Bottom Fishing Grounds in the Gulf of Maine: Effects on Habitat and Macrofaunal Community Structure." Fogler Library, University of Maine, 2003. http://www.library.umaine.edu/theses/pdf/SimpsonAW2003.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

15

Paradis, Vilar Sarah. "Physical and Biogeochemical Impacts of Deep Bottom Trawling in Sedimentary Environments of the Western Mediterranean." Doctoral thesis, Universitat Autònoma de Barcelona, 2020. http://hdl.handle.net/10803/670718.

Full text

Abstract:

La pesca d’arrossegament és considerada una de les activitats antròpiques més nocives pel medi marí, degut a la seva extensió global, i l’elevada freqüència i intensitat. Com que aquest art està en contacte continu amb el fons marí, pot modificar la morfologia del fons i resuspendre grans volums de sediment, que poden ser advectats, erosionant els caladors i alterant les propietats del sediment. Amb la expansió global de la pesca d’arrossegament a caladors més profunds des dels anys 1950, s’estima que els impactes ocasionats per aquesta activitat poden ser intensificats, però encara hi ha una manca d’estudis d’aquests. L’objectiu d’aquesta tesi era estudiar els impactes físics i biogeoquímics de la pesca d’arrossegament profunda al marge occidental Mediterrani. Els impactes físics es van estudiar als canyons submarins catalans mitjançant l’anàlisi de més de 30 testimonis de sediment dels flancs i eixos dels sis canyons més importants de la costa. Aquest estudi va observar que els caladors, als flancs dels canyons, estaven erosionats, i aquest sediment és desplaçat als eixos dels canyons, duplicant i quadruplicant els ritmes de sedimentació degut a la expansió dels caladors a ambients més profunds als anys 1960 i 1970. Aquest impacte només s’observa en zones properes als caladors, i els ritmes de sedimentació induïts per la pesca disminueixen a major distància dels caladors. Un segon augment en el ritme de sedimentació va ser identificat en un dels canyons al principi dels 2000 degut a una modernització recent de la flota d’arrossegament, ressaltant la relació entre la tecnificació de la flota i les alteracions en els règims sedimentaris. Aquestes alteracions físiques del fons marí també modifiquen la biogeoquímica dels caladors, disminuint el contingut de matèria orgànica. Al Golf de Castellammare (Sicília), l’acumulació de matèria orgànica fresca i nutritiva en un calador erosionat i empobrit en nutrients (20-60 % menys matèria orgànica) va estimular la resposta microbiana. Tot i això, la elevada freqüència dels vaixells d’arrossegament ràpidament erosiona aquest sediment recent, inhibint la recuperació dels caladors del Golf de Castellammare. Aquest fet ens va suggerir que èpoques de veda podrien mitigar els impactes de la pesca d’arrossegament. No obstant, la comparació de testimonis de sediment agafats en diferents èpoques, incloent al final d’una veda de 2 mesos, als caladors del canyó de Palamós va demostrar que aquesta estratègia és insuficient per mitigar els impactes de la pesca d’arrossegament. El contingut de matèria orgànica als caladors estaven especialment empobrits en els compostos més làbils (52-70 % menys), perjudicant la preservació de matèria orgànica als sediments profunds i reduint la qualitat nutritiva dels caladors, el qual podria tenir impactes transcendentals a les comunitats bentòniques, incloent les espècies comercials. Aquests impactes van persistir durant totes les èpoques de mostreig, fins i tot després de la veda, degut als baixos ritmes de sedimentació en aquesta zona. Aquests resultats ressalten la vulnerabilitat i baixa resiliència d’ambients profunds, i recalca que la pesca d’arrossegament profunda perjudica la integritat dels fons marí més enllà de la seva capacitat de recuperació. Considerant l’expansió global dels caladors de pesca d’arrossegament, aquests impactes podrien ocórrer en talussos continentals a escala global. La pesca de arrastre es considerada una de las actividades antrópicas más nocivas para el medio marino, debido a su extensión global, y la elevada frecuencia e intensidad. Puesto que este arte de pesca está en contacte continuo con el fondo marino, puede modificar la morfología del fondo y resuspender grandes volúmenes de sedimento, que pueden ser advectados, erosionando los caladeros y alterando las propiedades del sedimento. Con la expansión global de la pesca de arrastre a caladeros más profundos desde los años 1950, se estima que los impactos ocasionados por esta actividad pueden ser intensificados, pero todavía hay una falta de estudios. El objetivo de esta tesis era estudiar los impactos físicos y biogeoquímicos de la pesca de arrastre profunda en el margen occidental Mediterráneo. Los impactos físicos se estudiaron en los cañones submarinos catalanes mediante el análisis de más de 30 testimonios de sedimento de los flancos y ejes de los seis cañones más importantes de la costa. Este estudio observó que los caladeros, en los flancos de los cañones, estaban erosionados, y este sedimento es desplazado a los ejes de los cañones, duplicando y cuadriplicando los ritmos de sedimentación debido a la expansión de los caladeros a ambientes más profundos en los años 1960 y 1970. Este impacto sólo se observó en zonas próximas a los caladeros, y los ritmos de sedimentación inducidos por la pesca disminuyen a mayor distancia de los caladeros. Un segundo aumento en el ritmo de sedimentación fue identificado en uno de los cañones a principio de los 2000 debido a una modernización reciente de la flota de arrastre, resaltando la relación entre la tecnificación de la flota y las alteraciones en los regímenes sedimentarios. Estas alteraciones físicas en el fondo marino también modifican la biogeoquímica de los caladeros, disminuyendo su contenido de materia orgánica. En el Golfo de Castellammare (Sicilia), la acumulación de materia orgánica fresca y nutritiva en un caladero erosionado y empobrecido en nutrientes (20-60 % menos materia orgánica) estimuló la respuesta microbiana. A pesar de esto, la elevada frecuencia de los barcos de arrastre rápidamente erosiona este sedimento reciente, inhibiendo la recuperación de los caladeros del Golfo de Castellammare. Este hecho nos sugirió que épocas de veda podrían mitigar los impactos de la pesca de arrastre. No obstante, la comparación de testimonios de sedimento recuperados en diferentes épocas, incluyendo al final de una veda de 2 meses, en los caladeros del cañón de Palamós demostró que esta estrategia de gestión es insuficiente para mitigar los impactos de la pesca de arrastre. El contenido de materia orgánica en los caladeros estaba especialmente empobrecido en los compuestos más lábiles (52-70 % menor), perjudicando la preservación de materia orgánica en los sedimentos profundos y reduciendo la calidad nutritiva de los caladeros, lo cual podría tener impactos transcendentales en las comunidades bentónicas, incluyendo las especies comerciales. Estos impactos persistieron en todas las épocas de muestreo, incluso después de la veda, debido a los bajos ritmos de sedimentación en esta zona. Estos resultados resaltan la vulnerabilidad y baja resiliencia de ambientes profundos, y recalca que la pesca de arrastre profunda perjudica la integridad del fondo marino más allá de su capacidad de recuperación. Considerando la expansión global de los caladeros de pesca de arrastre, estos impactos podrían ocurrir en taludes continentales a escala global. Bottom trawling is considered one of the most harmful anthropogenic activities in the marine environment given its widespread occurrence, high frequency, and intensity. Since bottom trawling gear are in continuous contact with the seafloor, it can modify seabed morphology by erasing natural sedimentary structures and resuspend large volumes of sediment, which can be advected from trawling grounds, eroding the seafloor and altering sediment properties. With the global expansion of bottom trawling to deeper fishing grounds since the mid-XXst century, it is expected that the impacts caused by this activity will be intensified, but studies assessing them are still scarce. The aim of this thesis was to study the physical and biogeochemical impacts of deep bottom trawling in the Western Mediterranean margin. The physical impact of bottom trawling in submarine canyons of the Catalan margin was studied through the analyses of over 30 sediment cores collected in canyon flanks and axes of six major submarine canyons incising the continental slope. This study observed that trawling grounds located along the canyon flanks are highly eroded, and this sediment is displaced towards the canyon axis, leading to a two- to four-fold increase in sedimentation rates in their axes since the expansion of bottom trawling grounds to deeper environments during the 1960s and 1970s. Trawling-enhanced sedimentation in these canyons are limited to areas located next to bottom trawling grounds, and trawling-derived sedimentation rates decrease towards the lower canyon axis with greater distance from bottom trawling grounds, leaving deeper areas unaffected. A second increase in sedimentation rates was observed in one of the canyons in the early XXIst century derived from the recent modernization of bottom trawling fleets, highlighting the clear interrelation between fleet technification and the modification of sedimentary regimes. These continuous physical alterations can also modify the biogeochemistry of deep bottom trawling grounds, depleting sedimentary organic matter. In the Gulf of Castellammare (Sícily), the accumulation of fresh and nutritionally rich organic matter in nutrient-deprived (20-60 % less organic matter) and eroded deep bottom trawling stimulated the microbial response, causing high turnover rates of labile organic matter. However, the high trawling frequency quickly erodes freshly-accumulated sediment, inhibiting the recovery of fishing grounds in the Gulf of Castellammare. This initially suggested that temporal trawling closures could mitigate the impacts of bottom trawling. However, the comparison of sediment cores collected during several seasons, including towards the end of a 2-month trawling closure in fishing grounds of Palamós Canyon revealed that this management strategy is insufficient to mitigate the impacts of bottom trawling. Organic matter in the trawled site was especially impoverished in the most labile biomarkers (52-70 % loss), hampering the preservation of organic matter in deep-sea sediments and diminishing the nutritional quality on trawling grounds, which could have transcendental impacts on benthic communities, including the targeted commercial species. These impacts persisted in every sampling season, even after the temporal trawling closure, since the low sedimentation rates of the area is not capable of restoring these fishing grounds. These results highlight the vulnerability and low resiliency of deep-sea environments, and stresses that deep-sea trawling damages the seafloor's integrity beyond repair. Considering the global expansion of bottom trawling grounds, these impacts could be occurring in trawled continental slopes worldwide.

APA, Harvard, Vancouver, ISO, and other styles

16

Mafwila, Samuel Kakambi. "Ecosystem effects of bottom trawling in the Benguela current system : experimental and retrospective data analyses." Doctoral thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/11664.

Full text

APA, Harvard, Vancouver, ISO, and other styles

17

Dorn, Martin William. "Hierarchical models of fishing behavior by factory trawlers in midwater-trawl fishery for Pacific hake (Merluccius productus) /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/5288.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Gilkinson, Kent Dennis. "Impacts of otter trawling on infaunal bivalves living in sandy bottom habitats on the Grand Banks." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ54847.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

Cotterell, Stephen Paul. "Fish landings, discards and benthic material from demersal trawling in the western English Channel (ICES VIIe)." Thesis, University of Plymouth, 2006. http://hdl.handle.net/10026.1/2751.

