Samuel L. Denes

Assessing marine ecosystem acoustic diversity across ocean basins

Abstract Concurrent with the elevation of the concern over the state of sound in the ocean, advances in terrestrial acoustic monitoring techniques have produced concepts and tools that may be applicable to the underwater world. Several index values that convey information related to acoustic diversity with a single numeric measurement made from acoustic recordings have been proposed for rapidly assessing community biodiversity. Here we apply the acoustic biodiversity index method to low frequency recordings made from three different ocean basins to assess its appropriateness for characterizing species richness in the marine environment. Initial results indicated that raw acoustic entropy (H) values did not correspond to biological patterns identified from individual signal detections and classification. Noise from seismic airgun activity masked the weaker biological signals and confounded the entropy calculation. A simple background removal technique that subtracted an average complex spectrum characteristic of seismic exploration signals from the average spectra of each analysis period that contained seismic signals was applied to compensate for salient seismic airgun signals present in all locations. The noise compensated (HN) entropy index was more reflective of biological patterns and holds promise for the use of rapid acoustic biodiversity in the marine environment as an indicator of habitat biodiversity and health.

Acoustic characteristics of ultrasonic coded transmitters for fishery applications: Could marine mammals hear them?

Ultrasonic coded transmitters (UCTs) producing frequencies of 69-83 kHz are used increasingly to track fish and invertebrates in coastal and estuarine waters. To address concerns that they might be audible to marine mammals, acoustic properties of UCTs were measured off Mission Beach, San Diego, and at the U.S. Navy TRANSDEC facility. A regression model fitted to VEMCO UCT data yielded an estimated source level of 147 dB re 1 μPa SPL @ 1 m and spreading constant of 14.0. Based on TRANSDEC measurements, five VEMCO 69 kHz UCTs had source levels ranging from 146 to 149 dB re 1 μPa SPL @ 1 m. Five Sonotronics UCTs (69 kHz and 83 kHz) had source levels ranging from 129 to 137 dB re 1 μPa SPL @ 1 m. Transmitter directionality ranged from 3.9 to 18.2 dB. Based on propagation models and published data on marine mammal auditory psychophysics, harbor seals potentially could detect the VEMCO 69 kHz UCTs at ranges between 19 and >200 m, while odontocetes potentially could detect them at much greater ranges. California sea lions were not expected to detect any of the tested UCTs at useful ranges.

Assessing the cross platform performance of marine mammal indicators between two collocated acoustic recorders

Equipment and deployment strategies for remote passive acoustic sensing of marine environments must balance memory capacity, power requirements, sampling rate, duty-cycle, deployment duration, instrument size, and environmental concerns. The impact of different parameters on the data and applicability of the data to the specific questions being asked should be considered before deployment. Here we explore the effect of recording and detection parameters on marine mammal acoustic data across two platforms. Daily classifications of marine mammal vocalizations from two passive acoustic monitors with different subsampling parameters, an AURAL and a Passive Aquatic Listener (PAL), collocated in the Bering Sea were compared. The AURAL subsampled on a pre-set schedule, whereas the PAL sampled via an adaptive protocol. Detected signals of interest were manually classified in each dataset independently. The daily classification rates of vocalizations were similar. Detections from the higher duty-cycle but lower sample rate AURAL were limited to species and vocalizations with energy below 4 kHz precluding detection of echolocation signals. Temporal coverage from the PAL audio files was limited by the adaptive sub-sampling protocol. A method for classifying ribbon (Histriophoca fasciata) and bearded seal (Erignathus barbatus) vocalizations from the sparse spectral time histories of the PAL was developed. Although application of the acoustic entropy as a rapid assessment of biodiversity was not reflective of the number of species detected, acoustic entropy was robust to changes in sample rate and window length.

Harbor seals respond with aversion to 69‐kHz pings: Implications for weighting procedures for marine mammal noise metrics.

Author Shane tracked cultured white seabass (Atractoscion nobilis) instrumented with 69‐kHz ultrasonic coded transmitters (UCTs) in the vicinity of harbor seals (Phoca vitulina), later finding the bones of fish associated with UCTs. This led the authors to suspect that seals had targeted and eaten instrumented fish. To determine whether seals could detect pings, four harbor seals and a ringed seal at SeaWorld San Diego were exposed to pings from two 69‐kHz and one 83‐kHz UCTs and their spontaneous responses observed. The seals were not expected to respond strongly because most of the energy in the pings was close to the upper limit of hearing, but three of the four harbor seals reacted with aversion to the 69‐kHz pinger with the highest source level (147 dB re 1 μPa), swimming into a refuge pool or jumping out of the water. The received level at the closest point of approach was estimated at 20 dB above sensation level or less. The results suggest that seals may be especially responsive to high‐frequency tonal signals, and that broadband weighting functions may not consistently yield efficient exposure metrics. [Funded by NOAA; in‐kind support from SeaWorld San Diego.]

