High-frequency Acoustic Recording Packages Research Articles

An automated approach for detection and classification of toothed whales in Hawai'i marine protected areas

Passive acoustic monitoring is an effective technique for studying cetacean presence within marine protected areas (MPAs). The Hawaiian archipelago is home to 18 species of resident toothed whales, but little is known regarding the spatio-temporal variability of false killer whales (Pseudorca crassidens—FKW) and short-finned pilot whales (Globicephala macrorhynchus) across Hawai‘i MPAs. Bottom-moored recorders were deployed inside and outside the Hawaiian Islands Humpback Whale National Marine Sanctuary and Papahānaumokuākea Marine National Monument through SanctSound and Pacific Islands Fisheries Science Center. High Frequency Acoustic Recording Packages (HARPs) and SoundTraps (200 kHz/48 kHz SR, respectively) deployed between 2018 and 2022, allowed leveraging of long-term datasets. Data used in this study include 27 deployments across 11 sites, encompassing >187 months of data. Here, we describe an automated approach for species classification which is challenging given the high spectral overlap in whistle features and acoustic masking during humpback whale season. PAMGuard detectors were used to detect whistles, clicks, and burst pulses. Features were extracted using PAMpal and species classified using BANTER models and confirmed from a Hawaiian Islands Ecosystem Assessment Survey annotated dataset. Acoustic monitoring provides vital information about the value of MPAs and a better understanding of endangered insular FKW habitat use.

Determining the spatial and temporal variability of false killer whales (Pseudorca crassidens) and short-finned pilot whales (Globicephala macrorhynchus) in the Hawaiian Islands from passive acoustic monitoring

False killer whales (Pseudorca crassidens) and short-finned pilot whales (Globicephala macrorhynchus) are resident, toothed whale species to the Hawaiian archipelago. False killer whales are considered of high concern in Hawai‘i with the insular population listed as endangered. Passive acoustic monitoring (PAM) is an effective technique for studying these highly social odontocete species on large temporal and geographical scales. Moored hydrophones were deployed inside and outside Marine Protected Areas (MPAs) through the SanctSound project, allowing leveraging of long-term datasets to assess the acoustic behavior of these species within and beyond the Hawaiian Islands Humpback Whale National Marine Sanctuary and Papahānaumokuākea Marine National Monument. High Frequency Acoustic Recording Packages (HARPs) (200 kHz SR) and SoundTraps (48 kHz SR), recording on various duty cycles, were deployed between 2018–2022 within MPAs (monument: n = 51 months; sanctuary: n = 76 months) and outside MPAs (n = 60 months). PAMGuard detectors were used to detect whistles, clicks, and burst pulses. Detection features were extracted using the PAMpal package and events classified to species using BANTER. Acoustic monitoring provides key information about the value of MPAs and a better understanding of habitat use and behavior of these species.

Characterizing the Long-Term, Wide-Band and Deep-Water Soundscape Off Hawai’i

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.

Geographic Variation in Bryde’s Whale Be4 Calls in the Gulf of California: An Insight to Population Dynamics

Although Bryde’s whale (Balaenoptera edeni) has worldwide distribution, it is considered one of the most difficult species of baleen whales to study. Two populations existing in the Gulf of California have been proposed, but difficulties in obtaining biopsies have complicated testing the hypothesis of discrete stock difference between north and south of the Gulf. On the other hand, bioacoustics analyses have been used to differentiate populations from other whale species. Therefore, to provide information for the previously proposed hypothesis, the most common Bryde’s call (Be4) in the region was analyzed. Acoustic data was collected using a High-frequency Acoustic Recording Package (HARP) system placed at two locations in the Gulf of California: one in the north from November 2006 to June 2007 and other one in the south from August to December 2008. Duration and frequency range were measured for calls with a signal-to-noise ratio (SNR) greater than 27 dB. The Mann–Whitney-Utest was performed to compare distributions in both geographic areas, and the results were compared with a photo-identification analysis. Of the 903 Be4 calls detected, 103 (north) and 92 (south) met the SNR requirement. Duration showed a significant difference (Mann–Whitney test,U= 11238,z-statistics = 2.91,p= 0.003) with southern calls being longer than the northern ones. The results suggest that the northern population remains resident in the north with some movement toward the south, also verified by photo-identification. A detailed inspection showed a double distribution in the south (Mann–Whitney test,U= 2211,z-statistics = −8.39,p= 4.4776e-17), suggesting the presence at the same time of resident and transient populations. The latter has been suggested to belong to the Eastern Tropical Pacific. The results suggest a geographic variation inB. edeniBe4 call type and support the existence of two populations within the Gulf of California.

