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Kate Stafford

Principal Oceanographer

Affiliate Associate Professor, Oceanography





Department Affiliation



2000-present and while at APL-UW

Effects of freshwater stratification on nutrients, dissolved oxygen, and phytoplankton in the Bay of Bengal

Sarma, V.V.S.S., et al., including K.M. Stafford," Effects of freshwater stratification on nutrients, dissolved oxygen, and phytoplankton in the Bay of Bengal," Oceanography 29, 222–231, doi:10.5670/oceanog.2016.54, 2016.

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1 Jun 2016

The Bay of Bengal (BoB) is strongly density stratified due to large freshwater input from various rivers and heavy precipitation. This strong vertical stratification, along with physical processes, regulates the transport and vertical exchange of surface and subsurface water, concentrating nutrients and intensifying the oxygen minimum zone (OMZ). Here, we use basinwide measurements to describe the spatial distributions of nutrients, oxygen, and phytoplankton within the BoB during the 2013 northeast monsoon (November–December). By the time riverine water reaches the interior bay, it is depleted in the nutrients nitrate and phosphate, but not silicate. Layering of freshwater in the northern BoB depresses isopycnals, leading to a deepening of the nutricline and oxycline. Oxygen concentrations in the OMZ are lowest in the north (<5 µM). Weak along-isopycnal nutrient gradients reflect along-isopycnal stirring between ventilated surface water and deep nutrient-replenished water. Picoplankton dominate the phytoplankton population in the north, presumably outcompeting larger phytoplankton species due to their low nutrient requirements. Micro- and nanoplankton numbers are enhanced in regions with deeper mixed layers and weaker stratification, where nutrient replenishment from subsurface waters is more feasible. These are also the regions where marine mammals were sighted. Physical processes and the temperature-salinity structure in the BoB directly influence the OMZ and the depth of the oxycline and nutricline, thereby affecting the phytoplankton and marine mammal communities.

Technological advancements in observing the upper ocean in the Bay of Bengal: Education and capacity building

Tandon, A., E.A. D’Asaro, K.M. Stafford, D. Sengupta, M. Ravichandran, M. Baumgartner, R. Venkatesan, and T. Paluszkiewicz, "Technological advancements in observing the upper ocean in the Bay of Bengal: Education and capacity building," Oceanography 29, 242–253, doi:10.5670/oceanog.2016.56, 2016.

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1 Jun 2016

Because the monsoon strongly affects India, there is a clear need for indigenous expertise in advancing the science that underlies monsoon prediction. The safety of marine transport in the tropics relies on accurate atmospheric and ocean environment predictions on weekly and longer time scales in the Indian Ocean. This need to better forecast the monsoon motivates the United States to advance basic research and support training of early career US scientists in tropical oceanography. Earlier Indian field campaigns and modeling studies indicated that an improved understanding of the interactions between the upper ocean and the atmosphere in the Bay of Bengal at finer spatial and temporal scales could lead to improved intraseasonal monsoon forecasts. The joint US Air-Sea Interactions Regional Initiative (ASIRI) and the Indian Ocean Mixing and Monsoon (OMM) program studied these interactions, resulting in scientific advances described by articles in this special issue of Oceanography. In addition to these scientific advances, and while also developing long-lasting collaborations and building indigenous Indian capability, a key component of these programs is training early career scientists from India and the United States. Training has been focusing on fine-scale and mixing studies of the upper ocean, air-sea interactions, and marine mammal research. Advanced methods in instrumentation, autonomous robotic platforms, experimental design, data analysis, and modeling have been emphasized. Students and scientists from India and the United States at all levels have been participating in joint cruises on Indian and US research vessels and in training participants in modern tools and methods at summer schools, at focused research workshops, and during research visits. Such activities are building new indigenous capability in India, training a new cadre of US scientists well versed in monsoon air-sea interaction, and forging strong links between Indian and US oceanographic institutions.

A review of blue whale studies from HARUphones in the Pacific

Stafford, K.M., "A review of blue whale studies from HARUphones in the Pacific," Listening in the Ocean, W.W.L. Au and M.O. Lammers, eds., 21-33 (Springer, 2016).

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3 Mar 2016

The earliest long-term monitoring of low-frequency signals of large whales was via cabled military arrays. These arrays provided valuable new data but were restricted in the locations that were monitored and there was no open access to the data collected. In order to monitor the low-frequency signals of large whales in different areas and over shorter time scales, Haruphones, single hydrophone, autonomous recording packages, were developed by the Pacific Marine Environmental Laboratory of the US National Oceanic and Atmospheric Administration and deployed in the Gulf of Alaska and the eastern tropical Pacific. By integrating the acoustic data from these broadly spaced deployments with other data streams, new discoveries about blue whales in the eastern Pacific Ocean were made. These included establishing the geographic range and migratory patterns of eastern north Pacific blue whales; establishing that the eastern tropical Pacific appears to be a blue whale "hot spot" where as many as four, but primarily three, acoustic populations of blue whales occur; determining that the Gulf of Alaska is a region where eastern and western North Pacific blue whales overlap in space and time; and showing that blue whale calling behavior has a diel pattern whereby animals produce more sounds at night than during the day. In aggregate, these data show that passive acoustic monitoring is a valuable tool for establishing blue whale population identity, determining habitat range, and studying behavioral ecology over long time periods and in remote regions of the ocean.

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A synthesis of year-round interdisciplinary mooring measurements in the Bering Strait (1990–2014) and the RUSALCA years (2004–2011)

Woodgate, R.A., K.M. Stafford, and F.G. Praha, "A synthesis of year-round interdisciplinary mooring measurements in the Bering Strait (1990–2014) and the RUSALCA years (2004–2011)," Oceanography, 28, 46-67, doi:10.5670/oceanog.2015.57, 2015.

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1 Sep 2015

The flow through the Bering Strait, the only Pacific-Arctic oceanic gateway, has dramatic local, regional, and global impacts. Advanced year-round moored technology quantifies challengingly large temporal (subdaily, seasonal, and interannual) and spatial variability in the ~85 km wide, two-channel strait. The typically northward flow, intensified seasonally in the ~10–20 km wide, warm, fresh, nutrient-poor Alaskan Coastal Current (ACC) in the east, is otherwise generally homogeneous in velocity throughout the strait, although with higher salinities and nutrients and lower temperatures in the west. Velocity and water properties respond rapidly (including flow reversals) to local wind, likely causing most of the strait's approximately two-layer summer structure (by "spilling" the ACC) and winter water-column homogenization. We identify island-trapped eddy zones in the central strait; changes in sea-ice properties (season mean thicknesses from <1 m to >2 m); and increases in annual mean volume, heat, and freshwater fluxes from 2001 to present (2013). Tantalizing first results from year-round bio-optics, nitrate, and ocean acidification sensors indicate significant seasonal and spatial change, possibly driven by the spring bloom. Moored acoustic recorders show large interannual variability in sub-Arctic whale occurrence, related perhaps to water property changes. Substantial daily variability demonstrates the dangers of interpreting section data and the necessity for year-round interdisciplinary time-series measurements.

A year in the acoustic world of bowhead whales in the Bering, Chukchi, and Beaufort Seas

Clark, C.W., C.L. Berchok, S.B. Blackwell, D.E. Hannay, J. Jones, D. Ponirakis, and K.M. Stafford, "A year in the acoustic world of bowhead whales in the Bering, Chukchi, and Beaufort Seas," Prog. Oceanogr., 136, 223-240, doi:10.1016/j.pocean.2015.05.007, 2015.

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1 Aug 2015

Bowhead whales, Balaena mysticetus, in the Bering-Chukchi-Beaufort (BCB) population, experience a variable acoustic environment among the regions they inhabit throughout the year. A total of 41,698 hours of acoustic data were recorded from 1 August 2009 through 4 October 2010 at 20 sites spread along a 2300 km transect from the Bering Sea to the southeast Beaufort Sea. These data represent the combined output from six research teams using four recorder types. Recorders sampled areas in which bowheads occur and in which there are natural and anthropogenic sources producing varying amounts of underwater noise. We describe and quantify the occurrence of bowheads throughout their range in the Bering, Chukchi, and Beaufort seas over a 14-month period by aggregating our acoustic detections of bowhead whale sounds. We also describe the spatial-temporal variability in the bowhead acoustic environment using sound level measurements within a frequency band in which their sounds occur, by dividing a year into three, 4-month seasons (Summer-Fall 2009, August - November 2009: Winter 2009-2010, December 2009 - March 2010: and Spring-Summer 2010, April - July 2010) and their home range into five zones. Statistical analyses revealed no significant relationship between acoustic occurrence, distance offshore, and water depth during Summer-Fall 2009, but there was a significant relationship during Spring-Summer 2010. A continuous period with elevated broadband sound levels lasting ca. 38 days occurred in the Bering Sea during the Winter 2009-2010 season as a result of singing bowheads, while a second period of elevated levels lasting at least 30 days occurred during the early spring-summer season as a result of singing bearded seals. The lowest noise levels occurred in the Chukchi Sea from the latter part of November into May. In late summer 2009 very faint sounds from a seismic airgun survey approximately 700 km away in the eastern Beaufort Sea were detected on Chukchi recorders. Throughout the year, but most obviously during this same November into May period, clusters of intermittent, nearly synchronized, high-level events were evident on multiple recorders hundreds of miles apart. In some cases, these clusters occurred over 2-5 day periods and appear to be associated with high wind conditions.

