Browsing by Subject "Cetacean"

Social structure is a key determinant of population biology and is central to the way animals exploit their environment. The risk of predation is often invoked as an important factor influencing the evolution of social structure in cetaceans and other mammals, but little direct information is available about how cetaceans actually respond to predators or other perceived threats. The playback of sounds to an animal is a powerful tool for assessing behavioral responses to predators, but quantifying behavioral responses to playback experiments requires baseline knowledge of normal behavioral patterns and variation. The central goal of my dissertation is to describe baseline foraging behavior for the western Atlantic short-finnned pilot whales (Globicephala macrohynchus) and examine the role of social organization in their response to predators. To accomplish this I used multi-sensor digital acoustic tags (DTAGs), satellite-linked time-depth recorders (SLTDR), and playback experiments to study foraging behavior and behavioral response to predators in pilot whales. Fine scale foraging strategies and population level patterns were identified by estimating the body size and examining the location and movement around feeding events using data collected with DTAGs deployed on 40 pilot whales in summers of 2008-2014 off the coast of Cape Hatteras, North Carolina. Pilot whales were found to forage throughout the water column and performed feeding buzzes at depths ranging from 29-1176 meters. The results indicated potential habitat segregation in foraging depth in short-finned pilot whales with larger individuals foraging on average at deeper depths. Calculated aerobic dive limit for large adult males was approximately 6 minutes longer than that of females and likely facilitated the difference in foraging depth. Furthermore, the buzz frequency and speed around feeding attempts indicate this population pilot whales are likely targeting multiple small prey items. Using these results, I built decision trees to inform foraging dive classification in coarse, long-term dive data collected with SLTDRs deployed on 6 pilot whales in the summers of 2014 and 2015 in the same area off the coast of North Carolina. I used these long term foraging records to compare diurnal foraging rates and depths, as well as classify bouts with a maximum likelihood method, and evaluate behavioral aerobic dive limits (ADLB) through examination of dive durations and inter-dive intervals. Dive duration was the best predictor of foraging, with dives >400.6 seconds classified as foraging, and a 96% classification accuracy. There were no diurnal patterns in foraging depth or rates and average duration of bouts was 2.94 hours with maximum bout durations lasting up to 14 hours. The results indicated that pilot whales forage in relatively long bouts and the ADLB indicate that pilot whales rarely, if ever exceed their aerobic limits. To evaluate the response to predators I used controlled playback experiments to examine the behavioral responses of 10 of the tagged short-finned pilot whales off Cape Hatteras, North Carolina and 4 Risso’s dolphins (Grampus griseus) off Southern California to the calls of mammal-eating killer whales (MEK). Both species responded to a subset of MEK calls with increased movement, swim speed and increased cohesion of the focal groups, but the two species exhibited different directional movement and vocal responses. Pilot whales increased their call rate and approached the sound source, but Risso’s dolphins exhibited no change in their vocal behavior and moved in a rapid, directed manner away from the source. Thus, at least to a sub-set of mammal-eating killer whale calls, these two study species reacted in a manner that is consistent with their patterns of social organization. Pilot whales, which live in relatively permanent groups bound by strong social bonds, responded in a manner that built on their high levels of social cohesion. In contrast, Risso’s dolphins exhibited an exaggerated flight response and moved rapidly away from the sound source. The fact that both species responded strongly to a select number of MEK calls, suggests that structural features of signals play critical contextual roles in the probability of response to potential threats in odontocete cetaceans.

Beaked 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.

