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2020
Frasier, KE, Solsona-Berga A, Stokes L, Hildebrand JA.  2020.  Impacts of the Deepwater Horizon oil spill on marine mammals and sea turtles. Deep Oil Spills. ( S. M, et al , Eds.).:431-462.: Springer, Cham   10.1007/978-3-030-11605-7_26   Abstract

The Gulf of Mexico (GOM) is one of the most diverse ecosystems in the world (Fautin et al. PLoS One 5(8):e11914, 2010). Twenty-one species of marine mammals and five species of sea turtles were routinely identified in the region by the end of the twenty-first century (Waring et al. NOAA Tech Memo NMFS NE 231:361, 2015), a decrease from approximately 39 species prior to intensive exploitation (Darnell RM. The American sea: a natural history of the Gulf of Mexico. Texas A&M University Press, College Station, TX, 2015). Life histories of these megafauna species range from hyperlocal residence patterns of bottlenose dolphins to inter-ocean migrations of leatherback turtles. All species are subject to direct and indirect impacts associated with human activities. These impacts have intensified with major development and extraction efforts since the 1940s. The Deepwater Horizon (DWH) oil spill represents a new type of injury to this system: Unlike previous large oil spills, it not only exposed marine megafauna to surface slicks, it also involved an unprecedented release of dispersed oil into deep waters and pelagic habitats, where effects are difficult to observe and quantify. This chapter synthesizes the research conducted following the DWH oil spill to characterize acute and chronic offshore effects on oceanic marine mammals and sea turtles. Marine mammals and sea turtles were exposed to unprecedented amounts of oil and dispersants. Local declines in marine mammal presence observed using passive acoustic monitoring data suggest that the acute and chronic population-level impacts of this exposure were likely high and were underestimated based on coastal observations alone. These population declines may be related to reduced reproductive success as observed in nearshore proxies. Long-term monitoring of oceanic marine mammals is a focus of this chapter because impacts to these populations have not been extensively covered elsewhere. We provide an overview of impacts to sea turtles and coastal marine mammals, but other more thorough resources are referenced for in depth reviews of these more widely covered species.

2019
Guazzo, RA, Schulman-Janiger A, Smith MH, Barlow J, D’Spain GL, Rimington DB, Hildebrand JA.  2019.  Gray whale migration patterns through the Southern California Bight from multi-year visual and acoustic monitoring. Marine Ecology Progress Series. 625:181-203.   10.3354/meps12989   Abstract

Sightings and acoustic recordings from eastern North Pacific gray whales in the Southern California Bight were analyzed for interannual changes and compared with concurrent environmental measurements during 7 migration seasons (2008-2009 to 2014-2015). Acoustic call counts recorded on an offshore hydrophone were highly variable from year to year. Assuming an average calling rate of 7.5 calls whale-1 d-1, the estimated number of whales migrating by this hydrophone would be <10% of the population within 20 km of the offshore hydrophone in most years. In contrast, the estimated number of gray whales migrating off Santa Barbara and Los Angeles based on visual surveys grew at a greater rate (11% yr-1 and 26% yr-1, respectively) than the population size growth rate (5% yr-1). Over the studied migration seasons it seems an increasing proportion of the population was using the nearshore migration corridor in the Southern California Bight, especially near Los Angeles. This trend could increase the negative anthropogenic impact on this species. Although several large-scale climatic events occurred between 2008 and 2015, neither water temperature in the Southern California Bight nor sea ice timing in the gray whale Arctic feeding area improved generalized additive models of gray whale nearshore sightings or offshore acoustic presence. Over these times, the gray whale migration timing appears to be driven more by their biological clock and instinct than by the extrinsic factors accounted for in the present analysis. Future work should test if other factors influence the gray whale migration over longer timescales.

Hildebrand, JA, Frasier KE, Baumann-Pickering S, Wiggins SM, Merkens KP, Garrison LP, Soklevilla MS, McDonald MA.  2019.  Assessing seasonality and density from passive acoustic monitoring of signals presumed to be from pygmy and dwarf sperm whales in the Gulf of Mexico. Frontiers in Marine Science. 6   10.3389/fmars.2019.00066   AbstractWebsite

