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The Atlantic coast striped bass fisheries collapsed in the late 1970's due to recruitment overfishing and poor habitat quality. Recovery of the fisheries in 1995 resulted from protection of mature females, favorable environmental conditions, and several years of strong recruitment. Today, the striped bass stock is overfished. The purpose of this study was to examine recruitment characteristics of juvenile striped bass during the pre- and post-recovery periods through (1) a comparison of mortality and hatch-date distribution between periods, and (2) to examine growth metrics of individuals from the post-recovery year classes. Lengths and otolith-derived daily ages from juvenile striped bass representing three year classes (2011, 2016, and 2017) from the James and Rappahannock subestuaries of the Chesapeake Bay were used to develop subestuary-specific age-length keys. Daily ages of juvenile striped bass from 32 year classes (1986 to 2017) spanning the pre- and post-recovery periods were projected from the age-length keys. Together with count data, the projected daily ages were used to estimate instantaneous daily mortality rates (Z, day-1) for each year class. Although daily Z estimates were relatively constant among the 32 year classes, mean hatch dates shifted earlier today (1996 to 2017) than prior to 1995. Within the post-recovery year classes, daily growth in length and weight was examined along with body condition (Fulton's K). All growth metrics varied by year class and subestuary, but daily growth rates and body condition were inversely related. The results of this study indicate that recruitment dynamics of juvenile striped bass in the Virginia portion of the Chesapeake Bay have changed over time, and within the post-recovery year classes, those changes varied among fish from the James and Rappahannock subestuaries.

Billions of birds fatally collide with human-made structures each year. These mortalities have impacts on species of conservation concern and potentially on avian populations as a whole. This source of human-wildlife conflict also places economic and operational constraints on various human industries. Furthermore, with continued increases in urbanization, the rate and extent of collisions continues to increase. Efforts to reduce collisions have largely centered on making structures more visible to birds but have been met with limited success. Currently, there is a call for solutions to be tailored to both the environmental context of hazardous structures and to the sensory ecology of at-risk birds. In Chapter 1, we review how and why sensory ecology will help reduce in-flight collision risk for birds. A growing understanding of the sensory systems of birds and of the interface between these systems and the environment will enable the design of appropriate warning and deterrent signals. In particular, we review avian auditory and visual sensory ecology to better understand the susceptibility of birds to collisions and to recommend effective signal design. We highlight the ubiquity and salience of multi-modal signals in avian ecology and evolution, particularly as warning signals, and propose the use of multi-modal signals in mitigating collisions. We encourage the use of animal behavior frameworks to assess collision risk and collision mitigation approaches. Behavioral analyses offer numerous advantages over traditional collision measures, such as mortality estimates. Behavioral data can be generated quickly, render large sample sizes, and allow more nuanced perspectives of the context-dependence of collisions. In Chapter 2, we investigate the use of acoustic signals to reduce avian collisions with structures in open airspace. Birds have largely evolved without tall human-made structures in their flight paths and, consequently, avian perception and behavior may not be suitably primed to detect these novel hazards. Our previous work in captive settings showed that acoustic signals aid in drawing the attention of flying birds to potential collision hazards, influencing flight behavior. The current work corroborates these findings in a field setting. We projected acoustic signals into open airspace surrounding communication towers and quantified movement patterns of birds, to indicate potential collision avoidance behavior. Our results show a ~15% reduction in overall bird activity surrounding towers during sound treatment conditions, compared with control trials. Furthermore, flight movement patterns during sound treatments were characterized by significantly greater distances from and greater displacement of travel direction relative to towers, compared with control trials. Flights during sound treatments also showed significantly slower velocities, compared with control trials. Lower frequency sound stimuli (4-6 kHz) produced larger effect sizes than higher frequency stimuli (6-8 kHz). Results also co-varied with tower location and data collection date, reinforcing an appreciation of the context-dependent nature of collision risk. Our findings will inform the field of avian sensory ecology and help to assess the use of acoustic signals in collision mitigation measures.

