Dissertations / Theses on the topic 'Bycatches (fisheries)'
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McGowan, Conor P. "Incidental take and endangered species demography." Diss., Columbia, Mo. : University of Missouri-Columbia, 2008. http://hdl.handle.net/10355/5595.
Full textThe entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on June 9, 2009) Vita. Includes bibliographical references.
Herrera, Guillermo E. "Spatial structure and informational asymmetry in the economics of multiple stock renewable resources /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/7425.
Full textRichter, Christoph. "Harbour porpoise and people : strategies for bycatch reduction in the Bay of Fundy /." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ36173.pdf.
Full textSecchi, Eduardo Resende, and n/a. "Modelling the population dynamics and viability analysis of franciscana (Pontoporia blainvillei) and Hector�s dolphins (Cephalorhynchus hectori) under the effects of bycatch in fisheries, parameter uncertainty and stochasticity." University of Otago. Department of Zoology, 2006. http://adt.otago.ac.nz./public/adt-NZDU20070118.162020.
Full textMackay, Alice I. "An investigation of factors related to the bycatch of small cetaceans in fishing gear." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/1888.
Full textWalmsley, 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 textWinship, Arliss J. "Estimating the impact of bycatch and calculating bycatch limits to achieve conservation objectives as applied to harbour porpoise in the North Sea." Thesis, St Andrews, 2009. http://hdl.handle.net/10023/715.
Full textLobo, 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 textGedamke, Todd. "Developing a stock assessment for the barndoor skate (Dipturus laevis) in the Northeast United States." W&M ScholarWorks, 2006. http://web.vims.edu/library/Theses/Gedamke06.pdf.
Full textBooth, Anthony John. "Biology, stock assessment and management of the panga Pterogymnus laniarius on the Agulhas Bank, South Africa." Thesis, Rhodes University, 1998. http://hdl.handle.net/10962/d1005085.
Full textFilmalter, John David. "The associative behaviour of silky sharks, Carcharhinus falciformis, with floating objects in the open ocean." Thesis, Rhodes University, 2015. http://hdl.handle.net/10962/d1018177.
Full textReis, Marcelo. "Chondrichthyan Bycatch: Risk Assessment, Spatiotemporal trends and Contributions to Management." Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/19985.
Full textPetersen, Samantha Lara. "Understanding and mitigating vulnerable bycatch in southern African longline and trawl fisheries." Doctoral thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/19137.
Full textScott-Denton, Elizabeth. "U.S. southeastern shrimp and reef fish resources and their management." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1676.
Full textLi, Yan. "Investigating ecosystem-level effects of gillnet bycatch in Lake Erie: implications for commercial fisheries management." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/76836.
Full textMaster of Science
Mangel, Jeffrey Charles. "Interactions of Peruvian small scale fisheries with threatened marine vertebrate species." Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/3483.
Full textWeidner, Tiffany A. "Combined Gut Content-Stable Isotope Trophic Analysis and Satellite Tagging of the Pelagic Stingray Pteroplaytrygon violacea (Bonaparte, 1832) from the Western North Atlantic Ocean." NSUWorks, 2014. http://nsuworks.nova.edu/occ_stuetd/10.
Full textAlfaro, Shigueto Joanna Olga Gissella. "Ecology and conservation of sea turtles in Peru." Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/3472.
Full textRice, Wayne Stanley. "Contextualising the bycatch 'problem' in the Olifants Estuary Small-Scale Gillnet Fishery using an Ecosystem Approach to Fisheries." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/19987.
Full textAguiar, Ana Raquel Batista. "Trends in deep-water shark fisheries in the Azores." Master's thesis, Universidade de Aveiro, 2015. http://hdl.handle.net/10773/15485.
Full textDeep-sea resources have been increasingly exploited, and due to that, several ecosystems and species have been considerably affected. Deep-water sharks populations have been of the most disturbed by practices of unselected fisheries, bycatch and discard, mainly due to their low commercial value. Those practices make deep-water sharks very vulnerable to overfishing given their life-history traits, increasing their extinction risk. With the prohibition of the direct fishery, and implementation of quotas and TACs (Total Allowable Catches) regarding the deep-sea shark landings, the official landings have dramatically decreased after the 1990s. However, the IUU (Illegal, unreported and unregulated) catch has exponentially increased. With the analysis of catch per unit effort (CPUE), the depths, and the mean weight of the individuals over the years for each one of the nine most caught species in the Azores, we produced a descriptive analysis of the effect of fisheries in those species. The results show that some of these species have been suffering from a great fishing pressure, and their populations will be greatly affected in the near future if drastic measures are not taken when it comes to managing their long term sustainability.