Cetaceans and seismic surveys in the Southern Adriatic Sea

The first long-term, broadband, passive acoustic monitoring effort was conducted in the south Adriatic Sea from October 2018 to December 2019 using a High-frequency Acoustic Recording Package (HARP). The recording effort coincided with seismic surveys that took place off Montenegro in the fall and winter 2018–2019. These surveys occurred at distances 70 to 125 km from the recording site, at water depths between 70 and 800 m. Recordings were manually reviewed with start and end times of air-gun encounters and ship passages marked. A generic energy detector and unsupervised clustering procedure were used to extract odontocete echolocation clicks. During the surveys, sound pressure levels (SPL) in the 15 to 200 Hz band increased by up to 20 dB during fall and up to 10 dB during winter survey, with an average increase of 7.5 dB. Cuvier's beaked whale echolocation clicks were very commonly detected in the recordings, but sperm whale clicks were only sporadically present. At least three additional echolocation click types were also detected and their attribution to particular species is underway. Although mortality related to seismic surveys has not been recorded, high levels of noise have the potential to cause long term disruption to cetaceans in this region.

Detections of Whale Vocalizations by Simultaneously Deployed Bottom-Moored and Deep-Water Mobile Autonomous Hydrophones

Advances in mobile autonomous platforms for oceanographic sensing, including gliders and deep-water profiling floats, have provided new opportunities for passive acoustic monitoring (PAM) of cetaceans. However, there are few direct comparisons of these mobile autonomous systems to more traditional methods, such as stationary bottom-moored recorders. Cross-platform comparisons are necessary to enable interpretation of results across historical and contemporary surveys that use different recorder types, and to identify potential biases introduced by the platform. Understanding tradeoffs across recording platforms informs best practices for future cetacean monitoring efforts. This study directly compares the PAM capabilities of a glider (Seaglider) and a deep-water profiling float (QUEphone) to a stationary seafloor system (High-frequency Acoustic Recording Package, or HARP) deployed simultaneously over a two week period in the Catalina Basin, California, USA. Two HARPs were deployed 4 km apart while a glider and deep-water drifter surveyed within 20 km of the HARPs. Acoustic recordings were analyzed for the presence of multiple cetacean species, including beaked whales, delphinids, and minke whales. Variation in acoustic occurrence at one-minute (beaked whales only), hourly, and daily scales were examined. The number of minutes, hours, and days with beaked whale echolocation clicks were variable across recorders, likely due to differences in the noise floor of each recording system, the spatial distribution of the recorders, and the short detection radius of such a high-frequency, directional signal type. Delphinid whistles and clicks were prevalent across all recorders, and at levels that may have masked beaked whale vocalizations. The number and timing of hours and days with minke whale boing sounds were nearly identical across recorder types, as was expected given the relatively long propagation distance of boings. This comparison provides evidence that gliders and deep-water drifters record cetaceans at similar detection rates to traditional stationary recorders at a single point. The spatiotemporal scale over which these single hydrophone systems record sounds is highly dependent on acoustic features of the sound source. Additionally, these mobile platforms provide improved spatial coverage which may be critical for species that produce calls that propagate only over short distances such as beaked whales.

Ship source levels in a National Marine Sanctuary

Ship noise in the ocean significantly contributes to low-frequency ambient noise. The Santa Barbara Channel is an ideal site to study noise from shipping because of the intense commercial vessel traffic travelling to the Port of Los Angeles and the Port of Hueneme. In response to concerns of increased ship noise in this area, the Channel Islands National Marine Sanctuary (CINMS) introduced a ship speed reduction program, in the hopes of reducing ship noise. In order to quantify source levels (SLs) of ships that participated in speed reduction, we compared source levels of 31 vessels that participated in the program with source levels of non-participating vessels over the same period. Recordings were made using a High-frequency Acoustic Recording Package at a depth of 580 m, approximately 3 km from the northbound shipping lane. For each ship passage, we measured received levels of passing ships in 1 minute intervals. Source levels (SLs) were calculated by accounting for transmission loss between the recording device and the ship locations obtained from Automated Identification System data. SLs quantified in this work will allow CINMS to evaluate the effectiveness of the speed reduction program for lowering noise inputs from vessels transiting through the sanctuary.

