Sofie M. Van Parijs

Geographic variation in northwest Atlantic fin whale (Balaenoptera physalus) song: Implications for stock structure assessment.

Passive acoustic data are increasingly being used as a tool for helping to define marine mammal populations and stocks. Fin whale (Balaenoptera physalus) songs present a unique opportunity to determine interstock differences. Their highly stereotyped interpulse interval has been shown to vary between geographic areas and to remain stable over time in some areas. In this study the structure of songs recorded at two geographically close feeding aggregations in the Gulf of St. Lawrence (GSL) and Gulf of Maine (GoM) was compared. Recordings were made from September 2005 through February 2006 in the GSL and intermittently between January 2006 and September 2007 at two locations in the GoM. 6257 pulse intervals corresponding to 19 GSL and 29 GoM songs were measured to characterize songs from both areas. Classification trees showed that GSL songs differ significantly from those in the GoM. The results are consistent with those derived from other stock structure assessment methodologies, such as chemical signature and photoidentification analysis, suggesting that fin whales in these areas may form separate management stocks. Song structure analysis could therefore provide a useful and cost-efficient tool for defining conservation units over temporal and geographical scales relevant to management objectives in fin whales.

Low frequency vocalizations attributed to sei whales (Balaenoptera borealis)

Low frequency (<100 Hz) downsweep vocalizations were repeatedly recorded from ocean gliders east of Cape Cod, MA in May 2005. To identify the species responsible for this call, arrays of acoustic recorders were deployed in this same area during 2006 and 2007. 70 h of collocated visual observations at the center of each array were used to compare the localized occurrence of this call to the occurrence of three baleen whale species: right, humpback, and sei whales. The low frequency call was significantly associated only with the occurrence of sei whales. On average, the call swept from 82 to 34 Hz over 1.4 s and was most often produced as a single call, although pairs and (more rarely) triplets were occasionally detected. Individual calls comprising the pairs were localized to within tens of meters of one another and were more similar to one another than to contemporaneous calls by other whales, suggesting that paired calls may be produced by the same animal. A synthetic kernel was developed to facilitate automatic detection of this call using spectrogram-correlation methods. The optimal kernel missed 14% of calls, and of all the calls that were automatically detected, 15% were false positives.

Patterns in the vocalizations of male harbor seals

Comparative analyses of the roar vocalization of male harbor seals from ten sites throughout their distribution showed that vocal variation occurs at the oceanic, regional, population, and subpopulation level. Genetic barriers based on the physical distance between harbor seal populations present a likely explanation for some of the observed vocal variation. However, site-specific vocal variations were present between genetically mixed subpopulations in California. A tree-based classification analysis grouped Scottish populations together with eastern Pacific sites, rather than amongst Atlantic sites as would be expected if variation was based purely on genetics. Lastly, within the classification tree no individual vocal parameter was consistently responsible for consecutive splits between geographic sites. Combined, these factors suggest that site-specific variation influences the development of vocal structure in harbor seals and these factors may provide evidence for the occurrence of vocal dialects.

Real-time reporting of baleen whale passive acoustic detections from ocean gliders

In the past decade, much progress has been made in real-time passive acoustic monitoring of marine mammal occurrence and distribution from autonomous platforms (e.g., gliders, floats, buoys), but current systems focus primarily on a single call type produced by a single species, often from a single location. A hardware and software system was developed to detect, classify, and report 14 call types produced by 4 species of baleen whales in real time from ocean gliders. During a 3-week deployment in the central Gulf of Maine in late November and early December 2012, two gliders reported over 25,000 acoustic detections attributed to fin, humpback, sei, and right whales. The overall false detection rate for individual calls was 14%, and for right, humpback, and fin whales, false predictions of occurrence during 15-min reporting periods were 5% or less. Transmitted pitch tracks--compact representations of sounds--allowed unambiguous identification of both humpback and fin whale song. Of the ten cases when whales were sighted during aerial or shipboard surveys and a glider was within 20 km of the sighting location, nine were accompanied by real-time acoustic detections of the same species by the glider within ±12 h of the sighting time.

