Maxwell B. Kaplan

Ambient noise and temporal patterns of boat activity in the US Virgin Islands National Park.

Human activity is contributing increasing noise to marine ecosystems. Recent studies have examined the effects of boat noise on marine fishes, but there is limited understanding of the prevalence of this type of sound source. This investigation tracks vessel noise on three reefs in the US Virgin Islands National Park over four months in 2013. Ambient noise levels ranged from 106 to 129dBrms re 1μPa (100Hz-20kHz). Boat noise occurred in 6-12% of samples. In the presence of boat noise, ambient noise in a low-frequency band (100-1000Hz) increased by >7dB above baseline levels and sound levels were significantly higher. The frequency with the most acoustic energy shifted to a significantly lower frequency when boat noise was present during the day. These results indicate the abundance of boat noise and its overlap with reef organism sound production, raising concern for the communication abilities of these animals.

Repeated call types in Hawaiian melon-headed whales (Peponocephala electra)

Melon-headed whales are pantropical odontocetes that are often found near oceanic islands. While considered sound-sensitive, their bioacoustic characteristics are relatively poorly studied. The goal of this study was to characterize the vocal repertoire of melon-headed whales to determine whether they produce repeated calls that could assist in recognition of conspecifics. The first tag-based acoustic recordings of three melon-headed whales were analyzed. Tag records were visually and aurally inspected and all calls were individually extracted. Non-overlapping calls with sufficient signal-to-noise were then parameterized and visually grouped into categories of repeated call types. Thirty-six call categories emerged. Categories differed significantly in duration, peak and centroid frequency, and -3 dB bandwidth. Calls of a given type were more likely to follow each other than expected. These data suggest that repeated calls may function in individual, subgroup, or group recognition. Repeated call production could also serve to enhance signal detection in large groups with many individuals producing simultaneous calls. Results suggest that caution should be used in developing automatic classification algorithms for this species based on small sample sizes, as they may be dominated by repeated calls from a few individuals, and thus not representative of species- or population-specific acoustic parameters.

Coral reef soundscapes may not be detectable far from the reef

Biological sounds produced on coral reefs may provide settlement cues to marine larvae. Sound fields are composed of pressure and particle motion, which is the back and forth movement of acoustic particles. Particle motion (i.e., not pressure) is the relevant acoustic stimulus for many, if not most, marine animals. However, there have been no field measurements of reef particle motion. To address this deficiency, both pressure and particle motion were recorded at a range of distances from one Hawaiian coral reef at dawn and mid-morning on three separate days. Sound pressure attenuated with distance from the reef at dawn. Similar trends were apparent for particle velocity but with considerable variability. In general, average sound levels were low and perhaps too faint to be used as an orientation cue except very close to the reef. However, individual transient sounds that exceeded the mean values, sometimes by up to an order of magnitude, might be detectable far from the reef, depending on the hearing abilities of the larva. If sound is not being used as a long-range cue, it might still be useful for habitat selection or other biological activities within a reef.

Singing whales generate high levels of particle motion: implications for acoustic communication and hearing?

Acoustic signals are fundamental to animal communication, and cetaceans are often considered bioacoustic specialists. Nearly all studies of their acoustic communication focus on sound pressure measurements, overlooking the particle motion components of their communication signals. Here we characterized the levels of acoustic particle velocity (and pressure) of song produced by humpback whales. We demonstrate that whales generate acoustic fields that include significant particle velocity components that are detectable over relatively long distances sufficient to play a role in acoustic communication. We show that these signals attenuate predictably in a manner similar to pressure and that direct particle velocity measurements can provide bearings to singing whales. Whales could potentially use such information to determine the distance of signalling animals. Additionally, the vibratory nature of particle velocity may stimulate bone conduction, a hearing modality found in other low-frequency specialized mammals, offering a parsimonious mechanism of acoustic energy transduction into the massive ossicles of whale ears. With substantial concerns regarding the effects of increasing anthropogenic ocean noise and major uncertainties surrounding mysticete hearing, these results highlight both an unexplored pathway that may be available for whale acoustic communication and the need to better understand the biological role of acoustic particle motion.

Automatic detection of tropical fish calls recorded on moored acoustic recording platforms

Passive acoustic recording of biological sound production on coral reefs can help identify spatial and temporal differences among reefs; however, the contributions of individual fish calls to overall trends are often overlooked. Given that the diversity of fish call types may be indicative of fish species diversity on a reef, quantifying these call types could be used as a proxy measure for biodiversity. Accordingly, automatic fish call detectors are needed because long acoustic recorders deployments can generate large volumes of data. In this investigation, we report the development and performance of two detectors—an entropy detector, which identifies troughs in entropy (i.e., uneven distribution of entropy across the frequency band of interest, 100–1000 Hz), and an energy detector, which identifies peaks in root mean square sound pressure level. Performance of these algorithms is assessed against a human identification of fish sounds recorded on a coral reef in the US Virgin Islands in 2013. Results in...

Tags, drifters, and Towfish: Using multiple recording platforms to characterize odontocete acoustic space

Bioacoustic tags can reveal novel information about the behavior and ecology of animals on which they are deployed. Yet tags are often placed off the animals’ acoustic axis, limiting some potential analyses. In order to broaden abilities to examine bioacoustic signals and behavior of several Hawaiian odontocetes we adapted recording methods to enhance data collection opportunities and free-field records. While bioacoustic DTAGs were deployed, we also used DMONs (digital acoustic recorders) in both a GPS-outfitted drifter buoy (Drifting Acoustic Wideband Gizmo = DAWG) and a Towfish around pantropical spotted dolphins (Sa), melon-headed whales (Pe), and short-finned pilot whales (Gm). Daytime tag recordings show Pe and Sa were limited to relatively shallow dives (< 50 m) but were relatively soniferous, whereas Gm made occasional deeper dives (to 700 m) and fewer individual calls. Group measures for Pe and Sa from the DAWG and Towfish revealed relatively high incidences of overlapping calls. Preliminary inve...

