Sharks In Danger: Pollution's Impact On Great Whites

Great white sharks are apex predators that have existed for 450 million years. However, their survival is now threatened by human activities, particularly pollution. Pollution affects great white sharks in various ways, including entanglement in plastic waste and fishing nets, ingestion of plastic, and exposure to toxic chemicals and heavy metals. The accumulation of pollutants in their bodies can lead to health issues and impact their reproductive and immune systems. Additionally, climate change and ocean warming are pushing great white sharks into new waters, disrupting ecosystems and potentially increasing encounters with humans.

Entanglement in plastic waste and fishing nets

One of the primary concerns regarding plastic pollution is the entanglement of marine animals, including great white sharks. The issue of entanglement has largely been overshadowed by other threats, such as overfishing and bycatch. However, researchers from the University of Exeter have brought attention to this issue by studying scientific literature and utilizing Twitter to find documented instances of shark entanglement. They found evidence of eight great white sharks entangled in plastic waste, including "ghost" fishing nets. These "ghost" nets are lost or discarded fishing nets that continue to trap marine animals.

The entanglement in plastic waste and fishing nets can have severe consequences for great white sharks. The ropes and nets can tighten around their bodies, causing pain, injuries, and even scoliosis of the back. The trapped sharks may also experience starvation, suffocation, and immobilization, ultimately leading to death. The suffering caused by entanglement raises significant animal welfare concerns.

The University of Exeter study identified over 1,000 entangled animals across different species, but the actual number is believed to be much higher due to the limited focus on this issue in scientific research. The researchers also noted that entanglement predominantly occurs in the Pacific and Atlantic Oceans, with a significant number of cases in the waters of the USA, the UK, and South Africa.

The factors that increase the risk of entanglement for great white sharks include their habitat and migration patterns. Great white sharks, as oceanic species, often feed in frontal zones where huge quantities of drifting plastic waste accumulate. Their long-distance migration also increases the likelihood of encountering plastic waste and abandoned fishing gear.

The impact of plastic pollution on great white sharks extends beyond entanglement. The ingestion of plastic fragments and microplastics is a significant concern, especially for filter-feeding species like whale sharks. Studies have estimated that whale sharks may ingest up to 137 plastic items per hour, leading to potential blockages, internal injuries, and the absorption of toxic chemicals.

The accumulation of pollutants in great white sharks poses risks not only to the sharks themselves but also to humans who consume shark meat. High concentrations of toxic chemicals, heavy metals, and organic pollutants have been found in shark tissues, exceeding recommended daily limits for mercury consumption. The consumption of shark meat has been linked to exposure to harmful substances, including mercury, PCBs, DDT, and heavy metals.

To address the issue of entanglement and plastic pollution, it is essential to reduce the use of disposable plastics and improve waste management practices to prevent plastic waste from reaching the oceans. Additionally, the creation of citizen science platforms and online report forms can help gather more data on entanglement incidents, raising awareness and facilitating further research.

Ingesting plastic and pollutants

Great white sharks are susceptible to ingesting plastic and pollutants, which can have detrimental effects on their health and survival. As top predators in the marine ecosystem, sharks are highly vulnerable to environmental pollution. Pollutants tend to bioaccumulate in their bodies, with the amount of toxins growing faster than their ability to excrete them. This is further compounded by biomagnification, where sharks inadvertently ingest additional pollutants through their prey.

One of the primary sources of pollution affecting great white sharks is plastic waste. The durability and lightweight nature of plastic have led to its mass production and disposal in oceans, with an estimated 14 million tons of plastic waste entering the ocean each year. Plastic debris can cause entanglement, internal injuries, and pollutant absorption in great white sharks. Discarded fishing gear, such as nets, poses a significant threat, entrapping and killing these majestic creatures.

In addition to plastic, great white sharks are exposed to various toxic chemicals and heavy metals that contaminate the ocean. High concentrations of toxic pollutants, including organic compounds like PCBs, DDTs, and inorganic substances like heavy metals and mercury, have been detected in shark tissues. The impact of these pollutants on shark health is still being studied, but research on other marine species has linked similar levels of pollutant exposure to neurological disorders, organ damage, reduced fertility, developmental issues, and cancers.

The accumulation of pollutants in great white sharks can have far-reaching consequences. As these toxins build up in their bodies, it can affect their reproductive and immune systems, compromising their survival. Additionally, when humans consume shark meat or products containing shark derivatives, they are also exposed to these toxic chemicals, posing a significant risk to human health. High mercury levels have been found in great white sharks, and consuming shark meat can expose individuals to more than three times the maximum recommended daily mercury intake.

