A main concern in fisheries science has been to identify an accurate index of fish abundance. An underlying paradigm in the science has been that the amount of effort (calculated in hours and standardized for boat size) spent fishing was the best variable to be used to account for the variation in catches. The use of the ratio, catch per unit of effort (cpue), assumes that variations in fish abundance are due to human-controlled processes above the ocean's surface. It does not account for variation due to oceanographic processes that affect fish behaviour and movement patterns below the ocean's surface. This study investigated the possibility that oceanographic factors such as temperature, salinity and depth could have effects on the variations observed in the apparent abundance of a demersal rockfish, Pacific Ocean Perch (Sebastes alutus. Gilbert). Simultaneous monitoring of physical variables and fish abundance estimation was achieved by attaching oceanographic equipment to the fishing gear of commercial vessels, monitoring the acoustic equipment and sampling the fish catch. It was found that Perch prefer a temperature range from 6.7 °C, down to at least 4.8 °C and that their movement patterns are linked to the movement of these temperatures by coastal wind patterns. Perch prefer areas with steep bathymetry, characterized by frontal activity due to interactions between the local bathymetry and tidal currents. Concerns that sampling only from highly successful commercial vessels may have biased abundance estimates, prompted the analysis of historical records of fish catch and government research surveys. Analyses between different boat sizes, different areas and different seasons from the original historical data base and a corrected subset revealed that it was mainly differences between areas that was responsible for the biasing of estimates. Deeper areas predictably produced more fish for all sizes of boats, but were fished more often by the larger boats used in the study. Therefore the field abundance estimates are likely to be biased towards areas of larger perch concentrations. / Science, Faculty of / Zoology, Department of / Graduate

A expansão natural de vegetação lenhosa sobre pradarias tem sido observada em escala global, mas os regimes de distúrbio influenciam a dinâmica da expansão. Basicamente dois padrões de expansão florestal podem ser considerados em áreas campestres excluídas de manejo: o avanço gradual a partir das bordas florestais e a colonização de indivíduos isolados na matriz campestre. Uma vez estabelecidas, as espécies colonizadoras de campos podem facilitar a dispersão de outras espécies sob suas copas (perch effect), servindo como poleiros naturais; e/ou ainda podem facilitar o estabelecimento dessas espécies, atuando como berçários (nurse plant effect). Neste contexto, Araucaria angustifolia é um exemplo de espécie colonizadora em campos que contribui para o processo de expansão. Além disso, A. angustifolia caracteriza-se pela formação de anéis de crescimento anuais em decorrência de variações climáticas sazonais, permitindo o estudo da dinâmica e estrutura etária das populações com o uso de métodos dendrocronológicos. Com base nisso, avaliamos nesta dissertação a estrutura etária de A. angustifolia em campos excluídos de manejo por 34 anos e a relacionamos com o processo de expansão florestal, bem como averiguamos o seu papel como facilitadora da dispersão e estabelecimento de espécies lenhosas colonizadoras de campos. Os resultados apontam para uma relação inversa entre a estrutura etária e a distância da borda florestal; e indicam que A. angustifolia atua mais como um poleiro para deposição de diásporos, do que propriamente como uma facilitadora do estabelecimento dessas espécies. / The natural expansion of woody vegetation over grassland has been observed worldwide, but the expansion dynamics is influenced by the disturbance regimes. Two patterns of forest expansion are well documented: gradual expansion from the forest borders and by the process of nucleation, which consists in the colonization of the grassland matrix by isolated trees. Once established, these colonizing species can facilitate the dispersion process by acting as perches, and/or as nurse plants by facilitating the recruitment of new colonizers. Araucaria angustifolia is an example of colonizer species in open areas contributing to forest expansion. Besides, A. angustifolia presents tree rings that reflect annual cycles of growth and dormancy, allowing us to study dynamics and population age structures using dendrochronological methods. In this dissertation, we evaluate the age structure of A. angustifolia in grasslands excluded from disturbance for 34 years and relate it to the expansion process. As well, we evaluate the role of A. angustifolia as perch (by facilitating seed dispersal) and as a nurse plant (by facilitating the establishment of other species under the crown). Our results point out to an inverse relationship between age structure and distance from the border and indicate that the role of A. angustifolia is more important as a perch than facilitating the establishment of other species.

