How Dolphins Suffer from Environmental Pollution?

Dolphins are lovely and smart animals, but dolphin population worldwide are facing a significant threat. According to Whale and Dolphin Conservation (WDC) (n.d.), human activities influence approximately 40 percent of marine systems and every area of the sea. In the eastern coast of the U.S., the death of about three thousand bottlenose dolphins is observed from 1987 to 1988. We have to pay close attention to this issue so that dolphins would not die out and species diversity could be preserved. Actually, environmental pollution is an important reason why the dolphin population dramatically reduces.

Dolphin population is significantly hurt by environmental pollution due to three major reasons. First, dolphins are easily hurtful by chemical contamination because of bioaccumulation in which damage dolphins' body systems. Second, noise pollution impairs dolphins' health and change their normal behaviors. Third, marine debris threat dolphins' life since dolphins may accidentally eat litters or be entangled by packaging. At the same time, there seems to an argument about whether environment pollution extremely harms dolphins. Some people argue that some studies contain limitations and the data are insufficient to support the position that the species of dolphin are significantly hurt by environmental pollution. However, environmental pollution has some clearly negative impacts on dolphins. One of the direct effects is that noise forces dolphins to consume more energy. Also, environmental pollution pollutes dolphins' habitats and kill smaller sea animals that could lead to the short of food for dolphins.

First of all, chemical pollution including oils spills and polluted water has a detrimental effect on dolphins' health. With the rapid development of industry, increasing industrial accidents happen and these accidents result in many serious consequences. Pitchford et al. (2018) study the influence of the huge 2011 oil spill in the Gulf of Mexico, and they find that the large number of bottlenose dolphins' death is related to the Deepwater Horizon oil spill (p. 14). In other words, dolphins are unable to completely avoid the area of oil slick, and sometimes they indeed swim into floating oil. There is a chance that the poisonous oil will enter dolphins' spiracles and mouths if they are encompassed by floating oil. What is more, Durante et al. (2016) believe that polluted prey also has an adverse impact on dolphins' health since toxins will be accumulated in dolphins' bodies eventually (p. 358).

Persistent Organic Pollutants (POPs) are perilous chemicals that released by industrial production and they are unlikely to break down in a short time. Sea animals will die if they absorb POPs at a certain level, and the amount of POPs in the ocean is rather huge. The majority of dolphins are at the top of food chains naturally, and so they are the ending point for POPs (Durante et al., 2016, P. 353). To be more precise, plankton absorbs PCBs from the environment, and small fish eats plankton to survive. A lot of small fishes are eaten by large fishes in their life, and dolphins eat plenty of large fishes over their lifetime. Finally, POPs from lots of smaller marine organisms are absorbed by dolphins. So, bioaccumulation caused by chemical is contamination really a big issue for dolphins.

In fact, anthropogenic chemical pollutant have more negative influences on dolphins than other animals. Rage et al. (2008) provide convincing evidence that the species of dolphin are not good at coping with pollution like POPs because there are scarcely any enzymes in their bodies to decompose hazardous chemical components (P. 472). Consequently, dolphins' reproductive and immune systems are likely weakened due to the damage of chemical contamination such as POPs. The injury to dolphins' reproductive systems can lead to serious problems. More specifically, a large ratio of POPs may be passed by female dolphins to their first babies via womb or milk , which is possibly fatal to offspring (Durante et al., 2016, P. 354).

In addition, the issues related to injured immune systems are also severe. For example, the massive death of dolphin population since the 20th century could be caused by virus transmission from animals to animals (Rage et al., 2008, P. 473). Immune system is the main defense against diseases, and injured immune system certainly increases diseases risk. Thus, chemical pollution puts dolphins in especial danger because toxins and poisons from dangerous chemicals severely impair dolphins' health.

Other than chemical contamination, noise also has a seriously negative impact on dolphin population. Dolphins live in the ocean where sound is the basic tool to communicate and look for direction. Nonetheless, human activities such as natural resources exploration, the operation of ships, and military maneuvers in the sea have made a very high level of noise, which puts dolphins in risk. There are plenty of studies from scientific literature illustrating the damage of noise to the species of dolphin. For instance, high-frequency and mid-frequency sonar from military vessels are recognized big worries for the health of sea mammals since they can lead to physical hurt or even death to marine animals like dolphins (Li et al., 2014, P. 496). Likewise, dolphins with excessive stress levels caused by high-intensity sounds may even behave aggressively, which can result in physical injuries (Harris, 2017, p. 212). This evidence clearly show that noise pollution has an adverse effect on the species of dolphin.

