Dolphin Danger: Understanding Plastic Pollution's Impact

Dolphins are incredibly intelligent creatures, but they are not immune to the dangers of plastic pollution. As plastic waste continues to infiltrate our oceans, dolphins are facing new threats to their health, food sources, and ecosystems. From ingestion of plastic debris to entanglement in discarded fishing gear, plastic pollution poses significant risks to dolphin populations worldwide.

Dolphins mistake plastic for prey

Dolphins are highly intelligent creatures, yet they sometimes mistake plastic for prey. This is a problem that is causing the deaths of dolphins and other marine mammals worldwide.

There are a few reasons why dolphins may mistake plastic for prey. One theory is that dolphins hunt for prey using their sense of hearing, and the sounds made by plastic objects in the ocean can be very similar to the sounds made by their prey. A study by Duke University found that 100% of the plastic debris tested had 'either similar or stronger acoustic target strengths' compared to the prey items. This means that dolphins may be mistaking pieces of dangerous plastic for their natural prey, such as squid or fish, because to them, they sound the same.

Another reason dolphins may mistake plastic for prey is that plastic bags floating in the water can look similar to squid or other prey items. Even species that don't identify prey by sight are not safe, as they may use echolocation to find their prey, and this can also be confused by unnatural objects in the water.

Once dolphins have ingested plastic, it can block their digestive systems, causing them to feel full and leading to starvation. It can also attract toxic substances, further threatening their health. Recent research has also found microplastics (tiny pieces of plastic) in the blow (exhalations) of bottlenose dolphins, indicating that their airways are contaminated with this material.

The problem of dolphins mistaking plastic for prey is just one of the many ways that plastic pollution is affecting dolphin populations. It is estimated that approximately 56% of the world's dolphins and whales have ingested plastic at some point, and this is contributing to the decline of these species.

Plastic ingestion blocks digestive systems

Dolphins are highly intelligent creatures, yet they are unable to distinguish plastic from prey. This is how ingested plastic ends up blocking their digestive systems.

Dolphins are often deceived by the appearance of plastic bags floating in the water, mistaking them for prey such as squid. They also use echolocation to hunt, but scientists believe that unnatural objects like plastic waste can confuse their natural sonar, leading them to mistakenly interpret plastic as food.

Once ingested, plastic blocks the digestive system of dolphins, preventing them from properly processing and extracting nutrients from their food. This results in starvation, even with a full stomach. A tragic example of this was seen in 2018 when a pregnant pygmy sperm whale beached itself in Melbourne, Australia. An autopsy revealed that its stomach was clogged with plastic, obstructing the rest of its digestive system.

The impact of plastic ingestion on dolphins is not limited to physical blockages. Recent studies suggest that plastic may also harbour bacteria and viruses, further compromising the health of dolphins. Additionally, plastic tends to attract toxic substances, adding to the toxins accumulated in the body of the dolphin.

The problem of plastic pollution in the ocean is pervasive, with an estimated 8 million tons of plastic entering the ocean each year. As a result, about 56% of the world's dolphins and whales have ingested plastic at some point, leading to devastating consequences for these magnificent creatures.

Plastic toxins impair dolphins' immune systems

Dolphins are incredibly vulnerable to plastic pollution. They are intelligent creatures, but plastic can be deceptively appealing to them, and ingestion is almost inevitable.

Once ingested, plastic blocks their digestive systems, causing a slow and painful death by starvation. It can also pierce the gut wall, leading to fatal infections.

Pollutants in plastic such as polychlorinated biphenyls (PCBs), lindane, dieldrin, and dichlorodiphenyltrichloroethane (DDT) impair dolphins' immune systems, making them more susceptible to infections. These toxins accumulate in the fatty tissue (blubber) of dolphins and are passed from mother to calf during pregnancy and breastfeeding.

