An estuary is the last stage of a river. It is where the river meets the sea. Estuaries are one of the most significant features of the South African coastline. In recent years, South Africa has witnessed an increase in the demand for freshwater for both industrial and domestic purposes. At the same time, there has been a gradual deterioration of river systems and their catchments. To add to this, there has been a gradual reduction in the amount of recorded rainfall, which is the primary source of freshwater for rivers. This has resulted in decreased freshwater inflow into estuaries, a situation which poses a serious threat to the biological functioning of these estuaries and the services rendered to its recreational users. A deterioration of estuary services reduces the yield for subsistence households and their appeal for recration. This study uses the contingent valuation method as its primary methodology to elicit users' willingness-to-pay to reduce the negative impacts of reduced freshwater inflow into selected western and southern Cape estuaries. Eight estuaries were selected for this study; the Breede, Duiwenhoks, Great Berg, Kleinemond West, Mhlathuze, Swartvlei and Olifants estuaries. The contingent valuation (CV) method is widely used for studies of this nature because of its ability to capture active, passive and non-use values. The CV method involves directly asking people how much they would be willing to pay for specific environmental services. In this case, users were asked what they would be willing to pay to sustain freshwater inflows into selected estuaries in order to prevent the negative impacts of reduced inflows. The travel cost method (TCM) was uesed to generate an alternative comparative set of values for the purposes of convergence testing. This is because convergence testing is highly desirable as a validity test for CV estimates.

There are about 259 estuaries in South Africa that can be classified as “functioning” and their “health” status is directly related to the quantity and quality of freshwater that flows into them. Many of South Africa’s estuaries have become smaller due to a steady decrease in the amount of freshwater that flows into them. This reduction in freshwater inflows decreases their ecological functioning and undermines the recreational activities and subsistence services available from them. The National Water Act (ACT No. 36 of 1998) recognises the right of the environment to water, but a large amount of data is still needed to make management decisions on the allocation of freshwater. The objective of this research was to contribute to the management of the allocation of freshwater in the catchment areas of the Bira, Bushmans, Kasouga, Keiskamma, Kleinemond East, Nahoon and Tyolomnqa rivers by determining the recreational value of the freshwater flowing into their estuaries. This recreational value was established using the contingent valuation method. The contingent valuation method (CVM) is a technique to establish the value of a good (or service) that is not bought or sold in an actual market. This technique is frequently applied in the valuation of environmental goods, e.g. the freshwater that flows into an estuary. The CVM establishes the economic value by asking the users of an environmental good to state their willingness to pay (WTP) for a hypothetical project to prevent or bring about a change in the current condition of the environmental good. The users’ WTP is then aggregated to establish a total willingness to pay (TWTP) for the population of the users of the environmental good. The hypothetical project presented in this study is that of an increase of freshwater inflows, that would prevent (bring about) predetermined changes in environmental services provided by the selected seven estuaries.

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<p>The need to protect size and age structures from selective harvest in order to maintain sustainable fish stocks has been emphasized in recent literature. The Big Old Fat Fecund Female Fish (BOFFFF) hypothesis has been influential in discussions of changing stock management strategies, and postulates that larger, older females have a disproportionate input into stock recruitment due to physiological advantages. In this study, we utilize a meta-analysis approach to test the assumption of the BOFFFF hypothesis, that larger female fish produce larger eggs and more viable offspring, at a broad scale. Following the meta-analyses, we assess whether larger females from a subset of studies use their gonadal investment more efficiently than small females. From our meta-analyses, we found positive, significant intraspecific relationships between female size and egg size. Moreover, we found positive associations between egg size and offspring viability (offspring size and survival). However, we found in a subset of studies that although proportional survival of offspring often increases with egg size, females that produced larger eggs yielded fewer surviving offspring per unit gonadal investment. This reduced efficiency in reproductive investment is a product of the trade-off between egg size and fecundity. We conclude that although larger females may appear to produce more viable individual offspring, their input to stock recruitment, according to total stock gonadal biomass, may not be disproportionate, as stated by the BOFFFF hypothesis. However, we did not account for whether the benefits of maternal effects extend beyond the larval stage.</p><p>The theory of optimal egg size implies that fish trade off between fecundity and individual gonad investment according to their environment. Past interspecific studies suggest that in general, fishes in large, marine systems produce smaller eggs than those in small, freshwater systems. This study aims to compare egg size intraspecifically among small and large systems. In particular, we focus on populations from the Laurentian Great Lakes, which exhibit similar broadscale physical processes as marine systems, and smaller inland lakes (<1,000 ha), whose ecosystems contain many of the same species. In 2018 and 2019, we collected egg samples from spawning walleye (<i>Sander vitreus</i>) and yellow perch (<i>Perca flavescens</i>) in both inland lake and Great Lake populations. From each female, we recorded total lengths, and measured average diameters of ten eggs. Using ANCOVA models, we compared mean length-adjusted egg diameters intraspecifically among populations of both species. For both walleye and yellow perch, we found that females from inland lakes produced larger mean length-adjusted egg diameters than those of the Great Lakes. This pattern was particularly evident for yellow perch, whereas for walleye the pattern was relatively weak, potentially due to stocking eroding population-specific selection for egg size. These intraspecific patterns are consistent with cross-system interspecific variation in fish egg size.</p>

