Browsing by Author "Myrick, Chris, committee member"

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Open Access
Accounting for spatial substitution patterns and bioeconomic feedback loops: an economic approach to managing inland recreational fisheries
(Colorado State University. Libraries, 2011) Deisenroth, Daniel B., author; Bond, Craig A., advisor; Loomis, John B., advisor; Goemans, Chris, committee member; Davies, Stephen, committee member; Myrick, Chris, committee member
This dissertation consists of three papers which address separate but related issues in recreational fisheries management. Paper one estimates the economic contribution of the private, recreation-based aquaculture industry in the Western United States. Paper two presents a method for combining models of site selection with input-output models in order to better estimate the true economic impacts of augmentation or deterioration of recreational sites. Finally, paper three presents a dynamic, bioeconomic model of a recreational fishery and uses that model to simulate what would happen over time to anglers and fish populations (as well as value to anglers) if fish stocking were to be halted at a single recreational fishery. All three papers are policy relevant today given the increased pressure from (and litigation filed by) environmental groups to reduce fish stocking due to conflicts with native and endangered species. Paper one explores the economic contribution of the private, recreation-based aquaculture industry in the Western United States. New sectors are constructed in IMPLAN input-output software using data gathered between 2007 and 2010 from producers and their direct customers (stocked fisheries). Information from a third survey of anglers in Colorado and California is integrated to predict the short-term shocks that would occur to various industries if anglers at privately stocked fisheries were to discontinue fishing (simulating a hypothetical collapse of the industry). Accounting for both the backward and forward linkages of the private, recreation-based aquaculture industry's production, model results indicate that for every dollar of fish stocking, $36 dollars of recreational angler-related expenditures are supported, and that the total economic contribution of this industry in the Western United States is roughly $2 billion annually. This is the first study addressing the forward linkages and total economic contribution of this industry in the Western United States. Paper two addresses a similar issue as paper one, but goes further to account for substitution patterns among anglers. Using information from a survey of anglers in 2009, a repeated nested logit (RNL) model of angler spatial substitution behavior is estimated. Then, the RNL is used to predict changes in angler days associated with changes in fishery attributes. By linking the RNL and input-output model, better insight is gained into the economic losses associated with augmentation or deterioration of stocked fishing sites. Results indicate that if a single site is closed within the region of analysis, of the 29,500 anglers that will no longer fish at that site, only 6,500 anglers will leave the region of analysis (the rest substituting to other in-region sites). Standard impact analysis would therefore overestimate the economic impacts of such a policy by 450%. Results are similar when catch rates are reduced by 50% at one site, with 14,000 anglers leaving that site but only 3,000 leaving the region. The third and final paper of this dissertation presents a means by which managers may manage inland recreational fisheries from a dynamic bioeconomic perspective. A discrete-time, discrete-space, infinite time horizon numerical model of a fishery is built in GAMS software to reflect responses of anglers to the fishery and responses of the fishery to anglers over time. A data-driven random utility model is used to inform angler response and value functions in this dynamic bioeconomic model. Results from one region in California indicate that a) current fish stocking levels may be inefficiently high, and b) elimination of fish stocking programs at popular lakes may not lead to a crash in fishery populations, since anglers will simply substitute to other nearby fisheries (rather than "fish-out" the lake). Managers who can predict the intertemporal effects of fishery management alternatives in this way will be able to better meet the demands of recreational anglers.
