Publications

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2017
Rice, A, Deecke VB, Ford JKB, Pilkington JF, Oleson EM, Hildebrand JA, Širović A.  2017.  Spatial and temporal occurrence of killer whale ecotypes off the outer coast of Washington State, USA. Marine Ecology Progress Series. 572:255-268.   10.3354/meps12158  
2016
Guass, O, Haapanen LM, Dowd SE, Širović A, McLaughlin RW.  2016.  Analysis of the microbial diversity in faecal material of the endangered blue whale, Balaenoptera musculus. Antonie Van Leeuwenhoek International Journal of General and Molecular Microbiology. 109:1063-1069.   10.1007/s10482-016-0698-1   AbstractWebsite

Using bacterial and fungal tag-encoded FLX-Titanium amplicon pyrosequencing, the microbiota of the faecal material of two blue whales living in the wild off the coast of California was investigated. In both samples the most predominant bacterial phylum was the Firmicutes with Clostridium spp. being the most dominant bacteria. The most predominant fungi were members of the phylum Ascomycota with Metschnikowia spp. being the most dominant. In this study, we also preliminarily characterised the culturable anaerobic bacteria from the faecal material, using traditional culture and 16S rRNA gene sequencing approaches. In total, three bacterial species belonging to the phylum Firmicutes were identified.

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.

Širović, A, Hildebrand JA, McDonald MA.  2016.  Ocean ambient sound south of Bermuda and Panama Canal traffic. Journal of the Acoustical Society of America. 139:2417-2423.   10.1121/1.4947517   AbstractWebsite

Comparisons of current and historic ocean ambient noise levels are rare, especially in the North Atlantic. Recent (2013-2014) monthly patterns in ocean ambient sound south of Bermuda were compared to those recorded at the same location in 1966. Additionally, trends in ocean traffic, in particular, Panama Canal traffic, over this time were also investigated. One year of ocean ambient noise measurements were collected in 1966 using cabled, omnidirectional hydrophones at the U.S. Navy Tudor Hill Laboratory in Bermuda, and repeat measurements were collected at the same location from June 2013-May 2014 using a High-frequency Acoustic Recording Package. Average monthly pressure spectrum levels at 44 Hz increased 2.8 +/- 0.8 dB from 1966 to 2013, indicating an average increase of 0.6 dB/decade. This low level of increase may be due to topographic shielding at this site, limiting it to only southern exposure, and the limit in the number of ship transits through the Panama Canal, which did not change substantially during this time. The impending expansion of the Canal, which will enable the transit of larger ships at twice the current rate, is likely to lead to a substantial increase in ocean ambient sound at this location in the near future. (c) 2016 Author(s).

Širović, A.  2016.  Variability in the performance of the spectrogram correlation detector for North-east Pacific blue whale calls. Bioacoustics-the International Journal of Animal Sound and Its Recording. 25:145-160.   10.1080/09524622.2015.1124248   AbstractWebsite

Spectrogram correlation has been used successfully for automatic detection of baleen whale calls. However, applying this method consistently to long time series can be challenging. To illustrate the potential challenges of the automatic detection process, recordings collected in the Southern California Bight between 2007 and 2012 were used for detection of North-east Pacific blue whale (Balaenoptera musculus) B calls. The effects of the following factors were investigated: blue whale B call frequency shift and appropriate kernel modification, seasonal variability in call abundance, analyst variability and noise. Due to intra- and inter-annual changes in the call frequency of blue whale B calls, seasonal and annual adjustments to the call detection kernel were needed. To account for seasonal variability in call production, evaluation of the detector against ground truth data was performed at multiple times during the year. Analyst variability did not affect overall long-term trends in detection, but it had an impact on the total number of detections, as well as call rate estimation. Noise, particularly from shipping, was negatively correlated with detections at hourly time scales. A detailed analysis of variability in the performance of spectrogram correlation detectors should be performed when applying this method to long-term acoustic data-sets.

