Degollada, E., Arbelo, M., André, M., Blanco, A., Fernández, A. Preliminary Ear Analysis Report of the 2002 Canary Islands Ziphius Mass Stranding. 17 th Annual Conference of the European Cetacean Society, Las Palmas de Gran Canaria, 2003 Resum: The analysis of the ears has become a challenging research in the post-mortem study of any stranded cetacean. Its importance and repercussion in cetacean stranding and/or death may exceed any estimation regarding cetacean acoustic impairment. In September 2002, a massive stranding of 14 animals belonging to three different ziphidae family species took place in the Canary Islands. The spatio-temporal coincidence of this event with NATO maneuvers, also reported in other historical mass strandings, made specially relevant an exhaustive study of the individuals acoustic apparatus in order to confirm or discard the implication of specific sound sources in the cetacean death. Necropsies on ten carcasses were performed between 24 and 72h postmortem following standard procedures. The ear regions of seven animals were carefully examined by extracting either a block with surrounding bone, the isolated ear complex or the periotic bone. Fixation was further performed either by immersion or by injection through the inner ear windows. The ears were analyzed by imaging techniques like CT and MRI and processed for routine H/E staining histopathology after decalcification. The paraotic sinuses did not show other alterations than being swollen with air and foam with partially empty surrounding venous plexuses. Except for three cases presenting slight peribullary and acoustic fat hemorrhages, the periotic complex and middle ear were not affected macroscopically. The middle ear rete mirabile was depleted with a certain degree of congestion. The most remarkable features were inner ear hemorrhages and edema starting in the VIIIth cranial nerve and extending into the spiral ganglion and the cochlear channels. In addition, inner ear structural damages were found. These findings are consistent with the lesions observed in other organs, in particular the brain, confirming as the only non-discarded cause of death, an acoustically induced trauma.