Atlantic bluefin tuna (Thunnus thynnus) are targeted by recreational anglers along the east coast of the United States, and the fishery is thought to be of considerable economic value. However, limited knowledge of the preferences and values of fishery participants impedes the ability of managers to maximize fishery benefits and predict harvest patterns, while an incomplete understanding of post-release mortality hinders efforts to estimate total mortality resulting from the fishery. This dissertation used a multidisciplinary approach that relied heavily on cooperative research with the recreational fishing community to examine these questions. A stated choice survey of private anglers permitted to target bluefin tuna (Chapter II) estimated a fishery consumer surplus of over $14 million in 2015 while revealing striking heterogeneity in angler preferences. Respondents placed a high value on harvesting bluefin tuna, but about half of anglers also valued non-consumptive aspects of bluefin tuna fishing such as catch-and-release. Preference segmentation was largely driven by income and recent bluefin tuna targeting behavior, with high-income anglers who had recently targeted bluefin tuna more likely to belong to the non-consumptive group. These results indicate that liberalization of harvest regulations could result in significant, non-linear increases in effort and harvest should consumptive-oriented anglers decide to re-enter the fishery. A second survey, of Atlantic bluefin tuna fishermen who possess a permit enabling them to fish either commercially or recreationally on a trip-by-trip basis, applied an online contingent sequential stated choice approach to better understand the decision-making of this unique group (Chapter III). Responses indicated that, while some permit holders consistently fish either recreationally or commercially, a substantial proportion of participants change trip type depending on fishery conditions such as prevailing fish size or regulations. The changing behavior of this latter group could potentially result in large shifts in targeting and lead to overages for the commercial handgear sector or recreational sector, and potentially the U.S. bluefin tuna quota as a whole. Lastly, post-release mortality was estimated for juvenile bluefin tuna caught in the increasingly popular light-tackle recreational fishery while also beta testing a newly developed, solar-powered pop-up satellite archival tag designed to enable large-scale, high-precision mortality studies (Chapter IV). Data were only obtained for 15 of 22 deployed tags, with 14 fish demonstrating behavior consistent with survival. One fish was predated upon, likely by a shortfin mako shark, after 17 days, and this was considered a natural rather than a fishing mortality. The low level of estimated post-release mortality, consistent with results from previous studies on different size classes of bluefin tuna caught with various angling gear types, suggests that catch-and-release angling, which Chapter II showed to be highly valued by some anglers, is a viable conservation strategy. Overall, this dissertation provides information regarding both angler preferences and fishery impacts that are of direct relevance to management. Future efforts should be directed to further engaging the recreational bluefin tuna fishing community in order to improve buy-in to management strategies and improve the ability of the United States to maintain fishing mortality within internationally prescribed limits.

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This study is an analysis of social differences in the value chain of small scale artisanal miners in the Shurugwi area in Zimbabwe. Artisanal mining drives the economy of several developing nations including Zimbabwe. However, the different actors in the value chain of the sector play different roles and the power they yield in the process affects what they get in the process and this in turn creates social differentiation. Therefore, the purpose of this study was to identify factors which influence inequalities (social differences) within the Shurugwi artisanal mining value chain. This was a qualitative case study where purposive sampling was used to come up with a sample of 20 gold miners, 8 buyers and 2 millers who operated in the Shurugwi area. Data was collected through interviews and analysis of data was done thematically. This study established that elite players in the gold mining value chain in Shurugwi District, derived most of the benefits while artisanal miners were confined to a life of perpetual poverty, which was a vicious circle and had become hereditary, with sons of miners following the livelihood paths of their fathers. The elite players on the other hand, were presented as sophisticated and although they were mostly not directly involved in the gold extraction activities, they reaped most of the rewards, either as owners of gold claims (who employed others to prospect for gold) or through cheap purchase and processing activities. The study recommends that clear guidelines, guiding the operations of small scale mining activities in the country be collaboratively formulated and implemented to evenly spread the benefits of small scale gold mining activities through the value chain. This research suggests that similar researches be carried out in other small scale gold mining areas in the country so that a more holistic picture of the nature of interactions in the small scale gold mining sector value chain can be grasped. Thereafter, appropriate intervention strategies can then be crafted to manage the nature of these interactions and the resultant social stratifications. / Dissertation (MA (Development Studies))--University of Pretoria, 2020. / Anthropology and Archaeology / MA (Development Studies) / Unrestricted

