Chumash Heritage National Marine Sanctuary

Ocean Sound Monitoring

The Chumash Heritage National Marine Sanctuary (CHNMS) was established in 2024 and is focused on building a wholistic, long-term, multi-knowledge based monitoring framework that informs and awareness and enhanced understanding of the ecosystem's health through relationality. Sound monitoring is a vital, non-invasive tool within a broader suite of instrumentation required for a multi-dimensional understanding of the complex relationships between biodiversity, humans, and shifting oceanographic conditions in this region of the central California coast proposed for increased human activities, such as offshore wind development, in coming years.

To characterize baseline understanding of acoustic conditions ahead of sanctuary designation, the CH-01 listening station was established off Point Estero, now situated between the boundaries of MBNMS and CHNMS, along with a Noise Reference Station (NRS-13) established in 2023 northwest of CHNMS's western boundary. Scripps Institution of Oceanography's Site C has been recording inside CHNMS boundaries off Point Conception since 2008 as part of the California Current Long-term Ecological Research Project and provides a rich time-series of marine mammal acoustic detections, including beaked whales, as well as vessel activity.

Summary of monitoring sites

Long-term Monitoring Site	Primary Monitoring Purpose	Oceanographic Setting	Depth (m)	Sampling Rate (kHz)	Known Biological Sounds	Vessel Traffic Setting	Latitude	Longitude	StartDate	Total Recording Days
CH01	This is a lively kelp forest off Point Estero that supports several chorusing fish species, and experiences recreational and commercial fishing vessel activity just north of the CHNMS boundary.	coastal-shallow	20	48	Chorusing fish species	Fishing and recreational vessels	35.467	-121.023	June 2023	nan
NRS13	This listening station in the far west area of CHNMS was initiated just south of the Morro Bay wind energy area specifically to characterize baseline low frequency soundscape conditions ahead of offshore wind development. This site supports many species of whales seasonally, as well as captures vessel sound associated with traffic transiting just outside the contiguous zone boundary.	offshore-deep	842	5	Baleen whales	Large commercial vessels transiting just west of the U.S. Contiguous Zone boundary (24 NM from shore)	35.312267	-121.586983	Mar 2023	982.0
SIO-C	Scripps Instituion of Oceanography has been listening at this location offshore Point Conception on the Arguello Terrace as part of the California Current Ecosystem Long Term Ecological Research program for almost two decades. This site provides a rich time series of soniferous species presence and human activities such as vessel traffic on the continental shelf at this important biophysical transition zone, at the head of Arguello Canyon.	offshore-deep	770	5	Offshore dolphins, baleen whales, and beaked whales	Large commercial vessels transiting north/south away from/into the Santa Barbara Channel Traffic Separation Scheme	34.321667	-120.8	2008-02-01 00:00:00	nan

Ocean Sound Conditions

Soundscapes vary across years, seasons, and even within a day. Differences are driven by shifts in wind and weather patterns, migration and behavior of animals, and patterns in human activities. We track how sound levels change in different frequencies using standardized soundscape metrics to understand these changes. Seasonal and annual percentiles of all the data, a measurement of data spread with the middle 50% falling between the 25th and 75th percentile, are used to define typical conditions.

What are the seasonal patterns across frequencies?

Season is often a main driver of soundscape differences: wind and weather patterns shift, species migrate or change behavior, and humans change their marine activities. As shown on the graphic(s) below, we can visualize the differences by looking at the variation across frequency (pitch of the sound in Hertz) shown on the x-axis and intensity (how loud the sound is in decibels) shown on the y-axis. The colored lines represent regionally-specific oceanographic seasons, vertical shaded bars are the frequency ranges that a sound source of interest can be heard, and the black lines bound the expected range of modeled sound intensity when only wind noise is present.
Here are some questions to consider when viewing the graph(s) below:
(1) Which season has the highest sound levels?
(2) Are there peaks in the sound levels for any of the sounds of interest?
(3) Are the low-frequency sound levels outside the expected range for wind noise?

Seasonal median sound levels (sound intensity measured by mean-square pressure in microPascal per Hertz) across a range of frequencies (~10 to ~24,000 hertz) at a given monitoring site, with annual recording effort represented by a bar graph underneath. Each season is a different colored line. Solid black lines show modeled ambient sound levels from wind at 1 m/s (lower line) and 22.6 m/s (upper line) based on hydrophone depth. Frequency bands indicative of a biological or anthropogenic sound source of interest are highlighted in semi-transparent gray and labeled; peak frequency for dominant fish species are labeled with vertical dashed lines. Credit: Megan McKenna and Emma Beretta/CIRES and NOAA

Processing raw audio files to calibrated sound levels (i.e., soundscape metrics) involves multiple steps to get a specified time frequency data product. All soundscape metrics visualized in the soundscape inventory reports are averaged from hybrid millidecade sound levels, calculated using either MANTA or PyPAM software packages. Both softwares calculate mean PSD (dB re 1 µPa^2/Hz) per minute in 1-Hz wide bins using Welch’s method with a Hann window, FFT length equal to the sample rate, and 50% overlap. Following calibration based upon instrument specific sensitivities, PSD values per minute were further processed in hybrid millidecade spectral densities, which are an efficient means of storing PSD spectra from high sample rate audio files using 1-Hz values up to 435 Hz, and then millidecade wide PSD values up to one half of the sample rate (Martin et al. 2021).