Acoustic monitoring and prey association for beluga whale, Delphinapterus leucas, and harbor porpoise, Phocoena phocoena, off two river mouths in Yakutat Bay, Alaska

Castellote, M., K.M. Stafford, A.D. Neff, and W. Lucey, "Acoustic monitoring and prey association for beluga whale, Delphinapterus leucas, and harbor porpoise, Phocoena phocoena, off two river mouths in Yakutat Bay, Alaska," Mar. Fish. Rev., 77, 1-10, doi:10.7755/MFR.77.1.1, 2015.

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1 Jul 2015

Little is known about the ecology of beluga whales, Delphinapterus leucas, and harbor porpoises, Phocoena phocoena, inhabiting Yakutat Bay, Alaska. Using passive, acoustic monitoring techniques, their year-round presence was monitored during June 2012–Mar. 2013 off the mouths of two glacial rivers: Esker Creek and Grand Wash. Fishery trawl transects were run in both areas during Mar.–Aug. 2013 to assess fish and invertebrate diversity and to identify potential beluga and harbor porpoise prey. Results supported year-round presence for both species, with restricted home range for beluga and a wider distribution for porpoise. Opposite diel patterns in beluga and harbor porpoise presence suggest potential competitive overlap in prey between species. Based on trawl abundance and ubiquity, several fish and crustacean species were identifi ed as potential prey for beluga and harbor porpoise. Results support the belief that shrimp, crab, and mysids may be an important part of beluga and porpoise diet in Yakutat. Both river mouth areas are used by harbor porpoises but their seasonality might not be driven solely by prey diversity or abundance. Beluga detection results during a coho salmon, Oncorhynchus kisutch, run were indicative of predation by belugas on this species during their spawning migration. This pilot study demonstrates the utility of remote, passive acoustic monitoring technology to better understand the seasonal distribution patterns and prey association of beluga and harbor porpoise in Yakutat Bay.

Song sharing and diversity in the Bering-Chukchi-Beaufort population of bowhead whales (Balaena mysticetus), spring 2011

Johnson, H.D., K.M. Stafford, J.C. George, W.G. Ambrose, Jr., and C.W. Clark, "Song sharing and diversity in the Bering-Chukchi-Beaufort population of bowhead whales (Balaena mysticetus), spring 2011," Mar. Mammal Sci., 31, 902-922, doi:10.1111/mms/12196, 2015.

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1 Jul 2015

Bowhead whales (Balaena mysticetus) of the Bering-Chukchi-Beaufort population migrate in nearshore leads through the Chukchi Sea each spring to summering grounds in the Beaufort Sea. As part of a population abundance study, hydrophones were deployed in the Chukchi Sea off Point Barrow, (12 April to 27 May 2011) and in the Beaufort Sea (12 April to 30 June 2011). Data from these sites were analyzed for the presence of bowhead whale song. We identified 12 unique song types sung by at least 32 individuals during ~95 h of recordings off Point Barrow. Six of these songs were detected at the Beaufort MARU site as well as six additional song types that were not analyzed. These results suggest a shared song repertoire among some individuals. This report represents the greatest number of songs to date during the spring migration for this population. We attribute this greater variety to population growth over the 30 yr since acoustic monitoring began in the early 1980s. Singing during early to mid-spring is consistent with the hypothesis that song is a reproductive display, but further research is necessary to understand the exact function of this complex vocal behavior.

Traditional knowledge and historical and opportunistic sightings of beluga whales, Delphinapterus leucas, in Yakutat Bay, Alaska, 1938–2013

Lucey, W.G., E. Henniger, E. Abraham, G. O'Corry-Crowe, K.M. Stafford, and M. Castellote, "Traditional knowledge and historical and opportunistic sightings of beluga whales, Delphinapterus leucas, in Yakutat Bay, Alaska, 1938–2013," Mar. Fish. Rev., 77, 41-46, do:10.7755/MFR.77.1.4, 2015.

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1 Jul 2015

A total of 76 confirmed sighting events of beluga whales, Delphinapterus leucas, were gathered from 1938 to 2013 in Yakutat Bay, Alaska. The sightings were a mix of incidental observations from airplane pilots and commercial fishermen as well as directed ground and aerial surveys. The earliest sightings are anecdotal, with the fi rst known observation recalled from the summer of 1938. Throughout the observation period the average group sighting
was 6 whales with a low of 1 animal and an estimated high of 26 animals. Overall, there is little traditional or historical knowledge about the Yakutat Bay belugas, including whether they were a hunted species. However, the study revealed the existence of the local name for belugas %u201CKuyeedaayee%u201D (skin under the stars), which was either of Tlingit origin or, possibly, from the now extinct Eyak language. The fact that there is a Tlingit/Eyak name for the animals supports the theory, and the genetic evidence, that they have inhabited Yakutat Bay for longer than the sighting record indicates. This report includes four summaries of observations from local residents who are most knowledgeable about Yakutat Bay.

The relationship between sea ice concentration and the spatio-temporal distribution of vocalizing bearded seals (Erignathus barbatus) in the Bering, Chukchi, and Beaufort Seas from 2008 to 2011

Macintyre, K.Q., K.M. Stafford, P.B. Conn, K.L. Laidre, and P.L. Boveng, "The relationship between sea ice concentration and the spatio-temporal distribution of vocalizing bearded seals (Erignathus barbatus) in the Bering, Chukchi, and Beaufort Seas from 2008 to 2011," Prog. Oceanogr., 136, 241-249, doi:10.1016/j.pocean.2015.05.008, 2015.

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26 May 2015

Bearded seals (Erignathus barbatus) are widely distributed in the Arctic and sub-Arctic; the Beringia population is found throughout the Bering, Chukchi and Beaufort Seas (BCB). Bearded seals are highly vocal, using underwater calls to advertise their breeding condition and maintain aquatic territories. They are also closely associated with pack ice for reproductive activities, molting, and resting. Sea ice habitat for this species varies spatially and temporally throughout the year due to differences in underlying physical and oceanographic features across its range. To test the hypothesis that the vocal activity of bearded seals is related to variations in sea ice, passive acoustic data were collected from nine locations throughout the BCB from 2008 to 2011. Recording instruments sampled on varying duty cycles ranging from 20% to 100% of each hour, and recorded frequencies up to 8192 Hz. Spectrograms of acoustic data were analyzed manually to calculate the daily proportion of hours with bearded seal calls at each sampling location, and these call activity proportions were correlated with daily satellite-derived estimates of sea ice concentration. Bearded seals were vocally active nearly year-round in the Beaufort and Chukchi Seas with peak activity occurring from mid-March to late June during the mating season. The duration of call activity in the Bering Sea was shorter, lasting typically only five months, and peaked from mid-March to May at the northernmost recorders. In all areas, call activity was significantly correlated with higher sea ice concentrations (p < 0.01). These results suggest that losses in ice cover may negatively impact bearded seals, not just by loss of habitat but also by altering the behavioral ecology of the BCB population.

Sources and levels of ambient ocean sound near the Antarctic peninsula

Dziak, R.P., et al. including K.M. Stafford, "Sources and levels of ambient ocean sound near the Antarctic peninsula," Plos One, 10, e0123425, do:10.1371/journal.pone.0123425, 2015.

