Browsing Electronic Theses by Subject "Animal behavior"
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- ItemA Characterization of Bottlenose Dolphin (Tursiops truncatus) Interactions with the Commercial Shrimp Trawl Fishery of South Carolina(2013-03-08) Greenman, Justin Theodore; McFee, Wayne; Environmental StudiesIn the United States, interactions between the shrimp trawl fishery and bottlenose dolphins (Tursiops truncatus) are known to exist, however the level of mortality is largely unknown. The current study attempted to determine if interactions between bottlenose dolphins and commercial shrimp trawlers pose a significant threat to dolphin populations and if fishery related mortality is underreported. This was accomplished with a combination of on-board observations, a shrimp fisher mail survey, and stranding record research. On-board observations were made during a 112 day field study consisting of fishery-dependent (Aug. - Dec. 2010) and fishery-independent (Apr. - Nov. 2010 & 2011) sampling. These observations focused on direct physical interactions with the gear and depredation behaviors. Additionally, a sub-sample of shrimp fishers in South Carolina was asked to participate in a mailed survey. The survey included questions related to gear, dolphin observations, and the status of the shrimp fishery. This study also utilized historical dolphin stranding data from the South Carolina Marine Mammal Stranding Network to ascertain signs of shrimp fishery interactions. A three-leveled flow diagram was developed to characterize each stranding case according to the likelihood that mortality resulted from trawler interaction. Field results point to significant dolphin presence around commercial trawlers (chi sq. = 23.406, p <0.001). In addition, survey results showed substantial evidence that fishery related mortality is higher than reported. Finally, stranding records revealed several more cases with signs of possible trawler interaction. Therefore, the current designation of the fishery as a Category II fishery is correct. In addition, increased observer coverage and improved communication with the fishery on the importance of reporting takes is warranted.
- ItemIncubation Temperature Effects on Hatchling Performance in the Loggerhead Sea Turtle (Caretta caretta)(2013-03-08) Fisher, Leah Rachel; Owens, David Wm.; Marine BiologyIncubation temperature has significant developmental effects on oviparous animals, including determining sex for several species. For the Northwest Atlantic loggerhead sea turtle (Caretta caretta), apparent population-wide female-biased hatchling sex ratios contrast with observations of juvenile populations, where sex ratios have remained constant at about 2 to 1 female-biased over the past 30 years. It has been suggested that some unknown factor is affecting loggerhead survival resulting in an unexplained differential loss of ~60% of female hatchlings per year. One theory to explain this hatchling mortality is tested in this project, that incubation temperature affects traits that influence survival. Furthermore, there may be differential survival between male and female hatchlings. I conducted laboratory experiments to test for an effect of incubation temperature on performance of loggerhead hatchlings. I tested 68 hatchlings produced from eggs incubated at 8 different constant temperatures ranging from ~27ºC to ~32.5ºC. Following their emergence from the eggs, I tested righting response, crawling speed, and conducted a 24-hour long hatchling swim test. Data indicate an effect of incubation temperature on survivorship, righting response time, crawling speed, change in crawl speed, and overall swim activity, with hatchlings incubated at 27ºC showing decreased locomotor abilities. No hatchlings survived when incubated at 32ºC and above. Differences in survivorship of hatchlings incubated at high temperatures are important in light of projected higher sand temperatures due to climate change, and could indicate increased mortality from incubation temperature effects.
- ItemLocomotory fatigue in the Atlantic blue crab, Callinectes sapidus(2013-03-08) Stover, Kristin; Burnett, Louis E; Marine BiologyThe Atlantic blue crab, Callinectes sapidus (Rathbun), is an important commercial and recreational fishing species that resides in the estuarine waters of the Atlantic Ocean and Gulf of Mexico. These highly mobile crustaceans must locomote to find food, evade predators, find mates and avoid adverse conditions such as hypoxia. In effect, maintaining continuous activity and resisting fatigue for extended periods of time may be necessary for the daily survival of blue crabs. In this study we investigated: 1) the impact of locomotion on the ability of a blue crab to produce a force with their walking legs to hold onto and guard a mate, and 2) the effects of two levels of hypoxia (10.4 kPa, 50% air saturation; 4 kPa, 20% air saturation) on fatigue during sustained continuous exercise. Fatigue was induced by an exercise trial that entailed continuous sideways hexapedal walking on an underwater treadmill. A repeated pull force test is described here that mimicked the way a male holds a female during mate guarding, by measuring the force crabs used to hold onto a mesh grid. The pull force decreased during walking in normoxia by 7.88% h−1. The results indicate that the more time a male crab spends searching for a mate, the less ability he will have to hold and, therefore, guard his mate. Fatigue, defined as a 33% decrease in pull force, was reached after a mean 6.19 h walking for crabs in normoxic seawater, 4 h in 50% air saturation and 2 h in 20% air saturation. Fatigue-resisting behaviors (180° turns, stopping and riding to the end) increased from the initial time point by 0.9 behaviors h−1 in normoxia, 4.1 in 50% air saturation, and 13.8 in 20% air saturation. The force and behavioral results indicate that performance is decreased and fatigue is reached more quickly as the level of hypoxia intensifies.