Final Report: Postmortem Research Feasibility Study on Cetacean Ears

Executive Summary The objective of this study is to assess the feasibility of investigating potential anthropogenic acoustic damage to cetaceans using histological examination of cetacean ears removed on post-mortem examination, predominantly from stranded or by-caught harbour porpoises (Phocoena phocoena) in UK waters. The research was conducted in collaboration with ongoing investigations at the Research and Technology Centre Westcoast, Büsum, Germany into traumatic damage, disease or other abnormalities potentially associated with exposure to loud noise or blast trauma. In this study, pairs of ears from 25 UK-stranded harbour porpoises were sent to Germany and 11 pairs were prioritised for histological analysis. Of the 11 ears prioritised for processing, three were analysed in detail, four were not analysed further due to heavy over-decalcification artifacts during preparation (i.e. broken and torn bone tissue, collapsed inner ear), and four were celloidin-embedded pending detailed examination. Of the three examined in detail, none had evidence of acoustic trauma although one animal had some missing structures in the inner ear due to mechanical artifacts, and so it was not possible to completely rule out noise-induced auditory lesions in this case. It would also be desirable to conduct surface preparations and immunohistochemical staining of tissue sections to examine the stereocilia attached to the outer and inner hair cells and the tectorial membrane in more detail. One porpoise did have total degeneration of the organ of Corti, but this was considered more likely to be an abnormal development of the organ of Corti and not induced by noise exposure. Important criteria for the examination of ear tissues in general, and especially for the assessment of potential noise-induced lesions, are the degree of fixation, the freshness of the tissue, and the state of decalcification. Soft ear tissue gradually decomposes within hours after death. In order to maximise tissue preservation, the auditory tissues should be fixed in formalin as soon after death as possible. It is also important to avoid introducing any additional changes (artifacts) due to mechanical and/or chemical steps while processing the ear in the laboratory. In this study, the degree of fixation or freshness of all three specimens examined in detail varied from very good to moderate, even though all three individuals were classed as " freshly dead " on initial post-mortem examination. Because the ear structures are encased in bony tissue, the decalcification of these tissues was necessary in order to prepare sections of the auditory tissues …