Stephanie Watwood’s research while affiliated with Naval Undersea Warfare Center and other places

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Publications (33)


Map of the study area with locations of observed foraging dives. In each panel, the SOAR range is outlined in black, the regions used in comparison are color-coded, and foraging dives are plotted with a unique symbol for each tagged whale. The regions established for this analysis include Region A, the San Nicolas Basin; Region B, an area encompassing Tanner Canyon, East Cortez Bank, and the San Clemente Basin; and Region C, additional areas in the Southern California Range Complex located outside of Region A or B. The top panel displays the entire study area along with all dives from whale ID 144029, which traveled south into Mexican waters. The bottom panel provides a closer view of the dives that occurred within Region A and Region B.
A scatter plot of dive depth (the maximum depth reached during the dive) versus estimated local bathymetric depth. Point shapes/colors distinguish between tagged whales, and the black line displays a 1:1 relationship.
Stacked histograms (top) and violin plots (bottom) of observed pulse and buzz depths for all 99 analyzed foraging dives by the six whales tagged in this study. Histogram bin segments are colored by whale ID. Violin plots for each whale have the same maximum width regardless of the number of echolocations/buzzes recorded, and median values are represented by the black horizontal line for each whale. Within each violin plot are gray points for each individual echolocation/buzz to visualize sample sizes between whales.
Box and whisker plot of the observed proportion of echolocation pulses and buzzes during three dive phases (descent, bottom, and ascent) across the study regions (Region A, Region B, and Region C). Box and whisker plot is overlayed with jittered points of observed values, and point colors and shapes distinguish between regions and tagged whales, respectively.
Scatter plots of echolocation duration by foraging dive depth. Colors indicate time of day, and shapes indicate whale ID. Data are displayed by oceanographic region.

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Insights into foraging behavior from multi-day sound recording tags on goose-beaked whales (Ziphius cavirostris) in the Southern California Bight
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  • Full-text available

September 2024

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68 Reads

Shannon N. Coates

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Erin A. Falcone

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Gregory S. Schorr

Goose-beaked whales (Ziphius cavirostris) are deep-diving cetaceans known for their elusive nature and specialized foraging behavior. In 2019 and 2020, six telemetry tags were deployed on these whales in Southern California, resulting in 395 h of acoustic and diving data. Foraging dives were manually identified by the presence of echolocation pulses and buzzes, and generalized additive models assessed factors influencing foraging behavior. The median bathymetric depth at foraging sites was 1,419 m (IQR = 359), and the maximum dive depth was highly correlated with bathymetry depth. Individuals started echolocating on descent at a median depth of 410 m (IQR = 74); pulses were not observed shallower than 292 m. Echolocation ceased during the bottom phase for 81.6% of dives, at a median depth of 1,265 m (IQR = 472); pulses were not observed shallower than 587 m on ascent. The median depth of buzzes was 1,215 m (IQR = 479) with 63% occurring during the bottom phase. Deeper dives correlated with longer durations of diving and echolocation, greater echolocation end depths, and wider bottom phase echolocation depth inter-quartile range. The median difference between dive depth and bottom phase median echolocation depth was 98.3 m (IQR = 48.5), suggesting whales in this region forage in a narrow band close to the seafloor. In the San Nicolas Basin, individuals exhibited longer echolocation durations, produced more pulses, and started and ended echolocating at greater depths compared to adjacent regions. These records validate and expand upon previous studies, providing insights into factors influencing foraging behavior in an area with high anthropogenic disturbance.

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The use of Navy range bottom-mounted, bi-directional transducers for long-term, deep-ocean prey mapping

March 2024

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5 Reads

The Journal of the Acoustical Society of America

Beaked whales have been shown to be particularly sensitive to mid-frequency active sonar but continue to spend considerable time on Navy training ranges, where exposure to sonar is frequent. Understanding the underlying movements of their prey could help to explain the distribution and abundance patterns seen for beaked whales. Beaked whales are among the deepest diving marine mammals and have been shown to feed near the ocean bottom, at depths up to 3000 m. Typical surface-deployed prey mapping technology is not suitable for probing these deep foraging depths. This pilot study aims to us the bi-directional nodes on Navy hydrophone ranges that were developed for underwater communications as a rudimentary prey mapping system. A 1 ms 2 kHz signal was broadcast on an 8 kHz carrier signal and resulting returns were processed to estimate depths of the reflectors. Data are presented from three different time periods on the Southern California Anti-Submarine Warfare Range.