Os recursos do mar profundo têm sido cada vez mais explorados, e devido a isso, vários ecossistemas e espécies têm sido gravemente afectados. As populações de tubarões de profundidade são das mais perturbadas, especialmente pelas práticas de pesca não seletivas, capturas acessórias e descarte, principalmente devido ao seu baixo valor comercial. Estas práticas tornam os tubarões de profundidade muito vulneráveis à sobrepesca dadas as suas características de história de vida, aumentando assim o seu risco de extinção . Com a proibição da pesca direta, e a implementação de quotas e TACs (Capturas Totais Admissíveis) na pesca de tubarões de profundidade, as capturas oficiais têm vindo a decrescer. No entanto, as capturas não reportadas têm vindo a aumentar exponencialmente. Com a análise da captura por unidade de esforço (CPUE), da profundidade, e do peso médio dos indivíduos ao longo dos anos de cada umas das 9 espécies de tubarões mais pescadas nos Açores, conseguimos fazer uma análise descritiva do efeito das pescas nestas espécies. Os resultados mostram que algumas destas espécies têm vindo a sofrer uma grande pressão por parte da pesca, e que as suas populações serão gravemente afetadas num futuro próximo se não forem tomadas medidas drásticas no que toca à gestão da sua sustentabilidade a longo prazo.
Montrond, Gilson. "Assessing sea turtle, seabird and shark bycatch in artisanal, semi-industrial and industrial of fisheries in the Cabo Verde Archipelago." Master's thesis, Faculty of Science, 2021. http://hdl.handle.net/11427/32854.
Full textSnouck-Hurgronje, Julia. "The Effects of Drifting Fish Aggregating Devices on Bycatch in the Tropical Tuna Purse Seine Fisheries in the Atlantic and Indian Oceans." W&M ScholarWorks, 2016. https://scholarworks.wm.edu/etd/1499449678.
Full textGraham, Larissa Joy. "Bycatch associated with a horseshoe crab (Limulus polyphemus) trawl survey: identifying species composition and distribution." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/34660.
Full textMaster of Science
Gahm, Meghan P. "The development and evaluation of small specialized turtle excluder devices to reduce sea turtle bycatch in various small shrimp gears." ScholarWorks@UNO, 2019. https://scholarworks.uno.edu/td/2665.
Full textBurns, Karen Mary. "Evaluation of the Efficacy of the Minimum Size Rule in the Red Grouper and Red Snapper Fisheries With Respect to J and Circle Hook Mortality and Barotrauma and the Consequences for Survival and Movement." [Tampa, Fla] : University of South Florida, 2009. http://purl.fcla.edu/usf/dc/et/SFE0002928.
Full textCortés, Serra Verònica. "Assessing and mitigating bycatch in the artisanal longline fisheries of the Mediterranean = Avaluació i mitigació de les captures accidentals d'ocells marins en la pesca artesanal de palangre del Mediterrani." Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/482134.
Full textBycatch mortality in longline fisheries is considered the main threat for numerous seabirds worldwide. In the Mediterranean, this mortality is seriously affecting the viability of some populations. However, the information available on the level and extent of its impact is scarce. Likewise, no mitigation strategy has yet been implemented in the fleet. The present thesis aims to asses and contribute to the knowledge about the seabird bycatch in longline fisheries of western Mediterranean, as well as to identify the most appropriate mitigation strategy for the fleet. The study has focused on demersal longliners, since they use the most dangerous gear for seabirds and also because there is little information available. This study shows a high seabird mortality on longlines, in particular of the three endemic shearwaters: Scopoli’s (Calonectris diomedea), Balearic (Puffinus mauretanicus) and Mediterranean (P. yelkouan), calling for urgent actions to reduce their bycatch rates. There are several factors influencing on bycatch risk, but the most important are the season and the setting time. Other influential factors are the bait type, wind conditions, longline configuration, proximity to the colonies and the number of hooks set. Moreover, in Scopoli’s shearwater, the reduction of discards by trawlers led to increased interaction between these seabirds and longliners, thus increasing the bycatch risk. Consequently, the incoming legislation that intends to ban discards will likely aggravate this problem. This study also shows adult- and sex-biased mortality in longline fisheries. In addition, this mortality is more pronounced but not limited to the local colonies. It appears that night setting would be the most effective method to reduce bycatch without compromising target or non-commercial species. However, this should be confirmed in longliners targeting species other than European hake. A temporal closure of the fishery is also a promising strategy, although its effects on fishing activity should be carefully evaluated. Others methods include increasing the longline sink rate and avoiding baits attractive to seabirds. The high diversity of strategies and gears hampers the identification of solutions applicable to the whole fleet. Consequently, it would be necessary to establish a set of different measures that can be adapted to the majority of fishing methods.
