Manatees And Marine Debris: News From Brazil

The Antillean manatee of Central and South America is one of the most endangered marine animals in Brazil. Known threats to the population include habitat degradation, low genetic diversity, and calf stranding, but the role of ocean debris in manatee welfare has not been well researched. This study examined debris ingestion in manatees that were previously released by the National Center for Research and Conservation of Aquatic Mammals of the Chico Mendes Institute for Biodiversity (CMA/ICMBio), a Brazilian rescue and rehabilitation center.

At the center, debris ingestion is inspected through clinical monitoring of live manatees and necropsy of dead ones that wash up onshore. Treatment of live manatees consists of feeding them a fibrous diet as well as lettuce, water, and vitamin supplements. They are monitored in individual enclosures and released back into the wild when they’re healed. From 1994 to 2015, the CMA/ICMBio reintroduction program released 40 manatees. Four of them, all of whom were males between 8 and 15 years old, were later found again with debris ingestion. The animals had all been initially rescued as calves (younger than 30 days old).

The first manatee found with debris ingestion had spent 2 years at the center, then 7 years, 4 months at an acclimatization enclosure in the Area de Protecao Ambiental, or APA for short. He escaped into the wild and turned up in a mangrove dead, three months later. He was still within the protected area. Necropsy revealed several plastic bags and knit fabric inside of his stomach. These were believed to have inhibited his ability to eat and digest, resulting in severe weight loss. Part of the manatee’s radio telemetry equipment had also gotten caught on mangrove, limiting his ability to move and causing him to drown.

The second manatee had a similar upbringing to the first but moved to a different coastal area after arriving at the APA. He was found in this area (about 90 km from the reintroduction location) six months later. The manatee was severely debilitated and had lost 66% of his body weight. One week after returning to CMA/ICMBio, he began to pass plastic debris in his feces. This persisted for three months. After four months, the manatee had recovered was re-released. A small amount of plastic was found at necropsy when he died 2 years, 6 months later, indicating he had recently ingested these plastics. Debris ingestion was, however, not determined to be the cause of death.

The third manatee had been rescued twice; in the second instance he spent over 8 years, 7 months recovering. He was found dead in an estuary just three months after being released. Necropsy revealed that much of the manatee’s gastrointestinal tract was clogged with debris such as plastic bags, raschel knit, and condoms. Debris ingestion was determined to be the cause of death. The fourth and oldest manatee had undergone three release attempts, the final of which he spent 24 months in the wild. He was found 600 km from his release site, surrounded by debris and eating ice cream and sanitary napkin packaging. He was taken to a different recovery center where he passed a small amount of plastic that smelled of oil.

The study ultimately concluded that plastic debris had the potential to seriously debilitate and even kill manatees through intestinal blockage, loss of appetite, and perforation. Controlling the amount of plastic debris that makes it to the ocean is therefore critical, as manatees tend to forage in shallow waters and cannot distinguish between debris and food. Though the study had a small sample size (just 10% of the manatees in the reintroduction program), the results in these cases show just how harmful plastic debris. These manatees were able to recover and be reintroduced (at least for a some time) thanks to the efforts of conservationists, but not all wildlife, and not all manatees, are so fortunate.