From the beginning of the Navy Marine Mammal Program (MMP), scientific research has been conducted to support the development of systems and technology and to gain a better understanding of the animals. The more we know about marine mammals, the better we can protect them. As a result, the MMP is the single largest contributor to the literature on marine mammals (over 1000 technical publications). This research, conducted by both staff and visiting scientists, has covered a broad spectrum of topics including hydrodynamics, sensory systems, anatomy and physiology, health care, behavior, reproduction, telemetry, open sea operations, and environmental ecology. This work is facilitated by well-trained animals that can participate in research in ocean pens, pools, or open water.
All of the animal research at the MMP has always been conducted under the oversight of an Institutional Animal Care and Use Committee (IACUC) that reviews all proposals for scientific value and validity, and to ensure safe keeping of the study animals. Our research is currently focused on several major areas with the continuing goal of safeguarding our forces at sea, responsibly protecting the marine environment, providing our animals with the best health care possible, and understanding marine mammal bioacoustics. Following are samples of some of the work underway.
To ensure the ongoing health and overall longevity of our animals, a major effort is made to explore and improve marine mammal medicine and care. Today veterinary techniques take advantage of animals cooperatively participating in routine medical examinations that involve the drawing of blood and the use of endoscopy and ultrasound scans to monitor the condition of each animal. Conducting research to detect, treat, and prevent infectious and metabolic diseases and determining the unique clinical needs on aging animals are critical to the health and operability of the Navy dolphins and sea lions. The MMP is also committed to the development of advanced technologies to determine population baselines and to diagnose and treat disease. Combining the extensive animal health database maintained by the NMMP and the frequent deployment of animals around the world, NMMP scientists are also investigating the possibility of our dolphins acting as environmental sentinels to monitor the condition of the world's oceans.
Marine mammal hearing
Sound is more effectively transmitted through water compared to light; as a result, marine mammals have evolved hearing abilities that allow them to exploit sound for communication, navigation, finding and capturing prey, and avoiding predators. Bottlenose dolphins and other odontocetes (toothed whales) are some of the most sophisticated listeners in the animal kingdom. Both dolphins and sea lions have ultrasonic hearing — they can hear sounds at frequencies above the range of human hearing. Dolphins can hear up to approximately 160 kHz (eight times higher than humans), with best hearing sensitivity between 40 kHz and 80 kHz. Their ability to detect and classify sounds in noisy environments is unrivaled by any human-made listening device. Sea lions can hear sounds up to about 40 kHz and have good underwater directional hearing.
Because these animals rely on sound to such a great extent, hearing impairment due to aging or environmental noise has the potential to adversely affect their performance and overall fitness. As a result, hearing tests have become a regular part of each of our animal’s physical examinations. The techniques developed to test their hearing have also been used to test animals at other marine facilities and to opportunistically test wild animals. The accumulation of this knowledge has been paramount in developing mitigation measures to protect marine mammals from harmful noise.
Behavioral (psychophysical) hearing tests
Testing human hearing is straightforward — an audiologist gives verbal instructions for taking the hearing test; for example, “sit quietly and press a button when you hear a tone”. We can’t give marine mammals complex verbal instructions on how to participate in a hearing test. Instead, operant conditioning techniques and positive reinforcement are used to train animals to perform a specific action, such as whistling, barking, or pushing a paddle, when they hear a tone. The amplitude of the tone is then adjusted, and the animal’s responses recorded, to determine the quietest sound that can be heard at a particular frequency. This is called the hearing threshold. This task is a type of psychophysical procedure — a way of conducting measurements to relate sensory perception to the measurable properties of a stimulus. Psychophysical hearing tests are also called behavioral tests, since the tasks require the animal to perform a specific behavior in response to the sounds. Behavioral techniques such as these have been used at the MMP since the late 1960s to determine hearing sensitivity and evaluate auditory system function in a variety of marine mammals, including dolphins, sea lions, and belugas. These techniques are very straightforward and intuitive — we are essentially “asking” the animals if they can hear a sound. The methods also produce reliable data, but can be very time consuming — it can take several months to train an animal to participate in a behavioral hearing test.
Behavioral hearing tests at the MMP are performed underwater in San Diego Bay or a quiet test pool. In-air testing is normally performed in an acoustically-treated room. Regardless of test environment, the experiments utilize a “listening station,” often constructed of PVC pipe. The listening station provides a fixed location for the hearing test and enables the sound levels to be accurately measured. The hearing tests are controlled using custom software to generate hearing test tones, and record and analyze the behavioral responses.
A bottlenose dolphin participating in a hearing test in a quiet pool. The PVC listening station contains an underwater sound projector to generate the hearing test tones and a hydrophone to monitor the sounds in the pool. The dolphin is positioned on a neoprene-covered “biteplate” to ensure that she is in the calibrated sound field.