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14 Apr 2015

Arrays of hydrophones were deployed within the Bransfield Strait and Scotia Sea (Antarctic Peninsula region) from 2005 to 2009 to record ambient ocean sound at frequencies of up to 125 and 500 Hz. Icequakes, which are broadband, short duration signals derived from fracturing of large free-floating icebergs, are a prominent feature of the ocean soundscape. Icequake activity peaks during austral summer and is minimum during winter, likely following freeze-thaw cycles. Iceberg grounding and rapid disintegration also releases significant acoustic energy, equivalent to large-scale geophysical events. Overall ambient sound levels can be as much as ~10–20 dB higher in the open, deep ocean of the Scotia Sea compared to the relatively shallow Bransfield Strait. Noise levels become lowest during the austral winter, as sea-ice cover suppresses wind and wave noise. Ambient noise levels are highest during austral spring and summer, as surface noise, ice cracking and biological activity intensifies. Vocalizations of blue (Balaenoptera musculus) and fin (B. physalus) whales also dominate the long-term spectra records in the 15–28 and 89 Hz bands. Blue whale call energy is a maximum during austral summer-fall in the Drake Passage and Bransfield Strait when ambient noise levels are a maximum and sea-ice cover is a minimum. Fin whale vocalizations were also most common during austral summer-early fall months in both the Bransfield Strait and Scotia Sea. The hydrophone data overall do not show sustained anthropogenic sources (ships and airguns), likely due to low coastal traffic and the typically rough weather and sea conditions of the Southern Ocean.

Seasonal occurrence of southeast Pacific blue whale songs in southern Chile and the eastern tropical Pacific

Buchan, S.J., K.M. Stafford, and R. Hucke-Gaete, "Seasonal occurrence of southeast Pacific blue whale songs in southern Chile and the eastern tropical Pacific," Mar. Mammal Sci., 31, 440-458, doi:10.1111/mms.12173, 2015.

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1 Apr 2015

Passive acoustic data were collected January 2012 to April 2013 at four sites in the Chiloense Ecoregion (CER) in southern Chile (~43°S – 44°S, 71°W – 73°W) and 1996–2002 from one site in the eastern tropical Pacific (ETP) (8°S, 95°W). Automatic detectors were used to detect the two songs (SEP1 and SEP2) described for southeast Pacific (SEP) blue whales. There was a strong seasonal pattern of occurrence of SEP songs in the CER from December to August, peaking March to May. In the ETP, the occurrence of songs was an order of magnitude lower but songs were present year-round, with a peak around June. These findings support austral summer/autumn seasonal residency in the CER and a seasonal movement of blue whales towards the ETP during June/July, returning in December. Interannual differences in the ETP were possibly linked to the 1997 – 1998 El Nino event. At both study sites, SEP2 was significantly more common than SEP1; both songs largely followed the same temporal trends. These findings contribute to our understanding of the seasonal movements of endangered SEP blue whales and can inform conservation strategies, particularly in the CER coastal feeding ground. We recommend future year-round passive acoustic studies in the CER and the ETP (e.g., near the Galapagos Islands), ideally coupled with oceanographic data.

Multipurpose acoustic networks in the integrated Arctic Ocean observing system

Mikhalevsky, P.N., H. Sagen, P.F. Worcester, A.B. Baggeroer, J. Orcutt, S.E. Moore, C.M. Lee, J. Vigness-Raposa, L. Freitag, M. Arrott, K. Atakan, A. Beszczynska-Moller, T.F. Duda, B.D. Dushaw, J.C. Gascard, A.N. Gavrilov, H. Keers, A.K. Morozov, W.H. Munk, M. Rixen, S. Sandven, E. Skarsoulis, K.M. Stafford, F. Vernon, and M.Y. Yuen, "Multipurpose acoustic networks in the integrated Arctic Ocean observing system," Arctic, 68, 5 (Suppl. 1), doi:10.14430/arctic4449, 2015.

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1 Jan 2015

The dramatic reduction of sea ice in the Arctic Ocean will increase human activities in the coming years. This activity will be driven by increased demand for energy and the marine resources of an Arctic Ocean accessible to ships. Oil and gas exploration, fisheries, mineral extraction, marine transportation, research and development, tourism, and search and rescue will increase the pressure on the vulnerable Arctic environment. Technologies that allow synoptic in situ observations year-round are needed to monitor and forecast changes in the Arctic atmosphere-ice-ocean system at daily, seasonal, annual, and decadal scales. These data can inform and enable both sustainable development and enforcement of international Arctic agreements and treaties, while protecting this critical environment. In this paper, we discuss multipurpose acoustic networks, including subsea cable components, in the Arctic. These networks provide communication, power, underwater and under-ice navigation, passive monitoring of ambient sound (ice, seismic, biologic, and anthropogenic), and acoustic remote sensing (tomography and thermometry), supporting and complementing data collection from platforms, moorings, and vehicles. We support the development and implementation of regional to basin-wide acoustic networks as an integral component of a multidisciplinary in situ Arctic Ocean observatory.

Seasonal migrations of North Atlantic minke whales: Novel insights from large-scale passive acoustic monitoring networks

Risch, D., et al., including K. Stafford, "Seasonal migrations of North Atlantic minke whales: Novel insights from large-scale passive acoustic monitoring networks," Movement Ecol., 2, doi:10.1186/s40462-014-0024-3, 2014.

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18 Nov 2014

Little is known about migration patterns and seasonal distribution away from coastal summer feeding habitats of many pelagic baleen whales. Recently, large-scale passive acoustic monitoring networks have become available to explore migration patterns and identify critical habitats of these species. North Atlantic minke whales (Balaenoptera acutorostrata) perform seasonal migrations between high latitude summer feeding and low latitude winter breeding grounds. While the distribution and abundance of the species has been studied across their summer range, data on migration and winter habitat are virtually missing.

Acoustic recordings, from 16 different sites from across the North Atlantic, were analyzed to examine the seasonal and geographic variation in minke whale pulse train occurrence, infer information about migration routes and timing, and to identify possible winter habitats.

Acoustic detections show that minke whales leave their winter grounds south of 30°N from March through early April. On their southward migration in autumn, minke whales leave waters north of 40°N from mid-October through early November. In the western North Atlantic spring migrants appear to track the warmer waters of the Gulf Stream along the continental shelf, while whales travel farther offshore in autumn. Abundant detections were found off the southeastern US and the Caribbean during winter. Minke whale pulse trains showed evidence of geographic variation, with longer pulse trains recorded south of 40°N. Very few pulse trains were recorded during summer in any of the datasets.

This study highlights the feasibility of using acoustic monitoring networks to explore migration patterns of pelagic marine mammals. Results confirm the presence of minke whales off the southeastern US and the Caribbean during winter months. The absence of pulse train detections during summer suggests either that minke whales switch their vocal behaviour at this time of year, are absent from available recording sites or that variation in signal structure influenced automated detection. Alternatively, if pulse trains are produced in a reproductive context by males, these data may indicate their absence from the selected recording sites. Evidence of geographic variation in pulse train duration suggests different behavioural functions or use of these calls at different latitudes.

Glider-based passive acoustic monitoring in the Arctic

Baumgartner, M.F., K.M. Stafford, P. Winsor, H. Statscewich, and D.M. Fratantoni, "Glider-based passive acoustic monitoring in the Arctic," Mar. Technol. Soc. J., 48, 40-51, 2014.

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1 Sep 2014

Persistently poor weather in the Arctic makes traditional marine mammal research from aircraft and ships difficult, yet collecting information on marine mammal distribution and habitat utilization is vital for understanding the impact of climate change on Arctic ecosystems. Moreover, as industrial use of the Arctic increases with the expansion of the open-water summer season, there is an urgent need to monitor the effects of noise from oil and gas exploration and commercial shipping on marine mammals. During September 2013, we deployed a single Slocum glider equipped with a digital acoustic monitoring (DMON) instrument to record and process in situ low-frequency (<5 kHz) audio to characterize marine mammal occurrence and habitat as well as ambient noise in the Chukchi Sea off the northwest coast of Alaska, USA. The DMON was programmed with the low-frequency detection and classification system (LFDCS) to autonomously detect and classify sounds of a variety of Arctic and sub-Arctic marine mammal species. The DMON/LFDCS reported regularly in near real time via Iridium satellite detailed detection data, summary classification information, and spectra of background noise. The spatial distributions of bowhead whale, bearded seal, and walrus call rates were correlated with surface salinity measured by the glider. Bowhead whale and walrus call rates were strongly associated with a warmand salty watermass of Bering Sea origin. With a passive acoustic capability that allows both archival recording and near real-time reporting,we envision ocean gliderswill become a standard tool for marine mammal and ocean noise research and monitoring in the Arctic.

Estimating historical eastern North Pacific blue whale catches using spatial calling patterns

Monnahan, C.C., T.A. Branch, K.M. Stafford, Y.V. Ivashchenko, and E.M. Oleson, "Estimating historical eastern North Pacific blue whale catches using spatial calling patterns," PLOS ONE, doi:10.1371/journal.pone.0098974, 2014.

