Olympic Coast National Marine Sanctuary Soundscape Report

Ocean Sound Monitoring

Ocean sound monitoring in Olympic Coast National Marine Sanctuary (OCNMS) and surrounding region has a long history, including efforts by the U.S. Navy and the NOAA Northwest Fisheries Science Center, who have maintained national security and protected endangered species like the Southern Resident Killer Whales. Extensive co-located acoustic telemetry sensors track important prey species, like salmon, and complements underwater sound recordings to more fully characterize the OCNMS ecosystems.

A Noise Reference Station was added to this region in 2014 and continues to provide long-term monitoring of offshore areas of the western sanctuary. Additionally, in 2019 sanctuaries began monitoring sanctuary soundscapes, as part of the Sanctuary Soundscape Monitoring Project, in four locations and currently maintains one of those stations critical for tracking the status and trends of cetaceans and ship noise on the U.S.-Canadian border, inside major shipping lanes at Swiftsure Bank.

Current ONMS ocean sound monitoring and analysis is maintained at two sites. Monitoring at OC02, near Swiftsure Bank, started in 2019. In this area, vessel traffic and whale activity dominate the soundscape, which is the middle of major shipping lanes on the international border, adjacent to a military testing range and inside Southern Resident Killer whale and humpback whale critical habitat. And, the Noise Reference Station site (NRS03) is a deep water site that captures large whale and orca activity offshore and is to the west of the traffic zones for commercial vessels transiting in/out of the Strait of Juan de Fuca. It monitors the northwestern area of the sanctuary, including for Naval testing and training activity.

To see historical monitoring sites that are no longer active, please visit Sanctuary Soundscape Project data portal.

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	Start Date	Total Recording Days
OC02	To monitor a site that supports seasonally high abundances of Atlantic cod and is located near a region of elevated commercial vessel activity.	coastal-shallow, on continental slope in the middle of Traffic Separation Scheme on the northern OCNMS boundary	94	48	Large baleen whales, orca	Constant large vessel activity in Traffic Separation Scheme for ports U.S. and Canada	48.49	-125	May 2019	850
NRS03	To monitor long-term trends in ocean noise, particularly from vessels and baleen whale species presence.	offshore-deep, just outside the northwestern OCNMS boundary	488	5	Baleen whales	Large vessel traffic	47.77	−125.52	Oct 2014	2593

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 are the seasonal biologically-important times for whales?

Orca vocalizations were detected at the OC02 listening station between 2019 and 2021. Despite data gaps, a consistent seasonal pattern of more orca acoustic detections during summer months is becoming clear. This time-series will be updated as more data is scanned.

The total number of orca whale (Orcinus orca) vocalizations (black dots) detected during a given week from March 2019 to October 2021 at listening station OC02 in the Olympic Coast National Marine Sanctuary. Shaded grey regions indicate weeks with no recording effort. The smoothed blue curve highlights seasonal patterns in whale calling activity, modeled using a generalized additive model (GAM), and the shaded band surrounding it represents the model-estimated 95% confidence interval. Credit: Emma Beretta/CIRES and NOAA

We partnered with Moss Landing Marine Laboratories and Stanford Hopkins Marine Station to analyze data from this site for humpback whale vocalization, both song and non-song calls, to understand seasonality and potential behavior associated with calls over time. Song calls have a repetitive structure made up of phrases and themes that occur in a specific sequence and are most often sung by male humpback whales on their breeding grounds. Non-song calls are short, do not have a repetitive structure, and have been found to be made by humpbacks while feeding or during social encounters. Visit Acoustic Presence of Humpback Whales in U.S. West Coast National Marine Sanctuaries and Unraveling Mysteries of Humpback Whale Song for more information.

The total number of humpback whale (Megaptera novaeangliae) song (blue dots) or non-song vocalizations (red dots) detected during a given week from December 2018 to December 2021 at listening station OC02 in the Olympic Coast National Marine Sanctuary. Shaded grey regions indicate weeks with reduced recording effort (less than 75% of the week, or <126 recording hours). The smoothed blue curve highlights seasonal patterns in whale calling activity, modeled using a generalized additive model (GAM), and the shaded band surrounding it represents the model-estimated 95% confidence interval. Credit: Emma Beretta/CIRES and NOAA