Estimates of the energetic costs of locomotion (COL) are necessary to understand one of the potential impacts of anthropogenic disturbance on marine mammals. A new generation of biologging devices has enabled the measurement of fine-scale behavioral responses to disturbance, but calibration experiments are required to convert these measured changes in activity level into energy expenditure. Such calibrations have been conducted in many terrestrial and avian taxa but, due to logistical constraints, have been performed with only a few marine mammals. Very few studies have tested these calibrations against independent estimates of energy expenditure, such as measurements of caloric intake and the doubly labeled water (DLW) method. Calibration studies will help us to better understand how best to estimate energy expenditure from activity measurements. In my dissertation, I ask whether short-term increases in activity caused by disturbance may impact marine mammal energy budgets. I address this question with the long-term resident community of common bottlenose dolphins (Tursiops truncatus) living in Sarasota Bay, Florida, which experiences very high levels of traffic from small vessels. I first correlated overall dynamic body acceleration (ODBA) and energy expenditure with bottlenose dolphins in human care. I combined measurements of ODBA derived from accelerometry tags with respirometry during submerged swim trials. I then subtracted measured resting metabolic rate (RMR) from the energy expenditure of each trial to estimate COL. I found a linear relationship between ODBA and COL. Next, I deployed tags on the same dolphins for longer periods (24 hours) and combined COL, RMR, and specific dynamic action (SDA; energy expenditure associated with digestion) to estimate total daily energy expenditure. I compared this estimate of total daily expenditure with estimates derived from measurements of caloric intake records and DLW. The COL+RMR+SDA values largely agreed with the calories ingested, but the smaller DLW sample was considerably more variable. I then used the correlation between ODBA and COL to estimate the cumulative energetic costs associated with responses to vessels by wild dolphins in Sarasota. I analyzed 12 digital acoustic tag (DTAG) records for the presence or absence of vessels. I used periods without vessels as controls to calculate baseline estimates of COL for each animal. I then subtracted this baseline from total COL to derive the cumulative COL attributable to vessels. The overall increase in COL attributable to the response to vessels was less than 0.3% of estimated daily energy expenditure, suggesting that avoidance, while necessary to prevent injury or death, does not contribute significantly to the daily energy budgets of these dolphins. The methods I developed can be applied to a variety of other marine mammals to study the fitness consequences of anthropogenic disturbance. Future studies should focus on sensitive species that are likely to exhibit significant avoidance responses to acoustic stimuli.

The intent of the work discussed in this dissertation is to apply the engineering methods of theory/modeling, numerics/computation, and experimentation to a diverse assemblage of projects. Several projects are discussed: probabilistic modeling of decompression sickness, comparative hydrodynamics of cetacean flippers, optimization of CT/MRI protocols, evaluation of modified catheters, rudder cavitation, and modeling of mass transfer in amphibian cone outer segments.

The first project discussed is the probabilistic modeling of decompression sickness (DCS). This project involved developing a system for evaluating the success of decompression models in predicting DCS probability from empirical data. Model parameters were estimated using maximum likelihood techniques, and exact integrals of risk functions and tissue kinetics transition times were derived. Agreement with previously published results was excellent including maximum likelihood values within one log-likelihood unit of previous results and improvements by re-optimization, mean predicted DCS incidents within 1.4% of observed DCS, and time of DCS occurrence prediction. Alternative optimization and homogeneous parallel processing techniques yielded faster model optimization times. The next portion of this project involved investigating the nature and utility of marginal decompression sickness (DCS) events in fitting probabilistic decompression models to experimental dive trial data. Three null models were developed and compared to a known decompression model that was optimized on dive trial data containing only marginal DCS and no-DCS events. It was found that although marginal DCS events are related to exposure to decompression, empirical dive data containing marginal and full DCS outcomes are not combinable under a single DCS model; therefore, marginal DCS should be counted as no-DCS events when optimizing probabilistic DCS models with binomial likelihood functions. The final portion of this project involved the exploration of a multinomial DCS model. Two separate models based on the exponential-exponential/linear-exponential framework were developed: a trinomial model, which is able to predict the probabilities of mild, serious and no-DCS simultaneously, and a tetranomial model, which is able to predict the probabilities of mild, serious, marginal and no-DCS simultaneously. The trinomial DCS model was found to be qualitatively better than the tetranomial model, for reasons found earlier concerning the utility of marginal DCS events in DCS modeling.

