Brian Barton
Sharks are keystone species in the ocean, and as such, they play a crucial role in maintaining the balance of marine ecosystems. However, they face numerous threats from human activity, including climate change, overfishing, ocean pollution, tourism, and habitat loss. While research on the impact of pollution on sharks is still in its early stages, studies on other marine organisms have found adverse effects such as neurological disorders, organ damage, and reduced fertility. Sharks are particularly susceptible to the harmful effects of pollutants due to their position at the top of the food chain, resulting in higher concentrations of harmful chemicals in their tissues. Additionally, as shark species are long-lived, they have more time for these harmful substances to accumulate in their bodies.
| Characteristics | Values |
|---|---|
| Type of pollutants | Microplastics, oil spills, algae bloom, chemical contaminants, long-lasting organic pollutants, heavy metals, crude oil, ocean garbage, plastic waste, fishing gear, mercury |
| Impact of pollutants | Neurological disorders, structural damage to organs and gills, reduced fertility, developmental effects, cancers, malnutrition, intestinal damage, physical abrasion, disruption of aquatic processes, habitat alteration, global decline in fish populations, extinction |
| Shark species affected | Blue Sharks, White Sharks, Shortfin Mako, Common Threshers, Whale Sharks, Silky Sharks, Dusky Sharks, Hammerheads, Oceanic White Tip Shark, Reef Manta Rays, Giant Manta Rays |
| Human actions causing pollution | Industrial fishing, recreational fishing, artisanal fishing, irresponsible consumerism, tourism |
| Actions to reduce pollution | Responsible consumerism, raising awareness through social media and word of mouth, writing to local government representatives |
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What You'll Learn
- Sharks are susceptible to pollutants due to their position at the top of the food chain
- Microplastics are ingested by sharks, impacting their health and behaviour
- Plastic waste causes physical injuries and entanglement, threatening shark survival
- Pollutants in sharks are passed on to humans who consume shark meat
- Climate change, caused by pollution, impacts prey availability and shark habitats
Sharks are susceptible to pollutants due to their position at the top of the food chain
Sharks are apex predators, meaning they are at the top of the marine food chain. They are also opportunistic scavengers, feeding on almost all other fish in the ocean. This makes them highly susceptible to pollutants, which they ingest through two primary pathways: direct and indirect ingestion. Direct ingestion occurs when shark species that filter-feed consume microplastics directly from polluted water. They do so because microplastics resemble plankton or algae, which they typically feed on. For example, a study found that whale sharks, a type of filter feeder, could mistakenly swallow hundreds of microplastics in just an hour.
Indirect ingestion occurs when sharks consume other fish that have microplastics in their systems. Since sharks are apex predators, they tend to feed on multiple fish species, thereby indirectly consuming accumulated microplastics. This process is known as biomagnification, where the amount of pollutants in the shark's body increases faster than its ability to excrete them. As a result, sharks can suffer from bioaccumulation, where pollutants build up in their bodies over time.
Sharks are also susceptible to pollutants due to their position at the top of the food chain, as they can accumulate high concentrations of toxic pollutants, including organic compounds and heavy metals like mercury. Studies have shown that a single serving of shark meat can expose adults and children to over three times the maximum recommended daily mercury consumption limit. This has led to recommendations from the US Food and Drug Administration and the Environmental Protection Agency to avoid consuming shark meat entirely. High mercury levels have been documented in various shark species, including blue sharks, silky sharks, and hammerheads.
In addition to microplastics and heavy metals, sharks are also threatened by other forms of pollution, such as oil spills, algae blooms, and chemical contaminants. These pollutants can have detrimental effects on the health and behaviour of sharks, leading to neurological disorders, structural damage to organs and gills, reduced fertility, developmental issues, and cancers. For example, a study on common threshers found that an adult female transferred 29-54% of the mercury and organic contaminants in her body to her near-term embryos.
Furthermore, plastic pollution poses a significant risk to sharks, primarily through ingestion and entanglement. While small plastic fragments usually pass through the intestinal tract without causing damage, they can still lead to malnutrition, as seen in the case of Reef Manta Rays in Indonesia, where the presence of plastic reduced the amount of zooplankton available for nutrition. Additionally, ingested plastics may release pollutants into the shark's body, further compounding the issue of bioaccumulation. Entanglement in discarded fishing gear, known as "ghost nets," is another major threat, particularly for migratory shark species that swim long distances to feed and breed.
