The Devastating Impact Of Water Pollution On Fish

Plastic pollution in the ocean is having a devastating impact on marine life, with an estimated 100 million marine animals, including fish, mammals, and seabirds, dying each year. While it is challenging to determine the exact number of fish killed by plastic pollution daily, the problem is undoubtedly severe and warrants immediate attention. The leading causes of death among fish are ingestion of plastic and entanglement in abandoned fishing gear, such as nets and lines. With an estimated 75 to 199 million tons of plastic waste currently in our oceans and the continuous increase in plastic production, the situation is dire for marine ecosystems and the fish that inhabit them.

Plastic ingestion

While it is difficult to know the exact number of fish that die from plastic ingestion, it is clear that plastic pollution is having a devastating impact on marine life.

Fish often mistake small plastic pieces for food, with plastic pellets and fragments sitting on the surface of the water being mistaken for prey. This is particularly true for seabirds, which feed off the surface of the ocean, and for turtles, which have been found to eat plastic bags. The ingestion of plastic can lead to malnutrition, starvation, suffocation, and toxic contamination. It can also cause physical changes, impair movement, and inhibit digestion. In some cases, plastic ingestion can result in fatal blockages.

The threat of plastic ingestion is not limited to individual fish but has the potential to affect entire food chains. For example, predators such as orca whales that feed on penguins can unknowingly ingest the plastic inside their prey, amplifying the potential damage caused.

In addition to the immediate harm caused by plastic ingestion, the long-term impacts of microplastics on fish are still being determined. Microplastics can adsorb toxins, which can then be transferred to the fatty tissues of the organisms that ingest them. As apex predators such as great white sharks and orcas feed on other marine creatures, the cumulative impact of microplastics in the food chain and the bioaccumulation of toxic chemicals is a large and understudied threat to these species.

Abandoned fishing gear

While it is challenging to determine the exact number of fish that die daily from water pollution, it is evident that plastic pollution in oceans is detrimental to marine life. Abandoned fishing gear, also known as derelict or ghost fishing gear, is a significant contributor to this issue. This gear, which includes lines, nets, pots, traps, and floats, is often lost or deliberately discarded into the ocean, where it continues to trap and kill marine creatures.

The impact of abandoned fishing gear on marine life is twofold. Firstly, marine animals can become entangled in the gear, leading to injuries, infections, and drowning. This is a particular threat to marine mammals, such as dolphins and whales, but also affects other species such as turtles, sharks, and birds. Secondly, the gear can damage sensitive seafloor habitats, such as coral reefs and seagrass beds, which are crucial for the survival of many marine species.

The problem of abandoned fishing gear is widespread, affecting even remote and protected marine areas. For example, in the Papahānaumokuākea Marine National Monument, the largest fully protected marine conservation area, over 50 metric tons of derelict fishing gear are found on its shores annually, threatening the survival of endangered species such as the Hawaiian green sea turtle and the Hawaiian monk seal. Similarly, a study in Chesapeake Bay estimated that 145,000 derelict crab pots in the area kill 3.3 million blue crabs yearly, impacting both the ecosystem and the local fishing industry.

To address the issue of abandoned fishing gear, organizations like the NOAA Marine Debris Program have initiated efforts to remove and prevent marine debris. The program provides collection bins for fishers to dispose of old, derelict, or unusable fishing gear, which is then recycled or converted into energy. Additionally, some fisheries have implemented measures to reduce gear loss, such as monitoring gear and incorporating biodegradable escape panels and tags to identify and retrieve lost gear.

It is important to note that the impact of water pollution, including abandoned fishing gear, on marine life is not limited to fish. Marine mammals, birds, and other creatures are also affected, and the full extent of the problem may be difficult to ascertain. However, by addressing the issue of abandoned fishing gear through removal, prevention, and sustainable practices, we can work towards mitigating the harmful effects of water pollution on marine ecosystems.

Water temperature rise

The rise in water temperatures has had a significant impact on fish populations and mortality rates. This phenomenon, known as "summerkill", is associated with warm temperatures and has led to an increase in mass fish die-offs, or "fish kills". Climate change is a significant contributor to this issue, with rising temperatures affecting both freshwater and marine fish species.

