Abstract

Cold stress is the leading cause of mortality in West Indian manatees (Trichechus manatus) in the northern Gulf of Mexico where manatee sightings and strandings have increased in recent years.^1,2 In January 2022, Dauphin Island Sea Lab’s Manatee Sighting Network (MSN) received a call about a live West Indian manatee in a shipping canal in Theodore, Alabama. Due to the concern for cold stress, MSN responders deployed to monitor the animal. There appeared to be mild skin bleaching on the manatee’s snout and evidence of emaciation. A rescue was scheduled two days after the initial sighting under the direction of the United States Fish and Wildlife Service and in partnership with the Florida Fish and Wildlife Conservation Commission and SeaWorld Orlando. The rescue event was successful; however, the animal was apneic and breath stimulation attempts (splashing water on the snout, manipulating nares, eyes, and mouth) were unsuccessful. Despite all efforts and emergency drug administration, the animal died during transport. This report describes the necropsy and histopathology findings of this animal as well as the case conclusions, which revealed multiple causes of death that are rarely described.

At necropsy, the carcass had signs of cold stress syndrome, including emaciation and skin bleaching and ulceration, in addition to grossly evident aortic stenosis and concentric left ventricular hypertrophy, as well as a plastic bag obstructing the esophagus. Histopathology of the aorta revealed non-atherosclerotic and non-inflammatory fibromuscular dysplasia, and there was secondary mitral valve endocardiosis and left-sided myocardial hypertrophy that likely resulted in cardiac insufficiency. On gross examination, there was abundant white foam throughout the bronchi, and the lungs were pale pink to white with interstitial fluid consistent with pulmonary edema. Histologically, there were occasional alveoli that contained fibrinous exudate and lightly eosinophilic proteinaceous substance (edema). In the caudal left and right lung lobes, there were multifocal alveolar spaces containing extravasated erythrocytes, a mild, focal interstitial infiltrate of lymphocytes and plasma cells, and multifocal perivascular expansion by clear spaces (edema). Pulmonary edema was presumed to be secondary to heart disease in this case. While heart disease has previously been documented in manatees, this is the first case report of fibromuscular dysplasia in this species.^3,4 Similarly, plastic ingestion is known to occur in manatees, with some studies finding ingested debris, including plastic packing or bags, in 11–14% of carcasses examined.^5,6 While marine debris is commonly found in the gastrointestinal tract of marine mammals,⁷ complete obstruction is less common. This case report provides an example of a multifactorial cause of death, illustrating the range of natural and anthropogenic factors that can contribute to manatee mortality throughout the species range and highlighting the importance of rapid response and thorough post-mortem examination to characterize these findings.

Acknowledgments

The Alabama Marine Mammal Stranding Network operates under a Stranding Agreement between the Dauphin Island Sea Lab and NOAA’s National Marine Fisheries Service. Research funding for this project was provided in part by the John H. Prescott Marine Mammal Rescue Assistance Grant Program and the Gulf of Mexico Energy Security Act (GoMESA). Additional support was provided by the Alabama Emergency Management Agency, the Dauphin Island Sea Lab, and our many volunteers, interns, students, and staff members. The views and conclusions in this document should not be interpreted as an endorsement by any of the funding agencies. We thank the United States Fish and Wildlife Service, the Florida Fish and Wildlife Conservation Commission, and SeaWorld Orlando for the collaborative effort put forth for this case. We also thank the reviewers for their helpful comments.

Literature Cited

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