Besides high-frequency and mid-frequency sonar, Harris discusses that low-frequency ocean noise also influences mammal behaviors. To be more specific, mammals like dolphins will go away from their habitat or breeding place because of excessive noise, which is observed on the coast of Baja California, Mexico ( Harris, 2017, p. 211). Similarly, Pitchford et al. (2018) claim that noises will drive dolphins from important areas to them so that the chance of illness and stranding to dolphins increases (p. 16). Basically, all noises made by humans influence extremely disrupt dolphins' life. Dolphins have to raise their voices to communicate with each other since plenty of ships in the ocean make many noises. Dolphins change the frequency, duration or amplitude, or they simply repeat their calls several times. Yet, these actions really hurt dolphins' health (Holt, 2015, p. 1648). Furthermore, exposure to shipping noise in long periods could cause temporary or permanent damage to dolphins' sense of hearing (Li et al., 2014, P. 501). Auditory system plays an essential role in dolphins' daily life, and it is hard to imagine how should dolphins survive in the sea without a sensitive sense of hearing. Therefore, dolphins' lives are significantly impacted by noise pollution because noises alter dolphins' normal behaviors and harm their heath including auditory system.

Dolphins are threatened by noise while the detrimental effects of marine debris on dolphins cannot be overlooked. Millions of tons of plastic garbage are dumped by people into the sea yearly worldwide (WDC, n.d.) The oceans are polluted by countless man-made litters, which is quite risky to dolphin population. When dolphins swim in coastal areas or along shorelines, marine litters containing plastic bags and other indecomposable substances can trap or choke them, young dolphins in particular (Pitchford et al., 2018, p. 16). To put it another way, dolphins can suffer or die once they are entangled in plastic bags. Moreover, researchers have found that more and more dolphins eat marine debris accidentally. Bearzi et al. (2014) discuss that one of the known cause of dolphins' mortality is obstruction of the digestive system by ingesting plastic (P. 393).

As a consequence, intestinal blockage, starvation, and inside damage are all possible injuries to dolphins. Similarly, Eo, Yeo, and Kwon (2013) explain that gastrointestinal foreign objects are a serious problem in cetaceans and dolphins (p. 251). For example, Eo et al. (2013) helped a male bottlenose dolphin to remove foreign objects from its forestomach, and they found that "The foreign bodies included a 10 ?— 3.5 cm plastic tube, 4 ?—2.0 cm stainless steel pipe, brush, and concrete debris" (p. 251). Consequently, the species of dolphin are significant hurt by man-made litters. Hence, marine debris as one of the chemical pollution poses a real threat to dolphins' lives because serious issues such as intestinal blockage, and internal injury are possibly happened due to ingestion of plastic litters and entanglement by packaging.

On the other hand, some individuals challenge that environmental pollution does not have a extremely negative effect on dolphins because of two main reasons. First, lots of scientific studies about how environmental contamination affects dolphin population are not optimal. For instance, some factors that would impact the results are not being quantified in the study of oil spills (Pitchford et al., 2018, p. 16). Additionally, the statistics are not sufficient because some data are rather difficult to collect. Durante et al. (2016) write that there is solely a low number of samples available (P. 358). Follett, Genschel, and Hofmann (2014) say that reliable conclusions cannot be drawn based on inadequate data and limited knowledge although oil discharge leads to huge destruction (p. 130). Scientists have to examine the death of many animals to confirm the cases that animals died due to environmental pollution (Follett et al., 2014, p. 130). In other words, humans indeed do not have adequate information about how the death of animals like dolphins is linked to environmental pollution since checking the actual cause of a large number of animals' death is quite challenging. Hence, the limitations of some scientific researches and the lack of data are the two major reasons why some individuals reject that dolphin population is significantly harmed by environmental contamination.

Nevertheless, there is compelling evidence demonstrating that environmental pollution has an adverse impact on food chain and ecosystem. Follett et al. (2014) note that oil spills can grow bacteria and kill smaller marine mammals that are the sources of food to dolphins although oil spills may not directly kill dolphin population (p. 122). It means that environmental contamination like oil spills obviously causes habitat destruction to dolphins as well as increase the risks that dolphins have diseases and lack food. Meanwhile, Holt et al. (2015) study a pair of bottlenose dolphins at the lab and conclude that the louder dolphins phonate, the more oxygen and energy they consume. Then Holt and her colleagues apply the uniform method to calculate how many extra calories dolphins in the wild have to get to compensating the extra consumption of energy, and they estimate dolphins need to obtain two extra calories for each two minutes (p. 1650). Though this extra metabolic cost is not huge, the consumption of energy will become quite large through the accumulation over time. More importantly, not all dolphins are able to find sufficient foods, especially for juveniles and pregnant females. Thus, environmental contamination indeed has dramatically negative influences on the species of dolphin.

To conclude, environmental pollution significantly harms the species of dolphin because of the three reasons. Chemical pollution enables toxins and poisons enter dolphin's bodies and then destroys their reproductive and immune systems. Through injuring dolphins' auditory system and disrupting the communication, dolphins' health is impaired by noise, and dolphins' normal behaviors are changed by noise pollution as well. Marine debris threat dolphins' life by raising the risk that dolphins ingest litters or be entangled by plastic bags, which leads to severely consequent issues like obstruction of the digestive system and asphyxia. Each person, every organization, and all countries ought to should the responsibility to tackle environmental pollution and protect the species of dolphin. Humans should take actions immediately before environmental pollution results in more seriously irreversible damage to dolphin population.

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