The passage and the lecture sheds light upon the declining population of the sea otters along the west coast of North America. Two possible reasons have been stated-increased environmental pollution and predation.
Firstly, the passage suggests that there are known sources of pollution along the Alaskan coast for instance, oil rigs and chemcial industries, that have led to an increased levels of chemicals which have reduced the sea otters' immunity against diseases. However, the lecturer points out that if this was true, dead bodies of sea otters would have washed up on the shore. The absence of such bodies, the lecturer opines, is an indication that otters are being hunted by other species and are "eaten immediately".
Secondly, a similar decline in population is observed in other animals like seals and sea lions in the area. The author of the passage feels the increased level of pollution will impact the entire ecosystem and not just one particular species and therefore supports the pollution theory. Another point which is highlighted in the passage, one that goes against the predation theory is that Orcas are major predators in the area and they prefer hunting larger game such as whales. The lecturer, on the other hand, mentions the fact that whale population has declined due to killing by humans and as a result, the orcas have adapted themselves to killing smaller animals like seals, sea lions and otters.
On the same lines of the orca predation theory, the lecturer goes on the explain the uneven decline in population of the sea otters. She points explains that the orcas are large in size and therefore cannot access shallow waters. Accordingly, the population of sea otters has remained relatively stable in areas where waters are not too deep and areas with deeper waters, where orcas can enter easily, have witnessed a steeper decline in population of the otters. The author of the passage on the other hand feels this uneven pattern is due to the uneven concentration of chemical pollutants in the water.