Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (leaves [156]-162).

The production functions commonly suggested in the fishery bio-economic literature are reviewed, and modifications are suggested to take into account direct and indirect gear externalities and gear saturation effects in a salmon gillnet fishery. This suggests a daily production function of the Cobb-Douglas variety, tested on Skeena River sockeye salmon data. Using the daily production function, a seasonal model is developed, which reflects the intra-seasonal peaking nature of the run, and the multiple day stock removal effect. The properties of this function are analysed, and to demonstrate the significance of the function, its shape is used to indicate the direction of bias in the Crutchfield and Pontecorvo estimates of dissipated rent in Bristol Bay and Puget Sound. / Arts, Faculty of / Vancouver School of Economics / Graduate

The bycatch of cetaceans in fishing gear is considered to be one of the biggest conservation threats to these species. Gear modifications have the potential to reduce these bycatches in global fisheries but there is little available information on how such modifications may change the fishing performance of gear, or indeed the behavior of cetaceans interacting with fishing gear. Generalized linear models (GLMs) were used to identify factors related to cetacean bycatches in UK bottom set gillnets. Rigged net height had a significant positive relationship with harbour porpoise (Phocoena phocoena) bycatch in ICES Area VII suggesting that lowering the profile of gillnets may have the potential to reduce bycatch rates. Modifications to gillnets, such as changing the amount of floatation or increasing the density of the meshes, were found to have significant effects on the active fishing heights of these nets. However, results from a bycatch mitigation trial in Argentina showed that the reduced fishing profile of one experimental net did not result in a concurrent reduction in the bycatch rate of Franciscana dolphins (Pontoporia blainvillei). While there was no significant difference in the rate, length or intensity of harbour porpoise encounters in the presence or absence of gillnets, the proportion of fast echolocation click trains were significantly higher when a net was present, indicating that porpoises either increased acoustic inspection of the net or foraging in the vicinity of the net. An analysis of underwater video footage collected inside trawl nets in an Australia fishery showed that bottlenose dolphins (Tursiops sp.) were present inside nets more frequently than they were caught and were actively foraging inside these nets. The orientation of dolphins inside these nets indicates that the current design of excluder devices used in this fishery could be improved to further reduce bycatch rates.

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

I determined differences in yellow perch gill-net catch-per-unit-effort (CPUE) at two depths (10 and 15 m) in the Indiana waters of Lake Michigan during June, July, and August from 1989 to 2006. I evaluated the abiotic factors of water temperature, water clarity, wave height, and wind direction to determine whether they influence the differences in yellow perch CPUE. This study suggests that yellow perch in southern Lake Michigan may select habitat based on water temperature during the summer, moving in response to thermocline changes. We also evaluated mortality rates for two distinct periods (1984-1994 and 2000-2007) in order to identify the response of the population to changes in exploitation. Yellow perch during 1984-1994 (high exploitation) and 2000-2007 (low exploitation) displayed an increase in mortality for fish of harvestable size. In addition, during 2000-2007 (low exploitation) we identified that female yellow perch reached exploitable size earlier in life than males. / Department of Biology