PCBs, in particular, are toxic and cause sterility, threatening the survival of entire populations. Dolphins struggle to metabolise and eliminate these toxins, and their bodies can be overwhelmed, leading to fatal health complications.

The impact of plastic pollution on dolphins is a pressing issue, and it is crucial that we address it through individual actions, policy changes, and behavioural campaigns to reduce plastic waste and protect these magnificent creatures.

Dolphins get entangled in plastic fishing gear

Dolphins are incredibly intelligent creatures, but even they can fall victim to the tricks played by plastic pollution. One of the most significant ways plastic pollution affects dolphins is through entanglement in discarded plastic fishing gear.

Fishing gear, such as nets, lines, and tackle, is often abandoned or lost by fishermen, becoming what is known as "ghost" fishing gear. This gear then floats aimlessly in the ocean, posing a deadly threat to marine life, including dolphins. The very nature of this ghost gear makes entanglement almost inevitable. As dolphins swim through the ocean, they can easily become entangled in these abandoned nets and lines, which can have devastating consequences.

The impact of entanglement in plastic fishing gear on dolphins is twofold. Firstly, it can cause direct physical harm to the dolphins. The tight grip of the nets can cut deep into their skin, leaving them vulnerable to deadly infections. Secondly, entanglement can impair the dolphin's ability to move and surface for air, leading to fatal drowning. The panic and struggle for air can also cause dolphins to dive rapidly, resulting in fatal decompression sickness.

The issue of abandoned fishing gear is widespread, with an estimated 640,000 tonnes of the 8 million tonnes of plastic entering the oceans each year being ghost fishing equipment. This equipment continues to ensnare marine creatures, including dolphins, causing injury and death. The impact of this plastic pollution is not limited to dolphins, as even their skeletons have been found in the ghost nets, along with other marine life such as sharks and fish.

To address this issue, several measures can be taken. Implementing minimum standards for loss-resistant or higher-quality fishing gear can reduce gear loss. Additionally, incentivising gear repairs and port disposal of damaged nets, as well as penalising high-risk fishing activities, can help mitigate the problem. Outreach and education for recreational fishers can also raise awareness of the harmful effects of discarded fishing gear.

Noise pollution impacts dolphins' echolocation

Dolphins are highly social mammals that communicate through squeaks, whistles, and clicks. They also use echolocation to navigate their environment and locate food and other objects. However, noise pollution from sources such as ship engines, military sonar, oil drills, and construction can severely impact their well-being.

Dolphins rely on sound for hunting, socialising, and navigation, and are sensitive to loud noises. Noise pollution can cause hearing loss or even death in dolphins. It has been observed that loud noises can cause panicked dolphins to dive rapidly, leading to fatal decompression sickness due to the abrupt change in pressure.

A study published in the journal Current Biology, titled 'Anthropogenic noise impairs cooperation in bottlenose dolphins', found that as underwater noise levels increase, dolphins have to "shout" to each other, raising the volume and length of their calls. The study also observed that the dolphins changed their body language, turning their bodies towards each other and swimming closer together to compensate for the noisy background. Despite these adjustments, the dolphins had less success in coordinating their tasks.

Noise pollution not only impacts the communication and behaviour of dolphins but can also affect their feeding habits. A recent study on narwhals exposed to seismic air guns used in the oil and gas industry found that they immediately began diving to escape the noise. These high-intensity dives used more energy than normal and put their health at risk. The lead author of the study, Professor Terrie Williams, explained that the escape time away from foraging and normal behaviours would negatively impact their health.

Additionally, shipping noise has been found to cause stress in whales, with the build-up of stress-related chemicals linked to growth suppression, lower fertility, and poor immune system function.

The impacts of noise pollution on dolphins highlight the urgent need to address this issue. Some regulatory actions and noise management practices have been proposed, such as construction bans in dolphin habitats and the introduction of speed limits for ferries. However, addressing noise pollution is a complex task, especially in highly urbanised areas.

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