Insights sobre um encalhe em massa de falsas orcas (Pseudorca Crassidens Owen, 1846)

False killer whales (FKWs; Pseudorca crassidens) are found in deep waters of temperate and tropical oceans worldwide. This species is considered near threatened and global populations’ trends are unknown although there is evidence of decline of various populations. The mass stranding of cetaceans remains an intriguing event and often the cause(s) are unclear or poorly investigated. In Brazil, cetacean mass strandings have been recorded yet they have not been investigated. In this study, we aimed to report the epidemiologic features of a mass stranding event involving 30 live FKWs occurred in northeastern Brazil in 2013. Releasing attempts and posterior monitoring data indicated successful outcome for 24 of 30 FKWs. Postmortem pathologic investigations confirmed live-stranding stress response and intestinal (Bolbosoma sp.) and otic (Stenurus sp.) endoparasitism. Toxicologic analyzes detected high concentrations of total mercury in liver correlating with liver damage, as indicated by elevated transaminases. In this mass stranding, key factors were early notification, organizational and operational framework, trained and sufficient personnel, resources and equipment, government support, and strategy and decision making. These results underscore the benefits of a rapid marine mammal network response, the importance of integrative multidisciplinary investigations, and set baseline information for mass strandings of cetaceans in Brazil.