Dolphin Population Declines: Understanding The Impact Of Pollution

Dolphins are highly intelligent, air-breathing mammals with complex societies and systems of communication. They are also one of the many marine animals that face a barrage of different types of pollution, from air and water to soil and light. These pollutants have a devastating impact on dolphins, affecting their health, sources of food, and ecosystems.

Dolphins are particularly vulnerable to chemical, plastic, and noise pollution. They face oil spills, ingest plastic, become entangled in discarded fishing gear, and suffer from disorientation due to underwater sounds. These pollutants can lead to respiratory ailments, immune dysfunction, failed pregnancies, and an increased risk of diseases and infections.

Additionally, dolphins are susceptible to bioaccumulation, where toxins build up in their bodies over time, leading to reproductive issues and birth defects. Noise pollution also affects their ability to communicate and navigate, causing stress and potentially leading to deafness.

The effects of pollution on dolphins highlight the urgent need for collective action to minimise the negative impact of human activity on the environment and improve the welfare of the animals that inhabit it.

Oil spills and chemical pollutants

Oil spills can also kill off smaller animals, such as krill, that are eaten by dolphins. Dolphins do not necessarily avoid floating oil slicks and may swim into them. Once surrounded by an oil slick, there is a risk that the toxic oil will enter their blowholes and mouths.

One example of the impact of oil spills is the Deepwater Horizon oil spill in the Gulf of Mexico in 2010. Researchers estimate that the local dolphin population lost over 50% of their population in the ten years since the spill. The dolphins breathed contaminated air, causing respiratory ailments and immune dysfunction, resulting in long-term increases in mortality, failed pregnancies, and an increased risk of other diseases or infections.

Another example is the Exxon Valdez oil spill in Prince William Sound, Alaska, in 1989. In the year and a half after the spill, two groups of killer whales swimming through the area experienced an unprecedented number of deaths. One pod lost 33% of its population, while the other lost 41%. One of these pods still hasn't reached its pre-spill numbers.

In addition to oil spills, chemical pollutants also pose a significant threat to dolphins. One particularly dangerous group of chemicals is PolyChlorinated Biphenyls (PCBs). PCBs were widely used in building materials for decades until a global ban was introduced in 2004. However, PCBs still leak into the environment through the careless disposal of products containing them and the failure of governments to tackle the 14 million tonnes of contaminated material worldwide.

PCBs build up in the food chain, with the highest amounts found in top predators such as dolphins. These chemicals are stored in the fatty tissue (blubber) of dolphins and can cause sterility and population decline. They can also impair the reproductive systems of bulls and cows and cause birth defects in calves. PCBs are also linked to immune system suppression.

Other chemical pollutants, such as lindane, dieldrin, dichlorodiphenyltrichloroethane (DDT), and mercury, have been found in high concentrations in river dolphins and have been linked to immune system suppression, reproductive issues, calf mortality, developmental abnormalities, and cancer.

Plastic pollution

The impact of plastic ingestion on dolphins is not yet fully understood, but it is clear that large amounts of plastic are consumed by many animals. Plastic can also contain bacteria and viruses that further hinder the health of dolphins. Microplastics, in particular, have been detected in the breath of dolphins, indicating that inhalation may be a significant route of exposure to these pollutants.

Plastics in the ocean absorb toxic persistent organic pollutants (POPs) from the surrounding environment. These toxins can pass through cell membranes and accumulate in the fatty tissue of living beings, impacting their immune systems and leaving them more vulnerable to disease. The toxins are biomagnified in predator species like dolphins, meaning they are more affected by the toxins than animals lower in the food chain.

The effects of plastic pollution on dolphins are not limited to ingestion and inhalation. Abandoned fishing gear, known as "ghost nets," can entrap dolphins and lead to fatal entanglement. Globally, 100,000 marine mammals die each year due to plastic pollution, with dolphins being particularly vulnerable.

To address this issue, some regions have implemented bans on single-use plastics and promoted the use of alternative materials. It is crucial for governments, businesses, and individuals to work together to reduce plastic pollution and protect dolphin populations.

Noise pollution

Dolphins are highly intelligent, air-breathing mammals with complex societies and systems of communication. They are curious about and friendly towards humans, and we are, in turn, charmed by their beauty and grace. However, human activities such as noise pollution can have a detrimental impact on dolphin populations.

