How Pollution Impacts The Lives Of Eels

Eels are an important species in the preservation of balanced ecology, and they are a top predator in many river or stream ecosystems. However, they are currently facing a variety of threats, including pollution. Pollution affects eels in different ways, including chemical pollution, plastic pollution, and noise pollution. Chemical pollution, such as pesticides and heavy metals, can contaminate the water and accumulate in the eels, leading to potential harm to their health and reproductive abilities. Plastic pollution, such as the accumulation of plastic waste in the Sargasso Sea, can negatively impact eel migrations and breeding. Noise pollution, caused by man-made noises like ships and underwater explosions, can distract eels and make them more vulnerable to predators. The impact of pollution on eels is a growing concern, and it is important to address these issues to protect eel populations and the ecosystems they inhabit.

Noise pollution impacts eels' ability to evade predators

Noise pollution is a matter of life or death for eels. Critically endangered European eels get distracted by man-made noise, making them more likely to get eaten by a predator. Researchers from the University of Exeter and the University of Bristol investigated how man-made noise might impact an animal’s ability to evade predators.

The researchers began the study with lab tests in which they individually exposed 48 eels to two-minute recordings of ships passing through a harbor, or else to control noise of the same harbor without the ships. They then used a well-established predator stand-in method called “the looming stimulus approach,” which mimics a real-world predatory strike by using a model fish on a swinging pendulum. They recorded the eels’ behavior with video cameras and later analyzed the footage for signs that the predator had startled the eel. They then measured the time it took for the eel to notice the predator after the threat had been introduced into the tank.

The results showed that when surrounded by ship noise, eels were half as likely to respond to a predator’s ambush than they were under normal circumstances. Those that did react to impending death did so at rates about 25 percent slower than usual. When the net-cum-predator gave the eels a chase, those terrorized animals were caught twice as often when conditions were noisy. The team decided to dig into some of the physiology behind these findings and discovered that—not unlike the human reaction to loud, irksome noises—eels simply become very stressed out when exposed to clamor. They filter water more quickly than normal (perhaps the eel version of hyperventilation?) and their metabolic rate increases. They also become clumsier, the team found, losing some of their right-left movement coordination.

The team suspects that eels are not alone in their detrimental reaction to noise, although more studies are needed to confirm how other aquatic animals (including the predators themselves) deal with this pervasive form of pollution. The researchers also think that eels’ abilities to forage or travel might be impacted by noise, although they point out that those behavioral changes probably aren’t as dire as the predator effect since “there is no way to compensate for being eaten after the disturbance goes away.”

Chemical pollution affects the immune, nervous and endocrine systems

Pollution has had a detrimental impact on eels, with chemical pollution being a driving force behind the decline in the recruitment and abundance of the European eel (Anguilla anguilla) and the American eel (Anguilla rostrata).

Chemical pollution affects the immune, nervous, and endocrine systems of eels. PBT contaminants, including organochlorine and organophosphorus pesticides, have been observed to cause erratic behaviour in eels, such as restlessness, convulsions, and loss of balance, before death. These pesticides are often found in the muscle tissue of eels, indicating bioaccumulation.

Eels inhabiting polluted hypersaline waters, such as the Mar Menor hypersaline coastal lagoon in SE Spain, are exposed to higher levels of waterborne contaminants and contaminated fish prey. This is due to the higher rate of water ingestion in marine eels compared to freshwater eels, which leads to greater exposure to contaminants.

The impact of chemical pollution on the immune system of eels has been studied through the analysis of biomarkers, such as micronuclei frequency (MN) in peripheral erythrocytes, which provides information on chromosomal damage. Additionally, the nervous system of eels is affected by neurotoxicity, with high levels of organochlorine contaminants detected in their muscle tissue.

The endocrine system of eels is also disturbed by chemical pollution, as indicated by fluctuations in biomarker responses, which are influenced by factors such as seasonal changes in seawater temperature and dietary habits. Overall, the effects of chemical pollution on the immune, nervous, and endocrine systems of eels vary depending on the type and concentration of individual pollutants and their mixtures.

Plastic pollution threatens the breeding range of eels

Plastic pollution is a significant threat to the breeding range of eels. The Sargasso Sea, for instance, is a critical breeding ground for both European and American eels. However, the accumulation of plastic in this sea has resulted in the formation of the North Atlantic Garbage Patch, which spans hundreds of kilometres. This plastic pollution negatively impacts the migration and breeding of eels.

Eels are already facing numerous threats, including overfishing, habitat degradation, migration barriers, increased natural predation, parasitism, ocean climate variation, and chemical pollution. The latter, in particular, has been identified as a driving force behind the decline in eel populations. Studies have found high levels of contaminants, including heavy metals, pesticides, and endocrine disruptors, in European and American eels. These pollutants can lead to genotoxic damage, immune system disturbances, and reproductive issues.