Roch, MA, Batchelor H, Baumann-Pickering S, Berchok CL, Cholewiak D, Fujioka E, Garland EC, Herbert S, Hildebrand JA, Oleson EM, Van Parijs S, Risch D, Širović A, Soldevilla MS.  2016.  Management of acoustic metadata for bioacoustics. Ecological Informatics. 31:122-136.   10.1016/j.ecoinf.2015.12.002   AbstractWebsite

Recent expansion in the capabilities of passive acoustic monitoring of sound-producing animals is providing expansive data sets in many locations. These long-term data sets will allow the investigation of questions related to the ecology of sound-producing animals on time scales ranging from diel and seasonal to inter-annual and decadal. Analyses of these data often span multiple analysts from various research groups over several years of effort and, as a consequence, have begun to generate large amounts of scattered acoustic metadata. It has therefore become imperative to standardize the types of metadata being generated. A critical aspect of being able to learn from such large and varied acoustic data sets is providing consistent and transparent access that can enable the integration of various analysis efforts. This is juxtaposed with the need to include new information for specific research questions that evolve over time. Hence, a method is proposed for organizing acoustic metadata that addresses many of the problems associated with the retention of metadata from large passive acoustic data sets. A structure was developed for organizing acoustic metadata in a consistent manner, specifying required and optional terms to describe acoustic information derived from a recording. A client-server database was created to implement this data representation as a networked data service that can be accessed from several programming languages. Support for data import from a wide variety of sources such as spreadsheets and databases is provided. The implementation was extended to access Internet-available data products, permitting access to a variety of environmental information types (e.g. sea surface temperature, sunrise/sunset, etc.) from a wide range of sources as if they were part of the data service. This metadata service is in use at several institutions and has been used to track and analyze millions of acoustic detections from marine mammals, fish, elephants, and anthropogenic sound sources. (C) 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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.

Hastings, PA, Širović A.  2015.  Soundscapes offer unique opportunities for studies of fish communities. Proceedings of the National Academy of Sciences. 112:5866-5867.   10.1073/pnas.1505897112   Abstract

Resource partitioning is a fundamental ecological concept in which cooccurring species reduce competition by using or specializing on different resources (1). It is widely accepted as a mechanism permitting similar species to cooccur, leading to increased levels of species diversity (2). Typically, resources are thought of as food, habitat, or behavioral features such as timing of foraging and pattern of prey capture. However, the concept applies equally well to any niche parameter that affects species success. This includes the “space” to effectively communicate with conspecifics (3). In PNAS, Ruppé et al. (4) document apparent resource partitioning in the acoustic communication behavior of a community of nocturnal marine fishes found in a cave environment on the rocky coastline of South Africa. They recorded and analyzed 2,793 instances of 17 distinctive sounds that differed in peak frequency and pulsing characteristics. They assumed those distinctive sounds represent separate species and found that sounds from sonic species recorded during the day were less acoustically distinct from one another than those recorded at night. The authors interpret this pattern as indicative of resource partitioning among nocturnal species that are largely limited to acoustic communication modalities. In contrast, the acoustic signals of diurnal species in the same community, for which visual displays undoubtedly play a larger role, are not so constrained and overlap considerably in frequency at the resolution used in their analysis (∼700 Hz).

Nichols, TA, Anderson TW, Širović A.  2015.  Intermittent noise induces physiological stress in a coastal marine fish. PLoS One. 10(9):e0139157.   10.1371/journal.pone.0139157   Abstract

Anthropogenic noise in the ocean has increased substantially in recent decades, and motorized vessels produce what is likely the most common form of underwater noise pollution. Noise has the potential to induce physiological stress in marine fishes, which may have negative ecological consequences. In this study, physiological effects of increased noise (playback of boat noise recorded in the field) on a coastal marine fish (the giant kelpfish, Heterostichus rostratus) were investigated by measuring the stress responses (cortisol concentration) of fish to increased noise of various temporal dynamics and noise levels. Giant kelpfish exhibited acute stress responses when exposed to intermittent noise, but not to continuous noise or control conditions (playback of recorded natural ambient sound). These results suggest that variability in the acoustic environment may be more important than the period of noise exposure for inducing stress in a marine fish, and provide information regarding noise levels at which physiological responses occur.