Sounds produced by individual white whales, Delphinapterus leucas, from Svalbard during capture (L)

Recordings were made of the sounds produced by white whales during capture events in Storfjorden, Svalbard, in the late autumn. Only four of eight captured individuals produced sounds. Four subadults, one female and three males, between 330 and 375 cm long, did not produce sounds during handling. The four animals that produced sounds were as follows: a female subadult of 280 cm produced repetitive broadband clicks; a solitary calf produced harmonic sounds, which we suggest may serve as mother–calf “contact calls,” and a mother–calf pair were the two animals that produced the most sounds in the study. The mother produced “crooning” broadband clicks and frequently moved her head toward her calf while producing underwater sounds. The calf produced three types of frequency-modulated sounds interspersed within broadband click trains. No sounds were heard from any of the animals once they were free-swimming, or during ad lib recording sessions in the study area, even though groups of white whales were sighted o...

Sounds produced by Norwegian killer whales, Orcinus orca, during capture

To date very little is still known about the acoustic behavior of Norwegian killer whales, in particular that of individual whales. In this study a unique opportunity was presented to document the sounds produced by five captured killer whales in the Vestfjord area, northern Norway. Individuals produced 14 discrete and 7 compound calls. Two call types were used both by individuals 16178 and 23365 suggesting that they may belong to the same pod. Comparisons with calls documented in Strager (1993) showed that none of the call types used by the captured individuals were present. The lack of these calls in the available literature suggests that call variability within individuals is likely to be large. This short note adds to our knowledge of the vocal repertoire of this population and demonstrates the need for further studies to provide behavioural context to these sounds.

NEPAN: A U.S. Northeast Passive Acoustic Sensing Network for Monitoring, Reducing Threats and the Conservation of Marine Animals

