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Marques, TA, Munger L, Thomas L, Wiggins S, Hildebrand JA.  2011.  Estimating North Pacific right whale Eubalaena japonica density using passive acoustic cue counting. Endangered Species Research. 13:163-172. Abstract
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McDonald, MA, Hildebrand JA, Wiggins SM, Johnston DW, Polovina JJ.  2009.  An acoustic survey of beaked whales at Cross Seamount near Hawaii (L). Journal of the Acoustical Society of America. 125:624-627.   10.1121/1.3050317   AbstractWebsite

An acoustic record from Cross Seamount, southwest of Hawaii, revealed sounds characteristic of beaked whale echolocation at the same relative abundance year-around (270 of 356 days), occurring almost entirely at night. The most common sound had a linear frequency upsweep from 35 to 100 kHz (the bandwidth of recording), an interpulse interval of 0.11 s, and duration of at least 932 mu s. A less common upsweep sound with shorter interpulse interval and slower sweep rate was also present. Sounds matching Cuvier's beaked whale were not detected, and Blainville's beaked whale sounds were detected on only one occasion. (C) 2009 Acoustical Society of America. [DOI: 10.1121/1.3050317]

McDonald, MA, Hildebrand JA, Wiggins SM, Thiele D, Glasgow D, Moore SE.  2005.  Sei whale sounds recorded in the Antarctic. Journal of the Acoustical Society of America. 118:3941-3945.   10.1121/1.2130944   AbstractWebsite

Sei whales are the least well known acoustically of all the rorquals, with only two brief descriptions of their calls previously reported. Recordings of low-frequency tonal and frequency swept calls were made near a group of four or five sei whales in waters west of the Antarctic Peninsula on 19 February 2003. These whales also produced broadband sounds which can be described as growls or whooshes. Many of the tonal and frequency swept calls (30 out of 68) consist of multiple parts with a frequency step between the two parts, this being the most unique characteristic of the calls, allowing them to be distinguished from the calls of other whale species. The average duration of the tonal calls is 0.45 +/- 0.3 s and the average frequency is 433 +/- 192 Hz. Using a calibrated seafloor recorder to determine the absolute calibration of a sonobuoy system, the maximum source level of the tonal calls was 156 +/- 3.6 dB re 1 microPa at 1 m. Each call had different character and there was no temporal pattern in the calling.

McDonald, MA, Hildebrand JA, Wiggins SM, Ross D.  2008.  A 50 year comparison of ambient ocean noise near San Clemente Island: a bathymetrically complex coastal region off Southern California. Journal of the Acoustical Society of America. 124:1985-92.   10.1121/1.2967889   AbstractWebsite

Repeated ocean ambient noise measurements at a shallow water (110 m) site near San Clemente Island reveal little increase in noise levels in the absence of local ships. Navy reports document ambient noise levels at this site in 1958-1959 and 1963-1964 and a seafloor recorder documents noise during 2005-2006. When noise from local ships was excluded from the 2005-2006 recordings, median sound levels were essentially the same as were observed in 1958 and 1963. Local ship noise, however, was present in 31% of the recordings in 1963 but was present in 89% of the recordings in 2005-2006. Median levels including local ships are 6-9 dB higher than median levels chosen from times when local ship noise was absent. Biological sounds and the sound of wind driven waves controlled ambient noise levels in the absence of local ships. The median noise levels at this site are low for an open water site due to the poor acoustic propagation and low average wind speeds. The quiet nature of this site in the absence of local ships allows correlation of wind speed to wave noise across the 10-220 Hz spectral band of this study.

McDonald, MA, Hildebrand JA, Wiggins SM.  2006.  Increases in deep ocean ambient noise in the northeast Pacific west of San Nicolas Island, California. Journal of the Acoustical Society of America. 120:711-718.   10.1121/1.2216565   AbstractWebsite

Recent measurement at a previously studied location illustrates the magnitude of increases in ocean ambient noise in the Northeast Pacific over the past four decades. Continuous measurements west of San Nicolas Island, California, over 138 days, spanning 2003-2004 are compared to measurements made during the 1960s at the same site. Ambient noise levels at 30-50 Hz were 10-12 dB higher (95% CI=2.6 dB) in 2003-2004 than in 1964-1966, suggesting an average noise increase rate of 2.5-3 dB per decade. Above 50 Hz the noise level differences between recording periods gradually diminished to only 1-3 dB at 100-300 Hz. Above 300 Hz the 1964-1966 ambient noise levels were higher than in 2003-2004, owing to a diel component which was absent in the more recent data. Low frequency (10-50 Hz) ocean ambient noise levels are closely related to shipping vessel traffic. The number of commercial vessels plying the world's oceans approximately doubled between 1965 and 2003 and the gross tonnage quadrupled, with a corresponding increase in horsepower. Increases in commercial shipping are believed to account for the observed low-frequency ambient noise increase. (c) 2006 Acoustical Society of America.