Open Access
Hempseed meal as an effective protein supplement for finishing wethers
(Colorado State University. Libraries, 2024) Butts, Mercer, author; Archibeque, Shawn, advisor; Dillon, Jasmine, advisor; Myrick, Chris, committee member
To address the needs of an increasing global population and decreased availability of arable land due to the continued expansion of monoculture farms for the use of feeding livestock, it is necessary that we begin to research more sustainable methods for feeding animals, and the people who consume them. This study aims to address those needs by presenting hempseed meal (HSM) as a protein alternative to more commercially available feeds such as soybean meal commonly used in finishing rations on animal feeding operations (AFOs) across the United States. To complete this task, forty Western White-Faced wethers were used in a completely randomized block design with 5 treatments. These treatments included diets formulated to be near isonitrogenous with 0%, 5%, 10%, 15%, or 20% of diet DM as hemp seed meal, primarily as a substitute for soybean meal. Wethers were fed the diets individually for 90 d, which was followed by a 5 d balance trial with a total collection of urine and feces. There were no differences in DM intake (P = 0.44) or N digestibility (P = 0.467) between treatments, although there was a slight increase in P digestibility as hemp meal inclusion increased until it represented 15% of the dietary DM (P = 0.047). There were no differences in urinary N excretion (P = 0.33) or urinary urea excretion (P = 0.34) between treatments.
Open Access
The population ecology of fathead minnows (Pimephales promelas) in estrogen contaminated environments
(Colorado State University. Libraries, 2013) Schwindt, Adam Richard, author; Winkelman, Dana L., advisor; Clements, William, committee member; Myrick, Chris, committee member; Ramsdell, Howard, committee member
Urban freshwater streams and rivers in arid climates are ecosystems dominated by wastewater effluent. Effluent contains a suite of bioactive chemicals including steroid and non-steroid estrogens that have been shown to disrupt vertebrate endocrine systems in laboratory studies. One of these steroid estrogens is 17alpha-ethinylestradiol (EE2), a synthetic steroid estrogen used in human oral contraceptives. EE2 enters waterways after incomplete removal during wastewater treatment and can disrupt reproduction in fishes. However, little understanding exists of the ecological consequences of reproductive disruption. My studies were initiated to evaluate how xenoestrogens might influence the population ecology of aquatic vertebrates. Specifically, I assessed the population ecology of fathead minnows (Pimephales promelas), a short-lived fish, that were exposed to early-life, life-time, and adult exposures of EE2. While assessment at the population-level was the goal, an understanding of environmental chemistry and ecotoxicology was needed to fully characterize the effects and consequences of EE2 and this is reflected in my dissertation that is organized into four chapters. Chapter 1, "Influence of community productivity on an estrogen added to aquatic mesocosms" identified chlorophyll a and nitrate as explanatory factors associated with the partitioning of EE2 to organic matter. In addition, it details the development of a high performance liquid chromatography tandem mass spectrometry method capable of quantifying EE2 at sub nanogram per liter concentrations. The method afforded the ability to accurately measure EE2 concentrations during the experiments. Chapter 2, "Linking multiple biomarkers and varying exposure history in estrogen contaminated environments: is a comprehensive profile of fish health possible?" concludes that EE2 induces many physiological changes in fish at multiple levels of biological organization. Our results suggest that, depending on the timing of exposure (early-life, life-time or exposure as an adult), linking effects between biomarkers may be possible. Here we also demonstrate that the EE2 concentrations used in our experiments are environmentally relevant because fish caged below a wastewater treatment plant displayed a similar physiological response as the fish in the experiments. Chapter 3 "Fish population failure caused by an environmental estrogen is long-lasting and regulated by direct and parental effects on survival and fecundity" presents the effects of EE2 on population dynamics with empirically derived results from a one year long series of experiments. This chapter is the first to demonstrate that an early-life EE2 exposure to the parents causes reduced offspring survival despite the offspring never being directly exposed to EE2. Additionally, we found that an early-life exposure to EE2 caused permanent reproductive disruption and life-time exposures caused reproductive failure. Surprisingly, the summer long exposure to adult fish induced significant declines in male survival culminating with 100% mortality at the highest concentrations. In chapter 4, "A stochastic stage-structured modeling approach to evaluate the effects of estrogenic exposure on population growth rate in a short-lived fish" we demonstrate that EE2 can drastically reduce population growth rate (PGR) mediated by reduced reproductive output and juvenile survival. Declines in PGR were evident despite the lack of statistical significance on the effects of EE2 on egg, embryo, and juvenile fish production seen in the experimental data. Overall my research demonstrates that by taking a holistic approach we can better understand the potential population-level and multigenerational effects of EE2, and the consequences for population growth.