Full text

Abstract:

This study examined the impact of inshore single boat otter trawling from Newlyn, Looe, Plymouth and Salcombe and pair boat demersal trawling from Looc and Plymouth on the benthic environment off the SW peninsula of the UK between 1998 and 2000. Fish and shellfish species (54 and 11 species respectively) were measured at sea and the non-fish material (124 species) was analysed later. Overall 79.8 % of the sample was landed fish and shellfish, 15.8 % was discarded fishes and 4.4 % was invertebrates and other material (by weight). Related information about the substrate and tide were generated from British Geological Survey data and a computer simulation of the maximum mean tidal strength. In agreement with the different abiotic regime, the dominant fishes were different in Newlyn and the other ports. According only to port, the Looe and Plymouth samples were not significantly different, either as full samples or for their fish and non-fish components. The Salcombe samples were not significantly different to those from Looc or Plymouth for the non-fish part of the sample. Including the type of trawling meant that the greatest similarity was for the non-fish part of the sample although the relative amounts of the components varied. The pair trawling samples contained more landed, less discarded and less non-fish material than their single boat equivalents. Pair trawl samples also contained fewer examples of large invertebrate species. Several within and between-species relationships were explored to assess the wider interpretation of the fish community data. This examined size of Raja spp., several predator-prey relationships and the utility of Marlhasterias glacialis as an indicator of fishing disturbance. Disturbance as measured by Abundance Biomass Comparison was similar whether according to the non-fish or full sample, and suggested that the whole region was relatively undisturbed (with Newlyn apparently the most impacted area). Analysis of the relative contribution of selected groups to taxonomic diversity showed the derived conservation priorities for 'orders' of fishes were Elasmobranches > Pleuronectiformes > Gadiformes. In general, the fact of 'losing' orders of fishes was more important for single rather than pair trawl samples, which suggests that single boat samples were collected from structurally more complex areas supporting a wider taxonomic diversity. The analysis of groups for conservation priority was also carried into the invertebrates with echinoderms being highly influential for Newlyn. Taxonomic diversity (A+ and A) was also proposed as an addition to the definition of 'Good Environmental Status' according to the proposed EU Marine Strategy Directive. When examining the abiotic and biotic data sets, the fish species bore the closest similarity to the abiotic data suggesting that much of the study area was dominated by similar invertebrate species that tended to be scavengers and in most analyses the positive influence of the voluntary Inshore Potting Agreement management regime was evident. In a novel analysis, there was broad agreement between the data and literature sources for the location of the fishes in relation to the substrates and for eight of the most commonly occurring species it was possible to be more precise in their substrate preferences than suggested from the literature. The landed fish part of the sample was shown to be a statistically good approximation of the landed part of the haul (for which the commercial data was known) in > 95 % of the hauls. Finally, data on the commercial landings for each port show that the boats sampled in this study were representative of these ports.

APA, Harvard, Vancouver, ISO, and other styles

20

Di, Maio Federico <1985&gt. "Spatial based approach to fisheries management. An application to bottom trawling in the strait of Sicily." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amsdottorato.unibo.it/10422/1/PhD%20Final%20Thesis_Federico%20Di%20Maio.pdf.

Full text

Abstract:

At the beginning of my thesis project, considering that some stocks are in overfishing status due to both high fishing effort and high level of juveniles in the catch, my main purpose was to understand how to contribute to improving the state of the fishery resources of the Mediterranean Sea. To mitigate the overfishing, the General Fisheries Commission for the Mediterranean (GFCM) adopted several Fishery Restricted Areas, which are geographically defined areas where some specific fishing activities are temporarily or permanently banned or restricted in order to reduce the exploitation patterns and conservation of specific stocks as well as of habitats and deep-sea ecosystems, including the Essential Fish Habitats (EFH) and the Vulnerable Marine Ecosystems (VME). Considering that GFCM established 3 Fisheries Restricted Areas (FRAs) in the Strait of Sicily (SoS) in 2016 aimed at protecting the nursery areas of the deep-water rose shrimp (DPS, Parapenaeus longirostris – Lucas, 1846) and the European hake (HKE, Merluccius merluccius – Linnaeus, 1758) to reduce the exploitation pattern of undersized species, in my thesis project I devoted myself to evaluate the effect of the FRAs on the status stock and the fishery performance using a spatial bio-economic model.

APA, Harvard, Vancouver, ISO, and other styles

21

Knight, Emily P. "The Effects of Trawling on Benthic Habitats: An Analysis of Recovery in the Western Gulf of Maine Closure." Fogler Library, University of Maine, 2005. http://www.library.umaine.edu/theses/pdf/KnightEP2005.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Atkinson, Lara Jane. "Effects of demersal trawling on marine infaunal, epifaunal and fish assemblages: studies in the southern Benguela and Oslofjord." Doctoral thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/6224.

Full text

Abstract:

This thesis investigates the impacts of the demersal trawl fishery on infaunal, epifaunal and fish assemblages in the southern Benguela upwelling system for the first time. In the absence of representative areas of similar habitat protected from trawling in the southern Benguela region, infaunal and epifaunal assemblages were compared between heavily and lightly trawled areas to assess the impacts of the otter-trawl fishery. Infauna were sampled at four sites, from southern Namibia to near Cape Town by means of five replicate grab samples at each paired heavily and lightly trawled area. Invertebrate epifauna were sampled at two sites in heavily and lightly trawled areas using a finemeshed otter trawl. Sites ranged in depth from 350-450 m in unconsolidated sediment habitat. Epifaunal assemblages showed greater differences at heavily trawled areas with significantly reduced species diversity, average number of species and individuals. Several epifaunal species were absent from heavily trawled areas highlighting their vulnerability to impacts of trawling. Multivariate analyses show significant differences in composition of both infaunal and epifaunal assemblages among the sites and between trawling treatments at all sites. The results of this study suggest that intense trawling activities are at least partially responsible for significantly altering benthic community composition, affecting epifauna to a greater measurable extent than infauna. Biological Traits Analysis (BTA) was used to explore potential changes in ecological functioning of benthic assemblages, comparing areas exposed to heavy and light trawl intensities in the Benguela system. BTA incorporates biological traits (life-history, morphology and behaviour) of infaunal and epifaunal species with biomass, capturing a broad range of information of marine benthic assemblages. Seventeen percent of the infaunal traits analysed showed a significant difference between heavily and lightly trawled areas. Twenty-four percent of epifaunal biological traits investigated were significantly different between areas of heavy and light trawling. This study suggests that more intense trawling modifies some trait constituents of the benthic assemblage in the southern Benguela region, confirming the sensitivity of functional traits analysis in detecting changes induced by trawling disturbance. Biological traits analysis of benthic invertebrates shows promise as a practical technique for incorporation into monitoring programmes and for developing indicators of benthic ecosystem health, needed for implementation of an ecosystem approach to fisheries management in South Africa. A lack of representative untrawled areas in the trawl grounds of southern Africa precluded investigations comparing trawl impacts with unfished reference sites. A bilateral agreement between South Africa and Norway (NORSA) provided the opportunity to conduct experiments in an untrawled area of Oslofjord, Norway, where a shrimp trawl fishery for Pandalus borealis operates nearby. Infauna Abstract 2 were sampled at four untrawled sites in Oslofjord with five replicate grabs after which an Agassiz beam sled was dragged across two of the sites (impact sites) four times, simulating a trawl disturbance. Infauna were re-sampled at all four sites immediately after trawling (post-impact), 14 days and 64 days after the impact to monitor recovery of infaunal populations. Multivariate analyses comparing the impact sites with paired control sites for each sampling occasion showed no significant differences in infaunal assemblages at any stage of the experiment. Whilst it is considered possible that the trawl simulation was not a sufficient impact to represent that of a commercial trawl effect, it is considered more likely that trawl activities in Oslofjord do not inflict measurable impacts on infaunal assemblages. However, the impact of trawling on epifaunal assemblages in Oslofjord was not investigated in this study. Annual research survey data collected over the past 24 years (1986-2009) provide an opportunity to explore long-term demersal fish assemblage composition changes on the west coast of South Africa. Differences in spatial (latitude and depth) and temporal (seasonal and annual) factors were examined using multivariate analyses. Possible long-term changes were investigated using the Sequential T-test Algorithm to detect Regime Shifts (STARS). Results indicate geographic differences in fish assemblage composition from the northern to the southern region on the west coast of South Africa. The fish community composition is also clearly influenced by depth with a distinct change in fish assemblages in the shelf break region between 300 m and 400 m. Multivariate analyses also show two clear temporal changes in assemblage composition, firstly, in the early 1990s and secondly, in the mid- 2000s. STARS analyses detect long-term shifts in 27% of demersal species with the majority of speciesâ shifts detected either in the early- to mid-1990s or in the past decade (2002 to 2009). Multivariate analyses among year groups reveal an increase in three fast-growing, early maturing species and decreases in two slow-growing, long-lived species. STARS analysis detected increases in two of the same fast-growing species, decreases in an additional four slow-growing, long-lived species, but four other slow-growing, long-lived species showed the opposite trend (i.e. increases). The hypothesis of an increase in fast-growing, early maturing species and a decline in slow-growing, longlived species in fished systems is therefore only partially supported by these findings. Shifts in demersal fish assemblages coincide temporally with spatial shifts observed in small pelagic species and west coast rock lobster. The shifts in the demersal fish assemblage composition detected in this study are probably a reflection of long-term indirect effects of fishing in combination with environmental changes. Abstract 3 The response of benthic invertebrate assemblages to two levels of fishing intensity in the southern Benguela region justifies regular monitoring of epifauna during existing annual demersal research surveys and infaunal monitoring through dedicated, periodic sampling initiatives. Demersal fish assemblage data should be regularly assessed for changes in community composition. Representative protected areas can serve as reference areas against which fishing impacts could be assessed and improve our understanding of ecosystem effects of demersal fishing.

APA, Harvard, Vancouver, ISO, and other styles

23

Jayiya, Terence Phinda. "Modelling the relative impacts of trawling and longlining on Cape hake Merluccius capensis on the inshore Agulhas bank." Master's thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/6105.