McKenna, MF, Katz SL, Wiggins SM, Ross D, Hildebrand JA.  2012.  A quieting ocean: Unintended consequence of a fluctuating economy. Journal of the Acoustical Society of America. 132:EL169-EL175.   10.1121/1.4740225   AbstractWebsite

Simultaneous long-term monitoring of underwater sound and ship traffic provided an opportunity to study how low-frequency noise correlated with ocean-based commercial shipping trends. Between 2007 and 2010 changes in regional shipping off southern California occurred as a consequence of economic and regulatory events. Underwater average noise levels measured before and during these events showed a net reduction of 12 dB. Statistical models revealed that a reduction of 1 ship transit per day resulted in 1 dB decrease in average noise. This synthesis of maritime traffic statistics with ocean noise monitoring provides an important step in understanding the magnitude and potential effects of chronic noise in marine habitats. (C) 2012 Acoustical Society of America

McKenna, MF, Wiggins SM, Hildebrand JA.  2013.  Relationship between container ship underwater noise levels and ship design, operational and oceanographic conditions. Scientific Reports. 3   10.1038/srep01760   AbstractWebsite

Low-frequency ocean ambient noise is dominated by noise from commercial ships, yet understanding how individual ships contribute deserves further investigation. This study develops and evaluates statistical models of container ship noise in relation to design characteristics, operational conditions, and oceanographic settings. Five-hundred ship passages and nineteen covariates were used to build generalized additive models. Opportunistic acoustic measurements of ships transiting offshore California were collected using seafloor acoustic recorders. A 5-10 dB range in broadband source level was found for ships depending on the transit conditions. For a ship recorded multiple times traveling at different speeds, cumulative noise was lowest at 8 knots, 65% reduction in operational speed. Models with highest predictive power, in order of selection, included ship speed, size, and time of year. Uncertainty in source depth and propagation affected model fit. These results provide insight on the conditions that produce higher levels of underwater noise from container ships.

McKenna, MF, Ross D, Wiggins SM, Hildebrand JA.  2012.  Underwater radiated noise from modern commercial ships. The Journal of the Acoustical Society of America. 131:92-103.   10.1121/1.3664100   AbstractWebsite

Underwater radiated noise measurements for seven types of modern commercial ships during normal operating conditions are presented. Calibrated acoustic data (<1000 Hz) from an autonomous seafloor-mounted acoustic recorder were combined with ship passage information from the Automatic Identification System. This approach allowed for detailed measurements (i.e., source level, sound exposure level, and transmission range) on ships of opportunity. A key result was different acoustic levels and spectral shapes observed from different ship-types. A 54 kGT container ship had the highest broadband source level at 188 dB re 1 mu Pa@1m; a 26 kGT chemical tanker had the lowest at 177 dB re 1 mu Pa@1m. Bulk carriers had higher source levels near 100 Hz, while container ship and tanker noise was predominantly below 40 Hz. Simple models to predict source levels of modern merchant ships as a group from particular ship characteristics (e. g., length, gross tonnage, and speed) were not possible given individual ship-type differences. Furthermore, ship noise was observed to radiate asymmetrically. Stern aspect noise levels are 5 to 10 dB higher than bow aspect noise levels. Collectively, these results emphasize the importance of including modern ship-types in quantifying shipping noise for predictive models of global, regional, and local marine environments. (C) 2012 Acoustical Society of America. [DOI: 10.1121/1.3664100]

Melcon, ML, Cummins AJ, Kerosky SM, Roche LK, Wiggins SM, Hildebrand JA.  2012.  Blue whales respond to anthropogenic noise. Plos One. 7:e32681.   doi:10.1371/journal.pone.0032681   AbstractWebsite

Anthropogenic noise may significantly impact exposed marine mammals. This work studied the vocalization response of endangered blue whales to anthropogenic noise sources in the mid-frequency range using passive acoustic monitoring in the Southern California Bight. Blue whales were less likely to produce calls when mid-frequency active sonar was present. This reduction was more pronounced when the sonar source was closer to the animal, at higher sound levels. The animals were equally likely to stop calling at any time of day, showing no diel pattern in their sensitivity to sonar. Conversely, the likelihood of whales emitting calls increased when ship sounds were nearby. Whales did not show a differential response to ship noise as a function of the time of the day either. These results demonstrate that anthropogenic noise, even at frequencies well above the blue whales' sound production range, has a strong probability of eliciting changes in vocal behavior. The long-term implications of disruption in call production to blue whale foraging and other behaviors are currently not well understood.