Furthermore, young great white sharks off the coast of Southern California have been found to have alarmingly high levels of mercury, PCBs, and DDTs. These pollutants can cause harmful physiological effects and increase the risk of adverse health outcomes. The cumulative impact of pollution, along with other stressors such as bycatch and coastal development, puts West Coast great white sharks at a heightened risk of extinction.

Climate change and ocean warming

Climate change and warming oceans are having a significant impact on great white sharks and marine life in general. The oceans are warming, and this is causing shifts in the distribution of fish populations, changes in migration patterns, and the availability of suitable habitats. As apex predators, great white sharks play a crucial role in maintaining the balance of oceanic ecosystems. Any changes in their behaviour or distribution can have far-reaching consequences for other species.

Research has shown that the ocean heating is pushing great white sharks into new waters, with young sharks moving hundreds of kilometres northwards off the coast of California in search of cooler waters. This shift has led to a dramatic increase in the number of sea otters killed by the sharks, causing populations of endangered wildlife to decline. The overall range of suitable waters for the sharks in the region has shrunk, forcing predator and prey closer together. This compression of the food web has resulted in a rapid decline in fish populations, including salmon.

The impact of warming waters on great white shark behaviour is also evident in their migration patterns. Juvenile great white sharks are now frequently spotted in large groups along the beaches of Southern California, in areas that provide warm water nursery habitats. These young sharks typically feed on fish before moving on to seals and sea lions as adults. The presence of these juvenile sharks in new areas can have implications for public safety, although the rate of shark attacks has generally decreased in recent decades.

Climate change is also expected to affect the growth and reproduction of great white sharks. Studies have found that higher water temperatures and increased carbon dioxide levels can impact the brain development of sharks, leading to potential changes in behaviour and decision-making abilities, as well as resulting in smaller brains.

The rapid rate of climate change poses a significant challenge for great white sharks. While they have endured evolutionary changes in response to natural climate fluctuations over millions of years, the current rate of change is unprecedented. The warming oceans, coupled with ocean acidification and more frequent storms, are creating conditions that great white sharks and other marine life struggle to adapt to.

Ocean acidification

Research has shown that increased ocean acidity can damage shark denticles, the microscopic tooth-like scales that cover their skin. These denticles play a crucial role in a shark's ability to swim efficiently. For great white sharks, denticles contribute to up to a 12% increase in swimming speed. If their denticles are worn away, great white sharks may struggle to hunt effectively and become more susceptible to injuries during hunting.

Furthermore, ocean acidification can impair shark hunting behaviour and growth. Studies have found that elevated CO2 levels can disrupt a shark's ability to locate prey through olfaction, reducing their hunting success. This can lead to decreased growth rates and increased vulnerability to malnutrition and predation.

While the effects of ocean acidification on shark denticles and behaviour are concerning, it is important to note that shark teeth may exhibit some resistance to acidified seawater. A study on Port Jackson shark teeth found that while warming waters led to more brittle teeth, the combination of warming and ocean acidification resulted in more elastic teeth that were less prone to physical damage. This suggests that sharks may possess some adaptive capabilities to withstand the impacts of ocean acidification.

However, it is worth noting that the resilience of shark teeth to ocean acidification may vary across species. More research is needed to fully understand the complex interactions between ocean acidification and shark biology, especially for pelagic shark species that depend on ram ventilation.

Coastal development

Coastal habitats like mangroves, kelp forests, and reef systems are important nursery and feeding grounds for many shark species, including great white sharks. These areas provide essential shelter for young sharks and support a diverse range of prey species. However, the proximity of these habitats to human settlements makes them vulnerable to destruction and degradation.

Dredging, a process where material is removed from the seafloor, has been known to negatively affect the survival of young lemon sharks in the Bahamas due to coastal development. Similarly, coral reefs and mangroves, which are crucial habitats for various shark species, have been in decline in terms of their extent and health.

The Ganges shark, for example, has almost completely disappeared from the lower reaches of the Ganges-Hooghli river system in India due to habitat degradation. Coastal development and human activities can also lead to pollution, affecting water quality to the extent that it becomes uninhabitable for shark species.

The cumulative impacts of multiple stressors, including coastal development, pollution, and climate change, put great white sharks on the West Coast at risk of extinction.

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