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.
Highlights
IntroductionDeep ocean a cacophony of sounds may greet the listening ear (or hydrophone)
Even in the vast, deep ocean a cacophony of sounds may greet the listening ear
We examined each event by looking at a time period that spanned 2 weeks before the event through 2 weeks following the event, and plotted multiple signal types during that time window, including wind speed measurements from the Kona International Airport, odontocete detections, vessel and echosounder detections and sound energy in different frequency bands
Summary
Deep ocean a cacophony of sounds may greet the listening ear (or hydrophone). Analysis of the marine soundscape has been used to characterize biodiversity (Bertucci et al, 2016; Harris et al, 2016), indicate ecosystem health (Mathias et al, 2016; Coquereau et al, 2017; Marley et al, 2017), and reveal changes in anthropogenic activity over time (e.g., Andrew et al, 2002; McDonald et al, 2006; Chapman and Price, 2011; McKenna et al, 2012a; Širovicet al., 2016) Most of these studies have been limited in recording depth (most shallower than 50 m), frequency spectrum (many below 2 kHz), and sample duration (e.g., only a few days or months). The frequency range covered by most studies does not span the full frequency range of animal hearing and sound production, in deep-water, open-ocean environments
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