Spinner Dolphins: Surviving In A Polluted Ocean

Spinner dolphins are slender, dark grey marine mammals with white underbellies, long thin beaks, and distinct stripes connecting their pointed flippers to their eyes. They are named for their mid-air spins, where they propel themselves out of the water, rapidly flipping their bodies. Spinner dolphins are threatened by human activity, including marine debris, toxins, entanglement in fishing nets, and acoustic disturbance. Pollution, in particular, poses a significant risk to these dolphins, impacting their health, food sources, and ecosystems.

Various forms of pollution, such as air, light, soil, and water pollution, can have detrimental effects on spinner dolphins. Chemical pollution, plastic pollution, and noise pollution are among the primary human-caused threats. Oil spills, for example, can cause respiratory ailments and immune dysfunction in dolphins, leading to increased mortality, failed pregnancies, and a higher risk of diseases or infections. Additionally, plastic pollution, such as discarded plastic bags and fishing gear, can block their digestive systems or entrap them, resulting in fatal consequences.

The impact of pollution on spinner dolphins is a pressing issue that requires collective efforts to minimize negative consequences and ensure the long-term survival of these fascinating creatures.

Chemical pollution

Spinner dolphins are probably the most frequently encountered cetaceans in the nearshore waters of the Pacific Islands Region. They are acrobatic and are well known for their habit of leaping from the water and spinning in the air.

The incidence of these compounds in the system of dolphins leads to deterioration in the functioning of their lungs, hormonal disturbances, and a weakened immune system. Studies suggest that female dolphins may transfer these substances to their offspring through the placenta or breast milk.

Polychlorinated biphenyls (PCBs), which are forms of industrial waste, are linked to immune system suppression and reproductive failure in dolphins. They exist in extremely high levels in the blubber of dead dolphins and whales worldwide. While PCBs are now illegal in the United States, they continue to leach into waterways from landfills.

In addition, chemical pollution can introduce and/or concentrate damaging or toxic compounds into the animal. For example, plastic debris can absorb organic pollutants that may be toxic to marine organisms that ingest them. These contaminants can then bioaccumulate as they move up the food chain to top predators such as spinner dolphins.

Plastic pollution

About 56% of the world's dolphins and whales have ingested plastic, and it is estimated that plastic pollution kills 100,000 marine mammals annually. While it is challenging to determine the exact number of marine animal deaths caused by plastic pollution, it is evident that it is a significant issue.

The impact of plastic pollution on spinner dolphins is twofold: ingestion and entanglement. Dolphins may consume plastic, mistaking it for prey, or they may become entangled in plastic-based fishing gear or "ghost" fishing gear, which is abandoned in the ocean. This abandoned fishing gear traps dolphins and other marine life, often leading to death.

The presence of plastic in the oceans poses a severe threat to spinner dolphins, impacting their health and survival. The ingested plastic accumulates in their bodies and can cause blockages, leading to starvation. Additionally, recent studies suggest that plastic may harbour bacteria and viruses detrimental to the animal's health. The plastic acts as a magnet for toxic substances, further endangering the dolphins that consume it.

The effects of plastic pollution on spinner dolphins are not fully understood, but the high consumption rates by these animals are concerning. With the increasing presence of plastic in the oceans, it is essential to address this issue through strict policies and individual actions to reduce plastic pollution and protect these magnificent creatures.

Noise pollution

Spinner dolphins are highly intelligent, acrobatic, and expressive mammals. They are also very sensitive to noise pollution, which can affect their ability to communicate, navigate, and coordinate with each other.

Noise from large commercial ships, military sonars, or offshore drilling can severely impact the well-being of dolphins. As the levels of underwater noise increase, dolphins have to raise their vocalizations to be heard. A study published in the journal Current Biology, 'Anthropogenic noise impairs cooperation in bottlenose dolphins', found that as it got noisier underwater, the dolphins changed their behaviour to communicate and work together. They raised the volume and length of their calls, turned their bodies towards each other, and swam across the lagoon to be closer to each other. Despite these attempts, the dolphins were less successful in completing their task, with cooperative task success dropping from 85% to 62.5% during the highest noise exposure.

The impact of noise pollution on spinner dolphins is especially concerning given their reliance on echolocation for communication and navigation. They use echolocation to locate food and other objects, and sound travels faster in water than in air, making it an important mode of communication that can convey a lot of information quickly and over long distances.

To protect spinner dolphins from the harmful effects of noise pollution, it is essential to reduce underwater noise levels and enforce regulations that limit noise-generating activities in their habitats.

Oil spills

The impact of oil spills on dolphins can be long-lasting and may lead to increased mortality and reproductive failure. For example, following the Deepwater Horizon spill, studies found that bottlenose dolphins in heavily oiled areas suffered increased mortality, failed pregnancies, and adverse health effects. The recovery of dolphin populations can take decades, and in some cases, the full extent of the impact may not be known for generations.

Reducing the occurrence of oil spills and minimizing the negative effects of human activity on the environment are crucial for protecting dolphin populations and the health of marine ecosystems.

Digestive blockages

Marine debris is a growing concern for spinner dolphins, as it poses multiple threats to their health and survival. One of the most significant dangers is the ingestion of debris, which can lead to digestive blockages and ultimately starvation.

Spinner dolphins feed on small fish, shrimp, and squid that inhabit deep waters during the day and migrate closer to shore at night. As they feed at night, spinner dolphins may inadvertently consume plastic debris, which can cause blockages in their digestive tracts. This obstruction prevents food from passing through the digestive system, leading to malnutrition and, in severe cases, starvation.

The impact of plastic ingestion on spinner dolphins is exacerbated by the ability of plastic to absorb organic pollutants. These pollutants, such as butyltin and organochlorine, are toxic to marine life and can bioaccumulate as they move up the food chain. When spinner dolphins consume contaminated prey, these chemicals accumulate in their bodies, particularly in their fatty tissues and blubber. This bioaccumulation can have detrimental effects on the dolphins' health, including impaired reproductive systems and a weakened immune system, making them more susceptible to diseases and infections.

In addition to ingestion, spinner dolphins may also become entangled in marine debris, causing external wounds, skin lesions, and impaired movement. The presence of marine debris in their habitat can further limit their ability to avoid predators and impair their feeding capacity.

The severity of the impact of marine debris on spinner dolphin populations is challenging to determine, as many deaths likely occur at sea and go undetected. However, the available data and research highlight the urgent need to address this growing threat to spinner dolphins and other marine life.

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