Pygmy sperm whales (Kogia breviceps) and dwarf sperm whales (Kogia sima) are deep diving cetaceans that commonly strand along the coast of the southeast US, but that are difficult to study visually at sea because of their elusive behavior. Conventional visual surveys are thought to significantly underestimate the presence of Kogia and they have proven difficult to approach for tracking and tagging. An approach is presented for density estimation of signals presumed to be from Kogia spp. based on passive acoustic monitoring data collected at sites in the Gulf of Mexico (GOM) from the period following the Deepwater Horizon oil spill (2010-2013). Both species of Kogia are known to inhabit the GOM, although it is not possible to acoustically separate the two based on available knowledge of their echolocation clicks. An increasing interannual density trend is suggested for animals near the primary zone of impact of the oil spill, and to the southeast of the spill. Densities were estimated based on both counting individual echolocation clicks and counting the presence of groups of animals during one-min time windows. Densities derived from acoustic monitoring at three sites are all substantially higher (4-16 animals/1000 km(2)) than those that have been derived for Kogia from line transect visual surveys in the same region (0.5 animals/1000 km(2)). The most likely explanation for the observed discrepancy is that the visual surveys are underestimating Kogia spp. density, due to the assumption of perfect detectability on the survey trackline. We present an alternative approach for density estimation, one that derives echolocation and behavioral parameters based on comparison of modeled and observed sound received levels at sites of varying depth.

2018
Varga, LM, Wiggins SM, Hildebrand JA.  2018.  Behavior of singing fin whales Balaenoptera physalus tracked acoustically offshore of Southern California. Endangered Species Research. 35:113-124.   10.3354/esr00881   AbstractWebsite

Fin whales Balaenoptera physalus produce stereotyped low-frequency calls (1530 Hz) that can be detected at great ranges and are considered song when produced in a repeated temporal pattern. These calls, referred to as 20 Hz calls, were localized and tracked using a 1 km aperture array of 4 passive acoustic recorders at approximately 800 m depth northwest of San Clemente Island, offshore of Southern California, USA, for 4 continuous weeks during late fall 2007. A total of 1454 calls were localized over the recording period. The average (+/- SD) estimated source sound pressure level was 194.8 +/- 0.2 dB(pp) re 1 mu Pa-2 at 1 m (where pp is peak-to-peak) and 180.9 +/- 0.2 dB(rms) re 1 mu Pa at 1 m (where rms is root mean square). The majority of these calls were in the form of a doublet song pattern, with average inter-pulse intervals of 13 and 18 s. These tracks are the first to be reported for transiting solitary singing fin whales using passive acoustic monitoring techniques. Acoustic tracking of fin whales provides insight into the ecology and behavior of this endangered species as well as vocal behaviors, which are important when studying the potential impact of anthropogenic noise. Call source sound pressure level, along with calling behavior, provides important parameters required for population density estimation. Furthermore, studying fin whale song patterns may aid in distinguishing different subpopulations.

Keen, KA, Thayre BJ, Hildebrand JA, Wiggins SM.  2018.  Seismic airgun sound propagation in Arctic Ocean waveguides. Deep-Sea Research Part I-Oceanographic Research Papers. 141:24-32.   10.1016/j.dsr.2018.09.003   AbstractWebsite

Underwater recordings of seismic airgun surveys in the deep-water Beaufort Sea and on the shallow-water Chukchi Sea shelf were made from sites on the continental slope and shelf break north-northwest of Point Barrow, Alaska. Airgun pulses from the deep-water survey were recorded more than 500 km away, and from the shallow-water survey up to similar to 100 km. In the deep-water, received sound pressure levels show spherical spreading propagation; whereas, sound exposure levels exhibit cylindrical spreading propagation. Over the shallow-water shelf, transmission losses were much greater than spherical spreading, due to energy loss in the seafloor. Understanding how sound propagates across large spatial scales in the Arctic Ocean is important for better management and mitigation of anthropogenic noise pollution in marine soundscapes, especially as diminished ice in the Arctic Ocean allows for longer range sound propagation.

Hodge, LEW, Baumann-Pickering S, Hildebrand JA, Bell JT, Cummings EW, Foley HJ, McAlarney RJ, McLellan WA, Pabst DA, Swaim ZT, Waples DM, Read AJ.  2018.  Heard but not seen: Occurrence of Kogia spp. along the western North Atlantic shelf break. Marine Mammal Science. 34:1141-1153.   10.1111/mms.12498   AbstractWebsite
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Harris, CM, Thomas L, Falcone EA, Hildebrand J, Houser D, Kvadsheim PH, Lam FPA, Miller PJO, Moretti DJ, Read AJ, Slabbekoorn H, Southall BL, Tyack PL, Wartzok D, Janik VM.  2018.  Marine mammals and sonar: Dose-response studies, the risk-disturbance hypothesis and the role of exposure context. Journal of Applied Ecology. 55:396-404.   10.1111/1365-2664.12955   AbstractWebsite

