The mark-recapture method would be best for sampling a population of _____.

• A. Sharks
• B. Birds
• C. Plants
• D. Bacteria

Answer: (A)

Mark-recapture is a way to estimate how many individuals are in a population when you can’t count them all directly. The idea is to capture a group, mark them in a harmless way, release them back, and then later capture another sample to see how many of the second group are marked. From the ratio of marked to total in the second sample, you infer the total population size, assuming the marked individuals mix back into the population and that capture chances are reasonably similar across the study period.

This approach works best for animals that move around and are hard to count exactly in the wild but can be safely captured and tagged and later re-encountered. Sharks fit that scenario well: they’re large, roam the ocean, and we can catch, mark, and release a subset, then later recapture to estimate the total number in the area. Plants don’t move, so you can count them directly in a plot; bacteria reproduce and their marks could be lost or confounded by division, making mark-recapture impractical. Birds can be banded too, but for this particular context, sharks are the classic example of where mark-recapture is most informative.