SÃtiro, Inah. "AbundÃncia de raias demersais apÃs proibiÃÃo de pesca de arrasto por embarccaÃÃes motorizadas na costa." Universidade Federal do CearÃ, 2013. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=12944.
Full textBycatch fisheries may be considered one of the greatest threats to marine life. The influence of these captures in marine ecosystems makes it one of the most pressing issues on nature conservation today. For decades, there was in Fortaleza, CE, a shrimp otter trawl fisheries activity conducted by motorized boats that accidently captured batoids. This activity has been prohibited by the Brazilian Ministry of Environment since 2003. The goal of the present study was to evaluate if the prohibition of shrimp otter trawl fisheries activity conducted by motorized boats on coastal areas (1) affects the abundance of demersal batoids; (2) which portion of these batoidsâ populations is under the effect of the prohibition of this fishery activity; and (3) if species considered by the current Brazilian legislation as under any level of threat also are effected by this prohibition. In the present study, fourteen scientific sampling were carried out on Mucuripe Bay, Fortaleza, CE, between September 2004 and November 2010. During each survey, 10 stations were sampled with otter trawl net, circa 14 m depth. In addition, unpublished data on the abundance of batoids captured as bycatch by shrimp fisheries in this same bay, between 1997 and 1998, were compiled. The prohibition of the shrimp fisheries using motorized boats, in coastal areas, affects positively the abundance of demersal batoids previously impacted by this activity. Furthermore, the coastal area studied is used by all size classes of the batoids Dasyatis guttata and Gymnura micrura and, therefore, it may be considered important for reproduction of these species. Lastly, this same Bay is also home for several species that currently are considered by the Brazilian legislation as endangered (n=4) or overexploited or threatened of overexploitation (n=7).
Louis-Jean, Laurent. "Étude de la pêche artisanale côtière aux filets de fond aux Antilles françaises afin de réduire les captures accidentelles de tortues marines et obtenir une activité plus durable." Thesis, Paris, EPHE, 2015. http://www.theses.fr/2015EPHE3028/document.
Full textThe national marine turtles recovery plan in FWI was adopted in 2006 by the National council for the nature conservancy. The bottom nets bycatch, i.e. the trammel, folle and gill nets, on the continental shelf are the main threat. Experimental nets with different heights, meshing and incline was compared to professional ones during 226 experimental trials. Trammel net is non selective. Low profile nets maintain a similar productivity and reduce the turtle bycatch. Trammel and folle nets cause more bycatch. The long soak times lead to more than 90 % of turtles mortality and more discards. Each year, about two thousands of turtles would be captured in FWI, with a mortality rate closed to 60 %. The mature turtles were captured during the nesting season and the resident ones are mostly juveniles or sub-adults, because of the local past overexploitation and indicator of non stable populations. The “fishery” threat is particularly important it affect nesting females, best stocks recovery hope. Closely to the marine professionals, the marine turtle and resources protection would be effective thanks to the reduction of the height and soak times nets and the total or partial ban of large meshing size nets
TOLOTTI, Mariana Travassos. "Ecologia e conservação do tubarão galha-branca oceânico (carcharhinus longimanus, poey 1861)." Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/17780.
