Publications

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2016
Dominello, T, Širović A.  2016.  Seasonality of Antarctic minke whale (Balaenoptera bonaerensis) calls off the western Antarctic Peninsula. Marine Mammal Science. 32:826-838.   10.1111/mms.12302   AbstractWebsite

The Antarctic minke whale (Balaenoptera bonaerensis) is a difficult species to study because of its low visual detectability and preference for living within the sea ice habitat, accessible only by ice-strengthened vessels. Recent identification of the Antarctic minke whale as the source of the seasonally ubiquitous bio-duck call has allowed the use of this sound, as well as downsweeps, to investigate seasonality trends and diel patterns in Antarctic minke whale call production, and their relationship to sea ice cover. Passive acoustic data were collected using an autonomous Acoustic Recording Package (ARP) off the western Antarctic Peninsula. Bio-duck calls were classified into four distinct call variants, with one variant having two subtypes. Bio-duck calls were detected between April and November, with increasing call duration during the austral winter, indicating a strong seasonality in call production. Downsweeps, which were also attributed to Antarctic minke whales, were present throughout most months during the recording period, with a peak in July, and an absence in March and April. Both bio-duck and downsweeps were significantly correlated with sea ice cover. No diel patterns were observed in bio-duck calls or in downsweep call production at this site.

2015
Širović, A, Rice A, Chou E, Hildebrand JA, Wiggins SM, Roch MA.  2015.  Seven years of blue and fin whale call abundance in the Southern California Bight. Endangered Species Research. 28:61-76.   10.3354/esr00676   AbstractWebsite

Blue whales Balaenoptera musculus and fin whales B. physalus are common inhabitants of the Southern California Bight (SCB), but little is known about the spatial and temporal variability of their use of this area. To study their distribution in the SCB, high-frequency acoustic recording packages were intermittently deployed at 16 locations across the SCB from 2006 to 2012. Presence of blue whale B calls and fin whale 20 Hz calls was determined using 2 types of automatic detection methods, i.e. spectrogram correlation and acoustic energy detection, respectively. Blue whale B calls were generally detected between June and January, with a peak in September, with an overall total of over 3 million detections. Fin whale 20 Hz calls, measured via the fin whale call index, were present year-round, with the highest values between September and December, with a peak in November. Blue whale calls were more common at coastal sites and near the northern Channel Islands, while the fin whale call index was highest in the central and southern areas of the SCB, indicating a possible difference in habitat preferences of the 2 species in this area. Across years, a peak in blue whale call detections occurred in 2008, with minima in 2006 and 2007, but there was no long-term trend. There was an increase in the fin whale call index during this period. These trends are consistent with visual survey estimates for both species in Southern California, providing evidence that passive acoustics can be a powerful tool to monitor population trends for these endangered species.

2013
Širović, A, Wiggins SM, Oleson EM.  2013.  Ocean noise in the tropical and subtropical Pacific Ocean. Journal of the Acoustical Society of America. 134:2681-2689.   10.1121/1.4820884   AbstractWebsite

Ocean ambient noise is well studied in the North Pacific and North Atlantic but is poorly described for most of the worlds' oceans. Calibrated passive acoustic recordings were collected during 2009-2010 at seven locations in the central and western tropical and subtropical Pacific. Monthly and hourly mean power spectra (15-1000 Hz) were calculated in addition to their skewness, kurtosis, and percentile distributions. Overall, ambient noise at these seven sites was 10-20 dB lower than reported recently for most other locations in the North Pacific. At frequencies <100Hz, spectrum levels were equivalent to those predicted for remote or light shipping. Noise levels in the 40Hz band were compared to the presence of nearby and distant ships as reported to the World Meteorological Organization Voluntary Observing Ship Scheme (VOS) project. There was a positive, but nonsignificant correlation between distant shipping and low frequency noise (at 40 Hz). There was a seasonal variation in ambient noise at frequencies >200Hz with higher levels recorded in the winter than in the summer. Several species of baleen whales, humpback (Megaptera novaeangliae), blue (Balaenoptera musculus), and fin (B. physalus) whales, also contributed seasonally to ambient noise in characteristic frequency bands. (C) 2013 Acoustical Society of America.