Browsing by Subject "Energetics"

Animals experience hydrodynamic forces (lift, drag, and side) and moments (pitching, yawing, and rolling) as a result of motion in an aqueous medium. Under selective pressure, most cetaceans, including porpoises, dolphins, and whales, developed a streamlined body shape and modified limbs, which delay the separation of flow, create lower drag when they swim, and therefore decrease their locomotor cost. In order to calculate the locomotor cost and propulsive efficiency of cetaceans, accurate estimates of drag on marine animals are required. However, extra momentum imparted into the fluid from lift and side forces as well as pitching, rolling, and yawing moments (here, the parasitic loads) results in extra drag force on the animal. Therefore, in addition to streaming and delaying flow separation, animals must also minimize excess fluid momentum resulting from parasitic loads. Given the endangered status of the North Atlantic right whale (Eubalaena glacialis; hereafter NARW), analyzing the hydrodynamic characteristics of the NARWs was the focus of this work. Additionally, previous studies showed that body shape of NARWs changes with life stages, reproduction status, nutritive conditions or prey abundance, and the effects of entanglement in fishing gear. Therefore, in this study, computational fluid dynamics (CFD) analysis was performed on multiple 10 m three-dimensional NARW models with different body shapes (e.g., normal condition, emaciated, and pregnant) to measure baseline measurements of flow regimes and hydrodynamic loads on the animal. Swimming speeds covering known right whale speed range (0.125 m/s to 8 m/s) were simulated in most scenarios. In addition to the hydrodynamic effects of different body shapes, drag was also considered a function of parasitic loads. The NARW models were embedded with bone segments that allowed one to manipulate the body pose of the model via adjusting the flippers or the spine of the animal before measuring hydrodynamic drag. By doing so, momentum from parasitic loads was expected to be eliminated. CFD simulations revealed that drag on NARWs is dictated by its irregular outline and that the drag coefficient (0.0071-0.0059; or dimensionless drag) of on NARWs is approximately twice that of many previous estimates for large cetaceans. It was also found that pregnant NARW model encounters the lowest drag coefficient due to delayed flow separation resulting from enlarged abdomen, whereas the emaciated NARW model experiences the highest drag coefficient possibly due to the concavity at the post-nuchal region. These results suggested that drag on NARWs and their thrust power requirements were indeed affected by its body shape but the differences between the three NARW models tested were small. Lastly, minimum drag, which corresponds to the elimination of the parasitic loads, can be obtained by adjusting the pose of the animal. Thus, minimum drag occurs at the neutral trim pose. For the static, normo-nourished NARW model, simulations revealed that by changing the angle of attack of the flippers by 4.03° (relative to the free-stream flow) and pitching the spine downward by 5° while maintaining fluke angle, the drag was lowered by approximately 11% across the flow speeds tested. This drag reduction was relative to the drag study conducted on the same animal model but without body pose adjustments. Together the studies included in the present work explored and highlighted the capability of numerical methods in investigating the hydrodynamics and energetics of cetaceans. Future studies should address how computer solutions can be used to solve problems from a wider aspect. For instance, extra parasitic loads caused by attached gear as well as possible injuries due to the encounter with fishing gear should also be considered while evaluating the energy budget of the North Atlantic right whales.

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 primary aim of this thesis was to quantify the ways Daubentonia uses its specialized feeding apparatus during naturalistic feeding behaviors. This can be divided into two main objectives. The first objective was to better understand how these extreme specializations function in the extractive foraging niche of Daubentonia. The second objective was to use Daubentonia to test for previously unmeasured behavioral modifications of bite forces using the post-cranial musculature. To do this I carried out two experiments measuring the kinetics of wood gnawing and the energetics of feeding behaviors. The main results of these experiments were: 1) Daubentonia does not generate relatively high magnitude bite forces during wood gnawing compared to their maximal voluntary bite force, but wood gnawing is extremely energetically costly compared to other feeding behaviors. 2) Daubentonia recruits post-cranial musculature during wood gnawing, most frequently generating a neck-extending moment that increased the magnitude of bite forces on the mandibular incisor. 3) The energetic costs of feeding were positively correlated with the toughness of foods. 4) The rate of energetic costs (J/s) incurred during the processing and mastication of whole nuts is not significantly greater than the rate of costs to masticate small pieces of nut kernels, but the increased handling time increases the net cost per gram of food consumed (J/g). Taken together, these experiments inform the primary aim of this study. Daubentonia appears to possess a highly specialized toolkit for fracturing stress-limited foods. Their large jaw adducting musculature, rodent-like incisors, and relatively short mandible allow them to produce large bite pressures to rapidly fracture the shells of nuts. Furthermore, it was demonstrated that Daubentonia transfers some forces from the post-cranial musculature to its incisors during wood gnawing and that the energetic costs of this wood gnawing behavior approach what is expected for sustained locomotor costs. This work illuminates a new avenue for investigation in jaw biomechanics: the assistance and modification of bite forces using the post-cranial musculature.