The sea otter is a small mammal that lives in waters along the western coast of North America from California to Alaska.
When some sea otter populations off the Alaskan coast started rapidly declining a few years ago, it caused much concern because sea otters play an important ecological role in the coastal ecosystem. Experts started investigating the cause of the decline and quickly realized that there were two possible explanations: environmental pollution or attacks by predators.
Initially, the pollution hypothesis seemed the more likely of the two.
The first reason why pollution seemed the more likely cause was that there were known sources of it along the Alaskan coast, such as oil rigs and other sources of industrial chemical pollution. Water samples from the area revealed increased levels of chemicals that could decrease the otters' resistance to life-threatening infections and thus could indirectly cause their deaths.
Second, other sea mammals such as seals and sea lions along the Alaskan coast were also declining, indicating that whatever had endangered the otters was affecting other sea mammals as well. This fact again pointed to environmental pollution, since it usually affects the entire ecosystem rather than a single species. Only widely occurring predators, such as the orca (a large predatory whale), could have the same effect, but orcas prefer to hunt much larger prey, such as other whales.
Third, scientists believed that the pollution hypothesis could also explain the uneven pattern of otter decline: at some Alaskan locations the otter populations declined greatly, while at others they remained stable. Some experts explained these observations by suggesting that ocean currents or other environmental factors may have created uneven concentrations of pollutants along the coast.
The reading states that the environmental pollution is more likely to be the cause of the decline in otters population. In response, the professor explains that the attack by predators is most likely to cause of the decline in otters population. And continues by
showing how the reasons in the article are weak.
First, the author supports the claim by explaining that the water sample shows increased level of chemicals that could decrease the otter's resistance to life threatening infections and cause indirectly their death.
However, the professor tells us the pollution cause is weakened by the fact that it is so hard to find dead otter in the other hand, the attacked otters are eaten immediately.
Second, the author supports the idea by saying that other mammals are also declined because of the pollution. In contrast, the professor says that other mammals decline is caused by orcas attack which tend to attack the smaller mammals due to humans hunting.
Third, the reading support the idea by explaining that the pollution is the causes of the uneven pattern of the decline. In response the professor tells us that it is caused by the deference in the location of the orcas which affect the decline place.
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