Delphine Mathias

Effects of Airgun Sounds on Bowhead Whale Calling Rates: Evidence for Two Behavioral Thresholds

In proximity to seismic operations, bowhead whales (Balaena mysticetus) decrease their calling rates. Here, we investigate the transition from normal calling behavior to decreased calling and identify two threshold levels of received sound from airgun pulses at which calling behavior changes. Data were collected in August–October 2007–2010, during the westward autumn migration in the Alaskan Beaufort Sea. Up to 40 directional acoustic recorders (DASARs) were deployed at five sites offshore of the Alaskan North Slope. Using triangulation, whale calls localized within 2 km of each DASAR were identified and tallied every 10 minutes each season, so that the detected call rate could be interpreted as the actual call production rate. Moreover, airgun pulses were identified on each DASAR, analyzed, and a cumulative sound exposure level was computed for each 10-min period each season (CSEL10-min). A Poisson regression model was used to examine the relationship between the received CSEL10-min from airguns and the number of detected bowhead calls. Calling rates increased as soon as airgun pulses were detectable, compared to calling rates in the absence of airgun pulses. After the initial increase, calling rates leveled off at a received CSEL10-min of ~94 dB re 1 μPa2-s (the lower threshold). In contrast, once CSEL10-min exceeded ~127 dB re 1 μPa2-s (the upper threshold), whale calling rates began decreasing, and when CSEL10-min values were above ~160 dB re 1 μPa2-s, the whales were virtually silent.

Relationship between sperm whale (Physeter macrocephalus) click structure and size derived from videocamera images of a depredating whale (sperm whale prey acquisition)

Sperm whales have learned to depredate black cod (Anoplopoma fimbria) from longline deployments in the Gulf of Alaska. On May 31, 2006, simultaneous acoustic and visual recordings were made of a depredation attempt by a sperm whale at 108 m depth. Because the whale was oriented perpendicularly to the camera as it contacted the longline at a known distance from the camera, the distance from the nose to the hinge of the jaw could be estimated. Allometric relationships obtained from whaling data and skeleton measurements could then be used to estimate both the spermaceti organ length and total length of the animal. An acoustic estimate of animal length was obtained by measuring the inter-pulse interval (IPI) of clicks detected from the animal and using empirical formulas to convert this interval into a length estimate. Two distinct IPIs were extracted from the clicks, one yielding a length estimate that matches the visually-derived length to within experimental error. However, acoustic estimates of spermaceti organ size, derived from standard sound production theories, are inconsistent with the visual estimates, and the derived size of the junk is smaller than that of the spermaceti organ, in contradiction with known anatomical relationships.

A comparison of acoustic and visual metrics of sperm whale longline depredation

Annual federal stock assessment surveys for Alaskan sablefish also attempt to measure sperm whale depredation by quantifying visual evidence of depredation, including lip remains and damaged fish. A complementary passive acoustic method for quantifying depredation was investigated during the 2011 and 2012 survey hauls. A combination of machine-aided and human analysis counted the number of distinct “creak” sounds detected on autonomous recorders deployed during the survey, emphasizing sounds that are followed by silence (“creak-pauses”), a possible indication of prey capture. These raw counts were then adjusted for variations in background noise levels between deployments. Both a randomized Pearson correlation analysis and a generalized linear model found that noise-adjusted counts of “creak-pauses” were highly correlated with survey counts of lip remains during both years (2012: r(10) = 0.89, p = 1e-3; 2011: r(39) = 0.72, p = 4e-3) and somewhat correlated with observed sablefish damage in 2011 [r(39) = 0.37, p = 0.03], but uncorrelated with other species depredation. The acoustic depredation count was anywhere from 10% to 80% higher than the visual counts, depending on the survey year and assumptions employed. The results suggest that passive acoustics can provide upper bounds on depredation rates; however, the observed correlation breaks down whenever three or more whales are present.

Wind dependence of ambient noise in a biologically rich coastal area

The wind dependence of acoustic spectrum between 100 Hz and 16 kHz is investigated for coastal biologically rich areas. The analysis of 5 months of continuous measurements run in a 10 m deep shallow water environment off Brittany (France) showed that wind dependence of spectral levels is subject to masking by biological sounds. When dealing with raw data, the wind dependence of spectral levels was not significant for frequencies where biological sounds were present (2 to 10 kHz). An algorithm developed by Kinda, Simard, Gervaise, Mars, and Fortier [J. Acoust. Soc. Am. 134(1), 77-87 (2013)] was used to automatically filter out the loud distinctive biological contribution and estimated the ambient noise spectrum. The wind dependence of ambient noise spectrum was always significant after application of this filter. A mixture model for ambient noise spectrum which accounts for the richness of the soundscape is proposed. This model revealed that wind dependence holds once the wind speed was strong enough to produce sounds higher in amplitude than the biological chorus (9 kn at 3 kHz, 11 kn at 8 kHz). For these higher wind speeds, a logarithmic affine law was adequate and its estimated parameters were compatible with previous studies (average slope 27.1 dB per decade of wind speed increase).

