Florida Keys National Marine Sanctuary

Ocean Sound Monitoring

The Florida Keys National Marine Sanctuary (FKNMS) protects a multitude of marine habitats that support high biodiversity found in its mangrove forests, seagrass meadows, open ocean, and famously the only living coral barrier reef in the continental United States. Visitor use of sanctuary water is widespread and includes many activities, from recreational diving and snorkeling to recreational fishing. Targeted sound monitoring has historically focused on understanding biological and human activity within the context of seasonal conditions as well as soundscape responses to coral stressors and restoration efforts. Multiple sites in the sanctuary were part of the Sanctuary Soundscape Monitoring Project, a 5-year (2018-2022) system-wide monitoring project to understand the diversity of sounds in sanctuary waters.

Current ONMS ocean sound monitoring and analysis is maintained at four sites (FK01, FK05, FK06, and FK08) within the coral reef tract of the lower keys. Collectively, these sites are being monitored for sounds produced by spawning fishes, such as groupers, snapping shrimp, and vessels to further understand the biological productivity of reef inhabitants and stakeholder use of these unique reefs. The comparison of sound with additional datatypes, such as temperature data and restoration activities, is also being explored to examine how soundscapes respond to environmental and habitat conditions in the context of different spatial and temporal management strategies.

To see historical monitoring sites that are no longer active, please visit Sanctuary Soundscape Project data portal.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	StartDate	Total Recording Days
FK01	A historical monitoring site with coral reef habitat that supports fish spawning aggregations for multiple species and receives heavy fishing pressure.	coastal-shallow, outer reef formation with mixed sand and hard bottom, separated from main reef complex by a deep sand channel	28	48	Snapping shrimp	Recreation vessels	24.43	-81.93	March 2023	574
FK05	A Sanctuary Preservation Area that contains shallow spur and groove reef structure. Site is included in restoration plans for Mission: Iconic Reefs. It is a popular location for recreational diving and snorkeling. Fishing is not allowed.	coastal-shallow	13	48	Snapping shrimp	Recreation vessels	24.45	-81.84	March 2023	621
FK06	A Sanctuary Preservation Area that contains shallow spur and groove reef structure. It is a popular location for recreational diving and snorkeling. Fishing is not allowed. Rock Key may be opened to fishing in near future.	coastal-shallow	13	48	Snapping shrimp	Recreation vessels	24.45	-81.85	May 2024	127
FK08	A Sanctuary Preservation Area that contains shallow spur and groove reef structure. It is a popular location for recreational diving and snorkeling. Fishing is not allowed.	coastal-shallow	13	48	Snapping shrimp	Recreation vessels	24.45	-81.87	April 2025	162

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 goliath grouper calling on their spawning aggregation site?

The Atlantic goliath grouper (Epinephelus itajara) is the largest reef fish in the Western North Atlantic. They are typically found alone or in small groups in shallow tropical waters among coral and artificial reefs throughout the Gulf of America and Florida Keys in the United States, but also undertake annual migrations to offshore spawning sites. They form aggregations of 100 individuals or more at specific locations (wrecks, rock ledges, and isolated patch reefs) where they are suspected to spawn June through December, with peak spawning activity July through September.

Once relatively common throughout Florida and the Caribbean, the species is now considered vulnerable to extinction due to overfishing and loss of juvenile mangrove habitat. These spawning aggregations are the only known time that reproduction occurs and are thus an important focus area for conservation efforts. However, few goliath grouper spawning sites have ever been documented.

The Office of National Marine Sanctuaries maintains four listening stations within the Florida Keys National Marine Sanctuary. While reviewing the data collected from these recorders, we found transient goliath grouper calls at one listening station (FK01), likely on a spawning aggregation site. Goliath grouper generate loud, single-pulsed low-frequency booms, and visual observations made by divers suggest that males boom at females during presumed courtship. Using the long-term acoustic recordings at this site, we documented the timing and duration of goliath grouper sound production during the spawning season to investigate patterns in their acoustic activity.

Based on tagging data at other aggregation sites, spawning activity for the goliath grouper is thought to be highly predictable in space and time, often occurring at night around the time of the new moon. At our recording location, peak call activity occurred in the months of August and September. Similarly, we also found that sound production was strongly diel, with peaks occurring between 1:00 - 4:00 am. However, we did not observe the same predictability of call activity around the new moon. There was no prominent pattern of call activity around the different moon phases at all. And different patterns were observed in different years.

The total number of goliath grouper calls detected daily during their peak spawning season from July through September in 2023 and 2024. Data were subsampled one minute for every 10 minutes. The light colored vertical grey bars indicate the occurrence of the full moon, and vertical dark grey bars indicate the occurrence of the new moon. Credit: Amelia Johnson/NOAA.

Barplots showing the number of goliath grouper calls per hour at listening station FK01 during peak spawning season from July through September in 2023 and 2024. Data were subsampled one minute for every 10 minutes. Grey shaded regions indicate nighttime. Credit: Amelia Johnson/NOAA.

When do whales contribute to the soundscape, indicating their presence nearby?

The National Marine Fisheries Service (NMFS) maintains the analysis of acoustic presence of many whale species from passive acoustic monitoring data within U.S. waters, including ONMS sites. Visit the interactive website to explore spatial and temporal patterns in different species.