The oceanographic conditions that define the Southern California Bight (SCB) dictate the distribution of prey resources and therefore the presence of mobile predators, such as Cuvier’s beaked whales (Ziphius cavirostris). Cuvier’s beaked whales are deep-diving odontocetes that spend a majority of their time foraging near the sea floor. Due to their cryptic behavior, little is known about how they respond to seasonal and interannual changes in their environment. This study utilizes passive acoustic data recorded from two sites within the SCB to explore the oceanographic conditions that Cuvier’s beaked whales appear to favor. Utilizing optimum multiparameter analysis, modeled temperature and salinity data are used to identify and quantify these source waters: the Pacific Subarctic Upper Water (PSUW), Pacific Equatorial Water (PEW), and the Eastern North Pacific Central Water (ENPCW). The interannual and seasonal variability in El Niño Southern Oscillation events and the fraction and vertical distribution of these three source waters may explain variability in Cuvier’s beaked whale presence. Mesoscale mixing was also investigated to explain variability in presence on a weekly or biweekly time scale. Cuvier’s beaked whale presence was highest during the winter and spring and decreased during the summer. These seasonal increases occurred at times of increased fractions of PEW in the undercurrent and decreased fractions of ENPCW in surface waters. On an interannual scale, years of increased presence occurred during El Niño events. These results establish a baseline understanding of the oceanographic characteristics that correlate with Cuvier’s beaked whale presence in the SCB. Furthering our knowledge of this elusive species is key to understanding how anthropogenic activities impact Cuvier’s beaked whales.

Blue whales, Balaenoptera musculus, are the largest animals on Earth and yet there is much unknown about their life history. Blue whales produce low frequency sounds including short (1-4 s) down-sweeping D calls, commonly associated with foraging. This study used long term passive acoustic monitoring to investigate a new sequence of D calls observed in data collected from 2007 to 2020 in Southern California and localized sequences on July 22nd 2019. On that day, 28 sequences occurred in a two hour and twenty-minute period. The D calls during this time had an average 7.3 s +/- 1.7 s inter-call interval within a sequence and 7 calls +/- 1 call per sequence. In the data from 2007 to 2020, sequences were present in all the years with a peak in sequences per day in 2019 with the maximum number of sequences per year also occurring in 2019. To understand how sequences were produced spatially, the D calls on July 22nd 2019 were localized. This resulted in 194 locations for all D calls and an average location for each sequence. Average locations were scattered within a 250 m by 350 m area, indicating that an individual whale may be producing the sequences. Using the location for each call, source level was computed using received level and transmission loss. The average root mean square source level calculated over 30 to 80 Hz was 162.3 +/- 2.2 dB re 1µPa at 1 m. By combining both observations of calling behavior and localizations, we can gather insight into the temporal and spatial behavior of blue whales when emitting D calls.

Although sperm whales are a cosmopolitan species, male and female sperm whales are sexually dimorphic, and the sexes have differences in behavior and habitat preference that result in differences in their distribution and seasonality. Understanding the complex spatiotemporal distribution patterns and demographic composition can be difficult with traditional, logistically challenging shipboard methods given the vast distances and depths these animals travel. Since sperm whales produce highly distinctive echolocation clicks while foraging and navigating, they’re excellent candidates for passive acoustic monitoring (PAM), an alternative method to eavesdrop on these deep-diving animals. Here we show the utility of PAM as a robust tool for advancing our understanding of sperm whale ecology. This study incorporates acoustic data from over 40 recording sites across the northern hemisphere, yielding valuable insights into demographics, acoustic density estimation, and the identification of high-use areas and habitat associations. In remote regions, PAM has enabled us to identify areas where sperm whales are adapting to changing environmental conditions by expanding their potential range in response to climate change, exemplified by observations in the eastern Canadian Arctic. Furthermore, our findings challenge conventional assumptions about male and female preferred habitats, as evidenced by the presence of females in high-latitude regions like the Gulf of Alaska and Bering Sea/Aleutian Islands. Our long-term PAM efforts have significantly expanded our knowledge of demographic specific presence, spatiotemporal distribution, acoustic density, and habitat associations of sperm whales. This underscores the importance of tailored conservation and management strategies that account for demographic variations for effective stewardship of this endangered species.