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The specific aim of this study is to show the significance of the natural resources of Texas and their potential possibilities as an adequate source of income for the State. Linked in with this discussion and underlying it is the thesis that adequate taxation of the natural resources will not only provide sufficient income for the State's needs but also conserve and utilize these resources.

To understand native species persistence in transformed landscapes we must evaluate how individual behaviors interact with landscape structure through ecological processes such as habitat selection. Rapid, widespread landscape transformation may lead to a mismatch between habitat preference and quality, a phenomenon known as ecological traps that can have negative outcomes for populations. I applied this framework to the study of birds inhabiting landscapes dominated by forest remnants and shade coffee plantations, a tropical agroforestry system that retains important portions of native biodiversity. I used two different approaches to answer the question: What is the role of habitat selection in the adaptation of native species to transformed landscapes? First, I present the results of a simulation model used to evaluate the effects of landscape structure on population dynamics of a hypothetical species under two mechanisms of habitat selection. Then I present the analyses of seven years of capture-mark-recapture and resight data collected to compare habitat preference and quality between shade coffee and forest for twelve resident bird species in the Sierra Nevada de Santa Marta (Colombia). I provide evidence for the importance of including the landscape context in the evaluation of ecological traps and for using long-term demographic data when evaluating the potential of novel ecosystems and intermediately-modified habitats for biodiversity conservation. Beyond suggestions to improve bird conservation in shade coffee, my findings contribute to theory about ecological traps and can be applied to understand population processes in a wide variety of heterogeneous landscapes.

As sea level rise (SLR) affects coastal wetlands, ecosystem responses can include vertical accretion, landward transgression, or submergence. Sea level rise-induced transitions can alter key biogeochemical transformations within wetland soils, impacting the ability of these systems to provide ecosystem services, specifically carbon (C) storage and water quality regulation. Through a series of complementary laboratory and field-based studies, biogeochemical responses to salinity, vegetation shifts, and submergence were investigated. Changes in nutrient dynamics associated with saltwater intrusion were evaluated by artificially adding saline water to different freshwater wetland soil types, indicating that potential exports of critical nutrients (forms of nitrogen, phosphorus, and C) out of freshwater wetland soils is mediated by soil type. A controlled laboratory experiment was conducted to determine the potential degradability of C stored within submerging coastal wetland soils under both aerobic and anaerobic conditions. Under aerobic conditions, 66% more carbon dioxide was produced than under anaerobic conditions and 4x greater carbon dioxide was produced at 90-100cm depths than at the surface. At the same site, the degradability of carbon stores was examined through organic matter fractionation, stable isotopic examination, and determining the abundance of key microbial genes. Both total soil C and stores of bioavailable nutrients increased with depth, while organic matter quality decreased. Finally, the biogeochemical impacts of two separate vegetation transitions occurring co-incidentally with sea level rise were investigated: mangrove encroachment into salt marsh, and more salt- and inundation-tolerant herbaceous encroachment into herbaceous marsh. Conclusions from these studies demonstrate that vegetation transitions alter both soil nutrient storage and fast-cycling nutrient pools, indicating that biogeochemical transitions occur in advance of changes in vegetative species dominance. Results from these chapters holistically address how biogeochemical functioning, specifically nutrient cycling, regulation of water quality, and C sequestration, within coastal wetlands responds to stressors associated with SLR.