A trainer prepares to begin a hearing test trial with a bottlenose dolphin in San Diego Bay. The dolphin is wearing a “jawphone” — an underwater sound projector embedded in a suction cup placed on the lower jaw. This is the site for high-frequency sound reception in dolphins.
A California sea lion participates in an in-air hearing test. Sounds are presented to the sea lion using headphones. The sea lion indicates that he is ready for the next trial by resting his chin on a tennis ball mounted on the listening station.
A sea lion participates in an underwater hearing test in a quiet pool. To accommodate sea lions, the dolphin listening station is modified by mounting a “chin rest” over the biteplate.
Electrophysiological hearing tests
In addition to behavioral methods, electrophysiological techniques can be used to assess hearing in marine mammals. Electrophysiological methods rely on the measurement of auditory evoked potentials (AEPs) — small (tens of nanovolts to microvolts) changes in the electrical activity of the brain produced when an animal hears a sound. Because the AEPs are automatically generated by the brain, this technique is ideal for individuals not specifically trained for behavioral hearing tests or for whom access is limited; for example, stranded and/or rehabilitating animals. Some AEPs are unaffected by attention and sleep, and can therefore be measured in sedated animals. AEPs are measured in marine mammals using electrodes placed on the head, similarly to the way AEPs are measured in human infants. The amplitude of the sound stimulus is then manipulated while the resulting AEPs are measured to find the hearing threshold — the quietest sound level that produces a measurable AEP.
AEPs can be measured using a variety of sound stimuli. One of the more commonly employed stimuli is a sinusoidal amplitude modulated (SAM) tone. The SAM tone has become a popular stimulus because it has relatively limited frequency content (so the measurements can be attributed to specific hearing frequencies) and it produces an AEP that can be objectively analyzed using statistical techniques. Using SAM tones modulated at different rates also allows hearing ability to be simultaneously assessed at multiple frequencies. At the Navy MMP, dolphin hearing has been simultaneously tested at nine frequencies and sea lion hearing has been simultaneously tested at seven frequencies in each ear (14 total). To date over 100 dolphins have been tested, revealing suspected effects of age, gender, and certain antibiotics on their hearing abilities. The relationships are similar to what is seen in people; for example, dolphins tend to lose their hearing as they get older, just like we do, and the males hear a little worse than the females. These data form an important complement to clinical physical exams and provide key information for animal trainers and clinicians. The data also provide important population-level parameters that help us understand what is “normal” hearing for marine mammals of different ages and life histories.
Dr. Jim Finneran at the MMP has developed a rugged, portable system for AEP measurements called EVREST (EVoked REsponse Study Tool). EVREST combines a rugged laptop computer with a custom software application designed for recording and analyzing auditory evoked potentials. With EVREST, a user can generate and calibrate up to 16 sound stimuli, measure evoked responses, and analyze and store data. EVREST has been used to measure AEPs in a variety of marine and terrestrial animals, including sea horses, fish, bottlenose dolphins, rough-toothed dolphins, harbor porpoises, a beaked whale, pilot whales, orcas, California sea lions, Steller sea lions, a harbor seal, Northern elephant seals, grey seals, and 11 species of non-human primates.
The EVREST hardware is centered around a rugged laptop computer with data acquisition capabilities and custom software. Gold-cup surface electrodes embedded in soft suction cups are placed on the head to measure the brain’s responses to tones. The sound projector is embedded inside a larger suction cup and placed on the dolphin’s lower jaw.
Screenshot of the EVREST software showing some of the options for generating sound stimuli.
Screenshot of the EVREST software showing the options for analyzing AEP data. The curve at right shows sea lion hearing thresholds simultaneously measured at seven frequencies, from 500 Hz to 32 kHz.
AEP hearing tests with dolphins are often conducted with the animals “beached” out of the water onto foam mats. Having the dolphin out of the water makes the AEPs easier to measure and allows the procedure to be performed simultaneously with physicals or other clinical care. For in-air measurements, jawphones are used to present the hearing test tones to the dolphins. Surface electrodes measure the brain’s responses.
AEP measurements on a stranded beaked whale at a rehabilitation facility. AEP methods can be used to evaluate the hearing of stranded animals, to assess the suitability of animals before release, and to better understand why the animal stranded.
Hearing tests being performed on an adult male Northern elephant seal at Año Nuevo State Reserve.
The unique capabilities of the MMP to conduct both behavioral and AEP tests with the same individual have also allowed AEP results to be validated against the more universally accepted behavioral data. This graph compares hearing thresholds measured in a California sea lion using behavioral and AEP methods. AEP thresholds are typically elevated compared to behavioral thresholds but accurately represent the shape of the audiogram — a plot of the hearing threshold versus sound frequency.
