Sharks In Danger: Plastic Pollution's Impact

Plastic pollution is a pressing issue that poses a significant threat to marine life, including sharks. With an estimated eight million metric tons of plastic entering our oceans each year, the consequences for sharks and other sea creatures are devastating. From entanglement in plastic waste to the ingestion of microplastics, sharks are vulnerable to the harmful effects of plastic pollution in various ways.

Sharks, as apex predators, occupy a crucial position at the top of the marine food chain. This makes them highly susceptible to the accumulation of toxins and pollutants present in their prey. Microplastics, resulting from the breakdown of larger plastic items, are of particular concern. These tiny plastic particles can be ingested by sharks, leading to internal injuries, digestive issues, and the release of toxins.

The impact of plastic pollution on shark populations is a growing area of research, and it is crucial that we address this issue to ensure the health and survival of these magnificent creatures.

Sharks ingest plastic, which can block digestive tracts, damage stomach linings, and cause starvation

As top predators, sharks are highly susceptible to environmental pollution. A study in 2002 found that 60 sharks (0.38% of those with recorded stomach contents) had ingested plastic debris, the most common items being plastic packets or sheets. Of these, 38 were tiger sharks. In 2013, a study found that the rate of plastic ingestion by the Brazilian sharpnose shark was at 33%.

Ingested plastics can block digestive tracts, damage stomach linings, or cause a reduction in appetite, ultimately leading to starvation. A dead whale shark that washed up on a beach in Thailand was found to have been killed by a single plastic straw that perforated its oesophagus. Two whale sharks in Japan also died from intestinal damage caused by ingested plastic.

While plastic ingestion by sharks usually results in the fragments passing through the intestinal tract without causing damage, there is a concern that individuals will suffer from malnutrition. Reef manta rays in Indonesia, for example, were found to be physically 'full' with only 52% zooplankton in their stomachs.

The ingestion of plastic by sharks is an understudied area. However, it is known that plastic pollution in the ocean is having a detrimental impact on marine life, including sharks.

Plastic toxins can alter shark hormones, impacting growth, development, metabolism, and reproduction

As apex predators, sharks are particularly vulnerable to bioaccumulation. This means that if a fish towards the bottom of the food chain is exposed to toxins or consumes plastic pollution, there is a significant chance that a shark consuming it will absorb those contaminants.

Plastics contain endocrine-disrupting chemicals (EDCs) that can wreak havoc on the hormone system. These chemicals act on the endocrine (hormone) system in possibly dangerous ways. For example, they can disrupt the normal functioning of the endocrine system, which helps to moderate everything from fertility and reproduction to growth, metabolism, immunity, and brain development.

The ingestion of plastic-associated toxins can alter the hormones that regulate the body's growth and development, metabolism, and reproductive functions, among other things. For instance, exposure to plastic-associated toxins such as heavy metals and phthalates can alter the hormones that regulate the body's growth and development, metabolism, and reproductive functions.

Furthermore, ingested plastics can cause physical damage to the gastrointestinal (GI) tract. They can cause abrasions and lesions, or physical disruption of the GI tract, as plastics compact in the gut. Plastic ingestion can also be detrimental to the health of sharks because indigestible particles fill the stomach and reduce the feeling of hunger, leading to starvation.

While the impact of plastic ingestion on shark hormones has not been extensively studied, it is clear that plastic pollution has the potential to significantly impact the growth, development, metabolism, and reproduction of sharks.

Sharks can get entangled in plastic, causing wounds and making it difficult to swim, catch prey, or avoid predators

Sharks are susceptible to getting entangled in plastic waste, which can cause grievous wounds and impair their ability to swim, hunt, or escape predators. Discarded or lost fishing gear, such as nets and ropes, is a significant source of entanglement, leading to animal welfare concerns. While it may not result in immediate death, entanglement can cause deep cuts and scoliosis in a shark's spine, as seen in the case of a shortfin mako shark that continued to grow despite being caught in a fishing rope.

The impact of plastic pollution on sharks is not limited to entanglement. Sharks can also ingest plastic debris, which can block their digestive tracts, damage their stomach linings, and reduce their appetite. This ingestion of plastic can lead to starvation and death in some cases. Additionally, plastic pollution can alter the shape and size of items, breaking down into microplastics, which are then consumed by smaller fish and eventually end up in the sharks' systems.

The presence of plastic in the ocean is a growing concern, with an estimated 8 million metric tons of plastic waste entering the oceans each year. This plastic waste does not biodegrade but breaks down into smaller pieces, making it impossible for animals, including sharks, to avoid. While plastic ingestion by sharks is understudied, a 2002 study found that 60 out of 28,687 large sharks caught in the nets off the coast of South Africa had ingested plastic debris, with the most common items being plastic packets or sheets.

The impact of plastic pollution on sharks highlights the need for better waste management practices and a reduction in the use of disposable plastics. It is crucial to address this issue to protect shark populations and maintain the delicate balance of marine ecosystems.

Plastic waste in the ocean is often mistaken for prey by sharks, such as jellyfish

Sharks can directly ingest microplastics or indirectly consume them when they have accumulated in the tissues of their prey. Once ingested, plastics can either be excreted or accumulated. They may pass out of the animal in its faeces or vomit, or they can become trapped in the gastrointestinal tract or be absorbed into tissues.

Sharks are not the only marine animals to mistake plastic for prey. Filter-feeding animals, like manta rays, ingest huge quantities of microplastics that float in the water column. Whale sharks in Indonesia ingest anywhere between 63 and 137 pieces of plastic every hour when they are feeding.

Plastic pollution in the ocean is a serious threat to marine life, and sharks are no exception. The ingestion of plastic debris can lead to severe health issues, including internal injuries, intestinal blockages, and starvation. In addition, plastics can release toxic chemicals that accumulate in the sharks' bodies, leading to long-term health problems.

To reduce the impact of plastic pollution on sharks and other marine life, it is essential to reduce plastic use, improve waste management, participate in clean-up initiatives, and support legislation to address the root causes of plastic pollution.

Microplastics can enter a shark's bloodstream and accumulate in various organs, causing unknown long-term effects

Sharks are susceptible to ingesting microplastics, which are plastic particles smaller than 5mm. These microplastics can enter a shark's body through ingestion or inhalation. Once ingested, the microplastics can remain in the shark's stomach for a long time, causing severe injuries to the stomach and intestinal mucosa through chafing. They can also clog up the digestive system, leading to starvation.

Microplastics can pass through the intestinal tract and enter the shark's bloodstream, accumulating in various organs or even cells. The long-term effects of this are currently unknown, but it is speculated that they may interfere with organ functioning and cell regeneration, potentially causing a range of health issues. Additionally, microplastics may act as endocrine disruptors, interfering with the body's hormones and leading to fertility issues, blood sugar imbalances, metabolic problems, and autoimmune diseases.

The impact of microplastics on shark health is a growing area of research, and while the exact mechanisms are not yet fully understood, there is concern that microplastics are contributing to health issues in shark populations.

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