Full text

Abstract:

Bibliograpy: leaves 87-101. A Geographic Information System (GIS) is used to elucidiate vertical and horizontal patterns of distribution of Merluccius capensis on the inshore south coast (20°-27°E) of South Africa. Catch data used to compare the size distribution in catches made by commercial trawls and longlines off the South Coast (20°E). Results show that M.capensis size increases with depth and that the distribution of fish < 30 cm is mostly west of 23° E with isolated pockets east of that region. No seasonal differences were found in the distribution of this species. Spatial mapping of survey trawl and longline grounds of the Agulhas bank whereas longlines operate over rocky areas. Size comparisons of the catches of the two fishing methods reveal that longlines catch very few fish that are < 60 cm whereas trawl cataches are dominated by M. capensis of length < 60 cm. Analyses also revealed sex compostion in longline cataches to be different to that of trawls. All these results are discussed in relation to the ecology of M. capensis and the areas where data come from. Using size selectivity properties, the potential impacts of longlining and commercial trawling on the South Coast M. capensis (east of 20° E) are modelled with a yield per recruit and spawner biomass per recruit model. First, the age-specific selectivity vectors of the two fleets are estimated from catch data (length frequencies).

APA, Harvard, Vancouver, ISO, and other styles

24

Fraser, Helen M. "Do fish predators in the North Sea live beyond their means is prey production sufficient to meet consumption? /." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources, 2008. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=24693.

Full text

APA, Harvard, Vancouver, ISO, and other styles

25

Babcock, Elizabeth A. "Dynamic programming models of fishermen's choice of target species assemblage in the U.S. west coast groundfish trawl fishery /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/5340.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

McCallum, Barry R. "The impact of mobile fishing gear on benthic habitat and the implications for fisheries management." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ62398.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

27

Wolf, Milena Regina [UNESP]. "Ecologia das populações e comunidades dos camarôes Decapoda no litoral norte de Santa Catarina." Universidade Estadual Paulista (UNESP), 2014. http://hdl.handle.net/11449/113943.

Full text

Abstract:

Made available in DSpace on 2015-01-26T13:21:24Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-02-27Bitstream added on 2015-01-26T13:30:32Z : No. of bitstreams: 1 000792978_20150127.pdf: 384795 bytes, checksum: e2d28327453e133ac0c4f145810767c2 (MD5) Bitstreams deleted on 2015-01-30T18:23:36Z: 000792978_20150127.pdf,Bitstream added on 2015-01-30T18:24:05Z : No. of bitstreams: 1 000792978.pdf: 3958190 bytes, checksum: 616d234386031ca87d88755d7374b280 (MD5) Frente aos impactos causados pela ação antrópica no ambiente marinho, a proposta desse trabalho foi fornecer subsídios para a conservação das espécies, na área adjacente à Baía da Babitonga, estado de Santa Catarina, Brasil. O objetivo foi inventariar as espécies existentes da comunidade de camarões marinhos, detectar e descrever padrões gerais na sua distribuição espaço-temporal e relação às variáveis ambientais que caracterizam seu habitat. Portanto, foram mensurados os índices ecológicos e testados os parâmetros ambientais aos biológicos com análise multivariada. Os camarões foram coletados em julho de 2010 a junho de 2011, junto às variáveis ambientais, como temperatura e salinidade da água e textura e conteúdo de matéria orgânica do sedimento. Utilizou-se um barco camaroneiro equipado com redes double-rig, o qual percorreu cinco pontos paralelos a costeira com profundidades de 5, 8, 11, 14 e 17 m. A riqueza total chegou a doze espécies, pertencendo a três superfamílias, seis famílias e onze gêneros. Dessas, seis espécies de camarões peneídeos são comercializados: Xiphopenaeus kroyeri, Artemesia longinaris, Pleoticus muelleri, Farfantepenaeus brasiliensis, Farfantepenaeus paulensis e Litopenaeus schmitti. As demais espécies de peneídeos, Rimapenaeus constrictus e Sicyonia dorsalis, e carídeos, Exhippolysmata oplophoroides, Alpheus intrinsecus, Nematopalaemon schmitti e Periclimenes paivai, pertencem à fauna acompanhante dos recursos pescados. X. kroyeri foi a espécie dominante (D) espacialmente e temporalmente, apresentando valores discrepantes de abundância relativa 97,7% quando comparada à segunda espécie de maior abundância P. muelleri (1,1%), circunstância que influenciou diretamente nos resultados das análises de agrupamento e nos valores de diversidade (H’) e equitabilidade (J’), que foram altos quando a abundância da espécie foi menor. Esse resultado corroborou aos padrões das ... Due to the impact caused by anthropic action on marine environment, the purpose of this work was to provide subsidies for species conservation at Babitonga Bay adjecent area in the state of Santa Catarina, Brazil. The aim was to catalogue existing species of marine shrimps communities, to detect and to describe general patterns in its temporal-spatial distribution and the relation to environmental variables that characterize its habitat. Therefore, ecological indexes were measured and environmental to biological parameters were tested with multivariate analysis. A shrimp boat equipped with double-rig nets was used and it travelled five parallel to the coast with a depth of stations 5, 8, 11, 14 e 17 m. The total richness reached twelve species, belonging to three superfamilies, six families and eleven genera. Of these, six species of peneid shrimps are marketed: Xiphopenaeus kroyeri, Artemesia longinaris, Pleoticus muelleri, Farfantepenaeus brasiliensis, Farfantepenaeus paulensis and Litopenaeus schmitti. The other species of peneids Rimapenaeus constrictus and Sicyonia dorsalis, and caridean shrimps Exhippolysmata oplophoroides, Alpheus intrinsecus, Nematopalaemon schmitti and Periclimenes paivai belong to bycatch of fisheries resources. X. kroyeri was a dominant (D) species in space and time, presenting discrepant values of relative abundance 97.7% when compared with the second most abundant species P. muelleri 1.1%, a circumstance that directly influenced the results of cluster analysis, the diversity (H’) and eveness (J’) values, which were high when the abundance of the species was lower. The patterns of the marine shrimp communities investigated in other regions were corroborated by the result of this study. Changes in shrimp communities could be related to variations in measured environmental variables and biological requirements specific to each species. The bottom temperature and sediment grain size were the preponderant ...

APA, Harvard, Vancouver, ISO, and other styles

28

Wolf, Milena Regina. "Ecologia das populações e comunidades dos camarôes Decapoda no litoral norte de Santa Catarina /." Botucatu, 2014. http://hdl.handle.net/11449/113943.

Full text

Abstract:

Orientador: Antonio Leão Castilho Banca: Maria Lúcia Negreiros Fransozo Banca: Sérgio Rosso Resumo: Frente aos impactos causados pela ação antrópica no ambiente marinho, a proposta desse trabalho foi fornecer subsídios para a conservação das espécies, na área adjacente à Baía da Babitonga, estado de Santa Catarina, Brasil. O objetivo foi inventariar as espécies existentes da comunidade de camarões marinhos, detectar e descrever padrões gerais na sua distribuição espaço-temporal e relação às variáveis ambientais que caracterizam seu habitat. Portanto, foram mensurados os índices ecológicos e testados os parâmetros ambientais aos biológicos com análise multivariada. Os camarões foram coletados em julho de 2010 a junho de 2011, junto às variáveis ambientais, como temperatura e salinidade da água e textura e conteúdo de matéria orgânica do sedimento. Utilizou-se um barco camaroneiro equipado com redes double-rig, o qual percorreu cinco pontos paralelos a costeira com profundidades de 5, 8, 11, 14 e 17 m. A riqueza total chegou a doze espécies, pertencendo a três superfamílias, seis famílias e onze gêneros. Dessas, seis espécies de camarões peneídeos são comercializados: Xiphopenaeus kroyeri, Artemesia longinaris, Pleoticus muelleri, Farfantepenaeus brasiliensis, Farfantepenaeus paulensis e Litopenaeus schmitti. As demais espécies de peneídeos, Rimapenaeus constrictus e Sicyonia dorsalis, e carídeos, Exhippolysmata oplophoroides, Alpheus intrinsecus, Nematopalaemon schmitti e Periclimenes paivai, pertencem à fauna acompanhante dos recursos pescados. X. kroyeri foi a espécie dominante (D) espacialmente e temporalmente, apresentando valores discrepantes de abundância relativa 97,7% quando comparada à segunda espécie de maior abundância P. muelleri (1,1%), circunstância que influenciou diretamente nos resultados das análises de agrupamento e nos valores de diversidade (H') e equitabilidade (J'), que foram altos quando a abundância da espécie foi menor. Esse resultado corroborou aos padrões das ... Abstract: Due to the impact caused by anthropic action on marine environment, the purpose of this work was to provide subsidies for species conservation at Babitonga Bay adjecent area in the state of Santa Catarina, Brazil. The aim was to catalogue existing species of marine shrimps communities, to detect and to describe general patterns in its temporal-spatial distribution and the relation to environmental variables that characterize its habitat. Therefore, ecological indexes were measured and environmental to biological parameters were tested with multivariate analysis. A shrimp boat equipped with double-rig nets was used and it travelled five parallel to the coast with a depth of stations 5, 8, 11, 14 e 17 m. The total richness reached twelve species, belonging to three superfamilies, six families and eleven genera. Of these, six species of peneid shrimps are marketed: Xiphopenaeus kroyeri, Artemesia longinaris, Pleoticus muelleri, Farfantepenaeus brasiliensis, Farfantepenaeus paulensis and Litopenaeus schmitti. The other species of peneids Rimapenaeus constrictus and Sicyonia dorsalis, and caridean shrimps Exhippolysmata oplophoroides, Alpheus intrinsecus, Nematopalaemon schmitti and Periclimenes paivai belong to bycatch of fisheries resources. X. kroyeri was a dominant (D) species in space and time, presenting discrepant values of relative abundance 97.7% when compared with the second most abundant species P. muelleri 1.1%, a circumstance that directly influenced the results of cluster analysis, the diversity (H') and eveness (J') values, which were high when the abundance of the species was lower. The patterns of the marine shrimp communities investigated in other regions were corroborated by the result of this study. Changes in shrimp communities could be related to variations in measured environmental variables and biological requirements specific to each species. The bottom temperature and sediment grain size were the preponderant ... Mestre

APA, Harvard, Vancouver, ISO, and other styles

29

Winger, Paul D. "Swimming endurance of American plaice (Hippoglossoides platessoides) and Atlantic cod (Gadus morhua) : implications for catchability by otter trawls /." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ36193.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Piredda, Laura. "Sustainability and valorization of small pelagics: implementation of a shark-free eco-label for pelagic trawling fisheries in the Adriatic Sea." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20441/.