Effects of noise on marine mammal hearing
MMP scientists also use behavioral and electrophysiological methods to study more complex auditory mechanisms such as auditory masking and noise-induced hearing loss. Masking occurs when a sound affects the ability to hear another, typically simultaneous, sound. People can experience auditory masking in environments such as restaurants or clubs where the background noise levels are elevated, making it difficult to hear others during conversation. Noise-induced hearing loss is formally called a noise-induced threshold shift. A noise-induced threshold shift is an elevation in hearing threshold after exposure to noise that persists after the cessation of the noise. People can experience noise-induced threshold shifts after exposure to noisy environments such as factories or rock concerts, after operating loud power tools or firearms, or listening to loud music through ear buds. If the hearing thresholds return to normal after a noise-induced threshold shift, the shift is called a temporary threshold shift (TTS). If the thresholds do not return to normal, and some permanent hearing loss remains, the remaining shift is called a permanent threshold shift (PTS).
TTS experiments at the MMP with dolphins, belugas, and sea lions have provided critical data to better understand the effects of noise on marine mammals. These
studies compare hearing thresholds measured before and after exposure to various sounds to determine the amount, if any, of TTS and the time required for recovery. The studies are similar to those conducted with people to determine safe exposure levels for people working in noisy environments. The resulting data are widely used by the Navy and others to predict and mitigate the effects of man-made noise on marine mammal hearing.
A bottlenose dolphin participates in a TTS study in a pool. The three suction cups on her head and back contain surface electrodes used to measure auditory evoked potentials (AEPs). She also wears hydrophones mounted on suction cups near her ears to measure the noise exposure.
Dolphins have highly sophisticated, natural sonar (biosonar) that allows them to detect objects in the most complex acoustic environments. By echolocating — emitting high-frequency pulses called “clicks” and listening to echoes returning from underwater objects, dolphins can acoustically “see” their aquatic environment in amazing detail. The dolphin's biosonar system has yet to be matched by any manufactured device.
Early dolphin biosonar studies used trained dolphins to detect and discriminate various underwater objects (“targets”), like small spheres and cylinders. The object size, distance, material composition, and background noise were manipulated and the dolphin’s echolocation clicks and performance measured to learn about the capabilities of the biosonar system.
More recent studies utilize “phantom targets” or “phantom echoes”. In these studies, there is no physical target; instead, a hydrophone is used to record the dolphin’s emitted click. The click is then used to electronically create a simulated echo based on the characteristics of some physical object. The echo waveform is scaled in amplitude, delayed in time, and broadcast to the dolphin using an underwater transmitter. In this fashion, each click emitted by the dolphin results in an echo, although there is no actual physical target. The advantage of using phantom echoes is that they can be manipulated in ways that would be difficult or impossible with physical targets.
Operation of the phantom echo generator. The presence of an underwater object is simulated by capturing the dolphin’s emitted echolocation clicks, then broadcasting delayed signals that resemble the echoes from distant targets.
As sound travels from a source it is naturally attenuated — this means that the echoes from underwater objects get smaller and smaller as the distance to the object increases. To help compensate for this natural change in echo strength with target range, dolphins have evolved several mechanisms, collectively referred to as “automatic gain control”. To study automatic gain control in dolphins, MMP scientists combine echolocation studies with AEP measurements. The AEPs can be measured in response to both the dolphin’s emitted click and the returning echo. AEPs can also be measured in response to external sounds to map changes in hearing sensitivity that occur with changes in target range.
Schematic of a dolphin participating in a phantom echo detection task while wearing surface electrodes embedded in suction cups for AEP measurements. The hoop station ensures that the dolphin’s position is consistent between trials relative to the sound projector and hydrophone.
Auditory evoked potentials (AEPs) measured from a dolphin during an echolocation task with the target range from 2.5 m to 80 m. The AEP caused by the dolphin’s own emitted click can be seen between 2–6 ms. The AEP from the echo occurs with an increasing time delay relative to the click — as the range increases it takes longer for the click to reach the target and the echo to travel back to the dolphin. We can learn about automatic gain control mechanisms by examining the rate at which the AEP amplitudes change with target range.
Passive acoustic monitoring for whales
Passive acoustic monitoring (PAM) in underwater environments refers to the use of acoustic sensors (hydrophones) to monitor for underwater sounds of interest. In our case, the sounds of interest are the sounds emitted by whales, natural environmental sounds(e.g., rain), and man-made sounds like active sonar. PAM methods can work in real-time or on previously recorded acoustic data. The techniques can be automated, but at the present time PAM methods are often manually intensive.
MMP scientists have been analyzing acoustic recordings from US Navy hydrophones at the Pacific Missile Range Facility (PMRF) instrumented underwater range, located off the west coast of Kauai, Hawaii, since 2002. The PMRF range includes over 200 hydrophones used to track underwater objects in support of US Navy undersea warfare training. Over 40 of the hydrophones can detect low frequency baleen whale calls, such as the 20-Hz pulses emitted by fin whales. Efforts at the Navy MMP have focused on analyzing existing PMRF data to detect, classify, and localize marine mammal species known to frequent the area and to estimate species’ densities. The techniques that have been developed can also be applied to acoustic data from other areas. Algorithms exist to automatically detect, classify and in many cases localize the following species of cetaceans: Balaenoptera borealis (sei), B. brydei (Bryde’s) and B. physalus (fin); Balaenoptera acutorostrata (minke) and Megaptera novaeangliae (humpback); and the Ziphiidae family of beaked whales. Further data processing can be used to localize individual baleen whales, determine beaked whale foraging group dives, estimate species’ densities and analyze in conjunction with US Navy mid-frequency active sonar (MFAS) training for monitoring the behavioral effects on marine mammals.