Continental scale acoustic monitoring program: One year of data

A multiyear project is underway to demonstrate the benefits of incorporating acoustic monitoring into the National Ecological Observatory Network (NEON). The NEON project seeks to generate data for the study of continental scale phenomena. Acoustic recordings can be used to determine the presence of acoustically active biota without the presence of field technicians. We have deployed stand-alone acoustic recorders at four NEON sites. Data from these recorders can be used to document spatio-temporal shifts in the presence of acoustically active species of birds, anurans, and insects. Amplitude, frequency band energy, and statistical detection methods have been compared to demonstrate the implementation of automated detection algorithms. Results from acoustic biota surveys are compared with traditional biota surveys. Comparisons of the relative contributions of acoustic energy from geophysical, biotic, and anthropogenic sources within and between sites will be examined. Preliminary results from the first ye...

Behavioral audiogram of the giant panda (Ailuropoda melanoleuca): Preliminary results

We used behavioral techniques to assess the hearing sensitivity of four, critically endangered, giant pandas at the San Diego Zoo. Study subjects included one adult male (age 19), two adult females (ages 5 and 19), and one sub-adult female (age 3). We used a down-up staircase presentation order and a go/no-go response paradigm and thus far have measured hearing thresholds between 250 Hz and 31.5 kHz. Test stimuli were 500 ms shaped tones, and catch trials represented 30% of presentations. All subjects were trained using positive reinforcement. Preliminary results suggest that giant pandas have good hearing sensitivity between 8 and 14 kHz, and best sensitivity was centered at 12.5 kHz. Low frequency hearing sensitivity declined at 250 Hz for all subjects. All bears retained functional hearing at 31.5 kHz: the younger females could hear tones as low as 15 dB, and the adults could hear to 25 dB. Preliminary results suggest that panda hearing sensitivity is similar to that of other terrestrial carnivores stu...

Effective area of acoustic lure surveys for Mexican spotted owls (Strix occidentalis lucida)

During acoustic lure surveys for birds, topography and ambient noise are likely to be important determinants of detectability. Examinations of propagation were conducted for acoustic lures (human‐made calls) and owl responses recorded during acoustic surveys for Mexican spotted owls in the Gila National Forest (2005). Lure surveys were designed based on formal agency protocols, which assumed a 0.43‐km detection range under typical conditions. A total of 558 points was called over a heavily forested, topographically complex 20×24‐km area. Real‐time measurements of owl calls and lures were made with a calibrated recording system. Ambient noise was collected using an array of 39 Larson‐Davis 820 and 824 sound‐level meters. The NMSIM (Wyle Laboratories) single‐event propagation simulator was used to model propagation of both owl and human calls. The resulting model of survey effort was compared with a simple two‐dimensional statistical model. Probability of detecting owls did not fit the expectations of the a...

Insights into airplane overflight effects on bioacoustic activity levels from long-term acoustic monitoring

The National Ecological Observatory Network (NEON) has established a framework through which a variety of environmental metrics will be continuously monitored measured for multiple decades at stations located across the United States. We describe a multiyear project that demonstrates the benefits of continuous acoustic monitoring at NEON sites. By utilizing long-term recordings, a wealth of data relating to species presence, animal behavior, and anthropogenic disturbance can be collected without the presence of human researchers. These recordings allow the measurement of contributions of anthropogenic activity to the cumulative sound energy at these locations and the response of all acoustically active species in the environment to individual events. Data from the NEON site at Harvard Forest, MA, were analyzed to assess the number of aircraft overflights detected at the location over the course of one year. The bioacoustic activity levels before, during and after were quantified for a subset of these even...

Comparison of managed care and wild walrus source characteristics

Male Pacific walruses perform acoustic displays while in rut. The purpose of these displays is unknown but are hypothesized to be for territory defense or mate advertisement. Understanding source characteristics will allow the estimation of perceptibility by conspecifics. The displays occur in the Bering Sea in late winter where direct human observation is difficult. Working with an animal in managed care provided the ability to make direct observations of a male producing breeding vocalizations and the direct calculation of source level. Source characteristics from recordings of managed care and wild walruses were analyzed. The mean peak source level of the impulsive knocks produced by the managed care male was 183 dB (re: 1 μPa). The mean peak source level from the wild recordings was 177 dB (re: 1 μPa). For both wild and managed care vocalizations, a significant relationship between ambient noise level and source level was identified. An increase of approximately 5 dB in source level was found for an i...

Transmission characteristics of Arctic pinniped vocalizations through ice

An experiment was conducted to measure the transmission loss of an acoustic signal in shallow water with a stable ice cover. Transmission loss was measured at acoustic receivers in the water and in air over 30 meters. Received levels at the microphones were greatly attenuated relative to the hydrophones with over 100 dB reduction across the spectrum. The experiment was modeled with the OASES model for estimating propagation in the time domain. Results indicated that despite the high transmission losses, enough acoustic energy can propagate through ice to air to make this a propagation pathway for ice dependent pinniped communication.