2014
Oleson, EM, Širović A, Bayless AR, Hildebrand JA.  2014.  Synchronous seasonal change in fin whale song in the North Pacific. PLoS ONE. 9: Public Library of Science   10.1371/journal.pone.0115678   AbstractWebsite

Fin whale (Balaenoptera physalus) song consists of down-swept pulses arranged into stereotypic sequences that can be characterized according to the interval between successive pulses. As in blue (B. musculus) and humpback whales (Megaptera novaeangliae), these song sequences may be geographically distinct and may correlate with population boundaries in some regions. We measured inter-pulse intervals of fin whale songs within year-round acoustic datasets collected between 2000 and 2006 in three regions of the eastern North Pacific: Southern California, the Bering Sea, and Hawaii. A distinctive song type that was recorded in all three regions is characterized by singlet and doublet inter-pulse intervals that increase seasonally, then annually reset to the same shorter intervals at the beginning of each season. This song type was recorded in the Bering Sea and off Southern California from September through May and off Hawaii from December through April, with the song interval generally synchronized across all monitoring locations. The broad geographic and seasonal occurrence of this particular fin whale song type may represent a single population broadly distributed throughout the eastern Pacific with no clear seasonal migratory pattern. Previous studies attempting to infer population structure of fin whales in the North Pacific using synchronous individual song samples have been unsuccessful, likely because they did not account for the seasonal lengthening in song intervals observed here.

Širović, A, Bassett HR, Johnson SC, Wiggins SM, Hildebrand JA.  2014.  Bryde’s whale calls recorded in the Gulf of Mexico. Marine Mammal Science. 30:399-409.   10.1111/mms.12036  
Širović, A, Johnson SC, Roche LK, Varga LM, Wiggins SM, Hildebrand JA.  2014.  North Pacific right whales (Eubalaena japonica) recorded in the Northeastern Pacific Ocean in 2013. Marine Mammal Science.   10.1111/mms.12189  
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.

Kendall, LS, Širović A, Roth EH.  2013.  Effects of construction noise on the Cook Inlet beluga whale (Delphinapterus leucas) vocal behavior. Canadian Acoustics. 41(3):3-13. Abstract

Cook Inlet beluga whales (Delphinapterus leucas) are listed as endangered under the US Endangered Species Act. Potential threats to this population include anthropogenic noise and coastal zone development. The Port of Anchorage Marine Terminal Redevelopment (MTR) Project, taking place in the Knik Arm of Cook Inlet, Alaska, involves multiple construction activities including dredging, gravel fill and pile driving. The impacts of construction noise on beluga vocalizations were investigated in this study. Passive sonobuoys were deployed in a four mooring array during 20 d in August and September 2009 near the MTR Project. Data were recorded in real-time at a shore-based observation station. No beluga whistles or noisy vocalizations were recorded during this period; however, beluga echolocation clicks were frequently detected. An energy summation method was used to automatically detect echolocation clicks. Times with and without construction noise (i.e., dredging and pile driving) were determined from long-term spectral averages. The detected hourly click rate was higher during times without (429 detected clicks/h) than with (291 detected clicks/h) construction activity; however, the difference was not statistically significant (t (24) = -0.56, P = 0.58). Lower frequency beluga whale vocalizations (e.g., whistles) were potentially masked, there may be have been an overall reduction in beluga vocalizations, or it is possible belugas were avoiding the area during construction activity.

Širović, A, Williams LN, Kerosky SM, Wiggins SM, Hildebrand JA.  2013.  Temporal separation of two fin whale call types across the eastern North Pacific. Marine Biology. 160:47-57.   10.1007/s00227-012-2061-z   Abstract

Fin whales (Balaenoptera physalus) produce a variety of low-frequency, short duration, frequency modulated calls. The differences in temporal patterns between two fin whale call types are described from long-term passive acoustic data collected intermittently between 2005 and 2011 at three locations across the eastern North Pacific: the Bering Sea, off Southern California, and in Canal de Ballenas in the northern Gulf of California. Fin whale calls were detected at all sites year-round, during all periods with recordings. At all three locations, 40 Hz calls peaked in June, preceding a peak in 20 Hz calls by 3-5 months. Monitoring both call types may provide a more accurate insight into the seasonal presence of fin whales across the eastern North Pacific than can be obtained from a single call type. The 40 Hz call may be associated with a foraging function and temporal separation between 40 Hz and 20 Hz calls may indicate the separation between predominately feeding behavior and other social interactions.

