Fat embolism and whale ship collisions in the Canary Islands

Abstract

The Canary Islands is a geographical area with an important overlap of high cetacean diversity and maritime traffic, including high-speed ferries. Sperm whales are present all year round in the Canarian waters and are listed as vulnerable species. Most stranded sperm whales in the Canaries present signs of ship strikes. Findings such as hematomas, hemorrhages or edema, point to an antemortem trauma. Nevertheless, it can be difficult, especially when carcasses are very decomposed, to distinguish if a whale was already dead when hit by a vessel. In these cases, lipids may play an important role to determine “in vivo” severe trauma, as it has already been demonstrated in other species. A ship strike might cause bone fractures or severe soft tissue damage, disrupting the tissue and enabling the entry of fat into the circulatory system. Lung is the target organ to detect those fat emboli as they get easily trapped in the pulmonary microvasculature. In the present study, we have studied the presence of fat emboli by histochemistry in lungs of fifteen sperm whales with signs of ship collision stranded and necropsied in the Canaries between 2000 and 2015. Many of these whales (n=11) were in advanced autolysis. As lipids substances are soluble in the processing solvents used when embedding tissues in paraffin, osmium tetroxide was used to fix the lipids within the tissue. Samples were stained with hematoxilin-eosin. Histological examination revealed the presence of fat emboli with different degrees of severity in 12 out of the 15 animals studied. These results demonstrate 1) the usefulness of fat as a diagnostic tool for in “vivo” trauma, even in decomposed tissues kept in formaldehyde for long periods of time; and 2) that, during this 15-year period, 80% of the sperm whales studied were alive at the moment of the collision and have died due to vessel collision in Canarian waters. This information is extremely important in order to implement proper mitigation measures in this area.