Food availability has been identified as a critical factor influencing the growth, individual health, and population dynamics of killer whales (Orcinus orca) in the coastal waters of the eastern North Pacific Ocean. Between 2014 and 2019 we conducted 113 hand-launched unmanned aerial system flights over mammal-eating Bigg’s killer whales around Vancouver Island, resulting in 20,545 aerial photographs of 95 individually identified animals. I conducted photogrammetric measurements from high-quality images in 91 individuals, a sample that ranged from first-year calves to mature adults of both sexes; this is the first study to estimate size, growth, and health of Bigg’s killer whales. Individual lengths ranged from a 2.4m neonate to an 8.3m 38-year-old male. Using a Richard’s growth curve model, I estimated asymptotic adult length at 6.4 ± 0.1m (standard error) in females and 7.3 ± 0.2m in males, as well as age of inflection at 14.2 ± 2.8 years in females and 18.4 ± 2.3 years in males. Comparison with sympatric salmon-eating Southern Resident killer whales found that both sexes of Bigg’s killer whale measured significantly longer than Southern Residents (female z-test P = 0.003; male z-test P = 0.093) but there was no significant difference in age of inflection between males (z-test, P = 0.53) or females (z-test, P = 0.45) between the two populations. Analysis of eye patch ratio (a proxy for body condition) revealed that all age/sex classes of Bigg’s killer whales were more robust than Southern Resident killer whales, and the difference was most significant when comparing calves (z-test, P < 0.0001) and juveniles (z-test, P < 0.0001) between the two populations. I propose that in the absence of major discrepancies in growth trends, morphometric divergences between the two populations are largely a function of prey availability.

In marine ecosystems, cetaceans are top predators that mostly exploit low- to mid-trophic level organisms. The presence and type of behavior displayed by cetaceans within a habitat is thus strongly driven by the physical oceanographic conditions that modulate the local prey. However, our understanding of how physical oceanography shapes foraging resources for cetaceans is still lacking due to the difficulty of simultaneously and continuously collecting prey and cetacean presence data. This study used passive acoustic, active acoustic, and in situ physical oceanographic observations collected from moorings located within the San Diego Trough, along with satellite-derived and ocean general circulation model measurements, to characterize the local ecosystem and generate generalized additive models to examine how physics influences the relationships between lower and higher trophic levels. Here, I show how seasonal changes in oceanography and mesoscale variability modulate prey availability and thus cetacean presence and behavior within the San Diego Trough. Specifically, I found that surface prey was modulated by changes in mesoscale activity, diel vertically migrating mesopelagic species were modulated by wind-driven upwelling and primary productivity, and krill in the mid-water column were modulated by wind-driven upwelling, salinity at ~300 m depth, and primary productivity. These relationships were then reflected in the cetacean models, where the presence and type of behavior displayed by a group of cetaceans was influenced either by both the presence of their prey and the physical oceanographic conditions that modulate their prey, or by just the physical oceanographic conditions that modulate their prey. These results describe the predator-prey dynamics of some of the cetaceans found within the San Diego Trough and may aid in developing more accurate spatially explicit management actions to better manage and conserve these species in similar ecosystems.

