–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
A technology that captures multiple dimensions of underwater sound is revealing how blue whales live, thereby informing whale conservation.
The most massive animal ever to evolve on Earth, the blue whale, needs a lot of food. Finding that food in a vast foraging habitat is challenging, and these giants must travel far and wide in search of it. The searching that leads them to life-sustaining nutrition can also lead them to a life-ending collision with a massive fast-moving ship. To support the recovery of this endangered species, we must understand where and how the whales live, and how human activities intersect with whale lives.
Toward better understanding and protecting blue whales in the California Current ecosystem, an interdisciplinary team of scientists is applying a technology called an acoustic vector sensor. Sitting just above the seafloor, this technology receives the powerful sounds produced by blue whales and quantifies changes in both pressure and particle motion that are caused by the sound waves. The pressure signal reveals the type of sound produced. The particle motion signal points to where the sound originated, thereby providing spatial information on the whales.
A blue whale in the California Current ecosystem. Image Credit: Goldbogen Lab of Stanford University / Duke Marine Robotics and Remote Sensing Lab; NMFS Permit 16111.
For blue whales, it is all about the thrill of the krill. Krill are small-bodied crustaceans that can form massive swarms. Blue whales only eat krill, and they locate swarms to consume krill by the millions (would that be krillions?). Krill form dense swarms in association with cold plumes of water that result from a wind-driven circulation called upwelling. Sensors riding on the backs of blue whales reveal that the whales can track cold plumes precisely and persistently when they are foraging.
The close relationships between upwelling and blue whale movements motivates the hypothesis that the whales move farther offshore when upwelling habitat expands farther offshore, as occurs during years with stronger wind-driven upwelling. We tested this hypothesis by tracking upwelling conditions and blue whale locations over a three-year period. As upwelling doubled over the study period, the percentage of blue whale calls originating from offshore habitat also nearly doubled. A shift in habitat occupancy offshore, where the shipping lanes exist, also brings higher risk of fatal collisions with ships.
However, there is good news for blue whales and other whale species in this region. Reducing ship speeds can greatly reduce the risk of ship-whale collisions. An innovative partnership, Protecting Blue Whales and Blue Skies, has been fostering voluntary speed reductions for large vessels over the last decade. This program has expanded to cover a great stretch of the California coast, and the growing participation of shipping companies is a powerful and welcome contribution to whale conservation.
Popular version of 2pAB8 – Moving Cargo, Keeping Whales: Investigating Solutions for Ocean Noise Pollution
Presented at the 186th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0027065
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Figure 1. Image Courtesy of ZoBell, Vanessa M., John A. Hildebrand, and Kaitlin E. Frasier. “Comparing pre-industrial and modern ocean noise levels in the Santa Barbara Channel.” Marine Pollution Bulletin 202 (2024): 116379.
Southern California waters are lit up with noise pollution (Figure 1). The Port of Los Angeles and the Port of Long Beach are the first and second busiest shipping ports in the western hemisphere, supporting transits from large container ships that radiated noise throughout the region. Underwater noise generated by these vessels dominate ocean soundscapes, negatively affecting marine organisms, like mammals, fish, and invertebrates, who rely on sound for daily life functions. In this project, we modeled what the ocean would sound like without human activity and compared it with what it sounds like in modern day. We found in this region, which encompasses the Channel Islands National Marine Sanctuary and feeding grounds of the endangered northeastern Pacific blue whale, modern ocean noise levels were up to 15 dB higher than pre-industrial levels. This would be like having a picnic in a meadow versus having a picnic on an airport tarmac.
Reducing ship noise in critical habitats has become an international priority for protecting marine organisms. A variety of noise reduction techniques have been discussed, with some already operationalized. To understand the effectiveness of these techniques, broad stakeholder engagement, robust funding, and advanced signal processing is required. We modeled a variety of noise reduction simulations and identified effective strategies to quiet whale habitats in the Santa Barbara Channel region. Simulating conservation scenarios will allow more techniques to be explored without having to be implemented, saving time, money, and resources in the pursuit of protecting the ocean.
Popular version of 5aUW-Underwater soundscapes at critical habitats of the endangered Hawaiian monk seal, presented at the 183rd ASA Meeting.
The ocean is a noisy place. From chatty marine mammals to territorial fish and hungry shrimp, marine animals use sound to communicate, navigate, defend territories, and find food, mates, and safe spaces to settle down. However, human activities are negatively impacting the abilities of marine animals to effectively use sound for critical life functions. For the endangered Hawaiian monk seal with a population size of approximately 1,570 seals, we’re finding that vocal communication (Audio File 1) may play an important role for reproduction, yet we lack a foundational knowledge of the seals’ acoustic environment, better known as a soundscape. In this study, we found that biological sounds produced by snapping shrimp, fish, and seals dominate and shape the underwater soundscapes at critical habitats of the Hawaiian monk seal, with little input from man-made sources (Figure 1).
