In the late 1980’s, the population of sea otters in the North Pacific

In the late 1980’s, the population of sea otters in the North Pacific Ocean began to decline. Of the two plausible explanations for the decline—increased predation by killer whales or disease—disease is the more likely. After all, a concurrent sharp decline in the populations of seals and sea lions was almost certainly caused by a pollution related disease, which could have spread to sea otters, whereas the population of killer whales did not change noticeably

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

(A) Killer whales in the North Pacific usually prey on seals and sea lions but will, when this food source is scarce, seek out other prey.

(B) There is no indication that substantial numbers of sea otters migrated to other locations from the North Pacific in the 1980’s.

(C) Along the Pacific coast of North America in the 1980’s, sea otters were absent from many locations where they had been relatively common in former times.

(D) Following the decline in the population of the sea otters, there was an increase in the population of sea urchins, which are sea otters’ main food source.

(E) The North Pacific populations of seals and sea lions cover a wider geographic area than does the population of sea otters

Let’s understand the details of the argument.
1) In the late 1980’s, the population of sea otters in the North Pacific Ocean began to decline.
2) Two possible explanations for the decline in the population of sea otters
• increased predation by killer whales
• disease

Author’s opinion/ Conclusion- Of the two explanations, disease is the more likely because-

There was a concurrent sharp decline in the populations of seals and sea lions caused by a pollution related disease, which could have spread to sea otters and there has been no noticeable change in the population of killer whales

We need to find an option that weakens the conclusion

(A) Killer whales in the North Pacific usually prey on seals and sea lions but will, when this food source is scarce, seek out other prey.

This means that Killer whales preyed on sea otters because there was a decline in populations of seals and sea lions (usual prey). This weakens the conclusion that the decline in the population of sea otters is not because of disease but because of increased predation by killer whales. Hence A is correct.

(B) There is no indication that substantial numbers of sea otters migrated to other locations from the North Pacific in the 1980’s.

B brings in and eliminates another probable cause for the decline in the population of sea otters in the North Pacific. Eliminate B

(C) Along the Pacific coast of North America in the 1980’s, sea otters were absent from many locations where they had been relatively common in former times.

The location of sea otters is not important. Eliminate C

(D) Following the decline in the population of the sea otters, there was an increase in the population of sea urchins, which are sea otters’ main food source.

Irrelevant. Eliminate D.

(E) The North Pacific populations of seals and sea lions cover a wider geographic area than does the population of sea otters

This is irrelevant to the argument. Eliminate E

Vishnupriya
CrackVerbal Prep Team