AUDITORY EVOKED POTENTIALS AND BEHAVIORAL CONSIDERATIONS WITH HEARING LOSS IN SMALL CETACEANS: APPLICATION AS A STANDARD DIAGNOSTIC TEST IN HEALTH ASSESSMENT.

The primary sense in odontocetes is hearing and a large portion of the odontocete brain is devoted to the auditory processing of echolocation signals. Hearing deficits in odontocetes potentially compromise the ability to forage, navigate, socialize, and evade predators. This presents a challenge to survival and reproduction in wild odontocetes and can affect the general welfare of odontocetes under human care. Currently, little empirical information on how odontocete behavior is affected by hearing loss exists. This study investigated hearing deficits in several species of stranded dolphins and age-related hearing deficits in dolphins kept under human care through auditory evoked potential (AEP) testing and evaluated whether individual behavior correlated with hearing impairment. Behavioral questionnaires for participating animals were completed by individuals with extensive knowledge of the animals' history and behavior. A chi-square analysis determined whether animals with hearing impairment demonstrated behaviors that differed significantly from those considered normal. All tested individuals under human care over 35 years of age had some degree of hearing loss, as did a large percentage of previously stranded animals. Individuals with hearing loss exhibited a range of behavioral changes, including delays in learning new behaviors, accepting novel enrichment, and habituating to new environments. Some individuals with profound hearing loss also displayed a change in vocalization rate in various situations. Findings within previously stranded animals suggest AEP studies should be conducted in all stranded individuals entering rehabilitation. It is further recommended that dolphins living under human care undergo hearing tests as part of their normal health assessments, with emphasis on aging individuals and animals that exhibit delayed learning, respond poorly to audible cues, or show atypical vocalization behavior.

Criteria and case definitions for serious injury and death of pinnipeds and cetaceans caused by anthropogenic trauma.

Post-mortem examination of dead and live stranded beach-cast pinnipeds and cetaceans for determination of a cause of death provides valuable information for the management, mitigation and prosecution of unintentional and sometimes malicious human impacts, such as vessel collision, fishing gear entanglement and gunshot. Delayed discovery, inaccessibility, logistics, human safety concerns, and weather make these events challenging. Over the past 3 decades, in response to public concern and federal and state or provincial regulations mandating such investigations to inform mitigation efforts, there has been an increasing effort to objectively and systematically investigate these strandings from a diagnostic and forensic perspective. This Theme Section provides basic investigative methods, and case definitions for each of the more commonly recognized case presentations of human interactions in pinnipeds and cetaceans. Wild animals are often adversely affected by factors such as parasitism, anthropogenic contaminants, biotoxins, subclinical microbial infections and competing habitat uses, such as prey depletion and elevated background and episodic noise. Understanding the potential contribution of these subclinical factors in predisposing or contributing to a particular case of trauma of human origin is hampered, especially where putrefaction is significant and resources as well as expertise are limited. These case criteria descriptions attempt to acknowledge those confounding factors to enable an appreciation of the significance of the observed human-derived trauma in that broader context where possible.