1. Marine mammals may be negatively affected by anthropogenic noise. Behavioural response studies (BRS) aim to establish a relationship between noise exposure conditions (dose) from a potential stressor and associated behavioural responses of animals. A recent series of BRS have focused on the effects of naval sonar sounds on cetaceans. Here, we review the current state of understanding of naval sonar impact on marine mammals and highlight knowledge gaps and future research priorities. 2. Many marine mammal species exhibit responses to naval sonar sounds. However, responses vary between and within individuals and populations, highlighting the importance of exposure context in modulating dose-response relationships. 3. There is increasing support from both terrestrial and marine systems for the risk-disturbance hypothesis as an explanation for underlying response processes. This proposes that sonar sounds may be perceived by animals as a threat, evoking a response shaped by the underlying species-specific risk of predation and anti-predator strategy. An understanding of responses within both the dose-response and risk-disturbance frameworks may enhance our ability to predict responsiveness for unstudied species and populations. 4. Many observed behavioural responses are energetically costly, but the way that these responses may lead to long-term individual and population-level impacts is poorly understood. 5. Synthesis and applications. Behavioural response studies have greatly improved our understanding of the potential effects of naval sonar on marine mammals. Despite data gaps, we believe a dose-response approach within a risk-disturbance framework will enhance our ability to predict responsiveness for unstudied species and populations. We advocate for (1) regulatory frameworks to utilize peer-reviewed research findings when making predictions of impact, (2) regulatory frameworks to account for the inherent uncertainty in predictions of impact and (3) investment in monitoring programmes that are both directed by recent research and offer opportunities for validation of predictions at the individual and population level.

Stanistreet, JE, Nowacek DP, Bell JT, Cholewiak DM, Hildebrand JA, Hodge LEW, Van Parijs SM, Read AJ.  2018.  Spatial and seasonal patterns in acoustic detections of sperm whales Physeter macrocephalus along the continental slope in the western North Atlantic Ocean. Endangered Species Research. 35:1-13.   10.3354/esr00867   AbstractWebsite

The distribution and seasonal movements of sperm whales Physeter macrocephalus are poorly understood in the western North Atlantic Ocean, despite a long history of human exploitation of the species. Cetacean surveys in this region are typically conducted during the summer, when weather conditions are amenable for visual observation, resulting in a seasonal bias in species occurrence data. In the present study, we conducted multi-year passive acoustic monitoring to assess year-round sperm whale occurrence along the continental slope between Florida and New England, USA. Between 2011 and 2015, we collected 2037 d of recordings using bottom-mounted recorders deployed at 5 sites. We analyzed these recordings for sperm whale echolocation clicks, which were detected commonly between New England and North Carolina, but infrequently off the coast of Florida. In the northern half of the study region, we observed distinct seasonal patterns in the daily prevalence of sperm whale clicks, with a winter peak in occurrence off Cape Hatteras, North Carolina, followed by an increase later in the spring at sites further north. South of Cape Hatteras, seasonal patterns were less apparent. We detected sperm whale clicks during all hours of the day throughout the study area, and did not observe strong diel patterns. Overall, our results provide a comprehensive year-round baseline on the occurrence of sperm whales across multiple recording sites, demonstrating the utility of passive acoustic monitoring to assess patterns in sperm whale occurrence across broad spatial and temporal scales.

2017
Frasier, KE, Roch MA, Soldevilla MS, Wiggins SM, Garrison LP, Hildebrand JA.  2017.  Automated classification of dolphin echolocation click types from the Gulf of Mexico. Plos Computational Biology. 13   10.1371/journal.pcbi.1005823   AbstractWebsite

Delphinids produce large numbers of short duration, broadband echolocation clicks which may be useful for species classification in passive acoustic monitoring efforts. A challenge in echolocation click classification is to overcome the many sources of variability to recognize underlying patterns across many detections. An automated unsupervised network-based classification method was developed to simulate the approach a human analyst uses when categorizing click types: Clusters of similar clicks were identified by incorporating multiple click characteristics (spectral shape and inter-click interval distributions) to distinguish within-type from between-type variation, and identify distinct, persistent click types. Once click types were established, an algorithm for classifying novel detections using existing clusters was tested. The automated classification method was applied to a dataset of 52 million clicks detected across five monitoring sites over two years in the Gulf of Mexico (GOM). Seven distinct click types were identified, one of which is known to be associated with an acoustically identifiable delphinid (Risso's dolphin) and six of which are not yet identified. All types occurred at multiple monitoring locations, but the relative occurrence of types varied, particularly between continental shelf and slope locations. Automatically- identified click types from autonomous seafloor recorders without verifiable species identification were compared with clicks detected on sea-surface towed hydrophone arrays in the presence of visually identified delphinid species. These comparisons suggest potential species identities for the animals producing some echolocation click types. The network-based classification method presented here is effective for rapid, unsupervised delphinid click classification across large datasets in which the click types may not be known a priori.

