TOEFL integrated writing The sea otter

Both the reading and the listening discuss the reasons behind the mass die-off of sea otters along the Alaskan coast. The author of the reading believes that environmental pollution mainly contributes to the phenomenon, and provides three supporting reasons. The lecturer, however, throws doubt on the claims presented in the article, by stating that, in fact, predation plays a significant role.
To begin, the reading points out that industrial pollutants found along the Alaskan beach brought about increased levels of the chemical in the water which could have endangered the life of sea mammals. In spite of this fact, the lecture argues that when infections break out, many dead bodies have to be washed up but nothing had been found on the shore, strengthening the hypothesis that the sea otters' population collapsed due to overhunting.
In addition, the reading states that the number of other sea mammals like seals and sea lions also are diminished, indicating that a common cause had affected all these animals. Moreover, it is pointed out that top-rank predators like orcs would not prey on them because they prefer to hunt large animals. On the other hand, the professor rebuts the author's statement by noting that as a result of excessive hunting of whales, the staple food of orcs, by humans, orcs had been compelled to change their diet and turn to smaller preys, including sea otters, to survive.
Lastly, according to the reading, the decline severity of otters defers from location to location depending on the concentration of pollution, and as the scientists, this reinforces the theory that polluted water killed otters. By contrast, the listening asserts that, in fact, this discovery proves the hitherto claim. Since orcs lacked the capability to near shallow banks, mammals fled there; Witness the shallower, rockier locations, the more populated area.