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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The development of a preservative for gill nets

Cave-Browne-Cave, Genille January 1940 (has links)
[No abstract available] / Science, Faculty of / Chemistry, Department of / Graduate
2

Statistical modelling of the selectivity of trawl nets

Holtrop, G. January 1998 (has links)
This thesis develops statistical methodology for modelling the selectivity of fishing nets, using data from covered codend experiments of fishing trawls. First, the effects of subsampling an experimental catch instead of measuring the entire catch are investigated. Often the subsample is not taken at random. This leads to bias in the selectivity parameter estimates. Simulations show that the effects of non-random subsampling are minimised when equal proportions are sampled from the test and the control net. A model is developed for describing the selectivity of a net with a window panel inserted. This model quantifies the selectivity of both the codend and the window panel, which can then be combined. The model is used to investigate the selectivity of different window panels and their contribution to the combined selectivity. Traditionally, selectivity has been modelled as a fixed and random effects model, estimated in two stages. As an alternative, Markov chain Monte Carlo techniques are explored. A Bayesian selectivity model is formulated, and the effect of the prior distribution on the variance components is investigated. The posterior distribution is relatively insensitive to a prior distribution having variation of similar magnitude as the variation present in the data. For model selection, the p-value approach applied to the posterior marginal densities is more useful than the Bayes and pseudo-Bayes factors. The Bayesian selectivity model is extended to include variation between seasons and variation between trips. The new model is applied to a data set containing seasonal variation. Finally, a Bayeisan multi-species model is developed that accounts for dependencies between species. This gives more precise selectivity parameter estimates. It also reduces bias in the parameter estimates by accounting for mechanisms behind non-random missing data.
3

Assessment of mesh size selectivity under commercial fishing conditions /

Perez-Comas, José Antonio. January 1996 (has links)
Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (p. [196]-205).
4

Hydrodynamic modeling of nets and trawls

Krishnamurthy, Muthusamy, January 1975 (has links)
Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 220-222).
5

Selective action of gillnets on sockeye (Oncorhynchus nerka) and pink salmon (O. gorbuscha) stocks of the Skeena River system, British Columbia

Todd, Ian St. Pierre January 1969 (has links)
Exploitation of Skeena River sockeye salmon (Oncorhynchus nerka) has been conducted almost solely by drift gillnets since inception of the commercial fishery in 1877. Selective action of gillnets is a factor which may have contributed to a long term decline in sockeye production and to other features of the population biology. This study was designed to determine the selective properties of nylon gillnets presently in use; to compare these with properties of linen nets used prior to 1955; to adjust age composition estimates of escapement levels prior to 1946; and to re-examine brood year production. In addition, the selective action was examined of the fishery as a whole on sockeye and pink salmon (O. gorbuscha) in 1968. The selective properties of six nylon gillnets ranging in mesh size between 4-5/8 inches and 5-5/8 inches, which corresponded with sizes normally used in the commercial fishery, were to be determined through a simultaneous fishing experiment, and selectivity curves were computed by Holt's (1963) normal probability technique. Unique selectivity curves for each mesh size could not be determined from the sockeye data. Mean size of age class l.2 sockeye (representing about 12 per cent of the sample) increased with mesh size but mean size of age class 1.3 sockeye (representing about 82 per cent of the sample) demonstrated no trend. Age class 1.3 sockeye were among the largest on record and it was postulated that fish of this age class were too large to gill properly in all mesh sizes used. A comparison of the predominant mesh of nylon gillnet (5-1/4 inch) with linen nets of the mesh used in the historic fishery (5-5/8 inch) was also influenced by the large size of age class 1.3 sockeye. Nylon nets were 2.5 and 2.7 times as efficient as linen for sockeye, and 8.0 and 9.0 times as effective for pink salmon. Nylon gillnets, although smaller, caught larger sockeye and pink salmon than did the linen gillnets. Variances about mean size of sockeye and pink salmon were also greater for catches in nylon as opposed to linen gillnets. In total, the selective properties of the commercial fishery reflected the results obtained in the nylon gillnet multi-mesh experiment. An overall selectivity curve computed for sockeye salmon by the direct method of Regier and Robson (1966) approximated a skew-normal distribution. Examination of the age-sex class components of the stock indicated that selection increased linearly over the length range of age 1.2 sockeye of both sexes, and decreased linearly over the length range of age class 1.3 sockeye. A selectivity curve was also computed for pink salmon and this curve, in total, also assumed a normal shape in spite of the extremely small size of pink salmon in 1968. The length-girth relationships of the two species were shown to differ and this accounted for most of the difference between the selectivity curves. The relationship between maximum efficiency and the maximum girth to perimeter mesh measure closely approximated the value of 1.2: 1.0 reported by McCombie and Berst (1969) for other species. Retention by gillnets declined once the girth/mesh ratio exceeded 1.2 for sockeye. For pink salmon, no females were of a size to equal this ratio; the descending limb of the selectivity curve was due solely to males as the retention rates declined once girth/mesh ratio exceeded 1.0. These findings suggest that in most years the gillnet fishery on the Skeena River would tend to select relatively larger sockeye salmon. In years such as 1968, however, selection would be against smaller fish. This frequent reversal combined with the intense modern fishery, which tends to remove virtually all fish during a short period and allows almost complete escapement in periods between fishing, suggested that selective fishing has probably not been a significant factor in decreased production. / Science, Faculty of / Zoology, Department of / Graduate
6