Wells, BK, Schroeder ID, Bograd SJ, Hazen EL, Jacox MG, Leising A, Mantua N, Santora JA, Fisher J, Peterson WT, Bjorkstedt E, Robertson RR, Chavez FP, Goericke R, Kudela R, Anderson C, Lavaniegos BE, Gomez-Valdes J, Brodeur RD, Daly EA, Morgan CA, Auth TD, Field JC, Sakuma K, McClatchie S, Thompson AR, Weber ED, Watson W, Suryan RM, Parrish J, Dolliver J, Loredo S, Porquez JM, Zamon JE, Schneider SR, Golightly RT, Warzybok P, Bradley R, Jahncke J, Sydeman W, Melin SR, Hildebrand JA, Debich AJ, Thayre B.  2017.  State Of The California Current 2016-17: Still Anything But "Normal" In The North. California Cooperative Oceanic Fisheries Investigations Reports. 58:1-55. AbstractWebsite

This report examines the ecosystem state of the California Current System (CCS) from spring 2016-spring 2017. Basin-scale indices suggest conditions that would support average to below average coast-wide production across the CCS during this time period. Regional surveys in 2016 sampled anomalously warm surface and subsurface waters across the CCS. Chlorophyll concentrations were low across the CCS in 2016 and, concomitant with that, copepod communities had an anomalously high abundance of subtropical species. Early in 2017 conditions between northern, central, and southern CCS were dissimilar. Specifically, surface conditions north of Cape Mendocino remained anomalously warm, chlorophyll was very low, and subtropical copepods were anomalously abundant. Southern and central CCS surveys indicated that environmental conditions and chlorophyll were within normal ranges for the longer time series, supporting an argument that biophysical conditions/ecosystem states in the southern and central CCS were close to normal. Epipelagic micronekton assemblages south of Cape Mendocino were generally close to longer-term average values, however the northern assemblages have not returned to a "normal" state following the 2014-15 large marine heatwave and 2016 El Nino. North of Cape Mendocino the epipelagic micronekton was largely composed of offshore and southern derived taxa. We hypothesize that stronger-than-typical winter downwelling in 2017 and a reduced spawning biomass of forage taxa are contributors to the anomalous forage community observed in the north. Also of note, surveys indicate northern anchovy (Engraulis mordax) abundance was greater than average (for recent years) and nearer shore in northern regions. Finally, record-low juvenile coho and Chinook salmon catches in the 2017 northern CCS salmon survey suggest that out-migrating Columbia Basin salmon likely experienced unusually high early mortality at sea, and this is further supported by similarities between the 2017 forage assemblage and that observed during poor outmigration survival years in 2004, 2005, and 2015. Generally, the reproductive success of seabirds in 2016 (the most current year available) was low in the north but near average in central California. At Yaquina Head off Oregon and Castle Rock off northern California some of the lowest reproductive success rates on record were documented. In addition to reduced abundance of prey, there was a northward shift of preferred seabird prey. Seabird diets in northern areas also corroborated observations of a northward shift in fish communities. Nest failure was attributed to a combination of bottom-up and top-down forces. At Castle Rock, most chicks died of starvation whereas, at Yaquina Head, most nests failed (95% of common murre, Uria aagle) due to disturbance by bald eagles (Haliaeetus leucocephalus) seeking alternative prey. Mean bird densities at sea for the 2017 surveys between Cape Flattery Washington and Newport Oregon were the lowest observed and may indicate continued poor reproductive performance of resident breeders in 2017. South of Cape Mendocino, where forage availability was typical, seabird reproductive success was also below average for most species in 2016, but did not approach failure rates observed in the north. Finally, in 2017, abundances of seabirds observed at-sea off southern California were anomalously high suggesting an improved foraging environment in that area. Marine mammal condition and foraging behavior were also impacted by the increased abundance and shifting distribution of the northern anchovy population. Increases in the abundance of northern anchovy in the Southern California Bight coincided with improved condition of sea lion (Zalophus californianus) pups in 2016. Namely, lipid-rich northern anchovy occurred in great frequencies in the nursing female diet. Increases in northern anchovy nearshore in the central and northern CCS may have also contributed to a shoreward shift in distribution of humpback whales (Megaptera -novaeangliae) in these regions. These shifts along with recovering humpback whale populations contributed to recent increases in human-whale interactions (e.g., fixed-gear entanglements).

