题目选项分析

In the late 1980s,the population of sea otters in the North Pacific began to decline.There are two plausible explanations for the decline:predation,possibly by killer whales,or disease.Of these two,disease is the more likely,since a concurrent sharp decline in populations of seals and sea lions is believed to have been caused by disease,and diseases that infect these creatures are likely to be able to infect sea otters also.

Which of the following,if true,most seriously weakens the reasoning?

【选项】There is no indication that the sea otter population at any North Pacific location declined in the 1980s because of substantial numbers of sea otters migrating to other locations.