Dolphin Danger: Understanding Pollution's Impact

Dolphins are highly intelligent, air-breathing mammals with complex societies and systems of communication. They are also one of the many species affected by human-caused pollution. From greenhouse gases to littering, human activity impacts every square mile of the ocean and about 40% of marine ecosystems. Dolphins are affected by pollution in numerous ways, from chemical and plastic pollution to noise pollution.

Oil spills

The dolphins breathed in contaminated air from the oil spill, which caused respiratory issues. Exposure to oil can also cause long-term increases in mortality, failed pregnancies, and an increased risk of other diseases or infections. Dolphins that inhale oil can experience lung disease from inhalation and aspiration, impaired stress response, and compromised immune function, which may lead to increased infection and disease. Oil spills can also affect dolphins' blowholes if there is a buildup of grease on the water's surface.

In addition to the direct health impacts on dolphins, oil spills can also displace dolphins from their habitats and make food sources scarce. Oil spills create dead zones in the water, where algae deplete the oxygen, causing fish and other marine animals to die. This can force dolphins to leave their homes in search of new food sources.

The effects of oil spills on dolphins can be long-lasting and devastating, and it is crucial to take measures to prevent such disasters and mitigate their impact on these intelligent and beloved marine mammals.

Fertilizer runoff

Fertilizers contain high levels of nitrogen, phosphorus, and potassium, which promote the growth of algae, leading to algal blooms. These blooms deplete the oxygen levels in the water, creating hypoxic conditions that are detrimental to aquatic life. The decomposition of the blooms consumes a large portion of the available dissolved oxygen, leading to reduced biodiversity and even large fish-kill events.

The toxins produced by these algal blooms can accumulate in the bodies of dolphins, a process known as bioaccumulation. Ingesting contaminated fish or breathing in the air containing these toxins can result in respiratory ailments, immune dysfunction, increased mortality, failed pregnancies, and a higher risk of other diseases and infections.

Agricultural practices, such as excessive irrigation and improper waste disposal, contribute to fertilizer runoff. When fertilizer-rich water reaches rivers and oceans, it can have devastating effects on the delicate ecosystems, including the dolphin populations that inhabit them.

To mitigate the impacts of fertilizer runoff on dolphins and other marine life, it is essential to implement sustainable farming practices, improve waste management, and raise awareness about the proper use and disposal of fertilizers.

Plastic pollution

Dolphins can mistake plastic for prey, such as squid, due to its similar appearance when floating in the water or when a plastic bag is filled with water. They use echolocation to hunt, but some scientists believe that unnatural objects like plastic waste can confuse their sonar, leading them to mistakenly interpret it as food. This was evident in the case of a pregnant pygmy sperm whale that beached itself in Melbourne in 2018. An autopsy revealed its stomach was clogged with ingested plastic, causing it to strand itself.

The impact of plastic pollution on dolphins goes beyond ingestion. Abandoned fishing gear, often referred to as "ghost" gear, poses a significant threat to dolphins. This discarded equipment, including nets and other parts, can entangle dolphins, leading to fatal consequences. The humpback dolphin, a rare species found only in the waters around Australia and New Guinea, has been observed with marine debris tightly wrapped around its body, causing deep cuts and risking deadly infections.

The presence of plastic in the ocean also indirectly affects dolphins. Plastic can act as a magnet for toxic substances, attracting and concentrating them on its surface. When dolphins ingest plastic-contaminated prey, they are exposed to these accumulated toxins, which can impair their immune and reproductive systems. Additionally, plastic pollution contributes to the creation of "dead zones" in the ocean. As pollution causes an overgrowth of algae, these organisms deplete the oxygen in the water, leading to areas where marine life, including dolphins, cannot survive or find sufficient food.

The far-reaching consequences of plastic pollution on dolphins highlight the urgent need for action. Reducing plastic waste and preventing it from entering our oceans is crucial. Individual efforts, such as recycling, using reusable items, and participating in beach clean-ups, are essential steps toward mitigating the impact of plastic pollution on dolphins and other marine life.

Noise pollution

Dolphins are highly intelligent and social animals that rely on sound to navigate, communicate, and hunt. However, their acoustic world is being disrupted by increasing levels of human-made underwater noise pollution. Shipping, drilling for offshore wind farms, fishing vessels, military sonar, and tourism are all major contributors to this growing problem. Noise pollution affects dolphins in various ways, and the consequences can be detrimental to their health, behaviour, and overall population.

Dolphins use a combination of whistles and echolocation to navigate and hunt. Echolocation is a sensory ability that allows dolphins to locate objects and other dolphins by emitting high-pitched sounds and listening for echoes. However, noise pollution can disrupt their echolocation, making it difficult for them to find food, socialise, and navigate underwater. This disruption can lead to a decrease in their foraging success and impact their ability to reproduce, which can have negative consequences for marine populations, food chains, and biodiversity.

Research has shown that dolphins struggle to communicate and cooperate in noisy environments. In a study conducted by the University of Bristol, researchers found that dolphins in a controlled lagoon had to increase the volume and length of their calls when exposed to increasing levels of noise pollution. They also adjusted their body positioning to face each other and moved closer together. Despite these adaptations, their success rate in cooperative tasks decreased significantly, indicating that noise pollution can hinder their ability to work together effectively.

The impact of noise pollution on dolphins is not just limited to communication difficulties. High-intensity noise, such as that produced by military sonar and seismic air guns, can cause panic and fear responses in dolphins, leading to increased energy expenditure and risk of exhaustion and decompression sickness. The hunt for fossil fuels and the use of seismic air guns in the oil and gas industry have been identified as significant contributors to this issue.

Addressing noise pollution is crucial to mitigating its harmful effects on dolphins. Regulations and noise management practices, such as construction bans in dolphin habitats, speed limits for vessels, and the development of quieter technologies, can help reduce the impact of human activities on these intelligent and socially complex marine mammals.

Bioaccumulation

The impact of bioaccumulation is not limited to individual dolphins but can affect entire populations. For example, the local dolphin population in the Gulf of Mexico has been severely impacted by the Deepwater Horizon oil spill in 2010. Researchers estimate that the population has declined by over 50% in the decade following the spill.

Furthermore, bioaccumulation can result in high concentrations of toxins in the blubber of dolphins. Studies have found elevated levels of lead, mercury, selenium, arsenic, and other toxic substances in stranded dolphins. These toxins can persist in the environment and continue to affect dolphin populations even after the initial source of contamination has been removed.

The accumulation of toxins through bioaccumulation highlights the far-reaching consequences of human-caused pollution on dolphin populations. It serves as a stark reminder of the delicate balance between human activities and the health of marine ecosystems.

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