Evidence of Atlantic midshipman ( Porichthys plectrodon) vocalizations from an unmanned surface vehicle in the U.S. South Atlantic

November 2023

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33 Reads

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1 Citation

The Journal of the Acoustical Society of America

An unmanned surface vehicle (USV; Wave Glider) was deployed to study the coastal soundscape in shallow (less than 30 m) coastal waters off the coast of Cape Canaveral, FL, in July 2020 and January 2022. These surveys documented temporal and seasonal trends in biological sounds across a variety of habitats within an 812-km2 survey area, including sand shoals, sand-mud plains, and natural hardbottom. Among a broader diversity of identifiable and unidentifiable fish choruses recorded during the survey, a distinct and previously unidentified fish chorus was recorded; corroborating evidence suggests it and other sounds with similar spectral properties may be produced by Atlantic midshipman. Putative Atlantic midshipman sounds included an agnostic grunt and a seasonal chorus of persistent hums that peaked 3 h after sunset in the summer survey. While Atlantic midshipman have been demonstrated to have well-developed sonic muscles on their swim bladder, their acoustic behavior has not been previously described. Our use of a mobile passive acoustic platform combined with bottom sampling of fish communities highlights an important opportunity to identify previously undocumented biological sound sources in coastal habitats.



Using individual-based bioenergetic models to predict the aggregate effects of disturbance on populations: A case study with beaked whales and Navy sonar

August 2023

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178 Reads

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5 Citations

Anthropogenic activities can lead to changes in animal behavior. Predicting population consequences of these behavioral changes requires integrating short-term individual responses into models that forecast population dynamics across multiple generations. This is especially challenging for long-lived animals, because of the different time scales involved. Beaked whales are a group of deep-diving odontocete whales that respond behaviorally when exposed to military mid-frequency active sonar (MFAS), but the effect of these nonlethal responses on beaked whale populations is unknown. Population consequences of aggregate exposure to MFAS was assessed for two beaked whale populations that are regularly present on U.S. Navy training ranges where MFAS is frequently used. Our approach integrates a wide range of data sources, including telemetry data, information on spatial variation in habitat quality, passive acoustic data on the temporal pattern of sonar use and its relationship to beaked whale foraging activity, into an individual-based model with a dynamic bioenergetic module that governs individual life history. The predicted effect of disturbance from MFAS on population abundance ranged between population extinction to a slight increase in population abundance. These effects were driven by the interaction between the temporal pattern of MFAS use, baseline movement patterns, the spatial distribution of prey, the nature of beaked whale behavioral response to MFAS and the top-down impact of whale foraging on prey abundance. Based on these findings, we provide recommendations for monitoring of marine mammal populations and highlight key uncertainties to help guide future directions for assessing population impacts of nonlethal disturbance for these and other long-lived animals.


Sharks associated with a large sand shoal complex: Community insights from longline and acoustic telemetry surveys

June 2023

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504 Reads

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3 Citations

Offshore sand shoals are a coveted sand source for coastal restoration projects and as sites for wind energy development. Shoals often support unique fish assemblages but their habitat value to sharks is largely unknown due to the high mobility of most species in the open ocean. This study pairs multi-year longline and acoustic telemetry surveys to reveal depth-related and seasonal patterns in a shark community associated with the largest sand shoal complex in east Florida, USA. Monthly longline sampling from 2012–2017 yielded 2,595 sharks from 16 species with Atlantic sharpnose (Rhizoprionodon terraenovae), blacknose (Carcharhinus acronotus), and blacktip (C. limbatus) sharks being the most abundant species. A contemporaneous acoustic telemetry array detected 567 sharks from 16 species (14 in common with longlines) tagged locally and by researchers elsewhere along the US East Coast and Bahamas. PERMANOVA modeling of both datasets indicate that the shark species assemblage differed more across seasons than water depth although both factors were important. Moreover, the shark assemblage detected at an active sand dredge site was similar to that at nearby undisturbed sites. Water temperature, water clarity, and distance from shore were habitat factors that most strongly correlated to community composition. Both sampling approaches documented similar single-species and community trends but longlines underestimated the shark nursery value of the region while telemetry-based community assessments are inherently biased by the number of species under active study. Overall, this study confirms that sharks can be an important component of sand shoal fish communities but suggests that deeper water immediately adjacent to shoals (as opposed to shallow shoal ridges) is more valuable to some species. Potential impacts to these nearby habitats should be considered when planning for sand extraction and offshore wind infrastructure.


