The objective was to design and evaluate a Suspension oyster tray unit to optimize conditions necessary for successful commercial culture of oysters in British Columbia for the half-shell market. The suspension system was tested against MacNicol and Nestier trays presently used by the industry. Units were located in two sites in Trevenen Bay. One location was sheltered and calm; the other a natural tidal raceway with intense current flow. The purpose was to test the ability of the design to provide more uniform growth, retard fouling, be easily handled and be commercially feasible to construct. Assessing tray performance was based on monitoring shell growth, condition index, fouling occurrence, materials handling and the capital costs of the systems. Field-experimentation began in June and terminated in October, 1979. The Nestier unit had the best shell growth in the calm environment but displayed variation in growth among trays in the stack, suffered retarded growth in the tidal raceway and had significant barnacle accumulation. The MacNicol performed on par with the Suspension system except for variations in growth due to vertical position, the accumulation of mussels and lowered performance at the tidal raceway site. Suspension tray units performed similarily at both sites, exhibited less variation in growth among trays in a stack, retarded fouling and proved the most economically feasible system for commercial use. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Thesis (MSc)--Stellenbosch University, 2013. / No abstract available.

Abstract ¡@¡@The present study was undertaken to understand the accumulation of PCBs in the marine environment of Taiwan. Samples including oyster drills, oysters, sediments and seawater were collected from the West coast of Taiwan and analyzed by GC/ECD and GC/MS. ¡@¡@The concentration of PCBs in sediments was 31.05¡ã406.38 pg/g dry wt with the highest one at Tong-Kung. The PCBs in cultural oysters from Tong-Kung was 3.80 pg/g wet wt. Concentrations of PCBs in wild oysters from Tai-Si, Chi-Ku, and Pu-Dai were 123.57 pg/g wet wt, 2.93 pg/g wet wt, and 2.08 pg/g wet wt, respectively. The concentrations of PCBs in snails were in the range of 78.24 to 796.96 pg/g wet wt with the highest one from Tong-Kung. A positive correlations between the concentrations of PCBs in seawater and sediment (r=0.78; p<0.01) and in oysters and snails were also observed(r=0.79; p<0.01). The bioaccumulation of PCBs from seawater to oysters was about 72 times, and the biomagnification of PCBs from oysters to snails was 10 times.