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Made available in DSpace on 2016-06-02T19:26:23Z (GMT). No. of bitstreams: 1 GUSMAO_Juliana_2013.pdf: 2002037 bytes, checksum: 764c92fab171e138eea762ca82c8ad4d (MD5) Previous issue date: 2013-11-18 / Financiadora de Estudos e Projetos / The Iguape-Cananéia Estuarine-Lagoon Complex has been described as an area for feeding and development of young sea turtles of the Chelonia mydas (green sea turtle) species, besides having recorded the incidence of other marine turtle species present at the Brazilian coast (Caretta caretta, Lepidochelys olivacea, Dermochelys coriacea and Eretmochelys imbricata). The region also presents several caiçara (population from coastal regions) nucleuses which have small-scale fishing as their main source of income, making important to analyze existing interactions between fishermen and sea turtles. The objective of the present study was to describe the interaction of the caiçara communities of Pedrinhas and Pontal de Leste with sea turtles, and the interaction between sea turtles and the artisanal gillnetting, from the fishermen s perspective. Field researches were performed using semi-structured interviews via Snow Ball technique, enabling the identification of the key informers by their peer s recognition. The results showed that the caiçara community of Pontal de Leste, more isolated from the urban centers and having fishing as exclusive activity, presented greater presence of sea turtles in its culture, as well as higher nutritional dependency from sea turtle meat when climate conditions render fishing impossible for long periods of time. At the Pedrinhas community, as it is closer to urban centers and as it has alternative income activities due to tourism, the presence of the sea turtle in the local culture resides mainly at the memories of the older interviewed community members. In both communities knowledge gaps were verified, which could be clarified with educational actions, and the importance of gillnetting for the caiçara and the negative impact it may cause to sea turtles were also verified, being thus vital, the execution of new studies which shall enable the understanding of the magnitude of such interaction. The results obtained aim at generating information for conservation plans so as to minimize the mortality of sea turtles, protecting cultural practices of such communities; thereby, educational activities and management guidelines were proposed, aiming at integrating the political management of natural resources and conservation strategies with the conduct of the local traditional community. / O Complexo Estuarino-Lagunar de Iguape-Cananéia foi descrito como uma área de alimentação e desenvolvimento para juvenis de tartarugas marinhas da espécie Chelonia mydas (tartaruga-verde), além de ter registrado a ocorrência das outras espécies de tartarugas marinhas presentes na costa brasileira (Caretta caretta, Lepidochelys olivacea, Dermochelys coriacea e Eretmochelys imbricata). A região apresenta também vários núcleos caiçaras que têm na pesca artesanal sua principal fonte de renda, o que torna, importante, avaliar as interações existentes entre os pescadores e as tartarugas marinhas. O objetivo deste estudo foi descrever a interação das comunidades caiçaras de Pedrinhas e Pontal de Leste, com as tartarugas marinhas e destas com a pesca de emalhe artesanal, sob a perspectiva dos pescadores. Foram realizadas pesquisas de campo utilizando entrevistas semi-estruturadas através da técnica Bola de Neve , que possibilitou identificar os informantes-chave pelo reconhecimento por seus pares. Os resultados evidenciaram que a comunidade caiçara de Pontal de Leste, mais isolada dos centros urbanos e tendo como única atividade a pesca, apresentou maior presença das tartarugas marinhas em sua cultura, assim como maior dependência nutricional da carne de tartaruga marinha quando as condições climáticas impossibilitam a pesca por longos períodos. Na comunidade de Pedrinhas, por estar próxima aos centros urbanos e ter atividades alternativas de renda, devido ao turismo, a presença da tartaruga marinha na cultura local reside principalmente na memória dos entrevistados mais antigos. Em ambas as comunidades evidenciou-se lacunas de conhecimento que poderiam ser esclarecidas com ações educativas, verificou-se também a importância da rede de emalhe para o caiçara e o impacto negativo que esta pode causar às tartarugas marinhas, sendo imprescindível, portanto, a realização de novos estudos que possibilitem compreender a dimensão desta interação. Os resultados obtidos visam gerar informações para planos de conservação de forma a minimizar a mortalidade das tartarugas marinhas, protegendo as práticas culturais dessas comunidades, desta forma, diretrizes de ações educativas e de gestão foram propostas, objetivando integrar a gestão política dos recursos naturais e estratégias de conservação com o comportamento da comunidade tradicional local.