Movements and diving behavior of Risso’s dolphins in the Southern California Bight

October 2022

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201 Reads

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5 Citations

Risso’s dolphins (Grampus griseus), uncommon prior to the 1970’s, are now regularly observed within the Southern California Bight. During long-term cetacean monitoring programs on United States Navy range areas in the Southern California Bight from 2009–2019, we deployed 16 Argos-linked satellite tags on Risso’s to acquire objective, detailed depictions of their movements and behaviors. Individuals were tracked for a median of 10.7 days (range = 0.8 – 19.7). Kernel density estimation suggested individuals utilized the entire Southern California Bight with the 50% core use area centered around San Clemente and Santa Catalina Islands where most of the tag deployments occurred. Grand median dive depth was 101 m (max = 528) and dive duration was 5.6 min (max = 11.1). We used generalized mixed models to assess seasonal and environmental effects on distribution and diving behavior including month, distance to shore, time of day, lunar phase, sea surface temperature, and chlorophyll-a residuals. Animals were further from shore (including islands) during a full versus new moon and from the mainland during the last versus first quarter moon. Animals also tended to be closer to land in the fall and early winter months. Dives were deeper yet shorter during the night, during a full moon, and when animals were further offshore. Animals conducted nearly twice as many dives at night compared to day, though deep dives (> 500 m) occurred at all times of day. This study provides insights into Risso’s distribution and behavioral trends while identifying priorities for future research.


Improved characterization of ambient sound levels in a coastal environment via use of an unmanned Wave Glider

October 2022

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10 Reads

The Journal of the Acoustical Society of America

No PDF available ABSTRACT In this project, we use an unmanned Liquid Robotics SV3 wave glider as a tool for basic research studying ambient acoustics in shallower, coastal waters off the coast of East-Central Florida. The primary objective is to characterize sound levels in varying conditions via collection of high-resolution environmental data. The SV3 is used to systematically characterize the acoustic environment in coastal waters, while simultaneously measuring oceanographic parameters such as wind speed, wind direction, and wave height. Quantifying the influence of these fundamental oceanographic influences on shallow water acoustics will provide improved characterization of surface noise and comparison with traditional ambient noise spectra. Ambient noise spectra will be presented for various sea states and wind scenarios, as measured at 25 foot depth using a towfish attached to the SV3. Some of these measurements are also compared to fixed station bottom recordings. Finally, this effort also includes characterization of unique sources of biological sounds recorded by the SV3, including not previously documented loud fish chorusing in this region.


Automated detection and classification of beaked whale buzzes on bottom-mounted hydrophones

September 2022

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86 Reads

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3 Citations

Frontiers in Remote Sensing

Beaked whales, like many other odontocetes, produce bouts of very rapid clicking that serve as a homing signal just prior to a prey capture attempt. For Blainville’s and Cuvier’s beaked whales ( Mesoplodon densirostris, Md, and Ziphius cavirostris, Zc, respectively) these homing sequences have been dubbed “buzzes.” Buzz clicks have both a structure that is markedly different from and a source level that is significantly lower than the foraging clicks produced by these animals. To date, most of the studies of beaked whale echolocation behavior, especially buzz production, have relied on analysis of data from acoustic recording tags placed on vocal animals. While tag data has allowed detailed description of the dive cycles and foraging behavior of the tagged animals, providing invaluable ground truth for other passive acoustic monitoring studies, it is of limited quantity. Tagging beaked whales is difficult and the spatial and temporal coverage of tagged animals remains sparse. Growing numbers of bottom-moored and bottom-mounted sensors are being used for passive acoustic monitoring and for the study of Md and Zc behavior and distribution. Buzzes from Md and Zc are detectable on such remote sensors and these buzz data can augment higher order studies, such as those on beaked whale habitat use and population health, as detected buzzes can serve as a proxy for prey capture attempts.