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3 Jun 2014

Blue whales (Balaenoptera musculus) were exploited extensively around the world and remain endangered. In the North Pacific their population structure is unclear and current status unknown, with the exception of a well-studied eastern North Pacific (ENP) population. Despite existing abundance estimates for the ENP population, it is difficult to estimate pre-exploitation abundance levels and gauge their recovery because historical catches of the ENP population are difficult to separate from catches of other populations in the North Pacific. We collated previously unreported Soviet catches and combined these with known catches to form the most current estimates of North Pacific blue whale catches. We split these conflated catches using recorded acoustic calls from throughout the North Pacific, the knowledge that the ENP population produces a different call than blue whales in the western North Pacific (WNP). The catches were split by estimating spatiotemporal occurrence of blue whales with generalized additive models fitted to acoustic call patterns, which predict the probability a catch belonged to the ENP population based on the proportion of calls of each population recorded by latitude, longitude, and month. When applied to the conflated historical catches, which totaled 9,773, we estimate that ENP blue whale catches totaled 3,411 (95% range 2,593 to 4,114) from 1905–1971, and amounted to 35% (95% range 27% to 42%) of all catches in the North Pacific. Thus most catches in the North Pacific were for WNP blue whales, totaling 6,362 (95% range 5,659 to 7,180). The uncertainty in the acoustic data influence the results substantially more than uncertainty in catch locations and dates, but the results are fairly insensitive to the ecological assumptions made in the analysis. The results of this study provide information for future studies investigating the recovery of these populations and the impact of continuing and future sources of anthropogenic mortality.

Marine mammal conservation and the role of research

Stafford, K.M., and M.F. Baumgartner, "Marine mammal conservation and the role of research," Current Conservation, 8, 18-25, 2014.

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1 Jun 2014

The tools and methods used to study marine mammals should be dictated by the research and conservation questions that need to be answered and the resources available to do so (from funding to ship time). Where very little is known about the community composition within a country's exclusive economic zone, a series of shipboard based visual surveys might be the best way to obtain baseline information on geographic and seasonal abundance of multiple species.

A new song recorded from blue whales in the Corcovado Gulf, Southern Chile, and an acoustic link to the Eastern Tropical Pacific

Buchan, S.J., R. Hucke-Gaete, L. Rendell, and K.M. Stafford, "A new song recorded from blue whales in the Corcovado Gulf, Southern Chile, and an acoustic link to the Eastern Tropical Pacific," Endang. Species Res., 23, 241-252, doi:10.3354/esr00566, 2014.

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24 Mar 2014

The identity, distribution and movements of blue whales Balaenoptera musculus that forage in the Chiloense Ecoregion in Southern Chile remain unclear. Studies of blue whale songs have identified acoustic populations with distinct song types, geographic ranges, migration routes and seasonal residencies%u2014information that is relevant to the conservation of this endangered species. Here, we characterized the song sequences of blue whales that use the Corcovado Gulf based on dipping hydrophone recordings from 3 austral summer field seasons (2008, 2009, 2011), and compare these data to previously described song types for the Southeast Pacific (SEP) in order to better understand meso-scale (versus basin-scale) variation in blue whale song. Two distinct songs, SEP1 and SEP2, emerged from our analysis. Neither of these songs is used by Antarctic blue whales. Although SEP1 was the first song recorded in the Corcovado Gulf area in 1970, we found SEP2 to be the more common song, despite never having been reported previously in this area. Our report of SEP2 adds a new song to the current description of the SEP blue whale repertoire. Our recording of SEP1 reaffirms the acoustic link already established between Chile and the Eastern Tropical Pacific (ETP); our recording of SEP2 establishes a new acoustic link for this song between Chile and the ETP. These findings provide the basis for future passive acoustic studies on the temporal and spatial distributions of endangered SEP blue whales and for understanding how these songs relate to the population structure.

Sounds in the ocean at 1–100 Hz

Wilcock, W.S.D., K.M. Stafford, R.K. Andrew, and R.I. Odom, "Sounds in the ocean at 1–100 Hz," Ann. Rev. Mar. Sci., 6, 117-140, doi:10.1146/annurev-marine-121211-172423, 2014.

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1 Jan 2014

Very-low-frequency sounds between 1 and 100 Hz propagate large distances in the ocean sound channel. Weather conditions, earthquakes, marine mammals, and anthropogenic activities influence sound levels in this band. Weather-related sounds result from interactions between waves, bubbles entrained by breaking waves, and the deformation of sea ice. Earthquakes generate sound in geologically active regions, and earthquake T waves propagate throughout the oceans. Blue and fin whales generate long bouts of sounds near 20 Hz that can dominate regional ambient noise levels seasonally. Anthropogenic sound sources include ship propellers, energy extraction, and seismic air guns and have been growing steadily. The increasing availability of long-term records of ocean sound will provide new opportunities for a deeper understanding of natural and anthropogenic sound sources and potential interactions between them.

Subarctic cetaceans in the southern Chukchi Sea: Evidence of recovery or response to a changing ecosystem

Clarke, J., K. Stafford, S.E. Moore, B. Rone, L. Aerts, and J. Crance, "Subarctic cetaceans in the southern Chukchi Sea: Evidence of recovery or response to a changing ecosystem," Oceanography, 26, 136-149, doi:10.5670/oceanog.2013.81, 2013.

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1 Dec 2013

The southern Chukchi Sea is one of the most productive areas in the world ocean. Over the past decade, there have been dramatic changes in this region in sea ice cover and in Bering Strait inflow, and it is now in the path of transpolar shipping and destinational ship traffic, including vessels supporting Arctic offshore oil and gas development and tourism, all of which are anticipated to increase with decreasing seasonal sea ice cover. Little research on cetaceans has been conducted in the southern Chukchi Sea, and most information on the occurrence of subarctic species (humpback whale Megaptera novaeangliae, fin whale Balaenoptera physalus, minke whale B. acutorostrata, and killer whale Orcinus orca) comes from the ships' logs of commercial whalers in the mid to late twentieth century and from observers stationed along the Chukotka Peninsula. Information on cetacean seasonal occurrence east of the International Date Line (IDL) in US waters is particularly scarce.

To address this information gap, we compiled visual sightings and acoustic detections of subarctic cetaceans in the southern Chukchi Sea during summer and early autumn from 2009 to 2012. Humpback whales were common on both sides of the IDL in August and September. Fin and minke whales were widely distributed east of the IDL from July to September, and killer whales were seen sporadically but were the most widely dispersed of the four species. Comparisons of our results with historical records indicate that the incidence of subarctic cetaceans may be increasing in the southern Chukchi Sea. An increase in occurrence may simply be a post-commercial whaling recovery of whale numbers and seasonal range by each species, or it may reflect responses to ongoing climate change. Understanding current stock identity, spatial and temporal distribution, habitat preference, relative abundance, and potential impacts of climate change on these species will require cetacean-focused research in this region of the Arctic.

Towards collective circum-Antarctic passive acoustic monitoring: The Southern Ocean Hydrophone Network (SOHN)

van Opzeeland, I., F. Samaran, K.M. Stafford, K. Findlay, J. Gedamke, D. Harris, and B.S. Miller, "Towards collective circum-Antarctic passive acoustic monitoring: The Southern Ocean Hydrophone Network (SOHN)," Polarforschung, 83, 47-61, 2013.

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1 Dec 2013

The Southern Ocean Research Partnership (SORP) is an international research program initiated within the International Whaling Commission (IWC) in 2009 to promote collaborative cetacean research, develop novel research techniques, and conduct non-lethal research on whales in the Southern Ocean (CHILDERHOUSE 2009). One of the original research projects of the SORP is the Blue and Fin Whale Acoustic Trends Project, which aims to implement a long term passive acoustic research program to examine trends in Antarctic blue (Balaenoptera musculus intermedia) and fin whale (B. physalus) abundance, distribution, and seasonal presence in the Southern Ocean through the use of a network of passive acoustic recorders: the Southern Ocean Hydrophone Network (SOHN).

Seasonal and geographic variation of southern blue whale subspecies in the Indian Ocean

Samaran, F., K.M. Stafford, T.A. Branch, J. Gedamke, J.-Y. Royer, R.P. Dziak, and C. Guinet, "Seasonal and geographic variation of southern blue whale subspecies in the Indian Ocean," Plos One, 8, e71561, doi:10.1371/journal.pone.0071561, 2013.