Munger, LM, Mellinger DK, Wiggins SM, Moore SE, Hildebrand JA.  2005.  Performance of spectrogram cross-correlation in detecting right whale calls in long-term recordings from the Bering Sea. Canadian Acoustics. 33:25-34. AbstractWebsite

We investigated the performance of spectrogram cross-correlation for automatically detecting North Pacific right whale (Eubalaena japonica) calls in long-term acoustic recordings from the southeastern Bering Sea. Data were sampled by autonomous, bottom-mounted hydrophones deployed in the southeastern Bering Sea from October 2000 through August 2002. A human analyst detected right whale calls within the first month (October 2000) of recorded data by visually examining spectrograms and by listening to recorded data; these manual detections were then compared to results of automated detection trials. Automated detection by spectrogram cross-correlation was implemented using a synthetic kernel based on the most common right whale call type. To optimize automated detection parameters, the analyst performed multiple trials on minutes-long and hour-long recordings and manually adjusted detection parameters between trials. A single set of optimized detection parameters was used to process a week-long recording from October 2000. The automated detector trials resulted in increasing proportions of false and missed detections with increasing data set duration, due to the higher proportion of acoustic noise and lower overall call rates in longer recordings. However, the automated detector missed only one calling "bout" (2 or more calls within a 10-minute span) of the 18 bouts present in the week-long recording. Despite the high number of false detections and missed individual calls, spectrogram cross-correlation was useful to guide a human analyst to sections of data with potential right whale calling bouts. Upon reviewing automatic detection events, the analyst could quickly dismiss false detections and search recordings before and after correct detections to find missed calls, thus improving the efficiency of searching for a small number of calls in long-term (months- to years-long) recordings.

Munger, LM, Wiggins SM, Moore SE, Hildebrand JA.  2008.  North Pacific right whale (Eubalaena japonica) seasonal and diel calling patterns from long-term acoustic recordings in the southeastern Bering Sea, 2000-2006. Marine Mammal Science. 24:795-814.   10.1111/j.1748-7692.2008.00219.x   AbstractWebsite

We assessed North Pacific right whale (Eubalaena japonica) seasonal and daily calling patterns in the southeastern Bering Sea (SEBS) using long-term hydrophone recordings from October 2000 through January 2006. We detected right whale calls on the SEBS middle shelf (< 100 m depth) as early as May, intermittently throughout summer and fall, and as late as December. Calls also were detected on one day in June 2005 on the SEBS slope (> 1,000 m), but were not detected near Kodiak Island from April to August 2003. In months with calls, detections occurred on more days in July-October (>= 6 d/mo), than from May to June or November to December (<= 3 d/mo). Calls were clustered in time and were usually detected on 1-3 consecutive days with a median interval of 6.5 d for calls > 1 d apart. Hourly calling rates were significantly higher at night than during the day. These data indicate that right whales occur in the SEBS later in the year than previously known, intermittently pass through the middle-shelf study region, and usually remain there no longer than a few days. Right whale habitat use in the SEBS may intensify in mid-summer through early fall based on higher monthly and daily call detection rates.

Munger, LM, Wiggins SM, Hildebrand JA.  2011.  North Pacific right whale up-call source levels and propagation distance on the southeastern Bering Sea shelf. Journal of the Acoustical Society of America. 129:4047-54.   10.1121/1.3557060   AbstractWebsite

Call source levels, transmission loss, and ambient noise levels were estimated for North Pacific right whale (Eubalaena japonica) up-calls recorded in the southeastern Bering Sea in autumn of 2000 and 2001. Distances to calling animals, needed to estimate source levels, were based on two independent techniques: (1) arrival-time differences on three or more hydrophones and (2) shallow-water dispersion of normal modes on a single receiver. Average root-mean-square (rms) call source levels estimated by the two techniques were 178 and 176 dB re 1 muPa at 1 m, respectively, over the up-call frequency band, which was determined per call and averaged 90 to 170 Hz. Peak-to-peak source levels were 14 to 22 dB greater than rms levels. Transmission loss was approximately 15 *log(10)(range), intermediate between cylindrical and spherical spreading. Ambient ocean noise within the up-call band varied from 72 to 91 dB re 1 muPa(2)/Hz. Under average noise conditions, call spectrograms were detectable for whales at distances up to 100 km, but propagation and detection distance may vary depending on environmental parameters and anthropogenic noise. Obtaining distances to animals and acoustic detection range is a step toward using long-term passive acoustic recordings to estimate abundance for this critically endangered whale population.