2012
Kerosky, SM, Širović A, Roche LK, Baumann-Pickering S, Wiggins SM, Hildebrand JA.  2012.  Bryde's whale seasonal range expansion and increasing presence in the Southern California Bight from 2000 to 2010. Deep-Sea Research Part I-Oceanographic Research Papers. 65:125-132.   10.1016/j.dsr.2012.03.013   Abstract

Bryde's whales (Balaenoptera edeni) are commonly found in tropical and subtropical regions of the Pacific Ocean, but few studies have explored the presence of Bryde's whales at the boundary of their distribution range. Such studies are increasingly relevant as climate impact models predict the range expansion of warm water species towards the poles in response to ocean warming. Like other baleen whales, Bryde's whales produce distinct low frequency (<60 Hz) calls, which can be used for long-term acoustic monitoring of whale presence in an area. Autonomous passive acoustic recorders deployed at five sites in the Southern California Bight (SCB) were used to investigate the presence of Bryde's whales in temperate waters from 2000 to 2010. Calling Bryde's whales were observed in the SCB from summer to early winter, indicating a seasonal poleward range expansion. There was a significant increase in the presence of calling Bryde's whales in the SCB between 2000 and 2010, but no significant correlation was found between Bryde's whale presence and local sea surface temperature. Bryde's whale occurrence is likely driven by prey availability within the California Current ecosystem, which is affected by seasonal and inter-annual changes in climate and oceanographic conditions. Continued monitoring of Bryde's whales and their prey in the eastern North Pacific is needed to provide a longer time series and determine the full effect of climate variability and ocean warming on the distribution of this species. (C) 2012 Elsevier Ltd. All rights reserved.

2011
Širović, A, Hildebrand JA.  2011.  Using passive acoustics to model blue whale habitat off the Western Antarctic Peninsula. Deep-Sea Research Part II-Topical Studies in Oceanography. 58:1719-1728.   10.1016/j.dsr2.2010.08.019   Abstract

Habitat preferences of calling blue whales were investigated using data from two multidisciplinary oceanographic cruises conducted off the Western Antarctic Peninsula (WAP) during the austral falls of 2001 and 2002. Data were collected on depth, temperature, salinity, chlorophyll a (Chl-a) concentration, krill biomass, zooplankton abundance, and blue whale call presence. In 2001, the study area was sea ice free, high Chl-a concentrations occurred over a small area, krill biomass and zooplankton abundance were high, and few blue whale calls were detected. In 2002 the sea ice covered the southern part of the survey area. Chl-a was high over a large area, krill and zooplankton were low, and there were more blue whale calls. Logistic regression analysis revealed blue whale calls were positively correlated with depth and SST, and negatively correlated with the mean zooplankton abundance from 101 to 300 m and the mean krill biomass in the top 100 m. The negative correlation between blue whale calls and zooplankton could occur if feeding animals do not produce calls. Our survey area did not cover the full range of blue whale habitat off the WAP, as blue whales probably follow the melting and freezing ice edge through this region. Passive acoustics can provide insight to mesoscale habitat use by blue whales in the Southern Ocean where visual sightings are rare, but the ability to localize on the calling animals would greatly improve the ability to model at a finer scale. (C) 2010 Elsevier Ltd. All rights reserved.

2009
Širović, A, Demer DA.  2009.  Sounds of Captive Rockfishes. Copeia. :502-509.   10.1643/cp-08-121   AbstractWebsite

Sound production by many fish species has been studied extensively, but little is known about sound production by rockfishes (genus Sebostes), and only a few species have been reported to be soniferous. To determine if additional rockfish species produce sounds, passive acoustic recordings were made during 2007/08 at Hubbs-SeaWorld Research Institute and Southwest Fisheries Science Center in tanks containing Bocaccio (S. poucispinis), Cowcod (S. levis), Starry Rockfish (S. constellatus), and Sunset Rockfish (S. crocotulus). Data were collected using pre-amplified hydrophones (HTI-94-SSQ) and digitized at sample rates of 44,100 or 8,000 Hz (using an Edirol R-09 recorder or Edirol UA-5 sound card and Ishmael software, respectively). Three distinct sounds were recorded in tanks containing only S. paucispinis and two of those sounds occurred at different rates during light and dark conditions. Their common characteristics were low frequency (below 800 Hz), short duration (<4 s), and low source levels (103-113 dB re: 1 mu Pa at 1 m). Also, there was evidence one or more other species produced sounds. These findings Indicate that more rockfishes produce sounds, and suggest passive acoustics could be a useful tool for remotely monitoring their populations.