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13 Aug 2013

Understanding the seasonal movements and distribution patterns of migratory species over ocean basin scales is vital for appropriate conservation and management measures. However, assessing populations over remote regions is challenging, particularly if they are rare. Blue whales (Balaenoptera musculus spp) are an endangered species found in the Southern and Indian Oceans. Here two recognized subspecies of blue whales and, based on passive acoustic monitoring, four "acoustic populations" occur. Three of these are pygmy blue whale (B.m. brevicauda) populations while the fourth is the Antarctic blue whale (B.m. intermedia). Past whaling catches have dramatically reduced their numbers but recent acoustic recordings show that these oceans are still important habitat for blue whales. Presently little is known about the seasonal movements and degree of overlap of these four populations, particularly in the central Indian Ocean. We examined the geographic and seasonal occurrence of different blue whale acoustic populations using one year of passive acoustic recording from three sites located at different latitudes in the Indian Ocean. The vocalizations of the different blue whale subspecies and acoustic populations were recorded seasonally in different regions. For some call types and locations, there was spatial and temporal overlap, particularly between Antarctic and different pygmy blue whale acoustic populations. Except on the southernmost hydrophone, all three pygmy blue whale acoustic populations were found at different sites or during different seasons, which further suggests that these populations are generally geographically distinct. This unusual blue whale diversity in sub-Antarctic and sub-tropical waters indicates the importance of the area for blue whales in these former whaling grounds.

Year-round acoustic detection of bearded seals (Erignathus barbatus) in the Beaufort Sea relative to changing environmental conditions, 2008–2010

MacIntyre, K.Q., K.M. Stafford, C.L. Berchok, and P.L. Boveng, "Year-round acoustic detection of bearded seals (Erignathus barbatus) in the Beaufort Sea relative to changing environmental conditions, 2008–2010," Polar Biol., 36, 1161-1173, doi:10.1007/s00300-013-1337-1, 2013.

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1 May 2013

Bearded seals (Erignathus barbatus) are pan-Arctic pinnipeds that are often seen in association with pack ice, and are known for their long, loud trills, produced underwater primarily in the spring. Acoustic recordings were collected from August 2008 to August 2010 at two locations and a single year (2008–2009) at a third location, in the western Beaufort Sea. Three recorders in 2008–2009 had a 30% duty cycle and a bandwidth of 10–4,096 Hz. One recorder in 2009–2010 had a 45% duty cycle and a bandwidth of 10–4,096 Hz and the second had a 20% duty cycle and bandwidth of 10–8,192 Hz. Spectrograms of acoustic data were examined for characteristic patterns of bearded seal vocalizations. For each recorder, the number of hours per day with vocalizations was compared with in situ water temperature and satellite-derived daily sea ice concentrations. At all sites, bearded seals were vocally active year-round. Call activity escalated with the formation of pack ice in the winter and the peak occurred in the spring, coinciding with mating season and preceding breakup of the sea ice. There was a change in the timing of seasonal sea ice formation and retreat between the two consecutive years that was reflected in the timing of peak bearded seal call activity. This study provides new information on fall and winter bearded seal vocal behavior and the relationship between year-round vocal activity and changes in annual sea ice coverage and in situ water temperature.

Monitoring white whales (Delphinapterus leucas) with echolocation loggers

Castellote, M., R.H. Leeney, G. O'Corry-Crowe, R. Lauhakangas, K.M. Kovacs, W. Lucey, V. Krasnova, C. Lydersen, K.M. Stafford, and R. Belikov, "Monitoring white whales (Delphinapterus leucas) with echolocation loggers," Polar Biol., 36, 493-509, doi:10.1007/s00300-012-1276-2, 2013.

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1 Apr 2013

Monitoring programmes for white whales (Delphinapterus leucas) have been called for repeatedly in recent years because this species is likely to be negatively impacted by climate change, but also because such a broadly dispersed, high trophic feeder can serve as an effective ecosystem sentinel. Arctic ecosystems are difficult to monitor because of the extensive winter ice coverage and extreme environmental conditions in addition to low human population densities. However, passive acoustic monitoring has proved to be a reliable method to remotely survey the presence of some marine mammals in the Arctic. In this study, we evaluate the potential use of echolocation loggers (T-POD and C-POD, Chelonia Ltd.) for remote monitoring of white whales. Captive experiments and open water surveys in three arctic/subarctic habitats (ice-noise-dominated environment, ice-free environment and low-turbidity waters) were used to document detection performance and to explore the use of logger angle and inter-click interval data to look at activity patterns and tidal influences on space use. When acoustic results were compared to concurrent visual observations, echolocation detection was only attributed to periods of white whale presence near the recorder deployment sites. Both T-PODs and C-PODs effectively detected echolocation, even under noisy ice. Diel and tidal behavioural patterns were identified. Acoustically identified movement patterns between sites were visually confirmed. This study demonstrates the feasibility of monitoring white whales using echolocation loggers and describes some important features of their behaviour as examples of the potential application of this passive acoustic monitoring method in Arctic and subarctic regions.

Correlation of a strong Alaska Coastal Current with the presence of beluga whales Delphinapterus leucas near Barrow, Alaska

Stafford, K.M., S.R. Okkonen, and J.T. Clarke, "Correlation of a strong Alaska Coastal Current with the presence of beluga whales Delphinapterus leucas near Barrow, Alaska," Mar. Ecol. Prog. Ser., 474, 287-297, doi:10.3354/meps10076, 2013.

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31 Jan 2013

Oceanographic features and physical processes in the ocean can create regions where prey, and therefore predators, may accumulate. Beluga whales Delphinapterus leucas are the most numerous cetacean in the Arctic. In the Alaskan Beaufort Sea, they prefer continental slope habitat in summer and autumn, presumably because such areas provide enhanced foraging opportunities. Passive acoustic detections of beluga whale calls, current velocity measurements, historical wind records, and 29 yr of beluga whale observations from aerial surveys were used to explore the hypothesis that the foraging success of beluga whales in Barrow Canyon and along the western Beaufort Sea slope is enhanced when the Alaska Coastal Current (ACC) is well-developed and flows east-northeastward and is diminished when the flow of the ACC and its shelf break extension are reversed. Aerial sightings of beluga whales, average observed beluga whale group size, and hours with whale vocalizations were more common when the ACC was well-developed and flowed east-northeastward. When the ACC flow is strong, it is separated from Arctic basin waters by a well-defined front that promotes aggregation of prey species. We speculate that the greater numbers of animals per group sighted and hours with recorded vocalizations may be indicative of enhanced foraging opportunities for beluga whales.

Spitsbergen's endangered bowhead whales sing through the polar night

Stafford, K.M., S.E. Moore, C.L. Berchok, Ø Wiig, C. Lydersen, E. Hansen, D. Kalmbach, and K.M. Kovacs, "Spitsbergen's endangered bowhead whales sing through the polar night," Endang. Species Res., 18, 95-103, doi:10.3354/esr00444, 2012.

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31 Jul 2012

Bowhead whales Balaena mysticetus are long-lived cetaceans, uniquely adapted among the baleen whales to live year-round in the Arctic. All bowhead whale populations were greatly reduced by commercial whaling from the 1600s through the 1800s, with the largest, the Spitsbergen population in the North Atlantic, depleted to the point of extinction. Recent sightings of bowhead whales west of Svalbard precipitated an effort to listen for their vocalizations via 2 recorders deployed in 2008 on oceanographic moorings spaced 95 km apart at 78.8° N latitude in the Fram Strait. Year-round acoustic records were examined for the occurrence of bowhead whale sounds. Simple calls, call sequences, and complex songs were recorded. Repeated call sequences or bowhead whale songs were detected nearly every hour from early November 2008 through late April 2009 on the western Fram Strait recorder. More than 60 unique songs were recorded from October 2008 to April 2009. In contrast, simple calls and call sequences were the most common signals recorded on the central Fram Strait instrument. Peak levels of song production coincided with the period of lowest water temperature, dense ice concentration, and almost complete darkness. Given the diversity, loudness, and period over which songs were recorded, western Fram Strait appears to be a wintering ground — and potentially a mating area — for this critically endangered population of bowhead whales.

First acoustic recordings of narwhals (Monodon monoceros) in winter

Stafford, K.M., K.L. Laidre and M.P. Heide-Jørgensen, "First acoustic recordings of narwhals (Monodon monoceros) in winter," Mar. Mammal Sci., 28, E197-E207, doi:10.1111/j.1748-7692.2011.00500.x, 2012.