Lake Liambezi in the Zambezi Region of Namibia, formerly known as the Caprivi Region, is shallow (<6m deep) and characterised by cyclic episodes of filling and drying. When full the lake supports a highly productive fishery and when dry the lake is completely dry and used for agriculture and grazing. In 2000 the lake filled, and between May 2011 and April 2012 was surveyed using beach seine, experimental gillnets and catch landing surveys to obtain information for conservation and management recommendations for the fishery. Littoral fishes in Lake Liambezi and the Kavango floodplain were sampled using seine net and physicochemical properties were measured. Seine net surveys demonstrated that Lake Liambezi littoral zones were dominated by fishes of the family Alestidae (59.7%) while Cichlids constituted the most diverse family. Juvenile Tilapia rendalli and Oreochromis macrochir were among the five most important species in the littoral zone, indicating that these commercially important species use the littoral zone as a nursery ground. Since T. rendalli and O. macrochir are commercially important species, because of this, it is advised that seine nets should not be used. Catch efficiency between monofilament and multifilament gillnets in Lake Liambezi offshore waters were assessed. Catch efficiency experimental fishing trials showed that monofilament gillnets catch per unit effort (CPUE) was three times higher than that of multifilament gillnets for Oreochromis andersonii, O. macrochir, T. rendalli, Serranochromis macrocephalus and Clarias spp. Oreochromis andersonii comprised over 66% of the overall CPUE for both net types combined indicating the importance of this species in the gillnet fishery on the lake. A fishery has been established on the lake with more than 300 canoes and 120 fishermen using monofilament and multifilament gillnets. CPUE was 15 kg/canoe/day and was significantly (P < 0.05) associated with monthly temperature and moon phase parameters indicating that the fishery of Lake Liambezi may be altered by climate and environmental factors. Annual catch from Lake Liambezi was estimated at 3193t with an estimated productivity of 106kg/ha, suggesting that Lake Liambezi makes a significant contribution to the fish supply in the Zambezi Region. Recommendations were made to manage the Lake Liambezi fishery by imposing restrictions on effort (number of fishing boats), gear type, mesh sizes and access. Proper fisheries management and monitoring should incorporate climatic and environmental factors such as temperature and moon phase to meet the challenges of global climatic changes as well as other environmental issues.

Puisque l’altération des habitats d’eau douce augmente, il devient critique d’identifier les composantes de l’habitat qui influencent les métriques de la productivité des pêcheries. Nous avons comparé la contribution relative de trois types de variables d’habitat à l’explication de la variance de métriques d’abondance, de biomasse et de richesse à l’aide de modèles d’habitat de poissons, et avons identifié les variables d’habitat les plus efficaces à expliquer ces variations. Au cours des étés 2012 et 2013, les communautés de poissons de 43 sites littoraux ont été échantillonnées dans le Lac du Bonnet, un réservoir dans le Sud-est du Manitoba (Canada). Sept scénarios d’échantillonnage, différant par l’engin de pêche, l’année et le moment de la journée, ont été utilisés pour estimer l’abondance, la biomasse et la richesse à chaque site, toutes espèces confondues. Trois types de variables d’habitat ont été évalués: des variables locales (à l’intérieur du site), des variables latérales (caractérisation de la berge) et des variables contextuelles (position relative à des attributs du paysage). Les variables d’habitat locales et contextuelles expliquaient en moyenne un total de 44 % (R2 ajusté) de la variation des métriques de la productivité des pêcheries, alors que les variables d’habitat latérales expliquaient seulement 2 % de la variation. Les variables les plus souvent significatives sont la couverture de macrophytes, la distance aux tributaires d’une largeur ≥ 50 m et la distance aux marais d’une superficie ≥ 100 000 m2, ce qui suggère que ces variables sont les plus efficaces à expliquer la variation des métriques de la productivité des pêcheries dans la zone littorale des réservoirs. / As freshwater fisheries become increasingly prone to habitat alteration, it is critical we identify the components of habitat that greatly influence fisheries productivity metrics. Using fish habitat modeling, we compared relative contributions of three types of habitat variables to explain variation in abundance, biomass and richness metrics, and identified habitat variables most effective at explaining these variations. During the summers of 2012 and 2013, fish communities in 43 littoral sites were sampled from Lac du Bonnet, a reservoir in southeastern Manitoba (Canada). Seven different sampling scenarios, consisting of different sampling methods, years and time periods, were used to measure relative abundance, biomass and richness metrics for all species combined per site. Three types of habitat variables were measured: local (i.e. within site), lateral (i.e. shore characterization) and contextual (i.e. position relative to landscape attributes) variables. Together local and contextual habitat variables explained on average 44% R2adj of the variation across fisheries productivity metrics, while only 2% R2adj of the variation was explained by lateral habitat variables. Specifically, macrophyte coverage, distance to tributaries ≥ 50 m wide, and distance to marshes ≥ 100,000 m2 ranked most significant across metrics, suggesting these habitat variables may be most effective at explaining variation in fisheries productivity metrics in the littoral zone of reservoirs.