A lake's fish population can be estimated by marking a sample of fish, releasing them, and later recording what fraction of a second catch carries marks. The method assumes marked fish mix evenly back into the population. Limnologist Rangi Hikuroa clipped a fin on five hundred fish and released them all from one jetty. Tracking a subset that also carried small tags, he found that marked fish in one lake remained clustered near the release point for weeks, and the second catch was taken there, where one fish in three carried a mark. His finding implies that the resulting estimate ______
Which choice most logically completes the text?
- A) is too low, since too few marked fish were recaptured in the second catch overall.
- B) is accurate, since the marked fish sample was large enough to provide reliable recapture data.
- C) is too low, since the second catch contained an unrepresentatively high fraction of marked fish. ✓
- D) is too high, since the marked fish were clustered and not evenly mixed throughout the population.
Why: The method assumes marked fish mix evenly back into the population, but the tagged subset stayed clustered near the jetty and the second catch was taken there, where one fish in three carried a mark. An inflated marked share makes the population look smaller than it is, so the estimate "is too low, since the second catch contained an unrepresentatively high fraction of marked fish." Answering that it "is too high, since the marked fish were clustered and not evenly mixed throughout the population." names the right cause with the wrong direction: clustering at the sampling spot raises the marked fraction, which pushes the estimate down. Answering that it "is too low, since too few marked fish were recaptured in the second catch overall." has the recapture backwards, since one in three is an unusually high marked fraction, not too few. Answering that it "is accurate, since the marked fish sample was large enough to provide reliable recapture data." rests on sample size, which the passage never questions; the problem is where the marked fish were, not how many were marked.