Both the reading and the lecture are discussing the decline of sea otter population in Alaskan coast. The reading asserts that the population declined is caused by the environmental pollution. However, the lecture opposes the idea of the passage and she believes that the predators are the reason behind the decline of sea otter's population. She offers several reasons for her opinion.
First of all, the reading states that there were known sources of the pollution along the Alaskan coast. The water samples from the area indicates increased levels of chemicals that result in the demise of these animals. This point is rebutted by the lecturer. She mentions that if the chemicals had killed the sea otters, their dead bodies should have been found. The fact that there are no dead bodies found can indicate that predators have eaten the sea otters and the dead bodies cannot be found as a whole.
Secondly, the passage argues that the population of some of the other sea mamals in that area has also declined. It means that whatever causing the death of the sea otters, is killing the other sea mamals as well. This can be pointed to a predator like orcas or the environmental pollution that affected the whole ecosystem. The orcas are interested in hunting the whales so as a result, the pollution must be the case. The lecturer challenges this idea and she aruges that because the whales are hunted by humans, the orcas had to change their diet, and they started eating smaller animals like sea otters and sea lions. Because of this change in diet, the sea otter population has decreased.
Finally, the author posists that the pollution hypothesis can explain why at some areas of the coast sea otter population remaned stable, while at others the population declined. The areas with no pollution is still suitable for sea otters but other polluted areas are not. The lecturer opposes this claim, she argues that because the orcas can't access the shallow waters and rocky environments, the population of the sea otters remined stable there, but at other areas that orcas have access to, they hunted the sea otters.