PAMscapes was used to calculate hourly median hybrid milli-decade bands (loadSoundscapeData(ncFile, keepQuals = c(1,2)) and binSoundscapeData(hmddata, bin = "1hour", method = c("median")). The hourly data were then matched with an estimate of wind speed at that location using matchGFS in PAMscapes (Global Forecast System (GFS) weather model). Long-term condition plots in these reports were generated by averaging the hourly median hybrid millidecade results within different time constraints (i.e. annual, seasonal) and percentiles (e.g., 25% and 75%) for each hybrid millidecade frequency band.

How are ocean sound conditions changing across years?

We can track changes in ocean soundscape conditions and its contributors by comparing annual sound levels. Efforts to reduce noise impacts to marine animals are underway on local to global scales. Strategies can include avoidance of times and areas when sensitive species are present to reduce vulnerability (e.g., a shipping lane), changing the operation of a potentially hazardous noise source (e.g., by slowing and therefore quieting vessels) or through the design and use of alternative, quieter sources (e.g., new, quieter ship design and/or technologies). The effectiveness of these approaches, and the scales over which they are effective, can be tracked through comprehensive monitoring efforts. A focused analysis is often necessary to tease apart the multiple drivers of ocean sound levels, however, annual summaries provide initial insights to overall patterns.
Here are some questions to consider when viewing the graph(s) below:
(1) Are levels lower in the most recent year of monitoring in any of the frequencies of interest?
(2) Are there peaks in the sound levels for any of the sounds of interest? Do they differ across years?

Annual median sound levels (sound intensity measured by mean-square pressure in microPascal per Hertz) across a range of frequencies (~10 to ~24,000 hertz) at a given monitoring site, with annual recording effort represented by a bar graph underneath. Each year is a different blue line, getting darker for every additional year of data. Solid black lines show modeled ambient sound levels from wind at 1 m/s (lower line) and 22.6 m/s (upper line) based on hydrophone depth. Frequency bands indicative of a biological or anthropogenic sound source of interest are highlighted in semi-transparent gray and labeled; peak frequency for dominant fish species are labeled with vertical dashed lines. Credit: Megan McKenna and Emma Beretta/CIRES and NOAA

Is the intensity (loudness) of sound sources of interest within typical range?

In some soundscapes, we can use specific frequencies as indicators for the presence of a source of interest (e.g. species presence and behavior). Monitoring sites are often chosen because a known source that we want to track is present and we can track this dominant sound energy contributor using their specific frequency or frequency range. For example, seasonal migration of humpback whales to Hawaiian Islands results in soundscapes dominated by their calling between 50 and 630 Hz. At sites near commercial shipping lanes, 63 and 125 Hz one-third octave level (TOL) are used as an indicator for ship noise (Haver et al. 2021)). At sites where snapping shrimp are present, 4,000 - 18,000 Hz can be used as an indicator of their sounds. Only frequencies that have been identified as reliable for tracking a source of interest are shown below.

Time series plot of daily median sound levels (sound intensity measured by mean-square pressure in microPascal per Hertz) for a specific frequency band(s) of interest at this site, separated by year. Background color shading (blue, purple, gold) indicates low (<25th percentile), typical (25-75th percentile), and high sound levels (>75th percentile) across this monitoring site's entire dataset at this frequency band(s) for comparability with annual medians, marked with horizontal black dashed lines. Pie charts on the right hand side of the graphic show the proportion of daily median sound levels that fell within each category for each year, following the same color-coding and percentile bins. Credit: Megan McKenna and Emma Beretta/CIRES and NOAA

Ocean Sound Indicators

We can use long-term monitoring of ocean sound to derive and track indicators of ocean conditions. These indicators track the status and trend of habitat condition, species presence, human-use patterns, and management activities. There are many analytical methods used to generate ocean sound indicators. Below are ocean sound indicators relevant to the sanctuary and available for condition tracking.

When does fish chorusing contribute to the soundscape?

Knowing when fish are calling helps identify important biological periods for fish species. A reduction in noise during these periods benefits fish communication. Use the graphics below to identify months of the year and times of the day with higher levels of fish chorus. For a more details on the analysis check out: Spatiotemporal patterns of fish chorusing in California National Marine Sanctuaries.

Boxplots showing weekly variability measured by total number of hours of fish chorusing detections aggregated across years of data for bocaccio (Sebastes paucispinis) and plainfin midshipman (Porichthys notatus) at listening station CH01 in the Chumash Heritage National Marine Sanctuary. Grey barplot shows the total number of hours spent recording at this location, from June 2022 to November 2023. Credit: Emma Beretta/CIRES and NOAA

Radial plots showing the proportion of sampled acoustic data containing detections of fish chorusing, summarized by hour of day, for bocaccio (Sebastes paucispinis), plainfin midshipman (Porichthys notatus), white seabass (Atractoscion nobilis), and two unknown fish species UF440 and UF310 at listening station CH01 in the Chumash Heritage National Marine Sanctuary. Recording at CH01 spanned from June 2022 to November 2023. Daily chorusing activity for each fish species is the number of days with chorusing presence per number of days recorded. Credit: Emma Beretta/CIRES and NOAA