Predator-prey interactions in the Southern California Bight

The Southern California Bight (SCB) is an important foraging area for a variety of cetacean species, including blue whales and beaked whales. However, the interactions of these species with their prey (krill and deep-water squid, respectively) can be very difficult to observe. Moorings combining passive and active acoustics were deployed at two locations in the SCB in two consecutive fall and winter seasons. A High-frequency Acoustic Recording Package sampling at 200 kHz recorded the full range of baleen and beaked whale signals. The active acoustic system on each mooring included two Simrad Wide Band Acoustic Transceivers (WBAT). A bottom-mounted WBAT had an upward looking 70 kHz transducer and the one at 300 m depth had upward looking 70 kHz and 200 kHz transducers. Over the course of four months, blue whale songs and social calls were recorded on both moorings. Beaked whale echolocation clicks were commonly detected on the mooring deployed offshore, with only rare beaked whale encounters on the coastal mooring. Backscatter data indicated overlap in the presence of cetacean predators and their prey. Scattering layer dynamics were dominated by regular diel migration, with differences in scatterer abundance between mooring sites, as well as on 2–5 day time scales.The Southern California Bight (SCB) is an important foraging area for a variety of cetacean species, including blue whales and beaked whales. However, the interactions of these species with their prey (krill and deep-water squid, respectively) can be very difficult to observe. Moorings combining passive and active acoustics were deployed at two locations in the SCB in two consecutive fall and winter seasons. A High-frequency Acoustic Recording Package sampling at 200 kHz recorded the full range of baleen and beaked whale signals. The active acoustic system on each mooring included two Simrad Wide Band Acoustic Transceivers (WBAT). A bottom-mounted WBAT had an upward looking 70 kHz transducer and the one at 300 m depth had upward looking 70 kHz and 200 kHz transducers. Over the course of four months, blue whale songs and social calls were recorded on both moorings. Beaked whale echolocation clicks were commonly detected on the mooring deployed offshore, with only rare beaked whale encounters on the coastal...

Central and western Pacific blue whale song and occurrence

Blue whale (Balenoptera musculus) occurrence in the central and western Pacific is not fully understood. However, passive acoustics offer an effective way to monitor remote sites. Blue whale songs are regionally distinct, and their stereotyped characteristics may be used to distinguish populations. Most blue whale song consists of multiple, pulsed and tonal units. However, song in the central and western Pacific consists of only simple tonal units. We investigated song variability of Hawaii, Wake Atoll, Palmyra, and Tinian in the Mariana Islands Archipelago, and highlight differences between blue whale songs amongst sites. Song calls of two different frequencies were recorded by High-frequency Acoustic Recording Packages. Detailed measures of call frequency were taken along the contours of tonal calls and patterning of song sequences was evaluated for recordings from the four locations during 2012 and 2013. The spatial and temporal occurrence of these patterns is discussed.

Blue whale song sequencing off Southern California

Blue whales off Southern California produce a unique song consisting of pulsed A unit and tonal B unit calls. These units are either sequenced in an alternating AB pattern, or a single A unit is followed by multiple B units (here denoted ABB). To investigate whether there is geographic variation in the occurrence of these different sequence types, data were analyzed from four High-frequency Acoustic Recording Packages deployed at two sites each inshore and offshore of the Channel Islands from September 2009 to June 2010. Additionally, fine-scale behavior associated with song and its sequencing was analyzed from acoustic tags deployed on blue whales in Southern California since 2000. A higher proportion of song bouts detected in offshore recordings were type ABB, whereas the dominant song type observed inshore was AB. This pattern may indicate geographic variability in song function. Most song units recorded on tags were produced during surface-travel dives, with the whale less than 30 m deep. Song bouts detected on tags occurred primarily at night, and whales did not interrupt their calling sequence with breathing intervals. The observed differences in calling and song preference off Southern California may be useful in identifying regionally distinct behavioral contexts for blue whales.

Ocean ambient sound south of Bermuda and Panama Canal traffic.

