The sea otter is a small mammal that lives in waters along the western coast of North America from California to Alaska. When some sea otter populations off the Alaskan coast started rapidly declining a few years ago, it caused much concern because sea ot

In this set of materials, the reading passage claims that sea otter populations in western coast of North America have been started declining because of environmental pollution rather than predator attacks and provides three reasons to support this. However, the lecturer finds all the ideas dubious and presents some evidence to show that predation is the most likely reason for declining number of sea otters.

The first reason that the author of the passage mentions to support the idea of invasive pollution is that there are contaminating sources and industries along the Alaskan coast that poses the otters' resistance to harmful infections, which, in turn, cause the otters' deaths. On the contrary, the professor states that the pollution is not the likely reason to decreasing sea otters since any dead sea otter has not been found at the coasts. If the pollution is the main reason to declining population of sea otters, the number of predators should have been decreased as well. Therefore, predation is the primary reason to disappearing of the sea otters.

The next reason uttered in the passage is that the number of other sea mammals, such as seals and sea lions, has decreased. In fact, a general reason like environmental pollution can affect the entire ecosystem. In contrast, the lecturer explains that the decrease in the number of sea otters in Alaskan coast is because human is hunting large predatory whales - an important prey for orcas - so that orcas have to change their diet to smaller sea mammals, like sea otters, seals, and sea lions. In this regard, the number of sea otters has decreased as a result of predation.

Finally, the reading passage asserts that the reduction in sea otters' populations is uneven along the coast that is the result of uneven ocean currents and other environmental factors, thereby erratic concentrations of pollutants along the coast. Conversely, the speaker draws attention to the accessible areas for orcas that is deeper places. As orcas are large animals, they cannot come and hunt in shallow and rocky areas, and the researches indicate that the shallow and rocky areas are where the number of the otters has not declined.