1 Apr 2012

Comparing marine mammal acoustic habitats in Atlantic and Pacific sectors of the High Arctic: year-long records from Fram Strait and the Chukchi Plateau

Moore, S.E., K.M. Stafford, H. Melling, C. Berchok, Ø. Wiig, K.M. Kovacs, C. Lydersen, and J.Richter-Menge, "Comparing marine mammal acoustic habitats in Atlantic and Pacific sectors of the High Arctic: year-long records from Fram Strait and the Chukchi Plateau," Polar Biol., 35, 475-480, doi: 10.1007/s00300-011-1086-y, 2012.

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1 Mar 2012

During the International Polar Year (IPY), acoustic recorders were deployed on oceanographic moorings in Fram Strait and on the Chukchi Plateau, representing the first coordinated year-round sampling of underwater acoustic habitats at two sites in the High Arctic. Examination of species-specific marine mammal calls recorded from autumn 2008–2009 revealed distinctly different acoustic habitats at each site. Overall, the Fram Strait site was acoustically complex compared with the Chukchi Plateau site.

In Fram Strait, calls from bowhead whales (Balaena mysticetus) and a variety of toothed whales (odontocetes) were recorded year-round, as were airgun pulses from seismic surveys. In addition, calls from blue whales (Balaenoptera musculus) and fin whales (B. physalus) were recorded from June to October and August to March, respectively. Conversely, at the Chukchi Plateau site, beluga (Delphinapterus leucas) and bowhead whale calls were recorded primarily from May to August, with airgun signals detected only in September–October. Ribbon seal (Phoca fasciata) calls were detected in October–November, with no marine mammals calls at all recorded from December to February. Of note, ice-adapted bearded seals (Erignathus barbatus) were recorded at both sites, primarily in spring and summer, corresponding with the mating season for that species.

Differences in acoustic habitats between the two sites were related to contrasts in sea ice cover, temperature, patterns of ocean circulation and contributions from anthropogenic noise sources. These data provide a provisional baseline for the comparison of underwater acoustic habitats between Pacific and Atlantic sectors of the High Arctic.

Seasonal detection of three types of 'pygmy' blue whale calls in the Indian Ocean

Stafford, K. M., E. Chapp, D.R. Bohnenstiel, and M. Tolstoy, "Seasonal detection of three types of 'pygmy' blue whale calls in the Indian Ocean," Mar. Mammal Sci., 27, 828-840, doi: 10.1111/j.1748-7692.2010.00437.x, 2011.

1 Oct 2011

Listening to marine mammals at basin to local scales

Moore, S.E., S.M. Van Parijs, B.L. Southall, and K.M. Stafford, "Listening to marine mammals at basin to local scales," J. Acoust. Soc. Am., 129, 2371, doi:10.1121/1.3587678, 2011.

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1 Apr 2011

The successful use of SOSUS to track broad-scale occurrence patterns in whale calls during the second half of the 20th century fostered the development of autonomous recorders that can be deployed virtually anywhere in the world ocean. Over the past decade, data from these recorders have provided dramatic insights to marine mammal ecology. Patterns of call reception have demonstrated the near year-round occurrence of some baleen whale species in Arctic and Antarctic waters, a discovery that challenges long-held assumptions about the phenology of seasonal migrations. Integration of year-long calling records with physical oceanographic measures at mooring-based ocean observatories provides a means to include large whales in ecosystem-based models. The reception of anthropogenic sounds on nearly all recorders, whether deployed in coastal or remote areas, emphasizes the need to develop regional "soundscapes" based upon integrative sampling and analytical protocols. Examples from several long-term research programs will be provided as the basis for the strong assertion that passive acoustic observation of marine mammals is a vital component of any ocean observing system. Opportunities for future collaborations and the challenges of data management and access will be discussed.

Singing behavior of fin whales in the Davis Strait with implications for mating, migration and foraging

Simon, M., K.M. Stafford, K. Beedholm, C.M. Lee, and P.T. Madsen, "Singing behavior of fin whales in the Davis Strait with implications for mating, migration and foraging," J. Acoust. Soc. Am., 128, 3200-3210, doi:10.1121/1.3495946, 2010.

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1 Nov 2010

Most baleen whales undertake migrations between low-latitude breeding grounds and high-latitude feeding grounds. Though little is known about the timing of their migration from the Arctic, fin whales are assumed to undertake a similar migratory pattern. To address questions about habitat use and migrations, the acoustic activity of fin whales in Davis Strait, between Greenland and Canada, was monitored continuously for two years using three bottom-moored acoustic recorders.

The acoustic power in the fin whale call frequencies peaked in November–December, showing that fin whales are present in Davis Strait much later in the year than previously expected. The closely timed peaks in song activity and conception time imply that not all fin whales migrate south to mate, but rather start mating at high latitudes rather than or before migrating. Singing activity was strongly linked to daylight hours, suggesting that fin whales might feed during the few daylight hours of the late fall and early Arctic winter. A negative correlation between the advancing sea ice front and power in fin whale frequencies indicates that future changes in sea ice conditions from global warming might change the distribution and migratory patterns of fin whales near the poles.

Including passive acoustic capability in Arctic ocean observing systems

Moore, S.E., K.M. Stafford, C.L. Berchok, H. Melling, and O. Wiig, "Including passive acoustic capability in Arctic ocean observing systems," J. Acoust. Soc. Am., 127, 1756, doi:10.1121/1.3383701, 2010

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20 Apr 2010

Over the past decade, long-term deployments of passive acoustic recorders have provided a new baseline on the seasonal occurrence of large whale species in remote regions of the world ocean. In the Arctic, passive acoustic sampling has identified both whale calls and sounds from anthropogenic sources (ships and seismic profiling), activities that are expected to increase with diminished sea ice cover. In 2008, NOAA capitalized on an opportunity to join on-going IPY projects by inclusion of recorders at three High Arctic mooring sites: one on the Chukchi Plateau and two on either side of Fram Strait. The recorders (AURAL–M2) provided a year of sub-sampled (9 min on/11 min off) recordings at 0.1 Hz to 4 kHz (8192 sampling rate), which encompasses the bandwidth of whale and ice seal calls. Data from the recorders were complemented by a suite of standard oceanographic measures from other instruments on the mooring line.

Provisional results show novel occurrence of both marine mammal and anthropogenic signals in the High Arctic. To realize the vision of a Global Ocean Acoustic Observing Network [Dushaw et al. (2009)], passive acoustic technology must become a standard sampling component, especially in the Arctic during this time of rapid climate change.

Where do the Chukchi Sea fin whales come from? Looking for answers in the structure of songs recorded in the Bering Sea and Western North Pacific

Delarue, J., D.K. Mellinger, K.M. Stafford, and C.L. Berchok, "Where do the Chukchi Sea fin whales come from? Looking for answers in the structure of songs recorded in the Bering Sea and Western North Pacific," J. Acoust. Soc. Am., 127, 1758, 2010.

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20 Apr 2010

Fin whales are common throughout the North Pacific and have recently been detected acoustically as far north as the northeastern Chukchi Sea. Non-acoustic evidence suggests that North Pacific fin whales are segregated into two populations wintering along the Asian and North American coast with at least some animals intermingling in the summer in the Bering Sea–Aleutian Islands area. Male fin whales produce regionally distinctive songs which are likely indicative of population structure. In this study we evaluated the relationship of fin whales recorded in the northeastern Chukchi (2007 and 2009) and southeastern Bering (2007–2008) seas by comparing the structure of their song. Additionally, we investigated whether fin whales detected in these areas could be part of an Asian population by comparing their songs to those recorded near the Emperor Seamounts in the western North Pacific (2007). The results will be discussed in light of the current knowledge on North Pacific fin whale population structure.

Biophysical ocean observation in the southeastern Bering Sea

Stafford, K.M., S.E. Moore, P.J. Stabeno, D.V. Holliday, J.M. Napp, D.K. Mellinger, "Biophysical ocean observation in the southeastern Bering Sea," Geophys. Res. Lett., 37, doi:10.1029/2009GL040724, 2010.

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30 Jan 2010

Integrated ocean observation, from physical and atmospheric forcing mechanisms to the distribution and abundance of top-level predators, is critical to the investigation of marine ecosystems and the impact of climate change on them. We integrated data from a biophysical mooring in the southeast Bering Sea to create a one-year snapshot of ocean dynamics in this remote large marine ecosystem.

Distinct patterns in production (chlorophyll), zooplankton biovolume (copepods and euphausiids) and the occurrence of zooplankton predators (fin and right whales) were defined and related to discrete features in the annual physical cycle. Peaks in prey and predator cycles were linked to spikes in fluorescence that occurred at the onset of water column stratification in late spring 2006 and the appearance of sea ice in late winter 2007. These data illustrate the capability and potential of integrated ocean observing systems (IOOS) to describe seasonal variability and linkages in a remote marine ecosystem.

