The Baikal seal is the only endemic mammal of Lake Baikal. In late October 2017, 132 dead Baikal seals were found on the shore of the lake. To identify causes of death, postmortem necropsy, virological, chemical toxicological, microbiological, and parasitological studies were carried out. Several hypotheses for explaining the causes of the deaths were put forward. The most probable causes are heart failure and asphyxia due to echo sounders (sonar). The causes were confirmed by the results of histological examination of the hearts and lungs of a large number of dead seals found on the southern shore of Lake Baikal (a center for the fishing industry).

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