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Accurate estimates of drag on marine animals are required to investigate the locomotive cost, propulsive efficiency, and the impacts of entanglement if the animal is carrying fishing gear. In this study, we performed computational fluid dynamics analysis of a 10 m (length over all) right whale to obtain baseline measurements of drag on the animal. Swimming speeds covering known right whale speed range (0.125 m/s to 8 m/s) were tested. We found a weak dependence between drag coefficient and Reynolds number. At a swimming speed of 2 m/s, we analyzed the boundary layer thicknesses, the flow regimes, and drag components. We found the thickest boundary layer at the lateral sides of the peduncle, whereas the boundary layer thickness over the outer part of the flukes was less than 1.7 cm. Laminar flow occurred over the anterior ~0.6 LoA and turbulent flow from ~0.8 LoA to the fluke notch. On the surfaces of the flukes outside of the body wake region, flow was laminar. Our most significant finding is that the drag coefficient (0.0071–0.0059) of a right whale for swimming speeds ranging from 0.25 m/s to 2 m/s is approximately twice that of many previous estimates for cetaceans.

Example of electrode placement on a bottlenose dolphin (A) and a killer whale (B). For the bottlenose dolphin, two electrodes were placed on the ventral side of the animal in line with the top edge of the pectoral fins (one on each side) and the third electrode was placed on the left side approximately 15 cm below the other two electrodes. For the other species, the electrodes were placed in a vertical line down the center of the ventral side of the animal between the pectoral fins approximately 10 cm apart.

Animal ID, species, location, sex, age in years, body mass in kg (Mb), and number of breaths analyzed (n) for all animals in the study.

Supplementary Figures and Tables

Supplemental Figure 1. A figure showing the distribution of call RL and background noise levels by individual ID. Lactating females are denoted with circles, other age/sex classes are denoted by squares. Supplemental Figure 2. A plot showing the k-means density plots by call RL for high and low amplitude clusters.

Marine mammals exploit the efficiency of sound propagation in the marine environment for essential activities like communication and navigation. For this reason, passive acoustics has particularly high potential for marine mammal studies, especially those aimed at population management and conservation. Despite the rapid realization of this potential through a growing number of studies, much crucial information remains unknown or poorly understood. This research attempts to address two key knowledge gaps, using the well-studied bottlenose dolphin (Tursiops truncatus) as a model species, and underwater acoustic recordings collected on four fixed autonomous sensors deployed at multiple locations in Sarasota Bay, Florida, between September 2012 and August 2013. Underwater noise can hinder dolphin communication. The ability of these animals to overcome this obstacle was examined using recorded noise and dolphin whistles. I found that bottlenose dolphins are able to compensate for increased noise in their environment using a wide range of strategies employed in a singular fashion or in various combinations, depending on the frequency content of the noise, noise source, and time of day. These strategies include modifying whistle frequency characteristics, increasing whistle duration, and increasing whistle redundancy. Recordings were also used to evaluate the performance of six recently developed passive acoustic abundance estimation methods, by comparing their results to the true abundance of animals, obtained via a census conducted within the same area and time period. The methods employed were broadly divided into two categories – those involving direct counts of animals, and those involving counts of cues (signature whistles). The animal-based methods were traditional capture-recapture, spatially explicit capture-recapture (SECR), and an approach that blends the “snapshot” method and mark-recapture distance sampling, referred to here as (SMRDS). The cue-based methods were conventional distance sampling (CDS), an acoustic modeling approach involving the use of the passive sonar equation, and SECR. In the latter approach, detection probability was modelled as a function of sound transmission loss, rather than the Euclidean distance typically used. Of these methods, while SMRDS produced the most accurate estimate, SECR demonstrated the greatest potential for broad applicability to other species and locations, with minimal to no auxiliary data, such as distance from sound source to detector(s), which is often difficult to obtain. This was especially true when this method was compared to traditional capture-recapture results, which greatly underestimated abundance, despite attempts to account for major unmodelled heterogeneity. Furthermore, the incorporation of non-Euclidean distance significantly improved model accuracy. The acoustic modelling approach performed similarly to CDS, but both methods also strongly underestimated abundance. In particular, CDS proved to be inefficient. This approach requires at least 3 sensors for localization at a single point. It was also difficult to obtain accurate distances, and the sample size was greatly reduced by the failure to detect some whistles on all three recorders. As a result, this approach is not recommended for marine mammal abundance estimation when few recorders are available, or in high sound attenuation environments with relatively low sample sizes. It is hoped that these results lead to more informed management decisions, and therefore, more effective species conservation.