Full text

Abstract:

This study analyses the willingness of consumers to pay an extra price for shark-free eco-label products of fresh small pelagics compared to the ordinary ones. The data collected for this study derives from a contingent valuation survey conducted among 200 consumers, in Ravenna and Pavullo nel Frignano, in a fish market and a supermarket each. There have been administrated further questionnaires to one wholesaler and to the sales manager of the two fishmongers and two supermarkets per town. Open-ended questions of the consumers’ questionnaires have been analysed through cross section linear regressions with ordinary least squares (OLS), using software Gretl, while qualitative analyses on the close-ended have been done using Excel. Freshness, origin and method of production are the aspects considered mostly by the consumers. Among all the interviewed, general knowledge of labels of is scarce. Maximum prices proposed by the consumers indicate that future shark-free eco-label of small pelagic could be sold with a price ranging from 7 to 10 €. The regression shows that the extent of the additional price that the consumer is willing to pay is related to the degree of information of the BIO label. Moreover, consumers could be interested in a shark-free eco-label. All vendors currently have no interest in promoting eco-labels, as joining the certification is considered a cost, as well as keeping the certified lines separate from the non-certified ones without mixing the products. None will assume the risk of joining the certification first, preferring to let others pave the way. An economic estimation of the amount of money that fishers gain from the by-catch has been calculated using pelagic trawling shark by-catch data provided by the Experimental Centre for Habitat Conservation (CESTHA) and fish prices from ISMEA and NISEA dataset. The economic loss due to the release of sharks is lower compared to how much the vessels could gain by joining the shark-free eco-label.

APA, Harvard, Vancouver, ISO, and other styles

31

Foster, Sarah Jane. "Is bycatch a big problem for small fish? Assessing and addressing the impacts of tropical shrimp trawling on small fish species." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/17458.

Full text

Abstract:

My research, focused on the industrial shrimp fishery in southern Gulf of California, aimed to determine whether tropical shrimp trawling is a problem for viability of incidentally captured small fish species. My first objective was to use life history information to evaluate possible impacts on four small fish species from their incidental capture. I applied length based indicators and qualitative criteria to information on captured sizes, reproduction, and distributions across the study site. My results suggested potential for overfishing silver stardrum and bigscale goatfish, largely because most sampled individuals were immature. Silver stardrum may be particularly affected because its occurrence and density declined during the trawling season whereas goatfish apparently recruited to the study area. Most sampled sandperch were mature, suggesting greater resilience to trawling. In contrast, sampled lumptail searobin, although mature, had not yet spawned, indicating potential for adverse fishing effects. Because human behaviour affects the success of fisheries management, my second objective was to shed light on the social dimensions of tropical shrimp fisheries management. My interviews with industrial trawl fishers suggested that proper enforcement and reliable governance are essential for a sustainable fishery. If enforcement were strong, then most fishers would support trawl free areas. The effort data I gathered point to areas where protection might be socially acceptable. My third objective considered the biological appropriateness of trawl closures for small fishes. The divergent distributions of bigscale goatfish and silver stardrum, just two of many small species in bycatch, implied that trawl restrictions would have to cover many depths and latitudes. Further, although my matrix model was of limited use for assessing population status of silver stardrum, it clearly indicated that precautionary management should focus on increasing survival of younger fish. This could be achieved with trawl closures where smaller fish live. While the approaches I used identified small fishes that might be vulnerable to trawling, they are too data intensive to be viable for the hundreds of such species in bycatch, and too inconclusive to confirm impact. It may be necessary to apply precautionary methods such as trawl closures to avoid potential effects of indiscriminate trawling.

APA, Harvard, Vancouver, ISO, and other styles

32

Lobo, Aaron Savio. "The dynamics and impacts of trawl fishing along the Coromandel Coast of India." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609292.

Full text

APA, Harvard, Vancouver, ISO, and other styles

33

Maree, R. C. "Environmental influences on the daytime vertical distribution of Cape hakes and implications for demersal trawl estimates of hake abundance off the west coast of South Africa." Thesis, Rhodes University, 2000. http://hdl.handle.net/10962/d1005122.

Full text

Abstract:

The demersal fishery off the west coast of South Africa experiences decreased catches per unit effort of hake, Merluccius capensis and M. paradoxus, following the onset of strong south easterly winds. Research has demonstrated that, during daylight hours, Cape hakes migrate vertically in the water column in response to strong south easterly winds, decreasing their availability to the bottom trawl. Hydroacoustic, trawl and environmental data were collected off the West Coast during both calm and wind-swept periods in an attempt to understand the forces that initiate this behaviour, its spatial variability and the implications for demersal trawl estimates of abundance. Near-bottom currents appear to be the primary factor influencing the vertical distribution of the demersal fish community, of which hake constitutes a large proportion, during daylight hours. Correlation between wind and near-bottom currents suggest that the poleward component of the currents increase in velocity within eight hours following the onset of south easterly winds. The fish avoid boundary layers where currents change direction and speed dramatically, and seem to concentrate in waters with relatively stable current regimes. This result questions the assumption of CPUE-based assessment models that hake availability to the bottom trawl is constant or varies randomly. The incorporation of acoustic assessment techniques to demersal surveys has potential, but may be most valuable by supplementing swept-area estimates of abundance, since the sampling efficiency of these methods varies within the water column. The incorporation of wind indices and gear performance data to Cape hake assessment models have been identified as useful considerations for the future.

APA, Harvard, Vancouver, ISO, and other styles

34

Nenadovic, Mateja. "The Effects of Bottom-Tending Mobile Fishing Gear and Fiber-Optic Cable Burial on Soft-Sediment Benthic Community Structure." Fogler Library, University of Maine, 2009. http://www.library.umaine.edu/theses/pdf/NenadovicM2009a.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Monteiro, Herbert Silva. "Análise quali-quantitativa dos Sciaenidae na pesca do camarão sete-barbas (Xiphopenaeus kroyeri), litoral de Santa Catarina Brasil." Universidade Federal de São Carlos, 2014. https://repositorio.ufscar.br/handle/ufscar/1830.

Full text

Abstract:

Made available in DSpace on 2016-06-02T19:30:05Z (GMT). No. of bitstreams: 1 6288.pdf: 1832069 bytes, checksum: 1b60b16b4da05304f9c4aadf5802ae6b (MD5) Previous issue date: 2014-06-04 Trawling with network-of-doors practiced by the artisanal fleet directed to-bobshrimp Xiphopenaeus kroyeri in central and northern coast of Santa Catarina is an efficient way to capture the target species. However, it has low selectivity and incidentally capture large contingent of demersal and benthic fauna, grouped on the designation of bycatch species, part of this is compounded by the Sciaenidae comprising teleost fish with great commercial importance. Based on this finding, the aim of this work was to evaluate qualitative and quantitative fish species present in the Sciaenidae accompanying fauna in three traditional areas of fishing-bob-shrimp. Seasonally, during the day, from September 2009 to July 2010, drags on traditional shrimp fishing areas in the municipalities of Bal. Barra South and Porto Belo, Santa Catarina, and monthly hauls were performed during the period September 2011 to August 2012 at easel Itapocoroy Penha, Santa Catarina. It appears that the composition of the Sciaenidae of accompanying fauna is dominated by demersal fish, belonging to two genera and three species Stellifer rastrifer, and S. brasiliensis Paralonchurus brasiliensis characterized dominant. The populations show seasonal fluctuations in abundance, with the highest catch rates in summer and lowest in winter. In general, the populations of the three species showed similar results in the evaluated parameters, experiencing a dominance of males in relation to females throughout the sampling period, with a predominance of males in the smaller length classes and the larger female. As the size of the first maturation of these species of approximately 9cm with the occurrence of two clutches per year. Trawling with network-of-doors practiced by the artisanal fleet operates intensely on juvenile population despite large share of the adult population. A pesca de arrasto com rede-de-portas praticada pela frota artesanal dirigida ao camarão sete-barbas Xiphopenaeus kroyeri no litoral Centro-Norte catarinense é considerada eficiente na captura da espécie-alvo. Entretanto, apresenta baixa seletividade e incidentalmente captura grande contingente da fauna demersal e bentônica, agrupados sobre a denominação de fauna acompanhante, parte desta é composta pela família Sciaenidae que compreende peixes teleósteos com grande importância comercial. Tendo por base essa constatação, objetivou-se no presente trabalho avaliar qualiquantitativamente as espécies de peixes da família Sciaenidae presentes na fauna acompanhante em três áreas tradicionais de pesca de camarão setebarbas. Sazonalmente, durante o dia, de setembro de 2009 a julho de 2010, foram realizados arrastos em áreas tradicionais de pesca de camarões nos municípios de Bal. Barra do Sul e Porto Belo, em Santa Catarina, e arrastos mensais durante o período de setembro de 2011 a agosto de 2012 na Armação do Itapocoroy, Penha, Santa Catarina. Constata-se que a composição da família Sciaenidae da fauna acompanhante é dominada por peixes demersais, pertencentes a dois gêneros e a três espécies Stellifer rastrifer, S. brasiliensis e Paralonchurus brasiliensis que se caracterizam dominantes. As populações apresentam flutuações sazonais na abundância, com as maiores taxas de capturas no verão e as menores no inverno. De modo geral, as populações das três espécies apresentaram resultados semelhantes nos parâmetros avaliados, ocorrendo uma dominância dos machos em relação as fêmeas ao longo do período de amostragem, com o predomínio dos machos nas menores classes de comprimento e das fêmea nas maiores. Sendo o tamanho da primeira maturação dessas espécies de aproximadamente 9cm, com a ocorrência de duas desovas por ano. A pesca de arrasto com rede-de-portas praticada pela frota artesanal atua de forma intensa sobre a população juvenil apesar de grande participação da população adulta.

APA, Harvard, Vancouver, ISO, and other styles

36

Chen, Dayuan. "Taiwanese offshore (distant water) fisheries in Southeast Asia, 1936-1977." Connect to this title online, 2007. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20070328.92412.

Full text

APA, Harvard, Vancouver, ISO, and other styles

37

Walmsley, Sarah Ann. "The assessment and management of bycatch and discards in the South African demersal trawl fishery." Thesis, Rhodes University, 2005. http://hdl.handle.net/10962/d1005071.