Acoustic and visual surveys for bowhead whales in the western Beaufort and far northeastern Chukchi seas

Moore, S.E., K.M. Stafford, and L.M. Munger, "Acoustic and visual surveys for bowhead whales in the western Beaufort and far northeastern Chukchi seas," Deep-Sea Res. II, 57, 153-157, doi:10.1016/j.dsr2.2009.08.013, 2010.

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1 Jan 2010

Two types of passive-acoustic survey were conducted to investigate the seasonal occurrence of bowhead whales (Balaena mysticetus) in the western Beaufort and far northeastern Chukchi seas: (1) an over-winter (2003–04) survey using autonomous recorders deployed northeast of Barrow, Alaska, and (2) a summertime dipping-hydrophone survey along the 2005 NOAA Ocean Exploration (OE) cruise track northwest of Barrow. The longest continuous sampling period from the over-winter survey was 3 October 2003 to 12 May 2004. During that period, bowhead whale calls were recorded from 3 to 23 October, intermittently on 6–7 and 22–23 November, then not again until 25 March 2004. Bowhead calls were recorded almost every hour from 19 April to 12 May 2004, with a call rate peak on 30 April (ca. 9400 calls) and a few instances of patterned calling (or, "song") detected in early May. Bowhead whale calls were never detected during the NOAA OE cruise, but calls of beluga whales (Delphinapterus leucas) were recorded at 3 of 16 acoustic stations. Opportunistic visual surveys for marine mammals were also conducted during the NOAA OE cruise from the ship (65 h) and helicopter (7.8 h), resulting in single sightings of bowhead whales (3–5 whales), beluga (16–20 whales), walrus (1), polar bear (2=sow/cub), and 17 sightings of 87 ringed seals from the ship and 15 sightings of 67 ringed seals from the helicopter.

Acoustic sampling for marine mammals in the Beaufort Sea July 2007-March 2008

Stafford, K., S. Moore, C. Berchok, and D.K. Mellinger, "Acoustic sampling for marine mammals in the Beaufort Sea July 2007-March 2008," J. Acoust. Soc. Am., 125, 2587, 2009.

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1 Apr 2009

As climate change is driving rapid, unprecedented warming of the Arctic, there is increasing interest in how such change will impact Arctic marine mammals. Impacts are anticipated from habitat alteration, including increasing ambient noise levels from shipping, seismic exploration for oil and gas and geophysical research, and (potentially) commercial fishing. In order to monitor natural and anthropogenic sources of noise, four autonomous recorders were deployed along the 100-m isobath between Cape Halkett and Barrow and recorded data from July 2007–March 2008. The instruments sampled at 8192 Hz on a schedule of 10 min on, 20 min off.

Marine mammal sounds recorded included pinnipeds (walrus and bearded seals) and cetaceans (bowhead and beluga whales), while anthropogenic sources included shipping and air gun sounds. Seasonal and geographic patterns for these sounds will be presented. These data form part of a broader-scale international, year-round monitoring program in the Arctic that we hope will eventually span the entire Arctic and provide a basin-wide acoustic observatory.

Environmental correlates of blue and fin whale call detections in the North Pacific Ocean from 1997 to 2002

Stafford, K.M., J.J. Citta, S.E. Moore, M.A. Daher, and J.E. George, "Environmental correlates of blue and fin whale call detections in the North Pacific Ocean from 1997 to 2002," Mar. Ecol. Prog. Series, 395, 37-53, doi:10.3354/meps08362, 2009.

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1 Jan 2009

A 6 yr time series of blue whale Balaenoptera musculus and fin whale B. physalus call detections in the North Pacific Ocean was correlated with 3 oceanographic variables (sea-surface temperature, chlorophyll a concentration, and mixed layer depth), to investigate the broad-scale calling behavior of these species. Monthly values for satellite-derived oceanographic data and whale call data were compared for 4 regions (30° longitude by 15° of latitude) encompassing the whole subarctic North Pacific and an area in the temperate northeastern Pacific.

To determine predictive models for whale call occurrence, generalized linear models were used to determine which, if any, oceanographic variables might influence whale calling behavior over such broad space and time scales. Sea-surface temperature was the best oceanographic variable for predicting whale call detections for both species and all regions.

Bowhead whale springtime song off West Greenland

Stafford, K.M., S.E. Moore, K.L. Laidre, and M.P. Heide-Jorgensen, "Bowhead whale springtime song off West Greenland," J. Acoust. Soc. Am., 124, 1-9, doi:10.1121/1.2980443, 2008.

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1 Nov 2008

Three songs were recorded from bowhead whales (Balaena mysticetus) in Disko Bay, West Greenland, during 59 h of recordings via sonobuoys deployed on seven days between 5 and 14 April 2007. Song elements were defined by units following the protocol of previous description of bowhead whale song. The two most prominent songs were loud, complex, and repeated in long bouts on multiple recording days while the third song was much simpler and recorded on only one day.

Bowhead whale simple calls and faint song elements were also recorded using digital audio tape recorders and a dipping hydrophone deployed from the sea ice approximately 100–150 km southwest of Disko Bay on three separate days suggesting that song is also produced in the central portion of Baffin Bay in winter. Songs recorded in Disko Bay are from an area where approximately 85% of the whales have been determined to be adult females. Although it is not known which sex was singing, we speculate that, as in humpback whales (Megaptera novaeangliae), male bowhead whales may sing to mediate sexual competition or mate selection behaviors. This is the first detailed description of springtime songs for bowhead whales in the eastern Arctic.

An overview of fixed passive acoustic observation methods for cetaceans

Mellinger, D.K., K.M. Stafford, S.E. Moore, R.P. Dziak, and H. Matsumoto, "An overview of fixed passive acoustic observation methods for cetaceans," Oceanography, 20, 36-45, 2007.

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1 Dec 2007

Cetaceans are increasingly being included as top trophic-level predators in models of ecosystem dynamics (Baumgartner and Mate, 2003; Tynan, 2004; Redfern et al., 2006). Traditional visual survey methods for cetaceans detect only a fraction of the animals present, both because visual observers can see them only during the very short period when they are at the surface, and because visual surveys can be undertaken only during daylight hours in relatively good weather (Mellinger and Barlow, 2003). Perhaps more importantly, visual survey results can be highly variable, due both to clumping of cetaceans into large groups and to their relatively limited spatial and temporal scales. Surveys are typically performed using a small number of observation points—one or a few vessels—for a few weeks to a few months of the year.

Including whale call detection in standard ocean measurements: Application of acoustic Seagliders

Moore, S.E., B.M. Howe, K.M. Stafford, and M.L. Boyd, "Including whale call detection in standard ocean measurements: Application of acoustic Seagliders," Mar. Tech. Soc. J., 41, 49-53, doi:10.4031/002533207787442033, 2007.

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1 Dec 2007

Over the past decade, fixed recorders have come into increasing use for long-term sampling of whale calls in remote ocean regions. Concurrently, the development of several types of autonomous underwater vehicles has demonstrated measurement capabilities that promise to revolutionize ocean science. These two lines of technical development were merged with the addition of broadband (5 Hz to 30 kHz) omni-directional hydrophones to seagliders. In August 2006, the capability of three Acoustic Seagliders (ASGs) to detect whale calls was tested in an experiment offshore Monterey, California. In total, 401 dives were completed and over 107 hours of acoustic data recorded. Blue whale calls were detected on all but two of the 76 dives where acoustic data were analyzed in detail, while humpback and sperm whale calls were detected on roughly 20% of those dives. Various whistles, clicks and burst calls, similar to those produced by dolphins and small whales, were also detected, suggesting that the capability of ASGs can be expanded to sample a broad range of marine mammal species. The potential to include whale call detection in the suite of standard oceanographic measures is unprecedented and provides a foundation for mobile sampling strategies at scales that better match the vertical and horizontal movements of the whales themselves. This capability opens new doors for investigation of cetacean habitats and their role in marine ecosystems, as envisioned in future ocean observing systems.

Seasonal variability and detection range modeling of baleen whale calls in the Gulf of Alaska, 1999-2002

Stafford, K.M., D.K. Mellinger, S.E. Moore, and C.G. Fox, "Seasonal variability and detection range modeling of baleen whale calls in the Gulf of Alaska, 1999-2002," J. Acoust. Soc. Am., 122, 3378-3390, doi:10.1121/1.2799905, 2007.