I ncreasing anthropogenic activities in our oceans and their subsequent impacts onmarine ecosystems are clear conservation issues of national and global concern. Habitat degradation and the indirect impacts on marine vertebrates from activities associated with oil and gas exploration, renewable energy development, and shipping or fisheries operations threaten marine ecosystem health (Kappel, 2005; Halpern et al., 2007; Read, 2008; Davidson et al., 2012; Rolland et al., 2012). Efficient and cost-effective means to assess species distribution, abundance, and exposure to anthropogenic impacts are critical to the conservation of those species and their habitat. The mission of some federal agencies, such as National Oceanic and Atmospheric Administration (NOAA) in theUnited States, includes the conservation and recovery of depleted or endangered marine species, in accordance with the Marine Mammal Protection Act and the Endangered Species Act. Essential to these mandates is an adequate understanding of marine animal abundance, population trends, and seasonal occurrence, as well as an assessment of sources of risks associated with human activities. Among these risks are the effects of underwater noise introduced by human activities on marine animal acoustic communication, hearing and behavior, and the direct interactions of individual animals with fisheries and shipping operations (Cholewiak, Risch et al., 2013). Sound propagates more readily and over greater distances through water than light. Given this and the fact that light is limited at depth, sound is the primary modality of choice for marine animal communication, foraging, and navigation. Many marine species are highly vocal and much of their social, reproductive, and foraging behavior is acoustically mediated. Studies of the vocalizations that these animals emit—although completely reliant on the animals actually vocalizing—can provide information on their occurrence, distribution, relative abundance, and habitat use (e.g., Moore et al., 2006; Van Parijs et al., 2009; Širović & Hildebrand, 2011; Van Opzeeland et al., 2013a; Risch et al., 2014). In the past decade, passive acoustic approaches for studying marine animal populations have seen a rapid expansion in both the tools available and the geographic scope in which studies have been conducted. Substantial imMarch/A provements in the capabilities, availability, and price of acoustic recorders now provide a suite of cost-effective options for researchers to characterize the acoustic ecology of many species. They also provide means to quantify human-introduced noise levels in continuous records gathered in broad areas and over long periods. Recording devices include (a) fixed bottom-mounted acoustic recorders (BMARs) that can record up to several years in a single deployment, (b) hydrophone arrays towed behind survey vessels, (c) acoustic tags that record individual animal calls, (d) autonomous underwater vehicles (such as gliders) and unmanned surface vehicles (capable of navigating along assigned routes) or (e) anchored surface buoys that transmit underwater acoustic data to a land-based location in near real-time (Figure 1a). Hardware pril 2015 Volume 49 Number 2 71 and software refinements now allow data collection in remote areas and detection of species that are difficult to observe using aircraftor vesselbased visual surveys. Emerging theoretical methodologies applied to passive acoustic data provide novel ways to address largescale ecological and behavioral questions. For example, using acoustic indices tomonitor biodiversity and species richness (Fay, 2009; McWilliam & Hawkins, 2013; Staaterman et al., 2013; Staaterman & Paris, 2014), modeling loss of “communication space” (i.e., the space over which the sounds of an animal can be heard by conspecifics, or a listening animal can hear sounds of conspecifics) (Clark et al., 2009; Hatch et al., 2012; Williams et al., 2014), and integrating visual data with passively obtained acoustic data to increase the 72 Marine Technology Society Journa value of each technique (Thompson et al., 2014). Studies of marine mammals, especially cetaceans, have traditionally been conducted visually, from either vessel or aerial platforms. However, visual surveys are limited by daylight and weather conditions, as well as the short amount of time that marine mammals spend at the surface and are therefore detectable (e.g., Clark et al., 2010). Unconstrained by visual detection limitations, passive acoustic studies consistently provide a far richer characterization of marine mammal occurrence and habitat use information beyond seasons and regions where visual surveys previously documented them (e.g., Vu et al., 2012; Van Opzeeland et al., 2013b; Širović et al., 2014). Such passive acoustic studies highlight the need to transition to techniques that more completely characterize the actual disl tribution, occurrence, and relative abundance of marine mammals. Recent passive acoustic studies have also been used to identify spawning fish stocks, map their distribution, and define their seasonal occurrence and longterm persistence (Hernandez et al., 2013; Wall et al., 2012). Combined with active acoustic technology (i.e., in this case active acoustics refers to the high-frequency pinging sound produced by tags implanted in individual mature fish), which provides detailed information on behavior, movement patterns, sex ratios, and site fidelity of fish populations (Dean et al., 2012, 2014; Zemeckis et al., 2014a, 2014b, 2014c), this blended approach offers a novel direction for fisheries management and the conservation of fish stocks. Consequently, the use of passive acoustic methods to describe animal distribution, occurrence, abundance, and behavior is increasingly being recognized as tools not only for basic research but also with clear monitoring roles that substantially improve our capacity to inform conservation strategies. These are conservation and monitoring strategies that undoubtedly further the mission of NOAA and those of its partner agencies. NOAA’s Current Involvement in Passive Acoustic Research and Development Within NOAA, passive acoustic research has steadily grown in importance as a valued technique for improving and modernizing the collection of biological and anthropogenic data. NOAA Fisheries’ Offices of Science and Technology and Protected Resources and the National Ocean Service’s Office of National Marine Sanctuaries are currently finalizing an agency-wide Ocean Noise Strategy that aims to guide NOAA’s science FIGURE 1 (a) This image depicts the range of passive acoustic technologies currently available for collecting data. These include bottom-mounted archival marine acoustic recorders, acoustic recording tags deployed on animals, acoustic arrays towed behind survey vessels and autonomous underwater vehicles or gliders, as well as surface-mounted buoys that report back data in near real time. (b) This image depicts the possible “soundscape” of an ocean habitat composed of sound contributions from invertebrates, fish, marine mammals, weather events, and anthropogenic sources such as vessels. Long-term measurements of changes in soundscapes, such as the decrease in biological or increase in anthropogenic sound sources, will enable the relative “acoustic health” of a habitat to be monitored. and management decisions toward a longer-term vision for addressing noise impacts to marine life (http:// cetsound.noaa.gov). The Strategy highlights three major areas: (1) the importance of sound use and hearing for a diverse array of NOAA-managed species, (2) the importance of acoustic habi ta t in support ing NOAA ’ s management of these species, and (3) the data collection, tools, and approaches necessary to characterize soundscapes (e.g., Figure 1b) in order to support speciesand habitat-based management approaches. The Northeast Passive Acoustic Sensing Network (NEPAN) is a premier example of how to go about collecting data to inform the Strategy in a broad reaching manner. NOAA’s Northeast Regional Passive Acoustic Research At NOAA’s Northeast Fisheries Science Center (NEFSC), the Passive Acoustic Research Program’s primary focus is collecting passive acoustic data throughout the westernNorth Atlantic Ocean using a variety of the fixed and mobile platforms identified above. Our work—along with research partners at the Stellwagen Bank National Marine Sanctuary (SBNMS) and regular collaborative interactions withNationalMarine Fisheries Service (NMFS) science centers and headquarters and academia—combines long-term monitoring of marine species to understand their distribution, abundance and ecology, and quantification of anthropogenic noise threats with research focusing on monitoring the soundscapes of various key habitats in our region. Ultimately, our aim is to support broad marine management and conservation strategies throughout NOAA as part of a larger network of scientists conducting passive acoustic research. A Vision for a Comprehensive Passive Acoustic Sensing Network We envision a passive acoustic monitoring network positioned over the continental shelf and upper continental slope off the East Coast of the United States that will employ archival and near real-time passive acoustic systems to meet pressing NOAAmanagement needs. The network would include both fixed and mobile assets that could monitor marine mammals, soniferous fish and ocean noise over both short (days to weeks) and long (months to years) time scales. Some of these assets would be deployed in sensitive or industrial areas, such as wind farm construction sites, shipping lanes, heavily fished areas, or marine reserves, while others would cover broad spatial scales to inform questions about species ’ ranges, migration routes, or presence in unexpected locations. Ideally, some network assets would be collocated with oceanographic observatories (e.g., Northeast Regional Association of Coastal an

