Browsing by Subject "Seasonality"
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Item Open Access Ecology of Beaked Whales and Sperm Whales in the Western North Atlantic Ocean: Insights from Passive Acoustic Monitoring(2017) Stanistreet, Joy EliaBeaked whales (family Ziphiidae) and sperm whales (Physeter macrocephalus) are apex marine predators found throughout the world’s deep oceans. These species are challenging to observe, and little is known about fundamental aspects of their ecology, including their spatiotemporal distributions and habitat use. Passive acoustic monitoring (PAM), can be used to detect their echolocation clicks during foraging dives, thereby providing an indication of species presence. My dissertation investigates the distribution, seasonal occurrence, and diel variability in acoustic detections of beaked whales and sperm whales in the western North Atlantic Ocean, using multi-year passive acoustic recordings collected along the continental slope between Florida and Nova Scotia. First, I describe spatiotemporal patterns in detections of beaked whale echolocation clicks from five beaked whale species and one signal type of unknown origin. At least two beaked whale click types were detected at each recording site, and detections occurred year-round, with site-specific variation in relative species occurrence. Notably, Cuvier’s beaked whales (Ziphius cavirostris) were regularly detected in a region where they have not been commonly observed, and potential habitat partitioning among Cuvier’s and Gervais’ (Mesoplodon europaeus) beaked whales was apparent within their overlapping ranges. To examine the potential effects of using duty-cycled recording schedules on the detection of beaked whale clicks, I performed a subsampling experiment, and found that short, frequent listening periods were most effective for assessing daily presence of beaked whales. Furthermore, subsampling at low duty cycles led to consistently greater underestimation of Mesoplodon species than either Cuvier’s beaked whales or northern bottlenose whales (Hyperoodon ampullatus), leading to a potential bias in estimation of relative species occurrence. Next, I examine the occurrence of sperm whale echolocation clicks, which were recorded commonly between southern New England and North Carolina, but infrequently off the coast of Florida. In the northern half of the study region, I observed distinct seasonal patterns in the daily prevalence of sperm whale clicks, with a winter peak in occurrence off Cape Hatteras, North Carolina, followed by an increase later in the spring at sites further north, suggesting a shift in sperm whale concentrations which may relate to enhanced productivity occurring at higher latitudes in the spring. Finally, I explore the variability in daily detection rates of beaked whales and sperm whales in relation to dynamic oceanographic conditions off the Mid-Atlantic coast. Detection rates did not appear to correlate with temporal environmental variability, and persistent habitat features may be more important in predicting the occurrence of these species. Together, my dissertation provides substantial baseline information on the spatiotemporal occurrence of beaked and sperm whales in the western North Atlantic Ocean, highlighting the diversity within this guild of deep-diving odontocetes and demonstrating the use of PAM to provide species-specific insight into their ecology.
Item Open Access Life History Parameters and Social Associations of Female Bottlenose Dolphins (Tursiops Truncatus) in North Carolina, USA(2008-04-25) Thayer, Victoria GravesIn this study, I describe the seasonality of reproduction in bottlenose dolphins by examining data from stranded animals, photographic surveys and focal follows. I examined inter-birth intervals from focal follows of known female dolphins. I found bottlenose dolphins that frequent the coastal waters of North Carolina to be comprised of at least two populations; one with a primarily spring birthing peak and a presumed second (or second and third) with two smaller birthing peaks in the fall and winter. These animals are reproducing at 2-3 year inter-birth intervals, which are shorter than bottlenose dolphin inter-birth intervals in the Moray Firth, Scotland, Shark Bay, Australia, or Sarasota Bay, FL. A decrease in reproductive intervals can indicate a density-dependent response to an anthropogenic disturbance or a natural change. Association patterns between and among these known females revealed relationships that have persisted for more than a decade. Most association patterns of the female dolphins in this area are long-term casual acquaintances which are evident in the fission-fusion grouping pattern, and individuals are not highly gregarious. Females appear to associate with most other females in the local area and do not form bands, as defined by researchers in Sarasota, FL (Wells et al. 1987). However, females do exhibit preferred associates, with whom they associate, regardless of reproductive state. Associations of females with young of the year were slightly stronger than associations between females with different aged calves, except for preferred associates. Future work will include genetic research on some of these known females, and continued study of the life and reproductive histories of these known females and their offspring.Item Open Access Periodic Autoregressive Conditional Heteroskedasticity(1996) Bollerslev, T; Ghysels, EMost high-frequency asset returns exhibit seasonal volatility patterns. This article proposes a new class of models featuring periodicity in conditional heteroscedasticity explicitly designed to capture the repetitive seasonal time variation in the second-order moments. This new class of periodic autoregressive conditional heteroscedasticity, or P-ARCH, models is directly related to the class of periodic autoregressive moving average (ARMA) models for the mean. The implicit relation between periodic generalized ARCH (P-GARCH) structures and time-invariant seasonal weak GARCH processes documents how neglected autoregressive conditional heteroscedastic periodicity may give rise to a loss in forecast efficiency. The importance and magnitude of this informational loss are quantified for a variety of loss functions through the use of Monte Carlo simulation methods. Two empirical examples with daily bilateral Deutschemark/British pound and intraday Deutschemark/U.S. dollar spot exchange rates highlight the practical relevance of the new P-GARCH class of models. Extensions to discrete-time periodic representations of stochastic volatility models subject to time deformation are briefly discussed.