Full text

Abstract:

Over the past few decades it has become recognised that an ecosystem approach is required to manage world fisheries. Management strategies must ensure that non-target (bycatch) as well as target catches are sustainable. To achieve this, detailed commercial catch and biological information is required. The composition of catches made by trawlers operating off the south and west coasts of South Africa was investigated. Distinct fishing areas were identified on each coast, based on target species and fishing depth. Catch composition differed markedly among the areas defined. Although hake Merluccius sp. dominated South Coast catches, a large proportion of the catch was composed of bycatch. On the West Coast, hake dominated catches and this domination increased with increasing depth. On both coasts approximately 90% of the observed nominal catch was processed and landed. Estimates of annual discards suggested that the fishery discarded 38 thousand tons of fish per annum (16% of the nominal trawl catch). The data also indicated that hake discarding, the capture of linefish and the increased targeting of high value species might be cause for concern. Spatial analysis indicated that a variety of factors such as trawling position, catch size and catch composition affects bycatch dynamics. The monkfish Lophius vomerinus is a common bycatch species that has been increasingly targeted by demersal trawlers. This study showed that L. vomerinus is a slow-growing, long-lived species (West Coast males L∞ = 68.50cm TL, t₀ = -1.69yr, K = 0.10yr⁻¹; West Coast females L∞ = 110.23cm TL, t₀ = -1.54yr, K = 0.05yr⁻¹; South Coast sexes combined L∞ = 70.12cm TL, t₀ = - 0.80yr, K = 0.11yr⁻¹), that matures at approximately 6 years of age. These traits could have serious management implications for the species. Per-recruit analysis suggested that the stock might be overexploited, although further investigation is required to confirm this. Solutions were suggested for each of the concerns raised, taking cognisance of the differences observed between the South and West Coasts and the economic dependence of South Coast companies on bycatch. The needs of future research were considered.

APA, Harvard, Vancouver, ISO, and other styles

38

Getabu, Albert. "A combined hydro-acoustic and bottom trawling study on the biomass distribution and population dynamics of the Nile perch, Lates niloticus in Lake Victoria, East Africa." Thesis, University of Hull, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397069.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

Wassenberg, Theodore John. "Fate of selected species of the by-catch from prawn trawlers in Moreton Bay, Queensland." Thesis, Queensland University of Technology, 1987. https://eprints.qut.edu.au/35933/1/35933_Wassenberg_1987.pdf.

Full text

Abstract:

Studies of the fate of discarded by-catch were carried out in the Moreton bay prawn trawl fishery between September 1983 and March 1986. These studies included the determination of the by-catch biomass composition as well as assessing the impact of trawling and various handling times on damage and mortality. The by-catch was made up of 52% Crustacea, 15% elasmobranchs, 8% bony fish, 18% chinoderms, 3% cephalopods and 4% debris by weight. Portunus elagicus represented ~5% of the crustacean biomass and the lpheids nearly 2.0% and of the bony fishes, cardinal fish represented 13%, winter whiting 7%, and the flounders 5%. Trawls in the Moreton Bay fishery are of about 60 minutes and require about 20 minutes to sort. Times recorded for trawl duration and sorting over the study averaged 65.8 min and 23.3 min respectively. Short term survival of Crustacea was high (about 85%) while survival of bony fish was variable (from 20% to 70%) between species. A study of the fate of discards that reach the seabed showed that Portunus pelagicus was the most common scavenger attracted to the bait; followed by several bony fish species (11%) (n = 881 photographs). No prawns were observed at any of the simulated discards. A comparative analysis of foregut contents of sand crabs (P. pelagicus) and two penaeid prawn species (Penaeus plebejus and P. esculentus) showed that the penaeid prawns do not feed on trawler discards but that the sand crabs had fed on discards (33% by weight of their diet). Measurement of the rate of scavenging of discards on the seabed showed that benthic scavengers were capable of consuming up to 11 g of fish per linear metre per hour. The amounts of discards that are partitioned to seabirds (terns, gulls and cormorants) and dolphins were estimated. Fish discarded into the sea separate into a floating group and a sinking group. Size was important in determining the fate of discarded fish. Fish less than 100 mm long were generally taken by terns and gulls (34% of fish biomass) while fish greater than 100 mm were eaten by dolphins (41%) and cormorants (15%) and the rest (10%) sink. Crustacea were not eaten by birds or dolphins. A model of the fate of prawn trawler discards is presented with quantified pathways. This model shows that energy, in the form of discarded fish, is removed from the Moreton Bay benthic biomass and some ecological consequences of this are discussed. This study has shown that earlier models and ideas about the fate of prawn trawler discards are misleading.

APA, Harvard, Vancouver, ISO, and other styles

40

Muntadas, Olivé Alba. "Benthic communities' response to different trawling impact levels: generalization towards developing a Mediterranean model = Resposta de les comunitats bentòniques a diferents nivells d’impacte de pesca d’arrossegament: generalització per al desenvolupament d’un model mediterrani." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/385357.

Full text

Abstract:

Fisheries management has definitively embraced the Ecosystem Approach to Fisheries (EAF) philosophy and new management policies are incorporating integrative measures that take into account not only target species but also other ecosystem and socioeconomic elements involved in the fisheries system. In this context, the main aim of this thesis is to assess benthic community (infauna and epifauna) response to commercial trawling in the Mediterranean continental shelf in order to increase the scientific knowledge necessary for an EAF implementation. This aim is addressed within an integrated framework, considering different fisheries’ aspects discussed in each chapter, which constitute the specific objectives of this thesis. As a first objective, the trawling fleet activity was described and the level of fleet disturbance, which depends on fishing effort, was assessed at the benthic community level. Fishing effort was estimated using different approaches: fisheries data, Vessel Monitoring System (VMS) data and Side Scan Sonar (SSS) data. From this study we obtained an accurate estimation of trawl fishing effort in our communities of interest, which is the basis for the following studies. Then, as a second objective, the effects of trawling on soft bottom habitats’ functionality was assessed by evaluating trawling impact on ecological units called Ecosystem Service Providers (ESP) and on benthic communities’ functional redundancy. ESPs were described as a group of species that perform an ecosystem function that will ultimately deliver ecosystem services and that are linked to key functions of soft-bottom habitats (e.g., nutrient cycling, carbon sequestration, production, benthopelagic coupling and habitat provision). The study revealed that these ESPs were favored by particular sediment types, and trawling effects overlapped this natural variability. On the other hand, functional redundancy on these communities was also assessed using two complementary approaches: redundancy achieved through trait abundance (i.e. large amounts of a trait), that was called “common traits”, and redundancy achieved through trait richness (i.e. large numbers of distinct taxa exhibiting the same trait), that was called “widespread traits”. Both measures were found to be affected by trawling, although the former differentiated more clearly between heavily fished and moderately fished areas. The role of rare species in both measures was also analyzed and it was found that generally they exhibited the same traits as the most abundant species. The subsequent objective was to assess the potential effects of the observed benthic communities’ functional changes on target species. As a case study, red mullet (Mullus barbatus) was chosen because of its commercial importance in Mediterranean fisheries and its close relationship with benthic communities. The study highlighted that functional changes caused by trawling on benthic habitats might result in an overall negative effect on the red mullets’ stock. A second part of this thesis focuses on the importance of communication among fisheries’ stakeholders and provides tools to share scientific knowledge in an understandable way. In this context, a DPSIR (Drivers–Pressures–State Change–Impact–Response) framework was adapted to the trawling fisheries system in the study area in order to integrate the complex relationships between human uses, ecosystem components and the demand for ecosystem services in trawling grounds. In line with the philosophy of making scientific knowledge understandable, this thesis developed a platform with a user-friendly interface that represents trawl impacts on the seabed in our study sites and includes the possibility of adding new study sites. The platform also includes a simulation model that allows the user to change fishing effort on the study sites and visualize the potential changes in the benthic community structure caused by this change. This platform is meant to be a deliberation support tool for fisheries’ decision actors. Finally, by integrating all the acquired knowledge on trawl driven changes on benthic communities as well as literature information, this thesis recommends several management measures, indicators and tools to be used in an EAF management plan for the Catalan trawl fleet, which might be also applied to other Mediterranean trawl fisheries. L’objectiu principal d’aquesta tesi és estudiar de manera integrada la resposta de la comunitat bentònica (infauna i epifauna) a la pesca d’arrossegament en els fons tous de la plataforma continental del Mediterrani per tal d’incrementar el coneixement necessari per a implementar una gestió de les pesqueries basada en l’ecosistema. Així doncs, el primer pas fou estimar de manera acurada la dinàmica de la flota de les àrees d’estudi i l’esforç pesquer a què estaven sotmeses les comunitats bentòniques. A partir d’aquesta estimació es va avaluar l’impacte de la pesca en la funcionalitat d’aquestes comunitats, estudiant-ne els possibles efectes sobre els proveïdors de serveis ecosistèmics i sobre la redundància funcional. És a dir, els efectes es van estudiar sobre les unitats ecològiques que duen a terme funcions ecosistèmiques i que en última instància determinaran la provisió dels serveis ecosistèmics. També es van avaluar els efectes potencials d’aquests canvis a nivell de les comunitats bentòniques en una important espècie comercial en el Mediterrani com és el moll de fang (Mullus barbatus). Un segon bloc de la tesi se centra en la importància de la comunicació entre els diferents actors involucrats en les pesqueries i per això calen eines fàcilment comprensibles per a compartir informació entre tots els estaments involucrats. En aquest context, aquesta tesi inclou una representació del sistema pesquer seguint la filosofia del DPSIR (Drivers – Pressures – State Change – Impact– Response: Activadors – Pressions - Canvi d’estat – Impacte - Resposta) amb la finalitat de fer més comprensibles les relacions entre els diferents elements del sistema pesquer. En aquesta mateixa línia s’ha desenvolupat una plataforma de coneixement que recopila informació sobre l’impacte de la pesca d’arrossegament en les zones d’estudi així com un model de simulació que permet a l’usuari simular un canvi d’esforç en una d’aquestes comunitats i visualitzar l’impacte d’aquest canvi en l’estructura de la comunitat bentònica. Tenint en compte els resultats obtinguts, com a última finalitat de la tesi es presenten una sèrie de recomanacions per a la implementació d’un pla de gestió basat en l’ecosistema per a la flota d’arrossegament catalana, que podrien ser extensibles a qualsevol flota d’arrossegament mediterrània.

APA, Harvard, Vancouver, ISO, and other styles

41

Angonesi, Luciana Garcia. "Dinâmica de curto prazo da macrofauna betônica em uma enseada estuarinada Lagoa dos Patos: efeitos antrópicos e mecanismos de persistência e resiliência." reponame:Repositório Institucional da FURG, 2005. http://repositorio.furg.br/handle/1/4050.