Full textMade available in DSpace on 2016-09-01T13:19:16Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) MTTolotti_EcologyConservationOceanicWhitetipShark_VF_FichaCatalografica.compressed aprovada.pdf: 5871232 bytes, checksum: 4af848c7c53529f3e28ffa5d085443f1 (MD5) Previous issue date: 2016-02-19
CAPEs
O objetivo principal da presente tese consistiu em agregar informações ao conhecimento sobre o tubarão galha-branca oceânico (Carcharhinus longimanus), principalmente no que se refere à sua distribuição, índices de abundância e preferências de habitat. Apesar de ser uma espécie muito capturada na pesca oceânica de atuns afins, informações acerca destes aspectos ecológicos são escassas e até mesmo ausentes na literatura relacionada à espécie. A tese é apresentada como um conjunto de capítulos autônomos, representando artigos científicos individuais. No primeiro capítulo-artigo foram discutidos os possíveis efeitos de medidas de manejo restritivas, implementadas recentemente por Organizações Regionais da Pesca Atuneira e que incluem algumas espécies de tubarões oceânicos. Medidas restritivas isoladas terão pouco impacto na redução da mortalidade de tubarões oceânicos. Um conjunto de medidas mitigadoras integradas será mais eficaz na conservação e recuperação das populações dessas espécies. No segundo capítulo-artigo foram analisados dados de captura e esforço de 14.835 lançamentos de espinhel pelágico realizados por embarcações arrendadas da frota atuneira brasileira, nos anos de 2004 a 2010. A CPUE nominal exibiu uma tendência de aumento gradual ao longo dos anos, variando de 0,04 em 2004 para 0,15 em 2010. A CPUE foi padronizada através de uma abordagem delta-GLM, entretanto, o índice de abundância padronizado não diferiu significativamente da CPUE nominal. Os modelos indicaram que as capturas de tubarões galha-branca são maiores para a estratégia de pesca espanhola, que se caracteriza pela utilização de anzóis em profundidades mais rasas. No terceiro capítulo-artigo, a interação entre tubarões galha-branca e a pesca de rede de cerco nos Oceanos Atlântico e Índico foi analisada, com o objetivo de investigar o potencial da utilização do banco de dados dessa pescaria para derivar índices de abundância e determinar tendências populacionais para a espécie. Dados de observadores de bordo da frota francesa combinados com dados históricos da União Soviética foram utilizados na análise. A série temporal combinada incluiu os anos entre 1986 e 2014. No Oceano Atlântico não foi possível determinar uma tendência populacional, uma vez que o índice de ocorrência foi muito baixo e não variou significativamente com o tempo. No Oceano Índico foi observada uma mudança bem-marcada no índice de ocorrência, oscilando em torno de 20% entre meados dos anos 80 e 90 e caindo para menos de 10% a partir de 2005. No quarto capítulo-artigo, a vulnerabilidade do tubarão galha-branca à pesca de espinhel pelágico foi avaliada utilizando dados dependentes e independentes da pesca. Os dados dependentes incluíram informações de diários de bordo (1999- 2011) e observadores embarcados (2004 a 2010), num total de 65.277 lançamentos de espinhel. Os dados independentes foram obtidos a partir de 8 tubarões marcados com marcas do tipo “pop-up satellite archival tag” na área onde a frota de espinhel operou. Locais de marcação e desprendimento das marcas foram relativamente próximos uns dos outros. Entretanto, os indivíduos marcados tenderam a viajar longas distâncias antes de retornar para a área de marcação. Foi observado um certo grau de filopatria à área. “Hotspots” de alta utilização dos tubarões marcados correspondeu à área sob forte pressão pesqueira. Todos os tubarões exibiram uma forte preferência por águas quentes e rasas da camada de mistura, gastando, em média, mais de 70% do tempo acima da termoclina e 95% acima de 120 m. Esse resultado justifica a maior capturabilidade da espécie em espinheis mais rasos. No quinto e último capítuloartigo, os movimentos verticais dos tubarões marcados foram analisados em detalhe. Apesar da distribuição vertical restrita, os dados indicaram que o tubarão galha-branca apresenta padrões de movimento complexos, incluindo padrões de migrações circadianas distintos e mergulhos profundos. O padrão circadiano mais frequentemente observado é caracterizado de um deslocamento à superfície durante o nascer do sol e uma tendência a permanecer em profundidades mais baixas durante o dia. Os movimentos verticais também foram influenciados pela temperatura da superfície do mar, o que pode indicar a ocorrência de termoregulação para espécie. A integração dos resultados de cada capítuloartigo proporcionou boas perspectivas para o desenvolvimento de medidas de mitigação. A evidência em relação à preferência do tubarão galha-branca por águas quentes e rasas é sólida, indicando que a remoção dos anzóis rasos do espinhel pode ser proposta para reduzir a captura incidental da espécie. O fato de variações na CPUE já terem sido observadas, sugere que esta pode ser uma medida eficaz. O comportamento filopátrico observado para o OCS também indica que a espécie pode se beneficiar com a criação de áreas marinhas protegidas.
