Dolphin Danger: Understanding Plastic Pollution's Impact

Dolphins are incredibly intelligent creatures, but plastic pollution is a serious threat to their survival. Dolphins, like many marine animals, are susceptible to the ingestion of plastic, which can block their digestive systems and cause death. They can also be entangled in discarded plastic fishing gear, which can lead to drowning. With an estimated 8 million tons of plastic entering the ocean each year, plastic pollution is a pressing issue that requires urgent action to protect dolphin populations.

Dolphins mistake plastic for prey

Dolphins are vulnerable to plastic pollution due to their feeding methods, which range from filtering to hunting. With high amounts of plastic in their ocean habitats, dolphins are at risk of ingesting plastic, mistaking it for prey.

Dolphins use echolocation to hunt for prey. They have a remarkably acute sense of hearing, and a recent study by Duke University in the USA has shown that the acoustic profiles of degraded pieces of plastic in their environment are very similar to those of their prey. Dolphins may be mistaking pieces of dangerous plastic for their prey, such as squid or fish, because they sound the same.

The acoustic 'target strength' of squid and squid beaks was compared with naturally weathered and fouled plastics from the North Carolina coastline. The study found that 100% of the plastic debris tested had 'either similar or stronger acoustic target strengths' compared with that of the prey items. This supported the hypothesis that the consumption of plastic by dolphins is driven by a misperception of acoustic signals.

Additionally, a plastic bag ballooned with water can resemble a squid or other prey to the marine mammals that hunt them. Even species that do not identify prey by sight, such as some dolphin species, use echolocation to find their prey, which can be confused by unnatural objects such as plastic waste.

The ingestion of plastic can lead to physical blockages, disruption of regular food intake, or starvation due to a false feeling of fullness. It can also cause tissue damage and inflammation, potentially leading to disease.

Plastic blocks their digestive system

Dolphins are among the many marine animals that are affected by plastic pollution. Plastic waste in the ocean is a human-caused threat to dolphins, and it can block their digestive systems, leading to fatal consequences.

Dolphins often mistake plastic for prey, such as squid, and end up ingesting it. This ingested plastic accumulates in their bodies, giving them a false sense of fullness. As a result, they stop hunting and feeding on nutritious food, ultimately starving to death. This was the case for a pregnant pygmy sperm whale that beached itself in Melbourne in 2018. An autopsy revealed its stomach was clogged with plastic, blocking the rest of its digestive system.

The impact of plastic pollution on dolphins is not limited to ingestion. Prey species, such as fish or squid, may have already consumed plastic themselves, which is then transferred to the dolphin when consumed. This transfer of plastic pollution through the food chain further exacerbates the problem.

Additionally, plastic in the ocean can act as a magnet for toxic substances, attracting and accumulating harmful chemicals on its surface. When dolphins ingest this contaminated plastic, it introduces toxins into their bodies, impairing their immune systems and making them more susceptible to infections and diseases.

The presence of plastic in the ocean also affects dolphins' hunting methods. Dolphins use echolocation to find their prey, but plastic waste can confuse their sonar, leading them to misinterpret plastic waste as food. This misinterpretation results in the accidental ingestion of plastic, further blocking their digestive systems.

The blocking of the digestive system by plastic waste is a significant and detrimental consequence of plastic pollution on dolphins, leading to starvation, impaired health, and even death.

Plastic can cause infection

Dolphins are susceptible to infection from plastic pollution in multiple ways. Firstly, ingesting plastic can block their digestive system, causing a long, slow death from starvation. This blockage can also impair a dolphin's ability to feed itself nutritious food, leading to malnutrition and further health complications.

Secondly, sharp pieces of plastic can pierce a dolphin's gut wall, causing infection and even death. Plastic can also carry bacteria and viruses that negatively affect a dolphin's health. The plastic acts as a magnet, attracting toxic substances to its surface, which are then transferred to the dolphin upon ingestion.

Additionally, dolphins are vulnerable to parasites such as nasitrema nematode worms, liver flukes, and tapeworms. When toxins from plastic pollution impair a dolphin's immune system, these parasites can flourish and become deadly.

The impact of plastic pollution on dolphins is far-reaching and complex, and the full extent of the damage is yet to be fully understood.

Dolphins get entangled in plastic

Dolphins are among the many marine animals that are routinely entangled in plastic in the ocean. A report by the ocean conservation group Oceana found that nearly 1,800 marine animals from 40 species suffered from contact with plastics between 2009 and 2018, with about 88% of these animals listed as endangered or threatened. Dolphins are particularly susceptible to entanglement in plastic-based fishing gear, also known as "ghost" fishing gear, which is abandoned in the ocean by fishermen. This gear can entangle dolphins and other marine creatures, leading to drowning, physical trauma, or infections.

Dolphins can also become entangled in other types of plastic debris, such as plastic bags, packing straps, and food wrappers. In one case, a dolphin was found with a plastic water bottle stuck on its snout, while in another, a food wrapper was lodged in a dolphin's oesophagus. These encounters can be life-threatening, causing deep injuries or hindering the animal's movement and ability to feed.

The impact of plastic entanglement on dolphins is not limited to physical harm. When dolphins are entangled, they may also be unable to avoid vessels, increasing the risk of vessel strikes. Additionally, the presence of plastic in their environment can disrupt their echolocation abilities, which they use to navigate and find prey.

The problem of plastic pollution and its impact on dolphins is a pressing issue. While some jurisdictions have moved to phase out single-use plastics, more action is needed to address this human-caused threat to dolphins and other marine life.

Noise pollution impacts their echolocation

Dolphins rely on echolocation to hunt and navigate their environment. They emit and receive sound waves that bounce off objects in the water, which are then translated into images by their brains. This allows them to see with sound, even in low-visibility environments.

Noise pollution from sources such as ship engines, military sonar, oil drills, and construction severely impacts their ability to echolocate. The loud noises can cause hearing loss or even death. As a result, dolphins have to shout to communicate with each other, and their communication range is significantly reduced. For example, in Hong Kong, dolphin populations have dropped by over 80% in 15 years due to noise pollution from industrialization.

A study published in the journal Current Biology, 'Anthropogenic noise impairs cooperation in bottlenose dolphins', found that as underwater noise levels increased, dolphins had to change their behaviour to communicate and work together. They raised the volume and length of their calls, turned their bodies towards each other, and swam closer to one another. Despite these adjustments, the dolphins were less successful in coordinating with each other.

The impact of noise pollution on dolphins' echolocation abilities highlights the importance of addressing this often-overlooked form of pollution. Conservation efforts and noise management practices are crucial to protecting dolphin populations and reducing the harmful effects of noise pollution on their communication and survival.

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