Comparisons of current and historic ocean ambient noise levels are rare, especially in the North Atlantic. Recent (2013-2014) monthly patterns in ocean ambient sound south of Bermuda were compared to those recorded at the same location in 1966. Additionally, trends in ocean traffic, in particular, Panama Canal traffic, over this time were also investigated. One year of ocean ambient noise measurements were collected in 1966 using cabled, omnidirectional hydrophones at the U.S. Navy Tudor Hill Laboratory in Bermuda, and repeat measurements were collected at the same location from June 2013-May 2014 using a High-frequency Acoustic Recording Package. Average monthly pressure spectrum levels at 44 Hz increased 2.8 ± 0.8 dB from 1966 to 2013, indicating an average increase of 0.6 dB/decade. This low level of increase may be due to topographic shielding at this site, limiting it to only southern exposure, and the limit in the number of ship transits through the Panama Canal, which did not change substantially during this time. The impending expansion of the Canal, which will enable the transit of larger ships at twice the current rate, is likely to lead to a substantial increase in ocean ambient sound at this location in the near future.

Underwater sound directionality of commercial ships

The underwater sound radiated by commercial ships is an unintended by-product of their operation and one of the most significant contributors to man-made noise at low frequencies in the ocean. To estimate the directionality of underwater sound radiated by current commercial ships, a seafloor array of five high-frequency acoustic recording packages (HARPs) deployed to 1 km depth with a maximum horizontal aperture of 1 km was used. As a ship of opportunity passed over the HARP array, the directions from the ship to each HARP along with the corresponding source levels were estimated for each ship location. Ships were tracked via satellites (Automatic Identification System—AIS) and acoustically by a frequency domain beamformer that was implemented for one of the HARPs configured with a volumetric hydrophone array (2 m maximum aperture). The directionality estimates of contemporary commercial ships exhibit significant stern-bow asymmetries among other quantitative characteristics that will be discussed.

Long-term monitoring of Physeteroidea (sperm whales, dwarf, and pygmy sperm whales) in the Central and Western Pacific

The superfamily Physeteroidea includes three extant species: the sperm whale (Physeter macrocephalus), the dwarf sperm whale (Kogia sima), and the pygmy sperm whale (K. breviceps). Despite extreme difference in size between the Kogia spp. and their large Physeter relative, all three share ecological and acoustic traits relating to their deep-diving behavior and high rates of acoustic activity. All three species can be found across the Central and Western Pacific ocean, an area that has been monitored using passive acoustics (High-frequency Acoustic Recording Packages, HARPs) for more than 10 years. We identified sperm whale and Kogia spp. signals in the long-term HARP records from 13 locations across the Central and Western Pacific ocean. A combination of automated tools and human analysis were used to record detection events of both types of signals. While sperm whales were found at all 13 locations, the Kogia species (which cannot yet be distinguished acoustically) were detected at approximately half of the sites. Presence of sperm whale signals was modeled to determine if temporal parameters, such as lunar cycle and day of the year, could explain patterns of presence. Across the whole region the best model included the day of the year and the recording site, while sub-regions and site-specific models had slightly different combinations of parameters.

Variations of fin whale's 20 Hz calls in the Gulf of California

The fin whale's song has been broadly described in different areas of the world, and it is well characterized, being the spectrogram the main representation used to extract descriptions and measures. Males produce the 20 Hz calls, which consist of a down-swept pulse series (18–30 Hz) with a fundamental frequency of 20 Hz. Each pulse has duration of approximately 1 s, with aggrupation patterns of singlet, doublets and triplets. A time analysis of calls recorded by a High-frequency Acoustic Recording Packages (HARPs) localized in Punta Pescadero and Bahía de los Ángeles, south and north of the Gulf of California, México in the 2004 through 2008, revealed variations of the pulse that are not easily discernable through the use of the spectrogram. Results of the preliminary analysis of 100 calls are presented. Regional differences in duration, structure, and shape found could indicate a geographical separation of population units of fin whales in the Gulf of California.

Glider-based passive acoustic marine mammal detection

Passive acoustic detection of delphinid sounds using the Wave Glider (WG) autonomous near-surface vehicle was compared with a fixed bottom-mounted autonomous broadband system, the High-frequency Acoustic Recording Package (HARP). A group of whistling and clicking delphinids was tracked using an array of bottom-mounted HARPs, providing ground-truth for detections from the WG. Whistles in the 5–20 kHz band were readily detected by the bottom HARPs as the delphinids approached, but the WG revealed only a brief period with intense detections as the animals approached within ~500 m. Refraction due to acoustic propagation in the thermocline provides an explanation for why the WG may only detect whistling delphinids at close range relative to the long-range detection capabilities of the bottom-mounted HARPs. This work demonstrated that sound speed structure plays an important role in determining detection range for high-frequency-calling marine mammals by autonomous gliders and bottom-mounted sensors.