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Microplastics are ingested by sharks, impacting their health and behaviour
Microplastics are tiny fragments of plastic that are less than five millimetres in size. They are formed by the weathering of larger plastics, created intentionally as raw materials for other plastic products, or used in other products, such as cosmetics.
Sharks are one of the species found to have the highest quantity of microplastics in their bodies. They accumulate these plastics through two primary pathways: direct and indirect ingestion. Direct ingestion occurs when shark species that filter-feed consume microplastics directly from polluted water. They do not intend to feed on these plastics but because microplastics resemble plankton or algae, they mistakenly ingest them. For example, a study found that whale sharks, which are filter feeders, could mistakenly swallow hundreds of microplastics in just an hour. Indirect ingestion occurs when sharks consume other fish that have microplastics in their systems. Since some shark species are at the top of the food chain, they feed on almost all other fish in the ocean, and thus, they indirectly consume microplastics by eating these fish.
The ingestion of microplastics has been shown to have detrimental impacts on the health, behaviour, and overall well-being of sharks, contributing to the global decline in their populations. Firstly, microplastics can cause physical abrasion when they come into direct contact with the surfaces of sharks, abrading their skin or protective coatings, and leading to injuries that make them more vulnerable to infections or other environmental stressors. Secondly, microplastics can disrupt aquatic processes by accumulating in the digestive and gastrointestinal tracts, interfering with normal absorption and digestion. This can lead to malnutrition and starvation over time as the ingested microplastics offer no nutritional value. Thirdly, microplastics can act as vectors of toxins by absorbing and releasing toxic additives and chemicals into the shark's body, leading to toxicological effects such as decreased fitness and overall health. Endocrine disruption can also occur when certain chemical additives are absorbed by the shark's body, interfering with hormonal balance and signalling systems, and potentially influencing the shark's behaviour.
The presence of microplastics in sharks has broader implications for the entire oceanic food web. As apex predators, sharks play a crucial role in maintaining the balance of marine ecosystems, and any threats to their health can have cascading effects on other species. Additionally, sharks that are consumed by humans, such as in the dish "shark-fin soup", may lead to negative impacts on human health through the consumption of contaminated shark meat. Therefore, it is essential to implement effective conservation strategies and reduce plastic pollution to protect these ecologically important species.
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Plastic waste causes physical injuries and entanglement, threatening shark survival
Plastic waste in the ocean is a significant threat to marine ecosystems, and its ever-growing production means this problem is likely to persist. As top predators, sharks play a crucial role in maintaining the balance of marine ecosystems, and their health is vital for the oceanic food web. Unfortunately, plastic waste causes physical injuries and entanglement, threatening shark survival.
Sharks are vulnerable to plastic entanglement, particularly in discarded fishing gear, or "ghost nets." These synthetic nylon nets are challenging for ocean wildlife to detect and can trap and kill animals for years. Migratory sharks, which swim thousands of kilometres each year to feed and breed, are among the worst affected. Oceanic species, such as silky sharks, whale sharks, white sharks, and giant manta rays, are especially susceptible as they feed in frontal zones where large amounts of drifting rubbish accumulate.
Entanglement in plastic debris can lead to severe trauma and even death for sharks. For example, circular plastic straps have caused severe injuries in tiger sharks, with plastic entanglement potentially contributing to cryptic mortality in this species. Removing plastic straps from entangled sharks may not always be effective in promoting their survival, as it can result in post-release mortality.
In addition to entanglement, sharks are also at risk of internal injuries from ingested plastic. While small plastic pieces may pass through the intestinal tract without causing damage, larger pieces can lead to intestinal blockages and even death, as seen in whale sharks in Japan. Furthermore, ingested plastics may release pollutants into the sharks' bodies, contributing to neurological disorders, structural damage to organs and gills, reduced fertility, developmental issues, and cancers.
Microplastics, tiny plastic fragments less than five millimetres in size, are another concern. Sharks can mistakenly ingest microplastics through direct and indirect ingestion, as they resemble plankton or algae. This leads to plastic accumulation in their digestive and gastrointestinal tracts, disrupting normal absorption and digestion. Microplastics can also settle on the seafloor, altering the habitat and impacting the abundance and diversity of benthic organisms.
The presence of plastic waste and microplastics in the ocean poses a significant threat to shark survival, highlighting the urgent need for measures to reduce plastic pollution and protect these ecologically important species.