Davis, GE, Baumgartner MF, Bonnell JM, Bell J, Berchok C, Thornton JB, Brault S, Buchanan G, Charif RA, Cholewiak D, Clark CW, Corkeron P, Delarue J, Dudzinski K, Hatch L, Hildebrand J, Hodge L, Klinck H, Kraus S, Martin B, Mellinger DK, Moors-Murphy H, Nieukirk S, Nowacek DP, Parks S, Read AJ, Rice AN, Risch D, Sirovic A, Soldevilla M, Stafford K, Stanistreet JE, Summers E, Todd S, Warde A, Van Parijs SM.  2017.  Long-term passive acoustic recordings track the changing distribution of North Atlantic right whales (Eubalaena glacialis) from 2004 to 2014. Scientific Reports. 7   10.1038/s41598-017-13359-3   AbstractWebsite

Given new distribution patterns of the endangered North Atlantic right whale (NARW; Eubalaena glacialis) population in recent years, an improved understanding of spatio-temporal movements are imperative for the conservation of this species. While so far visual data have provided most information on NARW movements, passive acoustic monitoring (PAM) was used in this study in order to better capture year-round NARW presence. This project used PAM data from 2004 to 2014 collected by 19 organizations throughout the western North Atlantic Ocean. Overall, data from 324 recorders (35,600 days) were processed and analyzed using a classification and detection system. Results highlight almost year-round habitat use of the western North Atlantic Ocean, with a decrease in detections in waters off Cape Hatteras, North Carolina in summer and fall. Data collected post 2010 showed an increased NARW presence in the mid-Atlantic region and a simultaneous decrease in the northern Gulf of Maine. In addition, NARWs were widely distributed across most regions throughout winter months. This study demonstrates that a large-scale analysis of PAM data provides significant value to understanding and tracking shifts in large whale movements over long time scales.

Guazzo, RA, Helble TA, D’Spain GL, Weller DW, Wiggins SM, Hildebrand JA.  2017.  Migratory behavior of eastern North Pacific gray whales tracked using a hydrophone array. PLOS ONE. 12:e0185585.: Public Library of Science   10.1371/journal.pone.0185585   Abstract

Eastern North Pacific gray whales make one of the longest annual migrations of any mammal, traveling from their summer feeding areas in the Bering and Chukchi Seas to their wintering areas in the lagoons of Baja California, Mexico. Although a significant body of knowledge on gray whale biology and behavior exists, little is known about their vocal behavior while migrating. In this study, we used a sparse hydrophone array deployed offshore of central California to investigate how gray whales behave and use sound while migrating. We detected, localized, and tracked whales for one full migration season, a first for gray whales. We verified and localized 10,644 gray whale M3 calls and grouped them into 280 tracks. Results confirm that gray whales are acoustically active while migrating and their swimming and acoustic behavior changes on daily and seasonal time scales. The seasonal timing of the calls verifies the gray whale migration timing determined using other methods such as counts conducted by visual observers. The total number of calls and the percentage of calls that were part of a track changed significantly over both seasonal and daily time scales. An average calling rate of 5.7 calls/whale/day was observed, which is significantly greater than previously reported migration calling rates. We measured a mean speed of 1.6 m/s and quantified heading, direction, and water depth where tracks were located. Mean speed and water depth remained constant between night and day, but these quantities had greater variation at night. Gray whales produce M3 calls with a root mean square source level of 156.9 dB re 1 μPa at 1 m. Quantities describing call characteristics were variable and dependent on site-specific propagation characteristics.

Gassmann, M, Wiggins SM, Hildebrand JA.  2017.  Deep-water measurements of container ship radiated noise signatures and directionality. Journal of the Acoustical Society of America. 142:1563-1574.   10.1121/1.5001063   AbstractWebsite

Underwater radiated noise from merchant ships was measured opportunistically from multiple spatial aspects to estimate signature source levels and directionality. Transiting ships were tracked via the Automatic Identification System in a shipping lane while acoustic pressure was measured at the ships' keel and beam aspects. Port and starboard beam aspects were 15 degrees, 30 degrees, and 45 degrees in compliance with ship noise measurements standards [ANSI/ASA S12.64 (2009) and ISO 17208-1 (2016)]. Additional recordings were made at a 10 degrees starboard aspect. Source levels were derived with a spherical propagation (surface-affected) or a modified Lloyd's mirror model to account for interference from surface reflections (surface-corrected). Ship source depths were estimated from spectral differences between measurements at different beam aspects. Results were exemplified with a 4870 and a 10 036 twenty-foot equivalent unit container ship at 40%-56% and 87% of service speeds, respectively. For the larger ship, opportunistic ANSI/ISO broadband levels were 195 (surface-affected) and 209 (surface-corrected) dB re 1 mu Pa-2 1 m. Directionality at a propeller blade rate of 8 Hz exhibited asymmetries in stern-bow (< 6 dB) and port-starboard (< 9 dB) direction. Previously reported broadband levels at 10 degrees aspect from McKenna, Ross, Wiggins, and Hildebrand [(2012b). J. Acoust. Soc. Am. 131, 92-103] may be similar to 12 dB lower than respective surface-affected ANSI/ISO standard derived levels. (C) 2017 Acoustical Society of America.

