Determining Critical Internesting and Foraging Habitats for the Conservation of Sea Turtles in Gabon, Africa Using Satellite Tracking and Stable Isotope Analysis

Understanding the horizontal and vertical habitat of olive ridley sea turtles (Lepidochelys olivacea), a threatened species, is critical for determining regions of protection that may effectively reduce bycatch, the largest threat to this species. Satellite transmitters were used to determine the movement and dive behavior of 21 female olive ridley turtles tagged in Pongara National Park, Gabon during the 2012, 2013, and 2015 nesting seasons. A switching state space model was used to filter the tracking data and categorize the internesting and post-nesting movements. Gridded utilization distribution (UD) home range analysis of tracking data revealed that the entire core habitat occurred in the Komo Estuary and overlaps with an important area for artisanal fishing (79% overlap) and commercial shipping traffic (58% overlap). Dive data revealed turtles spent a majority of their time resting on the estuary seabed (20% of all dive time), indicating that bottom set gear may pose the greatest potential for fisheries interactions. The results from this study provide data that can inform the design and implementation of marine protected areas and fishery zones, currently underway. Additionally, post-nesting foraging sites are not well defined for this population. δ13C and δ15N stable isotope analysis of 149 epidermis samples from female nesting olive ridley turtles in Gabon, 38 of which also had satellite transmitters, was used to determine if distinct foraging locations exist for this population. Tracked turtles allow for visualization of foraging areas, which can then be correlated to their distinct isotopic signatures and further matched to untracked turtle signatures. Cluster analysis of the isotope ratios from all turtles produced two significant clusters with a 95% predictability rate. Track visualization of each cluster did not show any foraging patterns and a generalized linear model determined that nesting beach, sampling year, and average straight-line distance from foraging location were not indicators for cluster assignment. Due to olive ridley turtles being opportunistic feeders and following a “looping” pattern to find new food sources, it is difficult to use stable isotope analysis to identify foraging habitat for non-tracked turtles in this population

The spatial ecology of Mediterranean marine turtles: insights from stable isotope analysis, satellite telemetry, and environmental observations

Understanding the spatial and foraging ecology of marine migrants is challenging, due to the vast distances travelled and the numerous habitats occupied within a dynamic seascape. Mediterranean marine turtles migrate thousands of kilometers and face numerous threats, including bycatch, in their marine realm. To help inform targeted conservation, this complex marine ecology must be better understood. This thesis focuses on Mediterranean loggerhead (Caretta caretta) and green turtles (Chelonia mydas). By complementing stable isotope analysis (SIA), satellite telemetry, and environmental observations, this thesis aims to enhance our understanding of the complexities of marine turtle spatial and foraging ecology, as well as determine how future climate conditions may influence their habitat use. In Chapter 1, I introduce the importance of conserving marine migrants and discuss the current knowledge of marine turtle spatial and foraging ecology as well as threats faced, with particular emphasis on Mediterranean loggerhead and green turtles. By conducting an extensive review in Chapter 2, I demonstrate how SIA has been used to enhance our understanding of marine turtle ecology, as well as help inform conservation initiatives. I also highlight knowledge gaps (for example, bias in the species studied) and provide recommendations for future SIA studies (for example, following standardised protocols), and use this information to inform latter chapters. In Chapter 3, using SIA I highlight the ecological complexity of juvenile Mediterranean loggerhead turtles, demonstrating there are inter- and intra-population variations in ecology, and that region- and habitat-specific fisheries management is required. In Chapter 4, I identify the foraging grounds for two major Mediterranean loggerhead turtle populations, demonstrate foraging site fidelity over decades, show the proportion of females recruiting from each foraging region does not differ across the multi-decadal study, and suggest site-specific management would be beneficial. Finally, in Chapter 5, I show that migratory dive behaviours of loggerhead and green turtles are influenced by changes in environmental conditions (e.g. wave height and temperature) and that the species-specific migratory corridors used may be due to factors such as feeding preference and physiology, rather than species-specific environmental tolerances, suggesting dynamic and species-specific conservation is required. In Chapter 6, I summarise and discuss the findings from this thesis within the wider context. In conclusion, this thesis emphasises the complexities of marine turtle spatial ecology, shows that habitat use will likely differ under future climate scenarios, and suggests targeted and dynamic conservation is required for effective long term conservation