A expansão natural de vegetação lenhosa sobre pradarias tem sido observada em escala global, mas os regimes de distúrbio influenciam a dinâmica da expansão. Basicamente dois padrões de expansão florestal podem ser considerados em áreas campestres excluídas de manejo: o avanço gradual a partir das bordas florestais e a colonização de indivíduos isolados na matriz campestre. Uma vez estabelecidas, as espécies colonizadoras de campos podem facilitar a dispersão de outras espécies sob suas copas (perch effect), servindo como poleiros naturais; e/ou ainda podem facilitar o estabelecimento dessas espécies, atuando como berçários (nurse plant effect). Neste contexto, Araucaria angustifolia é um exemplo de espécie colonizadora em campos que contribui para o processo de expansão. Além disso, A. angustifolia caracteriza-se pela formação de anéis de crescimento anuais em decorrência de variações climáticas sazonais, permitindo o estudo da dinâmica e estrutura etária das populações com o uso de métodos dendrocronológicos. Com base nisso, avaliamos nesta dissertação a estrutura etária de A. angustifolia em campos excluídos de manejo por 34 anos e a relacionamos com o processo de expansão florestal, bem como averiguamos o seu papel como facilitadora da dispersão e estabelecimento de espécies lenhosas colonizadoras de campos. Os resultados apontam para uma relação inversa entre a estrutura etária e a distância da borda florestal; e indicam que A. angustifolia atua mais como um poleiro para deposição de diásporos, do que propriamente como uma facilitadora do estabelecimento dessas espécies. / The natural expansion of woody vegetation over grassland has been observed worldwide, but the expansion dynamics is influenced by the disturbance regimes. Two patterns of forest expansion are well documented: gradual expansion from the forest borders and by the process of nucleation, which consists in the colonization of the grassland matrix by isolated trees. Once established, these colonizing species can facilitate the dispersion process by acting as perches, and/or as nurse plants by facilitating the recruitment of new colonizers. Araucaria angustifolia is an example of colonizer species in open areas contributing to forest expansion. Besides, A. angustifolia presents tree rings that reflect annual cycles of growth and dormancy, allowing us to study dynamics and population age structures using dendrochronological methods. In this dissertation, we evaluate the age structure of A. angustifolia in grasslands excluded from disturbance for 34 years and relate it to the expansion process. As well, we evaluate the role of A. angustifolia as perch (by facilitating seed dispersal) and as a nurse plant (by facilitating the establishment of other species under the crown). Our results point out to an inverse relationship between age structure and distance from the border and indicate that the role of A. angustifolia is more important as a perch than facilitating the establishment of other species.

A expansão natural de vegetação lenhosa sobre pradarias tem sido observada em escala global, mas os regimes de distúrbio influenciam a dinâmica da expansão. Basicamente dois padrões de expansão florestal podem ser considerados em áreas campestres excluídas de manejo: o avanço gradual a partir das bordas florestais e a colonização de indivíduos isolados na matriz campestre. Uma vez estabelecidas, as espécies colonizadoras de campos podem facilitar a dispersão de outras espécies sob suas copas (perch effect), servindo como poleiros naturais; e/ou ainda podem facilitar o estabelecimento dessas espécies, atuando como berçários (nurse plant effect). Neste contexto, Araucaria angustifolia é um exemplo de espécie colonizadora em campos que contribui para o processo de expansão. Além disso, A. angustifolia caracteriza-se pela formação de anéis de crescimento anuais em decorrência de variações climáticas sazonais, permitindo o estudo da dinâmica e estrutura etária das populações com o uso de métodos dendrocronológicos. Com base nisso, avaliamos nesta dissertação a estrutura etária de A. angustifolia em campos excluídos de manejo por 34 anos e a relacionamos com o processo de expansão florestal, bem como averiguamos o seu papel como facilitadora da dispersão e estabelecimento de espécies lenhosas colonizadoras de campos. Os resultados apontam para uma relação inversa entre a estrutura etária e a distância da borda florestal; e indicam que A. angustifolia atua mais como um poleiro para deposição de diásporos, do que propriamente como uma facilitadora do estabelecimento dessas espécies. / The natural expansion of woody vegetation over grassland has been observed worldwide, but the expansion dynamics is influenced by the disturbance regimes. Two patterns of forest expansion are well documented: gradual expansion from the forest borders and by the process of nucleation, which consists in the colonization of the grassland matrix by isolated trees. Once established, these colonizing species can facilitate the dispersion process by acting as perches, and/or as nurse plants by facilitating the recruitment of new colonizers. Araucaria angustifolia is an example of colonizer species in open areas contributing to forest expansion. Besides, A. angustifolia presents tree rings that reflect annual cycles of growth and dormancy, allowing us to study dynamics and population age structures using dendrochronological methods. In this dissertation, we evaluate the age structure of A. angustifolia in grasslands excluded from disturbance for 34 years and relate it to the expansion process. As well, we evaluate the role of A. angustifolia as perch (by facilitating seed dispersal) and as a nurse plant (by facilitating the establishment of other species under the crown). Our results point out to an inverse relationship between age structure and distance from the border and indicate that the role of A. angustifolia is more important as a perch than facilitating the establishment of other species.

