Manatees And Plastic Pollution: A Deadly Threat?

Manatees, also known as sea cows, are large aquatic mammals that play an important role in maintaining a healthy ecosystem. They are incredibly graceful creatures, despite their size, and are often used as a poster species in conservation campaigns. Manatees are herbivores, feeding on a mix of grasses, weeds, and algae in the ocean. They spend a lot of time grazing, allowing them to eat up to 10% of their body weight a day.

Manatees are one of the thousands of marine species impacted by plastic pollution. They accidentally ingest small pieces of plastic waste and can become entangled in fishing nets. A study by researchers from Eckerd College found that more than 73% of 26 dead manatees from Tampa Bay, Florida, had plastic particles or microplastics in their gastrointestinal systems, and 76% had some form of plastic in their digestive tracts. Another report by Oceana found that 99% of 700 Florida manatees had swallowed some type of plastic between 2009 and 2018.

The impact of plastic pollution on manatees is a growing concern, and it is clear that plastic waste poses a significant threat to their survival.

Plastic ingestion

Manatees are herbivorous mammals that feed on a mix of grasses, weeds, and algae in the ocean. They spend a significant amount of time grazing on food, allowing them to eat up to 10% of their body weight daily. This grazing behaviour, combined with their aquatic habitat, makes them particularly vulnerable to ingesting plastic pollution.

A study by researchers from Eckerd College examined the remains of 26 dead manatees from Tampa Bay, Florida, over a 28-month period. They found that more than 73% of the animals had plastic particles or microplastics in their gastrointestinal systems, and 76% had some form of plastic in their digestive tracts. The most common type of plastic found in the manatees was monofilament fishing line.

Another report published in 2020 analysed 700 Florida manatees and found that 99% had swallowed some type of plastic. This is particularly concerning given that manatees are a species threatened with extinction. Plastic ingestion can obstruct digestion, damage intestines, and lead to starvation and death.

Manatees are not the only marine species affected by plastic pollution. According to a report by Oceana, titled "Choked, Strangled, Drowned: The Plastics Crisis Unfolding in Our Oceans," most of the cases (88%) involved animals listed as endangered or threatened with extinction. The report also highlights the impact of plastic on northern fur seals in the North Pacific Ocean and Bering Sea, who consumed plastic up to 50 times more often than average for eared seals.

The ingestion of plastic by manatees and other marine species is a significant issue that requires urgent attention. It is essential to address the root cause of plastic pollution and find alternatives to single-use plastics to protect these vulnerable species and maintain the health of marine ecosystems.

Plastic entanglement

Manatees are particularly susceptible to plastic entanglement because they live in estuaries and coastal regions and primarily feed on bottom vegetation, where debris can settle, or on floating vegetation, in which debris can become entangled.

Brandon Bassett, a biologist at the Florida Fish and Wildlife Conservation Commission, recalled a manatee that died after ingesting a large number of plastic bags and other types of plastic. The plastic formed a ball in the manatee's stomach and intestine, causing its death.

In another case, a plastic strap wrapped around a manatee's body, leaving a 10-centimetre-long gash. The manatee was rescued and brought to a rehabilitation centre, where its wound was treated.

Manatees are not the only species affected by plastic entanglement. Northern fur seals in the North Pacific Ocean and Bering Sea, and some sea turtle groups, are also impacted.

Boat strikes

The faster a boat is moving, the more force is applied to a strike. For instance, the force of a strike at 30 miles per hour is four times that of a strike at 15 miles per hour. If a watercraft strikes a manatee in the head, the animal may die immediately. Strikes in other areas can result in acute injuries that lead to death within days, weeks, or longer, or chronic injuries that linger for extended periods before the manatee eventually succumbs. Internal injuries, such as broken or dislocated ribs, can cause death from internal bleeding or infection.

To protect manatees from boat strikes, it is recommended that boaters abide by posted speed zone signs in areas known to be used by manatees or when observations indicate their presence. Boaters should also wear polarized sunglasses to reduce glare on the water's surface, making it easier to spot manatees. Staying in deep-water channels, avoiding seagrass beds and shallow areas, and maintaining a distance of at least 50 feet from manatees when operating a powerboat are also essential for manatee conservation.

Habitat loss

Manatees need warm, shallow water to survive. However, due to ongoing development, they are losing their natural habitats.

Manatees are a subspecies of the West Indian manatee and are found in the coastal and inland waters of the southeastern United States. During the summer, they can be found as far west as Texas and as far north as Massachusetts. However, during the winter, they congregate in Florida, as they require warm-water habitats to survive.

The loss of warm-water habitat is a significant threat to manatee populations. As water temperatures rise due to climate change, manatees struggle to find suitable habitats and are forced to disperse to neighbouring states. Additionally, the closure of power plants and the destruction of natural springs have further reduced the availability of warm-water refuges for manatees.

The loss of seagrass beds, a primary food source for manatees, has also contributed to habitat loss. Poor water quality, harmful algal blooms, and increasing harmful algal blooms have led to a drastic reduction in seagrass beds. This has resulted in starvation and emaciation in manatee populations, with researchers attributing the unusual mortality events to the loss of seagrass.

Human activities, such as pollution and the release of oil, pesticides, and fertilizers, have further degraded manatee habitats. These pollutants can harm the health of manatees and even lead to their death.

Algal blooms

The issue is not limited to the IRL. In 2021, over 700 manatees died in Florida due to toxic algal blooms, which have been caused by climate change and human nutrient pollution. Warmer water temperatures, increased sunlight, and higher carbon dioxide levels contribute to the growth of toxic blue-green algae, which thrives in these conditions.

The impact of algal blooms on manatees is devastating. Not only do they lose their primary food source, but the toxins produced by the algae can also cause severe health problems, including respiratory irritation and seizures, which can lead to drowning. Manatees can be exposed to these toxins through inhalation, ingestion of toxic food, or by taking in seawater containing the toxins.

The situation is critical, and immediate action is needed to address the nutrient pollution causing these harmful algal blooms. Efforts are already underway to restore the IRL and improve water quality, but more needs to be done to protect manatee habitats and prevent further loss of seagrass.

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