The distribution of highly mobile, top marine predators such as cetaceans is largely driven by oceanographic conditions that shape foraging grounds and modulate the abundance and distribution of prey resources. However, due to their oceanic habitat and cryptic behavior, little is known on how deep-diving foragers respond to changes in the water column. This study used passive acoustic data collected at two sites in the Southern California Bight along with environmental data to examine spatial and temporal patterns of Cuvier’s beaked whale (Ziphius cavirostris) occurrence in relation to oceanographic conditions over time. Here, I show that seasonal changes in oceanographic conditions and mesoscale dynamics influence seasonal patterns of Cuvier’s beaked whale presence across the study region. Specifically, I found that Cuvier’s beaked whales were more likely encountered in winter and spring when water temperature, salinity, and relative vorticity at the surface were low while temperature at 200 m were high. Consequently, fluctuations in detection rates of Cuvier’s beaked whales from year-to-year and between sites suggest that abrupt changes in these oceanographic variables seem to influence interannual variability in seasonal patterns of presence. These results provide baseline data on spatio-temporal distribution of Cuvier’s beaked whales in the Southern California Bight and emphasize the value of coupling long-term acoustic monitoring with environmental data to better understand elusive cetacean species’ habitat use and relationship to oceanographic changes, which may aid the development of management strategies related to global climate change and anthropogenic noise.

Studies of marine mammals using passive acoustic monitoring (PAM) tools are becoming more and more common. This methodology allows for documentation of biologically relevant factors such as movement patterns or animal behaviors while remaining largely non-invasive and cost effective. In the Hawaiian Islands, a set of PAM recordings covering the frequency band of most toothed whale (odontocete) echolocation clicks were collected from 2008-2019 at sites off the islands of Hawaiʻi, Kauaʻi, and Pearl and Hermes Reef (otherwise known as ‘Manawai’). However, due to the size of this dataset and the complexity of species-level acoustic classification, multi-year, multi-species analyses had not yet been completed. In this dissertation, a machine learning toolkit was used to effectively mitigate this problem by detecting and classifying echolocation clicks using a combination of unsupervised clustering methods and human-mediated analyses. Classified clicks were distilled into timeseries of species’ presence in order to document, and propose reasons for, observed patterns. Habitat modelling employing Generalized Additive Models (GAMs) with and without Generalized Estimating Equations (GEEs) was used to elucidate these trends in combination with oceanographic variables. The machine learning pipeline used distilled eight unique echolocation click types, attributable to eight or more species of odontocetes. Species composition differed amongst considered sites, and this difference was robust to seasonal movement patterns. Temporally, hour of day was the most significant predictor of detection across species and sites, followed by season. When considered in conjunction with sea surface variables, temperature had the strongest relationship to detections. Of the climate indices considered, El Niño Southern Oscillation (ENSO) may have the most effect on species detections at monitored sites. This study demonstrates that PAM is an invaluable tool in studies of oceanic top predators, and that machine learning tools can mitigate issues related to the size and complexity of PAM datasets. Using these tools and habitat modelling analyses, we can gain valuable insights into top predator behavior in relation to temporal variables, surface conditions, and long-term climate indicators.

Cuvier’s beaked whales are a deep-diving cetacean species known to forage in the submarine canyons of the Southern California Bight. Although this species is a top predator in deep-sea ecosystems, little is known about their social or foraging strategies because of their extreme diving behavior. In this analysis, time-difference-of-arrival (TDOA) localization is used to track the position of Cuvier’s beaked whales from echolocation clicks recorded on seafloor-mounted hydrophone arrays. This approach yielded 162 final tracks with estimated swim speeds of diving Cuvier’s beaked whales at one acoustic monitoring site from July 2021 to October 2022. The number of individual whales captured on a single track ranged from 1 to 7, with a mean of 2.24. Tracks including four or more individuals were captured most often during the day, with notable peaks in July 2021, February 2022, and July 2022. Three distinct diving behaviors were observed, differentiated by minimum depth, change in depth, and lateral movement: initial descent dive segments (1.657 ± 0.441 m/s), consistent trajectory dive segments (0.913 ± 0.596 m/s), and variable trajectory segments (1.298 ± 0.438 m/s). This long-term monitoring effort and TDOA localization approach collected data from Cuvier’s beaked whale foraging dives to reveal spatial use, group size, and diving behavior trends at our acoustic monitoring site. This extensive tracking dataset gives valuable insight into the social and foraging behavior at depth of Cuvier’s beaked whales offshore Southern California.

