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No description available.

North American Pacific salmon (Oncorhynchus spp.) are heavily exploited in coastal fisheries of the gantlet class (Paulik and Greenough, 1966). The Canadian fishery of Juan de Fuca Strait, British Columbia, is a particularly complex example involving four gear types: gillnet, seine, troll and sport which harvest, at various times, large numbers of all salmon species. Because salmon are highly available to fishing gears, exploitation must be carefully regulated. This study, based on various field data and catch statistics, documents factors affecting exploitation: seasonal timing of exploitable salmon, distribution and amount of fishing gear, relative gear efficiency, accessibility of salmon to the gear, vulnerability of salmon to the gear. All species and gears are covered to varying degrees. Each species has a characteristic seasonal timing, but species vary in run duration and timing consistency between years. There are considerable overlaps in species timing which complicate intraseasonal management. In general sockeye (O. nerka) enter in July and August followed by pink (O. gorbuscha) from mid-August to early September, coho (O. kisutch) in September, and chum (O. keta) in October. Chinook (O. tshawytscha) migrations intermingle with all species. Additionally, chinook and coho are exploited on oceanic migrations. Fishing gears are distributed over ninety linear miles from the Bonilla-Tatoosh net line to Victoria. During the August-October net fishery seines fish within five to ten miles of the net line; gillnets fish offshore, from the net line to Sheringham Point, the eastern commercial boundary. Sports fishermen are clumped near shore, east of Sheringham Point, in close proximity to launching or marina facilities. Gear types showed obvious overall differences in relative gear efficiency, based on catch and effort statistics from two or more gear types operating at the same time in a particular area. For example on coho, one seine equals 265 sport units; one gillnet, 63 sport units; and one troller, 8 sport units. Migrating salmon of all species favoured offshore Canadian waters except near Sooke; all species avoided waters east of Race Rocks where 30 per cent of the sport fleet fishes, the discrepancy was least pronounced for chinook. Based on troll catches using standardized gear, coho favoured surface waters above 27 meters; chinook were most abundant below 36 meters. During periods of spawning migration activity, all species favoured the 18-36 meter depth stratum. Gillnets were directionally size selective for all species, but direction and intensity of selection varied between species and between months within species. Because fleet mesh distribution remains relatively constant each year, changes in fish size will have a pronounced effect on gillnet exploitation. Troll gear was species and size selective; however of importance, subtle fishing techniques have a significant effect on selectivity of lures and may be a serious source of bias in empirical lure studies. Coho decreased in susceptibility to hook and line gear between mid-August and mid-September, apparently due to decreased feeding intensity; this has the effect of lowering hook and line catch success for constant abundance. Future studies on lure selection should stress selective mechanisms rather than empirical description. The complexity of inter seasonal and intraseasonal management strategies applicable to the Juan de Fuca fishery undoubtedly are best studied using techniques of systems analysis. However, present gantlet fishery simulation models (Royce et al., 1963; Paulik and Greenough, 1966, detailed in Greenough, MS 1967), although highly sophisticated, lack sufficient generality for direct application to the Juan de Fuca situation. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (Ph. D.)--University of Washington, 2008. / Vita. Includes bibliographical references (leaves 100-107).

A 5km swath-width SeaMARC I sidescan sonar survey, conducted over the zone of overlap between the southern rift zone of Axial Volcano and the northern tip of the Vance spreading segment on the Juan de Fuca Ridge (between 45°24'N and 45°50'N latitude), was analyzed to locate the present position of the Juan de Fuca spreading axis, and to determine the tectonic and volcanic structure of the seafloor. Sidescan data were processed in concert with the ship's Loran-C navigation to construct navigated, orthorectified mosaics of the sidescan imagery. In order to navigate the sidescan swaths, a simple numerical model was developed to describe the tracking behavior of the towed sidescan vehicle. Successive positions and orientations of the sidescan towfish were estimated, and were used to assign latitude/longitude values to individual sidescan pixels. Navigated sidescan pixels were mapped by computer onto an absolute (latitude/longitude) reference grid, and the resulting sidescan mosaic was compared directly to existing high-resolution SeaBeam bathymetry in order to discriminate the effects of large- and small-scale roughness on the observed backscatter distribution. The Juan de Fuca spreading axis between 45°25'N and 45°39'N is located within the axial valley of the Vance segment. Relative age relationships, based on crosscutting and superposition principles, indicate that the most recent volcanism within the axial valley has occurred along the valley's central ridge, and that the most recent resolvable extension within the axial valley has been concentrated between the central ridge and west valley wall. The Vance segment terminates at 45°39'N, and is not associated with a transform fault. The south rift zone of Axial volcano is a constructional volcanic feature that is not faulted, and a discrete axis of spreading over the south flank of Axial volcano is not resolvable in the sidescan imagery; however, the spreading locus north of 45°39'N is constrained to a zone between 130°06'W and 129°54'W. The lack of a well-defined spreading axis north of 45°39'N indicates that the physical manifestation of the divergent plate boundary has been modified or masked by hotspot volcanic processes associated with Axial volcano such that a definitive locus of spreading is not expressed in the surface morphology. / Graduation date: 1989

