TOEFL integrated writing: The sea otter

During a few years ago, some sea otter populations off the Alaskan coast started declining. Based on expert investigations, there are two feasible explanations: environmental pollution and attacks by predators. The passage says that the pollution hypothesis is more important, however, the professor in the lecture claims that predation is the more important cause for otters’ decline.

The first reason which is mentioned in the passage explains that oil and industrial chemical pollutions infect the otters' settlement and cause their deaths. But the professor disagrees with this point of view and says because nobody find any dead sea otter washing off on beaches, so the pollution hypothesis are weakened. On the other hand, predation hypothesis is strong enough is this case, because the predators eat immediately the otters after prey and you can not see any dead sea otter.

Second, It is assumed in the passage that whatever had endangered the otters was affecting other sea mammals like seals and sea lions which were declining. The passage explains that only orca could have the same effect which is interested in other whales. The lecture corrects this statement by saying that whale are disappeared by human hunters. Therefore, orcas changed their diet and have eaten small mammals like sea lions and seals!

Third, the passage believes the uneven pattern of otter decline based on pollution hypothesis however the lecture based on the predation. The professor explains that the accessibility of the otters' location to orcas is very important in declining their population. The number of the otters in shallow and rocky locations has not declined because the orcas could not enter into this area.