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Pollutants in sharks are passed on to humans who consume shark meat
Sharks are highly susceptible to environmental pollution. They accumulate pollutants in their bodies through direct and indirect ingestion of microplastics, which resemble plankton and algae, their primary food sources. As a result, sharks inadvertently consume plastic waste, including discarded fishing gear ("ghost nets"), that can cause internal injuries and pollutant offloading. Additionally, shark meat and other products often contain high levels of toxic pollutants, such as mercury, arsenic, and urea, which can be passed on to humans who consume them.
Mercury is a significant concern in shark meat, with concentrations exceeding the recommended daily limit by up to 66%. Methylmercury, in particular, is a dangerous form of mercury that bioaccumulates in consumers' systems, posing a severe health risk. Other pollutants found in shark meat include pesticides, fossil fuels, and metals, and dichlorodiphenyltrichloroethane (DDT), which have been linked to various health issues in humans, including impaired motor skills, fertility issues, and nervous system problems.
The consumption of shark meat is a common practice in many cultures and communities, especially those relying on fishing as the primary industry. However, the presence of high levels of pollutants in shark tissue has led to concerns about the potential health risks for consumers. Studies have found that a single serving of shark meat can expose adults and children to over three times the maximum recommended daily mercury consumption limit. As a result, the US Food & Drug Administration and Environmental Protection Agency have advised against consuming shark meat entirely.
Furthermore, the issue of mislabelling in the seafood industry has contributed to the unintentional consumption of shark meat. Shark meat is often sold as "cod," "white fish," or other regularly consumed fish, making it difficult for consumers to make informed choices. This practice not only poses health risks but also contributes to the overfishing of sharks and the catastrophic impact on ocean ecosystems.
While research on the impact of pollutants on sharks is still ongoing, it is evident that the consumption of shark meat contaminated with pollutants can have detrimental effects on human health. It is crucial for consumers to be aware of the potential risks associated with eating shark meat and for regulatory bodies to implement measures to ensure the safety of seafood products.
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Climate change, caused by pollution, impacts prey availability and shark habitats
Sharks and rays are shifting their geographic distributions in response to changing prey and habitat availability. For example, the thresher shark, commonly found off the coast of southern California, is expected to become more prevalent off the coast of Alaska as the Pacific Coast warms. The smooth dogfish may gain suitable habitat in Atlantic waters, while the thorny skate may lose habitat as the northeastern United States region warms.
The impacts of climate change on shark and ray populations are likely to vary by species. Sharks may have lower overall vulnerability to climate change than other marine organisms like shellfish, salmon, or eels. However, due to their extensive range, they are likely to shift their distributions or expand into new habitats to find preferable ocean conditions.
Some shark species, such as the scalloped hammerhead, are particularly vulnerable to climate change impacts due to their dependence on coastal habitats. Intense storms and flooding caused by climate change can increase freshwater runoff and sedimentation, altering water temperature and nutrient cycles and decreasing productivity in coastal nursery areas.
Pollution, a major driver of climate change, also directly impacts sharks and rays. They can suffer from neurological disorders, structural damage to organs and gills, reduced fertility, developmental effects, and cancers due to pollutant exposure. Sharks can also inadvertently transfer pollutants to their developing pups, as seen in a study where an adult female common thresher transferred 29-54% of the mercury and organic contaminants in her body to her embryos.
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Frequently asked questions
Plastic pollution in the ocean poses a major threat to sharks, who can suffer internal injuries and ingest plastic pieces, leading to intestinal damage and malnutrition. Sharks can also get entangled in discarded fishing gear and other plastic waste, causing death.
Microplastics are tiny plastic fragments less than 5mm in size, formed by the breakdown of larger plastics or intentionally created as raw materials. Sharks mistake microplastics for plankton or algae and ingest them, leading to plastic accumulation in their digestive tracts and potential health issues.
Sharks, as top predators, are susceptible to harmful pollutants in the ocean, such as heavy metals, crude oil, and chemical contaminants. These substances accumulate in their tissues over time, potentially causing neurological disorders, organ damage, reduced fertility, and cancers.
Pollution, along with overfishing, climate change, and tourism, threatens the survival of shark populations and their ecosystems. Sharks are long-lived, allowing more time for pollutants to accumulate in their bodies, and they struggle to process these compounds. This can impact their reproductive and immune capacity, contributing to population decline.