Human activities are causing a global loss of plant and animal species, degrading ecosystem properties and threatening ecosystem services. One indicator of these losses is the increasing proportion of fish stocks in decline, and the Challenger oyster fishery in Tasman Bay, central New Zealand is an example of one such fishery. Anthropogenic effects from land-based activities, and towed-gear fishing have been implicated as contributors to the decline of shellfisheries and degradation of the marine ecosystem in Tasman Bay. Increased sedimentation in the bay caused by soil erosion and runoff associated with forestry, agriculture and subdivision is likely to have a range of negative effects on the benthic community. Also towed-gear fishing, dredging and trawling homogenise benthic habitat structure (reduce habitat heterogeneity) and facilitate sediment resuspension as well as causing removal and direct physical damage to benthic biota. There is an imperative to seek to mitigate these effects and look at ways to restore the benthic community including the commercial shellfish species. In this context, my central hypothesis was that enhancement of the benthic habitat by returning waste shell to the seabed would increase oyster production for the fishery. Related to this main goal of oyster fishery enhancement, a primary objective of the study was to fill knowledge gaps relating to the biology and ecology of the oyster in Tasman Bay. The second main topic of my thesis was to investigate how this form of habitat enhancement would alter the benthic community structure, and potentially aid in restoration of the wider ecosystem in the bay. I sought to link the twin goals of fishery enhancement and ecological restoration by considering potential management measures to promote a sustainable oyster fishery and at the same time facilitate ecological restoration within Tasman Bay. The investigations focused on four main themes: temporal patterns of oyster larval abundance, spatial patterns of spatfall and larval dispersal, effects of habitat enhancement on oyster population productivity, and effects of habitat enhancement on the benthic faunal community. Laboratory and field studies were conducted between October 2004 and May 2009. A peak period of oyster reproductive activity began in late spring and continued through summer in each year. Maximum rates of adult oysters brooding larvae were 17% in November 2004 and 2005, and 23 % in December 2006. Over the entire summer breeding period it was estimated that 55 to 78 % of adult oysters incubated larvae. A very low level of brooding activity (1 %) occurred during winter. Temporal trends in larval settlement closely tracked brooding patterns. Settlement on collectors deployed in Tasman Bay was greatest between November and January, and there were very low rates in winter. Results are useful in optimising the timing of substratum deployment in an enhancement program for the oyster fishery. Spat settlement density was strongly related to background adult oyster density. Spat settlement on experimental arrays deployed through the water column only occurred within a narrow vertical range very close to (<1 m above) the seabed. If suitable habitat is available for settlement, oysters tend to settle within a few hours after release, but approximately half of the larvae settled in a laboratory experiment were capable of remaining viable for several days. Oyster distribution assessed at the scale of the shellfishing industry’s annual biomass survey (median distance between sample tows ~ 1 km) is adequate to broadly predict spat settlement distribution in the subsequent settlement season, and the distribution of mature oysters is a key determinant in the placement of shell for habitat enhancement to maximise spat settlement. Deployment of waste whole scallop shell on the seabed as settlement substratum increased oyster spat density significantly. Available settlement surface on enhanced shell plots decreased by 82% in the five months after deployment, due to fouling by numerous invertebrates and sedimentation. Survival of oysters recruited to enhanced habitat was generally very low, and varied greatly among 4 experimental sites and through time. After 3+ years, survival among site/treatment combinations ranged from 0% to 0.04%. At the site where survival was greatest, the absolute density of oysters surviving to 3.41 years on enhanced habitat was estimated as 0.4 m⁻². This equated to an increase in relative density of commercial sized oysters from ~0.01 m⁻² prior to enhancement, to ~0.14 m⁻² at the end of the experiment, and demonstrated that habitat enhancement can elevate adult oyster densities to commercial levels on areas of seabed where oysters were previously below threshold densities for commercial fishing (0.02 m⁻²). Peaks in mortality occurred within experimental plots when oysters were less than one year old, and three years old. Growth modeling indicated that after 4.25 years, 98% of living oysters would attain legal size (≥ 58mm length), and 92% would attain sufficient shell depth (≥ 20 mm) to provide high grade (grade A in the industry) meat. Shell depth was a better morphometric predictor of meat weight than either shell height or shell length. The species assemblages on the shell-enhanced habitat were distinct from those on adjacent non-enhanced seabed. Measures of taxonomic and functional richness, faunal densities, and taxonomic redundancy within functional groups all increased in enhanced habitat. Beta and gamma diversity also increased due to patchiness of the habitat created within enhanced experimental sites. Large scale habitat enhancement in Tasman Bay via the deposition of waste shell on the seabed is likely to confer benefits to ecosystem function associated with those community level effects. To sustain an oyster fishery in Tasman Bay, an ecosystem-based approach to fishery management is recommended to facilitate restoration of benthic habitats and communities and to help maintain ecosystem function supporting all components of the benthic community, including the oyster population. Planning and implementation of a combination of specific management measures including habitat enhancement, rotational fishing, permanent exclusion of towed fishing gear from a network of protected areas, and integration of the management of the oyster, scallop, and finfish fisheries would provide the best chance for restoration and maintenance of a sustainable oyster fishery.

Thesis (M.M.P.)--University of Delaware, 2007. / Principal faculty advisor: George R. Parsons, College of Marine and Earth Studies. Includes bibliographical references.

