Spatial and temporal variability of blackfish inside and outside marine protected areas in Hawaiʻi from moored recorders

Understanding the spatial and temporal patterns of odontocetes using passive acoustic monitoring (PAM) within and surrounding marine protected areas (MPAs) is imperative for monitoring habitat use and distribution of resident populations. Moored hydrophones were deployed in the Hawaiian Islands Humpback Whale National Marine Sanctuary (shallow, n = 4 sites), Papahānaumokuākea Marine National Monument (deep, n = 1 site), and outside MPAs (deep, n =2 sites) between 2010–2022. Whistle and click detection, feature extraction, and species classification were conducted using PAMGuard and R packages PAMpal/BANTER to evaluate patterns in blackfish presence. Overall, diel blackfish presence was observed with higher relative presence at night. Blackfish were detected at the Oʻahu/Kauaʻi sites but not detected at the Maui/Hawaiʻi sites likely due to masking by humpback whale chorusing. Overall, 42% of blackfish events (deep) were classified with higher confidence as false killer whales (Pc) and West Kauaʻi appears to be a Pc hotspot. Higher relative blackfish presence at deep sites than shallow sites reflects soundscape differences (humpback presence) and potentially preferential habitat use of offshore waters. This study exemplifies the cross-platform capability of a Pc classifier on moored PAM data for effective conservation and targeted management efforts in biologically important areas.