The next project discussed is comparative hydrodynamics of cetacean flippers. Cetacean flippers may be viewed as being analogous to modern engineered hydrofoils, which have hydrodynamic properties such as lift coefficient, drag coefficient and associated efficiency. The hydrodynamics of cetacean flippers have not previously been rigorously examined and thus their performance properties are unknown. By conducting water tunnel testing using scale models of cetacean flippers derived via computed tomography (CT) scans, as well as computational fluid dynamic (CFD) simulations, a baseline work is presented to describe the hydrodynamic properties of several cetacean flippers. It was found that flippers of similar planform shape had similar hydrodynamic performance properties. Furthermore, one group of flippers of planform shape similar to modern swept wings was found to have lift coefficients that increased with angle of attack nonlinearly, which was caused by the onset of vortex-dominated lift. Drag coefficient versus angle of attack curves were found to be less dependent on planform shape. Larger cetacean flippers were found to have degraded performance at a Re of 250,000 compared to flippers of smaller odontocetes, while performance of larger and smaller cetacean flippers was similar at a swim speed of 2 m/s. Idealization of the planforms of cetacean flippers was found to capture the relevant hydrodynamic effects of the real flippers, although unintended consequences such as the lift curve slope changing from linear to nonlinear were sometimes observed. A numerical study of an idealized model of the humpback whale flipper showed that the leading-edge tubercles delay stall compared to a baseline (no tubercle) flipper because larger portions of the flow remaining attached at higher angles of attack.

The third project discussed is optimization of CT/MRI protocols. In order to optimize contrast material administration protocols for Computed Tomography (CT) and Magnetic Resonance Imaging (MRI), a custom-built physiologic flow phantom was constructed to model flow in the human body. This flow phantom was used to evaluate the effect of varying volumes, rates, and types of contrast material, use of a saline chase, and cardiac output on aortic enhancement characteristics. For CT, reducing the volume of contrast material decreased duration peak enhancement and reduced the maximum value of peak enhancement. Increasing the rate of contrast media administration increased peak enhancement and decreased duration of peak enhancement. Use of a saline chase resulted in an increase in peak enhancement. Peak aortic enhancement increased when reduced cardiac output was simulated. For MRI, when the same volume of contrast material was injected at the same rate, the type of contrast material used has a significant effect on the greatest peak signal intensity and duration peak signal intensity. A higher injection rate of saline chaser is more advantageous than a larger volume of saline chaser to increase the peak aortic signal intensity using low contrast material doses. Furthermore, for higher volumes of contrast material, the effect of increasing the volume of saline chaser makes almost no difference while increasing the rate of injection makes a significant difference. When a saline chaser with a high injection rate is used, the dose of the contrast material may be reduced by 25-50% and more than 86% of the non-reduced dose peak aortic enhancement will be attained.

The next project discussed is evaluation of modified angiocatheters. In this study, a standard peripheral end hole angiocatheter was compared to those modified with side holes or side slits by using experimental techniques to qualitatively compare the contrast material exit jets, and by using numeric techniques to provide flow visualization and quantitative comparisons. A Schlieren imaging system was used to visualize the angiocatheter exit jet fluid dynamics at two different flow rates, and a commercial computational fluid dynamics (CFD) package was used to calculate numeric results for various catheter orientations and vessel diameters. Experimental images showed that modifying standard peripheral intravenous angiocatheters with side holes or side slits qualitatively changed the overall flow field and caused the exiting jet to become less well-defined. Numeric calculations showed that the addition of side holes or slits resulted in a 9-30% reduction of the velocity of contrast material exiting the end hole of the angiocatheter. With the catheter tip directed obliquely to the wall, the maximum wall shear stress was always highest for the unmodified catheter and always lowest for the 4 side slit catheter. Modified angiocatheters may have the potential to reduce extravasation events in patients by reducing vessel wall shear stress.

The next project discussed involves studying the effect of leading-edge tubercles on cavitation characteristics for marine rudders. Three different rudders were constructed and tested in a water tunnel: baseline, 3-tubercle leading edge, and 5-tubercle leading edge. In the linear (non-stall) regime, tubercled rudders performed equally to the smooth rudder. Hydrodynamic stall occurred at smaller angles of attack for the tubercled rudders than for the smooth rudder. When stall did occur, it was more gradual for the tubercled rudders, whereas the smooth rudder demonstrated a more dramatic loss of lift. At lower Re, the tubercled rudders also maintained a higher value of lift post-stall than the smooth rudder. Cavitation onset for the tubercled rudders occurred at lower angles of attack and higher values of cavitation number than for the smooth rudder, but cavities on the tubercled rudders were localized in the slots as opposed to the smooth rudder where the cavity spread across the entire leading edge.