The ultimate goal of this thesis was to generate knowledge regarding the ecology of the oceanic whitetip shark (Carcharhinus longimanus) and contribute for an ecosystem-based fishery management. The work focuses on the interactions between tuna fisheries and the species and its habitat preferences. Despite being frequently caught on high-sea fisheries, there are wide knowledge gaps regarding the ecology of the oceanic whitetip shark. The thesis is presented as a set of selfcontained standalone chapters, constructed as individual research articles. The first article-chapter provides a discussion concerning pelagic sharks and the recent species-specific banning measures implemented by Regional Fishery Management Organizations (RFMOs) in charge of tuna fisheries. It is unlikely that banning measures alone can reduce the high level of fishing mortality and recover pelagic shark’s depleted populations. Managers should be fully aware that the development and implementation of mitigation measures are critical for a more effective conservation strategy. In the second article-chapter, catch and effort data from 14,835 longline sets conducted by foreign tuna longline vessels chartered by Brazil, from 2004 to 2010, were analyzed. The nominal catch per unit of effort (CPUE) exhibited a gradual increase, varying from 0.04 sharks/1000 hooks in 2004 to 0.15 in 2010. A CPUE standardization was performed using a delta-GLM approach, but the standardized index of abundance did not differ significantly from the nominal CPUE. The models indicated that the catches of oceanic whitetip sharks are higher for the Spanish fishing strategy, which is characterized by the deployment of hooks at shallower depths. In the third article-chapter, the interaction between oceanic whitetip sharks and the purse seine fishery in the eastern Atlantic and western Indian oceans was analyzed, in order to investigate the potential of using this fishery’s database to derive abundance indexes and determine population trends for the species. Observer data from the French purse seine fleet combined with a historic database from the Soviet Union were used in the analyses. The combined time series spanned from 1986 to 2014. The occurrence index was very low for Atlantic Ocean and no marked temporal trend was observed. For the Indian Ocean a well-marked change on the occurrence index was observed, fluctuating around 20% from mid 80’s to mid 90’s and dropping to less than 10% as from 2005. In the fourth article-chapter, a combination of fisheries dependent and independent data was used to assess the vulnerability of the oceanic whitetip shark to pelagic longline fisheries. Fisheries dependent data included information from logbooks (from 1999 to 2011) and onboard observers (2004 to 2010), totaling 65,277 pelagic longline sets. Fisheries independent data were obtained from 8 oceanic whitetip sharks tagged with popup satellite archival tags in the area where longline fleet operated. Tagging and pop-up sites were relatively close to each other, although individuals tended to travel long distances before returning to the tagging area. Some degree of philopatry was observed. High utilization hotspots of tagged sharks fell inside the area under strongest fishing pressure. All sharks exhibited a strong preference for the warm and shallow waters of the mixed layer, spending on average more than 70% of the time above the thermocline and 95% above 120 m. This result explains the higher catchability of the species on shallow longline gear. In the fifth and last article-chapter, the vertical movements of tagged oceanic whitetip sharks were analyzed in detail. Despite its restricted vertical distribution, the analyses reveled that oceanic whitetips perform complex movement patterns, including distinct diel patterns and deep diving behavior. A correlation between vertical movements and sea surface temperature was also observed, suggesting the occurrence of thermoregulation for the species. The combined results of each article-chapter have provided good insights towards the development of mitigation measures. The evidence regarding oceanic whitetip shark’s preference for warm and shallow waters is solid and this information suggests that the removal of the shallow hooks from the longline gear could be proposed as a technique to reduce OCS bycatch. The fact that CPUE variations were already observed suggests that this might be an effective measure. The philopatric behavior observed for the OCS also indicates that the species could benefit from time-area closure measures.
Stewardson, Carolyn Louise, and carolyn stewardson@anu edu au. "Biology and conservation of the Cape (South African) fur seal Arctocephalus pusillus pusillus (Pinnipedia: Otariidae) from the Eastern Cape Coast of South Africa." The Australian National University. Faculty of Science, 2002. http://thesis.anu.edu.au./public/adt-ANU20030124.162757.
Full textHood, Catherine Catania. "Incidental capture of harbour porpoise, Phocoena phocoena, in three gillnet fisheries of the northwest Atlantic : an investigation of possible factors /." 2001.
Find full textHoover, Krutzikowsky Vicki. "Bycatch in the ocean shrimp Pandalus jordani fishery." Thesis, 2001. http://hdl.handle.net/1957/29968.
Full textGraduation date: 2002
Robins, Julie Belinda. "A scientific basis for a comprehensive approach to managing sea turtle by-catch: the Queensland east coast as a case study." Thesis, 2002. https://researchonline.jcu.edu.au/1251/1/01front.pdf.
Full textRobins, Julie Belinda. "A scientific basis for a comprehensive approach to managing sea turtle by-catch : the Queensland east coast as a case study /." 2002. http://eprints.jcu.edu.au/1251/1/01front.pdf.
