Variably buoyant, dead Cetacea may float, or sink and later bloat to refloat if ambient temperature and pressure allow sufficient decomposition gas formation and expansion. Mortality can result from acute or chronic disease, fishery entanglement, vessel collision, noxious noises, or toxicant spills. Investigators often face the daunting task of elucidating a complex series of events, in reverse order, from when and where an animal is found, and to diagnose the cause of death. Various scenarios are possible: an animal could die at sea remaining there or floating ashore, or strand on a beach alive, where it dies and, if cast high enough, remain beached to be scavenged or decompose. An animal that rests low on a beach may refloat again, through increased buoyancy from decomposition gas and favorable tides, currents, and wind. Here we review the factors responsible for the different outcomes, and how to recognize the provenance of a cetacean mortality found beached, or floating at sea. In conclusion, only some carcasses strand, or remain floating. Negatively buoyant animals that die at depth, or on the surface, and sink, may never surface, even after decomposition gas accumulation, as in cold, deep waters gas may fail to adequately reduce the density of a carcass, precluding it from returning to the surface.

Very little is known about marine mammal susceptibility to primary blast injury (PBI) except in rare cases of opportunistic studies. As a result, traditional analysis techniques relied on methods developed more than 30 years ago using terrestrial mammals as surrogates. Modeling tools available today have the computing power to vastly improve calculation of safe ranges and injury zones from underwater explosions (UNDEX) employing morphologically accurate proxies with material properties similar to marine mammal tissues. The Dynamic System Mechanics Advanced Simulation (DYSMAS) fluid–structure interaction (FSI) software is being used to simulate the complex phenomena of UNDEX, shock wave, and bubble pulse propagation through the water and transmission of energy to a cetacean focusing on the dynamic response of the thoracic cavity and air‐filled lungs to a shock wave. The approach integrates fluid and structural analyses with the material properties of blubber, bone, and muscle using marine mammal morphometrics to eliminate unnecessary assumptions made during more traditional approaches to analysis developed before these types of data and computational power were available. DYSMAS analyses of a 1D gas bubble surrounded by water was found to closely match the classical bubble dynamics models. Further, DYSMAS models of a spherical gas bubble surrounded by tissue and rib structure demonstrate a global radial oscillation of the gas bubble, but also show significant local deflection and material strain in response to the UNDEX loading. The intended result of the investigation is an improved and scientifically defensible understanding of the effects of UNDEX on marine mammals. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 302:718–734, 2019. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

Recent mass strandings of beaked whales (Ziphiidae, Cetacea) coinciding with the use of midfrequency range (1–10 kHz) active sonar have caused speculation about the potentially adverse effects of these sound sources. Particular questions of the research and regulatory communities concern whether beaked whale sensitivity to midfrequency sound exposure is influenced by oceanographic characteristics present at the time of the mass stranding events. This study investigated the interaction between beaked whale habitat characteristics and the nature of a midfrequency signal by analyzing the oceanographic factors affecting underwater acoustic propagation. Three types of model sites were selected from five specific geographical locations where beaked whales have been regularly recorded or where a mass stranding event has been reported. A ray-trace acoustic propagation model was used to generate transmission loss for a 3-kHz signal over a representative 60-km transect at each locality. Model outputs visually demonstrated how the combination of site/event-specific oceanographic characteristics affects the sound propagation of a moving source. A parametric sensitivity comparison and statistical analysis were conducted to identify influential factors between environmental parameters, source depth, and the resulting transmission loss. Major findings of this study as well as future research direction are discussed. [Research supported by NAVSEA.]

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