Figure 1 | A) Spectrogram of a 24-hour period on 11 May 2021 at Lehua Rock. A spectrogram is a visual representation of a sound where the x-axis is time, the y-axis is frequency (or pitch), and the color represents the amplitude of the sound (how loud or soft the sound is). The black icons indicate the source of the sound: snapping shrimp, boat, scuba divers, humpback whale song, Hawaiian monk seal vocalizations, and the vertical migration of the deep scattering layer. B) Spectrogram showing overlapping Hawaiian monk seal vocalizations from 0-1 kHz and humpback whale song from 0.5-5 kHz (listen to this in Audio File 1).
We sought to describe the underwater soundscape, or the acoustic environment, at locations that Hawaiian monk seals utilize for foraging, breeding, communication, and other critical life functions. We wanted to know 1) how loud are ambient (background) sound levels, 2) are sound sources biological, geophysical, or manmade, 3) how do sound sources and levels change throughout the day, and 4) how does the soundscape compare between the more-densely human-populated main Hawaiian Islands and the remote Northwestern Hawaiian Islands. To do this, we deployed passive acoustic recorders, known as SoundTraps, at four critical habitats of the Hawaiian monk seal: Rabbit Island, Oahu; Lehua Rock, Niʻihau; French Frigate Shoals; and Pearl and Hermes Reef. The SoundTraps recorded sounds from 20 Hz up to 24 kHz – this includes low-frequency sounds like earthquakes to high-frequency sounds like dolphin echolocation.
Our results indicate that sound levels are generally loud at these nearshore reef environments thanks to the persistent crackling sounds of snapping shrimp, low-frequency vocalizations of monk seals, and a variety of fish sounds. With little input from manmade sound sources, except at the popular scuba diving site Lehua Rock, we suspect that the elevated sound levels are indicative of healthy reef environments. This is good news for Hawaiian monk seals – less manmade noise means less acoustic masking making it easier to hear and “speak” to each other under water. We also opportunistically recorded sounds from Hurricane Douglas (Category 4) and a 6.2 magnitude earthquake around the time Kilauea began erupting. Overall, this study provides the first description of underwater soundscapes at Hawaiian monk seal critical habitats. These measurements can serve as a baseline for future studies to understand the impact of human activity on underwater soundscapes.
Suzi Wiseman – sw1210txstate@gmail.com Texas State University-San Marcos Environmental Geography 601 University Drive, San Marcos, Texas 78666 Preston S. Wilson – wilsonps@austin.utexas.edu University of Texas at Austin Mechanical Engineering Department 1 University Station C2200 Austin, TX 78712
Popular version of paper 2aAB7, “Nocturnal peace at a Conservation Center for Species Survival?” Presented Tuesday morning, May 19, 2015 at 10.15am 169th ASA Meeting, Pittsburgh
The acoustic environment is essential to wildlife, providing vital information about prey and predators and the activities of other living creatures (biophonic information) (Wilson, 1984), about changing weather conditions and occasionally geophysical movement (geophonic), and about human activities (anthrophonic) (Krause 1987). Small sounds can be as critical as loud, depending on the species trying to listen. Some hear infrasonically (too low for humans, generally considered below 20 Hz), others ultrasonically (too high, above 20 kHz). Biophonic soundscapes frequently exhibit temporal and seasonal patterns, for example a dawn “chorus”, mating and nurturing calls, diurnal and crepuscular events.
Some people are attracted to large parks due in part to their “peace and quiet” (McKenna 2013). But even in a desert, a snake may be heard to slither or wind may sigh between rocks. Does silence in fact exist? Finding truly quiet places, in nature or the built environment is increasingly difficult. Even in our anechoic chamber, which was purpose built to be extremely quiet, located in the heart of our now very crowded and busy urban campus, we became aware of infrasound that penetrated, possibly from nearby construction equipment or from heavy traffic that was not nearly as common when the chamber was first built more than 30 years ago. Is anywhere that contains life actually silent?
Figure 1: In the top window, the waveform in blue indicates the amplitude over time each occasion that a pulse of sound was broadcast in the anechoic chamber, as shown in the spectrogram in the lower window, where the frequency is shown over the same time, and the color indicates the intensity of the sound (red being more intense than blue). Considerable very low frequency sound was evident and can be seen between the pulses in the waveform (which should be silent), and throughout at the bottom of the spectrogram. The blue dotted vertical lines show harmonics that were generated within the loudspeaker system. (Measurements shown in this study were by a Roland R26 recorder with Earthworks M23 measurement microphones with frequency response 9Hz to 23kHz ±1/-3dB)
As human populations increase, so do all forms of anthrophonic noise, often masking the sounds of nature. Does this noise cease at night, especially if well away from major cities and when humans are not close-by? This study analyzed the soundscape continuously recorded beside the southern white rhinoceros (Ceratotherium simum simum) enclosure at Fossil Rim Wildlife Center, about 75 miles southwest of Dallas Texas for a week during Fall 2013, to determine the quietest period each night and the acoustic environment in which these periods tended to occur. Rhinos hear infrasound, so the soundscape was measured from 0.1 Hz to 22,050 kHz. Since frequencies below 9 Hz still need to be confirmed however, these lowest frequencies were removed from this portion of the study.
