published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

Microphytobenthos are the dominant primary producers on estuarine mudflats playing a key role in the functioning of the ecosystem. Studies into microphytobenthic ecology have previously been limited by scale but the advent of fine scale analysis techniques (gm) as well as non-destructive sampling has enabled the system to be examined at a level not previously possible. This study examined the formation, structure and function of microphytobenthic biofilms using non-destructive (remote sensing by PAM fluorescence; fibreoptic light microprofiling) and destructive (cryo-freezing and Low temperature scanning electron microscopy) sampling. Many microphytobenthic organisms are motile and have evolved complex migratory strategies. Microphytobenthic migratory patterns are widely described but much remains to be elucidated about the controlling factors. The fluorescence parameter F015 (minimum fluorescence yield after 15 minutes dark adaptation) was used to monitor short-term changes in biomass at the sediment surface. Light, tidal state, endogeny and combinations thereof were all shown to control migration, demonstrating that predictable migratory rhythms cannot be assumed. Microscale sectioning showed that chlorophyll a was always concentrated in the top 400 gm (the photosynthetically active biomass). Clear migratory patterns were not detected using microscale sectioning therefore indicating that migration occurs over a scale < 400gm. Despite no changes in the chlorophyll a content in the surface layers, LTSEM analysis demonstrated diurnal taxonomic shifts providing circumstantial evidence that microphytobenthic cells sub-cycle at the sediment surface to optimise fitness. The light extinction co-efficient (k) of microphytobenthic biofilms significantly vaned with site, assemblage and also over time. 90% of the surface PPFD had always been attenuated by 400, and in many cases before 200. Traditional microphytobenthic primary productivity models do not account for changes in the spatial and temporal distribution of biomass or light attenuation and therefore their applicability to the real situation may be limited.

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No description available.

Marine reserves have increasingly been recognised for their potential to address the pervasive problem of unsustainable harvest of fisheries worldwide. Biologists advocate the benefits of increased spawning biomass, larger modal sizes and greater densities of fish within marine reserves, and the possibility of spillover to adjacent fishable areas. Bioeconomic studies, however, find that pay-offs from stand-alone marine reserves rarely compete with sustainable yield management schemes, but that they can be beneficial when stocks are heavily exploited. Most of these bioeconomic models are analytical and deterministic in nature, and therefore ignore the redistribution of effort in response to closure and the inherent uncertainty of the marine environment. We present a bioeconomic analysis of a network of no-take areas around Stewart Island in New Zealand applied to the shellfish species paua (abalone) that incorporates both predicted redistribution and reduction in effort, as well as stochastic recruitment. A nested logit model is applied to spatially recorded catch and effort data by the Ministry of Fisheries between 1998 and 2003 to capture the two level decision-making process of divers. On any given day, divers decide whether to go diving at all, and if so, which of the 16 statistical areas around Stewart Island to visit. Weather conditions, spatially varying levels of catch per unit of effort and distance are used as explanatory variables to select areas for closure according to the �least economic impact� in terms of loss of diving trips. An age-structured biological model is developed with parameters specifically applied to paua stocks around Stewart Island. Virgin paua biomass as of 1974 is estimated on the basis of growth, survival, post-larval recruitment and egg production in the absence of fishing. Historic catch rates are then applied to find overall and area-specific levels of exploitation rates, spawning biomass, egg production, legal biomass and numbers of paua. In a final step, the economic model is linked to the biological model to simulate the imposition of no-take areas when taking account of the initial disproportional shift of harvest to fished areas in the first year, and the increase in overall pressure on legal biomass in the years thereafter. We contribute to the marine reserve debate by showing that in the very long run, the overall yield under closure of a relatively small area approaches and even slightly surpasses the yield under no closure for an assumed spillover gradient of 40% despite the redistribution of effort. The most important benefits of marine reserves emerge when stochastic recruitment is included in the recruitment function. In practice, predictions about the stock status and the impact of different harvest levels become much more difficult when acknowledging the inherent variability of the marine environment. The likelihood of stock collapse depends on the assumed value of two recruitment parameters, which highlights the effects of parameter uncertainty and emphasizes the role of marine reserves for population persistence. We also show that under uncertainty average yields under a management regime of a network of no-take areas in addition to the quota system can equal yields under no closure for an assumed spillover gradient of 40%, despite the increased pressure on areas adjacent to the closed areas. Our findings have significant implications for the management of the paua fishery at Stewart Island. For a heterogeneously abundant species, such as paua, spatial management in addition to quota limits could be vital in ensuring the long-term sustainability of the fishery given the inherent variability of the marine environment.

