According to the reading, the writer says that the cause of the decline of sea otter along the Alaskan coast is pollution rather than attacks by predators. However, the speaker in the lecture believes that predation can be the main explanation for the decrease in population of the otters.
First, the lecturer says that there is no finding of death sea otters along the Alaskan coast. She mentions that if pollution made the death of the otters, the body of the dead sea otter should be found. Therefore, predation is the main reason for this phenomenon because the otters were eaten by predators so that the dead otters cannot be found. This contradicts from the reading's assertion that industrial chemical pollution caused the death of sea otters.
Second, the speaker argues that orcas are predators of many small sea mammals including the otters and they caused the decline of many small sea mammals. She mentions that there was a lot of death of whales because of human hunting and this caused the orca to change their diet habit from large mammals to small sea mammals to adapt to the environmental change. Therefore, the orca can explain the decrease in many sea mammals which contradicts from the reading’s view.
Third, she says that the uneven pattern of otter decline is a better explanation of orca predation. She mentions that orca can get in large areas rather than shallow locations so that they predate more otters at the large locations rather than shallow and rock locations. This counters from the reading's viewpoint that there is uneven pattern of decrease in the otters because of the uneven concentrations of pollutants along the coast.