New gas and fat embolic pathology in beaked whales stranded in the Canary islands

Abstract

Recently, evidence of acute and chronic gas bubble lesions in tissues of different stranded cetacean species. Acute gas and fat embolic lesions have als o been described in a mass stranding of beaked whales exposed to anthropogenic sonar signals (Neotapón, 2002). These findings raise some important pathological questions: 1) What is the postmortem interval and necropsy technique necessary to diagnose acute gas emboli? 2) Are fat emboly common pathological findings in stranded cetaceans? (3) Do fat emboly develop at sea (i.e. prior to stranding) or during the stranding process? Recent strandings in the Canary Islands provide valuable data to help address these questions. Firstly, two fresh stranded Blainville’s beaked whales (M. densirostris), one young adult female (stranded, 2003) and an old male (stranded, 2004) necropsied between 4 and 8 hours after death had massive, acute gas-bubbles within the porto-mesenteric system. Intravenous gas bubbles were found in other organs (e.g. in the epicardial veins and meninges). Secondly, 18 out of 115 stranded cetaceans of six different species showed diverse grades of lung fat embolism. Most of the cetaceans with fat emboli in lung tissue belonged to deep and long duration diving species. The majority died due to anthropogenic causes like severe trauma caused by ship collision, or were associated with naval exercises and sonar activities. In some cases the cause of death could not be determined. Finally, four beaked whales arrived around the Canary Islands coasts approximately one week after the Majestic Eagle naval exercises conducted more than 100 km north of the Canaries in July 2004. The probability that the animals died at the sea is extremely high. All three beaked whales showed fat embolism (the fourth was not able to be analyzed due to extreme autolysis). Although mid frequency sonar was certainly used during the naval exercises, the use of other possible acoustic sources (e.g. explosions, torpedos, etc…) is currently unknown.