Freshwater fish, in particular, face a grave threat from climate change-induced increases in maximum water temperature. A study modelling future flow and water temperature extremes found that in a 3.2 °C warmer world, 36% of freshwater fish species would have over half of their present-day geographic range exposed to climatic extremes. This poses a severe risk to global biodiversity and highlights the urgency of addressing climate change to protect these vulnerable species.

The relationship between water temperature and fish mortality is well-established. Warmer water has a reduced oxygen-carrying capacity, leading to oxygen depletion or "ecological hypoxia". This lack of oxygen in the water results in mass suffocation among fish populations, with larger specimens being more affected than smaller fish. Additionally, rising temperatures can fuel harmful algal blooms, further reducing oxygen levels and disrupting the ecological balance in water bodies.

The frequency and severity of fish kills are expected to increase in the future. Modelling based on local water temperature projections predicts an approximate six-fold increase in the frequency of fish mortality events by 2100, with some regions experiencing even higher rates. These events can have far-reaching consequences, impacting ecosystems, endangering existing fish populations, and reducing the global food supply.

To mitigate the impact of rising water temperatures on fish populations, experts recommend adopting sustainable practices in aquaculture, reducing pollution, and promoting the conservation of water bodies. Strategies such as increasing green cover, improving land management practices, and ensuring the release of sufficient water into rivers during summer can help prevent fish kills and maintain the health of aquatic ecosystems.

Chemical pollution

While it is challenging to determine the exact number of fish that die daily from water chemical pollution, it is evident that chemical pollution significantly harms fish populations. Chemical pollution in water can lead to fish kills, also known as localized mass die-offs of fish populations.

Another consequence of chemical pollution is the creation of "dead zones," areas with low oxygen levels where marine life cannot survive. Eutrophication, or the increase in chemical nutrient concentration in water bodies, can cause mass decay, reducing oxygen levels and creating these dead zones. Human activities, such as fertilizer runoff from farms and lawns, contribute to this process. The Mississippi River, for instance, annually releases 1.5 million tons of nitrogen pollution into the Gulf of Mexico, contributing to the formation of a dead zone.

While the daily number of fish deaths from chemical pollution is challenging to determine, it is clear that chemical pollution has severe and far-reaching impacts on fish populations and their ecosystems. The exact number of fish deaths would depend on various factors, including the type and concentration of pollutants, the resilience of the fish species, and the specific environmental conditions.

Oil rigs and cargo ships

While it is challenging to determine the exact number of fish that die daily from water pollution due to oil rigs and cargo ships, several studies and incidents provide insights into the significant impact on marine life.

Oil spills from rigs and ships are a major contributor to water pollution and have severe consequences for fish populations. The 1989 Exxon Valdez oil spill in Alaska's Prince William Sound had a lasting impact on the region's wildlife. Research indicates that the number of resident killer whales in the area has steadily and significantly declined since the spill. Although no oil-coated whales were observed, the presence of oil in the water and the subsequent decline in the whale population strongly suggest a connection.

Oil spills can also directly kill fish, especially in shallow or confined waters. Light oils and petroleum products, such as diesel fuel and gasoline, can cause acute toxicity in fish. For example, the 1994 Barge Morris J. Berman spill off Puerto Rico severely affected the local reef fish population. Additionally, fish eggs in shallow waters, such as salmon eggs in streambeds, are highly vulnerable to oil spills. The type of oil and the timing of the release play a role in the severity of the impact on fish.

Cargo ships further contribute to water pollution through the discharge of waste and the transport of invasive species. It is estimated that 50% of ship cargo is considered dangerous to the environment, and the items discarded from ships, such as plastics and ghost fishing equipment, pose significant risks to marine life. Abandoned fishing gear, such as nets and lines, can entangle and kill fish and other marine animals. The Great Pacific Garbage Patch, located in the North Pacific Subtropical Gyre, is the largest trash site on the planet. It covers twice the surface area of Texas and contains significant waste from cargo ships and oil rigs, including 705,000 tons of fishing nets.

While the exact daily toll on fish populations is unknown, the cumulative impact of oil spills and cargo ship pollution is substantial. The widespread pollution from the BP oil spill led to fishing closures across 88,500 square miles, and scientists continue to observe the long-term effects on marine life. The federal government collected 128 dead or affected dolphins and whales attributed to the BP spill, but the actual number of affected marine mammals may be much higher.

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