The reading passage argues that the number of sea otters dropped because of environmental pollution, while the lecturer points out that it was the predators that caused the decline.

First of all, the reading passage thinks that the water samples from the Alaskan coast did contain increased levels of contaminated chemicals, which could make the sea otters lose their resistance to dangerous infections and die in the end. On the other hand, the lecturer argues that people couldn’t see the dead bodies of sea otters onshore, so predators may have eaten the otters, which strongly supports the predator hypothesis.

Second, the reading passage asserts that other sea mammals along the coast were declining as well. Under this fact, the pollution seemed to be harmful to the entire ecosystem and could cause the death of many species. However, the lecturer contradicts this idea by saying that humans hunted the whales so that Orcas couldn’t predate whales for food. In this way, only smaller animals like seals, sea lions could be available for Orcas to eat, which will cause a decrease in the number of sea otters.

Third, the reading part notes that the pollution hypothesis could explain the uneven decrease of otters. The decline of otters is severe at some locations of Alaskan, while slight at others. Some experts suggest that some environmental factors like ocean currents may be the reason. By contrast, the speaker mentions that the locations whether the otters were accessible to Orcas were very important because Orcas couldn’t reach large and shadow rocks. Correspondingly, the number of sea otters on these rocks hadn’t declined, which lends support to the predator hypothesis.