As redes comerciais da pesca e o urbano no amazonas: o caso da Vila de Copatana, município de Jutaí – AM

Bezerra, Janderson Meireles, 92-991323990 23 February 2018 (has links)
Submitted by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2018-06-19T17:41:54Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissetação_Janderson Bezerra.pdf: 8617622 bytes, checksum: 5001f5fb78a2b7198bb277673a7aead3 (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2018-06-19T17:42:04Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissetação_Janderson Bezerra.pdf: 8617622 bytes, checksum: 5001f5fb78a2b7198bb277673a7aead3 (MD5) / Made available in DSpace on 2018-06-19T17:42:04Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissetação_Janderson Bezerra.pdf: 8617622 bytes, checksum: 5001f5fb78a2b7198bb277673a7aead3 (MD5) Previous issue date: 2018-02-23 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The Amazon in general, in terms of human occupation, is known as a demographic void, but it is known today that this discourse does not proceed. There are historical records that prove that the Amazon was always occupied by people who lived in the region. The Amazonian floodplains were so populated that these peoples migrated to populate the rest of the South American continent, as Fausto states (2010, 31). "From their floodplains, as rich as they were fought by an ever-growing population, would have led to migratory waves that would populate the South America¨. In this imaginary context of "demographic", we are struck by the contemporary process of urbanization to which this biome belongs. In this process the Vilas in Alto Solimões / Amazonas, with a total population of more than 1.000 inhabitants. In this work we will deal with the Copatana Village, located in the Alto Solimões / Amazonas microregion belonging to the municipality of Jutaí. The region has agriculture as the main source of income, however, it was the fishing bias that best describes the relationship between the city and the village. In this sense, the main objective of this work was to understand, through commercial fishing networks, the role of Copatana Village in the structuring of the urban network of the Alto Solimões / Amazonas microregion. In order to achieve this objective, it was extremely important to implement monitoring. This was one of the options we thought and carried out as one of the ways of collecting primary data, in this case, fishing. Tracking was inspired in the works of VanVliet et al. (2015) and TavaresPinto (2015), both conducted their research on wild animal hunting networks on the Brazil- Peru-Colombia triple border. Due to the lack of specific secondary data for the site, the field work carried out in the town of Copatana was crucial for the research and understanding of the processes that occur. At the end of the research, it was concluded that the commercial fishing network and the urban network in Amazonas are totally interconnected from the town of Copatana, in the municipality of Jutaí, to cities like Tabatinga and Manaus or other cities outside the state and the country through commercial fishing networks. / A Amazônia de forma geral, em termos de ocupação humana, é conhecida como um vazio demográfico, mas sabe-se hoje que esse discurso não procede. Existem registros históricos que comprovam que a Amazônia sempre foi ocupada por povos que viviam na região. As várzeas amazônicas eram tão povoadas que estes povos migravam para povoar o resto do continente Sul- Americano, como afirma Fausto (2010, p. 31) "De sua várzea, tão rica quanto disputada por uma população sempre crescente, teriam partido levas migratórias que iriam povoar a América do Sul". Neste contexto imaginário de "vazio demográfico" nos chama a atenção o processo contemporâneo de urbanização a qual este bioma se insere. Neste processo ressaltam-se as Vilas no Alto Solimões/Amazonas com população total acima de mil habitantes. Neste trabalho trataremos sobre a Vila de Copatana, localizada na microrregião do Alto Solimões/Amazonas pertencente ao município de Jutaí. A região possui a agricultura como principal fonte de renda, contudo, foi pelo viés da pesca que melhor conseguimos descrever as relações existentes entre a cidade e a Vila. Neste sentido, o trabalho teve como principal objetivo compreender por meio das redes comerciais de pesca o papel da Vila de Copatana na estruturação da rede urbana da microrregião do Alto Solimões/Amazonas. Para alcançar tal objetivo, foi de suma importância a implantação de um monitoramento foi uma das opções que pensamos e realizamos como uma das formas de colher dados primários, neste caso, de pesca. O monitoramento foi inspirado nos trabalhos de Van-Vliet et al. (2015) e Tavares-Pinto (2015), ambos realizaram suas pesquisas sobre as redes de caça de animais selvagens na tríplice fronteira Brasil-Peru-Colômbia. Devido à quase inexistência de dados secundários específicos para o local os trabalhos de campo realizados na Vila de Copatana foram cruciais para a pesquisa e o entendimento dos processos que ocorrem. Ao final da pesquisa chegou-se à conclusão de que a rede comercial da pesca e o urbano no Amazonas está totalmente interligado desde a Vila de Copatana, no município de Jutaí, às cidades como Tabatinga e Manaus ou outras cidades fora do estado e do país por meio de diversas redes comerciais de pesca.

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