Cuvier’s beaked whale foraging dives identified via machine learning using depth and triaxial acceleration

June 2022

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61 Reads

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6 Citations

Marine Ecology Progress Series

Knowledge of Cuvier’s beaked whale Ziphius cavirostris behavior has expanded through the utilization of animal-borne tags. However, many tag types do not record sound—thus preventing echolocation click detections to identify foraging—or have short deployments that sample a limited range of behaviors. As the quantity of such non-acoustic tag data grows, so too does the need for robust methods of detecting foraging from non-acoustic data. We used 692 dives from 5 sound-recording tags on Cuvier’s beaked whales in southern California, USA, to develop extreme gradient boosting tree models to detect foraging based on 1 Hz depth and 16 Hz triaxial acceleration data. We performed repeated 10-fold cross validation using classification accuracy to tune 500 models with randomly partitioned training and testing datasets. An average of 99.9 and 99.2% of training and testing dataset dives, respectively, were correctly classified across the 500 models. Dives without associated sound recordings (n = 2069 from 7 whales including 4 non-acoustic tags) were classified via a model that maximized training information using dive depth and duration, ascent and descent rates, bottom-phase average vertical speed, and roll circular variance during dive descents and bottom phases. Of all long, deep dives (conventionally assumed to include foraging), 2.4% were classified as non-foraging dives, while 0.3% of short, shallow dives were classified as foraging dives. Results confirm that conventional depth and/or duration classifiers provide reasonable estimates of longer-term foraging patterns. However, additional variables previously listed enhance foraging detections for unusual dives (notably non-foraging deep dives) for southern California Cuvier’s beaked whales.


Citations (15)


... These studies are essential 532 to define a more general theory of the functioning of multi-trophic interactions in pelagic deep-533 sea ecosystems. We urgently need such theory to better understand and predict how deep-sea 534 communities across trophic levels, including deep-diving cetaceans as the largest top-predators 535 in these systems, will respond in the face of increasing anthropogenic pressures in this era of 536 global change [92,93,94,95]. 537 . ...

Reference:

Population regulation in semelparous deep-sea squid is driven by ecological conditions in surface waters and whale predation at depth
Using individual-based bioenergetic models to predict the aggregate effects of disturbance on populations: A case study with beaked whales and Navy sonar

... Furthermore, a preference for moderate salinities would not explain the preferential use of the high-salinity nearshore waters off Cape Canaveral to the moderate salinities found in portions of the Indian River Lagoon in east-central Florida. Therefore, it is likely that additional abiotic factors that were not addressed in the present studyperhaps turbidity, which was also found to be positively associated with YOY and juvenile S. lewini catch rates by Yates et al. (2015) and Reyier et al. (2023) also influence habitat use patterns and should be examined in follow-up studies. ...

Sharks associated with a large sand shoal complex: Community insights from longline and acoustic telemetry surveys

... Tagged rough-toothed dolphins off the coast of Kauaʻi, Hawaiʻi showed both diel and lunar trends in both dive depth and dive timesuggesting a strong link with prey abundance and availability [30]. Another study showed lunar patterns in dive time/depth, dive frequency and animal distribution of Risso's dolphins in the Southern California bight [12]. Not only are odontocetes found to have behavioral changes relating to the lunar cycle but also differences in detection frequency. ...

Movements and diving behavior of Risso’s dolphins in the Southern California Bight

... Very few species of beaked whales have been documented producing an echolocation click type like those produced by dolphins. When they are documented, it has been primarily in the form of a terminal foraging buzz(Jarvis et al. 2022;Johnson et al. 2006Johnson et al. , 2008. Baird's (Berardius bairdii), Longman's (Indopacetus pacificus), and Northern bottlenose (Hyperoodon ampullatus) beaked whales are the main exceptions, with a multitude of signals produced (DeAngelis et al., 2023; Hooker & Whitehead, 2002; Rankin et al., 2011). ...

Automated detection and classification of beaked whale buzzes on bottom-mounted hydrophones

Frontiers in Remote Sensing

... For pinnipeds and toothed whales, it is widely assumed that plastic debris is visually mistaken as common prey resources -either by shape, color, or behavior of the object in the water column -particularly plastic bags and films that physically resemble gelatinous prey species like squid and jellies (Carson, 2013;Savoca et al., 2016Savoca et al., , 2017. However, deep diving whales such as sperm whales and beaked whales forage at great depths below the photic zone (Quick et al., 2020;Sweeney et al., 2022;Watwood et al., 2006). Instead of sight, these animals rely on echolocation to hunt. ...