Full text

Abstract:

Tese(doutorado) - Universidade Federal do Rio Grande, Programa de Pós–Graduação em Oceanografia Biológica, Instituto de Oceanografia, 2005. Submitted by Cristiane Gomides (cristiane_gomides@hotmail.com) on 2013-10-11T14:35:10Z No. of bitstreams: 1 Luciana.pdf: 2390598 bytes, checksum: de111a9f52b7b4847e9447d50f43891d (MD5) Approved for entry into archive by Sabrina Andrade (sabrinabeatriz@ibest.com.br) on 2013-10-17T17:43:17Z (GMT) No. of bitstreams: 1 Luciana.pdf: 2390598 bytes, checksum: de111a9f52b7b4847e9447d50f43891d (MD5) Made available in DSpace on 2013-10-17T17:43:17Z (GMT). No. of bitstreams: 1 Luciana.pdf: 2390598 bytes, checksum: de111a9f52b7b4847e9447d50f43891d (MD5) Previous issue date: 2005 O presente trabalho objetivou avaliar a estrutura e dinâmica de curto prazo da associação de macroinvertebrados bentônicos estuarinos da Lagoa dos Patos frente a perturbações antrópicas e naturais, bem como avaliar os mecanismos de persistência e resiliência da população de algumas espécies estuarinas. No capítulo I, através de um experimento de campo, foi avaliado o efeito de duas redes de arrasto de pesca artesanal de camarão (Rede de Coca e Rede de Berimbau) sobre a associação de macroinvertebrados bentônicos de fundos moles. O experimento, realizado com dois tratamentos (arrastos com Rede de Coca e Berimbau) e um Controle, onde não foram efetuados arrastos, foi desenvolvido em 7 etapas, nas quais amostras da macrofauna bentônica (seis réplicas por tratamento), foram tomadas em diferentes intervalos de tempo após os arrastos com as redes (cinco arrastos em cada etapa). Os resultados das diferentes análises estatísticas empregadas não foram conclusivos devido à dificuldade em se identificar efeitos diretos das redes sobre a macrofauna. Durante o período de estudo, aproximadamente 3 meses, foi possível a identificação de mudanças temporais na estrutura das associações bentônicas, as quais foram melhor analisadas no Capítulo 2. Este capítulo objetivou acompanhar a dinâmica de curto-prazo das associações de invertebrados bentônicos durante o período de verão-outono (quando ocorrem os principais processos de recrutamento da macrofauna bentônica na região), relacionando-os às variações de curto prazo da salinidade, precipitação pluviométrica, profundidade da coluna d’água, intensidade e direção do vento e variações na granulometria e matéria orgânica do sedimento. A variabilidade temporal de curto prazo da macrofauna bentônica foi acompanhada: 1) durante um período no verão de 2002; 2) durante dois períodos entre o verão e início do outono de 2004; e 3) entre estes três períodos realizados em anos distintos (período amostral de 2002 e os dois períodos amostrais de 2004). O acompanhamento temporal de curto prazo, em cada um dos períodos, foi realizado em 7 etapas, através de amostragens em intervalos de 1, 2, 4, 8, 16 e 32 dias após a amostragem inicial (dia 0 = Etapa 1). Seis amostras da macrofauna bentônica foram tomadas em cada uma das etapas nos três períodos de amostragem Os resultados mostraram diferenças significativas na estrutura dessas associações a partir de um período de 15 dias e que as variáveis ambientais medidas, reflexo de fatores meteorológicos, são de grande importância na determinação das variações temporais das associações. No Capítulo 3, objetivou-se reunir as informações publicadas e inéditas sobre as estratégias de adaptação de algumas espécies de macroinvertebrados bentônicos residentes na região estuarina da Lagoa dos Patos, relacionando-as aos seus mecanismos de persistência e resiliência frente a perturbações naturais e antrópicas. Informações sobre as estratégias de adaptação de Erodona mactroides (molusco bivalvo), Heleobia australis (molusco gastrópode), Laeonereis acuta (poliqueta), Kalliapseudes schubartii (crustáceo tanaidáceo) e Melita mangrovi (crustáceo anfípode) indicaram evidentes mecanismos de persistência e resiliência destes organismos, tais como proteção à desova, recrutamentos massivos, várias coortes ao ano, ocupação e assentamento em uma diversidade de hábitats que ofereçam alimento e abrigo contra a ação de predadores e mecanismos de escape frente à situações desfavoráveis. The present study aims to analyze the short-term dynamics of the Patos Lagoon estuarine soft-bottom macrobenthic community subjected to natural and anthropogenic disturbances, as well as to assess the mechanisms of persistence and resilience of some estuarine species. Chapter 1 aims at evaluating the effects of two different shrimp artisanal trawling nets (Coca and Berimbau nets) upon the soft-bottom macrobenthic associations, through a field experiment conducted in the estuarine region of Patos Lagoon. The experiment, performed with two treatments (Coca and Berimbau net trawling) and a control, where no trawling was performed, was conducted in seven stages, where benthic samples (six replicates in each treatment) were taken in different times after trawling. The results of the distinct statistical analysis used were not conclusive due the difficulty in showing clear effects on the soft bottom community. During the study period, about 3 months, were identified temporal changes on the structure of benthic associations, which were better analyzed in the Chapter 2. This chapter aimed to assess short-term macrobenthic dynamics during summer-fall period (when the main benthic recruitment processes occur), relating it to the short-term changes in: salinity, precipitation, water column depth, wind intensity, direction and changes in sediment granulometry and organic matter. The short-term benthic macrofauna variability was studied: 1) during summer of 2002; 2) during two periods between summer and beginning of fall of 2004; and 3) between these three periods carried out in different years. Short-term variability, in each period, was carried out in seven stages, through samples in different time scales (1, 2, 4, 8, 16 and 32 days) after the initial sampling (day 0 = stage 1). Six macrobenthic samples were taken in each stage and sampling periods. The results showed significant differences in the benthic macrofauna structure starting from 15 days, and the environmental variables measured, reflecting meteorological factors, are of great importance for determining temporal benthic fauna fluctuations. The Chapter 3 aimed at joining published and unpublished information about adaptation strategies of some macrobenthic estuarine resident species from Patos Lagoon, assessing the relationships between its persistence and resilience mechanisms and natural and anthropogenic disturbances. Data about Erodona mactroides (bivalvia), Heleobia australis (gastropoda), Laeonereis acuta (polychaeta), Kalliapseudes schubartii (tanaid) and Melita mangrovi (amphipod) adaptation strategies showed evident persistence and resilience mechanisms, such as spawn protection, massive recruitments, many cohorts a year, settlement in many habitats which offer food and shelter against predators, escape mechanisms in unfavorable situations, among others.

APA, Harvard, Vancouver, ISO, and other styles

42

Thomas, Nathan D. "Trawl and gill net selectivity of yellow perch in southern Lake Michigan, 1993-2006." Virtual Press, 2007. http://liblink.bsu.edu/uhtbin/catkey/1366503.

Full text

Abstract:

Selectivity of trawl and experimental gill nets was determined for yellow perch taken from southern Lake Michigan in 1993 to 2006. Gill nets were comprised of 51-, 64-and 76-mm size mesh and showed female modal lengths of 205-, 245-, and 295-mm, respectively, while values for males were 200-, 230-, and 267-mm. Differences between females and males increased with mesh size and was significant. Comparison of nine anterior morphometric features of female and male fish indicated no differences in shape were identified that would cause the disparity in selectivity. Rather, differences in male and female selectivity were more likely due the variant population size structure of the local population sampled, with females the larger sex. A new method to estimate trawl selectivity was developed using a modified catch-curve analysis, which showed a maximum selectivity length value (1.0) of 190-mm for females and 170-mm for males. However, trawls fail to capture larger yellow perch when compared to gill nets using based on length-frequency distributions. Revealing such gear biases may lead to more efficient capture methods, resulting in improved sampling and quantitative assessment of fish populations. Department of Biology

APA, Harvard, Vancouver, ISO, and other styles

43

Klaer, Neil L., and n/a. "Changes in the structure of demersal fish communities of the South Eastern Australian Ccontinental Shelf from 1915 to 1961." University of Canberra. Resource, Environmental & Heritage Sciences, 2006. http://erl.canberra.edu.au./public/adt-AUC20060804.154133.

Full text

Abstract:

Haul-by-haul steam trawler catch and effort data for 1918�23, 1937�43 and 1952�57, which covers a large portion of the history of steam trawling in the Australian South East Fishery, were examined in detail for the first time. There were 64,371 haul records in total. The catch-rate for all retained catch combined shows a strong decline overall, with a brief recovery during World War II, probably due to increased retention of previously discarded species. The fishing fleet moved to more distant fishing grounds and deeper waters as the catch-rate declined. The catch-rates of the main commercial species followed a similar pattern in a number of regions within the fishery. The catchrate of the primary target species � tiger flathead (Neoplatycephalus richardsoni) � dropped considerably from the early, very high, catch-rates. Chinaman leatherjacket (Nelusetta ayraudi) and latchet (Pterygotrigla polyommata) � species that were apparently abundant in the early years of the fishery � virtually disappeared from catches in later years. The appearance of greater catches of jackass morwong (Nemadactylus macropterus), redfish (Centroberyx affinis), and shark/skate during the war and afterwards was probably due to increased retention of catches of these species. The disappearance of certain species from the catch may be due to high fishing pressure alone, or to a combination of fishing pressure, changes in the shelf habitat possibly caused by the trawl gear, and environmental fluctuations. Catch-rates in weight per haul per species were standardised to annual indices of abundance using a log-linear model. Standardised annual index trends for flathead, latchet and leatherjacket indicate a strong to severe decline over the period covered by the data. All species showed seasonal patterns, but the peak season varied depending on the species. The distribution of standardised catch-rate by area also differed greatly by species, and no single area showed consistent differences across all species. Day trawls caught more flathead, redfish and latchet, while night trawls caught more morwong and leatherjacket. Moon phase had less influence on catch-rates than the other factors examined. Correlation of annual index trends with a number of annual mean environmental factors was examined and no strong correlations were found. Annual catches of the major commercial trawl species on the SE Australian shelf were estimated from recorded total trawl catches, catch species composition from subsamples and estimates of the rate of discarding. These annual catches, standardised indices of abundance and biological population parameters were used in single-species stock reduction models to estimate absolute biomass trends. Biological population parameters and the biomass estimates were used to calculate management reference point fishing mortality rates F0.1, Fspr30 and Fmsy. Results showed that simple plausible population models can be constructed that account for catches over the long period of time from 1915 to 1961. Simple mass-balance ecosystem models were built for the demersal community of the SE Australian shelf for 1915 and 1961 using the Ecopath software. Model inputs were consistent with a more comprehensive SE marine ecosystem model in development by CSIRO. The models demonstrate that biomass estimates produced by the single species stock reduction models can be consistently integrated into simple plausible massbalance ecosystem models. Modern stock assessments for the main commercial species in this fishery today mostly used data collected since about 1985. Abundance indices and total catch estimates from this study have been used in the most recent assessments for tiger flathead and morwong, allowing construction of the exploitation history for these species spanning almost 100 years. Use of the historical information has increased confidence in the estimates of the modern stock assessments � particularly management reference points, and has allowed us to quantify changes in fish abundance that have simply been documented anecdotally in the past.