Temporal patterns in detections of sperm whales (Physeter macrocephalus) in the North Pacific Ocean based on long-term passive acoustic monitoring

Sperm whales (Physeter macrocephalus), a long-lived, cosmopolitan species, are well suited for long-term studies, and their high amplitude echolocation signals make them ideal for passive acoustic monitoring. NOAA’s Pacific Islands Fisheries Science Center has deployed High-frequency Acoustic Recording Packages (200 kHz sampling rate) at 13 deep-water locations across the central and western North Pacific Ocean since 2005. Recordings from all sites were manually analyzed for sperm whale signals, and temporal patterns were examined on multiple scales. There were sperm whale detections at all sites, although the rate of detection varied by location, with the highest rate at Wake Island (15% of samples), and the fewest detections at sites close to the equator (<1%). Only two locations (Saipan and Pearl and Hermes Reef) showed significant seasonal patterns, with more detections in the early spring and summer than in later summer or fall. There were no significant patterns relating to lunar cycles. Analysis of diel variation revealed that sperm whales were detected more during the day and night compared to dawn and dusk at most sites. The variability shown in these results emphasizes the importance of assessing basic biological patterns and variations in the probability of detection before progressing to further analysis, such as density estimation, where the effects of uneven sampling effort could significantly influence results.

Deep-diving cetaceans and the Deepwater Horizon oil spill

The Gulf of Mexico is home to at least six species of deep-diving cetaceans, including beaked whales, sperm whales, and dwarf and pygmy sperm whales. These species are all found in the region that was impacted by the Deepwater Horizon oil spill. Using High-frequency Acoustic Recording Packages (HARPs), we monitored for their presence at three deep-water sites. From over two years of wideband (10 Hz—100 kHz) recordings, the detections of deep-diving cetacean sounds were related to environmental and anthropogenic factors using Generalized Additive Models to identify relevant features. The modeling showed that the significance of habitat parameters varies by species and site, although lunar illumination and sea surface height anomaly were significant for most species at all sites. The relationships between the acoustic presence of the cetaceans and their environment help provide an understanding of the ecology of these species as well as the potential impact of the oil spill on their habitat. This material is based upon work supported by BP and NOAA under Award Number 20105138. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the BP and/or any State or Federal Natural Resource Trustee.

Baleen whale calls in the Southern California Bight from 2009 to 2012

Baleen whales are an important contributor to the Southern California Bight soundscape. Calls from some species only contribute seasonally, while others are part of the soundscape year-round, albeit at varying levels. Passive acoustic monitoring has been conducted at the U.S. Navy’s Southern California Offshore Range (SCORE) since 2009. Data were collected at two sites concurrently using High-frequency Acoustic Recording Packages (HARPs). Analysis in the low frequency band (10 Hz—1 kHz) has yielded results on the seasonal and interannual variation in the presence of calling blue (Balaenoptera musculus), fin (B. physalus), Bryde’s (B. edeni), and humpback whales (Megaptera novaeangliae). Calls of most species (blue, Bryde’s, and humpback whales) were only present during part of the year, indicating seasonal migration common for these species. On the contrary, fin whale calls were prevalent year-round, although the abundance of their 20 Hz calls tended to decrease in the summer. The link between the relativ...

Bryde's whale calls recorded in the Gulf of Mexico

Bryde's whale calls recorded in the Gulf of Mexico

Migrating gray whale vocalizations and concurrent visual observations near Santa Barbara, California

The vocalizations of migrating eastern North Pacific gray whales (Eschrichtius robustus) are not well understood, but studying these sounds may provide insights to their behaviors and encounters along their migratory route. To record migratory gray whale sounds over long periods, a high frequency acoustic recording package (HARP) was deployed from March to May 2010 off the north coast of the Santa Barbara Channel, an area where the gray whale northbound migration is close to shore. The HARP recorded continuously and concurrently with a shore-based visual survey of marine mammals. Comparisons of calls and sightings were conducted to relate calling repertoires with various types of migrating whale behaviors and groups (e.g., cow/calf pairs, juveniles, etc.). The spatial and temporal overlap of the visual and acoustic data enabled the estimation of call detection ranges and source levels. Characterization of gray whale vocalizations also will help with the development of automatic detectors which will aid in future the investigations of long-term gray whale recordings, including potential responses to anthropogenic activity.