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Recreational use, social and economic characteristics of the Smith River and Philpott Reservoir fisheries, VirginiaHartwig, Jonathan J. 25 August 2008 (has links)
I used on-site interviews and angler counts to estimate angler effort, catch and harvest rates, and total catch and total harvest. On the Smith River, angling pressure per km was most intense in the special management area, with most use occurring on weekend days. Anglers harvested approximately 90% of the rainbow trout they caught, and 63% of the rainbow trout stocked during the study period. Anglers harvested only 5% of the brown trout they caught. Philpott Reservoir was overwhelmingly a nonconsumptive black bass fishery (anglers harvested only 9% of the black bass they caught). I also estimated net economic value of both fisheries using the travel cost method (TCM) and contingent valuation method (CVM). In addition to estimating net economic value for the fisheries under current fishing conditions, I also explored changes in economic value under different fishing scenarios and alternative flow regimes. On the Smith River, doubling an angler's chance of catching a large trout (> 16 in.) had the highest net economic value of any scenario in all three river sections. The wild trout scenario had the highest net economic value in the special management area. On Philpott Reservoir, doubling an angler's chance of catching a black bass had the highest net economic value. Total economic value (including angler expenditures) of both fisheries was $656,140, only $13,000 less than the value of power produced at Philpott Dam during Fiscal Year 1995. / Master of Science
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Effects of fishing on a coral reef fish assemblage in Northeastern BrazilDe Moraes Carvalho, Felipe 15 February 2022 (has links)
Reef fisheries are important activities that support the livelihoods of millions of people. Reef fisheries exploit different habitats and typically target a diversity of species caught with a matching diversity of fishing gears. However, previous studies of reef fisheries have generally lacked detailed information on the catch and effort by gear and habitat type. In this dissertation, the sustainability of a coral reef fishery at the Marine Protected Area Costa dos Corais, Northeastern Brazil is assessed. In 1,833 landing interviews with local fishers, 100 fished species were identified and the total catch in kilograms for each species, the size composition of captured individuals and the habitat type exploited were recorded. First, the dissertation explores how fishing gears selected for distinct functional traits. A low competitive interaction between different gears was noted. Gears used in reef habitats selected for sedentary and benthic species, while gears used in coastal lagoons targeted highly mobile and pelagic. Second, the dissertation assesses how different gear affected the catch rates of coral reef fishes. Gears used on coral reef habitats had a more negative effect on catch rates than those used in coastal lagoons. The three gear types that affected catch rates more severely were hook and line, gillnet and cast net. Based on the results it is argued that the effects of reef fisheries on catch rates were highly depended on the vulnerability of target species. Finally, the dissertation assesses the ability of the fishing-down concept to assess the sustainability of the local fishery; the fishing-down is used to describe the process of moving away from catching large fish to progressively targeting smaller fish. I found strong support for the fishing-down, as fisheries decreased the average size of the fish assemblage and affected more heavily the catch rates of fishes with higher index of vulnerability. Overall results show that fisheries management should focus on the conservation of vulnerable taxa that are responsible for key ecological processes in coral reefs such as herbivory and coral predation. The decision-making process on management measures must be based on clear discussions with all stakeholders involved. / Doctor of Philosophy / Coral reefs are one of the richest environments on the planet, but overfishing threatens their conservation. Reef fishers use many techniques, or fishing gears, such as hook and line and nets, to catch a high diversity of fish species. Reef fisheries are often unsustainable as fishers are allowed to employ high levels of effort. Thus, studies are needed to assess the sustainability of coral reef fisheries and determine which gears are more negative to reef fishes. In a series of three studies, I investigated how reef fisheries affected fish communities in Northeastern Brazil. I used a total of 1,833 interviews with fishers in which I recorded the total catch for each species, obtained size of fish individuals, and asked about the environment that was exploited, coral reefs or coastal lagoons. First, I evaluated how the different gears selected for groups of species with unique life-history characteristics, such as size, mobility and period of activity. I found that gears such as hook and line and harpoon selected for species with sedentary traits that live near the bottom of the ocean, whereas nets selected for very mobile species that inhabit surface waters. In general, fishers did not compete for the same resources with different gears. Second, I assessed how the different gears affected the relative abundance of coral reef fishes. The three gear types that affected more heavily the relative abundance of fishes were hook and line, gillnet and cast net. I argue that the negative effects occurred because these gears caught species with characteristics that made them vulnerable to exploitation, such as slow body growth. Third the dissertation assesses the ability of the fishing-down concept to assess the sustainability of the local fishery; the fishing-down is used to describe the process of moving away from catching large fish to progressively targeting smaller fish. I found strong support for the fishing-down as the studied fisheries impacted the size and the abundance of local fishes. My results suggest that fisheries management should focus on the conservation of vulnerable fish responsible for key ecological processes such as herbivory and coral predation. The decision-making process regarding fisheries management must also be based on clear discussions with all stakeholders involved.
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Ecologia e conservação do tubarão galha-branca oceânico (carcharhinus longimanus, poey 1861)TOLOTTI, Mariana Travassos 19 February 2016 (has links)
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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.
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