Reyes Reyes, MV, Baumann-Pickering S, Simonis A, Melcón ML, Trickey J, Hildebrand J, Iñíguez M.  2017.  High-frequency modulated signals recorded off the Antarctic peninsula area: Are killer whales emitting them? Acoustics Australia.   10.1007/s40857-017-0103-x   Abstract

High-frequency modulated signals with a stereotyped down-swept contour were recorded in the northwestern Antarctic Peninsula using an autonomous recorder and a towed hydrophone array. Signals have a mean start frequency at 21.6 kHz, end frequency at 15.7 kHz, −10 dB bandwidth of 5.9 kHz, and duration of 65.2 ms. Bouts of signals were generally recorded with a median inter-signal interval of 2.1 s. HFM signals partially modulated in the non-ultrasonic range similar to the ones described in this paper have already been reported for killer whales in the North Pacific, Western South Atlantic and Western Australian coast. The HFM signals were recorded in the presence of other odontocete sounds such as whistles, echolocation clicks and burst-pulsed sounds. The similarities of these sounds with vocalizations described for killer whales in the Western Australian coast lead us to strongly believe that the described HFM signals were produced by Antarctic killer whales. This paper described for the first time HFM signals in Antarctica and discussed evidence suggesting that Antarctic type A killer whales are the most probable candidates to produce such signals. However, a visual confirmation is still needed and the function of the HFM signals remains unknown.

Simonis, AE, Roch MA, Bailey B, Barlow J, Clemesha RES, Iacobellis S, Hildebrand JA, Baumann-Pickering S.  2017.  Lunar cycles affect common dolphin Delphinus delphis foraging in the Southern California Bight. Marine Ecology Progress Series. 577:221-235.   10.3354/meps12247   Abstract

In the Southern California Bight, the common dolphin Delphinus delphis is the most abundant dolphin species and preys upon small pelagic fish, mesopelagic fish, and cephalopods. Mesopelagic fish and many cephalopods are available throughout the year, and they form deep scattering layers, some of which characteristically undergo strong diel vertical migrations. The extent of vertical migration depends on the degree of sea surface solar and lunar illumination. At their daytime depth, mesopelagic prey are beyond the range of shallow-diving dolphins. Autonomous acoustic recorders were used to monitor dolphin echolocation at 2 offshore recording locations from 2009 to 2014. Manual and automated classification techniques were used to identify periods of high echolocation activity, indicative of common dolphin foraging. Clear lunar patterns existed in cool months, when echolocation activity was highest during the darkest periods of the night and lunar month, indicating times when dolphins were foraging, possibly on mesopelagic prey. Echolocation was more abundant during warm months, but diel and lunar patterns in echolocation were weaker. Generalized additive mixed models show that the observed patterns in echolocation activity are correlated with lunar day and position of the moon in the night sky. Seasonal patterns may represent geographic shifts in common dolphin populations, shoaling scattering layers, or prey switching behavior during the warm months, whereby dolphins target small pelagic fish not associated with the deep scattering layers. Overall, dolphin foraging activity declined from 2009 to 2014 during warm months, which may be related to a declining abundance of small pelagic fish.

Soldevilla, MS, Hildebrand JA, Frasier KE, Dias LA, Martinez A, Mullin KD, Rosel PE, Garrison LP.  2017.  Spatial distribution and dive behavior of Gulf of Mexico Bryde's whales: potential risk of vessel strikes and fisheries interactions. Endangered Species Research. 32:533-550.   10.3354/esr00834   AbstractWebsite

Bryde's whales Balaenoptera edeni are the only resident baleen whale species in the Gulf of Mexico (GoM), where they are extremely rare, have a restricted distribution, and re present a unique evolutionary lineage. The reasons for the restricted distribution and small population size are unknown, but high levels of industrial activity in the GoM may be a major factor. We evaluated the geospatial overlap of GoM Bryde's whales with 2 industries known to impact baleen whale species: commercial shipping and commercial fisheries. We further evaluated the potential for impacts by examining the first dive behavior data collected from a kinematic tag attached to a GoM Bryde's whale for 3 d. Vessel traffic and fishery effort are low in GoM Bryde's whale habitat compared to the rest of the northern GoM, but several shipping lanes transit through the habitat, and the reef fish bottom longline fishery exerts considerable effort within the habitat. The tagged whale exhibited diel diving behavior with diurnal deep dives and foraging lunges at or near the sea floor, and shallow nocturnal diving, with 88% of its nighttime spent near the surface within the draught depths of most large commercial vessels. Given the location of commercial shipping traffic in GoM Bryde's whale habitat, ship strikes may pose a threat to this population if the whales commonly spend time near the surface, especially at night. Also, if bottom or near-bottom feeding is a normal feeding strategy for these whales, there is potential for entan-glement in bottom longline gear. Managing these threats may improve population recovery.