Full textBache, Sali Jayne. "National approaches to bycatch : the development of Australian and United States fisheries conservation policy." Phd thesis, 1999. http://hdl.handle.net/1885/147795.
Full textAnjos, Mariana. "Bycatch in bivalve fisheries of Algarve." Master's thesis, 2016. http://hdl.handle.net/10400.1/9907.
Full textThe present study assessed bycatch in Algarve grid dredge fisheries and estimated fishing gear inflicted damage and mortality, with the purpose of formulating mitigation measures, specifically fishing gear modifications. Bycatch using this dredge has been shown to surpass target species catch and, although it would not be a major problem if the discarded individuals survive, it nonetheless creates an issue of concern for fishers. Fishing surveys were conducted bimonthly onboard commercial fishing vessels in the same coastal areas near Olhão, throughout six months, in order to ascertain seasonal variation. Fishing targeted commercially valuable clam species, either Donax trunculus, using the DDredge, or Spisula solida and Chamelea gallina, using the SDredge. All individuals captured were attributed scores from a damage table ranging from 1 to 4, where 1 or 2 equate organism survival and 3 or 4 mortality. Results showed significant differences between fisheries regarding total catch composition, confirming dredge capacity to maximize target catch, but none for bycatch, demonstrating similar benthic communities in all sampled sites. Bycatch reached a maximum of 57.5% in abundance, and was significantly higher using the DDredge. Damage and mortality, although overall low, varied as a result of the morphological characteristics of the taxa itself, as such Echinodermata was presented as most subject to damage. Higher percentages of bycatch in the DDredge indirectly led to higher mortality rates as well. Seasonality analysis indicated the influence of spring on an increase of bycatch abundance in the DDredge. The implementation of a BRD and net bag in the grid dredge are proposed to reduce bycatch, as well as its damage and mortality, while maintaining fishing yield. Comparative studies are advised as to evaluate BRD effects on catch composition, bycatch amount, mortality, and discard rates. Additionally, the re-evaluation of the damage table through survival experiments is recommended.
A pesca acidental ou acessória é geralmente definida como a captura não intencional de organismos que não se enquadram na definição de captura alvo, por exemplo, indivíduos de espécies sem importância comercial ou juvenis das espécies alvo. A captura acessória inclui todos os indivíduos que são descartados para o mar, as rejeições e aqueles que, apesar de não serem considerados captura alvo, por qualquer outra razão sejam retidos e desembarcados. A pesca acessória é, assim, a diferença entre a captura total e a captura alvo. Portugal é um pequeno país com a terceira maior Zona Económica Exclusiva (ZEE) da União Europeia. As comunidades costeiras portuguesas dependem da pesca e de atividades com ela relacionadas como meio de subsistência, sendo estas uma forte componente do património cultural português. Apesar de a atividade pesqueira ser regulada por legislação própria, continua a ser um elemento perturbador dos ecossistemas e das comunidades marinhas. Este projecto focou-se na frota pesqueira que se dedica à captura de amêijoa branca (Spisula solida), pé-de-burrinho (Chamelea gallina) e conquilha (Donax trunculus) com ganchorra de grelha. A ganchorra de grelha é utilizada na pesca de bivalves ao longo da costa algarvia e em especial na área do presente estudo. Esta ganchorra é composta por uma boca com um pente de dentes na barra inferior, acoplada a uma armação de grelha metálica onde a captura é retida. Os indivíduos de pequenas dimensões, incluindo juvenis da espécie alvo, isto é, abaixo dos 25 mm de tamanho mínimo legal, escapam por entre as barras da grelha, enquanto a captura alvo e indivíduos maiores da captura acessória são mantidos e trazidos a bordo. Encontra-se demonstrado para o uso desta ganchorra uma redução da captura de juvenis da espécie-alvo e uma rápida recuperação dos indivíduos que escapam através das barras da grelha. No entanto, a sua utilização acarreta consequências, já que esta arte de pesca não é tão seletiva como seria desejável, promovendo capturas acessórias e, consequentemente, rejeições. O presente trabalho tem como objetivo avaliar a importância das capturas acessórias na pesca de bivalves com ganchorra de grelha no Algarve, determinar o dano e mortalidade causados por esta arte de pesca à captura total, aferir a existência de