Final design of a space debris removal system

The objective is the removal of medium sized orbital debris in low Earth orbits. The design incorporates a transfer vehicle and a netting vehicle to capture the medium size debris. The system is based near an operational space station located at 28.5 degrees inclination and 400 km altitude. The system uses ground based tracking to determine the location of a satellite breakup or debris cloud. This data is unloaded to the transfer vehicle, and the transfer vehicle proceeds to rendezvous with the debris at a lower altitude parking orbit. Next, the netting vehicle is deployed, tracks the targeted debris, and captures it. After expending the available nets, the netting vehicle returns to the transfer vehicle for a new netting module and continues to capture more debris in the target area. Once all the netting modules are expended, the transfer vehicle returns to the space station's orbit, where it is resupplied with new netting modules from a space shuttle load. The new modules are launched by the shuttle from the ground, and the expended modules are taken back to Earth for removal of the captured debris, refueling, and repacking of the nets. Once the netting modules are refurbished, they are taken back into orbit for reuse. In a typical mission, the system has the ability to capture 50 pieces of orbital debris. One mission will take about six months. The system is designed to allow for a 30 degree inclination change on the outgoing and incoming trips of the transfer vehicle

Characterizing and managing risk from environmental release of pathogens of concern

The 2001 anthrax letter attacks not only caused the deaths of 5 people, the distribution of prophylactic antibiotic therapy to more than 30,000 people, and the cost of hundreds of millions of dollars to decontaminate the affected buildings, but also reminded decision makers of the urgency of having a risk management framework for response and recovery from a biological incident in a timely manner. In order to address this concern, the overall objective of this dissertation is to develop mathematical models to promote the understanding of a biological attack, to reduce uncertainty and variability in risk assessments of bioterrorism agents, and to provide information for decision-making steps to minimize the associated mortality and economic loss. This dissertation first adopted the Bayesian Monte Carlo (BMC) method to validate a previously published risk assessment framework by the author, which developed surface concentration standards for B. anthracis by linking surface contamination levels with estimates of risk to exposed individuals. The benefit of this analysis significantly reduced uncertainties in the estimated human health risk, which provided more accurate information for the decision makers seeking to identify the proper response. Then this dissertation focused on characterizing the risk of a biological release. It developed a 7-step evaluation framework for choosing the sampling and modeling approach which most accurately recovers details of a release from surface samples. The findings of this analysis not only answered the question "what is the best place to sample?", but also provided insights as to the quantity of samples that should be taken. The last chapter of this dissertation extends the fate, transport, and risk assessment model by synthesizing available information on five Category A pathogens (Bacillus anthracis, Yersinia pestis, Francisella tularensis, Variola major and Lassa) to develop quantitative guidelines for how environmental pathogen concentrations may be related to human health risk. These findings provide critical information for developing a risk-informed biological attack response system. Questions such as "how to estimate if risks warrant the distribution of prophylactic antibiotics?", and "how to choose between active or passive decontamination approaches?" were addressed.Ph.D., Environmental Engineering -- Drexel University, 201

Fine-Grained Source Code Tracking and Visualization in Commit History

CodeTracker is the current state-of-the-art program element change history generator with a reported precision and recall of 99.9% in method and variable tracking [1]. In this thesis, we extend the granularity of CodeTracker to support the tracking of control-flow blocks (e.g., for, while, if, try, catch, etc.) with a precision and recall of 98.12% and 97.62% respectively, providing researchers and developers with finer-grained information about the evolution of source code. We accompany this extension with a manually validated oracle, which includes the change histories of 1280 code blocks. These code blocks are contained within 200 methods from 20 open-source Java projects (10 methods from each project) comprising the method change history oracle created by Grund et al. [2]. We also present a code change history visualization and navigation tool for CodeTracker, named CodeTracker Visualizer, that overlays the GitHub user interface with change history information enabling users to track code elements directly from the commit page by simply selecting the desired code element. Finally, we compare CodeTracker’s block tracking precision and recall using two different tools that provide statement mappings, namely RefactoringMiner [3, 4], the current state-of-the-art refactoring detection tool, and GumTree [5], the current state-of-the-art Abstract Syntax Tree (AST) Diff tool. The enhanced version of CodeTracker along with the extended oracle are made publicly available to facilitate reproducibility and future research on code element tracking techniques [6]