Variability in coral reef soundscapes, spatiotemporal differences, biophysical and behavioral drivers, and associations with local biota

Coral reefs harbor some of the highest biodiversity on the planet. Their rich ecoacoustic soundscape may provide a way to track both animal activities and community level structure. To do so, it is critical to identify how reef soundscapes are influenced by biotic and abiotic parameters, and establish how soundscapes change over time and across habitats. Here we present results from 18 coral reefs in the U.S. Virgin Islands and Maui, Hawaii, with the overall goals to quantify soundscape variability across multiple spatial and temporal scales (days to years), test how soundscape parameters relate to local biological communities, and address how biophysical parameters (light, temperature, and rugosity) influence these eco-soundscapes. Acoustic measurements were made in-tandem with benthic and fish visual surveys. Analyses were carried out using high and low-frequency bands corresponding to the primary soniferous taxa on reefs, snapping shrimp and fish. Overall, these results indicate that certain acoustic metrics can be linked to visual survey results. Snapping shrimp exhibit complex spatiotemporal patterns, with strong diel rhythms shifting over time and varying substantially over short spatial scales. Furthermore, long-term recordings are necessary to provide a robust baseline measurement of acoustic variability and better quantify changes in coral reef ecosystems.Coral reefs harbor some of the highest biodiversity on the planet. Their rich ecoacoustic soundscape may provide a way to track both animal activities and community level structure. To do so, it is critical to identify how reef soundscapes are influenced by biotic and abiotic parameters, and establish how soundscapes change over time and across habitats. Here we present results from 18 coral reefs in the U.S. Virgin Islands and Maui, Hawaii, with the overall goals to quantify soundscape variability across multiple spatial and temporal scales (days to years), test how soundscape parameters relate to local biological communities, and address how biophysical parameters (light, temperature, and rugosity) influence these eco-soundscapes. Acoustic measurements were made in-tandem with benthic and fish visual surveys. Analyses were carried out using high and low-frequency bands corresponding to the primary soniferous taxa on reefs, snapping shrimp and fish. Overall, these results indicate that certain acoustic m...

Variation in the soundscapes of Pacific coral reefs over multiple spectral, temporal, and spatial scales

Biological sounds occurring on coral reefs are increasingly recognized as important factors influencing reef dynamics and ecological processes. Soundscapes of coral reefs can be broadly divided into a low-frequency band (<1 kHz), dominated by sounds produced by acoustically active fish, and a high-frequency band (2–20 kHz) dominated by snapping shrimp and other invertebrates. Because acoustic activities in both bands are influenced by a variety of ecological (biotic) and environmental (abiotic) factors, coral reef soundscapes are characterized by considerable spatial and temporal variability. The drivers of this variability are not yet well understood, but likely provide important insights into ecosystem processes and condition. We report on an effort to quantify the acoustic activity in both the fish and snapping shrimp frequency bands across twelve coral reef sites in the Pacific Ocean separated by distances ranging from hundreds of meters to thousands of kilometers, including reefs across the Hawaiian ...

Did humpback whales go missing off Maui, Hawaii? A comparison of song activity between the 2014/15 and 2015/16 breeding seasons

Each winter, thousands of humpback whales (Megaptera novaeangliae) migrate from their high latitude feeding grounds in Alaska to mate and calve in the shallow tropical waters around the Main Hawaiian Islands. Population estimates suggest that up to 10,000 animals winter in Hawaiian waters, making up more than half of the total North Pacific stock. However, in the 2015/16 season, anecdotal reports from commercial operators and researchers tell of an unusually low number of whales compared to previous years off the island of Maui. To examine this issue, data from long-term passive acoustic monitoring with autonomous Ecological Acoustic Recorders (EARs) during the 2014/15 and 2015/16 seasons off the west coast of Maui were analyzed using male chorusing levels as a proxy for relative whale abundance. Root-mean-square sound pressure levels (SPLs) were calculated to compare low frequency acoustic energy (0-1.56 kHz) between both seasons. The data showed that chorusing levels dropped in early January 2016. Altho...

Loud and clear: Characterization of particle motion in Humpback whale song and its potential role in communication

Acoustic communication can rapidly transfer a substantial amount of information, yet emitted signals must be conveyed with enough clarity to allow appropriate responses. Many mysticete calls such as humpback whale (Megaptera novaeangliae) song can be detected over large distances as a result of the propagating acoustic pressure wave, yet little is known regarding the particle motion component of these signals. To explore the particle velocity of humpback whale song, three singing whales were recorded from a vessel off Maui, HI in March 2015, using a sensor that contained a digital magnetometer, tri-axial accelerometer, and an omnidirectional hydrophone. The median magnitude of the acoustic particle velocity signal was substantial (64.5 dB re: 1m/s) for song components with a median pressure of 135.4 dB re: 1μPa. As vessel and sensor gradually drifted away or toward the whales, acoustic particle velocity and sound pressure correspondingly decreased or increased (range: 49.3-77.9 dB re: 1m/s and 118.4-148.1...