The crustal structure of a young (<10 My) ocean basin is imaged by two multichannel seismic reflection lines comprising 230 km recorded over the central part of the northern Juan de Fuca plate off western Canada. The more northerly line ties previously interpreted deep seismic reflection lines across the Juan de Fuca ridge and the Cascadia subduction zone; the southern line ties with another interpreted line across the subduction zone. Both lines trend obliquely to the spreading direction. A marine refraction profile crossing the eastern end of the lines provides velocity constraints. The processing sequence applied to the data includes a prestack inside-trace mute of CMP gathers to reduce noise levels on the deep data, CMP stack, post-stack dip filtering, f-k migration and bandpass. Coherency-filtered stacks are helpful in tracing weaker reflectors. The stacked sections reveal a horizontally layered sedimentary sequence overlying a rugged and prominent basement reflector dipping slightly landward. A strong, fairly continuous reflection from the base of the crust at about 2 s two-way-time below the basement surface generally mimics the basement topography and shows the characteristic doubling and tripling of reflections seen in other similar surveys. Although in general the crust appears acoustically transparent, weaker, discontinuous intracrustal reflectors are observed over 40 km at the eastern end of the northern line, and are interpreted to arise from the oceanic Layer 3A/3B and Layer 2/3 boundaries. The im-persistence of these reflectors is an indication of the complexity of the processes producing intracrustal reflectivity, and an indication of the lateral variability of crustal formation. Pseudofault traces of propagating rifts are crossed at three different locations on the two lines, the first MCS crossings of such structures. Crust associated with the pseudofault traces is related to both subhorizontal and dipping subcrustal events which are interpreted as zones of crustal thickening or underplating. Although the crustal thickness elsewhere on the lines varies by only about 10%, crust associated with the pseudofaults is as much as about 25% thicker than average, suggesting that magma supply at transform-type offsets may at times be large. A small seamount discovered on the southern line may result from the excessive magma production at the ridge postulated at propagating rift zones. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Endeavour Ridge is a segment of the Juan de Fuca Ridge, an active spreading centre which lies off western North America between the Pacific and Juan de Fuca plates. This segment is a bathymetric high and a site of hydrothermal activity—both characteristics suggest an underlying heat source such as an axial magma chamber which is associated with crustal generation. To investigate the creation and evolution of oceanic crust, a detailed refraction survey was carried out over the Endeavour Ridge in the fall of 1985. As a component of this survey, a diamond-shaped array consisting of eight OBS along a 20-km line across the ridge and two OBS placed along it at distances of 10 km on either side of the cross-ridge line was deployed to define the shallow crustal structure near and beneath the ridge, especially the possible existence of an axial magma chamber. Airgun shots at 0.2 km intervals along ~300 km of profiles provide conventional reversed and unreversed refraction lines as well as multiple full azimuthal coverage of the region. Travel-time and amplitude data from fifteen in-line airgun profiles recorded on the inner array were forward modelled using an algorithm based on asymptotic ray theory with a starting model obtained from a concurrent study. Two-dimensional models were constructed and then combined to obtain the three-dimensional structure of the region. These models consist of four layers, with the average model correlating well to the classic model of oceanic crust. Layer 2A averages 0.40 km in thickness and has velocities of 2.6 km/s and 2.8 km/s at the top and bottom of the layer, respectively. To achieve such a low velocity, Layer 2A must consist of highly fractured vesicular basalts. A sharp velocity increase to 4.8 km/s marks the transition to Layer 2B. This velocity discontinuity is also visible as a reflector on a. multichannel reflection line obtained through the centre of the study region and is caused by an abrupt decrease in porosity. Layer 2B averages 0.67 km in thickness, has a velocity of 5.4 km/s at its base and consists of less fractured pillow basalts and sheet flows. The Layer 2B-Layer 2C interface is a velocity increase to 5.8 km/s and is the pillow basalt-sheeted dike contact. A small velocity increase from 6.3 to 6.5 km/s delineates the base of the 0.95 km-thick Layer 2C which is the boundary between the sheeted dikes and cumulate gabbros in Layer 3. Layer 3 has the lowest velocity gradient (0.30 s⁻¹) and a velocity of 7.3 km/s at 4.65 km below the seafloor, the maximum depth constrained