Scott Cramer

Hyperbaric computed tomographic measurement of lung compression in seals and dolphins.

SUMMARY Lung compression of vertebrates as they dive poses anatomical and physiological challenges. There has been little direct observation of this. A harbor and a gray seal, a common dolphin and a harbor porpoise were each imaged post mortem under pressure using a radiolucent, fiberglass, water-filled pressure vessel rated to a depth equivalent of 170 m. The vessel was scanned using computed tomography (CT), and supported by a rail and counterweighted carriage magnetically linked to the CT table movement. As pressure increased, total buoyancy of the animals decreased and lung tissue CT attenuation increased, consistent with compression of air within the lower respiratory tract. Three-dimensional reconstructions of the external surface of the porpoise chest showed a marked contraction of the chest wall. Estimation of the volumes of different body compartments in the head and chest showed static values for all compartments except the lung, which showed a pressure-related compression. The depth of estimated lung compression ranged from 58 m in the gray seal with lungs inflated to 50% total lung capacity (TLC) to 133 m in the harbor porpoise with lungs at 100% TLC. These observations provide evidence for the possible behavior of gas within the chest of a live, diving mammal. The estimated depths of full compression of the lungs exceeds previous indirect estimates of the depth at which gas exchange ceases, and concurs with pulmonary shunt measurements. If these results are representative for living animals, they might suggest a potential for decompression sickness in diving mammals.

BIOMECHANICAL AND STRUCTURAL MODELING OF HEARING IN BALEEN WHALES

Anthropogenic noise may be a major source of habitat degradation for cetaceans. To assess and mitigate the effects of noise pollution on marine mammals, we need information on how and what they hear. Although hearing in odontocetes, or toothed whales, is well studied, few data are available for mysticetes, or baleen whales. Behavioural and electrophysiological hearing tests are presently impractical for mysticetes, but biomechanical, structural modelling provides hearing estimates based on auditory system anatomy. In this research, three101 dimensional models were produced for minke Balaenoptera acutorostrata, blue Balaenoptera musculus, and humpback Balaenoptera novaeangliae whale inner ears from CT scans and histology to measure key features for estimating hearing ranges, e.g., basilar membrane thickness-towidth ratios. Full head reconstructions were also produced for minke whales based on head CT images and dissections.

Great Ears: Low-Frequency Sensitivity Correlates in Land and Marine Leviathans.

Like elephants, baleen whales produce low-frequency (LF) and even infrasonic (IF) signals, suggesting they may be particularly susceptible to underwater anthropogenic sound impacts. Analyses of computerized tomography scans and histologies of the ears in five baleen whale and two elephant species revealed that LF thresholds correlate with basilar membrane thickness/width and cochlear radii ratios. These factors are consistent with high-mass, low-stiffness membranes and broad spiral curvatures, suggesting that Mysticeti and Proboscidea evolved common inner ear adaptations over similar time scales for processing IF/LF sounds despite operating in different media.

DIAGNOSIS AND MANAGEMENT OF INTESTINAL PARTIAL OBSTRUCTION IN A LOGGERHEAD TURTLE (CARETTA CARETTA)

Abstract: A loggerhead sea turtle (Caretta caretta) was suspected of ingesting rubber suction cups during rehabilitation following a cold-stun event. Survey radiographs were inconclusive. Computed tomography (CT) was performed to determine whether the objects had been ingested after traditional radiographs failed to resolve the material. The items were identified, and a partial obstruction was diagnosed. The case was managed with medical therapy using white petrolatum and light mineral oil administered to the turtle in fish for 3 wk. The CT exam was repeated 2 wk into the therapy. A persistent partial obstruction was identified; however, progression of the foreign objects through the intestinal tract was evident and continued medical mangement was deemed appropriate. The foreign bodies were passed with feces 26 days after ingestion.

Non anthropogenic deafness in marine mammals: Hearing that is going, going, gone.

In humans, hearing is absent or diminished as a result of congenital defects, aging, noise exposures, traumatic events, and disease. Until concern arose about anthropogenic noise impacts on marine mammals, little was known about the mechanisms or incidence of marine mammal hearing losses. Over the past decade, we have gained substantial information from behavioral and electrophysiologic audiometres, in vivo imaging, and postmortem examinations. Dr. Sam Ridgway has been a pivotal element in these investigations, pioneering many of the techniques and facilitating broad collaborative studies. In this paper, the results of computerized tomographic and histologic studies of pinniped and cetacean ears, the majority of which Dr. Ridgway supplied, will be presented. The data show that marine mammals sustain precipitous and progressive hearing loss from multiple etiologies, including labyrinthitis, infestations, trauma, chronic multistage otitis, and presbycusis. In particular, older dolphins and seals develop deg...

Twists and turns, in cochlear anatomy: Curvatures related to infra vs ultrasonic hearing

Microchiropteran bats and odontocete cetaceans are sophisticated echolocators with acute ultrasonic hearing operating in radically different media. Similarly, elephants and mysticetes share the ability to generate and respond to infrasonics. In this study, the heads, outer, middle, and inner ears of 32 specimens from 11 species of bats, dolphins, elephants, and whales were analyzed with microCT (11 to 100 micron isotropic voxel imaging; Siemens Volume Zoom and X-Tek CT units). Canal length, basilar membrane dimensions, and cochlear curvatures varied widely among all species. Length correlates with body mass, not hearing ranges. High and low frequency limits correlate with basilar membrane ratios and radii ratios, which are a measure of the radius of curvature. The ears of the known echolocators were significantly different from the mid to low frequency ears, with increased stiffness, thicker membranes, and outer osseous laminae supporting up to 60% of the basilar membrane. Anatomical correlates of “foveal...

Cochlear structural variants in echolocators

Although microchiropteran bats and odontocete cetaceans operate in radically different media, both have sophisticated sonar capabilities and evident similarities in their ability to detect and analyze ultrasonic signals. This paper compares the similarities and differences of cochlear cytoarchitecture and its implications for ultrasonic encoding and acuity amongst these groups through the use of three-dimensional models obtained via micro-CT imaging of intact heads and temporal bones. Inner ear anatomy was fundamentally similar with notable parallels in fenestral placement and ratios, membrane dimensions, and neural density and distribution across bats and dolphins with common cochlear types. Specialist ears are present in both groups, suggesting that like some CF-CM bats, one or more odontocete species have cochleae with specialized basilar membrane “foveal” regions. Cochlear specializations in both groups are primarily linked to peak spectra of signal, expanded frequency representation, and may enhance ...

Great ears: Functional comparisons of land and marine leviathan ears

Elephants and baleen whales are massive creatures that respond to exceptionally low frequency signals. Although we have many elephant and whale vocalization recordings, little is known about their hearing. Playback experiments suggest hearing in both proboscideans and mysticetes is tuned similarly to low or even infrasonic signals. This raises several interesting issues. First, they emit and perceive signals in two media, air and water, with radically different physical acoustic properties: 4.5‐fold differences in sound speed, three‐fold magnitude difference in acoustic impedance, and, for common percepts, whales must accommodate 60‐fold acoustic pressures. Also, a commonly held tenet is that upper hearing limit is inversely correlated with body mass, implying there should be virtually no whale‐elephant hearing overlap given body mass differences. This study analyzed how inner ears in these groups are structured and specialized for low‐frequency hearing. Computerized tomography and celloidin histology sec...