Critical Reasoning (CR) | Re: Global surveys estimate the earth’s population

Global surveys estimate the earth’s population of nesting female leatherback turtles has fallen by more than two-thirds in the past 15 years. Any species whose population declines by more than two-thirds in 15 years is in grave danger of extinction, so the leatherback turtle is clearly in danger of extinction.

Which one of the following is an assumption that the argument requires?

(A) The decline in the population of nesting female leatherback turtles is proportional to the decline in the