Širović, A, Hildebrand JA, Wiggins SM, Thiele D.  2009.  Blue and fin whale acoustic presence around Antarctica during 2003 and 2004. Marine Mammal Science. 25:125-136.   10.1111/j.1748-7692.2008.00239.x   Abstract

Seasonal and spatial variations of blue (Balaenoptera musculus) and fin whale (B. physalus) calls were analyzed from recordings collected with Acoustic Recording Packages (ARPs) deployed between January 2003 and July 2004 at four circumpolar locations: the Western Antarctic Peninsula (WAP), the Scotia Sea (SS), Eastern Antarctica (EA), and the Ross Sea (RS). Call characteristics were compared among sites using the average pressure spectrum levels from 1 month of data at each location. Presence of calls was analyzed using automatic call detection and acoustic power analysis methods. Blue whale calls were recorded year-round, with the highest detections in February-May and November. This suggests that the blue whale population may not migrate synchronously, and may indicate long duration calls are more common during migrations. Fin whale calls were detected only during February-July. Two distinct fin whale call types were recorded, suggesting a possible separation into two populations. The calls at the EA site had a secondary frequency peak in the pressure spectrum at 99 Hz and the calls at the WAP and the SS sites had a peak at 89 Hz. No fin whale calls were detected at the RS site. Acoustics are a good tool to monitor large whales in the Southern Ocean.

Širović, A, Cutter GR, Butler JL, Demer DA.  2009.  Rockfish sounds and their potential use for population monitoring in the Southern California Bight. Ices Journal of Marine Science. 66:981-990.   10.1093/icesjms/fsp064   Abstract

Non-lethal methods are being developed to assess and monitor the depleted rockfish stocks off southern California. For example, data from multifrequency echosounders and underwater cameras have been combined to map the dispersions and estimate the abundances of rockfish at the historical fishing sites within this region. From August to October 2007, this ship-based technique was augmented with two passive-acoustic moored recorders. One collected data at the 43 Fathom Bank for 46 days, while the other was serially deployed at 13 locations for shorter periods (1-8 d). Passive-acoustic data were analysed for the presence of rockfish sounds. Potential sources of five pulsing sounds were identified from the optically estimated species compositions at each location, as well as from known rockfish recordings collected in aquaria. All sounds had a low frequency (<900 Hz). Some were short, individual pulses (0.1 s), others were repetitive. A repetitive pulsing from bocaccio (Sebastes paucispinis) was the most commonly recorded sound and it occurred mainly at night. The daily calling rates at each site were quantitatively compared with the rockfish abundance estimates obtained from the active-acoustic survey, and they were positively correlated. The feasibility of using passive-acoustic tools to monitor changes in rockfish populations efficiently is discussed.

2007
Širović, A, Hildebrand JA, Wiggins SM.  2007.  Blue and fin whale call source levels and propagation range in the Southern Ocean. Journal of the Acoustical Society of America. 122:1208-1215.   10.1121/1.2749452   Abstract

Blue (Balaenoptera musculus) and fin whales (B. physalus) produce high-intensity, low-frequency calls, which probably function for communication during mating and feeding. The source levels of blue and fin whale calls off the Western Antarctic Peninsula were calculated using recordings made with calibrated, bottom-moored hydrophones. Blue whales were located up to a range of 200 km using hyperbolic localization and time difference of arrival. The distance to fin whales, estimated using multipath arrivals of their calls, was up to 56 km. The error in range measurements was 3.8 km using hyperbolic localization, and 3.4 km using multipath arrivals. Both species produced high-intensity calls; the average blue whale call source level was 189±3 dB re:1 uPa-1 m over 25–29 Hz, and the average fin whale call source level was 189±4 dB re:1 uPa-1 m over 15–28 Hz. Blue and fin whale populations in the Southern Ocean have remained at low numbers for decades since they became protected; using source level and detection range from passive acoustic recordings can help in calculating the relative density of calling whales. © 2007 Acoustical Society of America.

2006
Širović, A, Hildebrand JA, Thiele D.  2006.  Baleen whales in the Scotia Sea in January and February 2003. Journal of Cetacean Research and Management. 8:161-171. Abstract