sazonalidade e propor medidas que minimizem a pesca acidental. Tais objetivos foram alcançados através da quantificação das capturas acessórias obtidas com ganchorras de grelha com diferentes espaçamentos entre as barras paralelas, 8 mm para a captura de D. trunculus (DDredge) e 12 mm para S. solida e C. gallina (SDredge). A amostragem decorreu duas vezes por mês, entre Fevereiro e Julho, a bordo de embarcações de pesca comercial na costa algarvia perto de Olhão. A determinação da mortalidade de cada indivíduo foi calculada através da atribuição de uma escala de dano de 1 a 4, em que 1 ou 2 implicam a sobrevivência do organismo rejeitado e 3 e 4 a sua morte. Foram encontradas diferenças significativas entre a composição das capturas totais das duas ganchorras, confirmando a capacidade de cada ganchorra maximizar a captura da sua respectiva espécie alvo. Porém, nenhuma diferença foi encontrada entre a composição da captura acessória, demonstrando a presença de comunidades bentónicas semelhantes em todos os locais de amostragem. A captura acidental atingiu um máximo de 57.5% em abundância e 35.1% em biomassa e foi significativamente maior usando a DDredge, devido à menor abundância da espécie alvo. Dano e mortalidade, embora baixos, variaram em resultado das características morfológicas de cada taxa. As espécies alvo mostraram, em geral, baixas mortalidades devido à natureza resistente das conchas destas espécies de bivalves, com S. solida como mais resistente e D. trunculus mais susceptível a dano. Tanto na pescaria de S. solida e C. gallina como na de D. trunculus, Echinodermata foi o phylum com maior mortalidade e dano, em particular a classe Echinoidea, devido à sensibilidade a dano mecânico das placas fundidas que compõem estes organismos. Elevadas percentagens de capturas acessórias na DDredge causaram, assim, indiretamente taxas de mortalidade significativamente maiores, já que se verificou menor abundância de espécies resistentes a dano. Análises de sazonalidade indicaram o aumento da abundância das capturas acessórias na DDredge desde o Inverno até à Primavera. Não foram observadas diferenças significativas entre o Verão e as restantes estações, presumivelmente devido ao baixo tamanho da amostra causado pelo fecho da pesca durante esses meses. Porém, visto que outros autores indicaram também a presença de sazonalidade na abundância das capturas da ganchorra de grelha, especificamente durante o Outono, torna-se evidente a necessidade de estudos adicionais que explorem estas variações. Recomenda-se a implementação de um aparelho que reduza a proporção de rejeições (BRD) na ganchorra de grelha. Este BRD consiste numa grelha articulada diagonalmente posicionada na armação metálica da ganchorra e na criação de uma abertura no topo da mesma. O espaçamento entre as barras da grelha do BRD deverá ser largo o suficiente para a permitir a entrada e retenção da espécie alvo, mas estreito de modo a prevenir a entrada de indivíduos da captura acessória de maiores dimensões, excluindo-os através da abertura mencionada. No entanto, é indispensável que esta alteração à ganchorra não cause redução no rendimento de pesca. Propõe-se, assim, que a grelha posterior da ganchorra seja eliminada e um saco de rede acoplado. Desta forma evita-se a perda de captura alvo pela abertura no topo da armação metálica durante a recolha da ganchorra, o único momento da operação de pesca em que esta se encontra numa posição vertical. Prevê-se que, com estas alterações, as rejeições sejam reduzidas, bem como o dano e mortalidade causados pela ganchorra de grelha, visto que a imediata exclusão de organismos lhes permitirá rápida recuperação de atividade e menor risco de predação. Estudos comparativos que avaliem o efeito das modificações propostas são aconselhados. Deste modo, deverá proceder-se ao arrasto simultâneo de ganchorras com e sem BRD, de modo a avaliar os efeitos do mesmo no rendimento de pesca, composição das capturas, proporção de capturas acessórias, mortalidade e taxas de rejeição. Recomenda-se também a reavaliação da tabela de danos usada através de experiências de sobrevivência.
Costa, Maria Esmeralda de Sá Leite Correia da. "Bycatch and discards of commercial trawl fisheries in the south coast of Portugal." Doctoral thesis, 2014. http://hdl.handle.net/10400.1/6793.
Full textHamilton, SA. "Assessment, evaluation and mitigation of marine mammal bycatch in commercial fishing gear." Thesis, 2020. https://eprints.utas.edu.au/38454/1/Hamilton_whole_thesis.pdf.
Full textDunn, Daniel Carl. "On the dynamic management of marine resources." Diss., 2014. http://hdl.handle.net/10161/9442.
