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Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2023)

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.

    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2022)
    "Gaze following"-when one individual witnesses another shift its orientation, and then re-orients in the same direction-has been observed in a wide range of species. Related work with dolphins has to date focused on human-dolphin interactions. In this conspecific study, we examined a group of dolphins orienting, in passing, to gateways between their pools, as opportunities for witnesses to demonstrate "gaze following". Seven bottlenose dolphins were synchronously videotaped on six underwater cameras, for 21 h over three days, and the recordings analyzed by trained observers. The identities of all animals present, their partner state, and whether and to what degree they had altered their access to the gate (e.g., from Monocular to Binocular, or Binocular to Visio-Echoic) was recorded. Compared to animals that did not witness such a change, witnesses of an increase in access by another dolphin were significantly more likely to also act to increase their own access. We observed 460 such cases of "gaze following" in these animals. Dolphins who were partnered (showed sustained swimming within 1 body length) were significantly more likely, than non-partnered animals, to "gaze follow". Dolphins also showed a significant tendency toward matching the kind of access they observed. No significant difference was found in the presence of animals in the back pools, during changes in orientation that were followed, versus in those that were not. These findings support adding bottlenose dolphins to the growing list of species that display conspecific "gaze following".
      Cover page: Conspecific "gaze following" in bottlenose dolphins
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2024)
      The oceanographic conditions of the Southern California Bight (SCB) dictate the distribution and abundance of prey resources and therefore the presence of mobile predators, such as goose-beaked whales (Ziphius cavirostris). Goose-beaked whales are deep-diving odontocetes that spend a majority of their time foraging at depth. 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 goose-beaked whales appear to favor. Utilizing optimum multiparameter analysis, modeled temperature and salinity data are used to identify and quantify these source waters: Pacific Subarctic Upper Water (PSUW), Pacific Equatorial Water (PEW), and Eastern North Pacific Central Water (ENPCW). The interannual and seasonal variability in goose-beaked whale presence was related to the variability in El Niño Southern Oscillation events and the fraction and vertical distribution of the three source waters. Goose-beaked whale acoustic presence was highest during the winter and spring and decreased during the late summer and early fall. These seasonal increases occurred at times of increased fractions of PEW in the California Undercurrent and decreased fractions of ENPCW in surface waters. Interannual increases in goose-beaked whale presence occurred during El Niño events. These results establish a baseline understanding of the oceanographic characteristics that correlate with goose-beaked whale presence in the SCB. Furthering our knowledge of this elusive species is key to understanding how anthropogenic activities impact goose-beaked whales.
        Cover page: Ziphius cavirostris presence relative to the vertical and temporal variability of oceanographic conditions in the Southern California Bight.
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