Different species of baleen whales display distinct spatial distribution patterns in the Scotia Sea during the austral summer. Passive acoustic and visual surveys for baleen whales were conducted aboard the RRS James Clark Ross in the Scotia Sea and around South Georgia in January and February 2003. Identified calls from four species were recorded during the acoustic survey including southern right (Eubalaena
australis
), blue (Balaenoptera musculus), fin (B. physalus) and humpback whales (Megaptera novaeangliae). These acoustic data included up calls made by southern right whales, downswept D and tonal calls by blue whales, two possible types of fin whale downswept calls and
humpback whale moans and grunts. Visual detections included southern right, fin, humpback and Antarctic minke whales (B. bonaerensis sp.). Most acoustic and visual detections occurred either around South Georgia (southern right and humpback whales) or south of the southern boundary of the Antarctic Circumpolar Current (ACC) and along the outer edge of the ice pack (southern right, blue, humpback and Antarctic minke whales). Fin whales were the exception, being the only species acoustically and visually detected primarily in the central Scotia Sea, along the southern ACC front. In addition to identifiable calls from these species, two types of probable baleen whale calls were detected: 50Hz upswept and pulsing calls. It is proposed that minke whales may produce the pulsing calls, based on their similarities with minke whale calls recorded in the North Atlantic Ocean. There was an overlap between locations of fin whale sightings and recordings and locations of 50Hz upswept calls in the central Scotia Sea, but these calls were most similar to calls attributed to blue whales in other parts of Antarctica. More study is required to determine if baleen whales produce these two call types, and if so, which species. The efficiency of acoustics and visual surveys varied by species, with blue whales being easier to detect using acoustics, Antarctic minke whales being best detected during visual surveys and other species falling in between these two extremes.

2004
Thiele, D, Chester ET, Moore SE, Širovic A, Hildebrand JA, Friedlaender A.  2004.  Seasonal variability in whale encounters in the Western Antarctic Peninsula. Deep-Sea Research II. 51:2311-2325.   10.1016/j.dsr2.2004.07.007   Abstract

Cetacean sighting surveys were conducted as part of nine multidisciplinary research cruises over late summer, autumn and winter of 2 years (2001–2003) during the Southern Ocean Global Ocean Ecosystems (SO GLOBEC) program. Seaice cover differed markedly between years, with apparent effects on cetacean distribution. No ice was present until late June in 2001, while the previous winter sea ice never fully retreated (>30% cover) during the 2002 or 2003 summer, thus increasing the proportion of thicker and more complex ice, including multi-year floes. Humpback (237 sightings; 537 individuals) and minke (103 sightings: 267 individuals) whales were the most commonly detected species. Data from seven comparable cruises were used to identify habitat for minke and humpback whales over five geographically distinct spatial divisions in the study area. In all years, both species were predominantly found in near coastal habitat, particularly in the fjords where complex habitat likely concentrated prey. In 2002 and 2003 the presence of sea ice provided additional feeding habitat, and the numbers of minkes (in winter) and humpbacks (late summer and autumn)
in the area doubled compared with 2001. Humpbacks in particular were concentrated at the ice boundaries during late summer and autumn, while minke numbers increased in the winter that followed and occupied ice-covered areas along the entire shelf edge. Important resource sites for these species are mainly located in near-coastal areas and are used in all years, but when ice margins exist and intersect with resource sites they attract much larger numbers of animals due to the dynamics between sea ice and prey.

Širović, A, Hildebrand JA, Wiggins SM, McDonald MA, Moore SE, Thiele D.  2004.  Seasonality of blue and fin whale calls and the influence of sea ice in the Western Antarctic Peninsula. Deep-Sea Research II. 51:2327-2344.   10.1016/j.dsr2.2004.08.005   Abstract

The calling seasonality of blue (Balaenoptera musculus) and fin (B. physalus) whales was assessed using acoustic data recorded on seven autonomous acoustic recording packages (ARPs) deployed from March 2001 to February 2003 in the Western Antarctic Peninsula. Automatic detection and acoustic power analysis methods were used for determining presence and absence of whale calls. Blue whale calls were detected year round, on average 177 days per year, with peak calling in March and April, and a secondary peak in October and November. Lowest calling rates occurred between June and September, and in December. Fin whale calling rates were seasonal with calls detected between February and June (on average 51 days/year), and peak calling in May. Sea ice formed a month later and retreated a month earlier in 2001 than in 2002 over all recording sites. During the entire deployment period, detected calls of both species of whales showed negative correlation with sea ice concentrations at all sites, suggesting an absence of blue and fin whales in areas covered with sea ice. A conservative density estimate of calling whales from the acoustic data yields 0.43 calling blue whales per 1000 nmi2 and1.30 calling fin whales per 1000 nmi2, which is about one-third higher than the density of blue whales and approximately equal to the density of fin whales estimated from the visual surveys.
(c) 2004 Elsevier Ltd. All rights reserved.