<p>Fish communities in agricultural headwater streams are known to be impacted by a variety of factors, including water chemistry, habitat modification, and hydrology. Little research has been conducted on how climate change influences these communities, yet the effects of climate on lake and river fish have been well documented. I hypothesized that fish community metrics would be reduced by the effects of climate change. I examined the effects of climate and hydrology metrics on fish communities at nine sites in the Saint Joseph River, Indiana and Michigan and at 18 sites in the Upper Big Walnut Creek, Ohio watersheds, from 2006 to 2019. Air temperature, water temperature, precipitation, water discharge, width, velocity, and depth metrics were calculated seasonally for each sampling year. Fish were examined seasonally with backpack electrofishing and seine netting and identified to species level. Principal component analyses were used to create axes which represented gradients of climate and hydrology metrics. Linear mixed effect and logistic regression modeling suggested that hydrology is a stronger predictor than climate, but that both influence fish communities. Percent Percidae, percent herbivore, and percent open substrate spawner were positively correlated with precipitation and water temperature. Presence herbivore was negatively correlated with precipitation and positively correlated with water temperature. My data only somewhat supported the hypothesis that climate would reduce fish community metrics. Gradients of hydrology were observed to be stronger predictors than gradients of climate. However, one must acknowledge relationships between climate and hydrology and the potential for climate to have indirect effects on fish communities through influences on hydrology. This study increases understanding of how fish communities in agriculturally dominated headwater streams are influenced, and emphasizes the need for further research on how these fishes will be impacted by a changing climate. </p>

<p>Aquatic macroinvertebrates of channelized headwater streams in agricultural landscapes are exposed to alterations in chemistry and physical characteristics of benthic sediments. These habitat alterations are known to influence communities of aquatic macroinvertebrates. Benthic sediments can have a wide range of impacts and influences on aquatic macroinvertebrates. I hypothesized that sediments would play a significant role in determining macroinvertebrate community structure within agriculturally dominated headwater streams. I evaluated the influences of sediment chemistry characteristics and physical characteristics on aquatic macroinvertebrate communities in Cedar Creek, Indiana and Michigan, and the Upper Big Walnut Creek, Ohio, during 2017 and 2018. Macroinvertebrates were collected twice per year using artificial substrate and leaf pack samplers and identified to the family level. Sediments were sampled two times per year and analyzed for seven physical characteristics and twenty sediment chemistry characteristics. Principle component analyses were used to create axes that are indicators of gradients of sediment chemistry and physical characteristics that occur among the samples. Macroinvertebrate community metrics used in the analyses included abundance, Shannon Diversity Index, Hilsenhoff Biotic Index scores, Invertebrate Community Index scores, percentage of collector-filters, percentage of scrapers, percentage of Chironomidae and a Berger-Parker Reciprocal Index of dominance. Linear Mixed Effect Model analyses revealed that both sediment chemistry and physical characteristics influence macroinvertebrate community metrics. Aquatic macroinvertebrate abundance was negatively correlated with increasing concentrations of simazine and decreasing concentrations of calcium. Percentages of Chironomidae were positively correlated with increasing percentages of sand and decreasing percentages of clay and decreasing diversity of sediment particle sizes. My data supported the hypothesis that benthic sediments play an important role in determining aquatic macroinvertebrate community structure in headwater streams of agriculturally dominated landscapes. Gradients of chemical characteristics containing simazine and calcium were observed to be negatively correlated with macroinvertebrate abundance. Gradients of physical characteristics including percentages of sand and clay along with the diversity of particle sizes were observed to be positively correlated with percentage of chironomids. My research increases the knowledge that benthic sediments, chemically and physically, can lead to alterations in aquatic macroinvertebrate communities within Midwestern headwater streams. </p>

<p>Infectious  diseases  are  becoming  increasingly  common  and  problematic  for  wildlife populations in many parts of the world. Disease prevalence and severity fluctuate over time, often due to the ubiquitous pressure of seasonality, or  the cyclic changes in ecological systems. However, for  many  host-pathogen  systems,  our  understanding of important  seasonal  drivers of  disease remains fragmented. For example, when seasonality of a disease is studied in medium and high latitudes, winter is often neglected, despite this being a period of physiological and immunological challenges associated with extreme environmental conditions. Therefore, my aim is to examine  drivers  of winter Infection dynamics of the amphibian fungal pathogen <em>Batrachochytrium dendrobatidis</em>. First, <em>B. dendrobatidis </em>infection prevalence was measured from spring through fall to understand local infection levels and anthropogenic influences (Chapter 1). Next, laboratory  experiments examined the effects of <em>B. dendrobatidis </em>on critical thermal minimum of two anuran species to identify how this pathogen influences the ability of hosts to survive winter (Chapter 2). Another laboratory experiment tested how road de-icing salt (commonly used in winter) influences <em>B. dendrobatids </em>and a tadpole host condition and subsequent host-pathogen interactions (Chapter 3). Finally, a field-based exploration of <em>B. dendrobatidis </em>infection dynamics was conducted during winter to understand how infections vary during in this season and between two overwintering strategies (Chapter  4). Winter  infection  dynamics  in  many  host-pathogen  systems are largely understudied, but the knowledge gained by this work can demonstrate how harsh environmental conditions of winter that can exacerbate otherwise benign infections, and affect the ability of hosts to sustain infections during winter. This work can therefore inform predictions and investigations of  infection  dynamics in  subsequent  seasons to  better  understand  the  seasonality  of  wildlife diseases.</p>

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