Wind dependence of shallow water ambient noise in a biologically rich temperate coastal area

The Iroise Marine Natural Park, created in 2007, is the first French natural marine park. This archipelago located in Western Brittany is a shallow water area that comprises 11 islands and hosts a rich variety of marine life, including seaweed fields, benthic organisms, endangered seals, and cetaceans. Three underwater autonomous recorders were moored at 10-m depth and sampled at 32 kHz from June 2011 to November 2011. Here we report on the dependency of shallow water ambient noise level on wind speed in a biologically rich environment. First we extract the ambient noise level in presence of transient sounds produced by benthic organisms by removing instantaneous sound pressure levels higher than a threshold computed using the kurtosis of the raw 10 sec time series. We then show that the ambient noise level allows to extract environmental information such as wind speed and biological rhythms, and that both are explaining 90% of its variance. Dependence of ambient noise and ocean noise level to wind speed ...

Polar coastal soundscapes: Tridimensional mapping of benthic biophony and ice geophony with a compact sensor array

Polar areas show fast changes linked to global warming. The reduction of the ice pack and the melting of the ice sheet modify the conditions of living of marine fauna. We propose the simultaneous monitoring of the ice and benthic fauna using passive acoustics. Thanks to a compact sensor array of 4 hydrophones (2m*2m*2m), we detected, localized and mapped in three dimensions ({azimuth, elevation} or {x, y, z}) the biophonic and geophonic contributions made up of short and wideband pulses. Tridimensional maps of benthic biophony and ice geophony of Antarctic and Arctic 7 days-long recording sessions (2015, 2016) are built and analyzed over a surface of the order of 1 km2. Benthic invertebrates emit high energetic pulses with peak frequencies ranging from 2 to 55 kHz, most of them below 15 kHz. Geophony is structured into two parts. The ice sheet, located several kilometers or tens of kilometers away, creates a stable spatial distribution of low energetic pulses (representing the majority of pulses in the soundscape) modulated by the temporal variability. The movements of isolated icebergs or pack ice produce localized acoustic events identifiable by the high sound levels and the stable peak frequencies of the emitted pulses.

Exploiting the sound-speed minimum to extend tracking ranges of vertical arrays in deep water environments

Underwater acoustic vertical arrays can localize sounds by measuring the vertical elevation angles of various multipath arrivals generated by reflections from the ocean surface and bottom. This information, along with measurements of the relative arrival times of the multipath, can be sufficient for obtaining the range and depth of an acoustic source. At ranges beyond a few kilometers ray refraction effects add additional multipath possibilities; in particular, the existence of a sound-speed minimum in deeper waters permits purely refracted ray arrivals to be detected and distinguished on an array, greatly extending the tracking range for short-aperture systems. Here, two experimental vertical array deployments are presented. The first is a simple two-element system, deployed using longline fishing gear off Sitka, AK. By tracking a tagged sperm whale, this system demonstrated an ability to localize this species out to 35 km range, and provide estimates of the detection range of these animals as a function...

Acoustic and foraging behavior of tagged sperm whales under natural and depredation foraging conditions in the Gulf of Alaska

Sperm whales have been depredating black cod (Anoplopoma fimbria) from demersal longlines in the Gulf of Alaska for decades, but the behavior has now become pervasive enough that it may be affecting government estimates of the sustainable catch, motivating further studies of this behavior. Over a three-year period, 11 B-Probe bioacoustic tags have been attached to seven adult sperm whales off Southeast Alaska, permitting observations of the animals’ dive profiles and acoustic behavior during natural and depredation foraging conditions. Two rough categories of depredation were identified: “deep” and “shallow.” “Deep depredating” whales consistently surface within 500 m of a hauling fishing vessel, have maximum dive depths greater than 200m, and display significantly different acoustic behavior than naturally foraging whales, with shorter inter-click intervals, occasional bouts of high “creak” rates, and fewer dives without creaks. “Shallow depredating” whales conduct dives that are much shorter, shallower,...

Using bioacoustic and satellite tags to study sperm whale depredation behavior, and to test new acoustic tracking methods

Sperm whales have been depredating black cod from demersal longlines in the Gulf of Alaska for decades, but the behavior has now become pervasive enough that it is starting to affect government estimates of the sustainable catch, motivating further studies of this behavior. In 2007 and 2009, 11 bioacoustic “BProbe” tags were attached to adult sperm whales off Southeast Alaska under both natural and depredation foraging conditions. Measurements of the animals dive profiles, acoustic behavior, and angular velocities allowed two categories of depredation to be identified. The dive depths and durations of “deep depredating” whales are similar to those of natural dives, but acoustic parameters show significantly significant differences. By contrast, “shallow depredating” whales conduct dives that are much shorter, shallower, and are four times more acoustically active than during natural foraging dives. In 2010, both a satellite and bioacoustic tag were deployed on a sperm whale near a two-element vertical tr...

Long-range tracking of bowhead whale calls using directional autonomous seafloor acoustic recorders

Since 2007 “Directional Autonomous Seafloor Acoustic Recorders” (DASARs) have been deployed at five sites across a 280 km swath of the Beaufort Sea continental shelf to record bowhead whale (Balaena mysticetus) calls during their autumn migration. Composed of an omnidirectional pressure sensor and two horizontal directional sensors measuring particle motion, DASARs provide information for determining the bearing to a sound source. In previous analyses, bearings obtained from multiple DASARs within a single site have been used to localize calls, with a maximum baseline separation of 21 km between instruments. Here, we use data collected from two different sites to exploit a 45 km instrument separation for tracking bowhead whale calls detected under low ambient-noise situations in 2009 and 2011. These data sets have been manually analyzed to extract a series of calls from individual whales swimming from one site toward another. The fact that the tracking method does not require relative arrival time informa...