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SC/69B/E/03
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Resource ID
22066
Access
Open
Document Number
SC/69B/E/03
Full Title
Preliminary Information on the Amazonian River Dolphin Unusual Mortality Event (September ? November 2023), Western Brazilian Amazon
Author
Thais Carneiro Santos Rodrigues, Cristiane Kiyomi Miyaji Kolesnikovas, Ayan Fleischmann, Aricia Duarte-Benvenuto, Jose Luiz Catao-Dias, Juliana M. Guerra, Natalia C.C.A. Fernandes, Winnie Brum, Rodrigo Hoff, Mirela d?Arc, Maria Cecilia
Authors Summary
In late 2023, an UME of Endangered Inia geoffrensis and Sotalia fluviatilis took place in the Western Brazilian Amazon. The UME occurred during a severe historic regional drought, causing the death of over 300 river dolphins. Water temperatures reached unprecedented values, coupled with abnormally high amplitude of temperature throughout the day. Air quality reached unhealthy and hazardous levels, incident solar radiation was higher than normal, and humidity fell around 40% from regular values. Ichthyotoxic euglenophycin-producing Euglena sanguinea blooms were noted in both lakes but fish mortality was deemed normal under drought conditions. Tef‚ Lake area
was reduced in 75%, and average depth was around 50 cm. The event affected both sexes and all age groups of both species. Most animals were adults, in good body condition, with none or little amount of gastrointestinal content. Necropsy findings included generalized passive congestion, pulmonary atelectasis, lung edema, lymphadenomegaly, splenomegaly, and diffuse renal cortical hemorrhage, and histopathology showed
generalized vasodilation and congestion and, less commonly, hemorrhagic processes. Comorbidities were reported in some specimens. Samples were negative for infectious agents and clostridial toxins. Sparse viral assembled sequences detected were not considered indicative of acute viral infection. Palytoxin was detected in a small proportion of the samples. Heavy metal values turned out low in comparison with other studies
worldwide. Research findings indicate the river dolphin mortality was most likely related to severe environmental distress triggered by the extreme drought, abnormally high-water temperatures, daily temperature range, and hazardous air quality.
Publisher
IWC
Publication Year
2024
Abstract
In late 2023, an UME of Endangered Inia geoffrensis and Sotalia fluviatilis took place in the Western Brazilian Amazon. The UME occurred during a severe historic regional drought, causing the death of over 300 river dolphins. Water temperatures reached unprecedented values, coupled with abnormally high amplitude of temperature throughout the day. Air quality reached unhealthy and hazardous levels, incident solar radiation was higher than normal, and humidity fell around 40% from regular values. Ichthyotoxic euglenophycin-producing Euglena sanguinea blooms were noted in both lakes but fish mortality was deemed normal under drought conditions. Tef‚ Lake area was reduced in 75%, and average depth was around 50 cm. The event effected both sexes and all age groups of both species. Most animals were adults, in good body condition, with none or little amount of gastrointestinal content. Necropsy findings included generalized passive congestion, pulmonary atelectasis, lung edema, lymphadenomegaly,
splenomegaly, and diffuse renal cortical hemorrhage, andÿ istopathology showed generalized vasodilation and congestion and, less commonly, hemorrhagic processes. Comorbidities were reported in some specimens. Samples were negative for infectious agents and clostridial toxins. Sparse viral assembled sequences detected were not considered indicative of acute viral infection. Palytoxin was detected in a small proportion of the samples. Heavy metal values turned out low in comparison with other studies worldwide. Research findings indicate the river dolphin mortality was most likely related to severe environmental distress triggered by the extreme drought, abnormally high-water temperatures, daily temperature range, and hazardous air quality.