Automatic grunt detector and recognizer for Atlantic cod (Gadus morhua)

Northwest Atlantic cod (Gadus morhua) have been heavily overfished in recent years and have not yet recovered. Passive acoustic technology offers a new approach to identify the spatial location of spawning fish, as well as their seasonal and long term persistence in an area. To date, the lack of a species-specific detector has made searching for Atlantic cod grunts in large amounts of passive acoustic data cumbersome. To address this problem, an automatic grunt detection and recognition algorithm that processes yearlong passive acoustic data recordings was designed. The proposed technique is a two-stage hypothesis testing algorithm that includes detecting and recognizing all grunt-like sounds. Test results demonstrated that the algorithm provided a detection probability of 0.93 for grunts with a signal-to-noise ratio (SNR) higher than 10 dB, and a detection probability of 0.8 for grunts with the SNR ranging from 3 to 10 dB. This detector is being used to identify cod in current and historical data from U.S. waters. Its use has significantly reduced the time required to find and validate the presence of cod grunts.

Calling depths of baleen whales from single sensor data: Development of an autocorrelation method using multipath localization

Multipath localization techniques have not previously been applied to baleen whale vocalizations due to difficulties in application to tonal vocalizations. Here it is shown that an autocorrelation method coupled with the direct reflected time difference of arrival localization technique can successfully resolve location information. A derivation was made to model the autocorrelation of a direct signal and its overlapping reflections to illustrate that an autocorrelation may be used to extract reflection information from longer duration signals containing a frequency sweep, such as some calls produced by baleen whales. An analysis was performed to characterize the difference in behavior of the autocorrelation when applied to call types with varying parameters (sweep rate, call duration). The methods feasibility was tested using data from playback transmissions to localize an acoustic transducer at a known depth and location. The method was then used to estimate the depth and range of a single North Atlantic right whale (Eubalaena glacialis) and humpback whale (Megaptera novaeangliae) from two separate experiments.

Effects of duty-cycled passive acoustic recordings on detecting the presence of beaked whales in the northwest Atlantic

This study investigated the effects of using duty-cycled passive acoustic recordings to monitor the daily presence of beaked whale species at three locations in the northwest Atlantic. Continuous acoustic records were subsampled to simulate duty cycles of 50%, 25%, and 10% and cycle period durations from 10 to 60 min. Short, frequent listening periods were most effective for assessing the daily presence of beaked whales. Furthermore, subsampling at low duty cycles led to consistently greater underestimation of Mesoplodon species than either Cuviers beaked whales or northern bottlenose whales, leading to a potential bias in estimation of relative species occurrence.