In the final project discussed, modeling of mass transfer in amphibian cone outer segments, a detailed derivation of a simplified (continuum, one-dimensional) mathematical model for the radio-labeled opsin density profile in the amphibian cone outer segment is presented. This model relies on only one free parameter, which was the mass transfer coefficient between the plasmalemma and disc region. The descriptive equations were nondimensionalized, and scale analysis showed that advective effects could be neglected as a first approximation for early times so that a simplified system could be obtained. Through numeric computation the solution behavior was found to have three distinct stages. The first stage was marked by diffusion in the plasmalemma and no mass transfer in the disc region. The second stage first involved the plasmalemma reaching a metastable state whereas the disc region density increased, then involved both the plasmalemma and disc regions increasing in density with their distributions being qualitatively the same. The final stage involved a slow relaxation to the steady-state solution.

The processes of locating and capturing food are critical components of a predator’s fitness, but can be difficult to observe, particularly in marine environments where foraging behavior is not often visible from the surface. Individuals and populations display a range of foraging adaptations, from stenophagous individuals who consume a single prey type to generalist populations that thrive with a variety of environments and prey taxa. Populations and individuals that show high levels of behavioral plasticity may be able to alter their foraging behavior when environmental conditions change, demonstrating new foraging strategies depending on the characteristics of the habitat and local prey fields. In this dissertation, I used high-resolution data from bio-logging tags deployed on three well-studied species of cetaceans (whales and dolphins) in novel environments, to analyze the role of environment in cetacean foraging strategies and kinematic behaviors. Bio-logging tags provide high-resolution information about predator foraging ecology, including foraging rates, kinematics of prey capture attempts, and even interactions between predators and prey. I first analyzed tag records from short-finned pilot whales (Globicephala macrorhynchus) foraging near the shelf-break off Cape Hatteras, North Carolina. In this analysis, I sought to determine if pilot whales forage near the seafloor when it is within reach, and whether such behavior affects their foraging rates and diel patterns. I tapped into the whale’s own sensory system, using the echoes of the animal’s echolocation clicks bouncing off the seafloor to demonstrate that many whales frequently foraged near the seafloor itself. I then used high-resolution kinematic data to investigate how benthic foraging affects the fine-scale details of prey capture attempts. Tagged whales were often upside-down while foraging benthically and appeared to pursue benthic prey as they attempted to escape by swimming away from the seafloor and into the water column. I used similar methods to study the foraging behavior of the offshore ecotype of common bottlenose dolphins (Tursiops truncatus) in pelagic waters near Bermuda. These offshore dolphins dive to considerable depths; I analyzed the effect of depth on the energetics and capture success rates of foraging attempts. I was able to eavesdrop on the echolocation clicks produced by dolphins during prey capture attempts to estimate the distance from the dolphin to its prey, and determine whether prey captures were successful. Dolphins foraging in deep dives encountered more prey and foraged with higher success rates than while foraging near the surface. Finally, I studied the fine-scale kinematics of humpback whales (Megaptera novaeangliae) foraging in winter feeding grounds near Virginia Beach, Virginia to determine how this extremely shallow water environment affected their foraging behavior. Humpback whales lunge-feeding in this area have limited maneuverability, likely due to the shallow nature of the environment, and exhibited simplified kinematics compared to studies in other areas. Nevertheless, these whales were still able to forage at high rates, with some evidence of higher foraging attempts made at dawn. The foraging ecology of these three species has been extensively studied elsewhere, but new environments present opportunities to discover novel foraging strategies. Overall, my dissertation illustrates the ways in which environmental features shape foraging behavior in these three species of behaviorally plastic cetaceans.