Metal-contamination of lakes simplifies food webs and reduces the efficiency of energy transfer to top trophic organisms, such as yellow perch (Perca flavescens). Benthic invertebrate community composition and yellow perch diet, growth and activity levels from lakes along a metal-contamination gradient were used to assess the importance of a naturally diverse prey base for maintaining energy transfer to growing fish, and how this is disrupted by metal-contamination. As perch grow larger, they shift their diet to larger prey; otherwise, the activity costs of foraging for many, small prey, instead of a few large prey, become too high and the fish stop growing. Metal contaminated lakes have less diverse zoobenthic communities, particularly the lack of large bodied invertebrate taxa, forcing perch to rely on smaller benthic prey. Perch from metal-contaminated lakes display slow growth and poor condition during benthivory. Estimates of fish activity, using the activity of the glycolytic enzyme Lactate dehydrogenase in perch white muscle tissue as a proxy, suggest that diet shifts to larger prey lower activity costs and may explain how diet shifts maintain growth efficiency as perch grow larger. Perch from metal-contaminated lakes cannot benefit from the energetic advantages of switching to larger prey and thus exhibit poor growth.

No description available.

No description available.

Conventional wisdom in ecotoxicology predicts reductions in organismal fitness to follow from exposure-related physiological effects. This expectation may be appropriate for controlled laboratory environments, but may not necessarily reflect what is likely to take place in the wild. In an extensive review of the ecotoxicology literature, it was revealed that fish condition factor (an index of energetic fitness) is just as likely to respond favourably to pollutant exposure as it is to respond negatively. The remainder of this thesis examines some of the ecological reasons for this apparent paradox. One possible cause of altered energetic status in wild, pollutant-exposed fish is variable food availability. Addressing this possibility, I showed that consumption rates (estimated using a 137Cesium mass-balance approach) were not related to growth reductions in hormonally-impaired yellow perch ( Perca flavescens) from metal-contaminated lakes. Another possibility is that fish forage less efficiently in metal-polluted lakes as a result of lowered prey choice. In this thesis, I develop an enzymatic and individual-based biomarker for fish activity costs (muscle lactate dehydrogenase, LDH, activity) and show, through the use of this tool that the cost of fish activity is intimately tied to prey type and the ability to make normal ontogenetic diet shifts. Through the application of LDH measurements, as well as through bioenergetic modelling, diet and prey community analyses, a link between decreased prey choice and high perch activity costs leading to zero growth efficiency (energetic bottlenecks) was demonstrated in yellow perch from metal-contaminated lakes. This finding provided one of the first examples in ecotoxicology of a mechanistic link between community and organismal endpoints. The findings of this thesis emphasize the need for ecotoxicology to consider ecology when looking for and interpreting ecologically relevant endpoints. The final chapter of this thesis ex

Metal contamination can disrupt the trophic links in food webs by altering the taxonomic composition and size structure of benthic invertebrate communities. Benthic invertebrate samples and perch (Perca flavescens) were collected from six lakes along a gradient of metal pollution in Rouyn-Noranda, Canada. The benthic communities of the contaminated lakes were less diverse and had smaller individuals (0.09 mg d.w. and 0.16 mg d.w. vs. 0.22 mg d.w. in the reference lake). The stomach contents of perch from contaminated lakes were less diverse, showed a greater reliance on chironomids or zooplankton, and cannibalism than perch from less polluted lakes. The mean size of prey in perch from contaminated lakes was smaller than in reference lakes (3.7 mg d.w. and 7.39 mg d.w. vs. 47.7 mg d.w. and 67.1 mg d.w. in reference lakes). (Abstract shortened by UMI.)

No description available.