The Virginia oyster industry changed markedly in the period between 1950 and the present. This change has been the result of a variety of forces which can be conveniently classified as economic, biological and institutional. In general, biological forces initiated a series of changes in the fishery which have had economic impacts and impacts on the institutional structure of the fishery. The biological forces have had a much more severe impact on the seed-planting, or private grounds, sector than on the public grounds sector. The dependence of the seed planting sector on public seed beds and the different regulatory regimes applicable to the public and private grounds makes it difficult to draw firm conclusions on the relative merits of alternative tenure structures. The magnitudes of economic, biological and public policy forces as contributing factors to the decline of the oyster fishery are estimated and it is concluded that the biological forces have played the dominant role in the decline of the Virginia oyster fishery. It is suggested that attention be focused on the physical and management inputs to the production of oysters and on methods for bringing forth an appropriate resource mix. It is argued that either a predominantly private grounds fishery, a predominantly public grounds ‘' fishery, with appropriate institutional modifications to allow efficient harvest technologies to be used without threatening the viability of the resource base, or a mixed tenure system could be used and with appropriate management could result in substantial revitalization of the Virginia oyster industry. However, because of the biological changes which have occurred, management, whether public or private, takes on a much more important role in determining the future of the Virginia oyster fishery. / Ph. D. / incomplete_metadata

No description available.

Food production systems need to keep pace with the rising global population. Food from aquatic environments comes from both capture fisheries and aquaculture. Industrial fishing pressure has caused a global loss of more than 90% of large predatory fishes and 80% of the world’s fish stocks are reported as fully exploited or overexploited. Global finfish, shellfish and aquatic plant aquaculture has been steadily increasing to meet the global demand for seafood. In British Columbia, aquaculture is primarily marine, with salmon and shellfish accounting for the majority of species cultured. Although shellfish aquaculture accounts for significantly less production and value compared to salmon aquaculture, the amount of foreshore dedicated to farming shellfish is nearly half (44%) the total area utilized by all aquaculture in the Province. Introduced Pacific oysters (Crassostrea gigas) (74%) dominate shellfish aquaculture in British Columbia. Pacific oysters are known to be very efficient generalist filter feeders that can grow faster and larger than native species. Extensive aquaculture is a form of aquaculture, where farmed animals feed exclusively on naturally occurring food in the surrounding water column. The goal of this research was to determine if there was a measureable depletion of phytoplankton around shellfish farms along the west coast of Canada and the United States. Chlorophyll-a, a pigment found within phytoplankton, was used as a proxy for phytoplankton abundance for this study. In field season one, two bays were studied, one exposed to shellfish culture (Westcott Bay) and one not exposed to shellfish culture (Fisherman Bay). The concentration of chlorophyll-a was measured in each bay at three locations at two depths (0.5 and 3 meters) and at two tidal heights (high and low). Chlorophyll-a concentration was found to be related to either depth or tide, with location in a bay showing no difference in either of the bays studied. In addition to water column measurements, 100 Pacific oysters were placed at two locations within Westcott Bay Seafarm to test for local differences in oyster growth. The results from this experiment showed that Pacific oysters grown in the center of a shellfish farm were smaller than oyster grown at the farm’s periphery. Field season two tested for spatial patterns between chlorophyll-a concentration and proximity to a shellfish farm in three different bays (Westcott Bay, Trevenon Bay and Gorge Harbour). A measureable depletion footprint of chlorophyll-a concentration was detected in the two sheltered shallow bays tested (Westcott Bay and Gorge Harbour), whereas no depletion footprint was detected in the exposed, deep bay (Trevenon Bay). Tide height played a significant role in predicating chlorophyll-a concentration in all three of the bays studied. These results suggested that some areas may be more suitable for shellfish culture than others. Taken together, this research demonstrated a measureable gradient of phytoplankton in sheltered shallow bays exposed to shellfish culture with depletion closest to the farm site, as well as greater oyster growth at the periphery of shellfish farms where phytoplankton would be predictably in greater abundance. / Graduate

Thesis (M.S.)--University of North Carolina Wilmington, 2007. / Includes bibliographical references (Leaves: 59-65)

Thesis--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 68-88).