The use of multibeam and split-beam echo sounders for assessing biomass and distribution of spring-spawning Atlantic cod in the Gulf of Maine

This research focused on advancing the application of split-beam and multibeam echo sounding to remotely locate and describe spatial distribution, and to provide a relative measure of abundance of the spring-spawning Atlantic cod (Gadus morhua) in the western Gulf of Maine. Specifically, the main objectives of this research were 1) to test the feasibility of a multibeam echo sounder to detect changes in volume backscatter proportional to incrementally decreasing quantities of cod held in a submerged cage, and to compare results to a split-beam echo sounder; 2) to describe the spatio-temporal distribution and estimate biomass of spring-spawning cod in the Gulf of Maine cod spawning protection area (GOMCSPA) by repeated acoustic and trawl surveys; and 3) to determine a predictive relation between target strength and length for 38-kHz and 120-kHz split-beam echo sounders and a 300-kHz multibeam echo sounder, and characterize other factors affecting backscattering of sound. The multibeam echo sounder detected a small and large reduction in volume backscatter proportional to reductions in stocking density of caged cod, while the split-beam echo sounder only detected a large reduction in stocking density. The spatial information from the multibeam echo sounder helped interpret and explain results from the split-beam echo sounder. Repeated acoustic and trawl surveys showed cod were relatively widespread in the survey area in May, but congregated at higher densities in areas adjacent to two elevated bathymetric features. Most cod converged to a single location in June, and were at a higher concentration than observations in May. This congregation decreased in size and density in July. Survey estimates of cod biomass ranged 184-494 mt in May, 138-617 mt in June, and 39-135 mt in July, depending on the estimation method. Based on echo classification and extrapolation, cod biomass to the GOMCSPA ranged 260-466 mt in May, 196-513 mt in June, and 91-198 mt in July. The biomass being protected by the closure may have represented 4-5% of the GOM cod spawning stock biomass at the time of the study based on these estimates. The three echo sounders synchronously collected acoustic data of individual free-swimming captive cod, while the movements of most individuals were observed with underwater video. The standard TS-L equations were TS = 20 log10(L) -- 66.4 at 38 kHz, TS = 20 log10(L) -- 67.4 at 120 kHz, and 〈TS〉 = 20 log10(L) -- 71.4 at 300 kHz. The study demonstrated a significant TS-L relation at 300 kHz from aggregated data collected by a multibeam echo sounder with narrow beams over multiple beam-pointing angles and without split-beam target tracking

Intimate partner violence among undergraduate student nurses at a tertiary institution in the Western Cape

Magister Curationis - MCurIntimate partner violence (IPV), a form of gender-based violence (GBV), has become one of the emerging serious public health issues. It affects all racial, ethnic, socioeconomic and religious groups. Internationally, IPV has also become an increasingly common phenomenon among students at tertiary institutions. In South Africa, there is a paucity of literature that investigates this phenomenon especially among undergraduate student nurses who are supposed to render care to survivors of IPV. The aim of this study was to determine the prevalence of IPV and factors associated with IPV among undergraduate student nurses at a tertiary institution in the Western Cape.A quantitative, descriptive study was conducted. An adapted version of the WHO’s instrument designed to measure partner violence was used to collect the data. This questionnaire was administered to the eligible respondents after lecture time. The total population consisted of 984 undergraduate student nurses. The printed class lists of the 1st-, 2nd-, 3rd- and 4th-year undergraduate student nurses were used as the sample frame. Stratified random sampling method was used to obtain a sample of 243 respondents to ensure that the sample size was representative of the population. The completed questionnaires were analysed quantitatively by using the Statistical Package for Social Sciences (SPSS) version 20. The results are presented in the form of tables, pie chart and graphs. Spearman’s correlations were used to calculate the strength of the relationship between the dependent variables. Multivariate analysis was done using the Mann-Whitney U test and the Kruskal-Wallis test to determine the associations between the different variables.The results from the study showed that 42% of undergraduate student nurses experienced IPV during their lifetime. The socio-demographic factors associated with IPV were age (p=0.009*), study year level (p=0.001*) and marital status (p=0.021*). The study also found that family history factors like the respondent’s mother’s educational status (p=0.005*), financial support during need (p=0.031*) and witnessing of abuse as a child (p=0.008*) were factors related to IPV. In this study, certain substance use factors such as dagga (p=0.004) and cigarette smoking (p=0.000*), alcohol use in their lifetime (p=0.000*), time elapsed since joining university(p=0.000*) and having male or female friends who drink (p=0.000*) were significantly associated with IPV. The study highlighted the need to raise awareness on IPV among undergraduate student nurses

High Post-Capture Survival for Sharks, Rays and Chimaeras Discarded in the Main Shark Fishery of Australia?