APA, Harvard, Vancouver, ISO, and other styles

44

Sousa, Aline Nonato de. "Biologia e ecologia do siri candeia Achelous spinimanus (Latreille, 1819) (crustacea, decapoda, portunoidea) em três enseadas da costa sudeste do Brasil." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/152231.

Full text

Abstract:

Submitted by ALINE NONATO DE SOUSA null (alinensousa1@gmail.com) on 2017-11-30T22:22:41Z No. of bitstreams: 1 SOUSA, A.N - BIOLOGIA E ECOLOGIA DE A.spinimanus.pdf: 3014087 bytes, checksum: 23b8e6cb1bad861f8c27a13900d0658c (MD5) Submitted by ALINE NONATO DE SOUSA null (alinensousa1@gmail.com) on 2017-12-04T14:43:24Z No. of bitstreams: 1 SOUSA, A.N - BIOLOGIA E ECOLOGIA DE A.spinimanus.pdf: 3014087 bytes, checksum: 23b8e6cb1bad861f8c27a13900d0658c (MD5) Submitted by ALINE NONATO DE SOUSA null (alinensousa1@gmail.com) on 2017-12-05T14:11:15Z No. of bitstreams: 1 SOUSA, A.N - BIOLOGIA E ECOLOGIA DE A.spinimanus.pdf: 3014087 bytes, checksum: 23b8e6cb1bad861f8c27a13900d0658c (MD5) Approved for entry into archive by ROSANGELA APARECIDA LOBO null (rosangelalobo@btu.unesp.br) on 2017-12-05T16:06:16Z (GMT) No. of bitstreams: 1 sousa_an_me_bot.pdf: 3014087 bytes, checksum: 23b8e6cb1bad861f8c27a13900d0658c (MD5) Made available in DSpace on 2017-12-05T16:06:16Z (GMT). No. of bitstreams: 1 sousa_an_me_bot.pdf: 3014087 bytes, checksum: 23b8e6cb1bad861f8c27a13900d0658c (MD5) Previous issue date: 2017-02-23 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) A fim de ampliar o conhecimento sobre a biologia de uma das espécies que compõem a fauna acompanhante, foi realizada esta dissertação, intitulada de “Biologia e ecologia do siri candeia Achelous spinimanus (Latreille, 1819) (Crustacea, Decapoda, Portunoidea) em três enseadas da costa sudeste do Brasil”, cujas informações sobre os comportamentos distribucionais e aspectos populacionais de A. spinimanus são abordados com a finalidade de promover informações complementares para gerar uma pesca racional e sustentável. Além disso, o fato dos siris terem sido amostrados em três enseadas com características fisiográficas distintas, pode colaborar na compreensão da complexa interação dos fatores ambientais com os padrões de distribuição dos indivíduos desta espécie. In order to increase the knowledge about the biology of one of the species that make up the companion fauna, this dissertation was entitled "Biology and ecology of the Achelous spinelanus crane (Latreille, 1819) (Crustacea, Decapoda, Portunoidea) in three coves of the southeastern coast of Brazil, "whose information on the distributional behaviors and population aspects of A. spinimanus are addressed in order to promote complementary information to generate rational and sustainable fishing. In addition, the fact that the crabs were sampled in three coves with distinct physiographic characteristics may help to understand the complex interaction of environmental factors with the distribution patterns of the individuals of this species. 94/4878-8 98/031134-6

APA, Harvard, Vancouver, ISO, and other styles

45

Payo, Payo Marta. "Modélisation du transport sédimentaire et des interactions morphodynamiques par les courants de turbidité dans les canyons sous-marins. Application à la Méditerranée Occidentale." Thesis, Brest, 2016. http://www.theses.fr/2016BRES0117/document.

Full text

Abstract:

Les courants de turbidité dans les canyons sous-marins contribuent largement au transfert sédimentaire à travers des marges continentales. L’étude géologique des canyons sous-marins et des systèmes turbiditiques associés a permis des avancées fondamentales dans la compréhension de l’évolution des courants de turbidité.Ces études sont cependant limitées à des interprétations a posteriori, basées sur la répartition des dépôts et des évidences morphologiques. Cette thèse vise à l’application de la modélisation numérique des courants de turbidité, sur la base des processus physiques, à deux canyons sous-marins de la côte Méditerranée Occidentale.Des courants de turbidité liés au chalutage de fond sont modélisés dans le canyon de La Fonera. Les résultats du modèle permettent de spatialiser ce transport; ainsi le modèle peut être un point de départ pour l’identification de zones de pêche au chalut avec un moindre impact. L’absence d’un plateau continental au niveau de Nice a permis une alimentation continue du système turbiditique du Var indépendamment des variations du niveau marin. Ainsi ce système s’avère un laboratoire naturel pour l’étude du contrôle climatique sur l’activité turbiditique. L’influence des forces de Coriolis dans l’évolution spatiale des courants de turbidité et dans la construction de la Ride sédimentaire du Var est modélisée et mise en évidence pour la première fois.La modélisation numérique des courants de turbidité ne peut pas fournir à présent des résultats de qualité prédictive du fait de la quantité limitée d’information disponible pour établir les conditions initiales de l’écoulement qui impactent largement son évolution et dépôts. Malgré ce fait, la modélisation numérique permet d’élargir les interprétations du fonctionnement sédimentaire des canyons étudiés, d’identifier les chemins empruntés par les écoulements et leur dépôt final et de mieux préparer des cibles (mouillages et carottage) lors des campagnes à la mer Turbidity currents in submarine canyons are the main contribution for sediment transfer across the continental margins. Geological studies of submarine canyons and associated turbiditic systems for more than 30 years led to an extraordinary breakthrough in the understanding of how turbidite systems evolve. However, these studies remain limited to a posteriori interpretations, based on the distribution of deposits and morphological evidences. The overarching aim of this thesis is to apply a 2DH process-based model to simulate large-scale turbidity currents on two different submarine canyons in the western Mediterranean coast.The work in La Fonera canyon, in the Catalan margin, focuses on the modelling of sediment transport and accumulation resulting from trawling activities on the canyon flanks. The numerical process-based provides a 3D visualization of potential trawling impacts on sediment dynamics. The study represents a starting point for the assessment of the sedimentary impact of bottom trawling in deep continental margins. The present work can help in the identification of trawling areas with lesser impacts. The Var Sedimentary System, located in the vicinity of Nice (France), is connected to the Var River during both low and high-stands and it can be considered as a natural laboratory for the study of the climatic control on the turbiditic activity. The influence of Coriolis forces on the spatial evolution of the hyperpycnal flows and hence in the construction of the Var Sedimentary Ridge (VSR) is evidenced and supported for the first time.The major drawback is the limited amount of information for the necessary initial and boundary conditions; hence modelling results might not be of predictive quality. However, modelling results provide a full-scale vision of the system allowing the identification of sediment pathways and deposition areas on the basis of physical processes and enlarge the present knowledge of the canyons studied. The results obtained may help in the identification of strategic mooring and coring sites to further advance the state of our knowledge on sediment dynamics of the different cases studies

APA, Harvard, Vancouver, ISO, and other styles

46

Mallol, i. Martínez Sandra. "Anàlisi dels descartaments efectuats per la flota d'arrossegament en el Golf de Lleó." Doctoral thesis, Universitat de Girona, 2005. http://hdl.handle.net/10803/7654.

Full text

Abstract:

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.

APA, Harvard, Vancouver, ISO, and other styles

47

Abdou, Khaled. "Evaluation des impacts environnementaux du chalutage de fond et de l'aquaculture en Tunisie : approche comparative par les Analyses de Cycle Vie (ACV)." Thesis, Brest, 2017. http://www.theses.fr/2017BRES0141/document.

Full text

Abstract:

L'aquaculture et la pêche impactent l'environnement, les ressources et le fonctionnement des écosystèmes. L’un des enjeux en écologie est de placer ces activités anthropiques dans un cadre de développement durable. Afin de quantifier et de limiter ces impacts, différentes méthodes d’évaluation environnementale ont vu le jour. L’Analyse de Cycle de Vie (ACV) est une méthode pertinente pour évaluer le bilan environnemental d'un produit en prenant en compte l’ensemble de ses étapes de vie, "du berceau à la tombe", depuis l’extraction des matières premières et leurs transformations pour l'élaboration du produit, jusqu’à la fin de vie. Cette thèse porte sur l’adaptation de l’ACV au domaine de l'aquaculture et de la pêche en Tunisie. Son objectif est d'explorer les perspectives offertes par cette méthodologie afin de mieux caractériser le fonctionnement des systèmes de production de poissons et leur lien avec l’environnement. Cette étude a montré que les pratiques aquacoles et la production d'aliment de poisson sont les contributeurs majeurs aux impacts environnementaux, ceci est expliqué par l'utilisation de farine et d'huile de poisson dans la fabrication de l'aliment. Les résultats ont également montré que les impacts du chalutage de fond sont proportionnels à la quantité de carburant nécessaire pour la production. Ce travail a permis d'étudier et comparer les impacts environnementaux de l'activité aquacole et de la pêche au chalutage de fond en Tunisie. Les résultats de cette thèse ont un intérêt pour les gestionnaires en proposant des voies d'amélioration et des recommandations stratégiques de gestion pour améliorer les deux secteurs afin de les placer dans un contexte de développement durable The main goal of ecology is to place human activities within a framework of sustainable development by enhancing their economic benefits, their social attractiveness and their environmental performances. Ecosystems that support fisheries and aquaculture are subject to several alterations of significant relevance to their functioning and to their abilities to provide goods and services. Therefore, the long-term sustainability of fishing and aquaculture is a major concern from an environmental and ecological viewpoint. Both activities carry risks of negative environmental impacts because of its close relation with the immediate environment. To better understand environmental impacts and ensure the sustainability of fishing and aquaculture, it is necessary to develop an integrative sciencebased approach to impact assessment. Life Cycle Assessment (LCA) has emerged as a robust method to estimate potential environmental impacts associated with a product. It allows the assessment of environmental impacts “from cradle to grave”, taking into account all stages of a product’s life. This thesis focuses on the adaptation of LCA to demersal trawling and aquaculture in Tunisia. The goal is to explore how LCA improves the environmental evaluation of seafood production systems and how it helps to better understand their links with the environment. Results revealed that rearing practices and fish feed were the greatest contributors to the impacts studied due to the production of fish meal and oil and the low efficiency of feed use. The study also showed that impact intensity of demersal trawling was proportional to the amount of fuel consumed. LCA is a valuable tool for assessing how to improve environmental sustainability of demersal trawling and aquaculture

APA, Harvard, Vancouver, ISO, and other styles

48

Mengual, Baptiste. "Variabilité spatio-temporelle des flux sédimentaires dans le Golfe de Gascogne : contributions relatives des forçages climatiques et des activités de chalutage." Thesis, Brest, 2016. http://www.theses.fr/2016BRES0109/document.