Cuvier’s beaked whale foraging dives identified via machine learning using depth and triaxial acceleration

Marine Ecology Progress Series

... Baleen whales are thought to be sensitive primarily to sounds in the low-frequency range (10 to 500 Hz) and are therefore particularly vulnerable to auditory masking from low-frequency sources such as vessel noise (Clark et al., 2009;Southall et al., 2023a) or to behavioral disturbance from low-frequency active sonar or airgun noise (Tyack and Clark, 1998;Miller et al., 2000;Dunlop et al., 2020;Gailey et al., 2022) Baleen whales may also respond to sounds in the mid-frequency range (500 Hz to 25 kHz). Observed behavioral responses of baleen whales to simulated mid-frequency active sonar (MFAS), used by the Navy in military training and testing activities, included termination of deep dives, directed travel away from sound sources, cessation of feeding, and changes in body orientation or swim speed, and were influenced by behavioral state, environmental context, prior exposure to similar sound sources, and received noise levels (Goldbogen et al., 2013;Southall et al., 2019b;2023b;Pirotta et al., 2022). ...

From individual responses to population effects: Integrating a decade of multidisciplinary research on blue whales and sonar

... While both animals continued to conduct deep dives during the exposure period, one animal did not conduct the very deep dives that were recorded before and after the exposure, and also conducted more mid-depth (400-800 m) dives than were recorded before or after the exposure (Joyce et al. 2019). These tag data were also combined to develop a discrete-space continuoustime model of exposure in order to estimate transition rates as animals avoided the MFAS by moving outside the range as well as their return to the range over time (Jones-Todd et al. 2022). ...

Discrete‐space continuous‐time models of marine mammal exposure to Navy sonar

... The combination of satellite coverage, limited transmission bandwidths and the limited surfacing periods of deep-diving whales means that the data are considerably less rich than the sub-second sampling frequency of DTAGs. Despite these limitations, various studies have employed these types of instruments; see, for example Tyack et al., 5 Moretti et al., 27 Falcone et al., 28 Schick et al., 26 von Benda-Beckmann et al., 29 and Wensveen et al. 7 While Tyack et al. 5 and Moretti et al. 27 were able to use fixed hydrophones to evaluate modeled SPLs at known locations, most of these studies share a similar workflow: (1) satellite tags are attached to animals; (2) the data from the tag(s) are preprocessed and outliers removed; (3) a continuous-time correlated random walk model 30 is fit to the x,y data; (4) predictions of an animal's position during a CEE are co-located with output from sound propagation models; and (5) the sound pressure levels are summarized across the collection of n predicted locations. ...

Diving behaviour of Cuvier's beaked whales exposed to two types of military sonar

... While some research exists on the responses of fishes and aquatic invertebrates to a variety of different sounds, less is known about how sounds specifically emitted from OSW energy development could potentially alter behaviors (e.g., Wahlberg and Westerberg, 2005;Siddagangaiah et al., 2021;Zhang et al., 2021). However, the available data suggest that behavioral changes resulting from exposure to sounds from OSW energy development could be a concern for at least some species (e.g., Perrow et al., 2011;Thomsen et al., 2012;Hawkins et al., 2014;Iafrate et al., 2016;Methratta and Dardick, 2019;Kok et al., 2021;Puig-Pons et al., 2021). A range of behavioral changes with potential fitness consequences have been hypothesized, in part, based on observations or inference from responses to other anthropogenic or environmental noise sources. ...

Effects of Pile Driving on the Residency and Movement of Tagged Reef Fish

... Second, considering that sound levels decrease as the distance from a source increases, it is reasonable to argue that most fishes in an area of anthropogenic sound will not be sufficiently near an intense source to be exposed to sounds intense enough to result in TTS. Thus, while some animals close to the source may be exposed to sufficiently intense sounds to result in TTS, these animals are likely to make up a very small part of the population of the species in an area, and even these animals are likely to move away from the source to areas of lower sound level (Iafrate et al. 2016a, b;Krebs et al. 2016;Watwood et al. 2016). ...

Behavioral Response of Reef Fish and Green Sea Turtles to Midfrequency Sonar
  • Citing Article
  • November 2015

Advances in Experimental Medicine and Biology