Underwater soundscapes and false killer whale acoustic ecology across the Hawaiian archipelago

Abstract

Passive acoustic monitoring (PAM) is an effective technique for long-term monitoring of the soundscape in marine protected areas (MPAs). This study leverages long-term PAM data sets from recorders deployed in the Hawaiian Islands Humpback Whale National Marine Sanctuary, Papahānaumokuākea Marine National Monument, and island-associated sites outside the sanctuary to investigate soundscapes and odontocete presence. This dissertation implements a multi-scale PAM approach to large-scale monitoring of MPAs, validates cross-platform detection/classification techniques for lesser-known species in biologically relevant areas, and highlights the importance of representative individual insights to inform our knowledge of animal behavior of an endangered population. In Chapter 1, the underwater soundscape was characterized and compared across multiple sites within the sanctuary. Generally, soundscapes were dominated by biological sources, most prominently the seasonal detection of humpback whale chorusing. Overall, we reported relatively low vessel detection rates. No COVID-19 impact could be observed acoustically using soundscape metrics which was likely due to the dominance of humpback whale chorusing. In order to better understand the habitat use of blackfish within the sanctuary boundaries, in Chapter 2, automated detectors were used on the full repertoire (whistles, clicks, and burst pulses) to determine the presence of these species on the same SanctSound datasets. Our findings revealed diel patterns in detections with relative presence of blackfish being significantly higher at night within the sanctuary. Additional more in-depth analyses were conducted to detect the presence of the false killer whales (Pseudorca crassidens) within the monument and sites outside the sanctuary. Results revealed that false killer whales were detected across all sites with some geographical variation. In Chapter 3, the acoustic behavior of Main Hawaiian Islands insular false killer whales was investigated using non-invasive animal borne tags. Greater repertoire diversity and signal complexity than previously described were observed with 52 stereotyped call types characterized. Predominant call types and call rates across dive states varied by individual. Most calls contained acoustically complex, nonlinear phenomena indicating potential functionality as contact calls when spatially distant. Call rates decreased as swim speed increased, indicating potential behavioral changes in response to conspecifics.