High-resolution bio-logging tools were used to examine the fine-scale foraging behaviors of humpback whales (Megaptera novaeangliae) in the coastal waters of the Western Antarctic Peninsula during the austral autumn of 2009 and 2010. Discrete feeding events (i.e., lunges) were inferred from the biologging records of thirteen whales, including a mother and her calf. In general, humpback whales exhibited efficient foraging behaviors that allowed them to maximize energetic gains and minimize energetic costs as predicted by optimal foraging theory. They fed at a continuous and high rate in the upper portion of the water column (< 100 m) from approximately dusk to dawn when their prey (Antarctic krill, Euphausia superba) were most vulnerable and less costly to acquire (i.e., near the surface). When forced to dive to greater depths, they adjusted their behaviors (e.g., descent and ascent rates) so that they could maximize their foraging durations and increase their lunging rates. In addition, humpbacks appeared to accept short term (i.e., dive by dive) costs associated with depleted oxygen stores in favor of maximizing long term (i.e., daily) energetic gains. Such efficient behaviors are particularly beneficial for mother-calf pairs who have additional energetic costs associated with foraging, such as lactation (mother), growth (calf), and maintaining proximity. In addition, because the physiology of humpback whales is poorly understood yet critically important for predicting their behaviors in response to fluctuations in their environmental conditions, foraging behaviors inferred from the bio-logging records were used to estimate their metabolic rates, oxygen storage capacities, and oxygen replenishment rates under the framework of optimal foraging theory. This research suggests that the current techniques used to estimate humpback whale oxygen stores is appropriate but that the estimation of metabolic rates of humpbacks while foraging and while traveling need to be addressed further. This work aims to increase the current understanding of humpback whale foraging behaviors along the Western Antarctic Peninsula so that appropriate measures can be taken to aid in their recovery and in the sustainability of the Antarctic marine ecosystem.

Locomotion in any environment requires the use of energy to overcome the physicalforces inherent in the environment. Most large marine vertebrates have evolvedstreamlined fusiform body shapes to minimize the resistive force of drag when ina neutral position, but nearly all behaviors result in some increase in that force.Too much energy devoted to locomotion may reduce the available surplus necessaryfor population-level factors such as reproduction. The population of North Atlanticright whales has not recovered following legal protection due to decreased fecundity,including an increase in the intercalf interval, an increase in the years to first calf andan increase in the number of nulliparous females in the population. This reproductiveimpairment appears to be related to deficiencies in storing enough energy to meet thecosts of reproduction. The goal of this study was to determine whether increases inmoving between prey patches at the cost of decreased foraging opportunities couldshift these whales into a situation of negative energy gain. The first step is tounderstand the locomotor costs for this species for the key behaviors of traveling andforaging.This study investigated the cost of locomotion in right whales by recording thesubmerged diving behaviors of free-ranging individuals in both their foraging habitatin the Bay of Fundy and their calving grounds in the South Atlantic Bight with asuction-cupped archival tag. The data from the tags were used to quantify the oc-currence of different behaviors and their associated swimming behaviors and explorethree behavioral strategies that reduce locomotor costs. First, the influence thatchanges in blubber thickness has on the buoyancy of these whales was investigatedby comparing the descent and ascent glide durations of individual whales with differ-ent blubber thicknesses. Next, the depth of surface dives made by animals of differentsizes was related to the depth where additional wave drag is generated. Finally, theuse of intermittent locomotion during foraging was investigated to understand howmuch energy is saved by using this gait. The final piece in this study was to deter-mine the drag related to traveling and foraging behaviors from glides recorded bythe tags and from two different numerical simulations of flow around whales. One, acustom developed algorithm for multiphase flow, was used to determine the relativedrag, while a second commercial package was used to determine the absolute mag-nitude of the drag force on the simplest model, the traveling animal. The resultingdrag estimates were then used in a series of theoretical models that estimated theenergetic profit remaining after shifts in the occurrence of traveling and searchingbehaviors.The diving behavior of right whales can be classified into three stereotyped be-haviors that are characterized by differences in the time spent in different parts of thewater column. The time budgets and swimming movements during these behaviorsmatched those in other species, enabling the dive shapes to be classified as foraging,searching and traveling behaviors. Right whales with thicker blubber layers werefound to perform longer ascent glides and shorter descent glides than those withthinner blubber layers, consistent with the hypothesis that positive buoyancy doesinfluence their vertical diving behavior. During horizontal traveling, whales madeshallow dives to depths that were slightly deeper than those that would cause ad-ditional costs due to wave drag. These dives appear to allow whales to both avoidthe costs of diving as well as the costs of swimming near the surface. Next, whaleswere found to glide for 12% of the bottom phases of their foraging dives, and theuse of `stroke-glide' swimming did not prolong foraging duration from that used bycontinuous swimmers. Drag coefficients estimated from these glides had an averageof 0.014 during foraging dives and 0.0052 during traveling, values which fall in therange of those reported for other marine mammals. One numerical simulation deter-mined drag forces to be comparable, while the other drastically underestimated thedrag of all behaviors. Finally, alterations to the behavioral budgets of these animalsdemonstrated their cost of locomotion constitutes a small portion (8-12%) of thetotal energy consumed and only extreme increases in traveling time could result in anegative energy balance. In summary, these results show that locomotor costs are nomore expensive in this species than those of other cetaceans and that when removedfrom all the other stressors on this population, these whales are not on an energetic`knife edge'.