Concentrated data collections from PMRF are also obtained during focused research efforts and before, during and after select US Navy training events involving surface ship MFAS such as the AN/SQS-53C sonar (on destroyers and cruisers) and the AN/SQS-56 sonar (on frigates). Automated PAM algorithms were developed and tuned to detect and localize these active sonar signals to aid in analysis of potential marine mammal behavioral effects due to MFAS activity. The data collections during MFAS training allow estimates of the levels of MFAS that marine mammals are exposed to by utilizing standard acoustic propagation modeling software such as the US Navy’s Personal Computer Interactive Multi-sensor Analysis Tool (PCIMAT). Estimates of received sound levels are currently being made not only for animals localized using PAM methods but also collaboratively with other researchers conducting animal tagging and marine mammal observations on board US Navy surface ships and aerial platforms.
Sample of graphical user interface showing three species of marine mammals detected and localized at the Pacific Missile Range Facility off Kauai, Hawaii on 12 Feb 2014. Approximate locations for the 62 hydrophones utilized in the analysis are indicated by blue numbers. Two individual minke whales indicated with the yellow X symbols and one fin whale indicated with the orange + symbols – these are repeated localizations over the 75 minute period of time from 10:22 to 11:37 GMT. Three beaked whale foraging dives detected and indicated by colored circles: one dive at hydrophone 190 indicated with one circle, one dive at hydrophone 2 indicated with one circle and one dive detected by hydrophones 33 and 34 indicated by two circles. The circles’ diameters and colors are coded in proportion to the number of FM foraging clicks detected in the ten minute period 11:27-11:37 GMT.
Medical imaging of auditory processes in dolphins
Dolphins have enlarged auditory processing centers within the brain, which reflect their ability to echolocate — to use high frequency biosonar for the purposes of navigation and foraging — and to efficiently process sound. In addition to their biosonar, dolphins also use sounds within the human range of hearing for communication (such as whistles). The two different types of sounds, and studies of the reception of those sounds, has led to the speculation that dolphins have a dual sound reception/processing system – one for dealing with lower frequency whistles, and another for processing the ultrasonic pulses associated with echolocation.
In an ongoing effort to understand how dolphins and other toothed whales process sound, MMP scientists study the anatomy and auditory physiology of dolphins in vivo, through the use of biomedical imaging techniques. The use of computed tomography (CT) and magnetic resonance imaging (MRI) permits the anatomy of living dolphins to be studied non-invasively and in detail. The use of single photon emission computed tomography (SPECT) and positron emission tomography (PET) permits physiological processes, such as regional rates of blood flow and tissue metabolism, to also be studied. The merging of structural and functional imaging data permits physiological processes to be tied to specific anatomical sites and provides a better understanding of auditory processing. To date, the effect of sleep on cerebral blood flow, the normal metabolic activity of the brain, and the effect of sounds on auditory processes within specific regions of the brain have been studied in dolphins through biomedical imaging methods.
The metabolic activity of the dolphin brain as determined from the registration and fusion of PET and CT images.
The anatomy of the dolphin brain as determined through MRI.
The relationship of reflective air spaces (red) to the ear bones (yellow) and skull (white) of the bottlenose dolphin as determined via CT.
Opportunities periodically exist for student interns to assist with data collection and analysis for bioacoustics research. For more information, visit the Internship Opportunities [LINK TO http://www.public.navy.mil/spawar/Pacific/71500/Pages/Internship.aspx ].
Finneran, J. J., Schroth-Miller, M., Borror, N., Tormey, M., Brewer, A., Black, A., Bakhtiari, K., and Goya, G. (2014). “Multi-echo processing by a bottlenose dolphin operating in ‘packet’ transmission mode at long range,” J. Acoust. Soc. Am. (in review).
Finneran, J.J., Branstetter, B.K., Houser, D.S., Moore, P.W., Mulsow, J., Martin, C., and Perisho, S. (2014). “High-resolution measurement of a bottlenose dolphin’s (Tursiops truncatus) biosonar transmission beam pattern in the horizontal plane,” J. Acoust. Soc. Am. (in review).
Mulsow, J., Finneran, J.J., and Houser, D.S. (2014). “Interaural differences in the bottlenose dolphin (Tursiops truncatus) auditory nerve response to jawphone stimuli,” J. Acoust. Soc. Am. (in review).
Manzano-Roth, R.A., Martin, S.W., Matsuyama, B. and Henderson, E.E. (2014). “Impacts of a U.S. Navy training event on beaked whale foraging dives in Hawaiian waters,” J. Acoust. Soc. Am. (in review).
Ruser, A., Dähne, M., Sundermeyer, J., Lucke, K., Houser, D., Finneran, J., Driver, J. r., Pawliczka, I., Rosenberger, T., and Siebert, U. (2014). “Evoked potential audiograms of grey seals (Halichoerus grypus) from the North and Baltic Seas,” PLoS ONE 9,
Finneran, J. J. and Branstetter, B. K. (2013). “Effects of noise on sound perception in marine mammals,” in Animal Communication and Noise, edited by H. Brumm (Springer-Verlag, Berlin), pp. 273-308.
Mulsow, J., Houser, D. S., and Finneran, J. J. (2013). “Aerial hearing thresholds and detection of hearing loss in male California sea lions (Zalophus californianus) using auditory evoked potentials,” Marine Mammal Science (in press).
Finneran, J. J., Mulsow, J., and Houser, D. S. (2013). “Auditory evoked potentials in a bottlenose dolphin during moderate-range echolocation tasks,” J. Acoust. Soc. Am. 134, 4532–4547.
Finneran, J. J., Wu, T., Borror, N., Tormey, M., Brewer, A., Black, A., and Bakhtiari, K. (2013). “Bottlenose dolphin (Tursiops truncatus) detection of simulated echoes from normal and time-reversed clicks,” J. Acoust. Soc. Am. 134, 4548–4555.
Branstetter, B., Trickey, J., Aihara, H., Finneran, J., and Liberman, T. (2013). “Time and frequency metrics related to auditory masking of a 10 kHz tone in bottlenose dolphins (Tursiops truncatus),” J. Acoust. Soc. Am. 134, 4556–4565.
Finneran, J. J., Mulsow, J., and Houser, D. S. (2013). “Using the auditory steady-state response to assess temporal dynamics of hearing sensitivity during bottlenose dolphin echolocation,” J. Acoust. Soc. Am. 134, 3913–3917.
Houser, D. S., Martin, S. W., and Finneran, J. J. (2013). “Exposure amplitude and repetition affect bottlenose dolphin behavioral responses to simulated mid-frequency sonar signals,” J. Exp. Mar. Biol. Ecol. 443, 123–133.
Martin, S.W., Marques, T.A., Thomas, L., Morrissey, R.P., Jarvis, S., DiMazio, N., Moretti, D., and Mellinger, D.K. (2013).
“Estimating minke whale (Balaenoptera acutorostrata) boing sound density using passive acoustic sensors,” Mar. Mam. Sci. 29, 142-158.
Marques, T. A., Thomas, L, Martin, S. W., Mellinger, D. K., Ward, J. A., Moretti, D. J., Harris, D., and Tyack, P. L. (2013).
“Estimating animal population density using passive acoustics,” Biological Reviews, 88, 287-309.
Finneran, J. J. (2013). “Dolphin ‘packet’ use during long-range echolocation tasks,” J. Acoust. Soc. Am. 133, 1796–1810.
Finneran, J. J. and Schlundt, C. E. (2013). “Effects of fatiguing tone frequency on temporary threshold shift in bottlenose dolphins
(Tursiops truncatus),” J. Acoust. Soc. Am. 133, 1819–1826.
Branstetter, B. K., Trickey, J. S., Bahktiari, K., Black, A., Aihara, H., and Finneran, J. J. (2013). “Auditory masking patterns in bottlenose dolphins (Tursiops truncatus) with natural, anthropogenic, and controlled noise,” J. Acoust. Soc. Am. 133, 1811–1818.
Au, W., Branstetter, B., Moore, P., and Finneran, J. (2012). “Dolphin biosonar signals measured at extreme off-axis angles: Insights to sound propagation in the head,” J. Acoust. Soc. Am. 132, 1199–1206.
Branstetter, B. K., Finneran, J. J., Fletcher, E. A., Weisman, B. C., and Ridgway, S. H. (2012). “Dolphins can maintain vigilant behavior through echolocation for 15 days without interruption or cognitive impairment,” PLoS ONE 7(10): e47478.doi:10.1371/journal.pone.0047478.
Mulsow, J., Houser, D. S., and Finneran, J. J. (2012). “Comparison of underwater psychophysical and aerial auditory evoked potential (AEP) audiograms in a California sea lion (Zalophus californianus),” J. Acoust. Soc. Am. 131, 4182–4187.
Branstetter, B. K., Tormey, M., Aihara, H., Moore, P., and Finneran, J. J. (2012). “Directional properties of bottlenose dolphin (Tursiops truncatus) clicks, burst-pulse, and whistle sounds,” J. Acoust. Soc. Am. 131, 1613–1621.
Au, W., Branstetter, B., Moore, P., and Finneran, J. (2012). “The biosonar field around an Atlantic bottlenose dolphin (Tursiops truncatus),” J. Acoust. Soc. Am. 131, 569–576.
Marques, T. A., Thomas, L., Martin, S. W., Mellinger, D. K., Jarvis, S., Morrissey, R. P., Ciminello, C.-A., and DiMarzio, N. (2012). “Spatially explicit capture–recapture methods to estimate minke whale density from data collected at bottom-mounted hydrophones,” J Ornithol 152, S445-S455.
Finneran, J. J. and Schlundt, C. E. (2011). “Subjective loudness level measurements and equal loudness contours in a bottlenose dolphin (Tursiops truncatus),” J. Acoust. Soc. Am. 130, 3124–3136.
Finneran, J. J., Mulsow, J. L., Schlundt, C. E., and Houser, D. S. (2011). “Dolphin and sea lion auditory evoked potentials in response to single and multiple swept amplitude tones,” J. Acoust. Soc. Am. 130, 1038–1048.
Mellinger, D. K., Martin, S. W., Morriessey, R. P., Thomas, L., and Yosco, J. J. (2011). “A method for detecting whistles, moans, and other frequency contour sounds,” J. Acoust. Soc. Am. 129, 4055-4061.
Mulsow, J. L., Finneran, J. J., and Houser, D. S. (2011). “California sea lion (Zalophus californianus) aerial hearing sensitivity measured using auditory steady-state response and psychophysical methods,” J. Acoust. Soc. Am. 129, 2298–2306.
Mulsow, J., Reichmuth, C., Gulland, F., Rosen, D. A. S., and Finneran, J. J. (2011). “Aerial audiograms of several California and
Steller sea lions measured using single and multiple simultaneous auditory steady-state response methods,” J. Exp. Biol. 214, 1138–1147.
Schlundt, C. E., Dear, R. L., Bowles, A., Reidarson, T., Houser, D. S., and Finneran, J. J. (2011). “Auditory evoked potentials in two short-finned pilot whales (Globicephala macrorhynchus),” J. Acoust. Soc. Am. 129, 1111–1116.
Trickey, J. S. , Branstetter, B. B., and Finneran, J. J. (2010). “Auditory masking with environmental, comodulated, and Gaussian noise in bottlenose dolphins (Tursiops truncatus),” J. Acoust. Soc. Am. 128, 3799–3804.
Finneran, J. J., Houser, D. S., Moore, P. W., Branstetter, B. B., Trickey, J. S., and Ridgway, S. H. (2010). “A method to enable a bottlenose dolphin (Tursiops truncatus) to echolocate while out of water,” J. Acoust. Soc. Am. 128, 1483–1489.
Houser, D. S., Moore, P. W., Johnson, S., Lutmerding, B., Branstetter, B. K., Ridgway, S. H., Trickey, J., Finneran, J. J., Jensen, E., and Hoh, C. (2010). “Relationship of blood flow and metabolism to acoustic processing centers of the dolphin brain,” J. Acoust.
Soc. Am. 128, 1460–1466.
Au, W., Houser, D., Finneran, J., Lee, W-J, Talmadge, L., and Moore, P. (2010). “The acoustic field on the forehead of echolocating Atlantic bottlenose dolphins (Tursiops truncatus),” J. Acoust. Soc. Am. 128, 1426–1434.
Finneran, J. J. and Schlundt, C. E. (2010). “Frequency-dependent and longitudinal changes in noise-induced hearing loss in a bottlenose dolphin (Tursiops truncatus),” J. Acoust. Soc. Am. 128, 567–570.
Houser, D. S., Finneran, J. J., and Ridgway, S. H. (2010). “Research with Navy Marine Mammals benefits animal care, conservation and biology,” Int. J. Comp. Psych. 23, 249–268.
Finneran, J. J., Carder, D. A., Schlundt, C. E., and Dear, R. L. (2010). “Temporary threshold shift in a bottlenose dolphin (Tursiops truncatus) exposed to intermittent tones,” J. Acoust. Soc. Am. 127, 3267–3272.
Finneran, J. J., Carder, D. A., Schlundt, C. E., and Dear, R. L. (2010). “Growth and recovery of temporary threshold shift (TTS) at 3 kHz in bottlenose dolphins (Tursiops truncatus),” J. Acoust. Soc. Am. 127, 3256–3266.
Finneran, J. J., Houser, D. S., Mase-Guthrie, B., Ewing, R. Y., and Lingenfelser, R. G. (2009). “Auditory evoked potentials in a stranded Gervais’ beaked whale (Mesoplodon europaeus),” J. Acoust. Soc. Am. 126, 484–490.
Finneran, J. J. (2009). “Evoked Response Study Tool (EVREST): a portable, rugged system for single and multiple auditory evoked potential measurements,” J. Acoust. Soc. Am. 126, 491–500.
Ridgway, Sam H., Keogh, M., Carder, D., Finneran, J., Kamolnick, T., Todd, M., and Goldblatt, A. (2009). “Dolphins maintain cognitive performance during 72 to 120 hours of continuous auditory vigilance,” J. Exp. Biol. 212, 1519–1527.
Finneran, J. J. (2008). “Modified variance ratio for objective detection of transient evoked potentials in bottlenose dolphins (Tursiops truncatus),” J. Acoust. Soc. Am. 124, 4069–4082.
Houser, D. S., Crocker, D. E., and Finneran, J. J. (2008). “Click evoked potentials in a large marine mammal, the adult male northern elephant seal (Mirounga angustirostris),” J. Acoust. Soc. Am. 124, 44–47.
Branstetter, B. K. and Finneran, J. J. (2008). “Comodulation masking release in bottlenose dolphins (Tursiops truncatus),” J. Acoust. Soc. Am. 124, 625–633.
Branstetter, B. K., Finneran, J. J., and Houser, D. S. (2008). “Frequency and level dependant masking of the multiple auditory steady state response in bottlenose dolphins (Tursiops truncatus),” J. Acoust. Soc. Am. 123, 2928–2935.
Houser, D. S., Gomez-Rubio, A., and Finneran, J. J., (2008). “Evoked potential audiometry of a small captive population of Pacific bottlenose dolphins (Tursiops truncatus gilli),” Mar. Mam. Sci. 24, 28–41.
Finneran, J. J., Houser, D. S., Blasko, D., Hicks, C., Hudson, J., and Osborn, M. (2008). “Estimating bottlenose dolphin (Tursiops truncatus) hearing thresholds from single and multiple simultaneous auditory evoked potentials,” J. Acoust. Soc. Am. 123, 542–551.
Finneran, J. J., London, H. R., and Houser, D. S. (2007). “Modulation rate transfer functions in bottlenose dolphins (Tursiops truncatus) with normal hearing and high-frequency hearing loss,” J. Comp. Physiol. – A 193, 835–843.
Finneran, J. J., Schlundt, C. E., Branstetter, B., and Dear, R. L. (2007). “Assessing temporary threshold shift in a bottlenose dolphin (Tursiops truncatus) using multiple simultaneous auditory evoked potentials,” J. Acoust. Soc. Am. 122, 1249–1264.
Schlundt, C. E., Dear, R. L., Green, L., Houser, D. S., and Finneran, J. J. (2007). “Simultaneously measured behavioral and electrophysiological hearing thresholds in a bottlenose dolphin (Tursiops truncatus),” J. Acoust. Soc. Am. 122, 615–622.
Finneran, J. J., Houser, D. S., and Schlundt, C. E. (2007). “Objective detection of bottlenose dolphin (Tursiops truncatus) steady-state auditory evoked potentials in response to AM/FM tones,” Aquat. Mammals 33, 43–54.
Houser, D. S., Crocker, D. E., Kastak, C., Mulsow, J., and Finneran, J. J. (2007). “Auditory evoked potentials in northern elephant seals (Mirounga angustirostris),” Aquat. Mammals 33, 110–121.
Hernandez, E. N., Kuczaj, S., Houser, D. S., and Finneran, J. J. (2007). “Middle- and long-latency auditory evoked potentials resulting from frequent and oddball stimuli in the bottlenose dolphin (Tursiops truncatus),” Aquat. Mammals 33, 34–42.
Reichmuth, C., Mulsow, J., Finneran, J. J., Houser, D. S., and Supin, A. Y. (2007). “Measurement and response characteristics of auditory brainstem responses in pinnipeds,” Aquat. Mammals 33, 132–150.
Finneran, J. J. and Houser, D. S. (2007). “Bottlenose dolphin (Tursiops truncatus) steady-state evoked responses to multiple simultaneous sinusoidal amplitude modulated tones,” J. Acoust. Soc. Am. 121, 1775–1782.
Houser, D. S., and Finneran, J. J. (2006). “Variation in the hearing sensitivity of a dolphin population obtained through the use of evoked potential audiometry,” J. Acoust. Soc. Am. 120, 4090–4099.
Houser, D. S., and Finneran, J. J. (2006). “A comparison of underwater hearing sensitivity in bottlenose dolphins (Tursiops truncatus) determined by electrophysiological and behavioral methods,” J. Acoust. Soc. Am. 120, 1713–1722.
Ridgway, S., Carder, D., Finneran, J., Keogh, M., Kamolnick, T., Todd, M., and Goldblatt, A. (2006). “Dolphin continuous auditory vigilance for five days,” J. Exp. Biol. 209, 3621–3628.
Howard, R. S. , Finneran, J. J., and Ridgway, S. H. (2006). “BIS Monitoring of unihemispheric effects in dolphins,” Anesthesia & Analgesia 103, 626–632.
Ridgway, S., Houser, D., Finneran, J., Carder, D., Keogh, M., Van Bonn, W., Smith, C., Scadeng, M., Mattrey, R., and Hoh, C. (2006).
“Functional imaging of dolphin brain metabolism and blood flow,” J. Exp. Biol. 209, 2902-2910.
Finneran, J. J. and Houser, D. S. (2006). “Comparison of in-air evoked potential and underwater behavioral hearing thresholds in four bottlenose dolphins (Tursiops truncatus),” J. Acoust. Soc. Am. 119, 3181–3192.
Cook, M. L. H., Varela, R. A., Goldstein, J. D., McCulloch, S. D., Bossart, G. D., Finneran, J. J., Houser, D., and Mann, D. A. (2006). “Beaked whale auditory evoked potential hearing measurements,” J. Comp. Phys. – A 192, 489–495.
Cox, T. M., Ragen, T. J., Read, A. J., Vos, E., Baird, R. W., Balcomb, K., Barlow, J., Caldwell, J., Cranford, T., Crum, L., D’Amico, A., D’Spain, G., Fernández, A., Finneran, J., Gentry, R., Gerth, W., Gulland, F., Hildebrand, J., Houser, D., Hullar, T., Jepson, P. D., Ketten, D., Macleod, C. D., Miller, P., Moore, S., Mountain, D. C., Palka, D., Ponganis, P., Rommel, S., Rowles, T.,
Taylor, B., Tyack, P., Wartzok, D., Gisiner, R., Meads, J., and Benner, L. (2006). “Understanding the impacts of anthropogenic sound on beaked whales,” J. Cetacean Res. Manage. 7, 177–187.
Finneran, J. J., Carder, D. A., Schlundt, C. E., and Ridgway, S. H. (2005). “Temporary threshold shift (TTS) in bottlenose dolphins (Tursiops truncatus) exposed to mid-frequency tones,” J. Acoust. Soc. Am. 118, 2696–2705.
Finneran, J. J., Dear, R., Carder, D. A., Belting, T., McBain, J., Dalton, L., and Ridgway, S. H. (2005). “Pure tone audiograms and possible antibiotic drug-induced hearing loss in the white whale (Delphinapterus leucas),” J. Acoust. Soc. Am. 117, 3936–3943.
Romano, T., Keogh, M., Kelly, C., Feng, P., Berk, L., Schlundt, C. E., Carder, D. A. and Finneran, J. J. (2004). “Anthropogenic sound and marine mammal health: measures of the nervous and immune systems before and after intense sound exposures,” Can. J. Fish. Aquat. Sci. 61, 1124–1134.
Houser, D. S., Finneran, J. J., Carder, D. A., Van Bonn, W., Smith, C. R., Hoh, C., Mattrey, R. and Ridgway, S. H. (2004).
“Structural and functional imaging of bottlenose dolphin (Tursiops truncatus) cranial anatomy,” J. Exp. Biol. 207, 3657–3665.
Finneran, J. J., Dear, R., Carder, D. A. and Ridgway, S. H. (2003). “Auditory and behavioral responses of California sea lions (Zalophus californianus) to single underwater impulses from an arc-gap transducer,” J. Acoust. Soc. Am. 114, 1667–1677.
Finneran, J. J. (2003). “Whole-lung resonance in a bottlenose dolphin (Tursiops truncatus) and white whale (Delphinapterus leucas),” J. Acoust. Soc. Am. 114, 529–535.
Finneran, J. J., Schlundt, C. E., Dear, R., Carder, D. A. and Ridgway, S. H. (2002). “Temporary shift in masked hearing thresholds (MTTS) in odontocetes after exposure to single underwater impulses from a seismic watergun,” J. Acoust. Soc. Am. 111, 2929–2940.
Finneran, J. J., Schlundt, C. E., Carder, D. A. and Ridgway, S. H. (2002). “Auditory filter shapes for the bottlenose dolphin (Tursiops truncatus) and the white whale (Delphinapterus leucas) derived with notched noise,” J. Acoust. Soc. Am. 112, 322–328.
Finneran, J. J., Carder, D. A. and Ridgway, S. H. (2002). “Low-frequency acoustic pressure, velocity, and intensity thresholds in a bottlenose dolphin (Tursiops truncatus) and white whale (Delphinapterus leucas),” J. Acoust. Soc. Am. 111, 447–456.
Schlundt, C. E., Finneran, J. J., Carder, D. A. and Ridgway, S. H. (2000). “Temporary shift in masked hearing thresholds of bottlenose dolphins, Tursiops truncatus, and white whales, Delphinapterus leucas, after exposure to intense tones,” J. Acoust. Soc. Am. 107, 3496–3508.
Finneran, J. J., Schlundt, C. E., Carder, D. A., Clark, J. A., Young, J. A., Gaspin, J. B. and Ridgway, S. H. (2000). “Auditory and behavioral responses of bottlenose dolphins (Tursiops truncatus) and a beluga whale (Delphinapterus leucas) to impulsive sounds resembling distant signatures of underwater explosions,” J. Acoust. Soc. Am. 108, 417–431.