Thesis (M. Sc.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 117-126).

Ten individuals of Cephalopholis cruentata, a marine serranid common on Caribbean coral reefs and important to artisanal reef fisheries, were implanted with acoustic transmitters on two reefs within the Soufriere Marine Management Area, St. Lucia. The mean home range area determined was 2120m2. Home range shape was non-circular, with a mean aspect ratio of 0.72. Neither home range size nor home range shape differed between the study sites or as a function of fish size. However, more active fish, as determined by movement per hour and displacement per hour, had larger home ranges. / Use of space within the home range was characterised as activity rates (movement per hour), displacement rates (maximum distance between fish locations per hour), and preferential use of specific areas (% of position fixes in different areas). All fish demonstrated a clear preference for specific areas in their home range. Activity, displacement and % time spent in the preferred reef area were not correlated with fish size. Activity and displacement were higher by night than by day, and consistent with this, fish spent less time in their preferred home range area by night than by day. Given the home range size and movement patterns of C. cruentata determined in the study, the effectiveness of the marine reserve zones in the Soufriere Marine Management Area in protecting C. cruentata is assessed.

Marine reserves have increasingly been recognised for their potential to address the pervasive problem of unsustainable harvest of fisheries worldwide. Biologists advocate the benefits of increased spawning biomass, larger modal sizes and greater densities of fish within marine reserves, and the possibility of spillover to adjacent fishable areas. Bioeconomic studies, however, find that pay-offs from stand-alone marine reserves rarely compete with sustainable yield management schemes, but that they can be beneficial when stocks are heavily exploited. Most of these bioeconomic models are analytical and deterministic in nature, and therefore ignore the redistribution of effort in response to closure and the inherent uncertainty of the marine environment. We present a bioeconomic analysis of a network of no-take areas around Stewart Island in New Zealand applied to the shellfish species paua (abalone) that incorporates both predicted redistribution and reduction in effort, as well as stochastic recruitment. A nested logit model is applied to spatially recorded catch and effort data by the Ministry of Fisheries between 1998 and 2003 to capture the two level decision-making process of divers. On any given day, divers decide whether to go diving at all, and if so, which of the 16 statistical areas around Stewart Island to visit. Weather conditions, spatially varying levels of catch per unit of effort and distance are used as explanatory variables to select areas for closure according to the �least economic impact� in terms of loss of diving trips. An age-structured biological model is developed with parameters specifically applied to paua stocks around Stewart Island. Virgin paua biomass as of 1974 is estimated on the basis of growth, survival, post-larval recruitment and egg production in the absence of fishing. Historic catch rates are then applied to find overall and area-specific levels of exploitation rates, spawning biomass, egg production, legal biomass and numbers of paua. In a final step, the economic model is linked to the biological model to simulate the imposition of no-take areas when taking account of the initial disproportional shift of harvest to fished areas in the first year, and the increase in overall pressure on legal biomass in the years thereafter. We contribute to the marine reserve debate by showing that in the very long run, the overall yield under closure of a relatively small area approaches and even slightly surpasses the yield under no closure for an assumed spillover gradient of 40% despite the redistribution of effort. The most important benefits of marine reserves emerge when stochastic recruitment is included in the recruitment function. In practice, predictions about the stock status and the impact of different harvest levels become much more difficult when acknowledging the inherent variability of the marine environment. The likelihood of stock collapse depends on the assumed value of two recruitment parameters, which highlights the effects of parameter uncertainty and emphasizes the role of marine reserves for population persistence. We also show that under uncertainty average yields under a management regime of a network of no-take areas in addition to the quota system can equal yields under no closure for an assumed spillover gradient of 40%, despite the increased pressure on areas adjacent to the closed areas. Our findings have significant implications for the management of the paua fishery at Stewart Island. For a heterogeneously abundant species, such as paua, spatial management in addition to quota limits could be vital in ensuring the long-term sustainability of the fishery given the inherent variability of the marine environment.

Thesis (Ph. D.)--University of Delaware, 2008. / Principal faculty advisor: George R. Parsons, College of Marine & Earth Studies. Includes bibliographical references.