Full textMismatches in the spatiotemporal variability of resource, resource users and management actions breeds inefficiency in the management of marine resources. To date, the spatiotemporal resolution and extent of fisheries management has been largely dictated by logistical and political constraints, and secondarily by the geographic range of the species or meta-population dynamics. Management units are rarely smaller than 1000 km2 in developed coastal fisheries, and management measures generally occur at resolutions larger than 100 km2. From a temporal perspective, the finest resolution of management measures is at best a month but more generally a year. As such, attempts to manage processes and patterns at sub-10 km, sub-1 month resolution often involve some level of spatiotemporal mismatch. To address the obvious spatiotemporal mismatch between a dynamic ocean and static management, to allow for a comprehensive implementation of ecosystem-based fisheries management, and to minimize inefficiency in our management of marine resources, we must seek to develop more dynamic management measures that allow managers to address scales, processes and patterns occurring under ten kilometers.
In this dissertation I apply point pattern processes, cumulative distribution functions, receiver operator characteristic curves, simulated annealing tools, regression models and clustering techniques to develop examples of two dynamic management measures and to compare the efficiency of static versus dynamic management measures. I show that autocorrelation analysis can inform the distances and times used in real-time closures based on move-on rules. Further, I identify optimum bottom temperature threshold values to separate individual species within the Northeast Multispecies Fishery from Atlantic cod. Results demonstrate that dynamic spatiotemporal management measures are widely applicable, and more effective and more efficient than static time-area closures. Unexpected trends in some results due to a changing climate indicate possible increasing thermal overlap between Atlantic cod and many other species in the fishery. Implications of scale in fisheries management and the importance of coarse scale (1 - 10km) ecological patterns to fisheries are discussed.
Dissertation
Dias, Vítor Hugo Ferreira. "Another brick in the restoration of gorgonians: assessment of coral bycatch in artisanal fisheries and its potential for restoration actions." Master's thesis, 2020. http://hdl.handle.net/10400.1/15536.
Full textCoral gardens and cold-water corals are key habitats for many marine organisms, providing several goods and services. Because of their ecological importance and susceptibility to degradation caused by human activities, these habitats are considered vulnerable marine ecosystems. Fisheries are likely the most destructive threat affecting these habitats and there is an urgent need to understand how different fishing gear affects them, as well as how to implement effective conservation and protection measures that mitigate these impacts. This study aims to provide baseline information on the impact of fisheries using bottom-set gillnet locally on coral assemblages, and to develop a time-effective and low-cost restoration pipeline for both deep- and shallow-water populations using coral bycatch. In order to assess the impact of bottom-set gillnet fisheries on coral assemblages, the fishing activity and coral bycatch of one vessel were documented over 42 days, determining coral composition, specimen size, fishing depth, location, number of fish caught, mesh size and soaking time for each net deployed. In total, 4,326 specimens of corals belonging to 22 different species of corals were collected from 118 bottom-set gillnets. Additionally, we report 4 hotspots of coral biodiversity. This study confirms anecdotal evidence on the destructive impact of bottom-set gillnets on benthic ecosystems, demonstrating that the impact is greater than previously observed. For the restoration component of the study, twelve artificial reefs were used to transplant 90 corals obtained from bycatch, which were divided in 4 treatments varying transplant density and species composition. On average, 78% of the colonies transplanted survived after 8 months. The results show that total branch length metric can detect the changes in growth of branching organisms better than maximum height metric. Additionally, this study demonstrates that octocorals grow much faster than generally assumed, but the constant dynamic of breakage and recovery that these species cope with maintains their net growth relatively low.
I would like to thank the fishermen community in Sagres, for all the help with the coral specimens, inside and outside of the vessel, as well as their friendship. I offer my gratitude to DOCAPESCA Baleira-Sagres for providing the warehouse where corals were measured, maintained and stored over this period, to the Autoridade Marítima Nacional for the accommodation provided in Sagres, and to the Instituto da Conservação da Natureza e das Florestas (ICNF) for providing the authorization for the deployments. Additionally, this study was co-funded by the project HABMAR- “Contribuição para potenciar a proteção e revitalização da biodiversidade marinha e de habitats especiais na costa continental portuguesa”, MAR2020 projeto MAR-01.04.02-FEAMP-0018 “HABMAR”
Drake, Andrew. "Quantifying the Likelihood of Human-mediated Movements of Species and Pathogens: The Baitfish Pathway in Ontario as a Model System." Thesis, 2011. http://hdl.handle.net/1807/29706.
Full textStewardson, Carolyn Louise. "Biology and conservation of the Cape (South African) fur seal Arctocephalus pusillus pusillus (Pinnipedia: Otariidae) from the Eastern Cape Coast of South Africa." Phd thesis, 2001. http://hdl.handle.net/1885/48199.
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