Rice, A, Deecke VB, Ford JKB, Pilkington JF, Oleson EM, Hildebrand JA, Sirovic A.  2017.  Spatial and temporal occurrence of killer whale ecotypes off the outer coast of Washington State, USA. Marine Ecology Progress Series. 572:255-268.   10.3354/meps12158   AbstractWebsite

Three killer whale Orcinus orca ecotypes inhabit the northeastern Pacific: residents, transients, and offshores. To investigate intraspecific differences in spatial and temporal occur rence off the outer coast of Washington State, USA, 2 long-term acoustic recorders were deployed from July 2004 to August 2013: one off the continental shelf in Quinault Canyon (QC) and the other on the shelf, off Cape Elizabeth (CE). Acoustic encounters containing pulsed calls were analyzed for call types attributable to specific ecotypes, as no calls are shared between ecotypes. Both sites showed killer whale presence year-round, although site CE had a higher number of days with encounters overall. Transients were the most common ecotype at both sites and were encountered mainly during the spring and early summer. Residents were encountered primarily at site CE and showed potential seasonal segregation between the 2 resident communities, with northern residents present mainly during summer and early fall when southern residents were not encountered. Offshore encounters were higher at site QC, with little evidence for seasonality. Spatial and temporal variability of residents and transients matches the distribution of their prey and can potentially be used for further inferences about prey preferences for different transient groups.

Stanistreet, JE, Nowacek DP, Baumann-Pickering S, Bell JT, Cholewiak DM, Hildebrand JA, Hodge LEW, Moors-Murphy HB, Van Parijs SM, Read AJ.  2017.  Using passive acoustic monitoring to document the distribution of beaked whale species in the western North Atlantic Ocean. Canadian Journal of Fisheries and Aquatic Sciences. : NRC Research Press   10.1139/cjfas-2016-0503   AbstractWebsite
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Paniagua-Mendoza, A, Gendron D, Romero-Vivas E, Hildebrand JA.  2017.  Seasonal acoustic behavior of blue whales (Balaenoptera musculus) in the Gulf of California, Mexico. Marine Mammal Science. 33:206-218.   10.1111/mms.12362   AbstractWebsite

Six years of passive acoustic monitoring data from the Gulf of California reveal seasonality and movements for the northeastern Pacific blue whales. Three sites were studied, one from the southern (Punta Pescadero) and two from the northern (Isla Tiburon and Canal de Ballenas) regions. A total of 4,953 h were analyzed, and 15,539 blue whale calls were detected, of which 2,723 (18%) were A calls, 11,249 were B calls (72%), and 1,567 were D calls (10%). A and B calls were produced both as song units (2,524) or AB singular calls (2,026). The high rate of songs and their seasonality suggest that the GC is a winter-breeding ground. A shift from AB call predominance in winter, to D calls in spring and early summer, especially at the entrance of the GC, suggests the importance of this area for reproduction and foraging. Analysis of calling frequency suggests a clear movement of blue whales from the southern region (Punta Pescadero) to the northern regions (Canal de Ballenas and Isla Tiburon), with subsequent southern movement in March. The seasonality and mobility of blue whales in the Gulf of California, inferred from their calling, contributes to the ecological understanding of this population.

2016
Reyes, MVR, Tossenberger VP, Iniguez MA, Hildebrand JA, Melcon ML.  2016.  Communication sounds of Commerson's dolphins (Cephalorhynchus commersonii) and contextual use of vocalizations. Marine Mammal Science. 32:1219-1233.   10.1111/mms.12321   AbstractWebsite

Cetaceans produce a variety of vocalizations to communicate; however, little information exists on the acoustic behavior displayed by Commerson's dolphins (Cephalorhynchus commersonii) in the wild other than their echolocation behavior. Most available literature suggests that Commerson's dolphins do not produce any other sound type besides narrow-band high-frequency (NBHF) clicks, such that no signals are emitted below 100 kHz. We conducted acoustic recordings together with sightings to study the acoustic behavior of Commerson's dolphins in Bahia San Julian, Argentina. This is the first study that provides evidence that this species produces a variety of acoustic signals, including whistles and broad-band clicks (BBC), with frequency content well below 100 kHz. Whistles were recorded mostly in the presence of mother and calf and were associated with parental behavior. BBC may be used for communication purposes by adults. These vocalizations are within the hearing range of killer whales and so could pose a risk of predation for Commerson's dolphins. Whether this population of Commerson's dolphins produce all these types of signals while they are in the open sea out of the waters of Bahia San Julian, which are apparently safe from predation, remains unknown.