Most sharks, rays and chimaeras (chondrichthyans) taken in commercial fisheries are discarded (i.e. returned to the ocean either dead or alive). Quantifying the post-capture survival (PCS) of discarded species is therefore essential for the improved management and conservation of this group. For all chondrichthyans taken in the main shark fishery of Australia, we quantified the immediate PCS of individuals reaching the deck of commercial shark gillnet fishing vessels and applied a risk-based method to semi-quantitatively determine delayed and total PCS. Estimates of immediate, delayed and total PCS were consistent, being very high for the most commonly discarded species (Port Jackson shark, Australian swellshark, and spikey dogfish) and low for the most important commercial species (gummy and school sharks). Increasing gillnet soak time or water temperature significantly decreased PCS. Chondrichthyans with bottom-dwelling habits had the highest PCS whereas those with pelagic habits had the lowest PCS. The risk-based approach can be easily implemented as a standard practice of on-board observing programs, providing a convenient first-step assessment of the PCS of all species taken in commercial fisheries

Processing of multibeam water column image data for automated bubble/seep detection and repeated mapping

Water Column Imaging Multibeam Echosounder Systems (MBES) are effective and sensitive tools for investigating free gas (bubble) release and its rise through the water column. The main advantages of MBES are the detection range and lateral coverage in the water column and at the seafloor; furthermore, they are becoming increasingly available on research vessels worldwide. However, high noise levels and systematic artefacts due to side-lobe induced signal interference degrade MBES Water Column Images (WCIs) and hampered automated bubble detection and related gas seepage investigations. We present a new technique advancing automated detection of bubble streams and moving toward a quantitative gas-release assessment. It is shown that bubble streams can be detected reliably by their spatio-temporal behavior even when they are discontinuous in WCI data. Using assumptions about the bubble rising trajectories, bubble release spots at the seafloor can be traced even if the source location is obscured by acoustic noise or unwanted acoustic targets. A map with acoustic response and source locations of bubbles being released can be produced and serves as a starting point for more detailed quantitative analyses. The efficiency of the method has been assessed at a methane seep site in the Dutch North Sea. Multiple survey lines are merged to a detailed acoustic map of the area. Processed results are in good agreement with manual investigations of the WCI data as well as ROV-based video analysis

Heating and Regenerative Cooling Model for a Rotating Detonation Engine Designed for Upper Stage Performance

Rotating detonation engines (RDE) have the potential to significantly advance the efficiency of chemical propulsion. They are approximately one order of magnitude shorter than constant pressure engines, a savings benefit that is especially important for upper stage engines. There are many challenges to advancing their technological readiness level, but one area this thesis attempts to help mitigate is the understanding of heat loads and the viability of regenerative jacket cooling. A one-dimensional, steady-state heat transfer and regenerative cooling model for the upper stage RL10A-3-3A (RL10) engine is developed in MATLAB. This model considers forced convection in the boundary layer between the combustion product gases and the hot-gas-side wall, conduction through the wall, and forced convection in the boundary layer between the hydrogen coolant and coolant-side wall. Variable gas and coolant transport properties are utilized to increase physical accuracy. The model also quantifies pressure drop through the cooling channels due to wall friction. This allows for overall heat flux, and consequently hot-gas-side and coolant-side wall temperatures to be predicted along the length of the engine. Properties of the coolant can also be predicted including the jacket outlet temperature and pressure. These cooling circuit final parameters, temperature rise and pressure drop, were matched to a more detailed, threedimensional, transient RL10 system model developed by NASA, thereby anchoring this model. An RDE is designed to notionally meet the thrust level of RL10. Model design decisions are documented and explained, and a detailed comparison of the two engine geometries is made. The regenerative cooling model is adapted for the RDE considering such unique aspects as detonative heat flux and the centerbody/plug nozzle. Steady state heating and cooling analysis is performed on the RDE and the results are compared to RL10. Investigation into the effects of the RDE’s differing cooling jacket output conditions on the turbine are calculated and discussed. Appendix analyses consider more realistic detonative heat flux approximations according to recent RDE calorimetry studies and the effect of altering detonation chamber heat flux. Even with the conservative assumption of throat-level heat flux everywhere in the RDE’s annular combustion chamber, regenerative jacket cooling shows promise as a means of thermal survival. Wall temperatures are reasonable, coolant temperature rise is lower, and coolant pressure drop is lower. The reduced temperature rise presents the new challenge of correctly powering the turbine since the incoming coolant is less energized. Further studies should also look at channel optimization specific to the RDE to maximize cooling performance and ease of system integration