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- Member of: ASU Electronic Theses and Dissertations
Description
Small-scale fisheries are globally ubiquitous, employing more than 99% of the world’s fishers and providing over half of the world’s seafood. However, small-scale fisheries face many management challenges including declining catches, inadequate resources and infrastructure, and overcapacity. Baja California Sur, Mexico (BCS) is a region with diverse small-scale fisheries; these fisheries are intense, poorly regulated, and overlap with foraging hot spots of endangered sea turtles. In partnership with researchers, fishers, managers, and practitioners from Mexico and the United States, I documented bycatch rates of loggerhead turtles at BCS that represent the highest known megafauna bycatch rates worldwide. Concurrently, I conducted a literature review that determined gear modifications were generally more successful than other commonly used fisheries management strategies for mitigating bycatch of vulnerable megafauna including seabirds, marine mammals, and sea turtles. I then applied these results by partnering with researchers, local fishers, and Mexico’s federal fisheries science agency to develop and test two gear modifications (i.e. buoyless and illuminated nets) in operating net fisheries at BCS as potential solutions to reduce bycatch of endangered sea turtles, improve fisheries sustainability, and maintain fisher livelihoods. I found that buoyless nets significantly reduced mean turtle bycatch rates by 68% while maintaining target catch rates and composition. By contrast, illuminated nets did not significantly reduce turtle bycatch rates across day-night periods, although they reduced mean turtle bycatch rates by 50% at night. Illuminated nets, however, significantly reduced mean rates of total bycatch biomass by 34% across day-night periods while maintaining target fish catch and market value. I conclude with a policy analysis of the unilateral identification of Mexico by the U.S. State Department under section 610 of the Magnusson-Stevens Fishery Conservation and Management Act for failure to manage bycatch of loggerhead turtles at BCS. Taken together, the gear modifications developed and tested here represent promising bycatch mitigation solutions with strong potential for commercial adoption, but fleet-wide conversion to more selective and turtle-friendly gear (e.g. hook and line and/or traps) at BCS, coupled with coordinated international conservation action, is ultimately needed to eliminate sea turtle bycatch and further improve fisheries sustainability.
ContributorsSenko, Jesse (Author) / Smith, Andrew (Thesis advisor) / Boggess, May (Committee member) / Chhetri, Nalini (Committee member) / Jenkins, Lekelia (Committee member) / Minteer, Ben (Committee member) / Arizona State University (Publisher)
Created2015
Description
One of the most pronounced issues affecting the management of fisheries today is bycatch, or the unintentional capture of non-target species of marine life. Bycatch has proven to be detrimental for many species, including marine megafauna and pelagic fishes. One method of reducing bycatch is illuminated gillnets, which involves utilizing the differences in biological visual capabilities and behaviors between species of bycatch and target fish catch. To date, all studies conducted on the effects of net illumination on bycatch and target fish catch have been conducted at night. In this study, the effects of net illumination on bycatch, target fish catch, and market value during both night and day periods at Baja California Sur, Mexico were compared. It was found that i) net illumination is effective (p < 0.05) at reducing bycatch of finfish during the day and at night, ii) net illumination at night is more effective (p < 0.05) at reducing bycatch for elasmobranchs, Humboldt squid, and aggregate bycatch than during the day, iii) time of day did not have an effect (p > 0.05) on sea turtle bycatch, and iv) net illumination did not significantly (p > 0.05)affect target catch or market value at night or during the day. These results suggest that net illumination may be an effective strategy for reducing finfish bycatch in fisheries that operate during the day or across 24 h periods, and is especially effective for reducing elasmobranch, Humboldt squid, and total bycatch biomass at night.
ContributorsDenton, Kyli Elise (Author) / Senko, Jesse (Thesis advisor) / Neuer, Susanne (Thesis advisor) / Pratt, Stephen (Committee member) / Arizona State University (Publisher)
Created2021
Description
The smalltooth sawfish (Pristis pectinata) is a critically endangered species endemic to the Atlantic Ocean basin, with its range historically extending from the Gulf of Mexico to Brazil. Over the past century, the species has experienced severe population declines and a shrinking habitat due to human activity, including bycatch, habitat degradation, and illegal trade of its rostrum. Although primarily restricted to the southern coast of Florida, remnant populations may still exist in the Bahamas and along the West African coast. To support conservation efforts, species distribution models (SDMs) were employed to map the current and potential habitats of the smalltooth sawfish, incorporating occurrence data from public encounters and environmental variables from satellite sources. This study also examines habitat preferences across different age classes, identifying critical areas for protection. Findings highlight the influence of sea temperature, benthic salinity, and dissolved oxygen on sawfish distribution and potential differences in influences based on age classes. They underscore the need for targeted conservation measures to aid in population recovery. Future research should focus on expanding data collection in underrepresented areas and age classes to refine habitat suitability models further.
ContributorsLoudy, Remie (Author) / Kinzig, Ann (Thesis advisor) / Suzart de Albuquerque, Fabio (Thesis advisor) / Senko, Jesse (Committee member) / Arizona State University (Publisher)
Created2024
Description
Mealworms (Tenebrio molitor), the larval stage of yellow mealworm beetles, are a popular feeder insect for birds, amphibians, reptiles, fish, and even human populations throughout the world. As such, the goal of this work was to understand how the diet of mealworms impacts their nutritional quality as variations in quality can impact the animals (and humans) that consume them. In this study, 500 mealworms were divided among each of the following substrates designed to model food sources available in urban versus rural, more natural areas: 100% wheat germ (control); 100% Styrofoam; mixture of soil, grasses, and leaves from urban lawns; a mixture of soil, grasses and leaves from rural lawns; 50% mixture of wheat germ + carrots; natural fertilizer; or fertilizer with weed killer. The mealworms were maintained at room temperature and the diets were replaced bi-weekly to prevent spoilage and to remove mealworm waste. Once a week for three weeks, mealworms were sampled from each substrate and frozen at -20°C. After 3 weeks, mealworms housed in wheat germ + carrots weighed significantly more than all other groups (p<0.05), whereas those housed in Styrofoam or urban lawn substrates weighed significantly less at week 3 as compared to week 1 (p<0.01). The urban lawn substrate resulted in greater molting and contained the highest number of pupae, but also the greatest mortality among the substrates. The Bradford method measured the total protein content of mealworms homogenized in phosphate-buffered saline. Mealworms maintained on wheat germ had significantly greater total protein content as compared to mealworms transitioned to any other diet (p<0.05). So, compared to wheat germ, urban foods generally reduced protein, total sugars, and crude fat, although they also decreased oxidized lipoproteins. Urban lawn had lower oxidized lipoprotein content than wheat germ, but levels were higher compared to wheat germ with carrots and natural fertilizer. In addition, urban foods generally increase the water content in mealworms. Urban foods were not much different from rural lawns as no there was difference between urban and rural lawns. Differences in body mass and total protein support the hypothesis that mealworms' nutritional quality is altered by ingesting urban substrates. These data suggest that mealworms (and potentially other insects) in cities may be exposed to food substrates that result in less nutritional value than those living in more natural areas as mimicked by the rural lawn substrates and wheat germ control, although they may be higher in water content.
ContributorsLockett, Rory Earle (Author) / Sweazea, Karen (Thesis advisor) / Deviche, Pierre (Committee member) / Senko, Jesse (Committee member) / Arizona State University (Publisher)
Created2024