Characterizing the Long-Term, Wide-Band and Deep-Water Soundscape Off Hawai’i

Abstract

Many animals use sound for communication, navigation, and foraging, particularly in deep water or at night when light is limited, so describing the soundscape is essential for understanding, protecting, and managing these species and their environments. The nearshore deep-water acoustic environment off the coast of Kona, Hawai’i, is not well documented but is expected to be strongly influenced by anthropogenic activities such as fishing, tourism, and other vessel activity. To characterize the deep-water soundscape in this area we used High-frequency Acoustic Recording Packages (HARPs) to record acoustic data year-round at a 200 or 320 kHz sampling rate. We analyzed data spanning more than 10 years (2007-2018) by producing measurements of frequency-specific energy and using a suite of detectors and classifiers for general and specific sound sources. This provided a time series for sounds coming from biological, anthropogenic and physical sources. The soundscape in this location is dominated by signals generated by humans and odontocete cetaceans (mostly delphinids), generally alternating on a diel cycle. During daylight hours the dominant sound sources are vessels and echosounders, with strong signals ranging from 10 Hz to 80 kHz and above, while during the night the clicks from odontocetes dominate the soundscape in mid-to-high frequencies, generally between 10 and 90 kHz. Winter-resident humpback whales are present seasonally and produce calls in lower frequencies (200-2,000 Hz). Overall, seasonal variability is relatively subtle, which is unsurprising given the tropical latitude and deep-water environment. These results, and particularly the inclusion of sounds from frequencies above 2 kHz, represent the first long-term analysis of a marine soundscape in the North Pacific, and the first assessment of the intense, daily presence of manmade noise at this site. The decadal time series allows us to characterize the dynamic nature of this location, and to begin to identify changes in the soundscape over time. This type of analysis facilitates protection of natural resources and effective management of human activities in an ecologically important area.

Comparing the underwater soundscape of the Hawaiian Islands Humpback Whale National Marine Sanctuary and potential influences of the COVID-19 pandemic

“…In this study, we observed the opposite trend at the Hawaiʻi site which had higher sound levels corresponding with humpback whale chorusing which likely reflects the variability in animal presence across islands annually. More recent long-term, broadband soundscape work off Kona, Hawaiʻi revealed more subtle seasonal trends in the deep-water soundscape, with sound levels within the Hawaiʻi range reported in this study but exhibited low frequency seasonality in the winter driven by humpback whales (Merkens et al, 2021). With the inclusion of consecutive years of data, this study expands on the comprehensive Hawaiian Archipelago wide soundscape analyses conducted in Lammers et al (2023a) within the sanctuary and monument.…”

“…This study shows the presence of inter and intra-island variations in the soundscape of HIHWNMS, which fluctuate annually due primarily to changes of biological sources (Kaplan et al, 2018;Kügler et al, 2020;Merkens et al, 2021). In temperate and tropical waters with relatively shallow reef environments, biological sources are often the primary drivers of temporal sound level fluctuations (e.g.…”

“…The primary objective of SanctSound was to implement a uniform approach to data collection and analysis to produce standardized data products that could be used to evaluate the soundscape and make system-wide comparisons of spatial, spectral, and temporal variability in ambient underwater sound levels. Recently published soundscape studies in and around HIHWNMS and PMNM have provided valuable insights into humpback whale abundance trends (Kügler et al, 2020(Kügler et al, , 2021Merkens et al, 2021;Lammers et al, 2023a) and patterns in archipelago-wide distribution (Lammers et al, 2023a). Thus, soundscape monitoring in the Hawaiian Islands provides managers with valuable insight into the soundscape at this remote location in the Central Pacific.…”

Discriminating and classifying odontocete echolocation clicks in the Hawaiian Islands using machine learning methods

“…An additional ‘junk’ class containing clusters of detections from noise sources such as ships and echosounders was included to prevent misclassifications of these sources as odontocetes. These noise sources were picked up by the detector due to their commonality in the data, particularly at the Kona site [ 44 ], and the similarity of these signals to echolocation clicks. Clusters of sperm whale, Physeter macrocephalus , echolocation clicks were also grouped into this ‘junk’ class due to the difficulty of separating these clicks from high-frequency ship noise as both can occupy the same frequency range between ~5–20 kHz.…”