The impact of noise pollution on dolphins is not just limited to physical effects but also behavioural ones. Dolphins use sound to communicate and navigate, so when their ocean becomes noisier due to increased boat traffic, seismic surveys, wind farms, and anti-predation devices, it affects their ability to communicate and can cause stress and fear. This noise pollution in the oceans is getting worse as the water becomes more acidic due to higher levels of carbon dioxide, making it less able to absorb low-frequency sounds. As a result, sounds travel further and can have a more significant impact on dolphin populations.

Additionally, noise pollution can cause deafness in dolphins, which is particularly concerning as their sense of hearing is crucial for navigation and communication. A deaf dolphin can easily become separated from its pod, making it more vulnerable to predators or other dangers.

To address the issue of noise pollution and its impact on dolphins, it is essential to reduce the amount of noise generated by human activities in dolphin habitats. This can include implementing regulations and policies to control noise levels, using quieter technologies, and increasing awareness about the impact of noise on marine life. By taking collective action to reduce noise pollution, we can help protect dolphin populations and ensure their long-term survival.

Bioaccumulation

Pollutants like polychlorinated biphenyls (PCBs) are extremely harmful to dolphins and exist in high levels in the blubber of dead dolphins and whales. PCBs are a form of industrial waste that has been banned in the United States, but they continue to leak into waterways from landfills. These toxins can impair the reproductive systems of bulls and cows and cause birth defects in calves. They can also suppress the immune system, making dolphins more susceptible to infections and diseases such as pneumonia and skin infections.

The effects of bioaccumulation are not limited to a single species of dolphins. River dolphins, such as those found in the Amazon/Orinoco, Ganges, Indus, Yangtze, Mahakam, Mekong, and Ayeyarwady river basins, are also at risk. Studies have found elevated concentrations of pollutants, particularly mercury from gold mining operations, in these river dolphins. Additionally, agricultural fertiliser and pesticide runoff can introduce heavy metal pollutants like arsenic, cadmium, mercury, and lead into river systems, further endangering river dolphins.

The impact of bioaccumulation on dolphins is a serious concern, and it highlights the need for collective action to minimise the negative effects of human activity on the environment and the welfare of dolphins and other marine life.

Human activity and water quality

Human activity has a significant impact on water quality, which in turn affects dolphin populations. One of the main sources of water pollution is runoff from land-based sources such as storm sewers and parking lots, as well as ocean-based sources like discarded fishing gear. This means that the garbage created by humans can end up in the oceans, affecting dolphins and other marine life.

Another source of water pollution is toxins that enter the marine environment through land-based runoff, air pollution, and ocean dumping. These toxins come from everyday items such as automobiles, air conditioners, and household products. High levels of toxins have been found in the blubber of stranded marine mammals, indicating that human activity is having a direct impact on their health.

One of the most well-known examples of water pollution affecting dolphins is oil spills. Oil spills can have lasting impacts on dolphin populations, such as the Deepwater Horizon oil spill in the Gulf of Mexico in 2010, which led to a 50% decline in the local dolphin population over ten years. Dolphins can breathe in contaminated air from oil spills, causing respiratory ailments and immune dysfunction, as well as increasing their risk of other diseases and infections.

In addition to oil spills, fertilizer runoff can also affect dolphin populations. Fertilizers can cause algal blooms, known as red tides, which produce toxins that dolphins breathe in or ingest through fish that eat the algae. These toxins accumulate in the dolphins' bodies, a process called bioaccumulation, and can lead to hundreds of deaths in local dolphin populations.

Plastic pollution is another major issue, with scientists estimating that approximately 56% of dolphins and whales worldwide have ingested plastic at some point. Plastic blocks their digestive systems and can lead to death. Entanglement in discarded fishing gear, or "ghost" gear, is also a serious threat to dolphins, often resulting in death.

Noise pollution from human activities such as shipping, military exercises, and oil drilling can also impact dolphins. Dolphins use echolocation to navigate and communicate, but noise pollution can interfere with their ability to do so and even damage their hearing. Loud noises can cause panic and lead to fatal decompression sickness if dolphins dive too rapidly.

Overall, human activity has a significant impact on water quality, which in turn affects the health and survival of dolphin populations. It is important to address these issues through conservation efforts and responsible waste management to minimize the negative effects on dolphins and other marine life.

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