Full text

Abstract:

L'étude de la variabilité spatio-temporelle des flux sédimentaires sous l'influence des forçages naturels et des activités de chalutage a été entreprise à l'échelle du plateau continental du Golfe de Gascogne, en associant des données in situ et une modélisation numérique 3D déterministe. Deux campagnes en mer spécifiques ont été menées pour quantifier les impacts physiques induits par un chalut professionnel au niveau de la Grande-Vasière, en termes de remise en suspension (panache turbide), et de perturbation de la structure et de la nature du sédiment superficiel. Ces données ont permis d'estimer à 0.13 kg.m-2 le taux d'érosion moyen. Leur croisement avec des données d'effort de pêche a conduit à une cartographie mensuelle du flux d'érosion par chalutage. D'autre part, un modèle hydro-sédimentaire 3D réaliste a été mis en place et calibré à partir de mesures au point fixe. Une attention particulière a été accordée au paramétrage de l'érosion naturelle sous l'influence combinée des vagues et des courants. Une nouvelle formulation de la loi d'érosion adaptée aux mélanges de sable fin et de vase classiquement rencontrés sur les plateaux continentaux a été proposée et a permis d'optimiser significativement la réponse du modèle en termes de turbidité. Deux simulations de 5 ans ont été réalisées en incluant ou non l'influence du chalutage de fond, dans le but de quantifier et comparer les contributions relatives des forçages naturels et anthropique sur les flux verticaux (érosion) et horizontaux (transport solide) de sédiments. La variabilité temporelle des flux est décrite en une succession de régimes caractéristiques répondant à divers forçages (e.g. marée, vent, vagues, chalutage), et les flux résiduels saisonniers et annuels sont commentés : sans tenir compte des apports fluviaux, le flux de matériel vaseux a été estimé à 1.6 Mt/an sortant par le nord (au droit de La Pointe du Raz) et à 0.62 Mt/an vers le talus continental (au niveau de l'isobathe 180 m) The spatio-temporal variability of sediment fluxes under the influence of natural forcings and trawling activities was assessed at the scale of the Bay of Biscay shelf, from in situ data and a 3D process-based numerical modelling. Two sea trials were carried out to quantify physical impacts induced by a professional trawling gear over an intensively trawled area of the shelf, the "Grande-Vasière", in terms of resuspension (turbid plume) and alteration of the surficial sediment nature and structure. These data enabled to estimate an average trawling-induced erosion rate of 0.13 kg.m-2. Their combination with fishing effort data led to monthly spatial distributions of trawling-induced erosion fluxes.Besides, a 3D realistic hydro-sedimentary model has been set up and calibrated from measurements acquired at a mooring station. The calibration task mainly consisted in assessing the natural erosion law setting under the influence of waves and currents. A new formulation of the erosion law has been proposed to describe the erosion of any mixture of mud and fine sand (sediment facies classically encountered on continental shelves) and led to a noteworthy improvement of the model response in terms of turbidity. Two 5-year simulations were performed accounting for natural forcings only or both natural and anthropogenic forcings in order to quantify and compare their respective contributions to sediment fluxes (vertical and horizontal sediment dynamics). The temporal variability of sediment fluxes is described in a succession of typical regimes occurring in response to various conditions of forcings (e.g. tide, wind, wave, trawling), and residual fluxes are assessed at seasonal and annual scales: without accounting for riverine sediment inputs, the mud flux is estimated to 1.6 Mt/yr outflowing northward (at the latitude of the Pointe du Raz) and to 0.62 Mt/yr toward the continental slope (through the 180 m isobath)

APA, Harvard, Vancouver, ISO, and other styles

49

Vallée, Vincent. "Changements à long terme de la structure et de la diversité des peuplements de poissons de fond du plateau continental de Guyane Functional richness and turnover patterns reveal assembly rules structuring marine fish communities on the continental shelf of French Guiana Diversity recovery and temperature induced species shift in tropical marine fish communities after a trawling fishery collapse Local and regional assembly rules on a long time period in marine fish communities on the continental shelf of French Guiana." Thesis, Guyane, 2020. http://www.theses.fr/2020YANE0004.

Full text

Abstract:

Dans le contexte actuel de surpêche et de réchauffement climatique, il est nécessaire d’adopter une gestion écosystémique des ressources halieutiques. Ce travail de thèse apporte des éléments de réponse à cette problématique en se penchant sur le cas de la pêcherie crevettière guyanaise et de son impact sur les communautés de poissons associées. Comme dans la plupart des régions tropicales, les eaux côtières de Guyane se sont réchauffées d’environ 1°C entre 1990 et 2017. En revanche, comme dans peu d’endroits au monde, la pression de pêche s’est quasiment effondrée sur cette même période. Ce cas d’étude est donc une bonne opportunité pour comprendre la réaction des communautés de poissons de cette région tropicale après une diminution progressive et à grande échelle de la pression de pêche dans un contexte de réchauffement climatique. Les résultats de ce travail montrent que les facteurs environnementaux jouent un rôle dominant dans la structuration des communautés de poissons marins en Guyane. Les analyses montrent notamment des augmentations de certains indicateurs de diversité, une augmentation du spectre des tailles maximales théoriques des espèces et une augmentation de la redondance fonctionnelle qui est un facteur clé pour la stabilité des peuplements. Ces éléments témoignent d’une restructuration des communautés et mettent en avant leur capacité à retrouver un état riche et stable en une période relativement courte d’une douzaine d’années voire moins. On observe néanmoins une tropicalisation des communautés qui pose des questions sur l’évolution future de la diversité des écosystèmes tropicaux au regard des différents scénarios climatiques In the actual context of overfishing and climate change we need to develop an ecosystem-based management of fisheries. This thesis work will try to bring answers to this issue by analyzing community assembly and the impact of French Guiana’s fishery on fish communities. As most of tropical regions, coastal waters in French Guiana have been subjected to an increase in temperature around 1°C between 1990 and 2017. However, as for only a few regions in the world, fishing pressure has collapsed in French Guiana during the same period. This case study is therefore a good opportunity to understand how tropical fish communities have responded to a progressive decreasing fishing pressure on a large scale and under climate change constraints. The aim of this work is to provide useful information for tropical fisheries with similar characteristics which tend to a more efficient ecosystem-based management with lower fishing pressure. The study showed that the environment plays a dominant role in community structure and that it has become more important over time. Results showed also significant increases in several diversity indices and an increase in theoretical maximum size spectra of surveyed fish which indicates a restructuring of communities. This recovery is associated with an increase of functional redundancy which is a key factor for the stability of ecosystems. Global results showed a great recovery capacity towards a richer and more stable state of communities in a relatively short period of time around 10 years

APA, Harvard, Vancouver, ISO, and other styles

50

Abdou, Khaled. "Evaluation des impacts environnementaux du chalutage de fond et de l'aquaculture en Tunisie : approche comparative par les Analyses de Cycle Vie (ACV)." Electronic Thesis or Diss., Brest, 2017. http://www.theses.fr/2017BRES0141.

Full text

Abstract:

L'aquaculture et la pêche impactent l'environnement, les ressources et le fonctionnement des écosystèmes. L’un des enjeux en écologie est de placer ces activités anthropiques dans un cadre de développement durable. Afin de quantifier et de limiter ces impacts, différentes méthodes d’évaluation environnementale ont vu le jour. L’Analyse de Cycle de Vie (ACV) est une méthode pertinente pour évaluer le bilan environnemental d'un produit en prenant en compte l’ensemble de ses étapes de vie, "du berceau à la tombe", depuis l’extraction des matières premières et leurs transformations pour l'élaboration du produit, jusqu’à la fin de vie. Cette thèse porte sur l’adaptation de l’ACV au domaine de l'aquaculture et de la pêche en Tunisie. Son objectif est d'explorer les perspectives offertes par cette méthodologie afin de mieux caractériser le fonctionnement des systèmes de production de poissons et leur lien avec l’environnement. Cette étude a montré que les pratiques aquacoles et la production d'aliment de poisson sont les contributeurs majeurs aux impacts environnementaux, ceci est expliqué par l'utilisation de farine et d'huile de poisson dans la fabrication de l'aliment. Les résultats ont également montré que les impacts du chalutage de fond sont proportionnels à la quantité de carburant nécessaire pour la production. Ce travail a permis d'étudier et comparer les impacts environnementaux de l'activité aquacole et de la pêche au chalutage de fond en Tunisie. Les résultats de cette thèse ont un intérêt pour les gestionnaires en proposant des voies d'amélioration et des recommandations stratégiques de gestion pour améliorer les deux secteurs afin de les placer dans un contexte de développement durable The main goal of ecology is to place human activities within a framework of sustainable development by enhancing their economic benefits, their social attractiveness and their environmental performances. Ecosystems that support fisheries and aquaculture are subject to several alterations of significant relevance to their functioning and to their abilities to provide goods and services. Therefore, the long-term sustainability of fishing and aquaculture is a major concern from an environmental and ecological viewpoint. Both activities carry risks of negative environmental impacts because of its close relation with the immediate environment. To better understand environmental impacts and ensure the sustainability of fishing and aquaculture, it is necessary to develop an integrative sciencebased approach to impact assessment. Life Cycle Assessment (LCA) has emerged as a robust method to estimate potential environmental impacts associated with a product. It allows the assessment of environmental impacts “from cradle to grave”, taking into account all stages of a product’s life. This thesis focuses on the adaptation of LCA to demersal trawling and aquaculture in Tunisia. The goal is to explore how LCA improves the environmental evaluation of seafood production systems and how it helps to better understand their links with the environment. Results revealed that rearing practices and fish feed were the greatest contributors to the impacts studied due to the production of fish meal and oil and the low efficiency of feed use. The study also showed that impact intensity of demersal trawling was proportional to the amount of fuel consumed. LCA is a valuable tool for assessing how to improve environmental sustainability of demersal trawling and aquaculture

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Trawling'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles