Sam H Ridgway

Sam H Ridgway
National Marine Mammal Foundation

DVM, PhD

About

295
Publications
95,509
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8,176
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Introduction
I currently provide corporate memory, mentor professionals, and serve as a knowledge resource for the Navy Marine Mammal Program. My current work can be described in three words: dolphin, brain, and ear. We have just started a project, “Sounds as Indicators of Health and Welfare,” where we will surreptitiously record dolphin sounds to identify their call repertoire. The dolphins will go about their regular tasks and behaviors without interference. We think that dolphin sound production may give

Publications

Publications (295)
Article
Full-text available
Animal managers from three institutions that hold Tursiops truncatus participated in a workshop directed at documenting survivability of Tursiops neonates (birth to 30 d of age) in their managed populations. Key information was generated for the period 1990 through 2009 for the three organizations. Included in the findings are (1) documentation of...
Article
Odontocetes (toothed whales) evolved from terrestrial mammals approximately 55 million years ago and have since remained on a unique evolutionary trajectory. This study used formalin-fixed tissue and light microscopy to quantify the size and number of fibers along the corpus callosum of the bottlenose dolphin (n = 8). Two other species, the Amazon...
Article
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According to the 'developmental constraint hypothesis' of comparative mammalian neuroanatomy, brain growth follows predictable allometric trends. Therefore, brain structures should scale to the entire brain in the same way across mammals. Evidence for a departure from this pattern for cerebellum volume has recently been reported among the anthropoi...
Article
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Responses of marine mammals to human-generated sound are of interest due to concern for protection of animals with sensitive hearing from acoustic harassment or injury. Goold and Fish [J. Acoust. Sec. Am. 103, 2177-2184 (1998)] compare their limited observations of wild common dolphins (Delphinus delphis) near operating seismic vessels off Wales, w...
Article
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Bottlenose dolphins have individually distinct signature whistles that are characterized by a stereotyped frequency-time contour. Signature whistles are commonly exchanged with short time delays between calls. Dolphin whistles are produced by pressurized nasal sacs that increase and then decrease in pressure over emission. This study found that the...
Preprint
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For the first time, dolphins wearing video cameras were observed capturing and eating live native fish. While freely swimming in San Diego Bay, one dolphin caught 69 resident fish, 64 demersal, 5 near surface, while the other caught 40, 36 demersal and 4 near the surface. Two other dolphins were observed capturing 135 live native fish in a sea wate...
Article
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Bottlenose dolphin signature whistles are characterized by distinctive frequency modulation over time. The stable frequency contours of these whistles broadcast individual identity information. Little is known however, about whether or not the amplitude contour is also stereotyped. Here, we examined the relative amplitude-time contour of signature...
Article
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Animal sounds are commonly used by humans to infer information about their motivations and their health, yet, acoustic data is an underutilized welfare biomarker especially for aquatic animals. Here, we describe an acoustic monitoring system that is being implemented at the U.S. Navy Marine Mammal Program where dolphins live in groups in ocean encl...
Chapter
Bowhead whales are one of the least encephalized mammals, possessing a small brain relative to their body size (e.g., a 3 kg brain in a 30,000 kg body). Features of the bowhead whale brain include a blunted temporal lobe and a gyrification index that is less than most cetaceans. Rather than having a cerebrum that is wider than long like odontocetes...
Article
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Bottlenose dolphins (Tursiops truncatus) have a worldwide distribution in temperate and tropical waters and often inhabit estuarine environments, indicating their ability to maintain homeostasis in low salinity for limited periods of time. Epidermal and biochemical changes associated with low salinity exposure have been documented in stranded bottl...
Preprint
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Background The National Marine Mammal Foundation presents a new veterinary and animal welfare monitoring tool, WAMS (i.e., Welfare Acoustic Monitoring System) for open-source use in PAMGuard. While the use of passive acoustic monitoring systems has been invaluable in wild conservation efforts, vocal behavior is a vastly underutilized welfare biomar...
Method
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New plug-in available for download https://www.pamguard.org/downloadpage.php?id=111 The National Marine Mammal Foundation’s Welfare Acoustic Monitoring System (NMMF WAMs) is a user-friendly interface for acoustic monitoring with stationary or towed arrays. It was built to monitor the whistle rate of a discrete population of bottlenose dolphins to...
Article
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Most commonly, animal communication systems are driven by shared call repertoires, with some individual distinctiveness encoded as a byproduct of voice cues. We provide evidence that bottlenose dolphins produce both individually distinctive whistles, and a shared whistle type. A stereotyped whistle contour (termed the group whistle) is shared by fi...
Article
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Since the work of Tower in the 1950s, we have come to expect lower neuron density in the cerebral cortex of larger brains. We studied dolphin brains varying from 783 to 6215g. As expected, average neuron density in four areas of cortex decreased from the smallest to the largest brain. Despite having a lower neuron density than smaller dolphins, the...
Article
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Bottlenose dolphins make many different sounds that have been recorded and described by researchers for over 60 years. This species, Tursiops truncatus, is arguably the most studied marine mammal. They have the ability to hear and produce sounds over a range of at least 150 kilohertz (kHz). Although the human hearing is limited in bandwidth to less...
Article
Biosonar capabilities of large-brained dolphins and small-brained bats: size does matter VanAlstyne, K. 1 Branstetter, B. K. 1 Ridgway, S. 1 Finneran, J. J. 2 Xitco, M. J. Jr2 1 National Marine Mammal Foundation, 2240 Shelter Island Drive, #200, San Diego, CA 92106 2 US Navy Marine Mammal Program, SSC Pacific Code 71510, 53560 Hull St., San Diego,...
Article
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Brain enlargement is associated with concomitant growth of interneuronal distance, increased conduction time, and reduced neuronal interconnectivity. Recognition of these functional constraints led to the hypothesis that large-brained mammals should exhibit greater structural and functional brain lateralization. As a taxon with the largest brains i...
Article
It is important for academic-minded human anesthesiologists to have an interdisciplinary perspective when engaging in cutting-edge research as well as the practice of human anesthesiology. This was a philosophy promoted by Dr. Robert Dripps, former pioneering Chairman of the Anesthesiology Department at the University of Pennsylvania (Philadelphia,...
Article
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The auditory brainstem response to a dolphin’s own emitted biosonar click can be measured by averaging epochs of the instantaneous electroencephalogram (EEG) that are time-locked to the emitted click. In this study, averaged EEGs were measured using surface electrodes placed on the head in six different configurations while dolphins performed an ec...
Article
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Two dolphins carrying cameras swam in the ocean as they searched for and marked mine simulators - buried, proud or moored. As the animals swam ahead of a boat they searched the ocean. Cameras on their harness recorded continuous sound and video. Once a target was detected, the dolphins received a marker to take to the simulator's location. During s...
Article
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In 2017 an emergency field effort was undertaken in an attempt to prevent the extinction of the world's most endangered marine mammal, the vaquita Phocoena sinus. The rescue effort involved 90 experts from 9 countries and cost US$ 5 million. Following a long decline due to entanglement in legal gillnet fisheries, the vaquita population had fallen f...
Article
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Why do neonatal and adult delphinids have much larger brains than artiodactyls when they have common ancestors? We explore relationships between neonatal brain size, gestation duration, maternal body mass, and body growth. Cetacean brains grow fast in the womb and longer gestation results in a larger brain. Allometry shows that the larger the mothe...
Article
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The auditory brainstem response (ABR) to a dolphin’s own emitted biosonar click may be measured by averaging epochs of the instantaneous electroencephalogram (EEG) that are time-locked to the emitted click. In this study, waves in the averaged EEG preceding the biosonar click-evoked ABR were measured using surface electrodes placed on the head in s...
Article
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We compared mature dolphins with 4 other groupings of mature cetaceans. With a large data set, we found great brain diversity among 5 different taxonomic groupings. The dolphins in our data set ranged in body mass from about 40 to 6,750 kg and in brain mass from 0.4 to 9.3 kg. Dolphin body length ranged from 1.3 to 7.6 m. In our combined data set f...
Article
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The evolutionary process of adaptation to an obligatory aquatic existence dramatically modified cetacean brain structure and function. The brain of the killer whale (Orcinus orca) may be the largest of all taxa supporting a panoply of cognitive, sensory, and sensorimotor abilities. Despite this, examination of the O. orca brain has been limited in...
Cover Page
We suggest how a basic physics problem becomes much richer when researchers of various disciplines converse. Our discussion explores Snell’s window from the perspective of what a dolphin might see. An aperture, Snell’s window, allows light to travel through the air-water interface. Outside this window, there is total reflection from under the water...
Article
Full-text available
We suggest how a basic physics problem becomes much richer when researchers of various disciplines converse. Our conversation explores Snell’s window from the perspective of what a dolphin might see. An aperture, Snell’s window, allows light to travel through the air-water interface. Outside this window, there is total reflection from under the wat...
Article
Full-text available
We have long observed dolphins producing recognizable sounds—bursts of pulses with sweeping peak frequencies—at prey capture. We call this the victory squeal. When dolphins forage, there are three sequential sounds: sonar clicks, terminal buzz, and the victory squeal. When dolphins find a fish with sonar clicks, but reject the fish during the termi...
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Dolphins fishing alone in open waters may whistle without interrupting their sonar clicks as they find and eat or reject fish. Our study is the first to match sound and video from the dolphin with sound and video from near the fish. During search and capture of fish, free-swimming dolphins carried cameras to record video and sound. A hydrophone in...
Article
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Similar to humans, bottlenose dolphins (Tursiops truncatus) can develop metabolic syndrome and associated high ferritin. While fish and fish-based fatty acids may protect against metabolic syndrome in humans, findings have been inconsistent. To assess potential protective factors against metabolic syndrome related to fish diets, fatty acids were co...
Article
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Objective-To evaluate annual survival and mortality rates and the longevity of a managed population of bottlenose dolphins (Tursiops truncatus). Design-Retrospective cohort study. Animals-103 bottlenose dolphins at the US Navy Marine Mammal Program (MMP). Procedures-Population age structures, annual survival and crude mortality rates, and median ag...
Conference Paper
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A geriatric, female bottlenose dolphin (Tursiops truncatus) with a history of bilateral nephrolithiasis was diagnosed with mild azotemia on a routine blood sample. In addition to long-term oral hydration therapy, she was receiving oral potassium citrate and citric acid treatment in an effort to decrease her risk of further stone formation. Ultrasou...
Conference Paper
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Coccidioidomycosis in a bottlenose dolphin was first reported in 1998. 1 In 2009, a 26-year-old female bottlenose dolphin (Tursiops truncatus) was diagnosed with pulmonary coccidioidomycosis. 2 To date, the disease has been successfully managed with input from Coccidioides immitis experts at the University of California-Davis, the University of Ari...
Article
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For many years, we heard sounds associated with reward from dolphins and belugas. We named these pulsed sounds victory squeals (VS), as they remind us of a child's squeal of delight. Here we put these sounds in context with natural and learned behavior. Like bats, echolocating cetaceans produce feeding buzzes as they approach and catch prey. Unlike...
Article
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The present study documents the morphology of neurons in several regions of the neocortex from the bottlenose dolphin (Tursiops truncatus), the North Atlantic minke whale (Balaenoptera acutorostrata), and the humpback whale (Megaptera novaeangliae). Golgi-stained neurons (n = 210) were analyzed in the frontal and temporal neocortex as well as in th...
Article
Cetaceans (whales, dolphins, and porpoises) are mammals whose ancestors developed on land. Bottlenose dolphins, like all cetaceans, have an apneustic style of breathing. The physiology of anesthesia is different from sleep, especially in cetaceans. Specific anatomic and physiologic adaptations of the respiratory and cardiovascular systems, although...
Article
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National Aquarium Bottlenose Dolphins The CEO (Science, 344, 951) tells Science about dolphin deaths and discomfort with seeing them in captivity. Two of us with 100 years of dolphin experiences see a wrong message for conservation, research, and the environment. Marine Parks and Aquariums have been loud voices for marine conservation. Visitors and...
Article
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Among cetaceans, killer whales and sperm whales have the widest distribution in the world's oceans. Both species use echolocation, are long-lived, and have the longest periods of gestation among whales. Sperm whales dive much deeper and much longer than killer whales. It has long been thought that sperm whales have the largest brains of all living...
Data
The neocortex of cetartiodactyls: I. A comparative Golgi analysis of neuronal morphology in the bottlenose dolphin (Tursiops truncatus), the minke whale (Balaenoptera acutorostrata), and the humpback whale (Megaptera novaeangliae) Abstract The present study documents the morphology of neurons in several regions of the neocortex from the bottle-nose...
Article
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In the 1960s, I explored some aspects of carbohydrate metabolism in healthy bottlenose dolphins (Tursiops truncatus). Their physiological picture resembled what had been described for hyperthyroid diabetics. Dolphins have elevated thyroid hormone turnover, and fasting dolphins maintain a relatively high level of plasma glucose. After dolphins inges...
Article
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As a rough measure of intelligence, brain weight: cord weight ratios in small delphinids compared favorably with, but were slightly less than, this ratio in man. Not all delphinids studied were found to achieve the minimum 1000 gm brain weight correlate of language development in the human child. The average adult brain size in some small pelagic c...
Article
Neuroanatomical research into the brain of the bottlenose dolphin (Tursiops truncatus) has revealed striking similarities with the human brain in terms of size and complexity. However, the dolphin brain also contains unique allometric relationships. When compared to the human brain, the dolphin cerebellum is noticeably larger. Upon closer examinati...
Article
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This brief communication describes the clinical presentation, antemortem diagnosis, and successful treatment of a pulmonary abscess associated with a Brucella sp. in a 27-yr-old female bottlenose dolphin (Tursiops truncatus). Ultrasound revealed a 3-cm diameter hypoechoic mass deep to the pleural lining in the left lung field. Multiple ultrasound-g...
Article
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Breath analysis, including measurement of nitric oxide (NO), is a noninvasive diagnostic tool that may help evaluate cetacean health. This is the first report on the effects of breath hold duration, feeding, and lung disease on NO in dolphin exhaled breath. Three healthy dolphins were trained to hold their breath for 30, 60, 90, and 120 s and then...
Article
Although dolphins (Tursiops truncatus) have been trained to match numbers and durations of human vocal bursts [1] and reported to spontaneously match computer-generated whistles [2], spontaneous human voice mimicry has not previously been demonstrated. The first to study white whale (Delphinapterus leucas) sounds in the wild, Schevill and Lawrence...
Article
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In dolphins, natural selection has developed unihemispheric sleep where alternating hemispheres of their brain stay awake. This allows dolphins to maintain consciousness in response to respiratory demands of the ocean. Unihemispheric sleep may also allow dolphins to maintain vigilant states over long periods of time. Because of the relatively poor...
Article
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Bottlenose dolphins (Tursiops truncatus) wore opaque suction cups over their eyes while stationing behind an acoustically opaque door. This put the dolphins in a known position and orientation. When the door opened, the dolphin clicked to detect targets. Trainers specified that Dolphin S emit a whistle if the target was a 7.5 cm water filled sphere...
Article
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Indirect evidence for multiple sonar signal generators in odontocetes exists within the published literature. To explore the long-standing controversy over the site of sonar signal generation, direct evidence was collected from three trained bottlenose dolphins (Tursiops truncatus) by simultaneously observing nasal tissue motion, internal nasal cav...
Article
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Delphinids produce tonal whistles shaped by vocal learning for acoustic communication. Unlike terrestrial mammals, delphinid sound production is driven by pressurized air within a complex nasal system. It is unclear how fundamental whistle contours can be maintained across a large range of hydrostatic pressures and air sac volumes. Two opposing hyp...