The influence of the lunar cycle on dolphin foraging behavior was investigated in the productive, southern California Current Ecosystem and the oligotrophic Hawaiian Archipelago. Passive acoustic recordings from 2009 to 2015 were analyzed to document the presence of echolocation from four dolphin species that demonstrate distinct foraging preferences and diving abilities. Visual observations of dolphins, cloud coverage, commercial landings of market squid (Doryteuthis opalescens) and acoustic backscatter of fish were also considered in the Southern California Bight. The temporal variability of echolocation is described from daily to annual timescales, with emphasis on the lunar cycle as an established behavioral driver for potential dolphin prey. For dolphins that foraged at night, the presence of echolocation was reduced during nights of the full moon and during times of night that the moon was present in the night sky. In the Southern California Bight, echolocation activity was reduced for both shallow- diving common dolphins (Delphinus delphis) and deeper-diving Risso’s dolphins (Grampus griseus) during times of increased illumination. Seasonal differences in acoustic behavior for both species suggest a geographic shift in dolphin populations, shoaling scattering layers or prey switching behavior during warm months, whereby dolphins target prey that do not vertically migrate. In the Hawaiian Archipelago, deep-diving short-finned pilot whales (Globicephala macrorhynchus) and shallow-diving false killer whales (Pseudorca crassidens) also showed reduced echolocation behavior during periods of increased lunar illumination. In contrast to nocturnal foraging in the northwestern Hawaiian Islands, false killer whales in the main Hawaiian Islands mainly foraged during the day and the lunar cycle showed little influence on their nocturnal acoustic behavior. Different temporal patterns in false killer whale acoustic behavior between the main and northwestern Hawaiian Islands can likely be attributed to the presence of distinct populations or social clusters with dissimilar foraging strategies. Consistent observations of reduced acoustic activity during times of increased lunar illumination show that the lunar cycle is an important predictor for nocturnal dolphin foraging behavior. The result of this research advances the scientific understanding of how dolphins optimize their foraging behavior in response to the changing distribution and abundance of their prey.

The California Current System (CCS) is a highly productive Eastern Boundary Upwelling System. Cross-shore transport of recently-upwelled water is driven by horizontal stirring from mesoscale eddies, fronts, and filaments, that shift surface productivity away from the narrow upwelling zone inshore. In addition to driving the cross-shore transport of upwelled water, mesoscale features form pelagic habitats through biophysical coupling, which create regions where the physical convergences and enhanced growth of plankton attract higher trophic levels. Mesoscale features are therefore important foraging habitats for many organisms. Climate variability, such as the El Niño Southern Oscillation, can drive large changes in ecosystems through physical processes such as changes in upwelling that can reverberate through the ecosystem. This dissertation combines a 25-year daily record of finite-size Lyapunov exponents (FSLEs), a measure of mesoscale features and horizontal stirring, with 21 years of satellite-derived chlorophyll a measurements and 18 years of quarterly marine mammal visual surveys in order to investigate the links between mesoscale features, chlorophyll, climate variability, and cetaceans in the CCS. The annual cycle of mesoscale stirring was found to be highly correlated with seasonal upwelling in the CCS. Interannual fluctuations in mesoscale stirring showed 3-12 month lagged responses to climate indices, with the CCS oscillating out of phase with waters west and north. Chlorophyll a was positively correlated with FSLE intensity in a meridional band 200-600 km offshore. Annual cetacean sightings (scaled for effort) were stable for most species but scaled sightings of Dall’s porpoise and Pacific white-sided dolphin decreased over the study period. During the 2014-2016 marine heatwave, scaled sightings of common and Risso’s dolphins increased, an effect driven by large groups in the winter and spring of 2015. Scaled sightings of several dolphin species were higher during El Niño events, whereas blue and fin whale summertime scaled sightings were higher during La Niñas. Blue, fin, and humpback whales showed habitat partitioning through a combination of geographic separation and species-specific preferences for certain mesoscale features. Dall’s porpoises had a strong association with rare, intense FSLE ridges.