by the modelling. Lateral heterogeneities on the scale of 2-3 km are superimposed on this basic velocity structure. These heterogeneities are effects of porosity changes, differential pressure changes, and alteration caused by hydrothermal circulation. Layer 2A thins and increases in velocity away from the ridge; ridge-parallel cracks create a velocity anisotropy of ~10-25%, the faster direction parallel to the ridge. Velocities within Layers 2B and 2C also increase by 0.1 km/s away from the axis of the ridge. Layer 3 velocities decrease by 0.1 km/s for arrivals travelling under the ridge. Increased Layer 2 velocities at the ridge crest reveal high lateral velocity constrasts in very young crust, but within 0.03 Ma the oceanic crust at the ridge has matured to the off-ridge structure. No firm evidence exists for a large magma chamber under Endeavour Ridge. Although the bathymetric high and high-temperature hydrothermal discharges are evidence for a magma chamber, the lack of recent sheet flows at the ridge crest and the presence of a rift along the crest indicate the magma chamber is waning and must be of a size (<1 km in width) not resolvable by seismic refraction data. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Two characterization studies were undertaken to assess the concentrations and environmental loadings of 125 pharmaceuticals, personal care products, illicit drugs and their metabolites (PPCPs) in screened municipal wastewaters being discharged into Juan de Fuca Strait from two marine outfalls in the Capital Regional District, British Columbia, Canada. Two up-stream pump stations were also sampled. The PPCP concentration profiles were generally similar between the four sampling locations. Qualitative seasonal patterns in PPCP concentrations were also observed, primarily due to rainfall events that diluted wastewater contaminants during the winter. Increases in wastewater flow volumes following a rain event appeared to result in consistent shifts in PPCP concentration profiles for at least three of the four sites. Results indicated that the concentrations of PPCPs were similar to those observed in influents from other jurisdictions. Predicted environmental concentrations were predominantly well below literature concentration thresholds known to induce acute or chronic effects in organisms in the environment. However, there was slight potential for adverse chronic effects as a result of the predicted environmental concentrations of ibuprofen around the outfalls based on comparison to literature environmental effects thresholds. In general, sub-lethal and chronic effects endpoints were relatively limited in availability in the literature, as were literature thresholds derived from exposures to PPCP mixtures. Additional adverse chronic effects of these substances may be discovered in the future. Comparisons were made to regional prescription rates and population demographics to determine whether these factors could be good predictors of PPCP concentrations or loadings. Although wastewater concentrations and loadings were proportional to both prescription rates and population size, the regression relationships were statistically weak or insignificant. As such, prescription rates and population size could not be used to accurately predict pharmaceutical wastewater concentrations and loadings on their own. No qualitative relationships were observed between wastewater PPCP concentrations and either population age or gender breakdown. Overall, wastewater flow volumes, derived population equivalents and analytical method variability were also important factors to consider. Minor proportional deviations were observed following a preliminary loading comparison based on the relative population equivalent sizes of each of the four wastewater system catchment areas. These deviations could have been a result of disproportional hospital loading inputs and/or wastewater system inflow and infiltration. Comparisons were also made between the concentrations of PPCPs and the concentrations of conventional wastewater parameters typically used to characterize bulk wastewater loadings (i.e., carbonaceous biochemical oxygen demand, biological oxygen demand, total suspended solids, volatile suspended solids). Only 18 of the 125 PPCPs were positively correlated with all four conventional parameters. This suggests that designing and optimizing treatment plants to efficiently reduce conventional parameter loadings may not lead to as efficient or consistent reductions in the concentrations of all of the assessed PPCPs. However, the PPCP results were based on analyses of the filtered aqueous fraction of the wastewater samples, whereas the conventional parameter results were based on whole unfiltered effluent samples. As such, there was no direct link between the two sets of results. / Graduate / 0306

Thesis (Ph. D.)--University of Washington, 1988. / Vita. Bibliography: leaves [264]-290.

Berlin, Freie Universiẗat, Diss., 2003. / Dateiformat: zip, Dateien im PDF-Format.