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1 Dec 2007

Five species of large whales, including the blue (Balaenoptera musculus), fin (B. physalus), sei (B. borealis), humpback (Megaptera novaeangliae), and North Pacific right (Eubalaena japonica), were the target of commercial harvests in the Gulf of Alaska (GoA) during the 19th through mid-20th centuries. Since this time, there have been a few summer time visual surveys for these species, but no overview of year-round use of these waters by endangered whales primarily because standard visual survey data are difficult and costly.

From October 1999–May 2002, moored hydrophones were deployed in six locations in the GoA to record whale calls. Reception of calls from fin, humpback, and blue whales and an unknown source, called Watkins' whale, showed seasonal and geographic variation. Calls were detected more often during the winter than during the summer, suggesting that animals inhabit the GoA year-round. To estimate the distance at which species-diagnostic calls could be heard, parabolic equation propagation loss models for frequencies characteristic of each of each call type were run. Maximum detection ranges in the subarctic North Pacific ranged from 45 to 250 km among three species (fin, humpback, blue), although modeled detection ranges varied greatly with input parameters and choice of ambient noise level.

Gray whale calls recorded near Barrow, Alaska, throughout the winter of 2003-04

Stafford, K.M., S.E. Moore, M. Spillane, and S. Wiggins, "Gray whale calls recorded near Barrow, Alaska, throughout the winter of 2003-04," Arctic, 60, 167-172, 2007.

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1 Jun 2007

Since the mid-1990s, gray whales (Eschrichtius robustus) have been reported with increasing frequency near Barrow, Alaska, during summer and autumn months. In collaboration with a broad-scale oceanographic study, three autonomous acoustic recorders were moored northeast of Barrow in October 2003 to provide capability for year-round detection of calls. Two recorders were recovered in September 2004, one from the continental slope (water depth = 316 m) and one from near the base of the slope (water depth = 1258 m). The shallow instrument recorded for roughly 3 months (87 days), and the deeper instrument for roughly 7.3 months (222 days). Gray whale calls were recorded on both instruments throughout their periods of operation. The calling rate at the shallower instrument was higher than at the deeper recorder, but surprisingly, the deeper instrument detected calls throughout the 2003–04 winter, though the calling rate diminished as winter progressed. Low-frequency N1/S1 pulses, the most common of the calls produced by gray whales, were recorded from deployment through December 2003 on the shallower of the two instruments and from deployment through May 2004 on the deeper instrument. Because this is the first-ever winterlong acoustic study, we cannot be certain that gray whales have not overwintered in the Beaufort Sea in the past. However, a combination of increasing population size and habitat alteration associated with sea ice reduction and warming in the Alaskan Arctic may be responsible for the extra-seasonal gray whale occurrence near Barrow.

Blue whale (Balaenoptera musculus) sightings and recordings south of the Aleutian Islands

Rankin, S., J. Barlow, and K.M. Stafford, "Blue whale (Balaenoptera musculus) sightings and recordings south of the Aleutian Islands," Mar. Mammal Sci., 22, 708-713, doi:10.1111/j.1748-7692.2006.00054.x, 2006.

1 Jul 2006

Listening for large whales in the offshore waters of Alaska

Moore, S.E., K.M. Stafford, D.K. Mellinger, and J.A. Hildebrand, "Listening for large whales in the offshore waters of Alaska," Bioscience, 56, 49-55, 2006.

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1 Jan 2006

In 1999, the first phase of a multiyear program was initiated at the National Oceanic and Atmospheric Administration's National Marine Mammal Laboratory and Pacific Marine Environmental Laboratory to advance the use of passive acoustics for the detection and assessment of large whales in offshore Alaskan waters. To date, autonomous recorders have been successfully deployed in the Gulf of Alaska (1999–2001), the southeastern Bering Sea (2000–present), and the western Beaufort Sea (2003–2004). Seasonal occurrences of six endangered species (blue, fin, humpback, North Pacific right, bowhead, and sperm whales) have been documented on the basis of call receptions in these remote ocean regions. In addition, eastern North Pacific gray whale calls were detected in the western Beaufort Sea from October 2003 through May 2004. Here we provide an overview of this suite of research projects and suggest the next steps for applying acoustic data from long-term recorders to the assessment of large whale populations.

Atypical calling by a blue whale in the Gulf of Alaska

Stafford, K.M., and S.E. Moore, "Atypical calling by a blue whale in the Gulf of Alaska," J. Acoust. Soc. Am., 117, 2724-2727, 2005

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1 May 2005

Worldwide, calls from blue whales share the characteristics of being long (>20 s), low-frequency (<100 Hz) signals that often exhibit amplitude and frequency modulation. Despite sharing these basic features, the calls of blue whales recorded in different ocean basins are distinct from one another, leading to the suggestion that populations and/or subspecies may be identified based on call characteristics. An example of anomalous calling behavior by a blue whale in the Gulf of Alaska is reported that may complicate this approach, and that suggests that blue whales can mimic each other's calls.

Diel variation in blue whale calls recorded in the eastern tropical Pacific

Stafford, K.M., S.E. Moore, and C.G. Fox, "Diel variation in blue whale calls recorded in the eastern tropical Pacific," Animal Behaviour, 69, 951-958, doi:10.1016/j.anbehav.2004.06.025, 2005.

2 Jan 2005

In The News

The whale wiretap: Oceanographer's underwater microphones eavesdrop on the secret lives of whales

KPLU Radio, Allie Ferguson

Deep down on the sea floor off the coast of Alaska, about a dozen underwater microphones sit. Kate Stafford listens back to these recordings with the help of high-tech software to learn more about whales. Sound Effect's Gabriel Spitzer talked with her about what she's learned and what it's like to eavesdrop on the ocean.

9 Apr 2016

Some whales like global warming just fine

National Geographic, Isabelle Groc

Humpbacks and bowheads are benefiting — for now, at least — from the retreat of polar sea ice: It's making it easier for them to find food.

5 Apr 2016

Arctic marine mammals swim up to the microphone

Scientific American, Christopher Intagliata

As Arctic sea ice melts, an underwater recording project reveals that the submerged ecology is undergoing change, with humpbacks and killer whales staying north later in the year.

5 Nov 2015

More News Items

Bowhead whales heard singing unique new songs

BBC, Melissa Hogenboom

The bowhead whale has the most impressive song repertoire of all whales, and scientists have just recorded 12 unique songs being sung by bowhead whales on their annual migration.

12 Jan 2015

Mystery of bowhead whale song

Everett Herald, Sharon Wootton

Oceanographer Kate Stafford of the University of Washington%u2019s Applied Physics Laboratory, is researching the sounds of bowhead whales in Fram Strait off the coast of Greenland. Based on the song diversity, loudness and period over which the songs were recorded, western Fram Strait appears to be a wintering ground and potentially a mating area, as well.

16 Mar 2014

Whales, ships more common through Bering Strait

UW News and Information, Hannah Hickey

The Arctic is home to a growing number of whales and ships, and to populations of sub-Arctic whales that are expanding their territory into newly ice-free Arctic waters.

26 Feb 2014

Scientists look to marine mammals to shed light on Arctic ice loss

Minnesota Public Radio, Kerri Miller

University of Washington marine mammal ecologist Kristin Laidre and Kate Stafford, principal oceanographer at the Applied Physics Laboratory at Washington University, are using their studies of Arctic mammals to unlock some of the mysteries of ice loss. Kerri Miller held a conversation with the two scientists at the World Science Festival.

4 Jun 2013

Are Spitsbergen whales making a comeback?

KUOW Radio, "The Conversation", Ross Reynolds

Commercial whaling almost drove Spitsbergen whales to extinction. Since the 1970s sightings have been few and far between. Kate Stafford and her colleagues are using hydrophones to observe these whales year-round.

9 Aug 2012

Capturing the winter songs of rare whales

New York Times, Kelly Slivka

Between Greenland and the northern island of Spitsbergen, Norway, in the blackness of the Arctic winter, a group of rare whales sing. Kate Stafford, a bowhead researcher, is the lead author of a new paper in the journal Endangered Species Research that paper describes the variegated calls of Spitsbergen's bowheads, captured on underwater acoustic recorders by Dr. Stafford and her colleagues.

7 Aug 2012

Under the ice, sounds of spring

The New York Times

Kate Stafford, an oceanographer at APL-UW, writes from Alaska for the New York Times Scientist at Work blog, where she is participating in a visual census of bowhead whales.

17 May 2011

Seaglider Monitors Climate-Related Ocean Circulation in the Arctic

U.S. News & World Report

An intelligent, ocean-going glider has spent six months on a record-breaking deployment to sample the icy waters off western Greenland.

10 Jun 2009

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