Noise pollution is another often-overlooked threat to eels. Research has shown that man-made noises, such as those from ships, can impact eels' ability to evade predators. When exposed to ship noise, eels were less likely to respond to a predator's ambush and were caught more easily. This type of pollution can also potentially affect eels' foraging and travelling abilities.

The impact of plastic pollution on eel breeding ranges is a growing concern, and efforts to reduce plastic waste and support legislation to decrease plastic use are crucial. Additionally, further research is needed to understand the full extent of plastic pollution's impact on eel populations and to develop effective management strategies.

The decline in eel populations has led to them being categorised as critically endangered by the European Union and the United Nations. Protecting eels is essential, as they play a vital role in maintaining biodiversity and preserving balanced ecology in river and stream ecosystems. Therefore, addressing plastic pollution and other threats to their breeding ranges is of utmost importance for the conservation of these unique and important species.

Pollution affects every life stage of an eel

The impact of chemical pollution on the European eel (Anguilla anguilla) in a Mediterranean hypersaline coastal lagoon has also been studied. Eels in this environment were exposed to high levels of contaminants, including legacy organochlorine compounds, recently banned pesticides (such as chlorpyrifos), and other emerging chemicals. The effects of these contaminants on the eels vary depending on the type and concentration of the pollutants and their mixtures. For example, acute exposure to certain pesticides caused restlessness, erratic swimming, convulsions, loss of balance, mucus secretion, and pale color before death.

Noise pollution also negatively affects eels. Researchers from the University of Exeter and the University of Bristol investigated how man-made noise impacts the ability of eels to evade predators. They found that when exposed to ship noise, eels were half as likely to respond to a predator's ambush and reacted at slower rates. Noise pollution can cause stress in eels, leading to increased metabolic rates and rapid water filtration, potentially impacting their health and ability to survive.

Additionally, plastic pollution poses a significant threat to eel breeding ranges. The accumulation of plastic in the Sargasso Sea, a critical habitat for both European and American eels, negatively impacts freshwater eel migrations and breeding. The North Atlantic Garbage Patch, formed by ocean currents accumulating plastic pollution, is estimated to span hundreds of kilometers, further endangering eel populations.

The decline in eel populations has been linked to various factors, including overfishing, habitat degradation, migration barriers, diseases, and pollution. While the interaction of these factors is complex, pollution and climate change stand out as the only factors affecting every single life stage of eels. The continuous and persistent declines in recruitment and abundance over past decades have led to the classification of European, American, and Japanese eels as outside safe biological limits, with some species being critically endangered.

Overfishing and habitat loss are causing a decline in eel populations

The European eel (Anguilla anguilla) is a critically endangered species. Over the past few decades, there has been a continuous and persistent decline in recruitment and abundance. The causes of this decline are not well understood, but overfishing, habitat loss, and pollution are believed to be significant factors.

Overfishing has had a detrimental impact on eel populations. The demand for eel aquaculture has drastically increased since the 1970s, leading to sharp declines in wild European and Japanese eel populations. The current market price of juvenile eels is 150 times higher than two decades ago, making eel fishing a lucrative business. This has resulted in a high demand for wild juveniles, as artificial propagation has not been successful for eels. The fishing and trade of European eels are widespread, even including a lucrative illegal component. Only a few countries have completely prohibited eel fishing.

Habitat loss is another critical factor contributing to the decline in eel populations. Eels are particularly vulnerable to chemical pollution in their habitats. Studies have shown that eels in polluted hypersaline waters, such as the Mar Menor lagoon in Spain, are exposed to high levels of hazardous organic contaminants, including banned pesticides and emerging chemicals. These pollutants can cause genotoxic damage and disturbances to the immune, reproductive, nervous, and endocrine systems. Additionally, noise pollution from ships and underwater explosions can affect eels' ability to evade predators and may impact their foraging and travelling abilities.

The combination of overfishing and habitat loss has severely impacted eel populations. Stock abundance and fishing yield have declined by approximately 5% per year, resulting in less than 10% of the historical levels. The recruitment of young eels has also consistently dropped by about 15% per year. These declines have led to a decrease in eel fishery yields in most European countries, and the populations of European, American, and Japanese eels are now considered outside safe biological limits.

To address the decline in eel populations, conservation efforts have been implemented. The EU has adopted temporal closures of eel fishing in all waters to protect spawning migration, and there is a focus on increasing the areas available for eel recruitment and rearing. However, more stringent enforcement of local and international laws may be necessary to protect all eel populations from extinction.

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