Frasier, KE, Wiggins SM, Harris D, Marques TA, Thomas L, Hildebrand JA.  2016.  Delphinid echolocation click detection probability on near-seafloor sensors. Journal of the Acoustical Society of America. 140:1918-1930.   10.1121/1.4962279   AbstractWebsite

The probability of detecting echolocating delphinids on a near-seafloor sensor was estimated using two Monte Carlo simulation methods. One method estimated the probability of detecting a single click (cue counting); the other estimated the probability of detecting a group of delphinids (group counting). Echolocation click beam pattern and source level assumptions strongly influenced detectability predictions by the cue counting model. Group detectability was also influenced by assumptions about group behaviors. Model results were compared to in situ recordings of encounters with Risso's dolphin (Grampus griseus) and presumed pantropical spotted dolphin (Stenella attenuata) from a near-seafloor four-channel tracking sensor deployed in the Gulf of Mexico (25.537 degrees N 84.632 degrees W, depth 1220 m). Horizontal detection range, received level and estimated source level distributions from localized encounters were compared with the model predictions. Agreement between in situ results and model predictions suggests that simulations can be used to estimate detection probabilities when direct distance estimation is not available. (C) 2016 Acoustical Society of America.

Naleway, SE, Yu CF, Hsiong RL, Sen Gupta A, Iovine PM, Hildebrand JA, Meyers MA, McKittrick J.  2016.  Bioinspired intrinsic control of freeze cast composites: Harnessing hydrophobic hydration and clathrate hydrates. Acta Materialia. 114:67-79.   10.1016/j.actamat.2016.05.019   AbstractWebsite

Bioinspired ZrO2-epoxy, two-phase composite materials were fabricated by the freeze casting fabrication technique followed by polymer infiltration. These materials were intrinsically controlled by adding varying concentrations of the monofunctional alcohols ethanol (EtOH), n-propanol (n-PrOH) and n-butanol (n-BuOH). The microstructures of freeze cast scaffolds created with these alcohol additives demonstrated maximum pore areas (peak A(p)) at concentrations of 10, 5-7 and 3 vol% for EtOH, n-PrOH and n-BuOH respectively. Differential scanning calorimetry analyses of binary mixtures of these additives and water suggested only n-PrOH was capable of developing clathrate hydrates. Measurements of the adiabatic compressibility of complete freeze casting slurries showed that a similar room temperature phenomenon, hydrophobic hydration, was occurring in all cases with the maximum effect occurring at the same additive concentrations as the peak Ap values. This highlights that effects occurring within the slurry at room temperature and before freezing may have a significant effect on the freeze casting process. Analysis of the mechanical properties shows that infiltration of the scaffolds can provide resistance to Euler buckling, resulting in strengths of similar to 3 orders of magnitude greater than uninfiltrated (and therefore unsupported) scaffolds. This suggests that layered structural design elements, found throughout nature, may be harnessing this Euler buckling resistance to increase strength. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Wiggins, SM, Hall JM, Thayre BJ, Hildebrand JA.  2016.  Gulf of Mexico low-frequency ocean soundscape impacted by airguns. Journal of the Acoustical Society of America. 140:176-183.   10.1121/1.4955300   AbstractWebsite

The ocean soundscape of the Gulf of Mexico (GOM) has not been well-studied, although it is an important habitat for marine mammals, including sperm and beaked whales, many dolphin species, and a potentially endangered baleen whale species. The GOM is also home to high levels of hydrocarbon exploration and extraction, heavily used commercial shipping ports, and significant fishery industry activity, all of which are known contributors to oceanic noise. From 2010-2013, the soundscape of three deep and two shallow water sites in the GOM were monitored over 10 - 1000 Hz. Average sound pressure spectrum levels were high, >90 dB re 1 mu Pa-2/Hz at <40 Hz for the deep water sites and were associated with noise from seismic exploration airguns. More moderate sound pressure levels, <55 dB re 1 mu Pa-2/Hz at >700 Hz, were present at a shallow water site in the northeastern Gulf, removed from the zone of industrial development and bathymetrically shielded from deep water anthropogenic sound sources. During passage of a high wind event (Hurricane Isaac, 2012), sound pressure levels above 200 Hz increased with wind speed, but at low frequencies (<100 Hz) sound pressure levels decreased owing to absence of noise from airguns. (C) 2016 Author(s).

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

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

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

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