Figure 2: Part of the white rhinoceros enclosure of Fossil Rim Wildlife Center, looking towards the tree line where the central recorder was placed
Figure 3: The sound pressure level throughout a relatively quiet day at the rhino enclosure. The loudest sounds were normally vehicles, machinery, equipment, aircraft, and crows. The 9pm weather front was a major contrast.
Figure 3 illustrates the rhythm of a day at Fossil Rim as shown by the sound level of a fairly typical 24 hours starting from midnight, apart from the evening storm. As often occurred, the quietest period was between midnight and the dawn chorus.
While there were times during the day when birds and insects were their most active and anthrophonic noise was not heard above them, it was discovered that all quiet periods contained anthrophonic noise, even at night. There was generally a low frequency, low amplitude hum – at times just steady and machine-like and not yet identified – and depending on wind direction, often short hums from traffic on a state highway over a mile away. Quiet periods ranged from a few minutes to almost an hour, usually eventually broken by anthrophonic sounds such as vehicles on a nearby county road, high aircraft, or dogs barking on neighboring ranches. However there was also a strong and informative biophonic presence – from insects to nocturnal birds and wildlife such as coyotes, to sounds made by the rhinos themselves and by other species at Fossil Rim. Geophonic intrusions were generally wind, thunder or rain, possibly hail.
The quietest quarter hour was about 4am on the Friday depicted in figure 3, but even then the absolute sound pressure level averaged 44.7 decibels, about the level of a quiet home or library. The wind was from the south southeast around 10 to 14 mph during this time. Audio clip 1 is the sound of this quiet period.
Figure 4: The quietest quarter hour recorded at Fossil Rim appears between the vertical red selection lines, with an average absolute sound pressure level of 44.5 decibels. The fairly constant waveform shown in blue in the top graph and the low frequency noise at the bottom of the spectrogram seemed to comprise the machine-like hum, the distant traffic hum which varies over time, and insects. The blue flashes between 3 and 5 Hz were mainly bird calls.
By contrast, the loudest of the “quietest nightly periods” was less than six minutes long, around 5am on Wednesday 23rd October, as shown between the vertical red lines in figure 5. Despite being the quietest period that night, it averaged a sound pressure level of 55.5 decibels, which is roughly the equivalent of a spoken conversation.
Figure 5: The loudest “quietest period each night” reveals broadband machine noise (possibly road work equipment somewhere in the district?) which continued for some hours and appears as the blue flecks across all frequencies. The horizontal blue line at 16.5 kHz is characteristic of bats. All species identification is being left to biologists for confirmation. Audio clip 2 is this selection.
Either side of the “quiet” minutes were short bursts of low frequency but intense truck and/or other machine noise indicated in red, some of which partially covered a clang when a rhino hit its fence with its horn, and distant barks, howls, moos and other vocalizations. The noise may have masked the extremely low frequency hums and insects that had been apparent on other nights or to have caused the insects to cease their activity. The strata below 2.5 kHz appear more ragged, indicating they are not being produced in such a uniform way as on quieter nights, and they are partially covered by the blue flecks of machine noise. However the strata at 5.5, 8.5, 11 and especially at 16.5 kHz that appeared on other nights are still evident. They appear to be birds, insects and bats. Audio clip 3 contains the sounds that broke this quiet period.
At no point during the entire week was anything closely approaching “silence” apparent. Krause reports that healthy natural soundscapes comprise a myriad of biophony, and indeed the ecological health of a region can be measured by its diverse voices (Krause 1987). However if these voices are too frequently masked or deterred by anthrophonic noise, animals may be altered behaviorally and physiologically (Pater et al, 2009), as the World Health Organization reports to be the case with humans who are exposed to chronic noise (WHO 1999). Despite some level of anthrophonic noise at most times, Fossil Rim seems to provide a healthy acoustic baseline since so many endangered species proliferate there.
Understanding soundscapes and later investigating any acoustic parameters that may correlate with animals’ behavior and/or physiological responses may lead us to think anew about the environments in which we hold animals captive in conservation, agricultural and even domestic environments, and about wildlife in parts of the world that are being increasingly encroached upon by man.
References: Krause, B. 1987. The niche hypothesis. Whole Earth Review . Wild Sanctuary. ———. 1987. Bio-acoustics: Habitat ambience & ecological balance. Whole Earth Review. Wild Sanctuary. McKenna, Megan F., et al. “Patterns in bioacoustic activity observed in US National Parks.” The Journal of the Acoustical Society of America 134.5 (2013): 4175-4175. Pater, L. L., T. G. Grubb, and D. K. Delaney. 2009. Recommendations for improved assessment of noise impacts on wildlife. The Journal of Wildlife Management 73:788-795. Wilson, E. O. 1984. Biophilia. Harvard University Press. World Health Organization. “Guidelines for community noise”. WHO Expert Taskforce Meeting. London. 1999.