The generation of acoustic waves by a modulated thermal source is examined for anisotropic materials. A wave equation is developed to include the effect of a thermoacoustic source for the anisotropic case. The dependence of the thermoacoustic source term upon the material elastic constants is identified for a thermal source varying in one dimension. This dependence is examined for several classes of crystalline anisotropy and it is found that thermoacoustic generation varies with crystallographic orientation. The directions of maximum and minimum thermoacoustic generation are not consistent for a given crystal class and are dependent upon the specific values of the elastic constants for the material.

Killer whales produce pulsed calls, which are used for communication. Calls are highly stereotyped and repertoires are unique to individual pods. Discrimination amongst these calls and comparison of call repertoires between pods can help determine population structure in killer whales and can be used to track pod movements. Calls were detected in underwater acoustic recordings in August and September 2017 in the Arctic waters of Eclipse Sound, in Nunavut, Canada. We present a repertoire of killer whale calls recorded. Eleven stereotypic call types, three biphonic and eight monophonic, were identified using manual call organization and manual whistle contour extraction. A higher diversity of calls was detected in the hydrophone located in the known narwhal aggregation site in Milne Inlet, than at the second hydrophone deployed at the mouth of Eclipse Sound which is the proposed entrance and exit point for the killer whales. The potential for increased killer whale presence and magnitude of predation on narwhals is a source of concern for management of the population and by Inuit subsistence hunters who rely on narwhals for food and economic benefit. Describing the acoustic repertoire of killer whales seasonally present in the Canadian Arctic may help understand their behavior and seasonal movements. The results presented may provide a basis for future acoustic comparisons across the North Atlantic and aid in characterizing killer whale ecotypes making seasonal incursions into Arctic waters.

Advancements in low-power and high-data-capacity consumer computer technology during the past decade have been adapted to autonomously record sounds from marine mammals over long periods. Acoustic monitoring has advantages over traditional visual surveys including greater detection ranges, continuous long-term monitoring in remote locations under various weather conditions and independent of daylight, and lower cost. However, until recently, the technology required to autonomously record whale sounds over long durations has been limited to low-frequency (< 1000 Hz) baleen whales. The need for a broader-band, higher-data capacity system capable of autonomously recording toothed whales and other marine mammals for long periods has prompted the development of a High-frequency Acoustic Recording Package (HARP) capable of sample rates up to 200 kHz. Currently, HARPs accumulate data at a rate of almost 2 TB per instrument deployment which creates challenges for processing these large data sets. One method we employ to address some of these challenges is a spectral averaging algorithm in which the data are compressed and viewed as long duration spectrograms. These spectrograms provide the ability to view large amounts of data quickly for events of interest, and they provide a link for quickly accessing the short time-scale data for more detailed analysis. HARPs are currently in use worldwide to acoustically monitor marine mammals for behavioral and ecological long-term studies. The HARP design is described and data analysis strategies along with software tools are discussed using examples of broad-band recorded data.

Mysticetes (baleen whales) often make long, annual migrations from high latitude summer feeding areas to low latitude wintering areas. Eastern North Pacific gray whales (Eschrichtius robustus) migrate within a few kilometers from shore for most of their route from summer feeding areas in the Bering, Chukchi, and Beaufort Seas to wintering areas in the lagoons along the south-western coast of the Baja California Peninsula in Mexico. This dissertation combines passive acoustic recordings, infrared camera video, and visual sightings to investigate gray whale behavior and how it changes across different timescales. I use a four-element hydrophone array in central California to present the first published full-season acoustic monitoring and tracking of migrating gray whales. I describe the characteristics of calls produced by migrating gray whales and analyze how these characteristics change due to propagation. I show that gray whale behavior changes on diel and seasonal timescales. Notably, gray whales increase their vocalizations at night but their mean swimming behavior does not change, contrary to previous assumptions used in population size estimates. Over seasonal timescales, vocalizing gray whale swimming behavior aligns with previous observations. I explore how passive acoustic and infrared camera monitoring can help quantify whales by calculating cue rates or call and blow rates for migrating gray whales. Acoustic calling rates indicate that the gray whale population size is greater than estimated using visual sightings alone and that calling rate increases over the southbound migration. Infrared camera blow rates are less affected by whale behavior and are useful for daytime and nighttime monitoring, but are limited by visibility and distance. To understand gray whale behavior over seven migration seasons, I use visual daily counts at two sites and single-hydrophone call detections which indicate that migratory behavior seems to be driven more by intrinsic than the tested environmental factors. I find that the proportion of the population using a coastal route through the Southern California Bight, especially past Los Angeles, increased over these years. Understanding the behavior of migrating gray whales will help improve abundance estimates and determine how these whales may be impacted by nearshore anthropogenic activities and climate change.

Arctic marine mammal habitats are changing rapidly while marine shipping is increasing in some areas of the Arctic. Passive acoustic monitoring can increase understanding of Arctic marine mammal responses to change and to stressors, like ship traffic. The strength of inference from underwater sound recordings is limited by several factors that I address in this dissertation with the aim of improving the usefulness of acoustic monitoring findings for Arctic marine resource management. I provide spatial context for acoustic detections of bowhead whale sounds, enabling direct comparisons of acoustic presence across different locations and environmental conditions. Ice cover and noise substantially reduce the predicted listening area around underwater sound recorders. Spatially normalized acoustic detections reveal that bowhead whales utilize an area at least 140 km north of Alaska during their spring migration, migrating through large areas of >90% sea ice cover. I describe acoustic characteristics of beluga and narwhal echolocation clicks, which differ substantially in frequency content and rhythmic patterns. Sound absorption by seawater and apparent changes in animal orientation strongly affect frequency spectra of recorded clicks. Finally, I measure the underwater soundscape within a narwhal summer habitat and quantify underwater noise added by commercial ship traffic. The natural soundscape, excluding periods with nearby ships, is relatively quiet in an acoustically sheltered fiord. Distant sounds from regional shipping are apparent at a less-sheltered location open to long-range sound propagation. When ships pass the recording locations, sound levels are elevated above the median levels of natural sounds for periods ranging from 30 minutes up to >4 hours with each transit. Icebreaker and tanker ships radiate more underwater noise than general cargo and bulk carrier ships. Ship sounds overlap with common social sounds produced by narwhals and ringed seals at distances of 5 to >30 km from passing ships, possibly interfering with animal communication. Improved detection distance estimates and understanding of detection probability estimation coupled with increased confidence in detection and identification of beluga, narwhal, and bowhead sounds will facilitate passive acoustic density estimation of Arctic marine mammals, investigation of their relationships with habitat, and studies of their behavioral responses to ship traffic.