Update on DMR's Right Whale Passive Acoustic Monitoring

By Jessie Mathews, Nicole Velandia, and Alex Marino,

Department of Marine Resources

The Department of Marine Resources’ (DMR) Division of Marine Mammal Research Passive Acoustic Monitoring (PAM) program aims to increase our understanding of where and when North Atlantic right whales (NARW) occur in the Gulf of Maine to assess where NARWs and fishing gear overlap. Once acoustic recordings have been analyzed and reviewed by DMR science staff, the NARW acoustic detection data will be uploaded to https://passiveacoustics.fisheries.noaa.gov/pacm/#/,a publicly available portal for viewing PAM detections over different periods of time and areas. This data will then be integrated into risk modeling efforts. This work was made possible by funding from the Consolidated Appropriations Act in 2023.

Passive Acoustics – Part of DMR’s Holistic Monitoring Program

DMR’s passive acoustic monitoring compliments its visual surveys. Visual surveys are limited by weather, daylight, and whether or not whales are at the surface. PAM can monitor continuously, but whales must be vocalizing, and it cannot determine the number of whales present or identify individuals like visual surveys can. Combining visual and acoustic data helps to overcome these limitations and provides more complete monitoring coverage.

To date, the DMR visual survey program has spotted, photographed, and identified nine NARWs since the program’s first survey in March 2024 (not including the response surveys conducted near Jeffrey’s Ledge in January 2025). The PAM program, however, has detected over 80,000 confirmed NARW calls since August 2023. DMR has been collecting continuous acoustic data at 26 sites throughout Maine’s portion of Lobster Management Area 1 (LMA1) and parts of LMA3 since November 2023. Eleven of these sites have been recording since August 2023. Moorings are swapped out, and data are retrieved for analysis every four months.

Interpreting Passive Acoustic Data

The following results are preliminary findings that have been analyzed by DMR science staff. These data represent the minimum number of calls that have been confirmed by our analysts and are the property of the State of Maine and not to be used or distributed without the express consent of the Division of Marine Mammal Research.

There are several important caveats for this acoustic dataset. The 26 PAM recorders were distributed in a 40X40km grid system to provide systematic coverage within the Gulf of Maine (see Figure 1). In the literature, it is assumed that the average distance that NARW upcalls can be picked up by a recorder is 10km. Thus, the recorders were not intended to provide total coverage for the entire Gulf of Maine and therefore some NARW acoustic presence will be missed. The distance sound travels and can be detected underwater also changes with ocean chemistry, bathymetry, and background noise, so NARW upcalls could be picked up at more or less than the 10km range at certain sites. Work is currently being conducted to determine detection ranges for NARWs at each PAM site location to assess spatial coverage.   

Following the standardized NARW acoustic protocol, NARWs are determined to be acoustically present if three or more upcalls are detected in a given day. The NARW upcall is a reliable vocalization for acoustically detecting NARW presence because it is used by all ages and sex classes, likely as a contact call. However, NARWs are highly variable callers and call less often during certain behavioral states, such as when they are feeding.

The absence of acoustic presence does not mean that there were no NARWs present, as NARWs could be present, but not calling, or the call may have been too faint compared to background noise to be picked up by the analyst. The number of NARW upcalls detected also does not equal the number of animals present.  

Monthly percent presence was calculated as the total number of days with confirmed NARW presence divided by the total number of days the acoustic recorder was recording in a given month (see Figure 2). There are months without recording days (represented as Xs in Figure 2) if the recorder was not in the water (only 11 sites were deployed Aug.-Nov. 2023) or if the mooring was not able to be recovered.

Figure 1. DMR's Passive Acoustic Monitoring sites located throughout the Gulf of Maine.

Figure 2. Percent monthly presence of NARW and percentage of month with recording effort from August 2023 through June 2025 by PAM site.

Key Takeaways

The primary findings from this data are that NARWs were acoustically present more days per month in offshore waters than inshore waters. The data also show a seasonal trend where NARWs were detected more days per month throughout the late fall and winter months. The highest monthly presence recorded was at PAM site 9 near Jeffery’s Ledge in January 2025, which aligns with visual observations of a large aggregation of at least 96 NARWs by New England Aquarium researchers during that month.  

The following monthly presence maps are a selection to highlight general seasonal trends over the past two years. The full set of maps are available on the DMR Passive Acoustic Monitoring website

https://www.maine.gov/dmr/science/right-whale/monitoring/passive-acoustic.

The highest NARW acoustic presence occurs during the late fall into winter and then tapers off during the later winter months (see Figure 3). There is another smaller peak in the spring, typically during May, and then acoustic presence is low again throughout the summer. The PAM sites surrounding the LMA1 Restricted area (PAM sites 11, 12, 13, 17, 18, and 19) also follow this trend where NARW acoustic presence is low in the months leading up to the October 1st closure, is high during the closure, and is low again in the months after the closure ends on January 31st.

Acoustic presence also varies between regions in the Gulf of Maine. It should be noted that to date, across all seasons, presence at the inshore PAM sites (sites 1-8) appears to be low. Also notable, Zone A (PAM sites 7, 8, and 15) appears to have the lowest levels of NARW acoustic presence. However, it should be considered that Zone A also has higher noise levels, particularly from tidal activity, so the distance from the acoustic recorder that NARW upcalls can be detected is likely lower at those sites than it is in other areas. 

Figure 3. A representative seasonal and spatiallook at percent monthly presence of NARWs for November, February, May and September.

Figure 4. Percent monthly presence of NARWs at all grid sites in January 2024 and January 2025.

There have also been differences in presence between years.  For example, January 2024 showed moderate (~20-70%) NARW acoustic presence at multiple sites throughout the Gulf of Maine, while in January 2025 the acoustic presence was concentrated at PAM site 9 near Jeffrey’s Ledge (see Figure 4).  

Due to the January 2025 Jeffrey’s Ledge NARW aggregation and the high NARW vocal activity at nearby PAM site 9, a near-real time acoustic glider was deployed to conduct a targeted survey in the Jeffrey’s Ledge area in mid-December 2025 and will continue recording through the beginning of March 2026. All acoustic whale detections will be uploaded to https://robots4whales.whoi.edu/recent-detections and NARW aggregations communicated directly to the fishery.

More information on the DMR PAM program can be found at https://www.maine.gov/dmr/science/right-whale/monitoring/passive-acoustic. The PAM program welcomes feedback and/or questions from the fishing community, which can be submitted to PassiveAcoustics.DMR@maine.gov.